Introduction to Renewable Energy and Energy Efficiency

GREEN SKILLS FOR JOBS

Student Book Renewable Energy Technologies NQF Level 2 Introduction to Renewable Energy and Energy Efﬁ ciency Textbook provided free of charge by the Skills for Green Jobs Programme ! For classroom use only! Not for resale or redistribution without further permission!

Editor

Skills for Green Jobs (S4GJ) Programme Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH Registered offces: Bonn and Eschborn GIZ Offce Pretoria P.O. Box 13732, Hatfeld 0028 Hatfeld Gardens, Block C, 1st Floor, 333 Grosvenor Street Pretoria, South Africa Tel.: +27 (0) 12 423 5900 E-mail: [email protected] www.giz.de

4th edition - revised

Responsible: Edda Grunwald Authors: S4GJ Team

Illustrations: WARENFORM Mascot and Comic Design: Björn Rothauge Photos Title: Ralf Bäcker, version-foto

Pretoria, September 2017 CONTENTS

List of Figures and Tables 5 Glossary 12 Preface 22 Foreword 23 Using this Textbook 24 Comic 1 188 Comic 2 264

1. Introduction to Renewable Energy Resources and Energy Efﬁciency 25

1.1 International and National Climate Change Policies 26 1.1.1 Causes and Impacts of Climate Change and Global Warming 27 1.1.2 Mitigation and Adaptation Concepts 36 1.1.3 International and National Policies on Climate Change 49

1.2 Differences between Energy Resources 56 1.2.1 Electrical Networks 57 1.2.2 Differences between Fossil and Renewable Energy Sources 65 1.2.3 Advantages and Disadvantages of Renewable Energy Resources 82

1.3 Signiﬁcance of Solar Radiation 88 1.3.1 The Sun as the Principal Source of Energy 89 1.3.2 Effects of Orientation and Tilt of Solar Arrays 98

2. Introduction to Electrical Energy and Energy Efﬁciency 109

2.1 Electrical Energy and Energy Efﬁciency: Basic Concepts 110 2.1.1 Electrical Energy: Basic Concepts 111 2.1.2 Energy Efﬁciency: Basic Concepts 130

2.2 Fundamentals of Electric Circuits 144 2.2.1 Electric Charge and the Proportionalities between Current, Potential, Resistance and Power 145

2.3 DC Circuits 165 2.3.1 Simple DC Circuits 166

3 3. Introduction to Occupational Health and Safety 191

3.1 Safe Work Practices 192 3.1.1 Basic Terms used in Health and Safety 194 3.1.2 Workplace Health and Safety 203 3.1.3 Workplace Hazards 223 3.1.4 Minimising Accidents through Clear Communication and Health and Safety Checklists 233 3.1.5 Effects and Consequences of Electrical Accidents on the Human Body and on Property 243

4. Basic Principles of Photovoltaic Systems 267

4.1 Photovoltaic System Components and Operational Principles 269 4.1.1 PV System Components 270 4.1.2 Semiconductor Materials and the Photovoltaic Effect 290 4.1.3 PV Module Datasheets and Output Parameters 301 4.1.4 Factors Affecting the Performance of PV Modules 311

4.2 Photovoltaic Experiments 323

4 LIST OF FIGURES AND TABLES Figures

Topic 1 Theme 1.1.1 Figure 1: Schematic illustration of the regions of our atmosphere 28 Figure 2: Solar radiation (simpliﬁed) 28 Figure 3: Eskom’s Arnot Power Station, Middelburg/Mpumalanga 29 Figure 4: Observed change in surface temperature 1901 – 2012 29 Figure 5: Schematic illustration of carbon dioxide’s function in the atmosphere 30 Figure 6: Schematic illustration of the greenhouse effect 31 Figure 7: Examples of current and possible future impacts and vulnerabilities associated with climate variability and climate change for Africa 33 Figure 8: How do we know that the world has warmed? 34

Theme 1.1.2 Figure 1: Adaptation and mitigation as different response options 40 Figure 2: A page from a comic book: Climate change is a global problem 43 Figure 3: The triangle diagram: adaptation - mitigation - inaction 44 Figure 4: An example for a climate change poster used in an awareness campaign in Sri Lanka 45 Figure 5: The Greening of Colleges handbook, supporting practitioners in awareness campaigns in South Africa’s TVET colleges 46

Theme 1.1.3 Figure 1: The Green Economy Accord (November 2011) aims to give effect to a greener economy 51 Figure 2: Technology Allocations New Build 2010 - 2030 51 Figure 3: Renewable energy project locations of the REI4P 54

Theme 1.2.1 Figure 1: Schematic illustration of electrical energy generation using resources such as coal, gas, nuclear, CSP and geothermal energy 57 Figure 2: Schematic illustration of transmission of electrical energy using a system of transformers and overhead transmission lines 58 Figure 3: Schematic illustration of distribution of electrical energy: Industry and residential homes are connected to the national grid 58 Figure 4: An invented and simplified illustration of the three basic energy generation regimes over an imaginary day and city 59 Figure 5: Eskom’s transmission network 60 Figure 6: Schematic and simplified illustration of Eskom’s distribution network 61 Figure 7: National grid development over time (schematic) 62 Figure 8: An invented and simplified illustration of the three basic energy generation regimes over an imaginary day and industrial area 63

5 Theme 1.2.2 Figure 1: Nitrogen and sulphur oxides: effects on the environment 66 Figure 2: Schematic illustration: How coal is converted into electrical energy 67 Figure 3: The Fukushima Daiichi nuclear disaster 68 Figure 4: Chernobyl: A quarter century later 69 Figure 5: Renewable energy resources 70 Figure 6: 5 photovoltaic panels are wired in series 71 Figure 7: A simplified schematic view into a wind turbine 72 Figure 8: A simplified schematic view into a hydropower facility 73 Figure 9: A simplified schematic view of a geothermal power plant 74 Figure 10: World energy consumption 2013 75 Figure 11: Reserves–to-Production (R/P) ratios for oil, gas and coal 76 Figure 12: Total energy consumption in South Africa, 2012 76 Figure 13: South Africa’s major coal deposits 77 Figure 14: South Africa’s energy mix in 2013 78 Figure 15: The UK’s energy mix in 2010 81

Theme 1.2.3 Figure 1: Electrical energy generated from renewable resources in the EU 2012 84

Theme 1.3.1 Figure 1: The Sun’s surface showing large eruptive prominences 89 Figure 2: A simplified illustration of hydrogen and helium atoms 90 Figure 3: A simplified schematic illustration of photosynthesis 90 Figure 4: Sunlight is a broad spectrum of electromagnetic rays 91 Figure 5: The average daily direct irradiation in South Africa 92 Figure 6: A pyranometer is used to measure solar radiation in W/m2 93 Figure 7: A digital silicon irradiance sensor 93 Figure 8: A simplified comparison of finite and renewable energy reserves 94 Figure 9: Experiment set-up and wiring diagram 95

Theme 1.3.2 Figure 1: A simplified schematic illustration of the three types of irradiation 99 Figure 2: The Earth is revolving in an elliptic orbit around the Sun 99 Figure 3: The path of the Sun in the southern hemisphere over the course of a year 100 Figure 4: Elevation angle (red) 101 Figure 5: Determining latitude and longitude 102 Figure 6: Azimuth angle 103 Figure 7: Simplified Sun path diagram for Johannesburg 104 Figure 8: Simplified irradiation differences 105

Topic 2 Theme 2.1.1 Figure 1: Relationships of SI units and derived units 113

Figure 2: Free-body diagram - Normal force (Fn ) 115

Figure 3: Free-body diagram - Friction (Ff ) 115

Figure 4: Free-body diagram - Tension (Ft ) 116 6 Figure 5: Free-body diagram - Buoyancy (Fb ) 117 Figure 6: Electrostatic force 118

Theme 2.1.2 Figure 1: An example of a typical demand profile of an office building 133 Figure 2: Power circuit for a typical fluorescent light 136 Figure 3: Energy-efficient lighting alternatives 136 Figure 4: Diagram of an LED (inductive load) 137

Theme 2.2.1 Figure 1: Electric charges 146 Figure 2: Simpliﬁed structure of an atom 147 Figure 3: Charge (Q) moving along a conductor gives rise to a current (I) 149 Figure 4: Two types of currents 150 Figure 5: A simple DC circuit 153 Figure 6: How to determine a factor (quantity) in Ohm’s law 157 Figure 7: How to determine a factor (quantity) in the relationship between power, potential and current 160

Theme 2.3.1 Figure 1: The parts inside an electric torch 167 Figure 2: A simple circuit diagram of an electric torch 167 Figure 3: Electrical symbols used in schematic circuit diagrams 168 Figure 4: Two possible arrangements of a battery and three light bulbs in a circuit 169 Figure 5: How to connect an ammeter into a circuit 170 Figure 6: How to connect a voltmeter to a circuit 170 Figure 7: How to connect an ohmmeter to a circuit element 171 Figure 8: Multimeter types 172 Figure 9: Resistors as potential dividers in series connections 173

Figure 10: Total resistance (Req) is equal to the sum of resistance of the individual resistors 174 Figure 11: Resistors as current dividers in parallel connections 175 Figure 12: Resistors connected in parallel 176 Figure 13: 1.5 V cells (batteries) are connected in series 177 Figure 14: Six 1.5 V cells (batteries) are connected in parallel 178 Figure 15: A diagram indicating a short circuit 179 Figure 16: Construct a series circuit 180 Figure 17: Construct a series-parallel circuit 181 Figure 18: Volt measurement across resistors and battery 183

Topic 3 Unit 3.1 Figure 1: Can you identify all potential site hazards at this work facility? 193

Theme 3.1.1 Figure 1: Keep your work environment accident free 195 Figure 2: Hierarchy of hazard control 196 7 Figure 3: Various examples of machine guarding 198 Figure 4: Material Safety Data Sheet (MSDS) for potassium dichromate 199

Theme 3.1.2 Figure 1: The accident pyramid 204 Figure 2: In 2013, the ISO graphical safety symbols changed slightly 205 Figure 3: Wear a hard hat to avoid accidents 208 Figure 4: Examples of face and eye protection devices 209 Figure 5: Ear plugs (disposable earplugs and earmuffs) 209 Figure 6: Wear a safety goggle and half mask respirator 210 Figure 7: Some results of long-term exposure to dust 211 Figure 8: Examples of different safety gloves 212 Figure 9: Foot protection poster 213 Figure 10: Eight useful hints on how to move a load 214 Figure 11: How to wear a safety harness 215 Figure 12: Different safety signs 219

Theme 3.1.3 Figure 1: Six different hazard categories 223 Figure 2: Spills on ﬂoors can result in slips, trips and falls 224 Figure 3: Chemical substance signs 225 Figure 4: Avoid hazards in an ofﬁce environment 226 Figure 5: Prompt reporting of hazards 228 Figure 6: Identify the various individual hazards 231

Theme 3.1.5 Figure 1: Electrical installations and serious accidents 244 Figure 2: Workers can be exposed to arc-ﬂash hazards 246 Figure 3: Damage caused by ﬁre 248 Figure 4: Damaged photovoltaic modules 249 Figure 5: Lockout/tagout procedures (1) 250 Figure 6: Convenient cable connectors 253 Figure 7: DC and AC disconnects and OCPDs 253 Figure 8: Different types of lugs for grounding connections 254 Figure 9: Lockout/tagout procedures (2) 256

Topic 4 Figure 1: Installations and installed PV capacity in various countries 268

Theme 4.1.1 Figure 1: Schematic illustration of some essential components of a grid-connected PV system 271 Figure 2: Schematic illustration of a PV cell, module and array 271 Figure 3: Schematic illustration of 36 single PV cells connected in series to form a module 272 Figure 4: Schematic illustration of the encapsulation of PV cells between various layers 273

8 Figure 5: Schematic illustration of different inverter conﬁgurations 274 Figure 6: A 500 W grid-interactive inverter (inside and outside view) 275 Figure 7: A 4 kW grid-interactive inverter (inside and outside view) 275 Figure 8: Simpliﬁed diagram indicating the maximum power point (MPP) of a 75 watt PV module 276 Figure 9: Schematic illustration of an inverter with dual-MPPT functionality 277 Figure 10: Two different types of charge controllers without MPPT functions 277 Figure 11: Different 12 V sealed gel batteries 279 Figure 12: DC and AC rated overcurrent protection devices (OCPD) 280 Figure 13: Mounting system components 281 Figure 14: Fixing stainless steel hooks or roof anchors into the rafters of the roof construction 282 Figure 15: A hook and rail system for a tiled roof 282 Figure 16: PV modules being attached to the rails 283 Figure 17: Cost reductions of residential PV rooftop systems in the USA 284 Figure 18: A self-sealing mounting base 285 Figure 19: A mounting system 285

Theme 4.1.2 Figure 1: The two main types of materials used for the construction of PV panels 291 Figure 2: Average effects of technology speciﬁc temperature coefﬁcients of power on PV module output performance 293 Figure 3: From sand to PV modules 294 Figure 4: Integrated circuit (IC) chips 295 Figure 5: The silicon (Si) atom 296 Figure 6: A boron (B) atom takes the place of an Si atom in the crystal lattice 297 Figure 7: A phosphorus (P) atom takes the place of an Si atom in the crystal lattice 297 Figure 8: ‘Doped’ or impure (compounded) silicon 298 Figure 9: The depleted P-N junction 298 Figure 10: Electric current in a PV cell 299

Theme 4.1.3 Figure 1: Relevant parameters indicated in a sample datasheet for a PV module 303 Figure 2: Diagram indicating the maximum power point (MPP) of a typical 75 watt PV module 305 Figure 3: Diagram with an I-V and P-V curve plotted together 306 Figure 4: I-V curves of a PV module 307 Figure 5: I-V curves of a PV module 307 Figure 6: A section from the datasheet contains the temperature characteristics of the module 308

Theme 4.1.4 Figure 1: Schematic illustration of 36 single PV cells connected in series to form a module 313 Figure 2: Two identical modules connected in series 314 Figure 3: Two identical modules connected in series 314 Figure 4: Four identical modules connected in series 314 Figure 5: Two identical modules connected in parallel 315

9 Figure 6: Two identical modules connected in parallel 315 Figure 7: Four identical modules connected in parallel 316 Figure 8: Eight identical modules connected in series-parallel 316 Figure 9: A shadow cast on a rooftop PV system 317 Figure 10: Uniform and partial shading 317 Figure 11: P-I curves indicating two illumination levels 318 Figure 12: The diode 319 Figure 13: Different types of diodes in a PV array 320 Figure 14: The function of bypass diodes in a string 321

Unit 4.2 Figure 1: The training set Solartrainer Junior 324

Tables

Topic 1 Theme 1.1.2 Table 1: Examples of adaptation initiatives in various countries 37 Table 2: Key mitigation technologies and practices 39 Table 3: Differences between adaptation and mitigation 40

Theme 1.1.3 Table 1: IRP total generation capacity projected for 2030 52 Table 2: Job creation and local content created by different renewable energy technologies 53

Theme 1.2.3 Table 1: Advantages and disadvantages of selected renewable technologies 83

Topic 2 Theme 2.1.1 Table 1: Base quantities (SI units) 112 Table 2: Examples of derived physical quantities and their SI units 112 Table 3: Multiples and divisions of the System of Units 113 Table 4: Observed velocity change (∆v) per unit time 119 Table 5: Relationship between the quantities force, mass and acceleration 120 Table 6: Explain the terms below as precisely as possible 127 Table 7: List of electrical devices and their average power rating in watt 129

Theme 2.1.2 Table 1: A section of a load inventory for an elementary school 133 Table 2: Light source comparison chart (average values from various sources) 135 Table 3: Cost comparison between LED, CFL and incandescent light bulbs 142

10 Theme 2.2.1 Table 1: Resistivity of different metals in Ω/m 148 Table 2: Different materials resist the ﬂow of electric charge according to their physical properties 152 Table 3: Volt measurement across resistors 183

Theme 2.3.1 Table 1: Determination of potential (V) and current (I) for batteries connected in series 177 Table 2: Determination of potential (V) and current (I) for batteries connected in parallel 178

Topic 3 Theme 3.1.2 Table 1: Colours, symbols and shapes of ISO graphical safety signs 206

Theme 3.1.4 Table 1: Introduction to basic health and safety regulations 236 Table 2: Basic electrical hazard checklist 237 Table 3: Safety representative inspection list 238

Theme 3.1.5 Table 1: Effects of various levels of electric currents on the body 245 Table 2: Safety aspects associated with solar energy applications 257 Table 3: Preventive measures associated with solar energy applications 259

Topic 4 Theme 4.1.1 Table 1: Comparison between PWM and MPPT charging 278

Theme 4.1.2 Table 1: Global market share of wafer based crystalline silicon cells and thin film technologies 291 Table 2: Conversion efficiencies (industrial mass production) of wafer based crystalline silicon cells and thin film technologies 292 Table 3: PV technologies and their different temperature coefficients 292

11 GLOSSARY

An unplanned event that causes harm to people or damage to Accident property.

A category of hazard control that uses administrative/ manage- Administrative controls ment involvement, such as job rotation, work/rest schedules etc., in order to minimise employee exposure to hazards.

Charge can vary with time in several ways, resulting in several types of current. An electric charge ﬂowing back and forth at a set frequency will, for example, result in a time-varying current called an alternating current. AC is a current that varies sinusoidally over Alternating current (AC) time, for example 100 times per second at a frequency of 50 hertz. AC is provided by most power stations and is transmitted through the national grid to residential and commercial power users.

Non-crystalline semiconductor material, such as copper indium diselenide, cadmium telluride, gallium arsenide, or amorphous Amorphous silicon. The layer used to make photovoltaic cells usually has a thickness of only a few microns or less. Also called thin ﬁlm.

Ampere is the SI unit for the electric current (I) and can be deﬁned Ampere (A) in terms of charge (Q) and time (t), i.e. 1 coulomb 1 A = 1 second

These words are entirely unnecessary in engineering as we have technical terms for these quantities: electrical current, electrical potential and power. Thus, we will avoid these words in this textbook wherever we can. In the context of PV technologies this Amperage, voltage, wattage is however not always practical, as technical terms such as

open-circuit voltage (Voc) or voltage at maximum power (Vmp) are very common and are even used in module datasheets and guidelines.

A comparison between one thing and another for the purpose of explanation. The notion of quantities such as energy, charge and current is abstract and heavily theoretical, often involving difﬁcult Analogies mathematical concepts which are for most of us simply beyond understanding. Thus, we use analogies and models to illustrate and simplify scientiﬁc concepts of quantities and particles of matter.

A number of PV modules or thermal collectors mounted together Array to collect sunlight and convert the solar energy into either electrical energy or heat (hot water).

An atom is the smallest particle that comprises a chemical Atom element.

The azimuth angle is the compass direction the sunlight is coming from. Simply stated, it describes the direction of the Sun from East to West in degrees (°). At solar noon, the Sun is always directly South in the northern hemisphere and directly North in the Azimuth angle southern hemisphere. The azimuth angle varies throughout the day. At the equinoxes, the Sun rises directly East and sets directly West regardless of the latitude. Throughout the year however, the azimuth angle varies with the latitude and time of year.

12 Represents all components and costs other than the PV modules. It includes design costs, site preparation, support structures, Balance of System (BoS) system installation, inverter, operation and maintenance, batteries, and other related costs (sometimes even land).

Organic material formed by living or recently dead plants. Biomass, such as wood, is a source of chemical potential energy. The chemical potential energy is the result of photosynthesis Biomass transforming the Sun’s energy into a stored form. Biomass can be used as a fuel in power generation, with less impact on global warming than burning fossil fuels.

A diode connected across one or more solar cells in a photovoltaic module to protect these solar cells from thermal destruction, in Bypass diode case of total or partial shading or cell string failures of individual solar cells while other cells are exposed to full light. See also reverse bias.

Carbon dioxide (CO2) is a naturally occurring gas in the atmosphere. It is released into the atmosphere when solid waste, fossil Carbon dioxide fuels (oil, natural gas, and coal), and wood and wood products are burned. In most countries, carbon dioxide is the dominant greenhouse gas emission and is caused by human activities.

Electric charge is a derived quantity and can be deﬁned in terms of electric current (I) and time (t), i.e. Q = I × t . Opposite charges (positive-negative) attract each other and similar charges (posi- Charge (Q) tive-positive and negative-negative) repel each other. Electric charge is a fundamental property of matter and is the cause of all electrical phenomena. The SI unit of charge has been termed coulomb (C).

An electronic device which regulates the electrical potential applied to a battery system from the PV array. A controller is Charge controller essential to ensuring that batteries obtain the maximum state of charge and subsequently their desired cycle life.

An electric circuit is an interconnection of electrical elements or, Circuit more precisely, a complete path through which an electric current (I) can be conducted.

Climate change refers to the variation in the Earth’s global climate or regional climates over time. It describes changes in the Climate change variability or average state of the atmosphere or average weather over time. Most recently, these changes often have been caused by human activities.

A power plant used for intermediate and base-load power generation Combined cycle gas turbine running on natural gas using a combined cycle mode to achieve high- (CCGT) er efﬁciencies, i.e. up to 60 % compared to single cycle gas turbines which achieve efﬁciencies between 30-40 %.

Capable of catching fire and burning, usually a material that has Combustible an early flash point, i.e. below 40°C. See also flammable.

A power plant used for base-load power generation. CSP plants generate electric energy via a steam turbine by using parabolic Concentrated solar power mirrors to concentrate solar thermal energy onto a ﬂuid deposit (CSP) receiver atop a tower. The ﬂuid in the receiver is heated up to 500–1000 °C and is the heat source for the steam turbine.

13 Measures designed to eliminate or reduce hazards or hazardous Controls exposures. Examples include: engineering controls, administrative controls, personal protective equipment etc.

A corrosive substance is one that will destroy and damage other substances with which it comes into contact. It may attack a great variety of materials, including metals and various organic com- Corrosive pounds, but people are mostly concerned with its effects on living tissue: it causes chemical burns on contact, particularly the skin and/or the eyes.

Coulomb is the SI unit for charge (Q). The coulomb is deﬁned as the electric charge transported through any cross-section of a conductor in one second by a constant current of one ampere, i.e. Coulomb (C) 1 C = 1 ampere × 1 second . The coulomb is a large unit for charges: in 1 C of charge, there are 6.24 × 1018 electrons (a number with eighteen zeros). In contrast, the elementary charges of a single electron or proton are incredibly small, only 160 × 10−21 C.

Electric current is a base quantity. Simply put, current can be defined as a flow of charge, however it is more accurate to define Current (I) electric current as a rate of flow of charge, i.e. I = ∆Q. The SI unit of ∆t current is ampere (A).

Current at maximum power The current at which maximum power is available from a module. (Imp)

Number of discharge-charge cycles that a battery can tolerate Cycle life under speciﬁed conditions before its capacity decreases, e.g. to 80 % of its nominal capacity.

A diode is the simplest possible semiconductor device. In PV systems, diodes are used to restrict current from ﬂowing back- Diode ward through solar cells, thus protecting the PV module against the risk of thermal destruction of its solar cells.

There can be several types of current as charge can vary with time in several ways. If the current does not change with time but Direct current (DC) remains constant, we call it a direct current (DC). Direct current is provided by batteries, photovoltaic cells and other DC generators.

Efﬁciency is the ratio of output to input. Easy to remember as Efﬁciency what you get divided by what you put in.

Electrical energy (E) is a speciﬁc form of energy. Simply stated, electrical energy is equal to electric power (P) multiplied by time (t), i.e. E = P × t. If we place the correct SI units into this formula, i.e. watt (W) for power and hours (h) for time, we can see that electrical energy is not expressed in joule but in units of watt Electrical energy hours (Wh). If an appliance consumes or if a generator provides 1 kilowatt of power over a period of one hour, then 1 kilowatt hour (1kWh) of energy exists in some form over the course of this hour. Larger amounts of electrical energy can be measured in megawatt hours (1 MWh = 1 000 kWh).

In everyday language the term ‘electricity’ has so many different meanings that, in this textbook, we will try to avoid this term Electricity wherever possible and replace it with more appropriate terms, such as ‘electric charge’ or ‘electrical energy’.

14 A sub-atomic particle of negative charge that surrounds the Electron positively charged nucleus of an atom.

Energy is a derived quantity and is deﬁned as the capacity to do work (W), i.e. E = P × t. As with work (W) the SI unit of energy (E) is the joule (J). Energy is a varying property of matter and appears in Energy (E) different forms, for example as thermal energy (heat), electrical energy or kinetic energy (motion). Energy is never created nor destroyed, but merely transformed (energy conservation). This principle is also known as the ﬁrst law of thermodynamics.

The environmental footprint describes the effect that a person, company, activity, etc. has on the environment, for example the Environmental footprint amount of natural resources that they use and the amount of harmful gases that they produce.

An applied science that studies the interaction between people Ergonomics and the work environment. It focuses on matching the job to the worker.

A substance, mixture or compound that is capable of producing an Explosive explosion.

The immediate care given to a person who is injured or who suddenly becomes ill. It can range from disinfecting a cut and First aid applying a bandage to helping someone who is choking or having a heart attack.

Capable of easily catching ﬁre and burning, usually a material that Flammable has a ﬂash point below 40°C. See also combustible.

Forces (F) are able to alter the motion of objects. A force can Force (F) manifest itself in many different ways for example as weight, tension, buoyancy or electromagnetic force.

Fuels formed slowly over millions of years from buried and Fossil fuels fossilised biomass (plants or animals).

Global warming is the observed increase in the average tempera- Global warming ture of the Earth’s atmosphere and oceans in recent decades.

The process in which the absorption of infrared radiation by an atmosphere warms a planet. The natural greenhouse effect is due Greenhouse effect to naturally occurring greenhouse gases, while the enhanced greenhouse effect results from gases emitted as a result of human activities.

Some greenhouse gases occur naturally in the atmosphere, while others result from human activities. Naturally occurring green- Greenhouse gases house gases include water vapour, carbon dioxide, methane, nitrous oxide and ozone. Certain human activities, however, add to the levels of most of these naturally occurring gases.

A PV system acting as an energy generator supplying power to the Grid-connected national grid.

Electrical connection of one or more conductive objects to the Grounding Earth through the use of cables and metal rods or other devices.

15 The potential of any machine, equipment, process, material Hazard (including biological and chemical) or physical factor that may cause harm to people or damage to property or the environment.

The World Health Organisation has deﬁned health as more than Health just the absence of disease. Rather, it is a state of complete physical, mental and social well-being.

An undesirable phenomenon that can appear in PV systems whereby one or more cells within a PV module act as a resistive Hot spot load, resulting in local overheating or melting of the cell. Bypass diodes aim to prevent this phenomenon.

The rate at which energy strikes the surface of, for example, a Incident power solar array (photovoltaic cell or thermal collector).

Derived from incident solar radiation – it is a measure of the solar Insolation energy received on a speciﬁc area over time (W/m2/day). Don’t confuse insolation with insulation!

When one amount or value decreases, the other value increases at the same rate. For example, the further you are away from a light, Inversely proportional the less bright it appears: As distance increases, brightness decreases. As distance decreases, brightness increases.

An electronic device that converts DC into AC either for stand- Inverter alone systems or for grid-connected systems.

The graphical presentation of current versus potential from a PV module as the load is increased from the short-circuit (no load) I-V curve condition to the open-circuit (maximum voltage) condition. The shape of the curve characterises module performance at constant conditions (irradiation and temperature).

The sum of all tasks carried out by a person toward the comple- Job tion of a goal.

Joule is the SI unit used to measure energy (E) and work (W). The joule is deﬁned as the work done when the point of application of Joule (J) a force of 1 newton (N) is displaced 1 metre in the direction of that force, i.e. 1 joule (J) = 1 N × 1 m

A junction box is an enclosure ﬁxed on the back of a PV module to Junction box connect the wiring. It is where protection devices can be located (usually bypass diodes).

Any device in an electrical circuit which, when the circuit is Load energised (turned on), draws power from that circuit.

A speciﬁc set of procedures to ensure that a machine, once shut down for maintenance, repair or other reason, is secured against Lockout accidental start-up or movement of any of its parts for the length of the shutdown.

Lockout/tagout procedures aim to prevent accidents as a result of LOTO unintended activation of electrical equipment.

Maximum power point The point on the current-voltage (I-V) curve of a PV module where (MPP) the product of current and potential is at its maximum.

16 A power-conditioning unit that automatically (electronically) Maximum power point operates the PV system at its maximum power point. An MPPT can tracker (MPPT) increase the power efﬁciency delivered to the system by 10 to 40 %.

Maximum power voltage The potential difference value of a given device, usually a PV

(Vmp) module, at its maximum power point.

In engineering and science, models are used to illustrate and simplify abstract concepts. The notion of quantities such as energy, charge and current is abstract and heavily theoretical, Model often involving difﬁcult to understand mathematical concepts. We thus use analogies and models to illustrate and simplify scientiﬁc concepts of quantities and particles of matter.

Semi-conductor material that is solidiﬁed in such a way that individual crystals are symmetrically arranged. Compared to the Mono-crystalline multi-crystalline random arrangement of crystals, the more symmetrical structure of mono-crystalline materials increases PV cell efﬁciency.

Semi-conductor material that is solidiﬁed in such a way that many Multi-crystalline small and irregular crystals form. Sometimes also referred to as polycrystalline.

An instrument used to measure various electrical properties, including potential difference (V) across a component in volt (V), Multimeter current (I) through part of a circuit in ampere (A), and resistance (R) of components in ohm (Ω).

Newton is the SI unit used to measure force (F). The newton is deﬁned as the force which, when applied to a mass (m) of one Newton (N) kilogram, will give it an acceleration (A) of one metre per second m per second, i.e. 1 N = kg × s2

Unwanted sound that can lead to hearing loss or stress and Noise interferes with the ability to hear other sounds or to communicate.

Nominal Operating Cell Temperature (NOCT) is deﬁned as the temperature reached by open circuited cells in a module under the conditions as listed below: Irradiance on cell surface = 800 W/m² Nominal Operating Cell Air temperature = 20° C Temperature (NOCT) Wind velocity = 1 m/s Mounting = open back side Note the somewhat lower insolation conditions. In addition, module performance is often measured at an operating temperature of 45° C instead of 20° C.

Reactions that involve changes in the nucleus of an atom (distinct from chemical reactions). These reactions release large amounts of energy when some of the mass in the nucleus is transformed Nuclear reactions into energy according to Einstein’s great equation E =mc2. Solar energy comes from nuclear fusion reactions in the Sun’s core, where hydrogen nuclei are forced to combine under tremendous heat and pressure into helium.

17 The development, promotion and maintenance of workplace Occupational Health and policies and programmes that ensure the physical, mental and Safety Act (OHS) emotional well-being of employees.

Ohm is the SI unit used to measure electrical resistance in a conductor. The ohm is deﬁned as the electrical resistance be- Ohm (Ω) tween two points of a conductor: when a constant potential difference of one volt is applied between those points, a current 1 volt of one ampere results, i.e. 1 Ω = 1 ampere . Ohm’s law describes the relationship between current, potential and resistance. It states that current (I) is inversely proportional to the overall resistance (R) in the circuit and directly proportional to the electric potential difference (V) impressed across the circuit. The term ‘inversely proportional’ describes the relationship between current and resistance, i.e. ampere values decrease at the same rate the ohm values increase. The term ‘proportional’ Ohm’s law here describes the relationship between current and potential difference, i.e. ampere values increase at the same rate as volt values increase. Written as mathematical expressions, Ohm’s law is: I = V / R V = I × R R = V / I

A power plant used for base-load power generation running on Open cycle gas turbines natural gas using a single cycle mode with an average efﬁciency (OCGT) of between 30-40 %.

The maximum possible potential across a photovoltaic cell or Open-circuit voltage (V ) oc module when no current is ﬂowing.

Overcurrent protection device. Make sure to select and use only Overcurrent protection OCPDs that are correctly rated for the level of current (ampere) or device (OCPD) power (watt) required for the installation.

Connecting two or more energy generating devices such as PV cells or modules by joining their positive leads together and their Parallel negative leads together. Such a conﬁguration increases the amount of current.

Any device worn by a worker to protect against hazards, for Personal protective example, respirators, gloves, ear plugs, hard hats, safety goggles equipment (PPE) and safety shoes.

Photon A particle of light that acts as an individual unit of energy.

The process by which the energy from sunlight is used to chemically combine the raw materials of carbon dioxide, gas and water into glucose sugar. This energy transformation from active radiant Photosynthesis energy (sunlight) to stored chemical potential energy (glucose) is carried out by tiny structures inside plant cells called chloroplasts. Chloroplasts contain the green molecule chlorophyll.

Photovoltaic is the technique used to convert radiation energy Photovoltaic (PV) from the Sun (light) into electrical energy.

18 An electronic device made of semiconductor material that transforms the radiant energy of sunlight into electrical energy. Photovoltaic cell The electric potential (V) generated by each cell is about 0.6 volt (DC), thus many cells are added in series to produce greater potential.

Several photovoltaic cells that are connected in series and/or in Photovoltaic module parallel to increase the electric potential form a photovoltaic module.

Usually a photovoltaic system consists of various components, including one or more photovoltaic modules connected to an Photovoltaic system inverter/controller. The system is designed to provide electrical energy (direct current).

Power is the rate of doing work and is measured in watt (W), i.e. 1 joule 1 W = 1 second . During this process, energy is transmitted and converted into another form of energy. Thus, power indicates the Power (P) rate at which: (i) An appliance uses electrical energy, or (ii) Electrical energy is provided by a generator.

Two quantities are proportional to each other when they have the same size, amount or value in relation to each other. For example, length and weight are in proportion to each other when: 20 m of copper cable weighs 1 kg 40 m of copper cable weighs 2 kg 200 m of copper cable weighs 10 kg etc. Thus, as one amount increases, another amount increases at the same rate. Here is another example, if you are paid R100 an hour Proportional how much you earn is directly proportional to how many hours you work. If you work more hours, you get proportionally more pay: If you work 2 hours you get paid R200 If you work 4 hours you get paid R400 etc. This relationship between wages and hours worked could be written as: Wages are proportional ( to hours worked. In other words, wages and hours worked have the same ratio. ∝) A prototype or protoboard is used to temporarily wire circuits for Prototype board experiments without soldering them.

A rate is a ratio that is used to correlate different types of quantities. A unit rate describes how many of the ﬁrst quantity corresponds to one unit of the second quantity. Some common unit rates include km per hour, kW per hour or more speciﬁcally coulomb per second. In any case the second unit, i.e. in our case either hour or second, is equal to 1. To determine a unit rate, you Rate need to scale the denominator of the original ratio to 1. For example, if a fridge absorbs 1 kW in 5 hours, the ratio is 1 000 to 5 or 1 000 . To determine the unit rate, you need to divide the 5 numerator and denominator by 5 so that the denominator is equal to 1, i.e. 200 = 200. The unit rate for this ratio is 200 W per 1 hour.

19 A ratio compares amounts or values and indicates how much of one amount there is in comparison to another amount. For example, a recipe for pancakes uses 3 cups of flour and 2 cups of milk. The ratio of flour to milk is 3 to 2. To make pancakes for Ratio more people we might need 4 times the quantity of ingredients, so we need multiply the values by 4, i.e. 3 × 4 and 2 × 4 is equal to 12 to 8, or 12 cups of flour and 8 cups of milk. Note, that the total amount of milk and flour for the pancakes has increased, but the ratio between milk and flour remains the same (3 to 2).

Renewable energy comes from a naturally occurring resource that Renewable energy is continually and naturally replenished.

An impedance to the ﬂow of charge in a circuit measured in ohm Resistance (R) (Ω).

A condition where the current-producing capability of a PV cell is signiﬁcantly less than that of other cells in its series string. This Reverse bias can occur when a cell is shaded, cracked, or otherwise degraded or when it is electrically poorly matched with other cells in its string.

The probability of a worker suffering an injury or health problem, Risk or of damage occurring to property or the environment as a result of exposure to - or contact with a hazard.

Roof penetration happens when the installation process of a PV Roof penetration system requires a modiﬁcation to the existing roof structure, e.g. holes need to be drilled or tiles require grinding and cutting.

Quantities, such as length (l) and time (t) which can be described Scalar by a magnitude (a numerical value) alone. For example, the SI units for length and time are meter (m) and second (s).

Any material that has a limited capacity for conducting electric current. Semiconductor materials generally fall between metal and insulators in conductivity. Certain semiconductors, including Semiconductor silicon, gallium arsenide, copper indium diselenide, and cadmium telluride, are uniquely suited for the photovoltaic conversion process.

A way of connecting two or more energy generating devices such as PV cells or modules by joining their positive leads to their Series negative leads. Such a conﬁguration increases the amount of potential.

The current ﬂowing freely from a photovoltaic cell through an

Short-circuit current (Isc) external circuit that has no load or resistance. It is the maximum current possible.

A chemical element (Si) and a common constituent of sand and Silicon quartz. Silicon is an excellent semiconductor and the most common material used in making photovoltaic devices.

Sine wave inverter Any type of inverter that produces utility-quality sine wave power.

A solar thermal collector is a device speciﬁcally intended to Solar thermal collector collect heat, i.e. to absorb sunlight, and to provide hot water (solar water heating, SWH).

20 An autonomous PV system not connected to the national grid. Stand-alone Such systems usually have power storage capacities (batteries).

Conditions under which a module is typically tested in a laborato- Standard test conditions ry, i.e. an irradiance intensity of 1000 W/m2 and at a cell (module) (STC) temperature of 25° C.

A solar thermal collector is a device speciﬁcally intended to Task collect heat, i.e. to absorb sunlight, and to provide hot water (solar water heating, SWH).

Toxic Harmful or poisonous.

Any of the various types of machine in which the kinetic energy of a moving ﬂuid, i.e. water, steam, air etc. is converted into mechan- Turbine ical energy by causing a bladed rotor to rotate. To transform the mechanical energy into electrical energy and convey electric charges, the turbine is attached to and spins a generator.

A label which distinguishes one type of measurable quantity from another type. For instance, length (l), mass (m) and time (t) are Unit distinctly different physical quantities and therefore have different unit names such as meter, kilogram and second. In this textbook we use the SI system of units.

Quantities, such as force and acceleration need to be described by both a magnitude and a direction. Free-body or vector diagrams can be used to represent forces. In these diagrams a force is Vector represented by an arrow. The size of the arrow indicates the magnitude of the force measured in newton. The direction into which the arrow is pointing reveals in which direction the force is acting.

The supplying, exchanging and circulation of air to an enclosed Ventilation machine, room or building.

Volt is the SI unit used to measure potential difference in a circuit. 1 volt is deﬁned as the potential difference between two points Volt (V) so that the energy used in conveying a charge of 1 coulomb from one point to the other is 1 joule, i.e. 1 joule 1 V = 1 coulomb.

The cycle by which water is moved in its various forms (liquid, solid, gas/vapour) from one reservoir (oceans, atmosphere, land Water cycle surfaces, plants and animals) to another through the processes of evaporation, condensation, precipitation, runoff, freezing, melting etc. The water cycle is driven by solar energy.

Watt is the SI unit of electrical power (P). The watt is deﬁned as Watt (W) the power resulting when 1 joule of energy (E) is dissipated in one 1 joule second, i.e. 1 W = 1 second .

Watt hour is a unit for energy (E) and deﬁned as the amount of Watt hour (Wh) power (P) in watt that is consumed or supplied in one hour (h). W and Wh are related but different units. Don’t confuse the two!

The surrounding conditions, inﬂuences and forces which an Working environment employee is exposed to in the workplace.

21 PREFACE

On behalf of the German Ministry of Economic Cooperation and Development (BMZ), the Skills for Green Jobs (S4GJ) programme, together with the South African Departments of Higher Education and Training (DHET) and Science and Technology (DST), jointly developed and implemented a number of activities which aim to:

1. Support qualif ed TVET lecturers in their continuous professional development through training in Renewable Energy and Energy Ef ciency Technologies. 2. Develop and support the implementation of a new optional vocational subject on Renewable Energy Technologies for NC(V) students. 3. Develop appropriate training material, such as student textbooks and lecture guides, for the new subject.

Subsequently, we are very happy that the student book for NC(V) level 2 Renewable Energy Technologies is now available in its 2nd revised edition. T e new subject and student book is for students of the technical NC(V) programmes who want to learn more about renewable energy technology, its potentials and limitations. T e student book introduces students to the relevant technical concepts, illustrates examples from real world applications, and of ers exercises and practical work/experiments.

Yours in renewable energy…

22 FOREWORD BY THE DIRECTOR-GENERAL OF THE DEPARTMENT OF HIGHER EDUCATION AND TRAINING

T e Department of Higher Education and Training is pleased to introduce the subject Renewable Energy Technologies in the National Certif cate (Vocational) NC(V) Electrical Infrastructure Construction programme. T is new subject is the latest addition to the vocational specialisation options of ered in Technical and Vocational Education and Training (TVET) colleges and has been developed for students who want to learn more about renewable energy generation and the technologies related therewith.

Outlined in Accord 4 of South Africa’s new growth path, government commits to the procurement of renewable energy, with the aim to expand and diversify the nation’s energy generation capacity, whilst lowering greenhouse gas emissions, in order to meet the challenges posed by climate change. To fully re- alize these commitments the economy needs informed and trained people in this f eld, which continues to be a signif cant driver for future employment. T e Industrial Development Corporation (IDC) and the South African Development Bank (SADB) estimated in 2011 that the total employment potential in the energy generation and energy and resource ef ciency categories would be 130 000 and 68000 new jobs respectively.

Under the auspices of the German Ministry of Economic Cooperation and Development (BMZ) and supported by the Department of Higher Education and Training (DHET) and the Department of Science and Technology (DST), the Skills for Green Jobs (S4GJ) programme drove the process of developing this new subject, the training material, student textbook and lecturer guide and trained TVET College lecturers on the subject matter content on new didactical training equipment as part of their continuous professional development so that they can teach the subject in a practical and progressive manner.

T us, in January 2015 the subject Renewable Energy Technologies was successfully implemented on NC(V) Level 2 in seven TVET colleges, namely Boland, East Cape Midlands, Ingwe, Northlink, Port Elizabeth, Umfolozi and West Coast TVET Colleges.

T e development and implementation of this new subject is the result of cordial collaboration and successful cooperation between Germany and South Africa and I wish the colleges, the lecturers and mostly our students a good start with Renewable Energy Technologies in 2015 and beyond.

Mr GF Qonde Director-General: Higher Education and Training

Foreword written by the Director-General for the f rst edition of the student book in 2015.

23 USING THIS STUDENT BOOK

T is textbook is comprised of 4 topics for NC(V) level 2.

T e structure of each topic includes various units, for example Unit 1 of Topic 1, International and National Climate Change Policies, and each unit is made up of several themes. In essence, the themes form the core of the student book. T ey contain keywords, the desired outcomes, technical terms and def nitions, illustrative examples, as well as questions, exercises and experiments through which the students can independently check their knowledge and understanding. Lastly, each theme ends with a bibliography section which will enable students to supplement the described subject matter.

24 TOPIC TOPIC

Introduction to Renewable Energy Resources and Energy Efﬁ ciency

Topic Overview

Climate change is happening. Rising global temperatures have been accompanied by changes in weather and climate. Many places have seen changes in rainfall, resulting in more ﬂ oods in some areas and droughts in others. The oceans are warming too, ice caps are melting, and sea levels are rising. As these and other changes become more pronounced in the coming decades, they will likely present challenges to our society and our environment. Today’s energy supply, mainly the burning of ever-greater quantities of fossil fuel such as coal and oil, is largely responsible for global warming. Thus, it is important not only to understand the main causes of climate change, but also to implement adequate response options for mitigation and adaptation.

Topic 1 covers the following units:

Unit 1.1 International and National Climate Change Policies Unit 1.2 Differences between Energy Resources Unit 1.3 Signiﬁ cance of Solar Radiation

25 Unit 1.1 Unit

UNIT 1.1 INTERNATIONAL AND NATIONAL CLIMATE CHANGE POLICIES

Introduction

Changes in the average weather that an area experiences over a long time is called climate change. T e warmer it gets, the greater the risk for more severe changes to the climate and the environment. Some changes to the climate already impact vulnerable groups and communities in South Africa. Although it is dif cult to predict the exact impacts of climate change, what is clear is that the climate we are accustomed to is no longer a reliable guide for what we can expect in the future. But by making choices that reduce the causes of climate change, specif cally greenhouse gas emissions, and by preparing for the challenges that are already underway, we can reduce the risks we will face from climate change. T us, our decisions on what kind of energy resources we want to use in future will shape our world and the world of the future – the world you, your children and grandchildren will live in. Unit Outcomes

At the end of this unit, you should be able to: (i) Explain the main causes of climate change. (ii) Describe and interpret potential impacts of climate change. (iii) Present climate change response options and explain why both mitigation and adaptation work best when applied at the same time. Themes in this Unit

Unit 1.1 covers three themes: T eme 1.1.1 Causes and Impacts of Climate Change and Global Warming T eme 1.1.2 Mitigation and Adaptation Concepts T eme 1.1.3 International and National Policies on Climate Change

26 THEME 1.1.1 CAUSES AND IMPACTS OF CLIMATE CHANGE AND GLOBAL WARMING

Introduction

Much of South Africa experiences arid or semi-arid conditions and is thus considered a stressed environment. T e country is prone to droughts and f ooding, and even a small variation in rainfall or temperature intensif es existing vulnerabilities. Increased temperatures have a far reaching impact on the climate, inf uencing phenomena such as precipitation (rain) and cloud cover. As a result, climate change has the potential to af ect almost every sector in South Africa, including agriculture, water, health, trade, transportation, infrastructural development, tourism and f nance. THEME 1.1.1 Keywords

Atmosphere Climate change Global warming Greenhouse gases Greenhouse ef ect Emissions Solar radiation Theme Outcomes

At the end of this theme, you should be able to: (i) Explain the main causes of climate change. (ii) Describe potential climate change impacts on our society and our environment.

Deﬁ nition of Terms Climate vs. Weather Weather is not the same as climate. Weather is the day-to-day change of the atmosphere, for example, today it is sunny, rainy and/or windy. Climate is the average weather that an area experiences over a long time, for example, a place like Durban usually has a sub-tropical (warm and wet) climate, while Cape Town typically has more of a Mediterranean type of climate (cold, wet winters and warm, dry summers). Climate Variability Climate variability refers to the way climate variables, such as temperature and rainfall, dif er from their average state in an area without changing the long-term average. Many places in the Eastern Cape Province, for example, might have an average summer temperature of 21°C, but daily temperatures could range from 20°C to 30°C. Climate Change Climate change refers to the long-term shif in weather patterns. It may involve a change in the average weather patterns (e.g. more or less rainfall) or in the frequency and/or intensity of events (e.g. more or fewer storms). Climate change can be the result of natural causes, such as volcanic eruptions, or it can have human causes, such as greenhouse gas emissions from the burning of petrol. Atmosphere T e atmosphere is a critical system that helps to regulate Earth’s climate around the globe. T e atmosphere is mainly composed of nitrogen, oxygen, argon, water vapour and a number of trace gases. T e Earth’s atmosphere extends over a few hundred kilometres above the planet’s surface and is divided into four layers, each of which has distinct thermal, chemical and physical properties. Today human actions are changing key dynamic balances in the atmosphere. More importantly, human activities are increasing greenhouse gas levels in Earth’s f rst layer, thereby increasing the amount of heat radiated from the atmosphere back to the ground.

27 THEME 1.1.1 28 the atmosphere (TOA) incoming radiation. (TOA) atmosphere radiation. the incoming TOA: top of to space. at the surface Earth’s the from escaping it from preventing radiation, infrared the (GHG) gases some Greenhouse of space. into trap slowly radiation) back heat (infrared the releases then T up and Earth. warms of the surface the eEarth to warm atmosphere the through 70% passes maining f re is re- of sunlight about 30% the while space, into back Earth Sun’s the ected reaches the As energy ch2-graphics/ Image source: GIZ/S4GJadapted from 2013,WGI_AR5_Fig2-11. IPCC http://www.climatechange2013.org/report/reports-graphic/ 2: FIGURE spectrum. electromagnetic the in UV and IR between positioned is which light, visible includes Sunlight rays. (UV) (IR) to ultraviolet infrared from ranging waves of electromagnetic amixture is sunlight, as known more popularly Sun, the from Radiation RadiationSolar http://www.esrl.noaa.gov/csd/research.html Administration. Atmospheric and Oceanic National U.S. from adapted GIZ/S4GJ source: Image FIGURE 1: FIGURE atmosphere Solar absorbed Incoming solar TOA Units (W/m UV/ Visible sunlight (0.2, 1.0) (74, 91) 0.6 79 SOLAR RADIATION RADIATION SOLAR (340, 341) 340 SCHEMATIC ILLUSTRATION OF THE REGIONS OF OUR OUR OF REGIONS THE OF ILLUSTRATION SCHEMATIC

O ATMOSPHERE

Imbalance z o 2

) n e surface down Solar la y e r (179, 188) Solar absorbed 185 (154, 166) surface 161 (5.5 miles) ~ 9km Mt. Everest Solar reﬂected TOA (22, 26) 24 (96, 100) 100 surface reﬂected Solar Evapo- ration ( STRATOSPHERE SIMPLIFIED TROPOSPHERE (70, 85) MESOSPHERE 84 Latent heat Sensible heat (15, 25) 20 ) (5 miles) up surface Thermal ~ 8km (394, 400) 398 radiation

Infrared Thermal outgoingThermal TOA 60°F (236, 242) 239

down surface -80°F (338, 348) Thermal

342 ~

(5.5 - 7.5 miles) radiation 5

Infrared

Atmospheric 0

Greenhouse

~ 9 - 12km m

window ( 3

gases

) 0°F Image source: IPCC 2013, WGI_AR5_FigSPM-1 (pane b). http://www.climatechange2013.org/report/reports-graphic/report- graphics/ 4: FIGURE activities. human by produced emissions by words, other trations of greenhouse gases originating from the ever-increasing use of fossil fuels (oil, petrol, and coal), in concen- atmospheric T (IPCC). increasing by fChange e caused Climate on Panel warming mainly e is ect crease by 2 – 6°C by the end of the century. T ese changes have been closely monitored by the International On average, temperatures have global over increasing are and predictedbeen decades last steadily tothe in- Global iswarming the general increase in temperature caused by human-related greenhouse gas emissions. Global Warming atmosphere. the in gases T of greenhouse amount the methods. have increased activities ese farming of certain practice the f and of forests, of land amounts cutting larger the and larger waste, ll of generation the coal, and petrol oil, as such fuel of fossil quantities of ever-greater burning the larly particu- of industrialisation, 150 is years temperatures for increasing reason main the scale, aglobal On Power_stations_in_South_Africa. Wikipedia, from: adapted source Image FIGURE 3: gas. natural and oil, coal, wood, as such fuels of carbon-based combustion the from mainly result activities produced by human Emissions factories. and power from plants leased re- of being most Emission gases greenhouse air, for example the into released being en refers to gases Emission

OBSERVED CHANGE IN SURFACE TEMPERATURE 1901 TEMPERATURE SURFACE IN CHANGE OBSERVED ESKOM’S ARNOT POWER STATION, MIDDELBURG/MPUMALANGA STATION, POWER ARNOT ESKOM’S – 2012 29

THEME 1.1.1 Greenhouse Gases (GHG) GHG are gases in the atmosphere that take in (absorb) and ref ect (emit) solar radiation. T is process is

the fundamental cause of the greenhouse ef ect. GHGs include carbon dioxide (CO2), methane (CH4), ni-

trous oxide (N2O), carbon monoxide (CO), nitrogen oxides (NOx), and chlorof uorocarbons (CFCs). T e primary source of carbon dioxide emissions is burning of fossil fuels and biomass. Additional carbon dioxide is released through industrial processes, such as the production of cement. T e primary sources of methane are paddy f elds, cattle and other animals, landf lls, and waste streams. A major source of nitrous oxide is from the use of fertilisers for crop production. CFCs are released during the manufacture of refrigerants and insulation. Nitrogen oxides come primarily from fuel combustion, during which nitrogen and oxygen combine at high temperature. Carbon dioxide is recognised as the biggest culprit to global warming. T is is due to the molecules of carbon dioxide letting the visible light from the Sun pass right through the atmosphere; however, when that visible light heats up the surface of the Earth, the Earth radiates out some of this heat as infrared

THEME 1.1.1 light (infrared radiation).

FIGURE 5: SCHEMATIC ILLUSTRATION OF CARBON DIOXIDE’S FUNCTION IN THE ATMOSPHERE

here osp Atm

Earth

Image source: GIZ/S4GJ Similar to other greenhouse gases, carbon dioxide will absorb infrared radiation and radiates half of it back towards the Earth (greenhouse ef ect). Greenhouse Effect T e Earth receives energy from the Sun in the form of solar radiation. T e Sun emits strongly in the visible light range, but it also produces ultraviolet and infrared radiation. T e Earth radiates heat back into space, mostly at much longer wavelengths than solar radiation (infrared rays). Some outgoing infrared energy emitted from the Earth however gets trapped in the atmosphere and is prevented from escaping to space by a natural process called the greenhouse ef ect. While nitrogen and oxygen, the most abundant gases in the atmosphere, neither absorb nor emit ter- restrial or solar radiation, water vapour (clouds) and greenhouse gases (GHGs) in the atmosphere can absorb longwave radiation. Life on Earth is only possible because the Sun provides the necessary energy and some of the gases in the atmosphere capture and hold the radiated energy simi lar to the glass of a greenhouse which keeps the plants inside warm. Without this ef ect all radiated heat would be lost into space and the surface of the Earth would be too cold to support life. T e “greenhouse ef ect” is named by analogy af er greenhouses. T e greenhouse ef ect and a real greenhouse are similar in that they both limit the rate of thermal energy f owing out of the system, only the mechanisms by which heat is retained are dif erent. A greenhouse works primarily by preventing absorbed heat from leaving the structure through heat transport (convection).

30 T e ever increasing use of fossil fuels (oil, petrol and coal), has resulted in increased GHG emissions, bringing the natural greenhouse process out of balance. T e increased amounts of man-made GHG emissions in the atmosphere absorb more and more longwave energy emitted from the Earth’s surface, preventing it from escaping into space. T e increased levels of GHG re-emit the absorbed energy towards Earth in all directions, warming the Earth’s surface progressively. T us, human activities have amplif ed the natural greenhouse ef ect and this is causing Earth’s surface temperature to increase. T e disastrous result is that heat is building up on the Earth’s surface and in the oceans, causing global warming and weather extremes.

FIGURE 6: SCHEMATIC ILLUSTRATION OF THE GREENHOUSE EFFECT

Short wavelength heat THEME 1.1.1 radiation from the Sun

Re-radiated long wavelength heat radiation

Image source: GIZ/S4GJ A greenhouse traps the Sun’s energy inside and keeps the plants warm. Simplif ed, it works like this: Sunlight, shortwave radiation, mostly passes through the glass and warms the interior of the greenhouse. T e glass absorbs longwave radiation almost completely and consequently traps the heat in the greenhouse’s interior. In this way, the interior of the greenhouse assumes a higher temperature inside than outside. Carbon Dioxide

Carbon dioxide (CO2) is considered the most signif cant greenhouse gas because its concentration in the atmosphere has increased at an exceptional rate over the last half of the century. Before the industrial era, atmospheric concentrations of carbon dioxide were relatively stable. Between 1850 and 2000, however, carbon dioxide emissions have drastically increased. T is increase is mainly man-made (anthropogenic) originating from the combustion of fossil fuels, changes in land use and the chemical processes involved in cement manufacture.

In 2005 the value of atmospheric carbon dioxide concentration in the atmosphere showed a 35% increase compared to pre-industrial levels, causing an additional heating ef ect. While various factors inf uence the climate, climatic models indicate that global temperature increases are linked to atmospheric greenhouse gas levels. T us, it is fairly certain that greenhouse gases emitted by human activities are contrib- uting to global warming. Climate Change Impacts Climate change impacts are the consequences of climate change on a human or natural system. For example, climate change causes less rain in some areas and heavy rains or storms in other areas. As a result, these changes give rise to impacts that could include droughts, crop failure, livestock death, damage to infrastructure, runaway f res and famine etc.

31 Vulnerability Our vulnerability will determine how seriously climate change will af ect us. An increase in diseases, threats to existing livelihoods or damage to household assets caused by climate change for example, will have the greatest ef ect on the poorest and most vulnerable in our society.

Examples

Over the last decades, global (mean) temperatures have been steadily increasing. In South Africa, we are currently experiencing the highest temperatures since direct measurements began. T e following climate trends have been observed in South Africa over the last f ve decades: THEME 1.1.1 (i) Temperatures: It is getting hotter. More specif cally, the mean annual temperature has increased by at least 1.5 times the observed global average of 0.65°C. Maximum and minimum daily temperatures have been increasing annually, and in almost all seasons. (ii) Rainfall: Drier conditions are evident in the west and south of the country, and wetter conditions in the east of the country. T us, there is a trend towards an increase in the intensity of rainfall events in some areas and increased dry spells in other areas.

From a socio-economic aspect, South Africa is particularly vulnerable to the impacts of climate change for a number of reasons. Firstly, a large proportion of the population lives in impoverished circumstances. Most townships and informal settlements are located in areas that are vulnerable to extreme weather events. Already, lack of adequate housing structures results in insuf cient protection against rain, wind and cold. Much of South Africa experiences low and variable rainfall. Ade- quate access to safe drinking water is also a problem for some communities as most of the surface water resources are already utilised to their full potential. T us, water shortages are a problem and climate change could exacerbate this challenge even further in the near future.

Your own notes

32 FIGURE 7: EXAMPLES OF CURRENT AND POSSIBLE FUTURE IMPACTS AND VULNERABILITIES ASSOCIATED WITH CLIMATE VARIABILITY AND CLIMATE CHANGE FOR AFRICA THEME 1.1.1

Image source: IPCC 2007, wg2/en/f gure-9-5. https://www.ipcc.ch/publications_and_data/publications_and_data_f gures_and_ tables.shtml

Note

T ese examples are indications of possible change and are based on models that currently have recognised limitations.

33 Exercises

(i) Use the CD and look at slide No. 8 from the IPCC (2013) PowerPoint Presentation, Figure SPM.1, Panel b: Observed change in average surface temperature 1901-2012. Notice the colours and notice the areas with the highest impact. Find South Africa and determine the temperature increase in Celsius (°C)! (ii) Climate change is the result of global warming, but what is the cause of global warming? (iii) Which greenhouse gases (GHG) in the atmosphere are responsible for absorbing and trapping outgoing radiation? Describe the greenhouse process with the help of a simple drawing!

FIGURE 8: HOW DO WE KNOW THAT THE WORLD HAS WARMED? THEME 1.1.1

Glacier volume

Air temperature in the lowest few km (troposphere)

Water vapor Temperature over land

Sea ice area

Snow cover Marine air temperature

Sea surface temperature

Sea level

Ocean heat content

Image source: GIZ/S4GJ adapted from IPCC 2013, Chapter 2, Box 1, WGI_AR5_FigFAQ2.1-1. http://ipcc.wikia.com/wiki/File:WGI_AR5_FigFaq2.1-1.jpg

Your own notes

34 (iv) Impacts of global warming: Try to identify the various impacts of climate change by interpreting the arrows of the various features in Figure 8. Present your results in the table below!

Features Impacts

Air temperatures

Glacier volumes

Temperature over land THEME 1.1.1

Snow cover

Sea level

Ocean heat content

Sea surface temperature

Marine air temperature

Sea ice area

Water vapour

Further Information (all materials are on the resource CD)

(i) DEA, 2013: LONG-TERM ADAPTATION SCENARIOS SUMMARY FOR POLICY-MAK- ERS. High-level/key messages emerging from LTAS Phase 1. (ii) http://www.environment.gov.za (iii) IPCC Fourth Assessment Report: Climate Change 2007: Working Group II: Impacts, Ad- aptation and Vulnerability. (iv) http://www.ipcc.ch/publications_and_data/publications_and_data_reports.shtml (v) IPCC, 2013: Summary for Policymakers. In: Climate Change 2013: T e Physical Science Basis. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 1–30. http://www.climatechange2013.org (vi) IPCC, 2013: PowerPoint presentation produced by IPCC. T e PPT is based on the f gures and approved text from the IPCC Working Group I Summary for Policymakers with some additional information. http://www.climatechange2013.org/press-events/ (vii) United States Environmental Protection Agency (EPA), 2014: Causes of Climate Change. http://www.epa.gov/climatechange/science/causes.html# (viii) Renewable Energy Systems Ltd (RES), 2007: GLOBAL WARMING a guide to its origins and ef ects. www.res-group.com (ix) WWF, 2006: Impact of Climate Change in Africa, Paul V. Desanker, Center for African Development Solutions, Johannesburg, South Africa. www.panda.org/climate

35 THEME 1.1.2 MITIGATION AND ADAPTATION CONCEPTS Introduction

T e evidence for man-made climate change is overwhelming and environmental challenges, such as the loss of biodiversity, are closely linked to climate change and to our customary industrial economic practices. T us, in view of the generally detrimental consequences of climate change, it is in our best interests to adapt to global warming and to mitigate global warming as far as possible. While adaptation strategies are essential in order to address the unavoidable impacts of climate change, serious reductions to greenhouse gas (GHG) emissions is the most ef ective course of action. GHG emissions can be reduced without af ecting economic growth if the worldwide demand for renewable energy technologies would

THEME 1.1.2 increase signif cantly. Country studies show that their aggregate mitigation potential is high. Barriers to the implementation of renewable energy technologies options need to be considered as priority policy measures. Keywords

Adaptation Mitigation Resilience Theme Outcomes

Societies can respond to climate change dif erently. At the end of this theme, you should be able to: (i) Explain the two major response concepts: adaptation and mitigation. (ii) Justify why both adaptation and mitigation are essential to reducing the impacts of climate change. (iii) Give good reasons why climate change awareness campaigns make sense.

Deﬁ nition of Terms Adaptation Adaptation refers to adjustments in ecological, social, or economic systems in response to actual or expected climatic changes and their ef ects or impacts. It refers to changes in processes, practices, and structures to moderate potential damages or to benef t from opportunities associated with climate change. Resilience Climate change resilience is the capacity of an individual, a community or a region to respond ef ectively to climate change impacts while continuing to function at an acceptable level. Simply put, it is the ability to survive and recover from the ef ects of climate change. Resilience includes the ability to understand and to plan for potential impacts and to take appropriate action before, during, and af er a particular impact to minimise negative ef ects and maintain the ability to respond to changing conditions. Table 1 lists examples of adaptation initiatives in various countries, undertaken relative to present climate risks (adapted from Climate Change 2007: Impacts, Adaptation and Vulnerability. Working Group II, Fourth Assessment Report).

36 TABLE 1: EXAMPLES OF ADAPTATION INITIATIVES IN VARIOUS COUNTRIES

Country Climate-related impacts Adaptation practices Egypt Requiring environmental impact assessment (EIA) for project Sea-level rise approval and regulating setback distances for new coastal infrastructure. Sudan Expanded use of traditional rainwater harvesting and water Drought conserving techniques. Building of shelter-belts and wind- breaks to improve resilience of rangelands. Monitoring of the number of grazing animals and cut trees. THEME 1.1.2 Set-up of revolving credit funds. Botswana National government programmes to recreate employment Drought options after drought. Capacity building of local authorities. Assistance to small subsistence farmers to increase crop production. Bangladesh Building of flow regulators in coastal embankments. Sea-level rise Use of alternative crops and low technology water filters. Salt-water intrusion Philippines Shift to drought resistant crops. Drought Use of shallow tube wells. Floods Rotation method of irrigation during water shortage. Construction of water impounding basins. Construction of fire lines and controlled burning. Adoption of soil and water conservation measures for upland farming. Philippines Provision of grants to strengthen coastal resilience and rehabil- Sea-level rise itation of infrastructures. Storm surges Construction of cyclone-resistant housing units. Retrofit buildings to improved hazard standards. Review of building codes. Reforestation of mangroves. Philippines Rainwater harvesting. Drought, Leakage reduction. Saltwater intrusion Hydroponic farming. Bank loans allowing for purchase of rainwater storage tanks. Canada Changes in livelihood practices including change of hunting Permafrost melt locations and diversification of hunted species. Change in ice cover United States Land acquisition programmes to acquire coastal lands dam- Sea-level rise aged/prone to damages by storms or buffering other lands. Mexico and Argentina Adjustment of planting dates and crop variety, e.g., inclusion of Drought drought-resistant plants such as agave and aloe. Accumulation of commodity stocks as economic reserve. Spatially separated plots for cropping and grazing to diversify exposures. Diversification of livestock operations. Set up provision of crop insurance.

37 Country Climate-related impacts Adaptation practices The Netherlands Building of storm surge barrier taking a 50 cm sea level rise into Sea-level rise account. Use of sand supplements added to coastal areas. Improved management of water levels through dredging, widening of river banks, allowing rivers to expand into side channels and wetland areas. Deployment of water storage and retention areas. Conducting of regular (every 5 years) reviews of safety characteristics of all protecting infrastructure (dykes, etc.). United Kingdom Coastal realignment converting arable farmland into salt marsh THEME 1.1.2 Floods and grassland to provide sustainable sea defences. Sea-level rise

Can you think of adaptation practices that should be used in South Africa?

Mitigation Societies can respond to climate change by reducing GHG emissions. T e capacity to mitigate ef ectively depends on socio-economic and environmental circumstances and the availability of information and technology. T us, governments can use a variety of policies and instruments to create the incentives for mitigation action. T ere are two ways to stop increasing the amount of GHG emissions in the atmosphere: (i) Reduce GHG emissions altogether (ii) Capture GHG in a more ef ective way

Reduction of GHG emissions is usually accomplished through: (i) Reducing energy use (energy ef ciency) (ii) Using renewable energy technologies such as photovoltaic or wind power plants, hydrogen fuel cells, geothermal power etc.

GHG capturing can be done through so-called carbon sinks or carbon sequestration, for example by pro-

tecting natural forests and by planting more trees in cities so that they can absorb more CO2 from the air. T ese two methods, reduction of GHG emissions and carbon capturing, are thought to be most ef ective in combination.

38 T e table below lists renewable energy technologies and carbon capture methods that are currently available (adapted from the IPCC, 2007, AR4 WG3 Summary for Policymakers, Table SPM.3).

TABLE 2: KEY MITIGATION TECHNOLOGIES AND PRACTICES FOR REDUCING GHG EMISSIONS AND CAPTURING OF CARBON

Sector Key mitigation technologies and practices

Energy Renewable heat and power generation, e.g. hydropower, solar, wind, supply geothermal and bioenergy. Hybrid vehicles and electric cars. Transport Shifting from road transport to rail and other public transport systems. Increased non-motorised transport, i.e. cycling, walking in cities. THEME 1.1.2 Efficient use of lighting and daylight. More efficient electric appliances and heating and cooling devices. Improved cooking stoves, insulation, and passive and active solar design for heating and cooling. Buildings Increased use of alternative refrigeration fluids and recovery and recycling of fluorinated gases. Integrated design of commercial buildings including renewable energy technologies and intelligent meters that provide feedback and control. More efficient end-use electric equipment. Improved heat and power recovery. More efficient material recycling and substitution. More efficient control of non-CO gas emissions. Industry 2 Advanced energy efficiency and Carbon Capture and Storage (CCS), e.g.

storage of removed CO2 from natural gas related to cement-, ammonia-, and iron manufacture. Use of inert electrodes for aluminium manufacture. Improved crop and grazing land management to increase soil carbon storage. Restoration of cultivated peaty soils and degraded lands. Improved rice cultivation techniques and livestock and manure manage- Agriculture ment to reduce CH4 emissions.

Improved nitrogen fertiliser application techniques to reduce N2O emissions. Dedicated energy crops to replace fossil fuel use and improved energy efﬁciency. Improved afforestation, i.e. the establishment of a new forest by seeding or planting on non-forested land. Forestry Reforestation and reduced deforestation to increase biomass productivity and carbon sequestration. Increased landﬁll methane recovery. Waste incineration with energy recovery. Waste Composting of organic waste. management Controlled waste water treatment. Recycling and waste minimisation.

Can you think of mitigation practices that should be used in South Africa?

39 The Difference between Adaptation and Mitigation Mitigation and adaptation are the two strategies for addressing climate change. Adaptation means to enhance resilience and reduce vulnerability of communities to actual or expected impacts caused by climatic changes. Mitigation refers to interventions to reduce GHG emissions or enhance greenhouse gas capture, e.g. in natural sinks such as forests and grasslands. FIGURE 1: ADAPTATION AND MITIGATION AS DIFFERENT RESPONSE OPTIONS

Global warming/Climate change THEME 1.1.2 Response options

Mitigation Adaptation

Mitigation efforts, e.g. Adaptation efforts, e.g. energy generation through rainwater harvesting or renewable energy other water conserving technologies techniques

Greenhouse gas emissions Climate change impacts (GHG) reduced reduced

Image source: GIZ/S4GJ

T us, adaptation and mitigation present some notable dif erences, particularly in their objectives. Mitigation addresses the causes of climate change, specif cally the accumulation of GHG in the atmosphere. Adaptation addresses the impacts of climate change. Both approaches are necessary to respond appropriately to climate change. Even if mitigation ef orts are applied at a large scale, e.g. using more renewable energy technologies for generation of electrical energy, the climate will continue changing in the next decades. Consequently, adaptation to these changes is necessary.

T e table below lists further dif erences between adaptation and mitigation, for example in terms of spatial and temporal scales, and concerned economic sectors.

TABLE 3: DIFFERENCES BETWEEN ADAPTATION AND MITIGATION

Mitigation Adaptation Spatial scale Provides national or interna- Mostly beneﬁts at the local tional/global beneﬁts scale particularly in coastal or low-lying areas Time scale Usually long-term effects Usually short-term effects Sectors Energy generation, transporta- Water, health, agriculture etc. tion, waste management etc.

40 Examples Municipal Level: Durban, KZN, South Africa

Impacts Given its coastal location, Durban faces multiple challenges from climate change, including increased coastal erosion and storm surges. In addition, rainfall patterns are changing with immediate consequences for agricultural productivity, water supplies, and biodiversity. Moreover, as temperatures rise, the large HIV positive population faces increased opportunistic infection rates and greater susceptibility to heat stress. Adaptation and Resilience Durban has launched a comprehensive ef ort to improve climate change resilience of its communi-

ties. T e municipality: THEME 1.1.2 (i) Developed a risk map for the city, outlining the dif erent risks of climate change and their potential impacts on each sector of the city. (ii) Def ned resilience-building activities. T is includes broadening water catchment basins and reservoirs to help supplement declining rainfall, adding additional services for the HIV-positive population, changing coastal development plans, and developing alternative agricultural and livestock management strategies to strengthen food security. (iii) Changed the structure of the city government, adding several positions to focus on resilience-building activities and is working to integrate climate resilience into all city functions. Country Level: South Africa Impacts South Africa is extraordinarily dependent on coal both for electrical energy and liquid fuel production. Most power stations in South Africa are owned and operated by Eskom and these plants account for 95% of all electrical energy produced in South Africa. South Africa has numerous coal deposits concentrated in the north-east of the country and as such the majority of South Africa’s coal-f red plants are located in Mpumalanga. Around 85% of the national primary energy is produced in thermal power stations f red by coal, oil and gas. Historically this has given South Africa access to seemingly cheap electrical energy, but it is also one of the leading causes of why the country is in the top 20 list of carbon dioxide emitting countries, with carbon emission levels for electrical energy generation of approximately 232 million tons in 2012. T e overall carbon emissions were 510 million tons. Mitigation South Africa has a high level of renewable energy potential and presently has in place a target of 10 000 MWh to be generated by renewable energy. Under the f rst bidding windows of the Renew- able Energy Independent Power Producer Procurement Programme (REI4P), a total of 64 projects have been awarded to the private sector, and the f rst renewable energy plants are already online. Private sector investment totalling around R140 billion has been committed, and projections indicate that these projects will generate over 3 900 megawatt (MW) of renewable power. T is is broadly in accordance with the capacity allocated to renewable energy generation in the government’s Integrated (energy) Resource Plan (IRP) 2010-2030. T us, the REI4P has been designed to contribute towards the target of 10 000 MWh and to start and stimulate the renewable industry in South Africa. T is consequently will assist South Africa to reduce its electrical energy-related carbon emission and to contribute to the country’s international carbon dioxide reduction commitments.

NOTE!

At level 2 you may f nd terms and measurements such as megawatt (MW) a bit confusing. Topic 2 will address the scientif c and technical concepts of power, energy and electric charges in more detail, but we will try to help you to understand enough about these scientif c terms and measures for Topic 1. However, it is already most important to remember that in everyday language, scientif c terms are of en used with a dif erent meaning, and energy, power and work are of en confused or used in a dif erent context, for example I have a lot of energy today...

41 Power and Energy Basics Power can be expressed in units of watts (W) such as 1 megawatt (MW) = 1 000 kilowatt (kW) = 1 000 000 watt. Other pref xes such as giga (G = 1 000 mega) and tera (T = 1 000 giga) watt are also common. Power and its unit watt indicate either the rate at which: (i) An appliance uses electrical energy (for example by a LED), or (ii) Electrical energy is produced (for example by a generator)

Electrical energy is expressed in units of watt hours (Wh). If an appliance consumes or if a generator provides 1 kilowatt of power over a period of one hour, then 1 kilowatt hour of energy exists in some form over the course of this hour (1 kilowatt times one hour = 1 kW/h = 1 000 Wh).Larger amounts of energy can be measured in megawatt hours (MW/h = MWh): 1 MWh = 1 000 kWh.

THEME 1.1.2 Watt hour is in a way analogous to an hourly wage (R/h) or speed of a vehicle km/h. Simply stated, energy is equal to power multiplied by time.

To repeat, for simplicity:

Watt (W, the unit of power) indicates the ability or strength of energy. Watt hour (Wh, the unit of energy) is the amount of power that is consumed or generated in one hour. W and Wh are related but dif erent units. Don’t confuse their usages!

Your own notes

42 Exercises

(i) A major transformation is needed to limit the impacts of climate change. In other words, we have to learn to live and to produce what we need in a more sustainable way. Any transformation of society must begin in the people’s mind. Scientists, politicians and citizens will have to work together to achieve this. Question: Do you think we can limit the impacts of climate change if engineers, business people and policy makers all pull together and if all work on a great transformation across national borders?

Have a look at the comic T e Great Transformation - Can we beat the heat, where nine top scientists show us how it could be done.

Question: Discuss your view with other students (group work) and present the challenges THEME 1.1.2 and opportunities of this proposed transformation!

FIGURE 2: A PAGE FROM A COMIC BOOK: CLIMATE CHANGE IS A GLOBAL PROBLEM

Image source: German Advisory Council on Global Change (WBGU) 2014. http://www.wbgu.de/en/comic-transformation/ T e world shares one atmosphere, therefore we will have to solve this problem together.

43 (ii) In general, there are two dif erent strategies when it comes to dealing with climate change. We can try to reduce future warming (mitigation of climate change) or we can f nd ways to live in our warming world (adaptation to climate change). T ere is, of course a third option: to do nothing. Figure 3 sums up these options. T e corners of the triangle represent 100% of each of these three options. Areas in the middle of the triangle represent a combination of approaches. T ere are costs associated with mitigation and adaptation. However, notice that with no action, we are facing a high cost associated with climate impacts because we will be ill prepared to deal with these impacts. Question: Try to interpret the triangle below and discuss your view with other students (group work). Present and defend your results!

THEME 1.1.2 FIGURE 3: THE TRIANGLE DIAGRAM SHOWS THE RELATIONSHIPS BETWEEN ADAPTATION, MITIGATION, AND INACTION

less

All mitigation

cost of mitigation

cost of impacts

No action All adaptation less

less cost of adaptation more

Image source: IPCC Forth Assessment Report, ar4-wg2-chapter18. http://www.ipcc.ch/graphics/ar4-wg2/jpg/f g-18-1.jpg

(iii) Have a look at the following examples for climate change awareness campaigns in Sri Lanka and South Africa. Answer the following questions and express your views!

Questions: 1. Do you have or have you had a similar awareness programme in your schools or college, ? for example a Greening of College initiative? 2. Are you personally participating in such an initiative? If so, why? If not, why not?

Activity: Why don’t you try to develop a poster for your college?

44 Sri Lanka’s Climate Change Awareness Campaign T e Sri Lanka Red Cross Society (SLRCS), supported by the International Federation of Red Cross & Red Crescent Societies (IFRC) and the German Red Cross has embarked on a programme to edu- cate, inform and raise awareness on climate change and its impact on Sri Lanka. T e programme started with the planting of 1250 trees in 130 schools in all 25 districts (f ve schools per district and 10 schools in Matale). On January 15th, Grade 6 schoolchildren in the 130 schools were given the responsibility of taking care of the plants throughout the year, thereby helping them to understand how the role of trees helps to mitigate the ef ects of climate change.

“Climate change poses severe threats to children’s survival and wellbeing as well as to their access to education and protection,” says the Director General of SLRCS Tissa Abeywickrama. “T ey (the children) will face more natural disasters, malnutrition and changing disease patterns as well

as severe water scarcity. To create a sustainable world for our children, we need to be aware that THEME 1.1.2 our current actions will have a critical bearing on our children’s future. T erefore, it is necessary to ensure that our actions today contribute to a safer, better and greener world for tomorrow.” A healthy ecosystem including forest canopies provides a long term carbon sink in the soil. T e future generations should understand the grave threat that climate change poses and be ef ective agents of change in mitigation and adaptation initiatives.

See more at: http://www.nation.lk/edition/component/k2/item/15011-adopt-and-adapt-climate-change-awareness-campaigns.html#sthash.n3DMSbFo.dpuf

FIGURE 4: AN EXAMPLE FOR A CLIMATE CHANGE POSTER USED IN AN AWARENESS CAMPAIGN IN SRI LANKA

Image source: http://umvietnamstudy.fles.wordpress.com/2013/01/climatechangeposter_089.jpg

45 South Africa’s Greening of College Initiative T rough promotion of a green economy South Africa has unique opportunities to address the concerns about climate change, including mitigation and adaptation. T is however, requires a mindset change within South Africa and the development of appropriate skill sets. In this context, Skills for Green Jobs developed and implemented an initiative for TVET colleges, fostering awareness-raising and cross-cutting themes for sustainable development. T ese pilot activities are currently taking place in all provinces. FIGURE 5: THE GREENING OF COLLEGES HANDBOOK, SUPPORTING PRACTITIONERS IN AWARENESS CAMPAIGNS IN SOUTH AFRICA’S TVET COLLEGES THEME 1.1.2

GREEN SKILLS FOR JOBS

Greening TVET Colleges Initiative in South Africa From individual competence development to institutional change

A guide for practitioners

Image source: GIZ/S4GJ

GCI Guide-x9.indd 1 25.08.14 17:10

46 Why do the following TVET colleges participate in the Greening of Colleges Initiative? See the selected responses:

„Green building on campuses is purposeful construction that decreases resource usage for the future. At Northern Cape Rural FET College we see the short and long term economic beneﬁts. Students at campuses where greening initiatives are being used will beneﬁt by increasing their potential to gain knowledge. T is will af ord the

opportunity to see the campus as environmentally THEME 1.1.2 „Boland College is participating in the Greening sustainable. Also this will make students aware of of Colleges Initiative because the college seeks to the issues the Earth faces with carbon emissions develop an ethos of environmental responsibility and increased consumption. in all its staf and students as well as in the man- Quote by: Ms Raquel Marinus, Northern Cape Rural FET College agement of its assets. Quote by: Mr Kabedi Mpopote, Boland College

„T e entire college management agreed that we, the Northlink College, as a collective commence „At Central Johannesburg College the concept with projects that would enhance the longevity of was initiated by the college principal between 2007 our planet by waste management initiatives energy and 2008 when the country was experiencing the savings programmes, resource management, etc shortage of electrical energy, based on the Govern- to address all of the pillars on which this initiative ment’s call to save and conserve electrical energy. is based. Everyone seemed very eager to get this T e principal outlined his vision for greening the of the ground and the Belhar Campus has been college, and he expected all members to cascade earmarked to spearhead the whole process. it to respective campuses and sites. He also urged Quote by: Mr Terence Slade, Northlink College each campus and site to organise a stakeholder grouping or committee that will take the initiative further. Quote by: Ms Gloria Tshabalala, Central Johannesburg College

Umfolozi College is situated in the heart of the „community in KwaZulu Natal which forms part of a wetland. We would like to teach students about the importance of energy conservation and about wise use of natural resources. Our intention is for students to take this message of conserving natu- „At Eastcape Midlands College we want to min- ral resources back into the community. imise our carbon footprint and reduce overhead Quote by: Ms Sheritha Singh, Umfolozi College cost with the introduction of solar and wind energy. Quote by: Mr Ziyaad Smith, Eastcape Midlands College

47 Further Information (all materials are on the resource CD)

(i) German Advisory Council on Global Change (WBGU), 2014: http://www.wbgu.de/wbgu_home_engl.html (ii) German Advisory Council on Global Change (WBGU), 2014: http://www.wbgu.de/en/comic-transformation/ T e PDF of the comic is available during COP 20 of the UNFCCC in December 2014. (iii) Greening TVET Colleges Initiative in South Africa, A guide for practitioners, GIZ/S4GJ 2014 (iv) DEA, 2013: LONG-TERM ADAPTATION SCENARIOS SUMMARY FOR POLICY-MAK- ERS. High-level/key messages emerging from LTAS Phase 1. hyyp://www.environment.gov.za

THEME 1.1.2 (v) Hot Topic: Climate Change & Mitigation 2012, http://www.mona.uwi.edu/physics/sites/default/f les/physics/uploads/07_CCAndMitigation.pdf

Your own notes

48 THEME 1.1.3 INTERNATIONAL AND NATIONAL POLICIES ON CLIMATE CHANGE

Introduction

T e detrimental environmental ef ects of burning fossil fuels imply that the current patterns of energy generation are unsustainable in the longer term. Carbon emissions from the combustion of fossil fuels have signif cantly raised the concentration of greenhouse gases in the atmosphere. T e continuation of these processes will enhance the greenhouse ef ect within the next decades, with major adverse impacts on food production, water supply and weather, for example intensif ed f oods and cyclones. Recognising

that this is a global problem which no single country can avert on its own, over 150 national governments THEME 1.1.3 signed the UN Framework Convention on Climate Change, which set up a framework for concerted action on the issue. T ere has been signif cant national leadership in response to the challenge of climate change: (i) South Africa is committed to GHG reductions: South Africa has committed to reduce its GHG emissions by 34% below the current emissions path by 2020; and by 43% by 2025. (ii) T e National Climate Change Response White Paper is the policy outlining how the country will achieve its targets on GHG reduction and adaptation. (iii) T e National Energy Ef ciency Strategy outlines South Africa’s energy ef ciency goals and how it aims to achieve them. (iv) T e Renewable Energy Independent Power Producer Procurement Programme (REI4P) aims to have 3 725 MW of renewable energy technology installed by 2016, as these technologies are much more compatible with sustainable development than fossil and nuclear fuels, both in regard to resource limitations and detrimental environmental impacts. Keywords

Green economy Integrated Resource Plan (IRP) Renewable Energy Independent Power Producer Procurement Programme (REI4P) Sustainable development Theme Outcomes

Societies can respond to climate change dif erently. At the end of this theme, you should be able to: (i) Explain why international frameworks and policies on climate change have been developed. (ii) List the priorities of the National Strategy on Sustainable Development. (iii) Explain the Green Economy Accord and its commitments. (iv) Explain the importance of the Integrated Resource Plans. (v) List and explain the goals of the National Energy Ef ciency Strategy.

Deﬁ nition of Terms International Frameworks and Policies on Climate Change Climate change is a global problem which no single country can avert on its own. T us, concerted action is needed to address the challenges. International frameworks and policies on climate change have subsequently been developed, and over 150 nations signed the United Nation’s Framework Convention on Climate Change. Sadly, concrete action is slow, in part because of the reluctance of governments in industrialised and middle income countries. As a signatory to the Convention on Climate Change and the Kyoto Protocol, South Africa has committed to combating climate change. Its voluntary reduction targets are ambitious, with a 34% reduction of emissions by 2020 and 42% by 2025. Even though South Africa is not yet obliged to commit formally to reducing emissions, it has nevertheless been playing an inf uential role in international negotiations in its capacity as a middle-income country.

49 Sustainable Development Sustainable development can be broadly def ned as living, producing and consuming in a manner that meets the needs of the present without compromising the ability of future generations to meet their own needs. Sustainable development has become a key guiding principle for policy in the 21st century. Worldwide, politicians, industri- alists, environmentalists, economists and theologians af rm that the principle must be applied at international, national and local level. However, actually applying it in practice and in detail is of course much harder! In South Africa the concept of sustainable development is well articulated and is a fundamental building block around which environmental legal norms and economic development have been fashioned. T e f ve priorities of the National Strategy on Sustainable Development include: (i) Priority 1: Enhancing systems for integrated planning and implementation (ii) Priority 2: Sustaining our ecosystems and using natural resources ef ciently (iii) Priority 3: Moving towards a green economy (iv) Priority 4: Building sustainable communities (v) Priority 5: Responding ef ectively to climate change THEME 1.1.3 Triple Bottom Line In the international context, the word ‘development’ refers to improvement in quality of life, and especially standard of living in the less developed countries of the world. T e aim of sustainable development is for the improvement to be achieved whilst maintaining the ecological and social processes on which life depends. At a local level, progressive businesses aim to report a positive triple bottom line, i.e. a positive contribution to the economic, social and environmental well-being of the community in which they operate. Green Economy Accord As an outcome of social dialog on the New Growth Path for South Africa, the Government and its social partner have signed a Green Economy Accord in November 2011. T e 12 commitment areas which were identif ed in the Green Economy Accord include: (i) Commitment 1 - Rollout of Solar Water Heaters: Government commits to a target of ensuring the installation of 1 million solar water heaters at household level by 2014. (ii) Commitment 2 - Investment in the Green Economy: T e parties to this accord recognise that new sources of funding and f nance will need to be developed and tapped into to ensure that green economy investment levels are rapidly improved. (iii) Commitment 3 - Rollout of Renewable Energy: Government commits to the procurement of renewable energy as part of the plan to expand the energy-generation capacity of the country. To this end, Govern- ment will secure commitments for the supply of 3 725 MW of renewable energy by 2016 as a f rst step to realising the goals for renewable energy under the Integrated Resource Plan 2010-2030. (iv) Commitment 4 - Energy Ef ciency: Energy ef ciency supports a number of key government objectives, including enhancing business competitiveness, strengthening energy security, creating jobs, reducing the economy’s energy-intensity and transitioning to a lower carbon economy as well as improving environmental quality. (v) Commitment 5 - Waste Recycling, Reuse and Recovery: A range of industries are engaged in a variety of activities to recycle, reuse or recover waste. (vi) Commitment 6 - Bioenergy: T e production of bio-fuels for mandatory blending in the petrol and diesel national fuel pool can contribute to lower carbon emissions, greater fuel supply security and signif cant job creation in the growing of feed stocks that do not compete with local food needs. (vii) Commitment 7 - Clean-Coal Initiatives: T e coal resources available in South Africa are massive and need to be exploited in a manner that recognises and minimises the damage already done by greenhouse gas emission associated with coal exploitation. (viii) Commitment 8 - Retrof tting: One of the opportunities to green the economy is to identify ways to improve the energy ef ciency of workplaces, homes and power stations. (ix) Commitment 9 - Reducing Carbon-Emission on our Roads: All parties to this accord commit to promote among South Africans the value and importance of public transport as a means, among other advantages, of reducing carbon emissions. (x) Commitment 10 - Electrif cation of Poor Communities and Reduction of Fossil-Fuel Open Fire Cooking and Heating: Government recognises that at least 3 million households still rely on traditional energy carriers like candles and f rewood, leading to continued environmental degradation particularly in rural areas and in urban informal settlements. (xi) Commitment 11 - Economic Development in the Green Economy: Promotion of localisation, youth employment, cooperatives and skills development. (xii) Commitment 12 - Cooperation around the United Nations Cop 17 and its follow-up talks on climate change.

50 FIGURE 1: THE GREEN ECONOMY ACCORD (NOVEMBER 2011) AIMS TO GIVE EFFECT TO A GREENER ECONOMY THEME 1.1.3

The Integrated Resource Plan (IRP) 2010 Update T e Integrated Resource Plan is South Africa’s master plan for generation of new electrical energy capacity for the period until 2030. Developed by the Department of Energy (DoE), the plan sets out the projected demand for electrical energy and then addresses how this demand is going to be met, taking into account the economic and political framework within which it operates. Since the initial version of the IRP 2010 was released, there have been many developments that af ect its underlying assumptions, specif cally those which might af ect capacity planning. T e DoE had the intention to update the IRP biennially with the aim to specify new estimates on power generation capacity and from which technologies new capacity will stem from.

FIGURE 2: TECHNOLOGY ALLOCATIONS NEW BUILD 2010 - 2030

5% Coal

Nuclear energy

Hydro (import) 29% Gas

Renewables 33% Other

17%

11% 5%

Image source: GIZ/S4GJ (based on IRP data 2013)

Figure 2 shows the projected energy mix in 2030. Thus, the new build capacity for fossil fuels (coal and gas) is about 40%, renewable energy technologies (including hydro) are estimated at 38% and nuclear energy form about 17% of the share.

51 The table below lists total generation capacity projected for 2030 in MW and percent, and the planned new allocations (new build) for various technologies as outlined in the IPR (adapted from IRP 2013, Table 1).

TABLE 1: IRP TOTAL GENERATION CAPACITY PROJECTED FOR 2030

Total Generating Capacity Planned Additional Technology in 2030 Capacity (2010 - 2030)

MW % MW % THEME 1.1.3 Coal 41071 47.4% 16383 29.1%

Nuclear 11400 13.2% 9600 17.0%

Hydro (import) 4759 5.5% 2609 4.6%

OCGT 7330 8.5% 3910 6.9%

CCGT 2370 2.7% 2370 4.2%

Wind 9200 10.6% 9200 16.3%

CSP 1200 1.4% 1000 1.8%

PV 8400 9.7% 8400 14.9%

Other (renew, co-gen, etc.) 890 1.0% 2874 5.1%

Total 86620 56346

Renewable Energy Independent Power Producer Procurement Programme (REI4P) An initial outcome of the IRP are grid-connected renewable energy independent power projects (IPPs). A tender programme has been developed by the DoE aiming to accelerate and sustain investment by the private sector into new energy-generating technologies. T e programme, known as the Renewable Ener- gy Independent Power Producer Procurement Programme (REI4P), has started its f rst bid round in Au- gust 2011. T e programme has attracted a multitude of international and local private project developers and investors who have channelled large amounts of private expertise and investment into grid-connected renewable energy in South Africa at competitive prices. In total, af er its f rst three bidding rounds, the REI4P has generated 64 new renewable energy IPP of dif erent sizes at dif erent sites, with the result that US$14 billion in investment has been committed for the construction of almost 4 000 MW of capacity in technologies including grid-connected wind turbines, PV and concentred solar power plants, as well as smaller amounts of hydro, landf ll gas and bioenergy. T is is indeed a success story, because in less than three years, South Africa secured more investment for more independent power generation than what has been achieved across the entire African continent over the past 20 years.

52 Examples

T e REI4P socio-economic outcomes in terms of job creation and local content created by dif erent technologies in the dif erent bidding rounds are optimistic and clearly make a case for a transition towards renewable energy. As Table 2 shows, the PV, wind turbine and CSP projects promised to generate approximately 20,000 temporary construction jobs and approximately 35,000 operations jobs in total. If these f gures are accurate and can indeed be realised, they ref ect a considerable achievement.

T e table below lists the REI4P socio-economic outcomes in terms of job creation and local content created by dif erent technologies in the dif erent bidding rounds (adapted from Public-Private In- frastructure Advisory Facility, PPIAF 2014). Please note that the values are projections/estimates.

TABLE 2: JOB CREATION AND LOCAL CONTENT CREATED BY THEME 1.1.3 THREE DIFFERENT RENEWABLE ENERGY TECHNOLOGIES

Technology Round 1 Round 2 Round 3

Photovoltaic (PV)

Local content % 38.4 53.4 53.8

Local construction jobs 2381 2270 2219

Local operation jobs 6117 3809 7513

Wind power

Local content % 27.4 48.1 46.9

Local construction jobs 1810 1787 2612

Local operation jobs 2461 2238 8506

Concentrated solar power (CSP)

Local content % 34.6 43.8 44.3

Local construction jobs 1883 1164 3082

Local operation jobs 1382 1180 1730

Your own notes

53 Exercises

(i) Have a more detailed look at the Renewable Energy Independent Power Producer Procure- ment Programme review (2014, on resource CD), particularly the introduction on page 6, and explain what exactly the programme’s aim is.

(ii) Where exactly are the locations of the renewable energy of the REI4P? Dif erentiate by province, bidding round and technology. Use the map below and the table and indicate the technologies for each province with a cross (X). THEME 1.1.3

FIGURE 3: RENEWABLE ENERGY PROJECT LOCATIONS OF THE REI4P (2014)

1 REI4P window 1 2 REI4P window 2 3 3 REI4P window 3 1 1 PV, CSP and CPV Biomasse

1 Wind Small hydro 3

Landﬁ ll gas 3 3 3

1 3 23 2 2 2 1 2 3 3 1 3 1 1 3 3 1 3 3 3 2 2 3 1 2 1

3 2 2 2 3 1 1 2 1 2 2 1 Saldanha Bay 1 33

Jeffreys Bay

Image source: GIZ/S4GJ adapted from http://www.energy.org.za/knowledge-tools/map-of-sites

Your own notes

54 Technology FS Limpopo NW NC WC EC

Photovoltaic (PV) and Concen- trated Solar Power (CSP)

Round 1

Round 2

Round 3

Wind power THEME 1.1.3 Round 1

Round 2

Round 3

(iii) Discuss and describe the relationship between the Green Economy Accord, particularly commitment 3, the Integrated Resource Plan (IRP) and the Renewable Energy Independent Power Producer Procurement Programme (REI4P). (iv) Have a more detailed look at the action plan of priority 5 of the National Strategy on Sustain- able Development (slide #31-34, on CD) and explain the links between the action plan’s goals and interventions and the Renewable Energy Independent Power Producer Procurement Programme (REI4P).

Further Information (all materials are on the resource CD)

(i) T e Green Economy Accord (November 2011) (ii) T e National Strategy on Sustainable Development (2011) (iii) T e Renewable Energy Independent Power Producer Procurement Programme Review 2014

Your own notes

55 Unit 1.2 Unit

UNIT 1.2 DIFFERENCES BETWEEN ENERGY RESOURCES Introduction

Reliable energy supply is essential in all economies for lighting, heating, communication, industrial processes, transport etc. T e outlook on the world’s fossil energy resources, such as coal and oil, is looking rather grim, because of issues such global warming, environmental worries, fossil fuel depletion and increasing growth and energy demands of large new economies. Consequently, many countries and international development agencies are actively working to advance and utilise renewable energy technologies to meet future demand, whilst reducing their dependence on fossil fuels. Renewable energy options include technologies such as hydropower, bioenergy, geothermal, waves and tides, and particularly wind and solar power. Adding an energy mix of alternatives into an integrated resource plan can be regarded as a reasonable approach for creating a desired stable energy future.

Unit Outcomes

At the end of this unit, you should be able to: (i) Describe and explain the functions of the main components of electrical networks. (ii) Clearly distinguish between fossil and renewable energy sources. (iii) Outline and explain the advantages and disadvantages of renewable energy resources.

Themes in this Unit

Unit 1.2 covers three themes: T eme 1.2.1 Electrical Networks T eme 1.2.2 Dif erences between Fossil and Renewable Energy Sources T eme 1.2.3 Advantages and Disadvantages of Renewable Energy Resources

56 THEME 1.2.1 ELECTRICAL NETWORKS Introduction

It is dif cult and costly to “store” electrical energy and thus, it is more appropriate to generate electrical energy at the time when it needs to be used. T is is the function of a national grid, balancing the supply and demand of electrical energy, second by second, minute by minute, hour by hour, day by day. T e vast majority of national networks operate at high voltages, for example between 400 000 and 275 000 Volts (400 kV and 275 kV). High voltages are used for the bulk transfer of electrical energy because this reduces the amount of energy lost during transmission. Distribution networks operate at lower voltages, for example at 132 kV and below, delivering the energy all the way to domestic properties at 230 Volts. Keywords

Basic regimes of electrical energy generation Distribution of electrical energy THEME 1.2.1 Electrical energy generation Load management Transmission of electrical energy Theme Outcomes

At the end of this theme, you should be able to: (i) Describe and explain the three main processes taking place in electrical networks (high and low voltage transmission lines). (ii) Explain key terms used in electrical networks and usage diagrams. Deﬁ nition of Terms Electrical Energy Generation Electrical energy is generated from a variety of energy resources. Today most electrical energy is produced from fossil fuels (coal and gas) in thermal power stations. Water in a boiler is heated by burning fuels, thereby creating steam. T is high-pressure steam passes over the turbine blades making the shaf rotate. T is turns the generator, producing an electric current. Nuclear fuels, concentrated solar power (CSP) and geothermal energy are used in a similar way (hot water generating steam, driving a turbine which turns a generator etc.). Wind turbines are used to turn the generators directly while photovoltaic cells (PV) can generate an electric current directly.

FIGURE 1: SCHEMATIC ILLUSTRATION OF ELECTRICAL ENERGY GENERATION USING RESOURCES SUCH AS COAL, GAS, NUCLEAR, CSP AND GEOTHERMAL ENERGY

22,000 volts Generator

Steam Boiler Turbine Condensor Generator transformer

Image source adapted from: Education & Skills, National Grid UK, http://www.nationalgrideducation.com/secondary/publica- tions_education-resources.php

57 Transmission of Electrical Energy T ermal power stations generate electrical energy at high voltages, for example at around 220 kV. T e 220 kV are increased by a factor of 10 or more by a transformer (for changing the potential dif erence), so that the transmission of electrical energy in a national grid can operate at high potential dif erence, for example 275 kV, 400 kV or 765 kV. Modern national networks consist of thousands of kilometres of overhead lines, thousands of transmission towers and hundreds of substations. T e substations are the connecting points for the system, and include transformers and circuit breakers for controlling the f ow of electrical charges.

FIGURE 2: SCHEMATIC ILLUSTRATION OF TRANSMISSION OF ELECTRICAL ENERGY USING A SYSTEM OF TRANSFORMERS AND OVERHEAD TRANSMISSION LINES THEME 1.2.1

22,000 volts

Generator transformer 275,000 or 400,000 volts Transformer

Image source adapted from: Education & Skills, National Grid UK, http://www.nationalgrideducation.com/secondary/publica- tions_education-resources.php

Distribution of Electrical Energy T e national network is connected to local distribution systems through substations, where the voltage is stepped down, again using transformers. T e distribution system supplies customers with a wide range of needs, and for residential use the potential dif erence is successively transformed down until it reaches our homes at 230 V.

FIGURE 3: SCHEMATIC ILLUSTRATION OF DISTRIBUTION OF ELECTRICAL ENERGY: INDUSTRY AND RESIDENTIAL HOMES ARE CONNECTED TO THE NATIONAL GRID

Light industry/ towns and villages 11,000 volts Heavy industry Homes, schools, shops 33,000 volts and businesses 230 volts

Plug

Smart meter Transformer 132,000 33,000 volts 11,000 volts 230 volts volts

Image source adapted from: Education & Skills, National Grid UK, http://www.nationalgrideducation.com/secondary/publica- tions_education-resources.php

58 Basic Regimes of Electrical Energy Generation Usually generation of electrical energy is commonly divided into three basic load regimes: base, intermediate and peak load. (i) Base load: plants operate at constant power output. (ii) Intermediate load: plants operate with slow variation in power output on regular schedules to follow expected variation in demand. (iii) Peak load: plants operate with fast variation, responding to minute peaks in demand above or below the pre-planned part of supply.

T e variability of demand can be predicted rather well and most daily, weekly, and annual f uctuations are very pronounced. T us, the bulk of load-following can be planned far ahead, making it a scheduled form of operation. However, from time to time, conventional base load plants, typically conventional coal or nuclear power plants in the GW range, need to be shut down: for refuelling, or regular maintenance, or upgrades. T is is a scheduled change in base load, hence, the task of compensation falls on intermediate load, which must have reserves of the proper magnitude. Further, the power of conventional base load plants can dissipate in an unplanned way and this usually happens rather fast, for example in the case of an accident or power line damage. In this scenario, compensation is a duty of peak load, which again must have reserves of the proper magnitude. THEME 1.2.1

FIGURE 4: AN INVENTED AND SIMPLIFIED ILLUSTRATION OF THE THREE BASIC ENERGY GENERATION REGIMES OVER AN IMAGINARY DAY AND CITY

Power Base load Intermediate load Peak load demand in GW

00:00 01:00 02:00 03:00 04:00 05:00 06:00 07:00 08:00 09:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00 24:00

Time

Image source: GIZ/S4GJ

In recent years, renewable energy technologies, more precisely solar power facilities such as photovoltaic (PV) and Concentrated Solar Power (CSP)plants, as well as wind power facilities gained signif cance and installations are now in the GW range. National utilities, like ESKOM, and Independent Power Pro- ducers (IPP) prefer to operate them without limitation whenever possible and it is common, at least in Europe, USA and China, to operate wind and solar technologies de facto as part of the base load. T e one dif erence of renewable energy technologies (wind and PV) compared to conventional base load, for example coal or nuclear, is their weather-related intermittency. Power output for both wind power and photovoltaic depends on weather, time of day, and season. However, in countries and regions with high wind penetration, grid operators use wind prediction methods that are by now suf ciently precise for the 24 or 36 hours ahead to enable the bulk of the balancing to be scheduled. Solar power technologies can be

59 predicted ef ciently as well. Hence, intermittency gives most of the balancing job to intermediate power, for example employing active energy storage options such as pumped hydro. Load Management Load management, also known as demand side management (DSM), is the process of balancing the supply of electrical energy on the network with the electric load by adjusting or controlling the load rather than the power station output. T is can be achieved by direct intervention of the utility in real time, by the use of frequency sensitive relays triggering circuit breakers (ripple control), by time clocks, or by using special tarif s to inf uence consumer behaviour. Load management can also help to reduce harmful emissions, since peaking plants or backup generators are of en dirtier and less ef cient than base load power plants.

Examples

Eskom Holdings owns most of South Africa’s power stations, the national grid including the net- THEME 1.2.1 work of high-voltage power lines linking the power station to the cities, towns, rural and residential areas where electrical energy is used. All energy that Eskom generates is fed into this grid for national distribution. However, Eskom does not distribute energy directly to all consumers. Most municipalities buy electricity in bulk from Eskom and resell it to consumers.

FIGURE 5: ESKOM’S TRANSMISSION NETWORK

Limpopo

Gauteng Mpumalanga North West

Free State

Northern Cape KwaZulu-Natal

Eastern Cape

Western Cape

Substations Future Lines Future Lines Currrent TDP 2015-2024 Created by: Substations Current Transmission

2 0 5 0 5 2 0 5 0 3 5 0175 50 300450 600 Grid Planning 0 13 22 27 40 76 13 22 27 40 53 76 Kilometers 2014/09/09

Image source: http://www.eskom.co.za/Whatweredoing/ElectricityGeneration/PowerStations/Documents/National.pdf

T e map shows existing and planned electrical networks with voltages ranging from 132kV to 765kV and the transmission substations where these networks terminate.

60 FIGURE 6: SCHEMATIC AND SIMPLIFIED ILLUSTRATION OF ESKOM’S DISTRIBUTION NETWORK

275 kV, 400 kV or 765 kV 275 kV, 400 kV or 765 kV

22 kV Substation 11 kV 275 kV Suburbs or 400 kV Substation 132 kV

Hospital 5 5 11 kV 11 kV Farm 380/220 V 11 kV 22 kV 11 kV 5 132 kV Distribution 380/220 V Town 4a Station 3 5 11 kV 4b 132 kV THEME 1.2.1

7 5 132 kV Commercial 380/220 V Light industries Business District 11 kV 380/220 V Village 6 8 25 kV or 50 kV Railways

5 Heavy industries 1 kV = 1000 volts Industries 380/220 V

Image source adapted from: http://www.eskom.co.za/AboutElectricity/FactsFigures/Documents/TD0003TransmDistribElec- tricityRev7.pdf

T e drawing covers existing and planned electrical networks with voltages ranging from 132 kV to 765 kV and the transmission substations where these networks terminate.

Your own notes

61 Smart Grids T e steady growth of renewable energy technologies and cost competitiveness of solar and wind power call for a smarter approach to power-grid management. A smart power grid is an electrical network that uses digital and other advanced technologies to monitor and manage the transport of electrical energy from all generation sources to meet the varying energy demands of end users. Smart grids coordinate the needs and capabilities of all generators, grid operators and end users to operate all parts of the system as ef ciently as possible, minimising costs and environmental impacts while maximising system reliability, resilience and stability. Smart grids include transmission and distribution systems and interfaces with generation, storage and end users. While many countries have already begun to ‘smarten’ their electrical energy systems, all countries will require signif cant additional investment and planning to achieve a smarter grid. Smart grids are an evolving set of technologies that will be deployed at dif erent rates in a variety of settings around the world, depending on local commercial attractiveness, compatibility with existing technologies, regulatory developments and investment frameworks.

FIGURE 7: NATIONAL GRID DEVELOPMENT OVER TIME (SCHEMATIC) THEME 1.2.1 Past Present Future

Energy service Transmission Distribution provider System Transmission Distribution control control centre operator control control centre centre centre

Electric vehicles

Industrial Industrial Energy Industrial customer customer storage customer

Sub- Sub- Sub- Sub- Sub- Sub- Commercial Commercial Commercial station station customer station station customer station station High- customer temperature super- conductor Residential Residential customer customer Storage Residential customer

Electrical infrastructure Communications

Image source: GIZ/S4GJ adapted from IEA, www.iea.org/publications/freepublications/publication/smartgrids_roadmap.pdf

Existing grid systems already incorporate elements of smart functionality, but this is mostly used to balance supply and demand. Smart grids incorporate information and communications technology into every aspect of electrical energy generation.

Exercises

(i) Describe and explain the three main processes taking place in electrical networks. (ii) Describe and explain the three basic energy generation regimes. (iii) Dif erentiate between base and peak load:

load occurs over the whole day on the power plant.

load responds to fast variation of energy demand.

power plants operate at relative low costs per MW and are capable of working continuously for long periods

62 (iv) Describe the following load diagram and relate specif c daytime demands (6am-6pm) demands with power demands (explain the peaks and the decreases).

FIGURE 8: AN INVENTED AND SIMPLIFIED ILLUSTRATION OF THE THREE BASIC ENERGY GENERATION REGIMES OVER AN IMAGINARY DAY AND INDUSTRIAL AREA

Power demand Base load Intermediate load Peak load in GW THEME 1.2.1

00:00 01:00 02:00 03:00 04:00 05:00 06:00 07:00 08:00 09:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00 24:00 Time

Image source: GIZ/S4GJ

(v) Indicate with a cross (x) which technologies you believe are best suited for:

Base load Intermediate load Peak load

Coal power plant

Nuclear plant

Gas turbine

CSP

Wind turbine

PV plant

Hydro plant

Pumped hydro

Diesel powered generator

63 Further Information (all materials are on the resource CD)

(i) Eskom Factsheet: TRANSMISSION AND DISTRIBUTION OF ELECTRICITY 2014, www.eskom.co.za/AboutElectricity/FactsFigures/Documents/TD0003TransmDistribElec- tricityRev7.pdf (ii) Eskom: Transmission Ten-Year Development Plan 2013-2022, www.eskom.co.za/ Whatweredoing/TransmissionDevelopmentPlan/Documents/TransDevPlanBro- chure2013-2022.pdf (iii) Enerweb: SMART GRID Information Report 2011, www.enerweb.co.za/brochures/ Smart%20Grid%20Information%20Report.pdf (iv) International Energy Agency. (2011). Technology Roadmap: Smart Grids, http://www.iea. org/publications/freepublications/publication/smartgrids_roadmap.pdf (v) Irena: SMART GRID AND RENEWABLES 2013, http://www.irena.org/DocumentDown- loads/Publications/smart_grids.pdf THEME 1.2.1

Your own notes

64 THEME 1.2.2 DIFFERENCES BETWEEN FOSSIL AND RENEWABLE ENERGY SOURCES

Introduction

For hundreds of years, ways have been invented to harness energy, such as using animals to do work or designing machines of varying sophistication to tap the power of wind or water. T is changed during the Industrial Revolution in the late 1800s, and as the United States and Europe industrialised, coal began to replace wood as primary fuel. T is also happened in South Africa and as industrialisation progressed, oil and natural gas started to replace coal for many applications. Nonetheless, South Africa has since relied heavily on coal for the majority of its energy needs. Recently however, South Africa has included renewable solar-based resources to its energy generation mix embodied by dispersed energy resources such as Photovoltaic (PV) and Concentrated Solar Power (CSP) plants, Solar Water Heater (SWH) technologies and wind turbines. T ese are quasi-ready-to-deploy technologies and are both capable and acceptable enough to provide the country’s economy and domestic needs with plenty of additional electrical energy and heat. THEME 1.2.2 Keywords

Environmental impacts Externalities Fossil fuels Nuclear energy Renewable energy Theme Outcomes

At the end of this theme, you should be able to: (i) List and describe the main energy resources currently in use in South Africa. (ii) Distinguish between fossil and renewable energy resources. (iii) Explain environmental problems associated with the use of fossil energy resources.

Deﬁ nition of Terms Differences between Renewable and Non-Renewable Energy Simply stated, energy supplies can be dif erentiated by using energy f ow as the main criterion. Other criteria are detrimental environmental ef ects and availability (lifetime). Non-renewable energy resources, also called Brown Energy, are obtained from potential or static energy stores, usually underground resources such as fossil or nuclear fuels. T eir potential or actual detrimental environmental ef ects are severe and well-known, and their supplies are limited (f nite). Renewable energy resources, which may also be called Green Energy or Sustainable Energy, are obtained from persistent f ows of energy. An obvious example is solar radiation (sunshine) which can be described as an energy f ux passing through the environment as a continuous natural current or f ow. T e potential or actual detrimental environmental ef ects are limited and less known, and their supply can be considered as unlimited (renewable). Environmental Impacts To attain coal or oil through mining or drilling, processing the raw materials, and ultimately putting them to use, usually results in detrimental impacts on the environment. Obtaining energy by burning fossil fuels for example, creates environmental problems of immense global proportions. It produces oxides of carbon, sulphur, nitrogen, air polluting soot and f ne-particulate ash. T e negative ef ect of greenhouse gases and their contribution to global warming have already been mentioned. Other severe impacts related to fossil fuels are air and water pollution, biodiversity losses (plants and animals) and cumulative impacts on ecosystem functioning and services (the ability of the environment to clean air and water etc).

65 Externalities (external costs) Environmental externalities Combustion of fossil fuels emits a variety of air pollutants that are not priced without a policy intervention. Some of these pollutants, including carbon, nitrogen, sulphur dioxides, soot and f ne-particulate ash present a health hazard, either directly as in the case of particulates, or indirectly as in the case of greenhouse gases. When harmful fossil fuel emissions are not priced, the unregulated market will overuse fossil fuels and underuse substitutes, such as renewable energy resources. Also, there will be no incentive for f rms and energy providers to employ technologies or processes to reduce the emissions or mitigate the external costs. T e evidence for environmental externalities from fossil fuel emissions has been proven and estimates of monetary costs for externalities are available for some countries (CD).

FIGURE 1: NITROGEN AND SULPHUR OXIDES, ONCE EMITTED THROUGH BURNING OF FOSSIL FUEL, ARE TYPICALLY CLEARED OUT BY RAINSTORMS AND CREATE ACID RAIN WITH LONG-TERM HARMFUL EFFECTS TO THE ENVIRONMENT THEME 1.2.2

) ) 2 X

Oxidation

NOX+ H20 = Nitric acid (HNO3) Oxidation Sulfur dioxideNitrogen (SO oxide (NO SO2+ H20 = Sulfuric acid (H2SO4)

) X

& (NO 2 Acid rain Acid snow SO

Acid particles & gases

Image source: GIZ/S4GJ

National Security Externalities Oil reserves and production around the world is highly geographically concentrated, of en in unstable regions or countries. T ese oil-rich countries and oil importing countries, have seen large security risks associated with oil production and imports. In response, these nations have, at least partly, laid out sub- stantial diplomatic and military expenditures in these regions in order to assure a steady supply of oil. T ese additional security risks represent external social and monetary costs associated with oil use. Fossil Fuels Fossil fuels are organic chemicals (hydrocarbons) created from living organisms, usually remains of pre- historic vegetation that originally accumulated in swamps and peat bogs around 300 million years ago. Dead plants and animals were buried in sediments, where over millions of years high pressures and temperatures concentrated and transformed them into energy-rich compounds, namely coal (a solid), crude oil or petroleum (a liquid) and natural gas. T e geological mechanism involved in the formation of these fuels and the extremely long time periods result in the fact that these fuels are essentially non-renewable resources. While coal reserves are vast in Southern Africa, they are not inf nite and would last at most a few generations if coal continues to be the predominant energy resource, not forgetting the environmental impact that would result from continual exploitation and utilisation.

66 Coal Similar to other fossil fuels, coal formation began during the so-called carboniferous period, 360 million to 290 million years ago. T us, the energy we get from coal today comes from the energy that plants absorbed from the Sun millions of years ago. All living plants store solar energy through a process known as photosynthesis. When plants die, this energy is usually released as the plants decay. Under conditions favourable to coal formation, the decaying process is interrupted, preventing the release of the stored solar energy locked into the coal. Due to its relative abundance and low market price, coal combustion is still the largest source of energy in the world, accounting for 40% of all electrical energy worldwide. Almost 90% of South Africa’s electrical energy is generated in coal-f red power stations. Unfortunately, coal combustion is a major contributor to global greenhouse gas emissions accounting for over 70% of carbon dioxide emissions from global power generation.

FIGURE 2: SCHEMATIC ILLUSTRATION: HOW COAL IS CONVERTED INTO ELECTRICAL ENERGY THEME 1.2.2

Electricity

Coal supply Stack

Conveyor

Boiler Steam turbine Generator Pulveriser/ Mill Substation/ transformer

Condenser Ash systems Water puriﬁ cation

Image source: GIZ/S4GJ

Some people claim that coal combustion is cheaper than using renewable energy for generation of electrical energy or heat. T is might be true, if one neglects all external cost from coal mining and combustion. However, when accounting for the true costs of energy generated from coal, most renewable energy sources are actually signif cantly cheaper in the long run. A major problem with coal is, that its full costs are usually not ref ected in its market price, and thus while we may seemingly purchase and burn coal cheaply, we are in reality paying a much higher cost in the long term, if we look at the big picture (environmental externalities). Economists refer to the impacts on human and environmental health which are not ref ected in the price of coal as externalities. T ose who benef t from the seemingly cheap energy don’t pay for these externalities directly, but the public eventually has to pay in the form of medical bills, acid mine drainage, dust and noise pollution, rehabilitation of mines, environmental monitoring and cleanups, and particularly subsidies. In addition, new coal plants, such as Medupi in Limpopo and Kusile in Mpumalanga, both still under construction and with an expected capacity of 4.8 GW each, are cumbersome and onerous projects. T eir huge size renders them prone to construction delays, currently approximately 3 years for Medupi, and to enormous capital expenditure. T ese two infrastructure projects created an enormous cost over- run compared to the initial cost estimates. Reliance on fewer power plants can be critical, because if a single coal plant goes down for whatever reason, it has a huge and of en crippling impact on the economy, especially as the existing f eet of old coal power stations are to be decommissioned.

67 Nuclear Energy Nuclear energy is a controversial energy source. It is not a renewable energy source, but because it is a technology not based on fossil fuels some people think nuclear power plants could play an important role in reducing carbon emissions. Others feel the risk of horrif c accidents, such as in Russia (Chernobyl) in 1986 and in Japan (Fukushima) in 2011, both rated level 7 (major accidents) on the International Nuclear Event Scale (INES), and the issues of storing nuclear waste for thousands of years are too signif cant to warrant the further development of this energy source.

FIGURE 3: THE FUKUSHIMA DAIICHI NUCLEAR DISASTER THEME 1.2.2

Image source: http://www.kisc.meiji.ac.jp/~sakai/presen/afpwaa-311-chap05-mat.pdf (see CD) T e Fukushima Daiichi nuclear disaster happened in March 2011 and forced over 120 000 people to f ee. Radioactive contamination still keeps many from their homes.

Your own notes

68 FIGURE 4: CHERNOBYL: A QUARTER CENTURY LATER

Smolensk

Dnieper Desna Bolv

a Sozh Minsk Mogilev Krychaw Russia Berezina Cherykaw Belarus Bykhov Slawharad Krasnapolle Bryansk Babruysk

Rahachow Sozh

DnieprChachersk

Vetka Novozybkov Desna THEME 1.2.2 Gomel Dobrush Kimovo Luninets Kuz'minichy Pripyat Kalinkavičy Mazyr

Khoiniki r Yelsk Narowla

Dniepe Vystupovichi Chernobyl Plant Chernihiv Pershotravneve Seym Pripyat Ovruch Desna Chernobyl Lypnyky Poliske Narodychi Confiscated/Closed Zone Korosten Kiev Greater than 40 curies per square Reservoir kilometer (Ci/km²) of Cesium-137 Permanent Control Zone 15 to 40 Ci/km² of Cesium-137

Dniepe Ukraine Kiev Periodic Control Zone Zhytomyr

r 5 to 15 Ci/km² of Cesium-137 Unnamed zone 1 to 15 Ci/km² of Cesium-137

0 50 100 Kilometers

0 50 100 Miles

Image source: http://upload.wikimedia.org/wikipedia/commons/2/23/Chernobyl_radiation_map_1996.svg

On April 26, 1986, as a combined result of design def ciencies and human error, reactor number four of the Chernobyl Nuclear Power Plant near the town of Pripyat, Ukraine, exploded. Radioactive material scattered over a wide area in Europe. In the vicinity of the Chernobyl Plant, the radiation level was so high that a 2,800 km2 area in Belarus, Ukraine, and Russia, including three cities and more than one hundred villages, had to be permanently abandoned. To prevent future nuclear accidents higher safety standards will drive up the cost of nuclear power. Albeit uranium reserves are large, they are far from limitless. In addition, even with the most speculative uranium reserve scenario and assuming the deployment of advanced fast reactors and fuel recycling, the total f nite nuclear potential would remain well below the one-year solar energy potential. For South Africa, a rollout of a large f eet of six new nuclear power plants with a total capacity of around 20 GW has been proposed in the IRP, the 20-year plan which estimates demand and recommends the required energy mix. In addition to potential accidents and the unsolved challenges of storing radioactive waste, nuclear plants possess the same constrictions as the large new coal plants Medupi and Kusile, but on an even larger scale. Given that the nuclear programme has not yet begun, the expectation is, that costs and construction time could be driven up substantially compared to the initial estimates for the new six nuclear power plants.

69 Renewable Energy Generally, renewable energy is def ned as energy that comes from resources such as sunlight, wind, tides, waves and geothermal heat. Similar to conventional (fossil) fuels, applications of renewable energy technologies are mainly placed in the category of electrical energy generation and heating. An obvious example for a principal renewable energy resource is the Sun. Solar radiation is passing through the environment as a current or f ow, irrespective of there being a device to intercept and harness this power or not. Several other renewable energy technologies, such as wind turbine and hydroelectric power plants derive from solar radiation. Yes, it is true that wind energy is simply a converted form of solar energy! T e Sun’s radiation warms dif erent parts of the Earth, oceans, and other bodies of water, at dif erent rates during night and day. T e result of this uneven heating is atmospheric change. Hot air rises, leaving lower atmospheric pressure near the Earth’s surface, and cool air is drawn in to replace it. T e result of this air exchange is wind. Just as wind is a converted form of solar energy, so is hydroelectric power. T e Sun powers the hydrologic cycle through evaporation and precipitation (rain), and water eventually reaches lakes, reservoirs and dams. T e latter are usually used to generate hydroelectric power. T us, solar energy in some form or other is always at work, in rays of sunlight, in air currents, and in the water cycle.

THEME 1.2.2 FIGURE 5: RENEWABLE ENERGY RESOURCES

Wind energy Sun energy

Wind turbines

Hot springs

Geothermal energy Ocean energy Geothermal reservoir

Image source: GIZ/S4GJ

Other, albeit less signif cant, examples for principal renewable energy resources are the motion and gravitational forces of the Sun, Moon and Earth. T ese forces are responsible for tides and currents. T e other principal renewable energy resources are geothermal energy derived from cooling, chemical reactions and radioactive decay in the Earth. Photosynthesis Photosynthesis is the making (synthesis) of organic structures and chemical energy stores by the action of solar radiation. It is by far the most important renewable energy process, because all living organisms are made from materials f xed by photosynthesis, and our activities rely on oxygen in which the solar energy is mostly stored. Despite photosynthesis being a physically induced process and the driving function of natural engineering, the subject is missing from most physics and engineering texts. To rectify this omission, we wanted to at least to mention this process that provides abundant stored energy, a natural phenomenon and an engineer’s dream.

70 Solar Thermal Applications and Photovoltaic (PV) Systems Solar energy relies on the nuclear fusion power from the core of the Sun and solar radiation is eventually absorbed on Earth. T is energy can be harnessed and converted in a few dif erent ways, for example by using photovoltaic panels for the direct conversion of sunlight to electrical energy or collectors for solar water heating for domestic use.

FIGURE 6: 5 PHOTOVOLTAIC PANELS ARE WIRED IN SERIES

+ - + - + - + - + - THEME 1.2.2

kWh Meter

to Grid DC disconnect Inverter AC disconnect 220 VAC

AC electrical panel to household loads

Image source: GIZ/S4GJ In this schematic view 5 photovoltaic panels are wired in series and used for the direct conversion of sunlight into electrical energy

Your own notes

71 Wind Power Most people can call to mind the image of wind mills used for centuries in many countries to grind grains or to pump water. While wind energy has long been used for such work, it is only fairly recently that wind turbines have been designed and constructed to generate electrical energy. T e primary components of most modern wind turbine systems include: (i) A rotor, which consists of two or more propeller-like blades that are tied to a rotating shaf . T e force of the wind turns the blades, which transfer the kinetic energy into a rotating shaf , which in turn spins a generator to produce electric charges. (ii) A nacelle, which is the enclosed body of the turbine. In a large wind turbine the nacelle hous- es the drive train, gearbox and generator, and in a smaller turbine a magnetic alternator and a gearless direct drive generator. (iii) A tower, which supports the rotor and nacelle. T e tower elevates the turbine in order to increase exposure to higher velocities of wind. (iv) A mainframe, which is a structure that contains the slip ring. It connects the nacelle and its wiring to the tower in such a way, that the rotor can spin freely and face into the wind.

Sub-Saharan Africa’s wind potential is estimated at around 1 300 GW (OECD/IEA 2014), which would THEME 1.2.2 produce several times the current level of total African electrical energy consumption. In respect to current and planned wind turbine plants South Africa and parts of East Africa are leading the way in increasing their wind power capacity with, for example, Kenya planning to add over 400 MW of wind capacity by 2020 and South Africa between 3 and 16 GW of wind power by 2050.

FIGURE 7: A SIMPLIFIED SCHEMATIC VIEW INTO A WIND TURBINE

Rotor blade

Wind Gear box Nacelle

Generator Switchyard

Power cables

Tower

Transformer

Image source: GIZ/S4GJ

72 Hydroelectric Power Hydroelectric power is very ef cient and convenient because it can respond quickly to f uctuations in demand. Reservoir gates can be opened or closed depending on daily use or demand in the community, for example, the production of hydroelectricity is of en slowed during the night when most people use less energy. Worldwide, about 20% of all electrical energy is generated by hydropower and some regions depend more on hydroelectric power than others. 75% of the electrical energy produced in New Zealand and over 95% produced in Norway come from hydropower for example. One major disadvantage of hydroelectric power is that all reservoirs eventually f ll up and require very expensive excavation to become useful again. Another is that, in most developed countries, all suitable locations for hydroelectric dams are almost already used. FIGURE 8: A SIMPLIFIED SCHEMATIC VIEW INTO A HYDROPOWER FACILITY

Reservoir THEME 1.2.2 Dam Transformer Power Lines Generator Powerhouse

Intake Control gate Penstock Turbine Outﬂ ow

Image source: GIZ/S4GJ adapted from https://wiki.uiowa.edu/display/greenergy/Hydroelectric+Power

Your own notes

73 Bioenergy Bioenergy refers to the energy content in solid, liquid and gaseous products derived from biomass, feed stocks and biogas. It includes solid biomass, bio-fuels and biogas. Biofuels are liquid fuels derived from biomass, usually sugar cane, or waste feed stocks and include ethanol and biodiesel. Biogas is a mixture of methane and carbon dioxide produced by bacterial degradation of organic matter and used as a fuel. Bioenergy in form of solid biomass, including wood and charcoal still dominates the sub-Saharan energy mix, while the modern use of solid biomass and biogas for power generation and heat makes up only a very small share. Hydrogen and Fuel Cells Hydrogen can be used in fuel cells which are in a way similar to batteries, to power for example an electrical motor in a vehicle with only water as the “combustion” product. However, signif cant production of hydrogen requires abundant power, and there are already several promising methods to produce hydrogen by using solar power, making fuel cell technologies more environmental friendly. Geothermal Power In certain areas the increase in temperature with depth is suf cient enough to run a turbine and gener- THEME 1.2.2 ate electrical energy. T is possibility is however, limited to a few locations on Earth and usually requires deep boreholes. Another form of geothermal energy is shallow geothermal or ground source heat, a result of the heat storage capacity in the soils or upper layer of the Earth. At around 50 meters soil tends to stay at a relatively constant temperature over the year and can be used with heat pumps to heat a building in winter and to cool a building in summer.

FIGURE 9: A SIMPLIFIED SCHEMATIC VIEW OF A GEOTHERMAL POWER PLANT

Geothermal Power Plant

Turbine Generator

3 2 Steam 4 Cooling tower

Hot Injection water well

1 5

Image source: GIZ/S4GJ adapted from http://epa.gov/climatestudents/images/4-1-5-geopower.gif

Your own notes

74 Examples Global Energy Consumption and Reserves In 2013, despite a stagnant global economy, energy consumption accelerated globally (an increase of 2.3%). With 32.9% of global energy consumption, oil remains the world’s leading fuel. Coal’s share of global energy consumption reached 30.1%, the highest it has been since 1970, and nuclear accounted for 4.4% of global energy consumption, the smallest share since 1984. Hydroelectric and other renewable resources in power generation both reached record shares of global primary energy consumption (6.7% and 2.2%, respectively) (all data based on BP 2014).

FIGURE 10: WORLD ENERGY CONSUMPTION 2013

Coal 13000 Renewables Hydroelectricity 12000

Nuclear energy THEME 1.2.2 Natural gas 11000 Oil 10000

9000

8000

7000

6000

5000

4000

3000

2000

1000

88 89 90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06 07 08 09 10 11 12 13

Image source adapted from: BP Statistical Review of World Energy 2014 (on CD)

Oil remains the world’s dominant fuel, but has lost market share for 14 years in a row. Coal increased by 3%, hydroelectric and other renewable resources increased by 6.7% and 2.2%, respectively. Some fossil fuel reserves, such as oil and gas, will probably be depleted within 50 years, while others, such as coal, will probably last for the next 100-120 years. T e fact is that neither one of these projections is very appealing for a global community that is so heavily dependent on fossil fuels to meet basic human needs. T e bottom line is we are going to run out of fossil fuels for energy and we have no choice but to prepare for a new age of energy production since, most certainly, human demands for energy will unfortunately not decrease any time soon.

Your own notes

75 FIGURE 11: RESERVES–TO-PRODUCTION (R/P) RATIOS FOR OIL, GAS AND COAL. COAL REMAINS THE MOST ABUNDANT FOSSIL FUEL BY R/P RATIO

500 Oil Natural gas Coal

400

300

200 THEME 1.2.2 100

OECD Non-OECD European Union Former Soviet Union World

Image source adapted from: BP Statistical Review of World Energy 2014 (on CD)

Eurasia holds the majority of proven coal reserves and the highest R/P ratios. On a global scale oil and gas, will probably be depleted within the next 50 years, while coal will probably last for the next 100-120 years. Energy Consumption and Reserves in South Africa In South Africa, the coal industry has been and continues to be the primary source of energy for. Over ninety percent of the country’s electrical energy is generated from coal, as does almost half its liquid transport fuel. But despite South Africa’s abundant endowment of coal, its continued use presents many challenges and its future contribution demands careful stewardship.

FIGURE 12: TOTAL ENERGY CONSUMPTION IN SOUTH AFRICA, 2012

Oil 22%

Natural gas 3% Coal 72% Nuclear energy 3%

Renewables 1%

Image source adapted from: BP Statistical Review of World Energy 2013 (on CD)

76 Most of South Africa’s coal mining currently takes place in centrally situated coalf elds that encom- pass a large area of the Highveld, a region that was once an uninterrupted sea of grassland and wetland before European settlement. T e grassland, when ploughed, turns into excellent cropland, and about half of South Africa’s soybeans and a quarter of its corn is now grown here. Coal mining has lef a ravaged landscape. Some important rivers are now so polluted by acid mine drainage, which seeps out of abandoned mines, that they can no longer be used by farms or factories. Underground coal seam f res, some of which have been burning for decades, cause smoking sinkholes to appear. In January 2012 the town of Carolina, which lies downstream of major coal mines, lost its entire municipal water supply overnight when a huge volume of acid mine drainage was washed into its drinking water reservoir by heavy rains. Residents rioted in protest. It took nine months for the state to restore clean water to the town.

FIGURE 13: SOUTH AFRICA’S MAJOR COAL DEPOSITS

N THEME 1.2.2

BOTSWANA Waterberg coalﬁ eld

Central SWAZILAND Johannesburg basin coalﬁ elds

SOUTH AFRICA Richards LESOTHO Bay coal terminal

Image source: http://e360.yale.edu/feature/in_south_africa_renewables_vie_with_the_political_power_of_coal/2719/

77 Although coal clearly maintains high-level political support, other energy sources may soon challenge its dominance. Renewable energy technologies are the answer to South Africa’s serious energy shortages, which threaten to impede industries and repeatedly af ected residential areas in major cities in recent years. In 2010, fossil fuels (coal and gas) made up more than 92% of the energy mix but the Integrated Resource Plan (IRP), setting out a path for South Africa’s long-term energy future, is proposing that coal should only contribute around 47% to the energy mix by 2030, renewable energy 27%, nuclear energy 13%, and gas turbines 11%.

FIGURE 14: SOUTH AFRICA’S ENERGY MIX IN 2013, WHERE FOSSIL FUELS MADE UP MORE THAN 86 % OF THE SHARE

2013 1%

4% 3% Coal

THEME 1.2.2 Gas 6% Pumped storage

Nuclear

Hydro

86%

2030 (projection/planned) 1%

1% Coal 10% Nuclear energy

Hydro (import)

11% OCGT 47% CCGT 3% Wind

CSP 8% PV

Other (renew, co-gen, etc.) 6% 13%

Image source: GIZ/S4GJ (based on IRP data 2013)

In 2030, renewable energy technologies could contribute about 27% and nuclear energy about 13% of the share. T e share of fossil fuels could be reduced to about 58% in 2030.

78 Exercises

(i) State the main dif erences between renewable and non-renewable energy resources. Give typical examples for each energy type, describe their kind of f ux (persistent/continuous vs static/potential) and their main environmental impacts, and specify their availability.

Renewable Non-renewable

Examples

Energy ux

Environmental effects

Availability THEME 1.2.2

(ii) Try to answer the following questions: • Just how limited are our fossil fuel reserves? • What is the original source of most of our energy technologies? • Is a rechargeable battery a renewable source of energy? (iii) For bioenergy, coal, natural gas, wind power, oil and geothermal energy, identify each energy resource as renewable or fossil (non-renewable) resource. Explain your reasoning.

Technology Renewable Non-renewable Reason

Bioenergy

Coal

Gas

Wind

Oil

Geothermal

79 (iv) Brief y indicate in South Africa’s projected energy mix for 2030 the shares per technology. Compare the dif erent shares with the energy mix of 2013 and state which technologies will require the highest increases for new builds? Which technologies are expected to decrease most?

Technology Projected share in Share increase? Share decrease? Percent (2030) (yes/no) (yes/no)

Coal

OCGT

CCGT THEME 1.2.2 Pumped storage

Nuclear

Hydro

Wind

CSP

Photovoltaic

Others

Your own notes

80 (v) Have a look at the f gure below indicating the UK’s energy mix in 2010 and in 2030. Com- pare the dif erent shares per technology (the percentages allocated for 2010 and for 2030). Which technologies will require the highest increases for new builds? Which technologies are expected to decrease most?

FIGURE 15: THE UK’S ENERGY MIX IN 2010 AND THE PROJECTED MIX FOR 2030

The UK‘s electrical energy sources in 2010

38% 28% THEME 1.2.2

17% 10%

3% 4% Carbon Other Coal Wind Nuclear Gas capture renewables Other 2% 4% 6% 10% 12%

30%

36% The UK‘s electrical energy sources projected for 2030

Image source: Education & Skills, National Grid UK, http://www.nationalgrideducation.com/secondary/publications_ed- ucation-resources.php

In 2030, renewable energy technologies could contribute about 50% and nuclear energy about 31% of the share. T e share of fossil fuels could be reduced to about 20% in 2030.

Further Information (all materials are on the resource CD)

(i) Fukushima Daiichi nuclear disaster. http://en.wikipedia.org/wiki/Fukushima_Daiichi_nuclear_disaster (ii) T e Guardian, Wednesday 10 September 2014, Fukushima nuclear disaster: three years on 120,000 evacuees remain uprooted. (iii) BP Statistical Review of World Energy 2014 (iv) Africa Energy Outlook, A FOCUS ON ENERGY PROSPECTS IN SUB-SAHARAN AFRI- CA, World Energy Outlook Special Report, International Energy Agency, www.iea.org (v) T e South African Coal Roadmap, Fossil Fuel Foundation (www.fossilfuel.co.za) and the South African National Energy Development Institute (www.sanedi.org.za). (vi) Climate change: T e opportunity cost of Medupi and Kusile power stations, James Blig- naut, Department of Economics, University of Pretoria. (vii) T e True Cost of Coal in South Africa, Paying the price of coal addiction, GREENPEACE 2012

81 THEME 1.2.3 ADVANTAGES AND DISADVANTAGES OF RENEWABLE ENERGY RESOURCES Introduction

Africa’s energy sector is vital to the continent’s future development. Sub-Saharan Africa has more than suf cient potential renewable energy resources to meet domestic needs, yet currently more than two- thirds of its population does not even have access to modern energy. However, several countries, including South Africa, have ambitious plans to obtain their power by integrating renewable energy technologies into their existing grid infrastructure to reach an integrated energy mix. From a pragmatic point of view and in the intermediate future, South Africa needs a balance of energy sources that includes wind, coal, solar and gas for power generation. T e advantages of renewable energy technologies are lower environmental costs and non-centralized opportunities. Renewable energy technologies also lead to greater consumer control and direct involvement. THEME 1.2.3 Keywords

Advantages and disadvantages of renewable energy technologies 100% Renewable energy Theme Outcomes

At the end of this theme, you should be able to list and explain the advantages and disadvantages of renewable energy resources.

Deﬁ nition of Terms 100% Renewable energy? How realistic is it for a country to generate 100% of its electric demand through renewable energy technologies? For a country with abundant renewable resources, which can be utilised in a cost ef ective and reliable manner, it is theoretically quite possible to transform current electrical energy generation schemes into 100% renewable energy resources. But, depending on the current energy generation and distribution infrastructure and the f nancial costs involved for such a transition, it would possibly require a few decades for any country to achieve such a target. What is the impact of renewable technologies on the environment? Renewable energy technologies derive their energy from the Sun, either directly or indirectly, and of er many climate friendly possibilities for the generation of electrical energy and heat. It is well established that the environmental footprint of electrical energy and heat generation via renewable technologies is considerably smaller than that of the fossil fuel technologies. T us, each kWh generated by PV or wind turbines displaces an otherwise climate unfriendly kWh and mitigates several of the following factors: greenhouse gases, nitrogen and sulphur dioxides emissions, mining degradations, ground water contamination etc. – factors, which are all present or postponed costs to society (externalities). T ere is however no reason to hide the fact that some renewable technologies can harm the environment too. More details on this issue can be found in the following table:

82 T e table below lists some economic, social and environmental advantages and disadvantages of selected renewable technologies. Not mentioned are the well-known benef ts such as no or limited fuel cost, no air pollution and no global warming ef ects when compared to fossil fuel technologies.

TABLE 1: ECONOMIC, SOCIAL AND ENVIRONMENTAL ADVANTAGES AND DISADVANTAGES OF SELECTED RENEWABLE TECHNOLOGIES

Technology Advantages Disadvantages

Hydro Predictable 24/7 power, can provide Limited locations available base, intermediate or peak load for Restricts areas with ﬂ owing water demand and creates environmental stress Can expand irrigation on water ecosystems Can provide drinking water Can destabilise relations between regions or neighbouring countries THEME 1.2.3 (up river and down river water rights) Dam building is very costly Often people have to be relocated

Wind Can provide electrical energy on a Variation of power density and decentralised scale (small to medium duration can be a problem without size installations) potentially beneﬁ t- modern forecasting and smart-grid ing local communities technology Some used land can be utilised Can be noisy simultaneously, both to produce elec- Can endanger biodiversity: moving trical energy and for agriculture turbine blades are a serious treat to birds and bats

CSP Predictable 24/7 power, can provide Limited locations available base, intermediate or peak load for High water demand in arid or demand due to unique storage option semi-arid environments CSP-plants can be placed in dry Can endanger biodiversity: CSP fa- inhospitable locations where human cilities are a “No Fly Zone”, lethal settlements are sparse to essentially all the birds, bats, and insects that have the misfor- tune of entering their airspace

Photovoltaic Electrical energy generation with- Intermittency issues, no or lim- out mechanically moving parts in a ited generation at night, during totally silent mode, a perfect solution daytime during cloudy or rainy for urban areas and for residential weather applications Land-mounted PV panel installa- Residential solar panels (rooftop) are tions require relatively large areas easy to install without any interfer- for deployment ence to residential lifestyle Further research is required for Electrical energy generation via PV recycling of PV modules coincides with energy needs for cooling and PV can provide an effective solution to energy demand peaks, especially in hot summer months where energy demand is high for cooling Operation and maintenance costs are low (almost negligible)

83 What is the impact of renewable technologies on energy security? Energy security and diversif cation of the current energy mix is a major policy driver for renewable technologies. Growth of renewable technologies generally contributes to energy diversif cation and their use can reduce fuel imports and insulate the country’s economy to some extent from fossil fuel price f uctuations. T is certainly increases energy security. Are renewable technologies competitive? Provided that appropriate policy frameworks are in place and enacted, the renewable energy sector in some countries such as Iceland, Norway, Austria, Sweden and other European nations has already demonstrated its capacity to be technically and f nancially feasible. Established technologies such as hydro and geothermal are of en fully competitive and non-hydro renewable technologies, such as wind turbines and PV facilities, are increasing at double-digit annual growth rates. Costs are decreasing as well and a portfolio of renewable energy technologies is becoming cost-competitive in an increasingly broad range of circumstances. However, economic barriers remain important in many cases and the costs of renewable technologies need to be reduced further. Moreover, fossil fuel subsidies and the lack of a global price on carbon are signif cant barriers to the competitiveness of renewable technologies.

THEME 1.2.3 Should renewable technologies be subsidised? More and more countries and international bodies such as the International Energy Agency (IEA) believe that further growth of renewable energy is essential for a secure and sustainable energy system. Transitional economic incentives that decrease over time are justif ed. Incentives are sometimes needed to stimulate cost reductions through technology learning, such as improvements in manufacturing, increased technology per- formances, economies of scale and larger deployment. T us, incentives for renewable technologies may also be justif ed to obtain additional energy security and environmental benef ts.

Examples Few countries have appropriate and abundant renewable energy resources to generate all of their electrical energy and heat demands at a competitive price. T e only two realistic nominees for such an endeavour are Iceland and Norway. Iceland’s electrical energy is produced almost entirely from renewable energy sources, i.e. hydroelectric (around 70%) and geothermal (around 30%). Norway is known for its particular expertise in the development of ef cient, environmentally friendly hydroelectric power plants. Nation- wide installed capacity of hydropower is over 29 GW and accounts for 98.5% of the national electricity demand. In addition to this, Norway is also generating electricity through wind turbines and geothermal energy. T e next two candidates are Austria (65.5 %) and Sweden (60.0 %). Both can at least generate three f f hs of all the electricity consumed from renewable energy sources, largely as a result of hydropower and bioenergy. T e f gures above are from the latest data available for 2012 from EUROSTAT and show that in Europe on average electrical energy generated from renewable energy resources contributed almost one quarter (23.5 %) of the 28 EU countries’ gross energy consumption. Data from the US Energy Informa- tion Administration indicates that in 2011, renewable energy resources contributed almost 13 % to the net electricity generation in the USA. FIGURE 1: PROPORTION OF ELECTRICAL ENERGY GENERATED FROM RENEWABLE RESOURCES IN THE EU 2012 (GROSS CONSUMPTION)

120 100 80 60 40 20 0 Italy Spain EU-28 France Cyprus Poland Austria Ireland Croatia Estonia Finland Norway Sweden Belgium Bulgaria Slovakia Portugal Slovenia Romania Germany Malta (1) Denmark Latvia (1) Latvia Lithuania Greece (1) Greece Hungary (1) Hungary Netherlands (1) Estimate Luxembourg

Source: Eurostat (online data code: tsdcc330) Republic Czech United Kingdom United

Image source adapted from: Eurostat 2012, http://epp.eurostat.ec.europa.eu/statistics_explained/index.php/Renewable_ener- gy_statistics 84 However, not all countries are blessed with either suf cient abundant renewable energy resources or the f nancial means to develop these appropriately. Consequently, it is advisable that these countries should focus on addressing the important issue of global warming and should aim to establish the lowest carbon emission system possible. In the process of such an approach all nations would have a fairly good chance to establish an appropriate energy mix with the help of renewable energy technologies and the best solution for a cleaner environment. South Africa, or rather the Depart- ment of Energy is trying to do exactly this with the help of the Integrated Resource Plan!

Exercises

(i) Brief y indicate the advantages and disadvantages of renewable energy technologies in the table below:

Technology Advantages Disadvantages THEME 1.2.3

Wind

CSP

Photovoltaic

(ii) Indicate with the symbols (coloured circles) in the diagram below where you would place the following energy resource: a) in respect to their ability to serve one or more of the three basic energy generation regimes, and b) in respect to their environmental impacts (EI).

High

Low

Base load Intermediate load Peak load

COAL NUCLEAR GAS WIND PV CSP

85 (iii) Have another careful look at Figure 1 (Proportion of electrical energy generated from renewable resources in the EU 2012). You will easily see that Norway is generating more energy from renewable resources (more than 100%) than it consumes itself. What is Nor- way doing with the additional available electrical energy?

Further Information (all materials are on the resource CD)

(i) US Energy Information Administration 2012, Energy review. http://www.eia.gov/totalenergy/data/annual/perspectives.cfm (ii) IEA 2014, International Energy Agency, Renewable energy outlook. http://www.worldenergyoutlook.org/media/weowebsite/2013/WEO2013_Ch06_Renew- ables.pdf THEME 1.2.3 (iii) BNEF 2012, Reconsidering the Economics of PV Power. (iv) OECD/IEA 2014, International Energy Agency, Technology Roadmap Solar T ermal Elec- tricity. www.iea.org

Your own notes

86 Your own notes THEME 1.2.3

87 Unit 1.3 Unit

UNIT 1.3 SIGNIFICANCE OF SOLAR RADIATION

Introduction

T e Sun supplies energy in the form of radiation, without which life on Earth could not exist. Energy is generated in the Sun’s core through the fusion of hydrogen atoms into helium. Part of the mass of the hydrogen is converted into energy. In other words, the Sun is an enormous nuclear fusion reactor. However, because the Sun is so far way from the Earth, only a tiny proportion of the Sun’s radiation reaches the Earth’s surface but nonetheless, the solar resource which does reach the Earth is still in order of magnitude larger than all the other energy resources combined.

Unit Outcomes

At the end of this unit, you should be able to: (i) Explain why the Sun must be considered as the principal source of energy. (ii) Measure irradiance from dif erent sources of light in watts per square meter (W/m2) (iii) Explain the ef ects of orientation and tilt of solar arrays on the amount of power produced.

Themes in this Unit

Unit 1.3 covers two themes: T eme 1.3.1 T e Sun as the Principle Source of Energy T eme 1.3.2 Ef ects of Orientation and Tilt of Solar Arrays on the Amount of Power Produced

88 THEME 1.3.1 THE SUN AS THE PRINCIPAL SOURCE OF ENERGY Introduction

T e Sun is the Earth’s nearest star and the source of virtually all energy available on Earth. Solar energy is or was always at work in rays of sunlight, in air currents, and in the water cycle. Solar energy is also embedded in fossil fuels, since the energy we get from coal or oil today comes from the energy that plants absorbed from the Sun millions of years ago.

FIGURE 1: THE SUN’S SURFACE SHOWING LARGE ERUPTIVE PROMINENCES THEME 1.3.1

Image source: SOHO consortium, a cooperation project between ESA and NASA. Web: http://sohowww.nascom.nasa.gov/gallery/ images/large/superprom.jpg Keywords

Earth’s solar potential Solar energy Solar radiation Theme Outcomes

At the end of this theme, you should be able to: (i) Explain why the Sun must be considered as the principal source of energy. (ii) Explain solar radiation using relevant key terms. (iii) Measure irradiance from dif erent sources of light in watts per square meter (W/m2). Deﬁ nition of Terms Solar Energy T e Sun can be described as a glowing ball of gas held together by its own gravity and powered by nuclear processes at its centre. T e core of the Sun is the engine of energy creation. Simply stated, the Sun’s energy is generated by a process known as nuclear fusion, the so-called proton-proton reaction or P-P chain, where four hydrogen atoms (the chemical symbol is H) fuse to form one helium atom (the chemical symbol is He). As a result of this fusion, energy is released and transformed into electromagnetic radiation by the time they reach the Sun’s surface.

89 FIGURE 2: A SIMPLIFIED ILLUSTRATION OF HYDROGEN AND HELIUM ATOMS, THE TWO COMPONENTS OF SOLAR NUCLEAR FUSION

4 H

He THEME 1.3.1 Image source: GIZ/S4GJ

T e Sun radiates its energy from a distance of about 150 million kilometres and the light travels the distance between the Sun and the Earth in only 500 seconds, i.e. a little more than 8.3 minutes. T e Sun must be considered as the principal and seemingly endless source of energy for our planet. Almost all renewable and non-renewable energies depend either directly or indirectly in one way or another on the Sun. Wind and hydroelectric power are the direct result of dif erential heating of the Earth’s surface which leads to air moving (wind) and precipitation (rain) forming as the air is lif ed. Photosynthesis, the making of organic structures and chemical energy stores, i.e. our food and the air we breathe, depends on solar radiation as well. Photosynthesis is by far the most important renewable energy process. All living organisms are made from materials f xed by photosynthesis, and our activities rely on oxygen in which solar energy is stored. Even fossil reserves, such as coal and gas, were once living organisms that gained their energy from photosynthesis. FIGURE 3: A SIMPLIFIED SCHEMATIC ILLUSTRATION OF PHOTOSYNTHESIS

Sunlight

Oxygen

Carbon dioxide

Water

Image source: GIZ/S4GJ

90 Solar Radiation Solar energy comes to Earth in the form of radiation, or sunlight, with dif erent spectral components. Sunlight is a broad spectrum of electromagnetic rays and the visible light that we see is just a small fraction of the electromagnetic spectrum and the total energy emitted by the sun.

FIGURE 4: SUNLIGHT IS A BROAD SPECTRUM OF ELECTROMAGNETIC RAYS

Increasing frequency (ν) 1024 1022 1020 1018 1016 1014 1012 1010 108 106 104 102 100 ν (Hz)

γ rays x rays UV IR Microwave FM AM Long radio waves Radio waves 10-16 10-14 10-12 10-10 10-8 10-6 10-4 10-2 100 102 104 106 108 λ (m)

Increasing wavelength (λ) Visible spectrum THEME 1.3.1

400 500 600 700 Increasing wavelength (λ) in mm

Image source: GIZ/S4GJ adapted from http://upload.wikimedia.org/wikipedia/commons/thumb/f/f1/EM_spectrum.svg/2000px- EM_spectrum.svg.png T e visible light we see, i.e. spectral components between the near infrared and the near ultraviolet, is just a small fraction of sunlight.

From a more scientif c point of view, sunlight can appear as either a wave or as a particle and this concept is called “wave-particle duality”. A complete physical description of the properties of light requires a quantum-mechanical analysis of light, since light is a type of quantum-mechanical particle called a photon. For solar thermal or photovoltaic applications this level of detail is seldomly required. However, one can better understand sunlight from two points of view, namely as waves and particles. T e f rst point of view is essential for all solar thermal applications and the second point of view is essential with regard to photovoltaic (PV) systems.

91 Examples

South Africa of ers optimal conditions for both, solar thermal applications and photovoltaic (PV) systems. T e country has one of the highest solar energy regimes in the world, with the most favourable areas being in the Northern Cape and some central areas.

FIGURE 5: THE AVERAGE DAILY DIRECT IRRADIATION IN SOUTH AFRICA THEME 1.3.1

Image source: Fluri 2009, http://geosun.co.za/wp-content/uploads/2012/07/TP-Fluri-T e-potential-of-concentrating-solar-power-in-South-Africa.pdf

Satellite data is used to show the average daily direct irradiation in South Africa for the whole year and for the months of March, June, September and December.

92 Measurement of Solar Radiation Scientif c measurement of solar radiation in W/m2 is done with the help of specif c instruments such as pyranometers. T e sensor is usually a thermoelectric detector (thermopile), which absorbs all solar radiation, and the horizontal assembly of the device measures the overall horizontal solar irradiation. Other, more reliable priced devices are using a photoelectric detector (photodiode) or a solar cell as an irradiance sensor (see also exercises below).

FIGURE 6: A PYRANOMETER IS USED TO MEASURE SOLAR RADIATION IN W/M2

3 4 5 2

1 THEME 1.3.1

7 11 8 10 9

Image source: http://en.wikipedia.org/wiki/Pyranometer#mediaviewer/File:Pyranometer_diagram_Huksef ux_SR20.svg T e most important components are: (1) cable, (3) glass inner dome, (4) thermopile sensor, (5) glass outer dome, (7) humidity indicator with desiccant and (11) connector.

FIGURE 7: A DIGITAL SILICON IRRADIANCE SENSOR

Image source: http://www.ib-mut.de A digital silicon irradiance sensor (based on mono-crystalline solar cells) for measurement of irradiance.

93 Earth’s Solar Potential How much energy is potentially available in the immediate environment? T at’s an interesting question! If one compares the current annual energy consumption of the world to the known reserves of the f nite fossil and nuclear resources and to the yearly potential of renewable alternatives, the direct side-by-side assessment shows that the solar resource is orders of magnitude larger than all the others energy resources combined. T is indicates that our energy future in respect of electrical energy and heat generation could be a solar-based one. T ere will of course be challenges, such as managing the locally variable solar energy and developing the necessary storage technologies and infrastructures. Solar energy blessed regions like Northern and Southern Africa however, could employ this quasi-ready-to-deploy resource more easily in the future than most developed countries.

FIGURE 8: A SIMPLIFIED COMPARISON OF FINITE AND RENEWABLE ENERGY RESERVES (IN TERAWATT)

Global energy ootential

TW 00 ,0 23 r la o S Coal THEME 1.3.1 900 TW Tidal 0.3 TW

World energy Wave 0.2-2 TW consumption 16 TW Geothermal 0.3-2 TW Uranium 90-300 TW Hydro 3-4 TW

Biomass 2-6 TW Oil 240 TW Wind 25-70 TW Natural 215 TW gas

Annually Total reserves

Image source: GIZ/S4GJ adapted from http://upload.wikimedia.org/wikipedia/commons/thumb/b/b6/Global_energy_po- tential_perez_2009_en.svg/2000px-Global_energy_potential_perez_2009_en.svg.png – Adapted af er Richard and Marc Perez 2009 (see CD).

T e volume of each sphere represents the total amount of energy recoverable from the f nite reserves (fossil fuels and nuclear) and the annual potential of renewable energy resources.

Your own notes

94 Exercises

(i) EXPERIMENT Measure the irradiance of dif erent sources of light in watts per square meter (W/m2).

INFORMATION Dif erent sources of light dif er in their spectral components or simply stated the colour (wavelength) of the light they emit. T e visible light we see are the spectral components between near infrared and near ultraviolet. Sunlight appears to be whitish due to the high share of blue spectral components. T e light of an old type of incandescent bulb appears to be more yellowish due to the high share of red spectral components. As indicated earlier a solar cell can be used as an irradiance sensor. Usually sensors are manufactured out of mono-crystalline solar cells connected to a low resistance bypass (shunt). T e cell operates next to short circuit current, which is almost proportional to irradiance.

COMPONENTS (available in the Solartrainer Junior set) Multimeter and solar cell irradiance sensor

FIGURE 9: EXPERIMENT SET-UP AND WIRING DIAGRAM THEME 1.3.1

OFF DC DC Spotlight V A (Halogen)

Volt (U) Ampere (I) Irradiation sensor Multimeter COM

Adjust irradiance to different levels!

95 ASSIGNMENT

(1) Select dif erent sources of light, for example a torch, spotlight, room light and the Sun. (2) Connect the sensor to a multimeter. (3) Set the multimeter range selector to DC V 2000 m (Voltmeter). (4) Let the sensor face in the direction of the source of light in a way that the rays fall direct and perpendicular on the sensor f eld and deliver maximum irradiances. (5) Measure irradiance for each device (source of light) at three dif erent distances, i.e. 10 cm, 20 cm and 30 cm. Only one measurement for sunlight is necessary. (6) List the results of your measurement in the table below:

Source of light Irradiance (W/m2) Irradiance (W/m2) Irradiance (W/m2) at 10 cm distance at 20 cm distance at 30 cm distance

Sun (Only one measurement is necessary)

Torch

THEME 1.3.1 Spotlight

Room light

(7) Which observations can be made, i.e. what are the dif erences of dif erent sources of light regarding their performance?

NOTE !

T e corresponding radiometric unit to irradiance (W/m2) is illuminance measured in lux. Luxme- ters are quite common devices used to determine the illuminance of an extensive range of applications involving illumination equipment, lighting work and facility management. However, there is no single conversion factor between lux and W/m2, because a dif erent conversion factor for every wavelength is required. T us, it is not possible to make a conversion unless one knows the exact spectral composition of the light source.

96 (ii) Fill the gaps in the paragraph below using the following word list: National grid, violet, sun, light (2x), electromagnetic waves (3x), direct, nuclear fusion, alternate, inverter, electric, heat.

Solar energy originates from in the core of the . It is radiated through space as , which are many ultra- , visible and infra . When solar energy is absorbed by a PV module electrons are released and can produce a direct current (DC), the PV systems convert only a small fraction of the energy to energy. T e main part of the are converted to . In a grid-tied system DC current is transformed by an inverter into alternating current (AC) before being transmitted into the . Most household appliances use current, but some use current.

Further Information (all materials are on the resource CD) THEME 1.3.1 (i) SOHO, New views of the sun (PPT). http://sohowww.nascom.nasa.gov/gallery/Presenta- tions/slides2002low.pdf (ii) T e potential of concentrating solar power in SouthAfrica, T omas P.Fluri 2009, http://geosun.co.za/wp-content/uploads/2012/07/TP-Fluri-T e-potential-of-concentrating-solar-power-in-South-Africa.pdf (iii) Solar Resource Mapping in South Africa (PPT/pdf), T omas P.Fluri 2009.

Your own notes

97 THEME 1.3.2 EFFECTS OF ORIENTATION AND TILT OF SOLAR ARRAYS Introduction

T e apparent motion of the Sun has a major impact on the amount of irradiation received on the Earth’s surface or by solar-thermal or PV applications (solar arrays). T us, the ef ect of orientation and inclination (tilt) of a solar array impacts directly on the ef ciency of the solar-thermal or PV application and therefore, it is important to position the installation appropriately. T e Sun’s movement over the course of a year, and the orientation and tilt of solar arrays is discussed in the following pages. Keywords

Irradiance Irradiation Orientation and inclination (tilt) Sun-Earth geometry Sun path diagram Theme Outcomes THEME 1.3.2 At the end of this theme, you should be able to: (i) Interpret Sun path diagrams for dif erent locations. (ii) Explain the ef ects of orientation and tilt of solar arrays on the amount of power produced by using diagrams and calculations. Deﬁ nition of Terms Irradiance Irradiance is the rate of solar radiation falling on a given area at a moment in time. Irradiance is measured in units of kW/m2 (read: kilowatts per square meter). Irradiation Irradiation is the amount of solar radiation (irradiance) over time. Irradiation is measured in units of kWh/m2/day (read: kilowatts per square meter per day). Solar radiation reaches the outside of our atmosphere with a constant irradiance of about 1360 watt per square meter (W/m2). T ree types of irradiation are dif erentiated: (i) Direct irradiation: A beam of sunlight goes straight from the Sun to the ground or to a solar application. (ii) Dif use irradiation: Scattered light comes from the whole sky. Dif use is completely absent on a crystal clear day with no clouds or haze and is highly available on cloudy/hazy days or in places with lots of smog. (iii) Albedo or ref ected light: T is is light ref ected or scattered by the ground or nearby surfaces. Snow gives of a lot of this albedo light while vegetation or soil gives of very little.

98 FIGURE 1: A SIMPLIFIED SCHEMATIC ILLUSTRATION OF THE THREE TYPES OF IRRADIATION (DIRECT, DIFFUSE AND ALBEDO)

Diffusion

Diffuse irradiation Albedo Direct irradiation THEME 1.3.2 Image source: GIZ/S4GJ

Sun-Earth Geometry Because the Earth orbits around the Sun, and due to Earth’s rotation around its own axis, the position of the Sun relative to a solar-thermal or photovoltaic system (solar array) is constantly changing through the day and the year. It is worth brief y outlining the major movements involved: (i) Revolution around the Sun: T e Earth orbits the Sun at a constant speed. T e period of this movement is called a year. (ii) Rotation around its own axis: T e period of this movement is approximately one day. T e most important ef ect for our purposes is that the axis of rotation is inclined at an angle of around 23.5° with respect to the plane of rotation. T is inclination results in seasonal changes, i.e. spring, summer, autumn and winter. FIGURE 2: THE EARTH IS REVOLVING IN AN ELLIPTIC ORBIT AROUND THE SUN (ILLUSTRATION IS NOT TO SCALE!)

Northern spring/ Northern winter/ Southern fall 21. March Southern summer

Periapsis Equinox 3. January

147 mill. km Line of solstice 21. June 21. December

Line of apsides

152 mill. km

Apoapsis 3. July 21. September

Northern summer/ Northern fall/ Southern winter Southern spring

Image source: GIZ/S4GJ adapted from http://upload.wikimedia.org/wikipedia/commons/thumb/f/f0/Seasons1.svg/2000px-Sea- sons1.svg.png

99 For a body such as the Earth orbiting the Sun the points of least and greatest distance are called respectively perihelion and aphelion. T e Earth also rotates around its own axis. Subsequently, solar radiation varies for any given place during the year due to the Earth’s orbit around the Sun (changes over a year) and due to the Earth’s rotation around its own axis (changes over the day). Solar Trajectories As everyone knows, in summer the Sun is higher in the sky and the days are longer, whereas in winter the Sun is lower in the sky and the days are shorter. Over the course of a year and as a result of the relative movements of the Earth and the Sun, the Sun appears in dif erent positions in the sky. During the day, the Sun rises on the horizon (sunrise) up to maximum height during midday and thereaf er declines until reaching the horizon again (sunset). T is movement happens every day of the year with dif erent trajectories over the sky. T e course of the Sun (its trajectory) lies between its summer and winter solstice. T ese events mark the shortest day and longest night in winter on 21st June and the longest day and shortest night on 21st December. T e Sun is at its lowest height in the sky on 21st September (winter solstice) and at its highest on 21st December (summer solstice). During the course of a year the Sun passes through the equinox twice, once in autumn on 21st March and again during spring on 21st September. On any day of the year, the Sun is found between the two outer most trajectories, i.e. the winter and summer solstice.

FIGURE 3: THE PATH OF THE SUN IN THE SOUTHERN HEMISPHERE THEME 1.3.2 OVER THE COURSE OF A YEAR

21 September and 21 March 21 December W Over the course of a year the Sun 21 June moves between the two solstices S

Image source: GIZ/S4GJ T e path of the Sun in the southern hemisphere over the course of a year with dif erent trajectories between the winter solstice (21st June) and summer solstice (21st December) passing through the autumn (21st March) and spring (21st September) equinox.

100 Sun’s Position Two coordinates describe the position of the sun at any given time: (i) Elevation angle: T e elevation angle or altitude angle is the angular height of the Sun in the sky measured from the horizontal. Simply stated, it measures how high the Sun is from horizon to zenith. T e elevation angle is 0° at sunrise, passes through the maximum angular height at any given day and is 00 again at sunset. T e maximum elevation angle of the Sun appears at solar noon (12:00) and is an important parameter in the design of solar-thermal and PV systems.

FIGURE 4: ELEVATION ANGLE (RED)

0°

90° W E THEME 1.3.2

Image source: GIZ/S4GJ During the day, the Sun rises on the horizon (sunrise) in the East (low angle) up to maximum height during midday (northern position) and thereaf er declines until reaching the horizon again in the West (sunset).

T e elevation angle can be calculated fairly easily using the following computations, but you would need to know the latitude of the location in question. Below you can see how to calculate (rule of thumb) the elevation angle and how to determine latitude.

Calculation of the elevation angle: Equinoxes: 90° minus latitude Summer solstice: 90° minus (latitude minus 23.5°) Winter solstice: 90° minus (latitude plus 23.5°)

101 FIGURE 5: DETERMINING LATITUDE AND LONGITUDE

North Poleo o 90 180 150 60 -150

-120 120 30 Latitude

o -90 o o 90 0 Equator

-30 -60 60

-60 e 30 o -30 o -90 0 South Pole Prime Meridian Longitud THEME 1.3.2 Image source: GIZ/S4GJ adapted from http://upload.wikimedia.org/wikipedia/commons/6/62/Latitude_and_Longitude_of_the_Earth.svg T e longitude meridians are half circles passing through the two poles at any given location. T e latitude meridians are full circles and uniquely def ned by the poles and the equator. Longitude, subsequently, requires an origin as well: it is the zero point or prime meridian passing through Greenwich, UK. A location on Earth can be specif ed by two coordinates, the latitude and the longitude, by either using a map, a GPS receiver (Global Positioning System) or consulting web resources. Longitude, latitude and time zone of locations throughout the world are for example available at www.timeanddate.com.

Your own notes

102 (ii) Azimuth angle T e azimuth angle is the compass direction from which the sunlight is coming. Simply stated, it describes the direction of the Sun from East to West in degrees (°). At solar noon, the Sun is always directly South in the northern hemisphere and directly North in the southern hemisphere. T e azimuth angle varies throughout the day. At the equinoxes, the Sun rises directly East and sets directly West regardless of the latitude. Over the year however, the azimuth angle varies with the latitude and time of year.

FIGURE 6: AZIMUTH ANGLE

90° W E THEME 1.3.2

Image source: GIZ/S4GJ T e reference plane for an azimuth is typically true North (00). Moving clockwise, East has an azimuth of 90°, South 180°, and West 270°.

Your own notes

103 Examples Sun Path Diagram A sun path diagram, also known as a sun or solar chart, plots the position of the Sun throughout the year. Simply stated, the diagram is a visualisation of the Sun’s path through the sky and is formed by plotting azimuth and elevation angles of the Sun. Sun path diagrams are very useful when designing and installing solar arrays. T ey of er the most important references to optimise the performance of the array by determining the best angle and avoiding shadows from trees, vents, other buildings, etc. (i) Orientation: For optimum performance of solar arrays, the absorbing surface of the applications must face the Sun when the Sun is at its highest and therefore irradiation at its strongest. T is is usually solar noon (12:00). To achieve this, the collector should be orientated to face the equator. So, in the southern hemisphere, solar arrays should face true North and in the northern hemisphere, solar arrays should face true South. South Africa is in the southern hemisphere therefore, for optimum performance, the solar arrays should be orientated to face true North. (ii) Finding North: One generally determines North with a compass however, this gives you magnetic North and not true North. T is is important, because the Sun moves across the sky in relation to the position of true North, not magnetic North. In South Africa, the dif erence (declination) between true North and magnetic North (declination) is between 150 and 250 West of North. Using an average declination of 20 0 for South Africa would be adequate to orientate the solar array to true North with limited ef ect on the system’s performance. THEME 1.3.2 FIGURE 7: A SIMPLIFIED SUN PATH DIAGRAM FOR JOHANNESBURG (L ATITUDE/LONGITUDE: 26.20 S/280 E) N

330° 30°

16:00 12:00 09:00 60° 300°

17:25 06:55

W E 15:00 09:00 80° 70° 05:15 18:58 60° 50° 120° 240° 40° 30° 20° 10° 150° 210° 0°

S Image source: GIZ/S4GJ.

Green line: winter solstice, red dotted line: equinox (March and September), blue line: summer solstice. T e yellow area shows the annual variation, i.e. the area in the sky where the Sun appears for this particular location. T e positions of the Sun for sunrise, 9:00, 12:00, 15:00 and sunset are indicated as well. T e outer circle (grey line) shows the azimuth angles (00 to 3600) and the elevation angles are indicated with the inner circles (00 to 900). It can be seen from the diagram that for example the Sun rises on 21st December from the East-South-East (azimuth ca. 1100) at around 05:15. Sunset happens at 18:58 when the Sun is in the West-South-West (azimuth ca. 2500). On these two days the elevation angle is approximately 850 at noon and around 500 at 9:00 and at 15:00.

104 Inclination (Tilt) To position a solar thermal or PV installation in an optimal way, it is not only necessary to consider orientation, but also the tilt angle of the absorbing surface of the solar array. Only when the Sun’s rays are perpendicular, at a 90° angle, to the absorbing surface of the applications, the light intensity is at its maximum and the ef ciency of the application is at its highest. However, as the angle between the Sun and the absorbing surface of the application changes, due to the changing azimuth and elevation angles, the light intensity on the surface is reduced. (i) Tilt angle (for f xed surfaces only): T e tilt angle has a major impact on the solar radiation incident on an absorbing surface (PV module or solar thermal collector). For a f xed tilt angle, the optimum over the course of a year is obtained when the tilt angle is equal to the latitude of the location or close to latitude (latitude times 0.8). (ii) Usually it is appropriate to mount solar arrays at a f xed tilt. However, because the Sun is higher in summer and lower in winter, one could generate more energy during the whole year by adjusting the tilt of the panels according to the season (at least twice in autumn and spring). Steeper tilt angles, for example latitude times 1.3, would of er optimised performance during winter. Lower tilt angles, for example latitude times 0.7, use a greater fraction of sunlight in summer. However, the ef ciency dif erence (direct irradiation in kWh/m2/day) if one adjusts the tilt angle twice a year (for example at the equinoxes) is

marginal, only a few percent. THEME 1.3.2

FIGURE 8: SIMPLIFIED IRRADIATION DIFFERENCES IN KW/M2/DAY BETWEEN A FIXED ANGLE SOLAR ARRAY AND FOR A WINTER ADJUSTED TILT ANGLE ARRAY

11 Annual ﬁ xed angle 30° 10 Winter adjusted angle 44° ) 2

6 Direct irradiance (kW/m irradiance Direct

3 0 20 60 90 120 150 180 210 240 270 400 330 360 Day of the year

Image source: GIZ/S4GJ adapted from http://pveducation.org/pvcdrom/properties-of-sunlight/solar-radiation-on-tilted-surface

T e diagram is based on a simulation for Port Elizabeth (latitude around 340). T e simulation calculates the maximum direct irradiation as a function of latitude and module angle. T e values should be regarded as maximum possible values at the particular location, here Port Elizabeth, as they do not include the ef ects of cloud cover. T e two curves visualise the ef ect of latitude and module tilt on direct irradiation received throughout the year. T e x-axis shows the number of days since January 1. T e y-axis shows direct irradiation value in kW/m2/day. Clearly, the irradiation dif erences between the f xed angle and the adjusted tilt angle are marginal, probably only a few percent in total.

105 Exercises

(i) Fill the gaps in the paragraph below using following word list: High, inclined, tilting, maximize, latitude, right, 25.7°, low, array surface,

We know that during the summer months the Sun is located in the sky, while in winter months the Sun is in the sky. To the amount of sunlight falling at the right angles on the array surface, solar geysers collectors should be up from the horizontal at the same number of degrees as the angle of . For example Pretoria’s latitude is around 25.7° and therefore, the must be inclined at for optimum system performance. By the array surface to the same angle of latitude as the location, at midday, the array receives the Sun’s radiation at almost angles.

THEME 1.3.2 Further Information (all materials are on the resource CD)

(i) Sun path http://en.wikipedia.org/wiki/Sun%20path?oldid=632625333 (ii) Performance calculator for solar array systems http://pveducation.org/pvcdrom/properties-of-sunlight/solar-radiation-on-tilted-surface (iii) Solar Resource Information: T e Renewable Resource Data Center (RReDC) of ers a collection of data and tools to assist with solar resource research. http://www.nrel.gov/rredc/solar_resource.html (iv) Sunrise, sunset, and irradiation data for worldwide locations http://www.gaisma.com

Your own notes

106 Your own notes NOTES

107 Your own notes NOTES

108 TOPIC

Introduction to Electrical Energy and Energy Efﬁ ciency

Topic Overview Scientiﬁ c principles and concepts are the fundamental building blocks of many NC(V) engineering subjects and programmes. Thus, knowledge and comprehension of relevant principles and concepts will allow you to understand the subject better and to later apply your knowledge and skills successfully at work. In this topic you are going to learn about various technical concepts such as force, work, power, energy, current, potential difference etc. It is important to stress that in engineering studies these terms have quite a different meaning than in everyday language and they do not necessarily correspond with your own understanding of them. For example, you would most probably associate a different meaning with the term ‘energy’ than a technician or an engineer would. In this textbook we will help you to rework your own personal concepts about these technical terms, enabling you to think of them and use them in a more appropriate way.

Unit 2.1 Electrical Energy and Energy Efﬁ ciency: Basic Concepts Unit 2.2 Fundamentals of Electric Circuits Unit 2.3 Simple DC Circuits

109 Unit 2.1 Unit

UNIT 2.1 ELECTRICAL ENERGY AND ENERGY EFFICIENCY: BASIC CONCEPTS

Introduction

We already indicated that most people have dif erent ideas and personal concepts about technical terms, such as work and energy, and usually they use these terms in everyday language in a dif erent context compared to how an electrician or an engineer would use them in the technical environment. T us, in the NC(V) engineering subjects we need to use these technical terms and concepts in a completely new way, and make a conscious ef ort to ensure that our everyday language and personal ideas about these terms do not get in the way. At f rst, technical concepts about quantities such as energy, charge, current etc. can become confusing, since these terms are seldomly used in everyday life. T erefore, these technical terms may at f rst appear to be abstract and dif cult to comprehend. To avoid unnecessary complica- tions we will not focus as much on the nature of those quantities and terms, i.e. what exactly energy or charge are, but will rather focus on what these quantities can do! Unit Outcomes

At the end of this unit, you should be able to: (i) Explain work, energy and power in engineering terms. (ii) Apply the concepts of work, energy and power using electrical household devices. (iii) Explain the need for and advantages of energy saving and environmentally sustainable work practices. (iv) Explain why behavioural change is an important step to achieving energy savings and environmental goals. (v) Explain how to audit a residential or commercial environment and recommend appropriate energy ef ciency solutions. (vi) Calculate and compare the power usage for various lighting devices or other electrical loads. Themes in this Unit

Unit 2.1 covers two themes: T eme 2.1.1 Electrical Energy: Basic Concepts T eme 2.1.2 Energy Ef ciency: Basic Concepts

110 THEME 2.1.1 ELECTRICAL ENERG: BASIC CONCEPTS Introduction

Engineering terms, such as the fundamental physical quantities force, work, energy and power have quite a dif erent meaning when compared to how these terms are used in everyday language. Force, for instance, is usually used as a synonym for strength or might and occurs in everyday language as mental force, force of life, police force, task force etc. In engineering terminology, force, similar to all other physical quantities, is precisely def ned by using the SI system of units (International Systems of Units) and mathematical equations. So, apart from learning technical language you will also be introduced to some basic maths. Some students do not like maths, but we need to concern ourselves with some mathematics THEME 2.1.1 as it is and remains the fundamental language of engineering. We will approach the relevant maths in a THEME 1.1.1 natural and less abstract way and explain related equations clearly with regards to the concepts of force, work, energy etc. You might think that you do not have a deep enough understanding of mathematics but, if taught in a precise and practical manner, maths will help you to understand crosscutting concepts, core ideas and engineering practices.

Keywords

SI units Quantities Force Work Energy Power

Theme Outcomes

At the end of this theme, you should be able to explain the concepts of work, energy and power in a precise and technical manner. Furthermore, you should be able to apply these concepts in practical problem solving.

Deﬁ nition of Terms Base uantities According to international convention, we dif erentiate seven fundamental or base quantities (listed in Table 1) from various other quantities called derived quantities (listed in Table 2). T e base quantities are length, mass, time, electric current, temperature, amount of substance, and luminous intensity. In this textbook we indicate the symbols of quantities by using italic fonts, for example (l) for length or (t) for time. By convention the base quantities are assumed to be independent and the derived quantities are def ned in terms of the seven base units. System of Units To describe quantities, units and symbols are used and engineering usually follows the International System of Units, also called SI units, from the French Systeme International des unites. SI units for the seven base quantities listed in Table 1 are meter, kilogram, second, ampere, kelvin, mole and candela. You will see that some symbols for SI units are printed in lower-case letters and others in capital letters. T e latter is used if the unit in question was derived from a proper name, honouring scientists who have worked and made critical discoveries related to a particular quantity. For example, James Watt (1736–1819) was an English inventor, who developed the steam engine. His name is used to represent the unit of power. Hence, watt is the unit for power and its symbol is (W). Another example is Andre M. Ampere (1775–1836), a French mathematician, chemist and physicist who experimentally quantif ed the relationship between electric current and the magnetic f eld. T e SI unit of electric current ampere is named af er him and its symbol is (A). For more detailed information on SI units regarding their def nitions and their historical context see the NIST publication (2008) on the CD.

111 TABLE 1: BASE UANTITIES (SI UNITS)

Quantity Symbol SI Unit Symbol

length l meter m

mass m kilogram kg

time t second s

electric current I ampere A

temperature T kelvin K

amount of substance n mole mol THEME 2.1.1

luminous intensity Iv candela cd

Derived uantities As indicated earlier, derived quantities are def ned in terms of the seven base units. Examples of SI derived quantities and their units are given in Table 2. Please note, that we use - × - to indicate a multipli- cation of two factors, i.e. 2 × 2 stands for 2 times 2!

TABLE 2: EAMPLES OF DERIVED PHSICAL UANTITIES AND THEIR SI UNITS

Derived Quantity Unit Relation to Relation to SI base SI unit quantity symbol symbol derived SI units units

frequency f hertz Hz - 1/s

force F newton N - m × kg/s2

work W joule J N m m2 × kg/s2

energy E joule J N m m2 × kg/s2

power P watt W J/s m2 × kg/s3

electric Q coulomb C - s × A charge

electric V volt V W/A m2 × kg/s3 × A potential

electric R ohm V/A m2 kg s-3 × A-2 resistance

celsius degree T oC - K temperature Celsius

illuminance Ev lux lx lm/m2 1/m2 × cd

As derived quantities and their units are formed by combining base quantities, some quantities are derived from a combination of base quantities. As an example for a derived quantity, we can consider power (P) and its SI unit watt (W). We already mentioned that most SI units have been given special names in honour of famous scientists and inventors whose research has contributed to our knowledge of the base and derived quantity concerned. T us, the derived unit for power is the watt, named af er James Watt, and is def ned as joule per second.

112 FIGURE 1: RELATIONSHIPS OF SI UNITS AND DERIVED UNITS

SI BASE Derived SI DERIVED UNITS WITH units without UNITS SPECIAL NAMES AND SYMBOLS special names

kg kg-m/s2 on kilogram MASS 3 wt N m ne FORCE VOLUME er m J/s met 2 N/m 1/s LENGTH m e t tz her joul J wat W Hz AREA ENERGY,WORK, POWER, HEAT FREQUENCY s QUANTITY FLOW RATE cond m/s THEME 2.1.1 se OF HEAT V-s TIME VELOCITY eber w Wb

e A m/s2 MAGNETIC A-s FLUX amper W/A ELECTRIC ACCELERATION lt CVvo CURRENT coulomb ELECTRIC POTENTIAL DIFFERENCE CHARGE V/A ELECTROMOTIVE FORCE ohm W

RESISTANCE

Image source: GIZ/S4GJ

In practice, one of en needs to describe quantities that occur in large multiples or small fractions of an SI unit and consequently, standard pref xes for multiples or divisions are used to denote powers of SI and derived units. For example, if a USB stick can store one thousand billion = 1 000 000 000 000 units of information, i.e. binary digits or bits expressed as either 0 or 1, you could write these one thousand billion bits as 109 bits = 1 giga bit (1 GB). T e most important pref xes are listed in Table 3.

TABLE 3: MULTIPLES AND DIVISIONS OF THE SSTEM OF UNITS

Factor Preﬁx Symbol Linguistic origin 101 deca da greek: ten (deka) 102 hecto h greek: hundred (ekato) 103 kilo k greek: thousand (khilia) 10001 106 mega M greek: big (megalos) 10002 109 giga G greek: giant (gigas) 10003 1012 tera T greek: four (tetratos) 10004 10−1 deci d latin: ten (decem) 10−2 centi c latin: hundred (centum) 10−3 milli m latin: thousand (mille) 1000−1 10−6 micro µ greek: small (mikros) 1000−2 10−9 nano n greek: dwarf (nanos) 1000−3 10−12 pico p italian: small (piccolo) 1000−4

113 Force (F) While we cannot directly see forces acting, we can clearly see, feel or measure their ef ects. We see the Moon orbiting the Earth or objects falling to the ground and birds f ying. All of these events happen due to forces acting around us. Many engineering textbooks def ne force (F) as a push or a pull. T is is a reasonable but informal def nition to help you to conceptualise what a force (F) could be. But what exactly is a push or a pull? How would you measure a push or a pull? And, most importantly, how does a push or a pull relate to the other quantities such as work, energy and power? Let us f rst focus on what forces can do before we try to def ne forces. Simply put a force (F) can: (i) Move an object (accelerate an object) (ii) Stop an object from moving (decelerate an object) (iii) Change the direction of a moving object

T us, a force (F) is clearly able to alter motion and one could say that force (F) is a quantity necessary

THEME 2.1.1 for change or more generally, force (F) is the agent of change. To fully describe a force acting on an object you need to list its magnitude and direction. T e magnitude indicates the numerical value of the force (F). In engineering it is common to represent forces using simple diagrams in which a force (F) is represented by an arrow. T e size or length of the arrow indicates the magnitude of the force (F). T e direction to which the arrow is pointing reveals in which direction the force (F) is acting. Such diagrams are known as free-body diagrams or vector diagrams. For the moment, our def nition of force (F) should be suf cient. A force can manifest itself in many dif erent ways and maybe we can expand on the concept of force (F) with some examples:

(i) Forces that act on all objects:

Weight (Fg) is the force of gravity acting on objects due to their mass (m). Weight is measured in newton (N) and mass is measured in kilogram (kg). Although weight and mass are of en used interchangeably in everyday language, these two terms refer to two dif erent quantities. T e mass of an object is a property of the object itself. It ref ects an object’s resistance to being accelerated, i.e. start moving, stop, or change in direction while moving. T e weight of an object is a measure of the

gravitational force (Fg) being exerted upon it. Consequently, the weight of an object varies depending

on the gravitational force (Fg) acting on the object. T us, the dif erence between the weight and mass

of an object is that its mass never changes, whilst its weight depends on the force of gravity (Fg) in the object’s environment. For example, an object with a mass of 10 kg has a dif erent weight on the Moon than it does on Earth. T e weight of an object with a mass of 10 kg on Earth is around 98 newton (N). In contrast,

the Moon’s gravitational force (Fg Moon = 1.6 N) is smaller, roughly one-sixth of Earth’s gravitational

force (Fg Earth = 9.8N). T erefore, the weight of an object with a 10 kg mass on the Moon is only about 16 newton (N).

(ii) Forces that exist when solids come into contact:

Normal (Fn) is the force between two solids in contact with each other. T e normal force (Fn) is directed at a 90 degree angle (perpendicular) to the surface. At f rst, the term ‘normal’ seems to be slightly odd. Generally the word ‘normal’ is used to indicate that something is ordinary, usual, or expected, but in geometry a line perpendicular to a surface is called normal, thus the name ‘normal force’.

To illustrate the normal force (Fn) a bit more clearly, put an object, for example a book on your table. T e book lies on the table because that is what books do, but something must keep the book

down. It lies on the table due to the fact that weight, i.e. the force of gravity (Fg), is acting on it and

keeps it down on the table. Unfortunately, the force (Fg) itself cannot be seen, only its ef ect on the book can. In Figure 2 we use a diagram, and draw a box to represent the book and an arrow com-

ing out of the centre of the box pointing down to represent weight (Fg). T e force of gravity (Fg) is

acting on the book and keeps it down, but why is the book, when Fg is acting on it, not changing its place and accelerating downwards? T e reason why the book remains in its place is that another force is acting on it with the same magnitude in exactly in the opposite direction. T is force prevents the book from passing through the table downwards to the centre of the Earth. What do we call this upward force? Given that the direction of this force is perpendicular to the table surface

we call it the ‘normal force’ (Fn).

114 FIGURE 2: FREE-BOD DIAGRAM - NORMAL FORCE (FN)

In engineering we try to simplify complex situ- the interaction between two forces, i.e. weight (Fg) ations by using free-body (or vector) diagrams. and the normal force (Fn). Weight (Fg) is a syn- Drawing a box on a line can represent an object, onym for the force of gravity. T e normal force such as a book on a table, and the arrows (also (Fn) is of similar magnitude and exactly opposite called vectors) indicate the magnitude (numerical to weight (Fg). T us, in this case normal force (Fn) value in newton) and the direction of the forces is equal to weight (Fn). Due to Fn = Fg the object acting on the object. T is simple diagram shows remains in its place.

NORMAL Fn THEME 2.1.1

WEIGHT Fg

Image source: GIZ/S4GJ

Friction (Ff) is another force acting between solid objects in contact with each other, for example the book on the table. Friction prevents the book from sliding across the table. T e direction friction acts in is parallel to the surface where two objects are in contact with each other.

Below: T ree more free-body diagrams: Remember, the length of the arrows indicate the magnitude and direction of a force. T e lef diagram for instance shows that the magnitude of the pushing force (Fp) is greater than the magnitude of friction (Fp > Ff). T us, Fp would overcome friction and the book, indicated by the box, would move to the right. Can you explain the interactions of Fp and Ff and what would happen to the book (box) in the middle diagram and in the diagram on the right-hand side?

FIGURE 3: FREE-BOD DIAGRAM - FRICTION (Ff)

NORMAL Fn NORMAL Fn NORMAL Fn

FRICTION Ff PUSH Fp FRICTION Ff PUSH Fp FRICTION Ff PUSH Fp

WEIGHT Fg WEIGHT Fg WEIGHT Fg

Ff < FP Ff = FP Ff > FP

Image source: GIZ/S4GJ

115 Tension (Ft) is the force exerted by an object being pulled from opposite ends, for example a rope during a tug of war (two teams pulling a rope). Tension is directed along the axis of the object.

FIGURE 4: FREE-BOD DIAGRAM - TENSION (Ft)

T e simple diagram on the lef -hand side shows the interaction between weight ( Fg) and tension (Ft).

Both forces are of similar magnitude and act in exactly opposite directions. Due to Ft = Fg the object remains in its place. T e diagram on the right-hand side is slightly more complex. Over a wedged surface a string connected to two objects passes over a pulley. T e pulley changes the direction of the

string and hence the direction of Ft , but the pulley does not change the magnitude of the tension of the string. As you can see, there are two other forces that are acting on the two objects in this diagram. Can you identify them? THEME 2.1.1 Ft1

Ft2

tension Ft

weight Fg

Image source: GIZ/S4GJ

Elasticity (Fs) is the force exerted by an object under tension or compression (deformation), allowing the object to return to its original shape when released. Examples are springs or rubber bands.

Your own notes

116 (iii) Forces associated with f uids, e.g. water, gases or air:

Buoyancy (Fb) is the force exerted on an object immersed in a f uid. Buoyancy is usually directed upwards.

FIGURE 5: FREE-BOD DIAGRAM - BUOANC (Fb)

T e diagram below shows the interaction between two objects in a f uid due to their mass (m). Again weight is a synonym for the force of gravity. Buoyancy is the force acting on the object in the directly opposite direction to weight. T us, if buoyancy is equal to weight (Fb = Fg) the object will swim or f oat on the surface. But if buoyancy’s magnitude is smaller than the magnitude of weight (Fb < Fg) the object will sink. THEME 2.1.1 buoyancy Fb

weight Fg

Image source: GIZ/S4GJ

Drag (Fd) is the force that resists the motion of an object through a f uid. Drag is directed in the opposite direction of the object’s motion relative to the f uid.

Lif (Fl) is the force that a moving f uid exerts as it f ows around an object, typically acting on a wing or similar structures. Lif is generally directed perpendicular to the oncoming f ow direction.

T r u s t (Ft) is the force that a f uid exerts when expelled by a propeller, turbine, rocket, a bird’s wing or a f sh’s body and tail. T rust is directed in the opposite direction of the f uid being expelled.

(iv) Forces associated with physical phenomena:

Electrostatic force (Fe) is the attraction or repulsion between charged particles. Charles A. Coulomb (1736–1806), a French engineer and physicist, published the laws of electrostatics between 1785 and 1791. His name is associated with the unit of charge. Mr. Coulomb described that opposite charges (positive-negative) attract each other and that similar charges (positive-positive and negative-negative) repel each other. In engineering we use the term electrostatic force to describe these attractions and repulsions. Electrostatic forces are much stronger when opposite charges are close to each other. T e further apart two opposite charges are, the weaker the electrostatic forces. Also, the greater the charges, the greater the electrostatic force. Electric energy is related to charges, and both electrons (negative) and protons (positive) carry a charge. T e SI unit for electric charge (Q) is named af er Mr. Coulomb, hence the unit of electric charge is coulomb (C). We will deal with electric charges in more detail in Unit 2.2.

117 FIGURE 6: ELECTROSTATIC FORCE THEME 2.1.1

Imag e source: shutterstock.com When a child slides down a plastic slide, each strand of its hair becomes positively charged. Each charged hair repels the other, causing single hairs to stand up.

Magnetic Force (Fm) is the attraction or repulsion between charged bodies in motion. Due to the Earth’s magnetic f eld a compass needle is moved by magnetic force, so that one end of the needle points north and the other end points south. Another example is a magnet in a door catch: this is a simple device that uses magnetic force of attraction to hold a door closed.

Your own notes

118 Forces and Basic Maths As illustrated earlier, forces are able to alter the motion of objects (acceleration or deceleration). T e mass (m) of an object is a property of the object itself, ref ecting its resistance to being accelerated or decelerat- ed, and as you learned earlier, mass (m) is measured in the SI unit kilogram (kg). Acceleration however, has something to do with a quantity called velocity. Velocity (v) is def ned as the distance (d) travelled per unit time (t). Note that ‘per’ means ‘divided by’, thus velocity is equal to distance divided by time. T is def nition of velocity gives us our f rst mathematical equation (formula) for a quantity and we can write this relationship as:

d (1) v = t (velocity = distance per time)

To dif erentiate the units in which velocity (v) can be expressed, we need to place the units for each quan-

tity into formula (1), i.e. meter (m) for distance (d) and second (s) for time (t). THEME 2.1.1

m (1a) v = s (velocity is expressed in meter per second)

Over the course of time a moving object can increase or decrease its velocity, in other words, it is either accelerating or decelerating. For simplicity’s sake let us just use the term acceleration to describe changes of velocity in the following example: We observe that a moving object changes its velocity (v) over the course of time in a uniform manner, for example from v1 (0 m/s) to v2 (5 m/s) in 5 seconds (5 s). In engineering, changes of a quantity are indicated with the symbol ∆ (delta, Greek letter). Changes of velocity, i.e. from v1 = 0 m/s to v2 = 5 m/s can be expressed as ∆velocity or ∆v. T e values for this observed acceleration are listed in Table 4. TABLE 4: OBSERVED VELOCIT CHANGE ∆ ) PER UNIT TIME

Time interval (s) Distance travelled (m) Total distance (m) v (m/s) 0 – 1 1 1 1 1 – 2 1 2 2 2 – 3 1 3 3 3 – 4 1 4 4 4 – 5 1 5 5

We have already def ned velocity (v), now we need to understand acceleration (a). Acceleration describes changes of velocity (v) over the course of time and can thus be def ned as the rate at which an object changes its velocity (v). Note that ‘rate’ is the quotient of two quantities, in our case, ∆v measured per unit time. T is def nition of acceleration gives us our second mathematical equation for a quantity and we can write this relationship as:

∆v (2) a= t (acceleration is equal to change of velocity per unit time)

v2 - v1 (2a) a= t (acceleration is equal to velocity2 minus velocity1 per unit time)

To dif erentiate the units in which acceleration (a) is measured, we need to place the units for each quantity, i.e. meter (m) per second (s) for velocity (v), and second (s) for time (t) into formula (2). T us, acceleration is measured in units such as: (meter per second) per second, and this can be expressed as meter per second squared (see equation 2b).

m (2b) a= 2 (acceleration values are expressed in meter per second squared) s

119 Example

We can now calculate the acceleration (a) of the object by using our observed values v1 = 0 m/s and

v2 = 5 m/s within a time interval (t) = 5 s, and insert these values into the formulas (2b) to (2e). v2 - v1 (2a) a = t

m m 5 s -0 s (2b) a = 5 s

m 5 s (2c) a = 5 s

m (2d) a = 1 s × s

THEME 2.1.1 (2e) a = 1 2 s Using our observed acceleration example, we can now say that the acceleration (a) of the object is m uniform and has a value of a = 1s2

T ese f ndings will help us to understand the concept of forces better. Let us recall the following: (i) Forces are able to accelerate objects. (ii) T e mass (m) of an object ref ects its resistance to being accelerated.

T ese two statements describe what forces can do, and if we put these two statements together into a simple algebraic form, our third mathematical equation for def ning a quantity can be written as:

(3) F = m × a (force is equal to mass times acceleration)

To dif erentiate the units in which force (F) is measured, we need to place the units for each quantity, i.e. m kilogram (kg) for mass (m), and meter per second squared (s2 ) for acceleration (a) into equation (3).

m (3a) F = kg × s2 (force values are expressed in kilogram times meter per second squared)

m T us, the unit for force is kilogram times meter per second squared (kg × s2 ). However, this expression is hardly ever used. T e SI unit for force is named af er Sir Isaac Newton (1642 – 1727). Newton was the English scientist responsible for the development of one of the most useful equation in physics and engineering, i.e. formula (3) F = m × a. T e most popular equation is probably E = m × c2 (energy is equal to mass times velocity of light squared), which was developed by the German scientist Mr Einstein in the early 20th century, but the equation with the most practical signif cance is probably still formula (3) F = m × a, developed by Mr Newton in the late 17th century.

T e aim of the mathematical deduction of force, starting with the base quantities length and time, and their derived quantities velocity, acceleration and mass was to illustrate the relationship and intercon- nectedness between quantities. T e relationship between these quantities is illustrated in Table 5.

TABLE 5: RELATIONSHIP BETWEEN THE UANTITIES FORCE, MASS AND ACCELERATION

Cause of change Resistance to change Rate of change Formula Quantity force (F) mass (m) acceleration (a) F = m × a

m m SI units newton (N) kilogram (kg) 2 s F = kg × s2

120 Example

How can we calculate the force (F) necessary to accelerate an object with the mass (m) of 1 kg at a m rate of 1 meter per second squared (a = 1s2 ) ?

By using equation (3a) and by placing the values of the above example, we can solve this problem and calculate the following:

m (3b) F = 1 kg × 1s2

m (3c) F = kg × s2 = 1 newton (N)

T e answer to the above problem is: THEME 2.1.1 m To accelerate an object with the mass (m) of 1 kg at a rate of 1 meter per second squared (a= 1 s2 ) a force (F) with a magnitude of 1 newton is necessary.

Your own notes

121 Work In everyday language, the term work usually describes the job one is doing or the amount of ef ort required to perform a task. In engineering, work is a physical quantity and has a far more specif c meaning. T e concept of work (W) is strongly related to the concept of force (F). Work (W) is def ned as application of a force (F) over a distance (d), for example if a body moves as a result of a force (F), the force is said to do work (W) on the body. We have already def ned force (F) and we know the quantity distance (d). Putting these two quantities into a simple algebraic form our fourth mathematical equation can be written as:

(4) W = F × d (work is equal to force times distance)

To dif erentiate the SI units in which work (W) is measured, we need to place the units for each quantity, m 2 THEME 2.1.1 i.e. newton (N) or kg × s for force (F) and meter (m) for distance (d) into equation (4).

(4a) W = N × m (work values are expressed in newton times meter), or

2 m kg × m (4b) W = kg × s2 × m = s2 kg × m2 (4c) W = s2 (work values are expressed in meter squared times kilogram per second squared) kg × m2 T us, work (W) can be measured in newton meter (N × m) or s2 . However, the SI unit for work (W) is named af er an English citizen, Mr James Joule (1818 - 1889) and hence the SI unit of work (W) and energy is called the joule (J). Mr Joule was a wealthy English brewer who was interested in various aspects of science and economics. Coal-f red steam engines were the primary source of industrial might at his time and electric energy was just emerging. Joule realised that mechanical work, thermal energy (heat), and electric energy were all interrelated and somehow convertible. Coal-f red steam engines are good examples to illustrate that thermal energy has the capacity to do work. When work is done heat is usually released as well. Furthermore, work is usually required to supply electric energy, of en by transforming thermal energy and, with the help of electrical energy, work can be done and heat will be released as a ‘by-product’. T ese statements seem to be confusing, but as you will see in the next themes, energy is a versatile actor and the quantities work, power and energy are interrelated and convertible. We will deal with the concept of energy and its relationship to work and power in more detail below. Joule’s experiment focused on determining a standard measure for thermal energy and his results were essential in the realisation that, despite appearing in multiple forms, energy was one thing. T us, when the call went out to name the SI units of work and energy, the answer was to use his name (Joule). T e unit joule is def ned as: Work with the amount of 1 joule (J) is done when a force (F) with a magnitude of 1 newton (N) is applied over a distance of 1 meter and under the condition that the force (F) acts in the same direction as the distance (d) moved. Simply stated, 1 joule (J) is the work (W) done when an object is moved 1 meter under the application of a force (F) of 1 newton in the direction of motion.

(4d) 1 joule (J) = 1 N × 1 m (1 joule is equal to a force (F) of 1 newton times 1 meter)

Example

Given the discrepancy of the meaning of work in everyday language compared to its use in engineering, let us look at a classroom example: in engineering we say that you do work (W) when you apply a force (F) to an object and the object moves in the direction of the applied force (F). Imag- ine that your lecturer is standing motionless before the class. Since he is not exerting any obvious forces on any outside object he will not displace any object outside of his body. So, the teacher is obviously not doing any work (W), but this seems so only at f rst glance. Most certainly, the lecturer is doing work (W), but the work (W) being done is not easily visible. Inside the body the heart is pumping blood, the digestive system is digesting the breakfast etc. T us, forces causing displacement are happening everywhere under our skins, even when it seems like no work is being done.

122 Power In engineering, the concept of power (P) is a measure of how rapidly work (W) is done. You might recall that velocity (v) is def ned as distance (d) travelled per unit time (t). We also noted that ‘per’ stands for ‘divided by’. If power (P) is def ned as work (W) done per unit time (t), then power (P) is equal to work (W) divided by time (t). Simply put, power (P) is the rate of doing work (W). Note, whenever we use the word ‘rate’ we always mean ‘per time’. T is def nition of power (P) gives us our f f h mathematical equation and we can write this relationship as:

W (5) P = t (power is equal to work divided by time)

To dif erentiate the SI units in which power (P) is measured, we need to place the units for each quantity, i.e. joule (J) for work (W) and second (s) for time (t) into formula (5). THEME 2.1.1 J (5a) P = s (power values are expressed in joule divided by seconds)

T us, power (P) can be measured in joule per second (J/s). However, the SI unit for power (P) is watt (W) named af er James Watt (1736–1819), an English inventor who developed the steam engine. His name is used to represent the unit of power (P). Note the dif erence between the symbol for work (W) and watt (W). Simply stated, 1 watt (W) is equal to 1 joule (J) divided by 1 second (s). In other words, if 1 joule of work is done every second, then the amount of power (P) is 1 watt.

J (5b) 1W = 1 (1 watt is equal to 1 joule divided by 1 second) s

Note In many parts of the world the power (P) of combustion engines and electric drives in automobiles is measured in horsepower. Horsepower was the unit of power established by James Watt in the late 18th century so that he could describe to the layman the relative power of his invention, the steam engine. Since horsepower (hp) and watt are both units of power (P) they are related to one another. One horsepower (hp) is equal to 746 watt and 1 kilowatt (kW) is equal to 1.34 horsepower (hp).

To recap, in general terms power (P) is a measure of how rapidly work (W) is done. Related to electrical energy (see below) power (P) is the rate of energy f ow or how fast energy is being used or transferred, for example to turn an electric motor or to light an electric lamp.

Electric power is always measured in watt (W), for example a household LED bulb usually has 4 watt power and an incandescent bulb can have 60 watt power. Larger amounts of electric power can be measured in kilowatt (1,000 watt = 1 kW) or in megawatt (1,000 kW = 1 MW). Furthermore, electrical power (P) can also be expressed in terms of electrical potential (V) and electrical current (I). We will only deal with these two new quantities in more detail in Unit 2.2.

123 Energy It is almost impossible to discuss work (W) and power (P) without discussing energy (E), another one of those engineering terms that is of en used in everyday language but in a dif erent context and with a completely dif erent meaning. Again, the technical notion of energy (E) is not the same as the everyday notion of energy. In engineering, energy (E) is def ned as the capacity to do work (W). When work (W) is done on an object, the system doing work (W) is ‘losing’ energy (E) to the other system. In fact, the energy (E) lost by a system is exactly equal to the amount of work (W) done by the system. As with work (W), the SI unit for energy (E) is the joule (J). T is follows as work (W) is just the transfer of energy (E) from one object to another. T ere are dif erent forms of energy and all have the capacity to do work, for example thermal energy (heat) or kinetic energy (motion). Since we are particularly concerned with electrical energy we can def ne this form of energy as electrical power (P) multiplied by time (t). T is def nition of energy (E) gives us our sixth mathematical equation and we can write this relationship as:

THEME 2.1.1 (6) E = P × t (energy is equal to power times time)

To dif erentiate the units in which electrical energy is measured, we need to place the units for each quantity, i.e. watt (W) for power (P) and hours (h) for time (t) into formula (6). T us, we can see that electrical energy is not expressed in joule but in units of watt hours (Wh).

(6a) E = W × h = Wh (electric energy values are expressed in watt hours)

When systems or objects interact, the energy (E) level of one object may increase at the expense of the other object. T is is called a transfer of energy (E). Af er this transfer one of the objects may have a higher level of energy (E) than before and in almost all energy transfer processes some energy ends up as heat (thermal energy). Systems or objects may exchange energy (E) in two ways, through work (W) or heat (thermal energy). T rough the concept of work (W) we can measure the energy (E) transferred during interactions between systems. Work (W) always requires motion of a system or parts of it. In contrast to work (W), thermal energy does not require macroscopic motion, rather, heat involves exchanges of energy (E) between systems on the microscopic level (waves) (see Topic 4).

A very important property of our universe is that energy (E) is never created nor destroyed, but merely transformed. T is principle is also known as the f rst law of thermodynamics. Energy conservation and the conservation of matter are the principles which classical mechanics are built on. T e total energy (E) in the universe is conserved but some energy is almost always transferred through non-conservative processes. In practical terms, this just means that if energy (E) is transferred from one object to another, some energy (E) will be transformed into thermal energy (heat). If energy in the form of heat is radiated into the environment during a transfer process, for example if you use your electric stove to boil water in a kettle, we say some heat is ‘lost’ in the process. T is is not entirely correct, as the unused energy is still there, although in another form, and thus still accounted for.

People or machines cannot do work (W) without energy (E). People get their energy (E) through the food they eat and machines are ‘fed’ with energy (E) contained in fossil fuels, such as coal, oil and gas, or they use energy (E) directly supplied from the sun (renewable energy). We earlier def ned energy (E) as the capacity to do work (W). T at is a very important statement, because without the capacity to do work (W) we could not produce anything, we could not stimulate economic growth and, on a more personal level, we could not live a comfortable life. T is is the reason why we need energy!

In a modern household energy is mainly provided in the form of electrical energy. Electrical energy is supplied by generators and can be consumed by appliances, such as lighting devices, refrigerators, stoves and washing machines. Simply stated, energy is equal to power (P) multiplied by time (t) thus, electrical energy is expressed in units of watt hours (Wh). If an appliance consumes or if a generator provides 1 kilowatt (kW) of power over a period of one hour, then 1 kilowatt hour of energy exists over the course of this hour.

(6b) 1 kilowatt × 1 hour = 1 kW/h = 1 kWh

Larger amounts of energy can be measured in megawatt hours (1 MWh = 1 000 kWh). Watt hour (Wh) is in a way analogous to an hourly wage in Rand per hour (R/h) or to the velocity (v) of a vehicle measured in kilometres per hour (km/h).

124 Demand of Electrical Energy To recap, power (P) is the measure of how rapidly work (W) is done and is measured in watt or kilowatt. Given that work (W) can also represent electrical energy that is transformed into other forms of energy demanded by industry or residential users, for example thermal energy, kinetic energy or light, power values tell us how fast energy is being used or provided. T us, power can be def ned as the rate of work (W) done or, simply stated how fast energy is being used or supplied.

Demand can be def ned as the rate of use of electrical energy. T e term demand is essentially the same as electrical power, although demand generally refers to the average power measured over a given time interval. T erefore, if we def ne energy as power (P) multiplied by time (t), we can also say that electrical energy is the average demand multiplied by time (t) expressed in units of watt hours (Wh = W × h). Or put simply, energy is a measure of how much power is consumed or provided over time. THEME 2.1.1

Your own notes

125 Examples

Power ratings of electrical appliances Electrical appliances convert electrical energy into other forms of energy, such as light, sound, thermal energy, kinetic energy and others. Power is the rate at which an electrical appliance converts electrical energy into other forms of energy. In simple terms, electrical energy makes electrical appliances do work. We can illustrate this by using our sixth mathematical equation and the respective units: (6) E = P × t (energy is equal to power times time)

(6a) E = W × h = Wh (electric energy values are expressed in watt hours)

THEME 2.1.1 T e power rating of an appliance, its load, indicates the amount of electrical energy the device will need over a given period. T is statement is expressed in the two formulas (6) and (6a) above. T us, the greater the power rating of an appliance, the greater the electrical energy consumption will be. If you use an electrical stove with 1500 watt power for 100 hours in a month at a cost of 1 Rand (R1) per kilowatt hour (kWh), you could calculate what it would cost you to operate the stove and what to expect with your next ESKOM or municipal energy provider’s bill.

Example 1

Power rating, energy demand and operating costs of an appliance

Problem Determine the operating costs of a stove

Solution (1) Known quantities (given values): Stove power (P) = 1 500 watt = 1.5 kW Used over time (t) = 100 hours = 100 h

(2) Quantities to be determined (what we need to calculate): Energy demand (E) in kWh Costs for operating the stove in Rand per month

(3) Analysis

To calculate the costs for operating the stove in kWh and per month, we f rst determine the amount of electrical energy (E) used over time (t) by using formula:

(6a) E = W × h = Wh

E = 1.5 kW × 100 h

E = 150 kWh

Next, we calculate the costs in Rand, which were set at R1 per kWh (R1/kWh). T us, by using the stove for 100 hours during one month your electricity bill for the stove alone would amount to:

150 kWh × R1/ kWh = 150 kWh × R1/ kWh = R150 (4) Answer

T e cost to operate the stove for 100 hours during one month would amount to R150.

126 Exercises

For all the following calculations, use the approach outlined in Example 1 (power rating, energy demand and operating costs of an appliance) by f rst stating the problem and then following the steps to f nd the solution (known quantities, quantities to be determined and analysis).

Exercise 1

With respect to the quantities explained in this theme, brief y explain the following terms using the table below.

TABLE 6: EPLAIN THE TERMS BELOW AS PRECISEL AS POSSIBLE THEME 2.1.1 Terms Explanation

energy

work

force

newton

power

weight vs mass

rate

acceleration

conservation of energy watt (W) vs watt hour (Wh)

Exercise 2

T e Moon’s gravitational force (Fg Moon = 1.6 N) is smaller, roughly one-sixth of Earth’s gravitational force (Fg Earth = 9.8 N). An astronaut with a mass of 120 kg is on the surface of the Moon, where the acceleration due the Moon’s force of gravity is 1.6 m/s2.

a) Which formula can you use to calculate the weight of the astronaut on the surface of the Moon? What is your result?

b) Why is the astronaut’s weight greater on Earth than on the Moon?

127 Exercise 3

A lunar buggy designed to travel on the surface of the Moon, where acceleration due to gravity is 1.6 m/s2, had a mass of 2000 kg on the Earth.

a) Which formula can you use to calculate the weight of the lunar buggy on the surface of the Earth? What is your result?

b) What is the mass of the buggy on the Moon?

THEME 2.1.1

Exercise 4

T e diagram shows the forces acting on an aircraf travelling horizontally at a constant velocity

through the air. Fl is the upward force (lif ) acting on the aircraf . Fw is the weight of the aircraf .

Ft is the force due to the propeller engines (thrust) and Fr is the force due to air resistance (drag).

Fr Ft

a) What happens to the aircraf when the force Fl is greater than the weight of the aircraf

(Fl > Fw) ?

b) What happens to the aircraf when the force Ft is greater than the force Fr (Ft > Fr) ?

Exercise 5

Select a number of electrical devices from Table 7 below:

(1) Determine the electrical energy the device will consume during the period of 50 hours in a month.

(2) Calculate the costs per month which ESKOM as the electric power company or your municipality would bill you for. Assume that they would charge you 1 Rand (R1) per kilowatt hour (kWh).

128 TABLE 7: LIST OF ELECTRICAL DEVICES AND THEIR AVERAGE POWER RATING IN WATT

Appliances Power rating in watt LED bulb 4 Compact ﬂuorescent lamps 40 Incandescence bulb 60 Refrigerator 300 TV 200 Kettle 2000 THEME 2.1.1 Washing machine 1000

Further Information (all materials are on the resource CD)

T e International System of Units (SI), NIST Special Publication 330, 2008, Force as a vector, http://www.mathcentre.ac.uk/resources/uploaded/mc-web-mech1-5-2009.pdf

Your own notes

129 THEME 2.1.2 ENERG EFFICIENC: BASIC CONCEPTS

Introduction

Why is saving electrical energy so important for South Africa? One of the reasons is that our fossil fuel resources for electrical energy generation, such as coal, gas and liquid fuels are not limitless. In addition, both the capacity of ESKOM’s power plants and the national grid are constrained and can no longer meet the demand for electrical energy from industry and residential users. Power cuts and related constraints are the result and it is up to us to become more energy wise, you, your family and your friends all need to start using electrical energy more ef ciently. THEME 2.1.2 Keywords

Ef ciency Power ef ciency Energy ef ciency Energy saving concepts Green industries Energy audits Electric load inventory Demand prof le Cost benef t analysis Careers in energy auditing Lighting system ef ciency

Theme Outcome

At the end of this theme, you should be able to: (i) Explain the need for and advantages of energy saving and environmentally sustainable work practices. (ii) Explain why behavioural change is an important step to achieving energy savings and environmental goals. (iii) Explain how to audit a residential or small-scale commercial building and recommend appropriate energy ef ciency solutions. (iv) Calculate and compare the power usage for various lighting devices or other electrical loads. Deﬁ nition of Terms Efﬁ ciency You learned that in almost all energy transfer processes some energy ends up as heat (thermal energy). T is principle suggests that for machine operation and technical processes in general, only a certain fraction of the (energy) input is used to do work (W) as the output, while another input fraction is transferred into heat. T us, no machine and no process can be designed to operate with 100 % ef ciency. T is is also the reason why we can never have a perpetual motion machine. T erefore, ef ciency with the symbol η (eta, Greek letter), can be def ned as the ratio (quotient) between output and input. T is concept is easy to remember as ‘what you get’ divided by ‘what you put in’. In engineering we of en assess the ef ciency of machines and processes and aim to improve their ef ciency percentage. T e formula to calculate how ef ciently a machine or device operates can be written as:

Output (7) Ef ciency = Input x 100 (ef ciency is equal to output divided by input times 100)

130 Power Efﬁ ciency Following the general description of ef ciency, power ef ciency can be def ned as the ratio of power output divided by power input.

Power Output (7a) ηp = Power Input x 100

ηp is the power ef ciency in percent (%)

Pinput is power consumption in watt (W)

Poutput is actual work done in watt (W) Energy Efﬁ ciency Building on the general description of ef ciency, energy ef ciency can be def ned as the ratio of energy output divided by energy input.

Energy Output THEME 2.1.2 (7b) ηp = Energy Input x 100

ηp is the energy ef ciency in percent (%)

Einput is power consumption in joule (J)

Eoutput is actual work done in joule (J) Concepts for Saving Electrical Energy - Mindsets and Skills How can we save electrical energy? We know that it is not possible to stop using energy altogether, but we can try to use energy in a much smarter way, that is, using electrical energy more cost-ef ectively and economically. Insulating a building for example allows the home owner to use less electrical energy for heating in winter and cooling in summer. Installing smart lighting components such as LEDs or compact f uorescent lamps (CFL) and making more use of natural daylight reduces the amount of electrical energy needed even more. Energy ef ciency in buildings now even goes a step further, making use of passive infrared systems (PIR) to automate the switch-of and -on functions of modern lighting systems, ensuring that only occupied areas in the building use electric lights. However, technological approaches and advances and specialised technical skills alone are not enough to address energy ef ciency and related climate and environmental challenges. Instead, a new social and economic approach is required and, as we have indicated in Topic 1, a transformation towards a green economy is necessary, which also means a social transformation in terms of lifestyles, habits and behaviour needs to take place so that, for example employees: (i) Understand the potential environmental impacts of their occupations / jobs better. (ii) Can contribute ef ciently to a cleaner environment and avoid environmental risks and damages at their workplaces, e.g. by handling hazardous substances correctly. (iii) Have the knowledge and skills to use energy and resources more ef ciently. Green Industries Suitable mindsets and the availability of technical skills for green jobs are crucial to capitalise on the opportunities a green economy of ers. In South Africa, with its emerging green economy, occupational opportunities are present in almost all sectors of the current economy. Here is a brief outline of four major potential sectors: (i) Energy generation by means of renewable energy technologies and their installation include activities that are aimed at developing, introducing and installing the various technologies. (ii) Green buildings and energy ef ciency is a category comprising various industries that are clus- tered around the purpose of making new and existing buildings more ef cient and environmentally friendly. Industries range from the manufacturing of more ef cient products and systems to the construction of new buildings and retrof tting of existing ones, as well as installation and repair of energy ef cient equipment. (iii) Transportation focuses on developing the technologies, manufacturing and servicing of vehicles that run on electrical energy and greening transportation infrastructure and logistics. (iv) Water and waste management includes the development and operation of systems connected to treatment, reticulation and conservation of water and the management of recycling of waste.

131 Energy Audits Energy audits are systematic surveys of a facility or residential home, aimed at establishing how much energy is currently used and identifying areas of potential savings. An energy audit consists of three main segments: (i) Understanding energy costs (the why, when, how and where energy f ows). (ii) Identifying potential savings. (iii) Proposing cost benef t recommendations.

T e potential benef ts of a professionally structured and performed energy audit for industry and the residential user are: (i) Optimised energy consumption (ii) Lower energy expenses (iii) Increased reliability, productivity and ef ciency

THEME 2.1.2 (iv) Increased comfort for building occupants and/or staf (v) Reduced environmental impacts

T e required consultation process for a detailed and professional (industrial) energy audit can be described as follows (audit steps): (i) Initial client meeting: T is provides the brief for the audit and enables the auditor to collect key information about the building and organisation to be audited. (ii) Historical data analysis: T is consists of a review of historical energy data of the building as an input into the preliminary walkthrough inspection. For instance, if a review of the energy consumption data indicated that there were large seasonal variations, more attention to the building envelope during the preliminary walkthrough inspection may be warranted. (iii) Preliminary walkthrough inspection: T is assesses the general state of repair, housekeeping and operational practices that have a bearing on energy ef ciency. It aims to f ag easily identif - able energy management opportunities and situations that have merit for further assessment as the audit is implemented. (iv) Analyse energy consumption and costs: T is stage collects, organises, summarises and analyses historical energy billings and the tarif s that apply to them. (v) Compare energy performance: T is stage determines energy use indices and compares them in- ternally from one period to another, from one facility to a similar one, or externally to measures of good practice within your industry. (vi) Establish the audit mandate: T is stage aims to secure commitment from management and def nes expectations and outcomes of the detailed audit. (vii) Establish the audit scope: T is stage def nes the energy consuming systems to be audited and clearly identif es what will be included and what not. (viii) Detailed walkthrough: T is stage includes detailed inspections and measurements of equipment and the building envelope in order to develop a detailed understanding of the general state and conditions. (ix) Prof le energy use patterns: T is consists of an analysis that determines the time relationships of energy use as indicated in the electricity demand prof le. (x) Inventory energy use: T is stage develops a list of all energy consuming loads in the audit area and quantif es their consumption and demand characteristics. (xi) Identify energy management opportunities: T is stage includes operational and technological measures to reduce energy waste. (xii) Assess the benef ts: T is stage qualif es the level of energy and cost savings along with any co-benef ts. (xiii) Audit report for action: Here the audit report is prepared and communicated as required for implementation. (xiv) Detailed assessment: T is stage def nes the need for more specialist studies and provides the brief for these. (xv) Engineering assessment: T is stage undertakes more specialist studies that are beyond the scope of a detailed audit. (xvi) Engineering report: T is stage would provide specialist reports resulting from the engineering assessment.

More details on energy audits and the required consultation processes are covered in the BEAT Module 5 (included on the resource CD).

132 Electric Load Inventory and Demand Proﬁ le For residential premises these audit steps are usually far too demanding and can be limited to steps (i), (ii), (viii), (xiii) and (x). Such an approach would allow for the development of a straightforward electric load inventory and a simplif ed demand prof le for the building. T e electric load inventory will result in a list of all relevant electric loads in a building. A demand prof le is a record of the power demand (rate of energy use) over time, i.e. a description of the electrical loads with regard to time of use. In essence, a demand prof le or load inventory will create the ‘electrical f ngerprint’ of the building or premises.

TABLE 1: A SECTION OF A LOAD INVENTOR FOR AN ELEMENTAR SCHOOL

Lighting Area No kW Total kW Div. Peak Hours Energy

Factor kW (h) (kWh) THEME 2.1.2

2 lmp Cust. Rm. 6 0.096 0.6 1 0.6 250 144

1 lmp ﬁx. Main Hall 30 0.096 2.9 1 2.9 250 720

2 lmp 2bal. Class Rms 130 0.105 13.7 1 13.7 250 3.413

U tubes Class Rms 25 0.096 2.4 1 2.4 250 600

2 lmp ﬁx. Class Rms 9 0.096 0.9 1 0.9 250 216

2 lmp 2bal. Library 25 0.105 2.6 1 2.6 250 656

2 lmp 2bal. Book Rm. 2 0.105 0.2 0.1 0.0 25 5 A section of a load inventory (lighting loads only) for an elementary school (Building Energy Auditor Training Programme, BEAT Module 5, p. 48). FIGURE 1: AN EAMPLE OF A TPICAL DEMAND PROFILE OF AN OFFICE BUILDING

4000

3500

3000

2500

2000

1500 kW / kVA(r)

1000

500

00:0001:00 02:00 03:00 04:00 05:00 06:00 07:00 08:0009:0010:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00

kW kVAr kVa PF

Image source: GIZ/S4GJ (Building Energy Auditor Training Programme, BEAT Module 5, p. 49)

133 In an electric load inventory an assessor should determine and check: (i) Lighting aspects a. Types and power ratings of the installed lights b. Whether outside lights are on during daytime c. Light intensities in various locations, especially where it is dark or very bright d. Whether lights are on timers or daylight switches and if so, conf rm the settings

(ii) Hot water production a. Hot water temperatures and thermostat set points b. State of the installation and condition of insulation c. Whether water ef cient appliances are in use d. Type and power ratings of hot water producing equipment

THEME 2.1.2 (iii) Power rating of main energy consumers (apart from geysers) a. Kitchen equipment (stove, dishwasher, kettle etc.) b. Washing machines and tumble dryers c. AC equipment d. Pumps

(iv) Building envelope (roof, walls, f oor, windows, doors etc.) a. What proportion of the facades is glazed b. Direction of glazing (windows) c. Shading of glazing d. Type of glass installed e. State of the main components of the building envelope, e.g. leaks, airtightness, loose f ttings etc. Electric Load Inventory: Lighting System T e assessment of the state and the ef ciency of an installed lighting system in a residential or industrial building is always part of an energy audit, particularly during a load inventory. To address the ef ciency of the light sources and to propose more suitable options, the following general recommendations can be made: (i) Use the most appropriate design: Reconsider the overall design of the present lighting system. T is should involve performing illumination level calculations and taking into consideration the number, position, type and maintenance of f xtures. (ii) Convert to a more ef cient light source: Of en converting from one light source to another will yield the same illumination level for a fraction of the energy cost. Consider the sources listed in Table 1 and their respective light ef ciencies. As part of the above design analysis, the light source ef ciency should be considered. Light Sources and their Characteristics Luminous ef cacy, a measure of how well a light source produces visible light, is the ratio of luminous f ux (lumen) to power (watt). Apart from ef ciency concerns, which can be expressed as luminous ef cacy, the quality of the light source is also an important consideration. T ere are two characteristics of the light source that def ne quality:

Colour Rendering Index: CRI is a unit of measure that def nes how well colours are rendered by dif erent illumination conditions in comparison to a standard, for example daylight. CRI is calculated on a scale from 1-100 where a CRI of 100 would represent a state in which all colour samples illuminated by a light source in question would appear to have the same colour as those same samples illuminated by a reference source (daylight). To put it another way, light sources with low CRI values cause colours to appear washed out or to have a dif erent hue, while light sources with high CRI values make all colours look natural and vibrant.

Colour Temperature: CT describes the colour of a light source by comparing it to the colour of a blackbody radiator at a given temperature. A blackbody is a perfect radiator of visible light. As the actual temperature of this blackbody is raised, it radiates energy in the visible range, f rst red, changing to orange, white, and f - nally bluish white. T e colour appearance of a halogen lamp, for example, is similar to a blackbody radiator heated to about 3 000 degrees kelvin, which is considered to be a warm colour temperature.

134 T e characteristics of various commonly used light sources are summarised in the tables and diagrams below.

TABLE 2: LIGHT SOURCE COMPARISON CHART (AVERAGE VALUES FROM VARIOUS SOURCES)

Lamp type lumen/watt life span (h) watt toxicity Incandescent 10 – 18 1 000 60 low CFL 50 – 70 8 000 11 – 21 high LED 45 – 65 30 000 4 – 8 low Metal halide 70 – 100 10 000 150 – 575 high THEME 2.1.2 Mercury vapour 35 – 65 20 000 250 high High pressure sodium 60 – 120 20 000 500 high Low pressure sodium 90 – 200 15 000 10 – 150 high

Your own notes

135 Fluorescent Lamps Fluorescent lamps are very common light sources and are used in residential and commercial buildings. T e bulb usually comes in a tubular form and functions as a low pressure mercury vapour gas-discharge lamp. An electric current in the gas excites the mercury vapour which produces short-wave ultraviolet light that then causes a phosphor coating on the inside of the bulb to glow. Fluorescent lamp f xtures are more costly than incandescent lamps because they require a ballast to regulate the current through the tube and maintain optimum electrode temperature. However, the lower energy cost typically of sets the higher initial cost. FIGURE 2: POWER CIRCUIT FOR A TPICAL FLUORESCENT LIGHT THEME 2.1.2

A: Fluorescent tube, B: Power (220 V), C: Starter, D: Switch (bi-metallic thermostat), E: Capacitor, F: Filaments, G: Ballast Image source: http://upload.wikimedia.org/wikipedia/commons/thumb/e/e1/Fluorescent_Light.svg/1280px-Fluorescent_Light.svg.png

Compact Fluorescent Lamps Compact f uorescent lamps are available from various manufacturers as replacements for incandescent lamps up to 100 W and are used as an energy-saving alternative in homes. T e 9 W CFL can replace a standard 40 W incandescent bulb, a 14 W CFL replaces a standard 60 W and a 18 - 21 W CFL replaces a standard 100 W incandescent bulb. T e CFL lamps, complete with electronic ballasts, are designed to f t into the lamp holders of incandescent lamps with no modif cations required. Unfortunately, all f uorescent lamps, including CFLs, contain toxic mercury which complicates their disposal. FIGURE 3: ENERG-EFFICIENT LIGHTING ALTERNATIVES

Image source: http://upload.wikimedia.org/wikipedia/commons/3/3a/Gluehlampe_01_KMJ.jpg, http://upload.wikimedia.org/ wikipedia/commons/3/31/06_Spiral_CFL_Bulb_2010-03-08_%28white_back%29.jpg, http://upload.wikimedia.org/wikipedia/ commons/e/e7/LEL-AW6L2_1.jpg On the lef is a typical incandescent light bulb (60 W) which has been used for decades for general lighting purposes around the world. However, incandescent bulbs are being phased out in many countries in favour of more energy-ef cient lighting alternatives such as CFLs (centre) and LEDs (right).

136 LEDs In the past, light-emitting diodes (LED) were mainly used as indicator lamps in many electric and electronic devices. By now, LEDs are available for general lighting purposes and many specif c applications. T e advantages of LEDs are that they: (i) Are extremely energy ef cient (ii) Have a very long life span (iii) Can emit light of an intended colour without the use of colour f lters (iv) Are ideal for use in applications that are subject to frequent on-of cycling (v) Can very easily be dimmed (vi) Radiate very little heat (vii) Are solid state components, making them more resistant to external shock (viii) Do not require external ref ectors, as their solid package can be designed to focus light (ix) Do not contain mercury and thus, when compared to most other ef cient light sources do not

complicate disposal and recycling. THEME 2.1.2

T eir main disadvantage is a high initial price, but it is likely that LED costs will decrease over time.

FIGURE 4: DIAGRAM OF AN LED (INDUCTIVE LOAD)

Epoxy lens/case Wire bond Reﬂective cavity

Semiconductor die

Anvil Leadframe Post

Flat spot

Anode Cathode

Image source: http://upload.wikimedia.org/wikipedia/commons/f/f9/LED,_5mm,_green_(en).svg

137 Lighting Energy Management Opportunities Apart from changing to more cost- and energy-ef cient lighting options, for example LEDs and CFLs, there are two additional very simple energy management opportunities available to reduce energy costs: (i) Switch of lights in unoccupied areas and in areas where daylight provides adequate lighting levels: Switching lights on or of can be done manually or by automatic control. Manual switching can be facilitated by providing light switches at strategic points. Automatic controls include photo cells, occupation sensors and time switches. (ii) Remove redundant f xtures: Many commercial buildings undergo modif cations and reorgani- sation. Areas are redesigned and equipment moved but of en the lighting system is not updated accordingly, resulting in some lights becoming redundant. An example of this would be an of ce that has been built into an existing covered area. T e original lighting over the new of ce becomes redundant and should be removed. Removal should also include f xtures, particularly f uorescent f xtures. T e f xture should be disconnected from the electric supply as the ballast

THEME 2.1.2 will continue to consume power, at approximately 15 % of the power consumed by the f uorescent tube. Electric Load Inventory: Plug Loads T e term plug load refers to those electric and electronic devices that are not permanently hard-wired into the building’s electrical distribution system. T ey include of ce equipment, kitchen and cafete- ria appliances, portable heaters and cof ee makers etc. T ese electric energy consumers can make up a signif cant portion of the total electric energy consumption of the building. T us, reducing plug loads is important for saving energy and costs. Plug loads can be reduced in the following ways: (i) Remove equipment: T e f rst step in controlling plug loads is to remove equipment that is not permitted to be used due to safety regulations. (ii) Switch of equipment: All equipment should be switched of when not in use. Ideally this should include switching of equipment at the socket to avoid standby losses, for example, setting up sof ware that switches computers of or puts them into a ‘sleep’ mode. Timers can also be used to switch printers and photocopiers of overnight or over weekends. (iii) Select the most energy ef cient equipment: Consider using LED monitors which emit less heat and use less energy and space than conventional monitors. Consider using notebooks instead of conventional desktop computers. T e former only use about 10 – 20 % of the energy of desktops. Only buy equipment that has an Energy Star® rating. T is enables you to compare the equipment to the most energy and cost-ef cient types on of er. Energy Star® is a government run program developed by the US Department of Energy, and has been adopted in many other countries. En- ergy Star® provides energy ratings for a wide range of electrical devices, both for domestic appliances as well as for of ce equipment, allowing you to comply with SANS 204 requirements. T e SANS 204-1 energy ef ciency in building regulations outlines that a) appliances f tted into new buildings shall have an energy rating, and b) of ce equipment shall have an energy rating and a stand-by energy reduction mode when not in use. T e latter allows users to directly control power savings of IT hardware, including automatically turning of components such as monitors and hard drives af er set periods of inactivity. In addition, a system may go into sleep mode, i.e. components such as the CPU and the system’s RAM are turned of . Cost Beneﬁ t Analysis For the auditor, the electric load inventory and the demand prof le are extremely useful tools with which energy and cost saving options, along with any co-benef ts, can be proposed to the building owner or tenant. Having identif ed new technologies and systems, the auditor needs to provide guidance on the feasibility of proposed measures and recommendations for implementation. To a large extent, the assessment of proposed measures focuses on a cost benef t analysis. T is requires a detailed economic analysis that may go beyond the parameters of an audit, nevertheless the auditor should be able to determine: (i) Benef ts to be taken into account (ii) Costs to be included in the analysis (iii) Return on investment, i.e. a realistic projection of the f nancial viability of a proposed measure over time

More details on cost benef t analysis are covered in the BEAT Module 8: Interpret the business case (included on the resource CD).

138 Careers in Energy Auditing Currently, two new qualif cations, namely the Energy Ef ciency Technician and the Energy Ef ciency Manager are in the process of being developed under the auspices of the Quality Council for Trades and Occupations (QCTO) and registered by the South African Qualif cations Authority (SAQA). As part of the green energy business sector, careers as energy assessors and auditors will advance even further in the coming decade. Consumers as a whole are becoming increasingly environmentally conscious and this has created a comfortable niche market in which energy assessors and auditors can earn a living. An even greater driving factor in the business of energy auditing is the constant rising f nancial cost of energy and power failures from ESKOM. Energy assessors and auditors can provide customers with action- able, real-world advice and a means of reducing the cost of energy in the long- and medium-term.

Your own notes THEME 2.1.2

139 Examples

Example 1

Let us illustrate power ef ciency with the following calculation: An electric motor has a Pinput value of 50 watt. T e motor was activated for 60 seconds (t) and produced work (W) with a value of 2700

joules (J) during this period. Determine the power ef ciency (ηp) of the motor in percent (%).

Problem

Determine the power ef ciency (ηp) of the motor in percent (%).

Solution

THEME 2.1.2 1. Known quantities:

Pinput = 50 W E = 2700 J t = 60 s

2. Quantities to be determined:

Poutput = E / t Power Output Power ef ciency in percent = ηp = Power Input x 100

3. Analysis

To calculate the power ef ciency (ηp) of the motor in percent (%), we f rst determine Poutput by using the following equation:

W (5) P= t and by substituting work (W) with energy (E) Poutput = E / t = 2700 J / 60 s = 45 W

Next, we calculate ηp (ef ciency in percent) by using formula (7a):

Power Output (7a) ηp = Power Input x 100

45 W (ηp) = 50 W x 100= 0.9 x 100 = 90 %

4. Answer T e power ef ciency of the motor is 90 %.

Your own notes

140 Example 2

To illustrate energy ef ciency, let us look at the following example: An incandescent bulb has a

power rating (Pinput) of 60 watt. T e bulb was activated for 60 seconds (t) and produced thermal energy (heat) with a value of 2800 joules (J) during this period. Determine the energy ef ciency

(ηp) of the bulb in percent (%).

Problem

Determine the energy ef ciency (ηp) for the bulb in percent (%).

Solution 1. Known quantities:

Pinput = 60 W

EHeat = 2800 J THEME 2.1.2 t = 60 s

2. Quantities to be determined:

Einput = Pinput × t

Eoutput = Einput - EHeat (since the light bulb should produce light and not heat) Energy Output Energy ef ciency in percent = ηp = Energy Input x 100 3. Analysis

To calculate the energy ef ciency (ηp) of the bulb in percent (%), we f rst determine Einput by using formula (6): (6) E = P × t Einput = Pinput × t = 60 W × 60 s = 3600 J

Next, we can calculate Eoutput by using Einput - EHeat :

Eoutput = Einput - EHeat = 3600 J – 2800 J = 800 J

Finally, we calculate ηp (ef ciency in percent) using formula (7b):

Energy Output (7b) ηp = Energy Input x 100

800 J (ηp) = 3600 J x 100 = 0.222 x 100 = 22.2 %

4. Answer

T e energy ef ciency (ηp) of the bulb is 22.2 %.

Your own notes

141 Example 3

Let us illustrate energy ef cient lighting systems by comparing dif erent types of common light bulb types (Table 3):

TABLE 3: COST COMPARISON BETWEEN LED, CFL AND INCANDESCENT LIGHT BULBS

LED CFL Incandescent Lifespan in hours 30 000 8 000 1 000 Watt (equivalent 60 8 14 60

THEME 2.1.2 watt incandescent) Cost per a bulb R150 R30 R20 Energy cost per hour R0.008 R0.014 R0.06 Daily energy cost R0.04 R0.07 R0.30 (5 h) Annual energy cost R14.6 R25.6 R110 (1 825 h) Energy cost for 30 000 hours R240 R420 R1 800 (LED lifespan) Bulbs needed for 1 3.75 (4) 30 30 000 hours Total cost for 30 000 hours (16.4 y) R410 R540 R2 400 including bulb price

Daily and annual costs are based on the assumption that each bulb runs for 5 hours a day at a cost of R1 per kWh.

Your own notes

142 Exercises

For all the following calculations the approach outlined in the previous example section must be used: First state the problem and then follow the steps to arrive at the solution (known quantities, quantities to be determined and analysis).

Exercise 1

Calculate the energy ef ciency of a CFL bulb with a power rating (Pinput) of 14 watt. T e bulb was activated for 60 seconds (t) and produced thermal energy (heat) with a value of 1 400 joules (J) during this period. Determine the energy ef ciency (ηp) of the bulb in percent (%).

Exercise 2

Calculate the energy ef ciency of a LED bulb with a power rating (Pinput) of 8 watt. T e bulb was THEME 2.1.2 activated for 60 seconds (t) and produced thermal energy (heat) with a value of 100 joules (J) during this period. Determine the energy ef ciency (ηp) of the bulb in percent (%).

Exercise 3 Perform an electric load inventory in your home and in your classroom and/or college workroom (lab). Te inventory shall result in a list of all relevant electric loads including their power ratings. Calculate the daily power demand of all listed appliances and the daily cost in Rand, assuming that all devices run for 2 hours a day at a cost of R1 per kWh.

Exercise 4 Try to calculate or estimate the return on investment (payback period) for a LED bulb compared to an incandescent bulb using the values from Table 3 (cost comparison between LED, CFL and incandescent light bulbs).

Exercise 5 Name and explain at least two energy management options for lighting systems which can easily be implemented.

Exercise 6 Explain the term plug load and clarify why reducing plug loads is important for energy and cost saving.

Further Information (all materials are on the resource CD)

Building Energy Auditor Training Programme, BEAT Module 5, GIZ/S4GJ 2012.

143 THEME 2.2.1 Unit 2.2 Unit

UNIT 2.2 FUNDAMENTALS OF ELECTRIC CIRCUITS Introduction In the industrialised world electric energy is probably the most useful source of energy. We consume electric energy and take for granted that it will run all electrical appliances in our homes, businesses and industry. Can you imagine what life would be like without electric energy and electric appliances which make our lives so comfortable? Before electric generation and distribution systems were established, oil lamps or candles were used at night to provide light and people used gas, paraf n or wood for heating and cooking. Some people still do, but most of them would probably prefer to have access to electric energy to live a more comfortable life. Today, electric appliances are indispensable to most of us and anyone who recently suf ered power outages knows the consequences and inconveniences of these power interruptions. However, despite our severe dependence on electric energy most people fail to understand that electric energy is based on a ubiquitous form of energy resulting from the motion of charges. T e following theme will explain this notion in more detail.

Unit Outcomes

At the end of this unit, you should be able to: (i) Explain what electric energy is based on. (ii) Describe and explain the fundamental concepts and relationships of charge, current, potential, resistance and power. (iii) Sketch basic circuit diagrams using symbols and explain their functions. (iv) State and explain Ohm’s law: the relationship between potential, current and resistance in an electrical circuit. Themes in this Unit

Unit 2.2 covers only one theme: T eme 2.2.1 Electric Charge and the Proportionalities between Current, Potential, Resistance and Power

144 THEME 2.2.1 ELECTRIC CHARGE AND THE PROPORTIONALITIES BETWEEN CURRENT, POTENTIAL, RESISTANCE AND POWER

Introduction

In this theme, you will be introduced to the concepts of electric charge and electromotive force as the underlying principles of electrical energy and their signif cance for quantities such as electrical current, potential and resistance. However, energy, charge, current and many other quantities are not concrete substances and usually only their ef ects on matter can be detected. Consequently, their concepts are rather abstract and we can describe these quantities only by what they can do and not by what they really are. Mathematical equations can be helpful in these instances, but in science and engineering we also use analogies which allow us to compare such incomprehensive concepts with more familiar ideas. We call such analogies ’models’. THEME 2.2.1 Unfortunately, most models cannot provide us with entirely correct ideas. In electrical engineering the current–water analogy, for example, is not a very convenient analogy. T is model tries to illustrate the relationship of electrical current, potential and resistance with water f ow and water pressure, and subsequently expresses electrical current almost as if it is an actual substance. But conceiving charge, current etc. as substance-type entities that occupy space is incorrect. Based on this misconception, many people believe that electric current resembles individually moving electrons which carry energy from a battery or a generator through the connecting wires of a circuit to the consumer. T ese ideas are, unfortunately, conceptually erroneous and need to be corrected. T us, in this theme you will be introduced to the more precise concepts behind electric charge, current, potential and resistance by focusing on what these quantities can do and what their relationships are to each other. Keywords

Electric charge Conductivity Electric current Models and misconceptions Electrical potential dif erence Electrical resistance Ohm’s law Electrical power Theme Outcomes

At the end of this theme, you should be able to explain the concepts behind electric charge and the proportionalities between current, potential, resistance and power in a precise and technical manner. Furthermore, you will be able to apply these concepts in practical problem solving. Deﬁ nition of Terms Electric Charge T e concept of electric charge is the underlying principle used to explain all electric phenomena. We have all probably experienced the ef ects of electric charge when we remove a woollen sweater and our hair becomes charged causing single hairs to stand up (see also T eme 2.1.1), or if we walk across a carpet and receive a tiny shock when we touch a door handle, a rail or anything else made out of steel. Even though they did not fully understand it, ancient people already knew something about electric charge, yet for most of that time, electric charges were simply regarded as either something to be feared, e.g. during lightning storms, or as a curiosity with its various phenomena regarded as entertainment for the curious. T e earliest studies of electric charge were conducted over 2 500 years ago by a Greek researcher, T ales of Milet, around 570 B.C. T ales realised that amber, a fossilised tree resin, attracts small objects such as dust and feathers af er being rubbed with wool. In fact, the term electric derives

145 from the Greek word ‘elektron’, which means amber. It was however not until 1752 that the scientif c community began to get a clearer picture of how electric charges worked. In that year Benjamin Franklin (1706–1790), an American scientist and inventor, ran his famous kite experiment and proved that lightning strikes were electrical in nature. He also presented the theory that electric charges had positive and negative elements and that their f ow was from positive to negative.

Approximately 30 years later, Mr Coulomb conducted several experiments to determine the variables af ecting an electric force. He revealed that opposite charges (positive-negative) attract each other and identical charges (positive-positive and negative-negative) repel each other. His work, published between 1785 and 1791, resulted in Coulomb’s law, which made it possible to determine electrostatic force (see T eme 2.1.1) and the mechanism behind attraction or repulsion of charged particles.

By the nineteenth century, despite still not fully understanding the nature of electric charge and its relation to energy, scientists such as Michael Faraday in England (1791–1867), Joseph Henry in the United States (1797–1878) and Georg Ohm in Germany (1789–1854) were already establishing the rules regarding electric charge behaviour, based on the results of their practical experiments. However, only from the late nineteenth century onwards the gradual accumulation of knowledge on the structure of the atom THEME 2.2.1 revealed the nature of electric charges and energy. FIGURE 1: ELECTRIC CHARGES

q- q+ q+ q+

Left: Opposite charges (positive-negative) attract each other. Right: Identical charges (positive-positive and negative-negative) repel each other.

Image source: GIZ/S4GJ

Your own notes

146 FIGURE 2: SIMPLIFIED STRUCTURE OF AN ATOM

qq+ PROTONSProtons

q-q- ELECTRONSElectrons qq+ NEUTRONSNeutrons q+q

q- THEME 2.2.1 q-

Each atom consists of electrons, protons and neutrons. The charge of an electron is negative and a proton carries a positive charge of the same magnitude as the electron.

Image source: GIZ/S4GJ

We now know from elementary physics that all matter is made up of fundamental building blocks known as atoms and that each atom consists of electrons, protons, neutrons and even tinier particles. T e electrons and the protons carry a charge, and the charge of an electron is negative, while a proton carries a positive charge of the same magnitude as the electron. Electric charge, either negative or positive, is the most basic quantity in an electric circuit.

Note

T e following properties of electric charges should be noted: (i) To honour Mr Coulomb for his achievements, the SI unit of charge has been termed coulomb (C) and the symbol for charge is Q.

(ii) T e coulomb is a large unit for charges. In 1 C of charge, there are 6.24 × 1018 electrons. T ese are 6 240 000 000 000 000 000 electrons (a number with sixteen zeros!). On the other hand, the elementary charges of a single electron or proton are incredibly small, only 160 × 10−21 C.

(iii) Electric charge is an intrinsic property of matter, inherent in its atomic structure.

(iv) T e concepts of charge and energy are related, and analogous with the law of conservation of energy, the law of conservation of charge states that charge can neither be created nor destroyed only transferred. T us the algebraic sum of electric charges in a system never changes.

147 Conductors and Insulators A unique feature of electric charge is the fact that it is mobile, i.e. charge can be mobilised and transferred from one place to another, where it can be converted into another form of energy. Usually, an electric charge f ows along materials which support its movement. Such materials are called conductors and the term electrical conductivity is used to describe and measure their capability to support electric charge f ow. T e resistance (R) or opposition to current f ow varies for dif erent materials. Resistance is measured in ohm, and the Greek letter ‘omega’ (Ω) has been assigned to the unit. T e resistivity (ρ) of a material is def ned as the resistance of a material sample per unit length, and thus resistivity is measured in Ω/m. T e Greek letter ‘rho’ (ρ) has been assigned to resistivity.

TABLE 1: RESISTIVIT OF DIFFERENT METALS IN Ω/M

Metal Resistivity (Ωm) Silver 16.4 × 10-9 THEME 2.2.1 Copper 17.5 × 10-9 Aluminium 28.5 × 10-9 Brass 75.0 × 10-9 Iron 100.0 × 10-9

One of the best metallic conductors is silver, but because of its cost, silver is only used for special applications such as relay contacts and printed circuit boards. Copper and aluminium are the most commonly used metallic conductors. Copper is a better conductor than aluminium but again, due to its high price and its lower mass, aluminium is the preferred conductor material for high-voltage transmission and distribution lines. Most non-metals are rather weak conductors, but there are always exceptions such as carbon, which is a semi-conductor. Some liquids are also excellent conductors; they are called electrolytes. Materials that do not support the f ow of electric charges very well or almost not at all are called insulators. T ese materials have a very low conductivity. In other words, they do not have the ability to allow electric charge to f ow. Plastic, wood, glass, rubber and porcelain are examples of good insulators. How- ever, even good insulators contain impurities and these impurities enable tiny charges to f ow. T us, in practice there is simply no perfect insulator and at high thermal activity (high temperatures) even a good insulator can conduct charges.

Your own notes

148 Electric Charge and Current Charge (Q) moving along a conductor or in an electric circuit gives rise to a current (I). Simply stated, current can be def ned as a f ow of charges, but it is more accurate to def ne electric current as the rate of f ow of charge, i.e. the time rate (∆t) of change of charge (∆Q) passing along a conductor. T is def nition of electric current gives us our eighth mathematical equation for a quantity and we can write this relationship as:

∆Q (8) I = (current is equal to change of charge per unit time) ∆t

FIGURE 3: CHARGE (Q) MOVING ALONG A CONDUCTOR GIVES RISE TO A CURRENT (I).

AREA THEME 2.2.1 q q

Image source: GIZ/S4GJ

Current can be def ned as the rate of f ow of charge passing through a conductor area.

To dif erentiate the units in which current (I) is expressed, we need to place the units for each quantity into formula (8), i.e. coulomb (C) for charge (Q) and second (s) for time (t):

C (8a) I = (current values are expressed as coulomb per second) s T e SI unit of current is called amperes (A), where 1 ampere is equal to 1 coulomb per second. T e name of the unit is a tribute to the French scientist, Mr Ampere (1775–1836).

1 C (8b) 1A = (1 ampere is equal to 1 coulomb per second) s Conventionally, current f ow is considered as the movement of positive charges. T is convention was introduced by Mr Franklin and although we now know that current f ow in metallic conductors is due to negative charges, we follow the universally accepted convention that current is the net f ow of positive charges. Please note that there can be several types of current as charge can vary with time in several ways. If the current does not change with time but remains constant, we call it a direct current (DC), i.e. a current that remains constant over time. Such a current is provided by batteries, photovoltaic cells and other DC generators. Almost all mobile electronic devices use direct current.

149 FIGURE 4: TWO TPES OF CURRENTS

I I

0 t 0 t THEME 2.2.1

Image source: GIZ/S4GJ Direct current (DC), a current that remains constant over time, is shown in the diagram on the lef -hand side. Alternating current (AC), a current that varies sinusoidal over time, is shown in the diagram on the right-hand side.

A common form of time-varying current is the sinusoidal current or alternating current (AC). Such a current is used in households, businesses and industry to run electric appliances such as computers, air conditioners, refrigerators and washing machines.

While the ef ects of a current within a conductor may be detected more or less instantaneously, there is nothing to visibly indicate the presence of an electric current in a conductor unless you use a multimeter. We most certainly would not be able to see any electric charges, but the presence of a current can indirectly be detected in an electric circuit by observing its ef ects. T ese ef ects produced by an electric current due to the resistance of all circuit elements are the: (i) Heating ef ect: We make practical use of this ef ect with incandescent lamps and electric heaters. However, this ef ect is also responsible for heat transfers away from a conductor into its sur- roundings which is known as thermal energy ‘losses’. (ii) Chemical ef ect: We make use of this ef ect in electrolysis (electroplating). T is ef ect however can also be detrimental, as it is responsible for some types of corrosion. (iii) Magnetic ef ect: An electric current produces a magnetic f eld which surrounds the conductor. We make use of magnetic forces to drive motors and to operate electromagnetic relays. However, strong magnetic f elds can be potentially harmful to the human body.

Electric current (I) is def ned as the rate of f ow of charge along a conductor and thus we can def ne electric charge in our ninth mathematical equation as:

(9) Q = I × t (charge is equal to current times time)

To dif erentiate the units in which charge (Q) is expressed, we need to place the units for each quantity into formula (9), i.e. ampere (A) for current (I) and second (s) for time (t):

(9a) Q = A × s (charge values can be expressed as ampere times second)

T us, charge (Q) can be measured in ampere times second (A × s). However, the SI unit for charge (Q) is coulomb (C). Simply stated, 1 coulomb (C) is the quantity of electric charge conveyed per second, by a current of 1 ampere. It might not be so important to memorise the def nition of 1 coulomb, but the ∆Q relationship between electric charge and electric current, i.e. I = needs to be understood. ∆t 150 Models and Misconceptions about Charge and Current T e nature of many quantities such as energy, charge and current are of en dif cult to comprehend and dif cult to explain in terms of mathematical abstractions. Energy, charge and current, for example, are not made up of any tangible substances and can only be described as invisible qualities of matter. In these instances scientists and engineers use analogies which allow us to compare and correlate incomprehensive concepts or phenomena with something more familiar. We call such analogies models.

A model provides us with a way of imagining what quantities such as charges or electric currents might really be. Based upon further observation and experiments, a model could be improved and used to predict how these quantities or particles of matter would behave under dif erent circumstances. Of en, a model will not necessarily represent all aspects of a physical quantity or its whole nature, and to employ the visible world of mechanics to explain the invisible world of energy is a dif cult task. T us, all models have limitations and some models are better than others. Good models use superior approximations and can describe the characteristics and behaviour of invisible structures or incomprehensible phenomena rather well. Bohr’s model of the atom is a good example: T is model resembles a miniature solar system with a nucleus (protons and neutrons) which corresponds to our Sun, surrounded by tiny negatively charged particles called electrons (corresponding to the planets), travelling in dif erent orbits called shells. Contrary to the real solar system which is controlled by gravitational forces, the behaviour of an THEME 2.2.1 atom is controlled by electric forces, i.e. by the attraction and repulsion between electric charges. It is important to note however, that no one has ever seen an atom and its sub-atomic particles and thus, we simply do not know if an atom really resembles a miniature solar system or not. It is simply a model!

Many electrical engineering textbooks use models to describe electric current or even ‘electricity’, a term which has so many dif erent meanings that we will try to avoid it. Usually, these models rely on the so-called current-water analogy. Regrettably, most of these models describe current almost as if it is an actual substance and that negatively charged particles (electrons) f ow freely through it. Clearly, this is a rather inadequate and oversimplif ed model which encourages some serious misconceptions. Conceiving charge or energy as a substance-type entity that occupies space is incorrect. It is rather unfortunate that based on these misconceptions many people tend to believe that electric current resembles moving electrons which carry energy from a battery or a generator through the connecting wires of a circuit to the consumer. Charge and energy are simply not similar to matter.

T is idea is already conceptually erroneous due to the fact that the velocity of electrons is just too slow and too randomly directed to carry energy fast enough through a circuit. We all know that when you switch residential appliances on, for example incandescent light bulbs, the bulb illuminates almost instantaneously. If the number of electrons per volume in a conductor, its diameter and the current in ampere is known, one can theoretically work out how fast the electrons would move along a conductor. In wires, with a diameter of 1 mm2, the velocity of electrons is about 0.01 mm per second, which is less than a millimetre per minute. T is slow movement is due to their mutual repulsion (remember identical charges repel each other) and other factors. T us, the velocity of individually free electrons along a conductor is far too slow to carry energy more or less instantaneously through a circuit.

Of course, we like the motto ‘keep electric engineering simple’, but if this motto comes into conf ict with scientif c validity we cannot just keep it simple. T us, to explain current and energy transfer we prefer to use the concept of charge: If an electromotive force is present, charges are compelled to move along conductors. T is motion of charges gives rise to an electric current. A unique feature of electric charge is the fact that charges are very mobile and can move extremely fast along a conductor, i.e. a charge can be conveyed from one place to another almost at the speed of light. In this process electric energy is converted into other forms of energy, for example into thermal energy and all applications of electrical energy are based on this principle.

151 Electrical Potential Difference If, as stated in the preceding section, moving charges give rise to a current, naturally some work needs to be performed by a force to convey or move the charges. T is force is called the electromotive force (emf), typically represented by a battery or generator. T is force is also known as the electrical potential dif erence (V). T e electromotive force is always associated with energy conversion, as it exists in batteries where chemical energy is transformed into electrical energy, and in generators where mechanical energy is transformed into electrical energy. Batteries, e.g. lead-acid batteries, store chemical energy and convert it to electrical energy on demand. Batteries do not store electrical charge. On demand, charge can enter one terminal of the battery, acquire electrical potential energy and exit from the other terminal at a lower electrical potential energy level. Note that in many textbooks the informal term ‘voltage’ is a popular expression for electrical potential difference. We prefer to avoid this rather misleading term for the reason that the term ‘voltage’ is not based on the SI system and contrary to potential difference, will not help you to conceptualise related terminology, units and quantities such as current, resistance and power. Potential dif erence (V) between two points in a circuit indicates the electrical potential energy required to move a charge from one point to the other. T is def nition of electric potential gives us our tenth equation for a quantity and we can write this relationship as: THEME 2.2.1 W (10) V = (potential is equal to work done per unit charge) Q

To dif erentiate the units in which potential dif erence (V) is expressed, we need to place the units for each quantity into formula (10), i.e. joule (J) for work (W) and coulomb (C) for charge (Q):

J (10a) V = C (potential values can be expressed as joule per coulomb)

T e SI unit of potential is called volt (V), in honour of the Italian physicist Alessandro A. Volta (1745– 1827) who invented the f rst battery. T erefore:

1 J (10b) 1V = C (1 volt is equal to 1 joule per coulomb)

Simply stated, potential dif erence (V) is an expression for the energy required to move a unit charge through a conductor. Potential dif erence is measured in volt (V) across a conductor. T us, potential dif erence is the change in energy levels measured across the load terminals. Similar to electric current, a constant potential is called DC potential, whereas a sinusoidal time-varying potential is called AC potential. DC potential is commonly provided by a battery whereas AC potential is provided by AC generators. Electrical Resistance Current and potential are two basic variables in electric circuits. But there are three basic variables in an electric circuit and Georg S. Ohm (1789–1854), a German physicist, investigated the relationship between potential and current and quantif ed the phenomenon of resistance. Resistance (R) is the third basic variable in an electric circuit and is def ned as the opposition to electric current being conveyed through a circuit. T e SI unit for resistance is called ohm, named in honour of Mr. Ohm and has been given the Greek letter ‘omega’ (Ω).

TABLE 2: DIFFERENT MATERIALS RESIST THE FLOW OF ELECTRIC CHARGE ACCORDING TO THEIR PHSICAL PROPERTIES

Metal Resistivity (Ωm) Material used as Due to Copper 17.5 × 10-9 Conductor low resistance Silicon 6.4 × 102 Semiconductor moderate resistance Glass 1012 Insulator high resistance Teﬂon 3 × 1012 Insulator high resistance

Electrical resistance (R) is a characteristic of resistors or loads impeding current f owing through a circuit. Similarly, there is a drop of potential across a resistor element when current f ows through the

152 element. Every component in an electric circuit shows dif erent qualities and levels of resistance. Various factors determine the extent or level of resistance of dif erent circuit elements (conductors), including: (i) Length of the conductor, e.g. if two wires are made from the same material and have the same diameter, then the longer wire has a higher resistance than a shorter wire. (ii) Diameter of the conductor, e.g. if two wires are made from the same material and have the same length, then the thinner wire has a higher resistance than a thicker wire. T e thinner wire also has a lower current capacity. (iii) Temperature increase usually results in resistance increase of circuit elements. (iv) Material characteristics determine resistance values of circuit elements. Metals for example, have a higher capability to support electric charge f ow and thus have a lower resistance than ceramic, glass, rubber or wood. (v) Damage to circuit elements, e.g. partially cut or nicked wires function as thinner wires with a higher resistance and thus have a lower current capacity.

FIGURE 5: A SIMPLE DC CIRCUIT THEME 2.2.1

Single switch

Filament bulb

Battery, two 1.5 V cells

Image source: GIZ/S4GJ A simple DC circuit consisting of (i) a source providing the electromotive force (potential dif erence), for example a battery; (ii) a load or resistor like a bulb; and (iii) a switch and conducting wires. Note that a resistor or a load can take the form of many dif erent components in an electric circuit, e.g. light bulbs or motors. Most of these components have their own unique symbols (see T eme 2.3.1 for more information on circuit diagrams). Ohm’s Law T ere is a def nite relationship between the three basic variables in electric circuits, i.e. current, potential and resistance and Mr. Ohm formulated this relationship as follows:

Current is directly proportional to potential and inversely proportional to resistance provided that the temperature in the circuit remains constant.

Note that the term ‘proportional’ describes the relationship between (two) quantities in terms of their size or magnitude. If two quantities are directly proportional, indicated by the symbol , then by whatever factor the one quantity changes, the other quantity will change by the same factor. For example if one quantity doubles, so will the other. ∝

Note also that if (two) quantities are termed to be ‘inversely proportional’ to each other, then by whatever factor the one quantity changes, the other quantity changes by the reciprocal of that factor. For example, if one quantity doubles, the other quantity is halved.

T is relationship between current, potential and resistance is called Ohm’s law and gives us our eleventh mathematical def nition (equation 11), although this time not only for a single quantity but also to describe the relationship between three quantities:

153 V (11) I = (current is equal to potential divided by resistance) R T e above equation (11) can also be arranged as:

(11a) V = I × R (potential is equal to current times resistance) V (11b) R = (resistance is equal to potential divided by current) I To dif erentiate the units in which these three quantities can be expressed in their relationship, we need to place the units for each quantity into formula (11, 11a and 11b), i.e. ampere (A) for current (I), volt (V) for potential (V) and ohm (Ω) for resistance (R):

V (11c) A = Ω (ampere can be calculated by volt divided by ohm)

(11d) V = A × Ω (volt can be calculated by multiplying ampere and ohm values)

V (11e) Ω = A (ohm can be calculated by volt divided by ampere) THEME 2.2.1 Understanding these relationships between current, potential and resistance is important for fast and accurate diagnostics of electrical installation problems. T us, let us have a second look at Ohm’s law:

Current is directly proportional to potential and inversely proportional to resistance provided that the temperature in the circuit remains constant.

Simply put, if in an electrical circuit the volt value goes up (increases), the ampere value will go up at the same rate, and vice versa. Also, as the ohm value goes up, the ampere value will go down (decreases) at the same rate and vice versa. Power, Current and Potential In the preceding section about potential dif erence, we indicated that some work needs to be performed by a force to move charges along a circuit and that this force is called potential dif erence (V) or, by using a somewhat equivalent term, electrical potential energy. We can write this relationship as:

W (10) V = Q (potential is equal to work done per unit charge)

In terms of its SI units, potential dif erence (V) is work (W) in joules (J) and charge (Q) in coulomb (C):

J (10a) V = C (potential values can be expressed as joule per coulomb)

T is earlier def nition of potential dif erence as work per unit charge allows us to conveniently reintroduce the concept of electrical power (P). Let us recall that power is def ned as the work done per unit time or, to put it another way, power is the time rate of providing or absorbing energy, measured in watt (W). We have written this relationship in our f f h mathematical def nition:

W (5) P = t (power is equal to work divided by time)

In terms of units, power (P) is work (W) in joules (J) and time (t) in second (s):

J (5a) P = s (power values are expressed in joule divided by seconds)

work W Given that potential (V) is def ned as work done per unit charge, i.e. V = charge = Q , and current is charge Q def ned as charge per unit time, i.e. I = time = t , power (P), either provided or absorbed by a circuit element, can be represented by the following relationship:

work work charge power = time = charge × time = potential × current or, by using the symbols for the quantities in question:

W W Q P = = × = V × I t Q t 154 T is relationship between power, potential and current gives us our twelf h mathematical def nition (equation 12) and we can write this relationship as:

(12) P = V × I

T e above equation (12) can also be arranged as:

P (12a) I = V (current is equal to power divided by potential)

P (12b) V = I (potential is equal to power divided by current)

To conf rm that power can indeed be expressed as potential times current, it is easy to verify that the units of potential, i.e. joules/coulomb (see formula 10a), times current, i.e. coulombs/second (see formula 8a), are indeed identical to the units of power, i.e. joules/second, or watts (see formula 5a).

(12c) power (watt) = joules = joules × coulomb = potential (volt) × current (ampere) THEME 2.2.1 second coulomb second T erefore it follows that: (12d) watt = volt × ampere W = V × A

Your own notes

155 Examples

Ohm’s law is the basic formula used in all AC and DC electrical circuits. If you know the values of two of the three quantities, you can calculate the value of the missing third quantity. Electricians and electrical engineers use Ohm’s law to quickly determine how much potential is required for a certain load like a motor, or to determine its resistance and/or how much current an appliance will require to fully perform its function. Let us illustrate Ohm’s law with the help of a few examples.

Example 1 Problem An electric iron requires 2 ampere (A) at 230 volt. Determine its resistance.

Solution 1. Known quantities: I = 2 A V = 230 V THEME 2.2.1 2. Quantities to be determined: V Resistance (R), review of formula (11c) R = I V and formula (11e) Ω = A

3. Analysis To calculate the resistance of the iron, we are using formula: V (11e) Ω = A 230 V Ω = = 115 V 2 A A 4. Answer T e resistance of the iron is 115 ohm (Ω).

Example 2 Problem Electrical energy is converted into heat energy in the electrical element (a resistor) of a toaster. How much current is required if the electrical element has a resistance of 60 ohm (Ω) and uses a 240 volt supply?

Solution 1. Known quantities: R = 60 Ω V = 240 V

2. Quantities to be determined: V Current (I), review of formula (11) I = R and formula (11c) A = V Ω 3. Analysis To calculate the current required by the toaster, we are using formula: V (11c) A = Ω 240 V V A = 60 Ω = 4 Ω

4. Answer T e heating element of the toaster requires 4 ampere (A).

156 Example 3

We said earlier that Ohm’s law can be put to good use in electrical troubleshooting and we can use simple DC circuits to demonstrate this. However, quite a few students in electrical programmes f nd it dif cult to transpose the initial formula (11) into formula (11a) and (11b) or memorise all three equations. T us, before we start problem solving with DC circuits, we would like to brief y introduce you to an easy and practical method to select the right equation for your respective problem. We call it the triangle method and it is simple: Review formula (11), (11a) and (11b). You need to place formula (11), i.e. I = V into a triangle in the following manner: R

V I R

To use the triangle method, place your f ngertip over the factor you want to determine. T is will tell THEME 2.2.1 you to either multiply or divide the other two factors so that you can determine the third factor. Let us assume you want to determine resistance. Place a f ngertip over its symbol, i.e. the R, and you V will see that you must divide potential (V) by current (I). T erefore, the answer is R = I , which is formula (11b). If you are trying to determine potential, just put a f ngertip over its symbol, i.e. the V, and you will see that you must multiply current (I) by resistance (R).

FIGURE 6: HOW TO DETERMINE A FACTOR (UANTIT) IN OHM’S LAW

I = AMPERE (CURRENT) V R = OHM (RESISTANCE) I R V = VOLT (POTENTIAL DIFFERENCE)

V V V I R I R I R

V V R = V = I x R I = I R

Image source: GIZ/S4GJ A simple illustration of how to determine a factor (quantity) in Ohm’s law. Use the triangle method to select the right equation.

157 Example 4 Problem Determine the current using the magnitudes for potential and resistance indicated in the DC circuit below. Take care to use the correct units for each quantity.

Resistor 1 kΩ

THEME 2.2.1 Battery, two 4.5 V cells

Solution 1. Known quantities: R = 1 kΩ V = 9 V

2. Quantities to be determined: Current (I)

3. Analysis Use the triangle method to select the right equation for your respective problem and in addition review formula (11) and formula (11c). To calculate the current in the circuit, we are using formula:

V (11c) A = Ω

9 V V -3 A = 1 000 Ω =0.009 Ω = 0.009 A = 9 × 10 A = 9 mA

4. Answer T e current in the circuit has a magnitude of 9 milli ampere (mA).

Example 5 Problem How much current is required to operate a toaster with a supply of 220 volt and heater elements with a given resistance of 25 Ω ?

Solution 1. Known quantities: R = 25 kΩ V = 220 V

2. Quantities to be determined: Current (I)

3. Analysis Use the triangle method to select the right equation for your respective problem and in addition review formula (11) and formula (11c).

158 To calculate the current in the circuit, we are using formula:

V (11c) A = Ω

220 V V A = 25 Ω = 8.8 Ω = 8.8 A 4. Answer T e current required to operate the toaster is 8.8 ampere (A).

Example 6 Problem Determine the magnitude of potential which must be applied to ensure a current with a magnitude of 2 mA in a DC circuit with 1 kΩ resistor.

Solution 1. Known quantities: R = 1 kΩ I = 2 mA THEME 2.2.1

2. Quantities to be determined: Potential (V)

3. Analysis Use the triangle method to select the right equation for your respective problem and review formula (11a) and formula (11d). To determine the required potential in the circuit, we are using formula:

(11d) V = A × Ω V = 2 mA × 1 kΩ = 0.002 A × 1 000 Ω = ( 2 × 10-3) × (1 × 103) = 2 V 4. Answer T e potential required in the circuit is 2 volt (V).

Example 7 Problem An electric kettle requires a supply potential of 230 V and a current of 5 A to operate successfully. Determine the resistance of the kettle’s heating element.

Solution 1. Known quantities: V = 230 V I = 5 A

2. Quantities to be determined: Resistance (R)

3. Analysis Use the triangle method to select the right equation for your respective problem and review formula (11c) and formula (11d). To determine the resistance of the heating element of the kettle, we are using formula:

V (11d) Ω = A

230 V V Ω = 5 A = 46 A 46 Ω

4. Answer T e resistance of the heating element of the kettle is 46 ohm (Ω).

159 Example 8

As with Ohm’s law which describes the relationship between three quantities, i.e. current, potential and resistance, the relationship between power, current and potential can also be illustrated by the triangle method. Students who f nd it dif cult to transpose the initial formula (12) into formula (12a) and (12b) or have dif culty memorising all three equations can use the triangle method as an easy and practical method to select the right equation for the respective problem.

P V I THEME 2.2.1 Again, place your f ngertip over the factor you want to determine. T is will tell you to either multiply or divide the other two factors so that you can determine the third factor. Let us assume that you want to determine current. Just place a f ngertip over its symbol, i.e. the I, and you will see P that you must divide power (P) by potential (V). T erefore, the answer is I = V , which is formula (12a). If you are trying to determine potential, place a f ngertip over its symbol, i.e. the V, and you P will see that you must divide power (P) by current (I), which is formula (12b), i.e. V = I . FIGURE 7: HOW TO DETERMINE A FACTOR (UANTIT) IN THE RELATIONSHIP BETWEEN POWER, POTENTIAL AND CURRENT

I = AMPERE (CURRENT) P V = VOLT (POTENTIAL DIFFERENCE) V I P = WATT (POWER)

P V P V R V I I I

P P I = P = V x I V = V I

Image source: GIZ/S4GJ A simple illustration of how to determine a factor (quantity) in the relationship between power, potential and current. Use the triangle method to select the right equation.

160 Problem

Familiarise yourself with the circuit diagram and identify its elements. T e battery’s potential (VB) is set at 12 volt (V) and the current in the circuit is 0.1 ampere (A). T e potential drop (VL) across the load is 8 volt (V). Determine the power provided by the battery and the power absorbed by the load. Determine the electrical energy consumed af er 1 hour in watt (W). What type of circuit is present?

Resistor load VL - THEME 2.2.1

Battery, two 6 V cells

Solution 1. Known quantities:

VB = 12 V I = 0.1 A

VL = 8 V

2. Quantities to be determined:

Power (PB) provided by the battery

Power (PL) absorbed by the load Electrical energy consumed by the load af er 1 hour

3. Analysis Use the triangle method to select the right equation for your respective problem and review formula (12) and formula (12d).

To determine the power (PB) provided by the battery, we are using formula: (12d) W = V × A W = 12 V × 0.1 A = 1.2

To determine the power (PL) absorbed by the load, we are using formula: (12d) W = V × A W = 8 V × 0.1 A = 0.8

To determine the electrical energy consumed by the load af er 1 hour, we are using formula: (6a) E = W × h = Wh (electric energy values are expressed in watt hours) E = 0.8 W × 1 h = 0.8 Wh

4. Answers T e power provided by the battery is 1.2 watt (W). T e power absorbed by the load is 0.8 watt (W). T e electrical energy consumed by the load af er 1 hour is 0.8 watt hours (Wh). It is a DC circuit.

161 Exercises

For all the following calculations, use the approach outlined in the example section by f rst stating the problem and then following the steps to arrive at the solution (known quantities, quantities to be determined and analysis).

Exercise 1 Indicate the missing quantity symbols, and the units and their symbols in the table below.

Quantity Symbol SI unit (and symbol) resistance R ohm (Ω) power current

THEME 2.2.1 energy charge potential efﬁciency time work

Exercise 2 An electric bulb requires 0.25 A when connected to a 12 V supply. Calculate the resistance of the bulb.

Exercise 3 Determine the potential dif erence that must be applied to a 2 Ω resistor if the current passing through a DC circuit is 750 mA.

Exercise 4 List some materials, not the same as those listed in Table 1 and 2, which are either used as conductors or insulators. Indicate where these materials are likely to be used (in homes/of ces or industry).

Metal Material used as To be found Gold Conductor Industry (electronics)

162 Exercise 5 An electric kettle with a power rating of 2 kW is connected across a 230 V supply. Determine the following quantities: 1. Current (I) in ampere (A) 2. Resistance (R) of the heating element in ohm (Ω) 3. Electrical energy consumed af er 1 hour in watt (W)

Remember, that electrical power (P) can also be expressed in terms of electrical potential (V) and electrical current (I). We recommend using the triangle diagram method for power, current and potential to select the right equation to solve the f rst problem, i.e. determining current, and ohm’s law to solve the second problem. Using formula (6a) will be adequate in solving the third problem, i.e. the energy consumed by the kettle af er 1 hour.

Exercise 6 A 60 W electric bulb is connected across a 220 V supply. Determine the: 1. Current in ampere (A) 2. Filament resistance of the bulb in ohm (Ω) THEME 2.2.1

Exercise 7 An electric kettle is connected to a 230 V supply. T e resistance of its heating element is 20 Ω. Determine the: 1. Current in ampere (A) 2. Power rating of the kettle in watt (W).

Exercise 8 An electric heater requires 0.5 mega joule (MJ) of electrical energy and is connected to a 220 V supply for 30 minutes. Calculate the power rating of the heater.

Further Information (all materials are on the resource CD)

(i) Electric Forces and Electric Fields, Dr.Wackeroth, PHY102A, 2005. (ii) Active Learning Exercises for Teaching Second Level Electricity – Addressing Basic Mis- conceptions, Aisling Flynn & NCE-MSTL 2011. (iii) Basic Electrical Installation Work, Fif h Edition, Trevor Linsley, 2008.

163 Your own notes THEME 2.2.1

164 THEME 2.3.1 Unit 2.3 Unit

UNIT 2.3

DC CIRCUITS Introduction

T e previous units and themes focused on the key quantities relevant for electric circuits, including electric potential dif erence, current and resistance. T e conceptual signif cance of these technical terms has been introduced, their relationships expressed in simple mathematical equations and applied in practice to solve problems. T is last unit of Topic 2 will focus on simple electric circuits (DC) and their elements. T e principles of electric potential dif erence, current and resistance, dealt with in the previous unit, will be applied and the same mathematical equations will be used to analyse the relationship of key quantities in the circuits. Unit Outcomes

At the end of this unit, you should be able to: (i) Explain how a multimeter can be used to test and measure key quantities. (ii) Sketch series, parallel and series-parallel circuit diagrams. (iii) Use Ohm’s law and apply appropriate formulas in calculations. (iv) Conduct experiments to demonstrate Ohm’s law using multimeters for measuring. (v) List and explain the factors that may cause variations between measured and calculated values. Themes in this Unit

Unit 2.3 covers one theme only: T eme 2.3.1 Simple DC Circuits

165 THEME 2.3.1 SIMPLE DC CIRCUITS Introduction

Successfully performing electrical work requires the ability to read and interpret circuit diagrams. Misinterpretation of diagrams and manuals, for example when installing a PV system or wiring a house, could have serious consequences and could cause damages, complaints, penalties and costs. T us, a good understanding of how to interpret information from electrical diagrams is an essential competence. Keywords

Circuit diagrams Circuit symbols Ammeter Voltmeter Multimeter Variations (measured vs calculated values) Series circuits

THEME 2.3.1 Equivalent resistance Drop in potential Potential divider Parallel circuits Current divider Short circuit and overload Theme Outcomes

At the end of this theme, you should be able to: (i) Sketch series, parallel and series-parallel circuit diagrams. (ii) Use a multimeter to test and measure key quantities. (iii) Apply Ohm’s law in calculations and experiments. (iv) List and explain the factors that may cause variations between measured and calculated values.

Deﬁ nition of Terms Electrical Circuits An electric circuit is an interconnection of electrical elements or, more precisely, a complete path through which an electric current (I) can be conducted. Circuit Diagrams It is possible to describe simple electric circuits with words only, for example: ‘A circuit is a light bulb connected to a battery’. However, picturing a more complex circuit with only the help of words is not easy for many people and thus it is more appropriate to describe a circuit by using a drawing or a schematic diagram. T e latter has the added advantage that it follows international norms, so all circuit elements can easily be interpreted. T us, working according to schematic diagrams will limit the risks of misinterpretations of electric installations. Let us illustrate this with an example: You could describe an electric torch with words only, e.g. ‘A torch has a light bulb which is connected to a battery and one can operate the torch with the help of a switch’. But have you ever dismantled an electric torch to f nd out how it works? Look at the following drawing below which shows the arrangement of the parts inside a torch. Does such a drawing describe the electric circuits better than words only?

166 FIGURE 1: THE PARTS INSIDE AN ELECTRIC TORCH

Casing Reﬂector Metal switch contacts Slide switch

+ - + -

Lamp Lamp Metal THEME 2.3.1 Cells/battery ﬁlament contact spring connected in series

Image source: GIZ/S4GJ

A dif erent way of describing the electric circuit in a torch is by using a schematic diagram in which all relevant parts of the torch are represented by a few symbols, i.e. two single electric cells (two 1.5 V batteries), a switch and a bulb. T e lines in the diagram represent the metal conductors, including the casing, wires or metal contacts which connect the torch system together. In order for the torch circuit to function, a closed conducting path is required. Closing the switch completes the circuit and allows current to be conveyed through the circuit by means of the batteries (electromotive force). If the torch fails to function, even though the batteries have enough chemical energy and can still do work, you need to investigate whether the circuit is incomplete, e.g. if the metal parts of the switch make proper contact or whether the f lament of the bulb is broken.

FIGURE 2: A SIMPLE CIRCUIT DIAGRAM OF AN ELECTRIC TORCH

Single switch Filament bulb

Battery, two 1.5 V cells

Image source: GIZ/S4GJ

167 Circuit Symbols Electric circuit diagrams use conventional circuit symbols for all circuit elements, aiming to follow international norms so that all circuit elements can be interpreted in an accurate manner. Some circuit symbols used in circuit diagrams are shown below. A single cell, the DC power source for example, is represented by two horizontal parallel lines, i.e. one long and one short line. T e longer line represents the positive terminal, and the shorter line the negative terminal. T e DC power source provides the electromotive force (potential dif erence). Of en a battery comprises of multiple cells and the two terminals of a single cell in a battery are indicated by several pairs of lines. An open switch is generally represented by a break in a straight line, lif ing a portion of the line upward at a diagonal. A simple resistor in a circuit can be represented by two symbols, either an open rectangle or a zigzag line. Note that a resistor or a load can take the form of many dif erent components in an electric circuit, e.g. light bulbs or motors. Most of these components have their own unique symbols (see Figure 3 below). Lastly, straight lines are used to represent connecting wires between any two components of the circuit. We recommend to either memorise these symbols or to refer to Figure 3 until you become accustomed to all the symbols.

FIGURE 3: ELECTRICAL SMBOLS USED IN SCHEMATIC CIRCUIT DIAGRAMS THEME 2.3.1

Single Motor Filament bulb M switch Photovoltaic Earth/ module switch Battery,2cells Light Photovoltaic dependent A module resistor (LDR) Ammeter Resistor LED V Voltmeter Diode Wire

Image source: GIZ/S4GJ Your own notes

168 Different Types of Connections Let us assume we connect a battery with four cells and three small bulbs in a circuit. T ere are two ways to represent this arrangement:

FIGURE 4: THE TWO POSSIBLE ARRANGEMENTS OF A BATTER AND THREE LIGHT BULBS IN A CIRCUIT THEME 2.3.1

Image source: GIZ/S4GJ

In Figure 4, diagram 1 (lef ) presents the three light bulbs in such a way that the charge f owing through the circuit would pass through each of the three light bulbs in a consecutive fashion. T e sequence in which the bulbs are arranged is called a series circuit. T is is however not the only way to arrange the three bulbs. Apart from the consecutive or series connection, we can connect the three bulbs in such a manner that the wires coming from the two terminals branch of from each other. T e two branching locations, one coming from the positive terminal and the other from negative terminal of the battery, are referred to as nodes. Between these two nodes all three light bulbs are connected in parallel to each other and are jointly connected to the positive terminal via one node and to the negative terminal of the battery via the other node. T e sequence in which the bulbs are arranged in this circuit is called a parallel circuit.

T ese two examples illustrate the two main types of electric circuits, i.e. the series or the parallel circuit. But before we introduce you to the distinction between series and parallel connections and the ef ects they have on electrical quantities such as electric current, potential and resistance, we will take a short detour by f rst introducing you to testing and measuring of electrical quantities with the help of measuring devices. Testing and Measuring of Electrical uantities In practical work, a device called a multimeter is used to measure electrical quantities in circuits. A multimeter combines these three functions into a single instrument: (i) A voltmeter for measuring potential dif erence (V) across a component in volt (ii) An ammeter for measuring current (I) through a part of a circuit in ampere (iii) An ohmmeter for measuring resistance (R) of components in ohm

But before we deal with multimeters in more detail, it is important to have a clear idea of how meters are connected into circuits. Testing and Measuring Electric Current using an Ammeter An ammeter measures current (I) through a part of a circuit in ampere. Ammeters must have a very low resistance to prevent them from altering the behaviour of the circuit. To measure current, the ammeter needs to be connected in series within the circuit, i.e. you need to open or disconnect the circuit so that the ammeter can be connected to the circuit in series. T us, you need to consider the practical changes you need to make to a circuit in order to include the ammeter into the circuit.

169 FIGURE 5: HOW TO CONNECT AN AMMETER INTO A CIRCUIT

Image source: GIZ/S4GJ T e diagram shows how to connect an ammeter into a circuit (series connection).

THEME 2.3.1 Testing and Measuring Electric Potential using a Voltmeter A voltmeter measures potential dif erence (V) across a component in volt. To measure potential dif erence, the circuit does not need to be changed. T e voltmeter is connected in parallel across a circuit element or across two points of a wire where the measurement is to be made. It provides a parallel pathway in the circuit and thus, the meter requires very little current. Simply put, a voltmeter should have a very high resistance. Due to the fact that measurements of potential (volt) are usually easier to perform during practical work, volt measurements are far more of en performed than current measurements. FIGURE 6: HOW TO CONNECT A VOLTMETER TO A CIRCUIT

Image source: GIZ/S4GJ T e diagram shows how to connect a voltmeter to a circuit (parallel connection).

170 Testing and Measuring Electric Resistance using an Ohmmeter An ohmmeter measures the resistance (R) of components in ohm. By conveying a small current through the component and measuring the resulting potential, ohmmeters test whether individual circuit components are functioning correctly. T us, it is not possible to measure the resistance of a particular circuit element if the circuit is connected to a power supply. If you want to measure the resistance of an individual circuit component, you must either take the component out of the circuit or disconnect the power supply and test the respective component separately. Take care not to test circuit components with an ohmmeter in a live circuit as this could damage the meter.

FIGURE 7: HOW TO CONNECT AN OHMMETER TO A CIRCUIT ELEMENT

W THEME 2.3.1

Image source: GIZ/S4GJ T e diagram shows how to connect an ohmmeter to a circuit element (disconnected from the circuit or from the power supply). Multimeter As indicated earlier, a multimeter is an instrument that can measure electric current, potential dif erence and resistance. In other words, a multimeter has many meters built into it. You can select which meter you want to use by turning a central knob into dif erent positions. When using a multimeter as an ohmmeter, ensure that the circuit is not energised and that the component is removed from the circuit to avoid damaging the unit.

T ere are a range of multimeter types available. Today, the most common ones are digital multimeters that display the measurement in numbers, usually on a liquid crystal display. Two main types of digital multimeters can be dif erentiated: (i) Switched range multimeters (ii) Autoranging multimeters

Switched range multimeters have a central knob and an array of dif erent positions for the various ranges of measurement you might want to take. You need to manually choose the quantity and the range of your measurement, for example 20 V DC, in which case 20 V is the maximum potential which can be measured. In autoranging multimeters the central knob has fewer positions and the meter automatically adjusts its range for a chosen quantity, for example to V or mV. T us, all you need to do is switch the meter to the quantity you want to measure. T e autoranging multimeter is more convenient to use but is also more expensive than a switched range multimeter model.

171 FIGURE 8: MULTIMETER TPES

0.00 0.00

V~ OFF V= 1000 750 W 200 200 A= V mA 20 200 m OFF 2000 2000 10A m m 200 20 m m 2000 200 k m 200 k 10A 20 k W 2000 10ADC 10A

VmW A VmW A

COM COM THEME 2.3.1 Image source: GIZ/S4GJ Multimeter types. T e image shows a switched range (lef ) and an autoranging multimeter (right).

Analogue meters are still available and with this type of multimeter, a needle moves along dif erent scales. T is is usually dif cult to read accurately for beginners. Each type of multimeter has its advantages: Digital meters are very convenient as voltmeters due to their high resistance when compared to an analogue multimeter with a similar volt range. Typically, analogue multimeters have a very low resistance and are thus very sensitive for current measurements down to 50 µA. Only more expensive digital multimeters can of er this feature. Factors that may cause Variations between Measured and Calculated Values In multimeters, the following factors may cause variations between measured and calculated values: (i) Limitations of the instrument: When an instrument such as a multimeter is calibrated, it is compared against a standard. T e calibration accuracy of any instrument depends on the precision with which it is constructed. Multimeters are designed and mass produced, thus every instrument has a margin of error which is expressed as a percentage of the instrument’s full scale of def ection. In addition, any meter connected into a circuit will af ect that circuit to some degree. Ammeters should have a very low resistance to prevent altering the behaviour of the circuit and voltmeters should have a very high resistance. An average quality multimeter usually of ers a compromise, i.e. a reasonably low resistance for measuring current and a high enough resistance for measuring potential. Finally, multimeters can also be disturbed by strong magnetic f elds occurring in electric circuits. (ii) Limitations of the user: Users can set the instrument incorrectly or even misread the meter, especially in analogue meters where dif erent scales are used. Further, incorrect positioning of instruments in a circuit can also be a source of errors. Resistor Loads Connected in Series We declare two or more circuit elements (resistor loads) to be combined in series if an identical current (I) is passing through each of the elements. T us, in a series circuit an identical current (I) passes through all parts of the circuit as a result of the potential dif erence (V) supplied by a battery.

172 FIGURE 9: RESISTORS AS POTENTIAL DIVIDERS IN SERIES CONNECTIONS

R Current (I1 ) 2 Current (I2 )

- V2 + + -

R1 V3 V1 R3 - + Battery (VT ) THEME 2.3.1 Current (IT ) Current (I3 )

Image source: GIZ/S4GJ

Resistors as potential dividers in series connections. Each resistor load (R1 + R2 + R3) in a series circuit creates a drop in potential, while current (I) values remain constant, i.e. I1 = I2 = I3.

If, for example three resistors (R1 + R2 + R3) are connected in series, the sum of the potential (V1 + V2

+ V3) across the three resistors is equal to the total potential (VT) provided by the battery. T us, each resistor in the circuit (R1 + R2 + R3) creates a drop in potential, measured in volt across that respective resistor. Based on Ohm’s law, drop in potential (∆V) will be determined by current (I) and resistance (R). Since in a series circuit current remains constant, it is resistance which determines the respective drop in potential. We would need a few mathematical substitutions and Ohm’s law to illustrate this. Let us start with:

(13) VT = V1 + V2 + V3 (total potential is equal to the sum of potential drops across the three resistors)

Let us now apply Ohm’s law. Can you recall the equation to establish potential (V) based on current and resistance? You can, for example use the triangle method or maybe you still remember equation (11a) V = I × R, i.e. potential is equal to current times resistance. Earlier we determined that in a series circuit current (I) remains constant and passes through all parts of the circuit. Hence, if current (I) remains a constant, then according to Ohm’s law, each potential (V1 + V2 + V3) across the three resistors (R1 + R2 +

R3) can be expressed as:

(13a) V1 = I × R1 V2 = I × R2 V3 = I × R3

We can now combine and simplify the three expressions as:

(13b) VT = I × (R1 + R2 + R3)

or by applying Ohm’s law again

(13c) I = R1 + R2 + R3

173 If we assume that each of the three resistors (R1 + R2 + R3) has a resistivity of 100 Ω, we can replace all

the three resistors with one equivalent resistor Req, i.e. a resistor with a resistivity of 300 Ω. We can now simplify the above expressions (13b) and (13c) even further:

(13d) Req = R1 + R2 + R3 (T e equivalent resistance of any number of resistors connected in series is the sum of the individual resistances.)

FIGURE 10: TOTAL RESISTANCE (RE) IS EUAL TO THE SUM OF RESISTANCE OF THE INDIVIDUAL RESISTORS

R=eq123R+R+R R2 Req

R1 R3 THEME 2.3.1

Image source: GIZ/S4GJ

In series circuits the total resistance (Req) is equal to the sum of resistance of the individual resistors (R1 +

R2 + R3).

With this approach we want to illustrate a key principle: In a series circuit, the three resistors appear as a

single equivalent resistance with the value of Req. Simply put, when resistors are connected in series, the

total resistance (Req) is equal to the sum of resistance of the individual resistors.

T erefore let us conclude, in a series circuit the:

(i) Total resistance (Req) is: Req = R1 + R2 + R3

Which can read as: T e sum of the three resistors R1, R2 and R3 is equal to the total resistance

(Req).

(ii) Total potential (VT) is: VT = V1 + V2 + V3

Which can read as: T e sum of potential drops V1, V2, and V3 is equal to the total potential in the

circuit current (IT). T us, by substituting equation (13b), we can determine total potential (VT)

as: VT = I × Req

(iii) Current remains: I = constant, and can be expressed as: I = V Req

Based on the above, we can f nally describe resistor loads connected in series as potential dividers, due

to the fact that the total potential (VT), in our example provided by the battery, divides among the three resistors. T is is called the principle of potential division in a series circuit.

174 Application To illustrate the principle of potential division in a series circuit let us assume that three bulbs acting as resistor loads are connected together in series. T e same current is passing through each bulb. If the bulbs have the same rating they will all illuminate with the same brightness but, the brightness will be af ected if the number of bulbs is increased or decreased. It is important to note that if one bulb fails in a series circuit, the circuit is no longer a closed loop and the other bulbs will fail to light up. Resistor Loads Connected in Parallel We declare two or more circuit elements (resistor loads) to be combined in parallel if an identical potential (V) acts across each circuit element. T us, in a parallel circuit potential values remain constant, whereas current (I) will divide when passing through a resistor.

FIGURE 11: RESISTORS AS CURRENT DIVIDERS IN PARALLEL CONNECTIONS

I1 I3 I1 THEME 2.3.1

IT R1 R2 R3

Image source: GIZ/S4GJ

Resistors as current dividers in parallel connections. Each resistor load (R1 + R2 + R3) in a parallel circuit divides the current and only a fraction of the current passes through the load.

If, for example three resistors (R1 + R2 + R3) are connected in parallel the sum of current (I1 + I2 + I3) passing through the three resistors is equal to the total current (IT) available in the circuit. T us, each resistor in the circuit (R1 + R2 + R3) divides the current and only a fraction of the current passes through the load. T is concept is analogous to the concept of potential dividers in series connection, but in parallel connections it is current that gets divided and potential remains the same as it appears across each circuit element. Again, we need to do a few mathematical substitutions and apply Ohm’s law to illustrate the above statements. Let us start with:

(14) IT = I1 + I2 + I3 (total current is equal to the sum of the divided currents passing through three resistors)

Let us now apply Ohm’s law: We determined that potential (V) remains a constant and it follows that according to Ohm’s law, each divided current (I1 + I2 + I3) passing through the three resistors (R1 + R2 +

R3) can be expressed as:

V V V

(14a) I1 = R1 I2 = R2 I3 = R3

To determine the equivalent resistance (Req) in a parallel circuit, similar to what we have done in the series circuit, we substitute the (14a) equations into equation (14).

V V V V (14b) I = = ( + + ) T Req R1 R2 R3

175 Due to the fact that the same potential appears across each resistor, we can divide both sides by potential

(V) which leaves us with the equation for equivalent resistance (Req) in parallel circuits:

1 1 1 1 (14c) = + + Req R1 R2 R3

FIGURE 12: RESISTORS CONNECTED IN PARALLEL

1 1 1 1 = + + Req R1 R2 R3

V V

IT R1 R2 R3 Req THEME 2.3.1 IT

Image source: GIZ/S4GJ

Resistors connected in parallel R1 + R2 + R3 are equivalent to a single resistor (Req) with a resistance equal to the inverse of the sum of the inverse resistances, i.e. 1 = 1 + 1 + 1 . Req R1 R2 R3

T erefore, let us conclude that in a parallel circuit:

1 1 1 1 (i) Total resistance (R ) is: = + + eq Req R1 R2 R3

Which can read as: T e equivalent resistance (Req) is less than that of the smallest of the resistors.

(ii) Total current (IT) is: IT = I1 + I2 + I3

Which can read as: T e sum of the current I1, I2, and I3 is equal to the total circuit current (IT).

T us, by substituting equation (14b), we can determine the total circuit current (IT) as:

IT = V × ( Req )

(iii) Potential (V) remains: V = constant T e potential across the battery is the same as the potential across the resistors.

Based on the above we can f nally describe resistor loads connected in parallel as current dividers, due

to the fact that the total current (IT) divides while passing through the three resistors. T is is called the principle of current division in a parallel circuit.

176 Application To illustrate the principle of current division in a parallel circuit let us assume that three bulbs acting as resistor loads are connected together in parallel. T e same potential is passing through each bulb. If the bulbs have the same rating they will all illuminate with the same brightness and the brightness will not be af ected if the number of bulbs is increased or decreased. But adding more bulbs will cause a higher current. It is important to note that if one bulb fails in a parallel circuit the other bulbs will still light up. DC Generators Connected in Series and in Parallel T e previous sections described the behaviour of resistor loads connected in series and introduced us to the principle of potential and current division. If resistor loads connected in series seem to act as potential dividers, how do batteries and other DC power supplies behave when connected in series? Similarly, if resistor loads connected in parallel seem to act as current dividers, how do batteries and other DC power supplies behave when connected in parallel?

Let us f rst consider DC generators connected in series. We connect six identical 1.5 V cells (batteries), one af er the other, in series while measuring each step’s potential (V) and current (I) with a multimeter. T e results of this experiment are indicated in Table 1 below: FIGURE 13: 1.5 V CELLS (BATTERIES) ARE CONNECTED IN SERIES THEME 2.3.1 A

R1 V

Image source: GIZ/S4GJ Six 1.5 V cells (batteries) are connected in series and measurements for potential (V) and current (I) are taken.

TABLE 1: DETERMINATION OF POTENTIAL (V ) AND CURRENT (I) FOR BATTERIES CONNECTED IN SERIES

Number of batteries Potential measured (V) Current measured (mA) 1 1,5 100 2 3 100 3 4,5 100 4 6 100 5 7,5 100 6 9 100

We can conclude from these results that when batteries are connected in series and the circuit has a constant resistance (R), the potential of each battery is added together, but current remains the same.

Let us now connect the six batteries in parallel, one af er the other while measuring potential (V) and current (I). T e results are indicated in Table 2 below:

177 FIGURE 14: SI 1.5 V CELLS (BATTERIES) ARE CONNECTED IN PARALLEL

R1 V

Image source: GIZ/S4GJ Six 1.5 V cells (batteries) are connected in parallel and measurements for potential (V) and current (I) are taken. THEME 2.3.1 TABLE 2: DETERMINATION OF POTENTIAL (V ) AND CURRENT (I) FOR BATTERIES CONNECTED IN PARALLEL

Number of batteries Potential measured (V) Current measured (mA)

1 1,5 100

2 1.5 200

3 1,5 300

4 1.5 400

5 1,5 500

6 1.5 600

We can notice from these results that when batteries are connected in parallel and the circuit has a constant resistance (R), the potential of each battery remains the same, but the current of each battery is added together.

T ese two principles for connecting DC generators are for instance used to build photovoltaic modules from individual PV cells. T e PV cells in a module can be wired to any desired potential and current, and photovoltaic modules can then be connected with each other to create PV arrays. We will explore these principles in more detail in Topic 4.

178 Short Circuit and Overloading

A short circuit can occur when an unintentionally high current or even the total current of a circuit (IT) passes through a shortened path in the circuit, i.e. through a shortened path of the circuit with very low resistance instead of passing through resistor loads.

Overloading can occur when too much current is passing through a conductor. T is for example can be the consequence of a short circuit or by connecting too many resistor loads (appliances) in a parallel circuit resulting in a very small total resistance (Req). Remember, total resistance (Req) in a parallel circuit 1 1 1 1 is def ned as: = + + = inverse resistances! T us, the equivalent resistance (R ) is smaller Req R1 R2 R3 eq than even the smallest of the individual resistances and adding more resistor loads to the circuit will result in an even smaller total resistance (Req). T e parallel circuit might then no longer be able to handle the increasing current, transferring too much thermal energy (heat) which can damage appliances and may even cause f re.

FIGURE 15: A DIAGRAM INDICATING A SHORT CIRCUIT THEME 2.3.1 I1 I2 I3

IT R1 R2 R3

Image source: GIZ/S4GJ

A diagram indicating a short circuit: IT = I3, I1 = 0, I2 = 0 and R3= 0. T is can for example happen when uncovered portions of the circuit touch or cross.

179 Examples and Experiments

Example 1: (groupwork)

For the following experiments you will need a battery (6 or 9 volt), a prototype board, four identical small bulbs (3 - 4 watt), sockets, and some cables (around 0.5 mm2 diameter).

Experiment 1

Construct a series circuit consisting of a battery and three identical light bulbs as shown in Figure 16. Ensure that all bulbs illuminate. Now unscrew bulb 1 from its socket and observe that bulb 2 and 3 no longer light up. Screw bulb 1 back into its socket and unscrew bulb 3 instead. Observe that bulb 1 and 2 will no longer light up.

FIGURE 16: CONSTRUCT A SERIES CIRCUIT

Bulb 2 THEME 2.3.1

Bulb 1 Bulb 3

Image source: GIZ/S4GJ Construct a series circuit for Experiment 1 as shown in the diagram.

Experiment 2

Use the circuit of Experiment 1 and observe that the brightness of all three bulbs is identical. Remove bulb 3 from the circuit and re-wire the circuit so that it includes only two bulbs. Observe that the brightness of the remaining bulbs is equal, but brighter than when there were three bulbs in the circuit. Remove the second bulb and re-wire the circuit so that the circuit includes only one bulb. Observe that the remaining bulb lights up even brighter than before.

Experiment 3

Construct a parallel-series circuit consisting of a battery and four identical light bulbs as shown in Figure 17. Ensure that all bulbs illuminate. Wire three bulbs (1, 2, and 3) in parallel. Add a fourth bulb (bulb 4) outside the parallel circuit. Bulb 4 will function as an indicator bulb for the

total current (IT) in the entire circuit. Observe that the brightness of bulb 1, 2 and 3 is the same. T e indicator bulb 4 lights up as well, but it is brighter than the three bulbs in the parallel circuit. Unscrew bulb 1 from its socket and observe that bulb 2 and 3 remain illuminated and that the brightness of indicator bulb 4 becomes dimmer than when all three bulbs 1, 2 and 3 were present in the parallel circuit.

180 FIGURE 17: CONSTRUCT A SERIES-PARALLEL CIRCUIT

Bulb 1, 2 and 3

Indicator Bulb

Image source: GIZ/S4GJ Construct a series-parallel circuit for Experiment 3 as shown in the diagram.

Questions THEME 2.3.1 Answer the following questions (groupwork):

(i) In which type of circuit does charge f ow through every light bulb in the circuit? a. Series circuit (Experiment 1 and 2) b. Series-parallel circuit (Experiment 3) c. Both series and serious-parallel circuits (Experiment 1, 2 and 3) d. Neither series nor parallel circuits (Experiment 1, 2 and 3)

(ii) Which type of circuit is characterised by the presence of branch locations (nodes) ? a. Series circuit (Experiment 1 and 2) b. Series-parallel circuit (Experiment 3) c. Both series and series-parallel circuits (Experiment 1, 2 and 3) d. Neither series nor parallel circuits (Experiment 1, 2 and 3)

(iii) Which one of the following conclusions is consistent with your observations in Experiment 1 and 2? a. Increasing the number of bulbs in the series circuit will decrease the current. b. Identical bulbs in a series circuit will light up equally bright regardless of their location. c. If one bulb in a series circuit is removed (fails), all other bulbs in the circuit remain illuminated. d. T e brightness of bulbs in a series circuit is inversely proportional to the number of bulbs.

(iv) Which of the following conclusions is supported by the f ndings of Experiment 2? a. T e more bulbs are added to a series circuit, the more the current decreases. b. Adding more bulbs to a series circuit causes each bulb to become dimmer. c. Current in a series circuit is af ected by the number of bulbs in the circuit. d. Bulbs that are closer to the battery light up brighter than bulbs that are further away from the battery.

(v) Which statement most accurately describes the purpose of Experiment 2? a. T e purpose of Experiment 2 was to determine how many bulbs can be illuminated by the battery. b. T e purpose of Experiment 2 was to determine if all branched bulbs would lighten up. c. T e purpose of Experiment 2 was to determine the current ef ects by decreasing the number of bulbs. d. T e purpose of Experiment 2 was to determine that unscrewing a bulb in the circuit would interrupt the charge f ow of the entire circuit.

181 (vi) Recall Ohm’s law describing the relationship between current, potential and resistance: Current (I) is inversely proportional to the overall resistance (R) in the circuit and directly proportional to the electric potential dif erence (V). Based on the results in Experiment 2, which one of the following series circuits has the greatest resistance? a. A series circuit with only 1 bulb. b. A series circuit with 2 bulbs. c. A series circuit with 3 bulbs. d. Resistance (R) is not dependent on the number of bulbs.

(vii) Recall Ohm’s law describing the relationship between current, potential and resistance: Current (I) is inversely proportional to the overall resistance (R) in the circuit and directly proportional to the electric potential dif erence (V). Based on the results in Experiment 2, which one of the following statements describes the ef ect of the number of bulbs on current and overall resistance best? a. Increasing the number of bulbs will cause an increase in both current and resistance. b. Increasing the number of bulbs will cause a decrease in both current and resistance. c. Increasing the number of bulbs will cause an increase in current and a decrease in resistance. d. Increasing the number of bulbs will cause a decrease in current and an

THEME 2.3.1 increase in resistance.

(viii) Which one of the following statements describes the function of the indicator bulb 4 in Ex- periment 3? a. Bulb 4 indicated whether the circuit was a series or a parallel circuit. b. Bulb 4 was included to have a series-parallel circuit. c. Bulb 4 indicated the rate of charge f ow (current) within the circuit. d. Bulb 4 controlled the amount of current in the parallel circuit.

(ix) Recall Ohm’s law describing the relationship between current, potential and resistance: Current (I) is inversely proportional to the overall resistance (R) in the circuit and directly proportional to the electric potential dif erence (V). Based on the results in Experiment 3, which of the following parallel circuits has the greatest resistance? a. A series circuit with only 1 bulb. b. A series circuit with 2 bulbs. c. A series circuit with 3 bulbs. d. Resistance (R) is not dependent on the number of bulbs.

(x) Which of the following statements describes the f ndings of Experiments 1, 2 and 3? a. Adding more bulbs in a series circuit decreases the current. In a parallel circuit, the opposite is the case. b. If one bulb is removed from a series circuit, the other bulbs do not work. In a parallel circuit, the opposite is the case. c. Decreasing the number of bulbs in a series circuit increases the current. In a parallel circuit, the opposite is the case. d. In series circuits, the bulb closest to the battery is the brightest. In a parallel circuit, the opposite is the case.

Example 2: For the following experiment you need a multimeter, a battery (6 or 9 volt), a prototype board, four 10 kΩ resistors (colour rings on resistor: brown, black, orange), four 100 Ω resistors (colour rings on resistor: brown, black, brown), and some cables (around 0.5 mm2 diameter). Connect the two meter probes to the multimeter in the following way: (i) T e black lead always needs to be connected to the socket marked COM, short for COM- MON. (ii) T e red lead needs to be connected to the socket labelled V mA. (iii) We do not use the 10A socket for the following experiments. (iv) Make sure the multimeter functions properly and has a full battery.

182 Experiment 1: Measurements of potential (volt)

Have a look at the circuit diagram shown below and assemble the circuit using a battery, a prototype board and the four 10 kΩ resistors. If you use a switched range multimeter, set the central knob to 20 V DC. In this case 20 V is the maximum potential which you can measure. If you have an autoranging multimeter set the central knob to V (volt) so that the meter can automatically adjust its range to V or mV. Measure the potential of the battery and then measure the potential at A, B and C. Record your measurements in the table below. FIGURE 18: VOLT MEASUREMENT ACROSS RESISTORS AND BATTER

ABC V

R1 R2 R3 R4 THEME 2.3.1

Image source: GIZ/S4GJ Volt measurement across resistors and battery. In this circuit the four 10 kΩ resistors are connected in series. T e voltmeter is connected in parallel across the resistors at three dif erent points and across the battery.

TABLE 3: VOLT MEASUREMENT ACROSS RESISTORS

Measurements taken across Volt

Battery Vbattery

Point A V1

Point B V2

Point C V3 Volt measurement across resistors at three dif erent points and across the battery.

Ref ection T e voltmeter measures potential dif erence (V) across selected components in volt. To measure potential dif erence, the circuit does not need to be changed. T e four resistors were connected in series and at each point (A, B, C) a drop in potential could be registered (see values in volt in the above table). T us, the measurements/results indicate that each resistor received a share of the potential provided by the battery and thus acted as a potential divider in the circuit. In other words, the potential of the battery is equal to the sum of drop in potential. T is concept can be expressed mathematically by the following equation:

ΔVbattery = ΔV1 + ΔV2 + ΔV3

183 Exercises

Exercise 1: Calculations and circuit drawing

For all the following calculations, use the approach outlined in the previous themes by f rst stating the problem and then following the steps to f nd the solution (known quantities, quantities to be determined and analysis).

(i) Two resistors of 10 Ω and 30 Ω are connected in parallel and connected across a 12 V battery. Draw and label the circuit diagram and determine:

a. Total resistance (Req)

b. Total current (IT)

R2 THEME 2.3.1

(ii) T ree resistors of 10 Ω, 30 Ω and 25 Ω are connected in series across a 12 V battery. Draw and label the circuit diagram and calculate:

a. Total resistance (Req)

b. Total current (IT) c. Potential drop across each resistor

R1 R3

(iii) T ree resistors of 2 Ω, 6 Ω and 4 Ω are connected in series across a 6 V battery. Draw and label the circuit diagram and determine:

a. Total resistance (Req) b. Current passing through the 6 Ω resistor

(iv) Two resistors of 2 Ω and 6 Ω are connected in parallel. T is combination is then connected in series with a 4 Ω resistor. T e potential of the whole circuit is 12 V. Draw and label the circuit diagram and calculate the following: a. Combined resistance in the parallel circuit

b. Total resistance (Req) in the circuit

c. Total current (IT) d. Drop of potential across each resistor e. Current f owing through the 6 Ω resistor f. Current f owing through the 2 Ω resistor

184 ABC V

R1 R2 R3 R4

(v) Use Ohm’s law and apply the appropriate equations: An electric iron is rated 230 V / 1 000 W. Calculate the current required from the supply.

(vi) Use Ohm’s law and apply the appropriate equations: A geyser connected across a 230 V supply is rated 2 kW. Calculate the resistance of the geyser element. THEME 2.3.1 (vii) Use Ohm’s law and apply the appropriate equations: An electric bulb requires 2 A and is connected across a 220 V supply. Calculate the resistance of the bulb and the power absorbed in kW.

(viii) Use Ohm’s law and apply the appropriate equations: Calculate the current required by a 40 W bulb which is connected across a 220 V supply. If the bulb in question is replaced by a 100 W bulb, which current is required?

Exercise 2: Connecting PV modules (DC generators in series and parallel)

For the following experiment you need to focus on completing the example designs below on paper. Remember, when PV cells or modules are connected in series, the nominal potential of the PV system is increased and current remains constant. T us, connect positive leads (+) to negative leads (-) to wire the PV circuits in series. Remember, when PV cells or modules are connected in parallel, the nominal current in the PV system is increased and potential remains constant. T us, connect positive leads (+) to positive leads and negative leads (-) to negative leads to wire the PV circuits in parallel. T e positive leads are on top and the negative leads are on the bottom of the modules.

Complete the diagrams below by wiring the PV modules together in series or parallel to generate the required potential. Let us assume that each module used in the diagrams below is rated at 12 V and 4 A.

(i) Design a 12 V system with four modules. Indicate the values for potential and current in your solution...... V ...... A

+ + + +

- - - -

185 (ii) Design a 24 V system with four modules. Indicate the values for potential and current in your solution...... V ...... A + + + +

- - - - (iii) Design a 48 V system with eight modules. Indicate the values for potential and current in your solution...... V ...... A + + + + THEME 2.3.1

- - - - + + + +

- - - -

(iv) Design a 24 V system with eight modules. Indicate the values for potential and current in your solution...... V ...... A + + + +

- - - - + + + +

- - - - 186 (v) Design a 24 V system with ten modules. Indicate the values for potential and current in your solution...... V ...... A + + + + +

- - - - -

+ + + + + THEME 2.3.1

- - - - -

Further Information (all materials are on the resource CD)

(i) How to use a Digital Multimeter, Ted Roberts, 2010. (ii) Basic Electrical Installation Work, Fif h Edition, Trevor Linsley, 2008.

Your own notes

187 Smart solutions – aren’t they?! COMIC

188 COMIC

189 Your own notes NOTES

190 TOPIC TOPIC

Occupational Health and Safety

Topic Overview

Renewable energy technology workplaces, such as the construction, installation or manufacturing sites of photovoltaic arrays, are not much different to conventional industries when it comes to health and safety. The health and safety of employees at the workplace is a fundamental issue which cannot simply be left to self-regulation by the parties involved. In South Africa, occupational health and safety is regulated by common law and statute. The Occupational Health and Safety Act (OHSA, Act 95 of 1993, on the included CD) outlines a series of regulations to protect the safety of workers. The OHSA not only outlines the employer’s obligation to provide a safe working environment, but also stresses the health and safety obligations of employees. Consequently, it is highly important for both employers and employees to know and understand their respective occupational health and safety obligations and rights. Thus, this topic aims to inform you on the relevant safety obligations of both employees and employers.

Topic 3 covers only one unit: Unit 3.1 Safe Work Practices

191 Unit 3.1 Unit

UNIT 3.1: SAFE WORK PRACTICES Introduction

T e OHSA regulates who is responsible for health and safety in the workplace and also explains workers’ rights in terms of health and safety. T e Act places the main burden for providing a healthy and safe workplace on employers, but also indicates the obligations of employees. It sets up two workplace structures that allow and encourage the involvement of employees in health and safety programmes at the workplace. T ese two structures are (i) health and safety representatives, and (ii) health and safety committees. If these two structures are taken up seriously by the workers, it will allow employees to take on a meaningful role with wide-ranging responsibilities at their workplaces.

Health and safety issues in the renewable energy industries, be it in construction, installation or manufacturing, are not much dif erent to conventional industry segments. Working on PV installations or wind turbine projects, for example, could involve high-risk tasks which need to be appropriately addressed. As renewable industry segments grow, more people will be employed and health risks at the workplace thereby potentially increase. Appropriate safety standards and procedures in order to minimise risks need to be known and understood by the PV installer or the wind turbine technician. T us, the following themes aim to introduce you to relevant health and safety terms, to hazards associated with the industry and to the importance of following rigid safety procedures.

192 FIGURE 1: CAN YOU IDENTIFY ALL POTENTIAL SITE HAZARDS AT THIS WORK FACILITY? UNIT 3.1

Image source: GIZ/S4GJ Unit Outcomes

At the end of this unit, you should be able to: (i) Explain basic terms used in health and safety. (ii) Identify and explain workplace health and safety. (iii) Identify and explain potential workplace hazards. (iv) Explain the importance of clear and ef ective communication in the workplace. (v) Explain how a work area should be arranged to minimise accidents and injury. (vi) Design a health and safety checklist that can be used at the workplace/ learning institution for accident prevention. (vii) Explain the ef ect and consequences of electrical shock and burns on the human body. (viii) Explain the ef ect and consequences of electrical accidents on property. (ix) Explain and demonstrate the correct procedures for isolation of electrical equipment.

Themes in this Unit

Unit 3.1 covers f ve themes: T eme 3.1.1 Basic Terms used in Health and Safety T eme 3.1.2 Workplace Health and Safety T eme 3.1.3 Workplace Hazards T eme 3.1.4 Minimising Accidents through Clear Communication and Health and Safety Checklists T eme 3.1.5 Ef ects and Consequences of Electrical Accidents on the Human Body and on Property

193 THEME 3.1.1 BASIC TERMS USED IN HEALTH AND SAFETY

Introduction

Occupational health and safety is relevant to all industries or businesses and af ects all aspects of work. Before a detailed discussion on health and safety can take place, it would be useful to understand the most basic technical terms. Keywords

THEME 3.1.1 Accidents Controls Danger zone Hazard Injury Risk Safety Task Work practices Theme Outcomes

At the end of this theme, you should be familiar with the basic terms used in health and safety and be able to explain some basic safety facts. Deﬁ nition of Terms Accidents An accident can be def ned as an unplanned and uncontrolled event caused by unsafe acts or unsafe conditions, resulting in physical harm to a person or damage to property. Accident Investigation T e process of systematically gathering and analysing information about an accident is called an accident investigation. T is is done for the purpose of identifying causes and making recommendations to prevent similar accidents from happening again. Accident Prevention Accident prevention is the systematic application of recognised principles to reduce incidents, accidents, or the accident potential of a specif c task in a certain job.

194 FIGURE 1: KEEP YOUR WORK ENVIRONMENT ACCIDENT FREE PEOPLE FIRST THEME 3.1.1

KEEP EVERYONE SAFE

Image source: GIZ/S4GJ T is poster of ers a direct and dynamic message that is hard to miss. Such posters can be displayed at places where employees congregate so that the message gets across to everyone. Controls T ese are measures designed to eliminate or reduce hazards or hazardous exposures. In most cases, the preferred approach is to eliminate the source of hazards, for example, noise. When elimination is not possible, substitution of loud equipment for quieter equipment may be the next best alternative to protect workers. If the hazardous noise can neither be controlled through elimination nor substitution, engineering controls may be installed to reduce noise to safer levels. Engineering controls require physical changes to the workplace, such as redesigning equipment to eliminate noise sources and constructing barriers that prevent noise from reaching a worker. If it is not possible to remove the hazard through elimination, substitution or engineering controls, the next step

195 is to reduce exposure through the use of administrative controls, for example, an employer may change an employee’s work schedule to avoid too much noise. T e use of personal protective equipment (PPE), such as ear plugs or other hearing protection devices, is the last option in the hierarchy of control. PPE is generally less ef ective than elimination, substitution and engineering controls, because they rely on human actions to reduce noise. Used in combination with other levels of control, such as administrative controls, PPE may provide worker protection when engineering controls do not adequately remove the identif ed hazard.

FIGURE 2: HIERARCHY OF HAZARD CONTROL

Most Remove Elimination THEME 3.1.1 effective hazard

Replace Substitution hazard

Isolate Engineering controls hazard

Administrative Change controls work processes

Least PPE Protect effective against hazard

Image source: GIZ/S4GJ Hierarchy of hazard control with the most ef ective measures illustrated on top and the least ef ective below.

Dangerous Occurrence T is is a near miss which could have led to serious injury or loss of life. Danger Zones T ese are areas or locations where the probability of health risks or injuries is high, for example in the vicinity of running saw blades or working underneath heavy loads. Emergency Plan Detailed procedures for responding to an emergency are outlined in an emergency plan. An emergency plan would come into force during emergencies, such as a f re or explosion, a chemical spill or an electrical shock. Such a plan is necessary to keep order and to minimise the negative ef ects of a disaster. Hazard A hazard is the potential of any machine, equipment, process, material or physical factor to cause harm to people or damage to property or the environment. Health In an occupational context, health aims to protect humans from injuries and illnesses resulting from materials, processes or procedures at the workplace. Health and Safety Policy A policy is a statement of intent, and a commitment to plan for coordinated management action. A health and safety policy should provide a clear indication of a company’s objectives and must provide directions for health and safety programmes. T e following is an example of an occupational health and safety policy statement:

196 ABC Transport OHS policy

January 1, 2015

To all employees,

At ABC Transport the safety and health of our employees comes ﬁ rst. Management is committed to do everything possible to prevent injuries and to maintain a healthy work environment. To this end:

1) All managers and supervisors are responsible for ensuring that THEME 3.1.1 their team members (employees) are trained in approved work procedures to obtain optimal output without accidents and injuries, and to ensure that employees follow safe work methods and all related regulations. 2) All personnel are required to support the OHS policy and make safety and health a part of their daily routine. 3) All personnel will be held accountable for implementing this policy. 4) All relevant laws and regulations are incorporated into our policy as minimum standards.

Peter Smith Company Director

Incident An incident is the occurrence of an undesirable event which causes or could cause an injury, illness or disease to a person and/or damage to plant equipment, and as a consequence, the interruption of business operations. Injury Any damaging physical force which is applied to the human body, leaving a person harmed or weakened in any way. Injury Analysis T is is the process of systematically evaluating injury statistics to identify trends in categories, including age, gender, occupation, body parts, machinery involved, process or work activity involved, time of day, location, frequency and severity. Machine Guarding Machine guarding is a precautionary safety feature on manufacturing or other engineering equipment. Usually, it is a shield or device covering hazardous areas of a machine to prevent contact with body parts or to control hazards like noise from exiting the machine. A guard is, for example, used on a circular saw for safety purposes so that an operator does not get injured. Machine guarding is of en the f rst line of defence protecting operators from injury while working on or around industrial machinery during normal operations.

197 FIGURE 3: EXAMPLES OF MACHINE GUARDING FOR A BENCH GRINDER AND A VERTICAL MILLING PRESS THEME 3.1.1

Image source: GIZ/S4GJ

Your own notes

198 Material Safety Data Sheet (MSDS) A form that contains detailed information about the possible health and safety hazards of a product and how to safely store, use and handle the product correctly. Suppliers must provide a MSDS for all hazardous materials.

FIGURE 4: PAGE 1 OF A MATERIAL SAFETY DATA SHEET

Health 4 Contact information: 0 Company name Fire 0 4 0 Company address Reactivity 0 Company contact numbers Personal E Protection THEME 3.1.1 Material Safety Data Sheet Potassium dichromate MSDS A: Chemical Product Identifcation ProductName:Potassium dichromate CatalogCodes: SLP5455, SLP2629 CAS#: 7778-50-9 RTECS: HX7680000 TSCA: TSCA8(b)inventory: Potassium dichromate CI#: Not available. Synonym:Bichromateofpotash; Dipotassium Dichromate; Potassium bichromate; Potassium dichromate(VI) Chemical Name: Not available. Chemical Formula: K2Cr2O7

B: Composition and Information on Ingredients Composition: Name: Potassium dichromate CAS#: 7778-50-9 %byWeight: 100 Toxicological Data on Ingredients: Potassium dichromate LD50: Not available. LC50: Not available.

C: Hazards Identifcation PotentialAcute Health Efects: Extremely hazardous in case of skin contact (permeator). Very hazardousin caseofskin contact (irritant),ofeye contact (irritant), of ingestion, . Hazardous in case of skincontact (corrosive, sensitizer),ofeye contact (corrosive),of inhalation (lung irritant). Prolonged exposure may result in skin burns and ulcerations.Over-exposurebyinhalation may cause respiratory irritation. Severe over-exposure can result in death. Inﬂammation of the eyeis characterized by redness, watering, and itching. Skin inﬂammation is characterized by itching, scaling, reddening, or,occasionally, blistering.

Potential Chronic Health Efects: Slightly hazardous in case of skincontact (sensitizer). CARCINOGENIC EFFECTS: ClassiﬁedA1(Conﬁrmed forhuman.) by ACGIH. MUTAGENIC EFFECTS: Mutagenicfor mammalian somatic cells. Mutagenic forbacteria and/or yeast. TERATOGENIC EFFECTS: Not available. DEVELOPMENTAL TOXICITY: Not available. The substancemay be toxic to blood, kidneys, lungs, liver, upper respiratory tract, skin, eyes. Repeatedor prolonged exposureto the substance can produce target organs damage. Repeated exposure to a highly toxic material may producegeneral deterioration of health by an accumulation in one or many human organs.

Image source: GIZ/S4GJ Page 1 of a Material Safety Data Sheet (MSDS) for potassium dichromate, a common inorganic chemical reagent most of en used in various laboratory and industrial applications.

199 Near Misses Near misses are incidents where no injury or property damage has occurred, but could potentially have happened. Risk Risk is the probability of a worker being injured and suf ering from a workplace related incident, or the probability of damage to property or the environment as a result of a workplace-related hazard. Safety Safety is the state of being free from danger or risk. Task A set of actions or sequences that make up a discrete part of a job are called a task. A job is a set of tasks

THEME 3.1.1 and work-related responsibilities designed to be performed by an individual in return for payment. Every job is made up of a collection of tasks. For example, carrying PV panels onto a roof and connecting them are tasks of a PV installer or electrician. Task Analysis A technique used to identify, evaluate and control health and safety hazards linked to particular tasks. A task analysis systematically breaks tasks down into their basic components. T is allows each step of the process to be thoroughly evaluated. Workplace Inspection A regular and careful check of a workplace facility or part of a workplace in order to identify potential health and safety hazards and to recommend corrective action is called a workplace inspection. Work Practices Procedures for carrying out specif c tasks which, when followed, will ensure that a worker’s exposure to hazardous situations, substances or physical agents is controlled by the manner in which the work is carried out.

Your own notes

200 Exercises

(i) With respect to health and safety, brief y explain the following terms using the table below:

Terms Explanation

Safety

Accidents THEME 3.1.1

Risk

Emergency plan

Machine guarding

Workplace inspection

Material Safety Data Sheet (MSDS)

Hazard

(ii) Review the section on ‘controls’, particularly Figure 2 ‘Hierarchy of hazard control’. Indi- cate which kind of measures have been introduced at your college workshops. Are these measures ef ective or not so ef ective? If they are not ef ective, discuss what must still be done to turn them into ef ective hazard control measures.

(iii) Apply some basic safety facts by answering the following four questions: 1. Common types of hazards at work include: a) Electrical hazards b) Slips and trips c) Excessive noise d) All of the above

2. T e best way to f x a hazard is to: a) Substitute it with something less dangerous b) Remove (eliminate) the hazard c) Add safeguards d) Use personal protective equipment

201 3. Material Safety Data Sheets (MSDS) provide essential information about: a) Personal protective equipment b) Hazardous substances c) Safe lif ing techniques for heavy objects d) Equipment used at work

4. Assessing risks involves: a) Working out how likely it is that a hazard will harm someone b) Working out how dif cult it will be to eliminate a hazard c) Working out how likely it is that a hazard will harm someone and how badly they could be hurt d) Keeping an eye out for things that might cause injury or harm THEME 3.1.1

Further Information (all materials are on the resource CD)

(i) Amended Occupational Health and Safety Act (OHSA) (ii) Glossary of Occupational Health and Safety Term, www.iapa.ca

Your own notes

202 THEME 3.1.2 WORKPLACE HEALTH AND SAFETY

Introduction

Creating a safe workplace is a must for any company and organisation and is one of the best ways to retain staf . At the same time, safe workplaces also maximise production time. For some new workers it may seem cumbersome having to implement safe work practices, i.e. using safety equipment and respecting safety signage. However, the consequences of doing nothing or too little with regards to safety can be severe. Employers have responsibilities regarding health and safety in the workplace and need to ensure that appropriate controls are in place to avoid unsafe work conditions. Furthermore, it is

important that employees do not create health and safety problems for themselves or for their colleagues. THEME 3.1.2 Keywords

Unsafe acts Unsafe conditions Safety signs Personal protective equipment Lif ing and handling Working at heights Noise Flammable and explosive substances Stress and violence HIV/AIDS at the workplace Theme Outcome

At the end of this theme, you should be able to identify and explain some relevant and basic workplace health and safety measures. Deﬁ nition of Terms Unsafe Acts Human error may cause actions or incidents which could in turn result in an injury, illness or damage. Unsafe acts may include: (i) Working at unsafe speed (ii) Working without authority (iii) Using equipment that you do not know how to use (iv) Not using safety devices correctly or using the wrong tool for the job (v) Taking chances (vi) Not adhering to worksite procedures (vii) Fooling around or “horseplay” (viii) Not using personal protective equipment correctly (ix) Working in an unsafe position (x) Working on moving machinery Unsafe Conditions T ese include any deviation from accepted safety standards which consequently may cause accidents or incidents. Examples are: (i) Lack of machine guards or lockouts (ii) Poor planning or poor work (iii) Overcrowding at a workplace (iv) Poor lighting at a workplace (v) Poor ventilation at a workplace (vi) Lack of preventative maintenance (vii) Poor housekeeping

203 Reports T e vast majority of all work-related accidents are due to human errors and most accidents could have been avoided by being proactive. As can be seen in the accident pyramid, the base is where we must concentrate. In fact, we of en forget what happens at this level. Everything must be reported, because: (i) Nothing can be learned from unreported incidents. (ii) Near misses are of en predictors of future serious accidents. (iii) Potential hazards can be corrected and employees can be of ered training.

FIGURE 1: THE ACCIDENT PYRAMID THEME 3.1.2 1 fatal injury

10 serious injuries

30 damages to property

600 near misses

Image source: GIZ/S4GJ For every fatal injury, there are 10 serious accidents, 30 property damage incidents and 600 incidents with no visible injury or damage known as “near misses”. T e ratio of near misses to fatal injuries (1:600) is of en expressed as a pyramid. If you reduce the size of the base of the pyramid by eliminating the near misses, you have a good chance of reducing the number of fatal and serious injuries. Unfortunately, very few near misses are reported and thus the opportunity to address and reduce the causes of potential accidents will not be realised. Consequently, near miss reporting programmes are important for workplaces to achieve an outstanding safety record.

204 Safety Signs T ere are f ve dif erent categories of safety signs: warning-, prohibitive-, mandatory-, emergency-, f rst aid- and f re f ghting signs. T e International Standards Organisation (ISO), of which South Africa is a member, has published recommendations on the use of symbolic safety signs. T ese signs are recommended for use throughout South Africa, because the ISO graphical symbols enable the public and employees at the workplace to overcome challenges, such as language barriers or illiteracy, so that they can understand safety messages and warnings wherever they might be. Safety signs should be displayed at appropriate and easily visible locations in all workplace facilities.

In 2003, ISO 7010 graphical symbols were created with internationally recognised symbols on safety signs. In January 2013, the signs were changed slightly. T ey still conform to the local regulations, which is SABS 1091.

FIGURE 2: IN 2013, THE ISO GRAPHICAL SAFETY SYMBOLS CHANGED THEME 3.1.2 SLIGHTLY

ISO 7010 became EN 7010 SAFETY SIGNS in January 2013 ARE CHANGING

Image source: http://blog.stocksigns.co.uk/wp-content/uploads/2012/10/BS-ISO-7010-safety-signs-f yer-3.jpg

205 T e table below illustrates the colours, symbols and shapes of ISO graphical safety symbols.

TABLE 1: COLOURS, SYMBOLS AND SHAPES OF ISO GRAPHICAL SAFETY SIGNS

An ISO graphical safety sign usually consists of the following colours, symbols and shapes:

Category Border Colour Background Symbol Shape

Hazard Black Yellow Black Triangular

Prohibition Red White Black Circle

THEME 3.1.2 Mandatory n/a Blue White Circle

Fire ﬁghting n/a Red White Square

First Aid n/a Green White Square

Housekeeping When we think of housekeeping in relation to the workplace, it is useful to think of the common phrase “A place for everything and everything in its place.” T is means having no unnecessary items lying around and keeping all necessary items in their proper places. A clean, well-ordered working area and good housekeeping improves a company’s image and ref ects a well-run business. Good housekeeping is also an important precondition for a safe working environment.

SOME BASIC ELEMENTS OF GOOD HOUSEKEEPING:

(i) Aisles must be wide enough for traffi c fl ow, should be colour-coded and should be kept clean and clear at all times. Aisles should not be used as temporary or permanent storage facilities. This also applies to passageways and emergency exits. (ii) Suffi cient and convenient space for tools and materials is available. (iii) There is enough space for workers to work. (iv) Adequate ventilation is available so that the workplace does not become too hot and unpleasant. (v) Adequate light is provided (preferably natural light). (vi) Clean, tidy toilet facilities and lockers for personal items are available. (vii) Waste products are removed from the site regularly to prevent overfi lling and accumulation. (viii) Floors are kept clean at all times. Spilled liquids must be cleaned up immediately. (ix) Adequate signs and labels to warn people of any dangers that may be present in the workplace are on display and clearly visible at all times. (x) Fire fi ghting equipment is regularly inspected. First Aid facilities are clean and fully stocked at all times. (xi) Anything that requires attention is seen to straight away. This includes loose handrails, broken or cracked fl oor tiles, broken window panes, leaking roofs, etc.

206 Benef ts of good housekeeping are: (i) Elimination of clutter or excessive material waste in the working area (all are common causes of accidents) prevents people from slipping, tripping and falling. (ii) Improved productivity and workmanship. (iii) A neater workplace that is comfortable and pleasant increases workers’ morale. (iv) Reduced chances of harmful materials such as dust or vapours entering the body. (v) It is easier to keep an accurate count of stock. (vi) Space is saved.

T ere are many signs of poor housekeeping: (i) Excessive material, waste or chips in the working area (ii) Congested aisles (iii) Tools and materials lef on machines

(iv) Dusty, dirty f oors and work surfaces THEME 3.1.2 (v) Overf owing waste containers (vi) Untidy or dangerous storage of materials, e.g. materials packed in corners or on overcrowded shelves (vii) Cluttered and poorly arranged work areas

Personal Protective Equipment (PPE) PPE can be def ned as all equipment, including clothing that protects against the weather, which is intended to be worn or held by employees and which protects them from risky situations that threaten their health and safety. In terms of the Health and Safety Act, employers must provide workers with personal protective equipment wherever there are risks to health and safety that cannot be adequately controlled in other ways. Examples of personal protective equipment are: (i) Safety helmets (ii) Ear protection (iii) Respiratory aids (iv) Hand protection (v) Footwear (vi) Protective clothing

Your own notes

207 FIGURE 3: WEAR A HARD HAT TO AVOID ACCIDENTS

WEAR THE PROPER HEAD PROTECTION THEME 3.1.2

GUARD FROM ANOTHER AGAINST DANGER DIRECTION

Image source: GIZ/S4GJ

208 Head Protection Where there is exposure to sharp and/or heavy falling objects or a hazard for other workers in the near vicinity, hard hats must be worn at all times. Face and Eye Protection During all grinding, cutting, drilling, handling of chemicals and welding you must wear safety goggles to protect your eyes and face. T e most common face and eye protection devices are: (i) Clear, anti-scratch safety glass (ii) Safety goggles (iii) Clear face masks

FIGURE 4: EXAMPLES OF FACE AND EYE PROTECTION DEVICES THEME 3.1.2

Image source: GIZ/S4GJ

Ear (Noise) Protection Where noise levels are high, ear protection should be worn. T ere are two main types of ear protection: (i) Airsof ear plugs (ii) High-attenuation earmuf s

FIGURE 5: EAR PLUGS (DISPOSABLE EARPLUGS AND EARMUFFS)

Image source: GIZ/S4GJ

209 Respiratory Protection Equipment To prevent inhaling fumes and particles, appropriate breathing equipment must be worn at all times, e.g. when you are grinding or chasing through walls. Some common respiratory equipment is: (i) Dust mask, usually disposable (ii) Standard single half mask respirator

FIGURE 6: WEAR A SAFETY GOGGLE AND HALF MASK RESPIRATOR

THE RISK IS GREATER THEME 3.1.2

IF YOU WEAR NO RESPIRATOR

Image source: GIZ/S4GJ Wear a safety goggle and half mask respirator to avoid injuries and inhaling poisonous fumes while spray painting.

210 FIGURE 7: SOME RESULTS OF LONG-TERM EXPOSURE TO DUST

HOW DOES DUST HURT YOU?

Pneumoconiosis Chronic Obstructive A group of ‘restrictive’ lung Pulmonary Disease diseases like silicosis, talcosis and asbestosis, where dust THEME 3.1.2 exposure causes debilitating COPD, also called Chronic lung scarring. Obstructive Airways Disease (COAD), a blanket term for ‘obstructive’ lung conditions like bronchitis and emphysema, Cancers reduces airfow out of the lungs. HSE estimates 15%-20% could Tumours, particularly of the lung be work-related. and nose, are related to substances commonly encountered at work, including asbestos, Asthma silica, chrome VI, nickel, cadmium and wood dust. These account for Another obstructive lung disease thousands of work- linked to exposure to irritants or related deaths each allergens (‘sensitisers’) at work. year. A reversible shortness of breath, between 15% and 20% of all cases are work-related. Heart Disease

Dust-affected lungs put extra Extrinsic Allergic strain on the heart, which can Alveolitis (EAA) lead to right-sided heart failure. Some occupational exposures, like hard metal dust, can cause An allergic condition which potentially fatal conditions like affects workers exposed to cardiomyopathy. biological dusts, causing Very fne dust particles cause conditions including farmers’ infammation of the heart and a lung and pigeon fanciers’ lung. higher risk of heart attacks.

Fibrosing Alveolitis Other Problems

Also known as pulmonary Exposure levels half the level fbrosis, can be caused by some allowable for most workplace occupational dust exposures, dusts overwhelm the body’s frst for example work with cobalt line of defence, the ‘mucociliary or ‘hard metals’ in cutting tools. clearance’ that flters out dust Related conditions, for example in the upper respiratory tract. ‘fock workers’ lung’ and This can leave the worker more ‘popcorn lung’ (Hazards 104), vulnerable to infections and have been discovered recently. more susceptible to occupational lung disease. Lots of other dust- related conditions occur, some specifc to particular exposures: beryllium is linked to sarcoidosis, chrome dust to chrome ulcers.

Image source: GIZ/S4GJ

211 Hand Protection T ere are dif erent types of gloves to protect your hands. Rubber gloves should be used when working with dangerous liquids such as acids. Leather gloves can protect against sparks, moderate heat, blows, chips and rough objects.

FIGURE 8: EXAMPLES OF DIFFERENT SAFETY GLOVES THEME 3.1.2

Image source: GIZ/S4GJ

Your own notes

212 Footwear Safety boots/shoes must be worn at all times in workshops or when working on site. T ey usually have steel caps to prevent damage to toes from falling objects.

FIGURE 9: ALWAYS MAKE SURE THAT YOU WEAR THE RIGHT SHOES BEFORE ENTERING A WORK AREA

EVERY JOB PRESENTS UNIQUE HAZARDS THEME 3.1.2

Before you enter any work area, make sure you are wearing the right foot protection

Image source: GIZ/S4GJ

213 Protective Clothing T e appropriate protective clothing required for any task will vary with the size, nature and location of the work to be performed. Overalls can be of two main types: the two-piece continental suit and the boiler suit.

Lifting and Handling Many accidents occur due to unsafe lif ing and handling of loads. Some safe practices to follow when lif ing loads are: (i) Do not lif a load manually if at all possible. Rather use mechanical or electrical means. (ii) Use trolleys. (iii) Plan properly so that any obstacles can be eliminated. (iv) Lif and lower gently.

THEME 3.1.2 (v) Use gloves to avoid injury to hands. (vi) Use safety signs to remind workers to lif correctly.

FIGURE 10: EIGHT USEFUL HINTS ON HOW TO MOVE A LOAD

Image source: GIZ/S4GJ Working at Heights When working in elevated positions, scaf olds are commonly used to protect the workers from the potential risk of a fall. However, working on scaf olds can also be risky and three kinds of fall hazards are usually dif erentiated: (i) Internal fall, e.g. during the placement or removal of scaf old planks (ii) External fall, e.g. from the open sides or ends of the scaf old (iii) Climbing fall, e.g. climbing from one lif of the scaf old to the next lif

Safety signs on scaf olds should display messages such as: “Danger! Scaf olding incomplete” or “Men working above”. Furthermore, edge protection systems, i.e. barriers erected around the edge of a building, structure or hole should be in place.

214 SOME SAFETY PRECAUTIONS TO ADHERE TO WHILE WORKING WITH OR ON SCAFFOLDS: (i) Scaffolds must be maintained at all times in accordance with the manufacturer’s recommendations. (ii) Scaffolds should not be altered or moved horizontally while they are in use or occupied and must be tied to a convenient and stable structure. (iii) Handrails must be provided around the working platform for the operator’s safety. (iv) Footing and anchorages must be sound, rigid and capable of carrying the maximum intended load without settling (movement within the load) or displacement. THEME 3.1.2 (v) The poles, legs or uprights of scaffolds must be plumb and securely braced to prevent swaying and displacement. (vi) Personal protective equipment such as safety helmets and safety shoes must be worn at all times. (vii) All exposed surfaces must be free from sharp edges, burrs or other safety hazards. (viii) All scaffold castors must be inspected to ensure that they are in good condition and that swivel locks are operational. (ix) When levelling of an elevated work platform is required, screw jacks or other suitable means for adjusting the height must be used. (x) Never pull scaffolds from the top - always push at base level. (xi) Use safety harnesses when erecting or dismantling scaffolds.

FIGURE 11: HOW TO WEAR A SAFETY HARNESS

Image source: GIZ/S4GJ

215 Noise Noise is unwanted sound that may damage a person’s hearing and is a major cause of hearing loss, which can be temporary or permanent. People of en experience temporary deafness af er leaving a noisy place. Although hearing usually recovers within a few hours, this should not be ignored, as it is a sign that if you continue to be exposed to the noise, your hearing could be permanently damaged. High noise levels can also interfere with communication in some jobs, causing potential safety problems. Employers thus have to: (i) Provide employees with hearing protectors. (ii) Identify hearing protection areas and mark them with signs. (iii) Take action to reduce the noise exposure that produces these risks. Flammable and Explosive Substances Some gases, liquids and solids can cause explosions or f re. For a f re to start, fuel, air and a source

THEME 3.1.2 of ignition are needed. Common materials may burn violently at high temperature in oxygen rich conditions, e.g. when a gas cylinder is leaking. Some f ammable and explosive substances are also corrosive or toxic and may pose risks to people’s health. T e main causes of accidents with gas cylinders are: (i) Inadequate training and supervision of users. (ii) Poor installation, maintenance, handling and storage. (iii) Faulty equipment and/or design (e.g. badly f tted valves and regulators). (iv) Inadequately ventilated working conditions.

RULES FOR STORAGE OF GAS CYLINDERS: (i) Storerooms should be of fi re-proof construction and so designed that in the event of fi re, the cylinders are easily removable. (ii) Storerooms should be well ventilated, top and bottom, must never be below ground level and should be protected from sunlight, rain, frost, wet soil and corrosive conditions. (iii) Light fi ttings, as well as all electric switches in stores containing fl ammable gases, should either be of the fl ame-proof type or should be placed outside the building, lighting the interior through fi xed windows. (iv) Signs such as NO SMOKING - NO NAKED LIGHTS should be posted in the area of the store. (v) Oxygen should never be stored with fl ammable gases. (vi) Prevent dirt, grit of any sort, oil or any other lubricant from entering the cylinder valves.

Stress and Violence at Work Stress can cause physical ailments such as depression, headaches and anxiety. Of en stress is work related, caused by tight deadlines and long working hours. Sometimes stress becomes so overwhelming that violence erupts. When this happens in the workplace, employees are put at physical risk. Layof s within a company can also cause stress among the remaining employees who may in response worry about their own jobs. Layof s can also lead to increased work duties for the remaining employees, increasing their stress as they struggle to meet deadlines. Employees of en carry problems from home into the workplace, where they seem even larger because of work demands. Workers may also feel bullied by demanding managers or co-workers, and may feel powerless to do anything about it.

216 Knowing the signs of stress can help avoid violence in the workplace. T ese indicators include: (i) Hostility towards co-workers (ii) Reduction in the quality of work (iii) Increased absenteeism (iv) Noticeable change in behaviour (v) Physical signs of exhaustion

HIV/AIDS at the Workplace

As you probably know, South Africa has the highest number of HIV-infected citizens in the world, with 6.1 million people living with the disease according to UNAIDS. In 2012 alone, South Africa recorded over 400 000 new HIV infections. HIV stands for Human Immunodef ciency Virus and prevents the

immune system from functioning properly, making people with HIV particularly vulnerable to other THEME 3.1.2 diseases as well, for example, tuberculosis (TB).

T e disease can have a negative ef ect on the individual at the workplace and subsequently on the productivity of the company. An HIV positive individual at the workplace might experience stigmatisation and discrimination against him/her or he/she might show signs of fatigue, especially when the work involves physical tasks. T e individual might also show increased absenteeism and stress related to f nancial constraints because of increased medical bills. Furthermore, there might be negative psychological ef ects because the individual might have the feeling that he/she cannot speak openly about his/her status and is forced to keep it a secret. In short, an employee with HIV has many very serious issues to deal with on a daily basis which might make life at work exhausting and challenging at times. South Africa has legislation and laws in place which guide HIV management in the workplace. Laws include: • T e protection of employees or new recruits from discrimination based on HIV status • Policies governing the right to conf dentiality in the workplace • Laws prohibiting forced HIV testing

T ere is no legal duty of an employee to disclose their HIV status to their employer or to other employees. An employee may also not be dismissed because he or she is HIV positive or has AIDS. However, where there are valid reasons related to their ability to continue working and where fair procedures have been followed, their services may be terminated.

Labour law also requires all companies to have a working HIV/AIDS policy and it is important that every employee is informed about the policy. An HIV /AIDS policy commonly acknowledges that HIV/ AIDS will be treated like any other life-threatening disease, provides assurances that conf dentiality will be respected and that disciplinary action will be taken against any member of staf who deliberately disclosed the HIV status of an employee to a third party.

Many companies also set up an HIV/AIDS workplace programme, which is an action-oriented plan that is implemented in order to prevent new HIV infections, to provide care and support for employees who are infected or af ected by HIV/AIDS, and to manage the impact of the epidemic on the company. T ere are multiple ways a company can address the issue of HIV/AIDS at the workplace. Commonly, such measures are: (i) Increasing knowledge about HIV/AIDS through information material that is available at the workplace. (ii) Increasing knowledge about ways to have protected sex. (iii) Providing access to means of protection, e.g. condoms, at the workplace. (iv) Creating a stigma- and discrimination-free workplace with regard to HIV and AIDS. (v) Increasing knowledge about workplace-related health and safety measures, and providing all health and safety equipment necessary to carry out required tasks safely. (vi) Ensuring that selected staf is properly trained in how to handle employees who may have been involved in an accident causing bleeding and to prevent people from being exposed to infection through the blood of an injured person.

217 Exercises

(i) Complete the following sentences by adding the missing word(s): An accident can be def ned as:

Unsafe acts include: THEME 3.1.2

Unsafe conditions include:

(ii) List three benef ts of safe working practices. 1.

(iii) Visit a workshop at your college when students are busy working and conduct an assessment of any unsafe acts and unsafe conditions. Record your f ndings in the table below. Use the second table and indicate all safe acts and safe working conditions to record what has already been done to address safe working practices.

Workshop: Date:

Unsafe Acts Unsafe Working Conditions

218 Workshop: Date:

Safe Acts Safe Working Conditions THEME 3.1.2

(iv) List the three important features of a symbolic safety sign. 1.

(v) Have a look at the f gure below. Use the table below and indicate which safety sign categories you can identify. Can you also identify six individual signs and explain their meaning?

FIGURE 12: DIFFERENT SAFETY SIGNS

Image source: http://img1.123freevectors.com/wp-content/uploads/new/signs-symbols/

219 Category Border Colour Background Symbol Shape THEME 3.1.2

(vi) Background colour of safety signs and their indications: Match column A elements (colours) with arrows to column B elements (indications).

Column A Column B

Background Colour: Used to indicate:

Yellow a) Danger

Green b) General information

Blue c) First Aid equipment

Orange d) Caution

Red e) Electrical equipment

(vii) T e following list includes results of either poor or good housekeeping. From the list below, tabulate the following results into the two dif erent categories (poor and good housekeeping). a) Reduced chances of an accident b) Low worker morale c) Space is saved d) People can get injured from items not packed correctly e) Ef cient workmanship f) Low productivity due to time wasted trying to f nd items

Results of poor housekeeping Results of good housekeeping

220 (viii) Indicate whether the following statements are true or false: a) Improving working conditions must not be the main aim of the employer. True or False b) Employers are obliged by law to provide certain standards of cleanliness and comfort in the workplace. True or False c) Washing facilities, including showers, should have running cold and hot water, soap, clean towels or other means of cleaning or drying. True or False d) Every employer shall provide a conspicuous sign outside the entrance sanitary facilities to indicate the sex of the persons for whom the room is intended. True or False

e) Scaf olds sometimes do not need to be maintained in a safe condition. THEME 3.1.2 True or False f) For ease of operation and convenience, scaf olds can be moved horizontally while they are in use. True or False

(ix) Practically demonstrate to your partner how you should wear a safety hat and a safety harness. Discuss the result of incorrect anchorage of a safety harness.

(x) Design a checklist to be used as a guide to help you identify good and poor housekeeping in the workshops at your college. Hint: Make use of the elements of housekeeping. Follow the example below:

Work area: Location: Date: Conducted by: Date previous check was done:

Meets standard: Y Does not meet standard: N Standard OK but needs attention: A Comments Clean N Aisles Materials stacked in aisles, Clear Y no space to work Well marked A Marking faded

221 Further information (all materials are on the resource CD)

(i) T e international language of ISO graphical symbols booklet, www.iso.org (ii) Safe Use of Flammable and Explosive Substances, www.gla.ac.uk/media/media_142387_ en.pdf (iii) Personal Protective Equipment, U.S. Department of Labour, Occupational Safety and Health Administration

Your own notes THEME 3.1.2

222 THEME 3.1.3 WORKPLACE HAZARDS

Introduction

As already indicated in the previous theme, it is fairly obvious that a workplace without potential hazards hardly exists. Consequently, it is important for all workers to be aware of potential hazards when they enter their workplace facility. An ef ective hazard communication programme that includes provision for responsible staf and employee training is thus recommended. All workers have the right to safety and health in the job without having to fear punishment or being earmarked as a troublemaker.

Keywords THEME 3.1.3

Hazard types Hazard Communication Programme Hazard register Hazard report Work area analysis Theme Outcome

At the end of this theme, you should be able to identify and explain potential workplace hazards.

Deﬁ nition of Terms Hazard Types (categories) A workplace hazard is anything that has the potential to cause harm to a person, for example, spills on f oors, blocked aisles, unguarded machinery, frayed cords on electrical equipment etc. T ere are various types of hazards and the following f gure indicates the six dif erent categories:

FIGURE 1: SIX DIFFERENT HAZARD CATEGORIES

Chemical & dust hazards Biological Ergonomic hazards hazards Work organisation Safety hazards Physical hazards hazards

Image source: GIZ/S4GJ

223 Safety Hazards T ese are the most common hazards and will be present in most workplaces at one time or another. T ey include unsafe conditions that can cause injury, illness and death. Safety hazards include: (i) Spills on f oors or tripping hazards (ii) Working at heights (iii) Unguarded machinery and moving machinery parts (iv) Electrical hazards like frayed cords, missing ground pins, improper wiring (v) Conf ned spaces (vi) Machinery-related hazards

FIGURE 2: SPILLS ON FLOORS CAN RESULT IN SLIPS, TRIPS AND FALLS. ALWAYS CLEAN UP THESE SAFETY HAZARDS! THEME 3.1.3 AVOID SLIPS, TRIPS AND FALLS

A LITTLE PREVENTION CAN SAVE A LIFETIME OF PAIN

Image source: GIZ/S4GJ

224 Biological Hazards Biological hazards are usually associated with working with animals, people or infectious plant materials. Work in schools, day care facilities, colleges and universities, hospitals, laboratories, emergency response, nursing homes, outdoor occupations, etc. may expose you to biological hazards. Types of things you may be exposed to include: (i) Blood and other bodily f uids (ii) Fungi/mold (iii) Bacteria and viruses (iv) Infectious plant materials (v) Insect and animal bites (vi) Animal and bird droppings Chemical Hazards

Chemical hazards are present when a worker is exposed to any chemical preparation in the workplace THEME 3.1.3 in any form (solid, liquid or gas). Some preparations are safer than others, but to some workers who are more sensitive to chemicals, even common solutions can cause illness, skin irritation or breathing problems. Beware of: (i) Liquids like cleaning products, paints, as well as acids and solvents, especially if chemicals are in an unlabeled container! (ii) Vapours and fumes that come from welding or exposure to solvents (iii) Gases like acetylene, propane, carbon monoxide and helium (iv) Flammable materials like gasoline, solvents and explosive chemicals (v) Pesticides

FIGURE 3: CHEMICAL SUBSTANCE SIGNS

Image source: http://upload.wikimedia.org/wikipedia/en/b/b7/Transportation_Placards.jpg Chemical substances need to be appropriately labelled and need to be indicated with the correct sign Physical Hazards Physical hazards are factors within the environment that can harm the body even without direct contact. Physical hazards include:

(i) Radiation: including ionising, non-ionising (microwaves, radio waves, etc.) (ii) High exposure to sunlight/ultraviolet rays (iii) Temperature extremes (iv) Constant loud noise

225 Ergonomic Hazards Ergonomic hazards occur when the type of work, body positions and working conditions put strain on your body. T ey are the hardest to spot, since you do not always immediately notice the strain on your body or the harm that these hazards pose. Short-term exposure may result in “sore muscles” the next day or in the days following exposure, but long-term exposure can result in serious long-term illnesses. Ergonomic hazards include: (i) Improperly adjusted workstations and chairs (ii) Frequent lif ing (iii) Poor posture (iv) Awkward movements, especially if they are repetitive (v) Repeating the same movements over a prolonged period of time (vi) Having to use a lot of force, especially if you have to do it frequently (vii) Vibration THEME 3.1.3 FIGURE 4: AVOID HAZARDS IN AN OFFICE ENVIRONMENT: SAFE WORKING CONDITIONS NEED TO BE MAINTAINED!

CAN OCCUR IN OFFICE ENVIRONMENTS TOO

Tripping on Power Cords

Bad Ergonomics

Open Cabinets ALWAYS USE GOOD SAFETY PRACTICES

Image source: GIZ/S4GJ

226 Work Organisation Hazards T ese are the hazards associated with workplace issues such as workload, lack of control and/or respect, etc. T ey are hazards or stressors that can cause stress (short-term ef ects) and strain (long-term ef ects). Examples of work organisation hazards include: (i) Workload demands (ii) Workplace violence (iii) Intensity and/or pace (iv) Control or say about things (v) Social support/relations (vi) Sexual harassment

HAZARD COMMUNICATION PROGRAMME (HCP) THEME 3.1.3

Employers that have hazardous chemicals in their workplaces are well advised to implement a Hazard Communication Programme. The programme must include the teaching of correct labelling for containers of hazardous chemicals and correct use of Safety Data Sheets (SDSs) for hazardous chemicals. Each employer must also document in writing how they will meet the requirements in each of these areas. These are the most appropriate steps to develop and implement an effective HCP for employers that use hazardous chemicals:

(i) Get familiar with best practice standards for hazard communication programmes. (ii) Identify responsible staff for the implementation of the programme. (iii) Prepare and implement a written HCP. (iv) Ensure that all containers of hazardous chemicals in the workplace are appropriately labelled. (v) Maintain Safety Data Sheets for each hazardous chemical in the workplace and ensure that Safety Data Sheets are readily accessible to employees. (vi) Train employees on the hazardous chemicals in their work area, as well as on appropriate protective measures, before initial assignment. (vii) Review the HCP periodically to make sure that it is still working and meeting its objectives. (viii) Revise the programme as needed to address changed conditions in the workplace, e.g. new chemicals, new hazards, etc.

Hazard Register A hazard register is a summarised record of the hazards identif ed in a business, where these hazards occur, and the tasks, machinery or situations with which they are associated.

Your own notes

227 Hazard Report Any hazard should be reported immediately to your supervisor. In fact, health and safety legislation requires employees to report hazards and hazardous conditions or practices to their supervisor immediately. T is allows for prompt corrective action.

FIGURE 5: PROMPT REPORTING OF HAZARDS AND SUBSEQUENT CORRECTIVE ACTION DEPEND ON EACH OTHER TO BE EFFECTIVE

THEME 3.1.3 BE PROACTIVE

REPORT HAZARDS!

Image source: GIZ/S4GJ

Workplace Inspection A regular and careful check of a workplace or part of a workplace in order to identify health and safety hazards and to recommend subsequent corrective action is called an inspection. Workplace factors that have the potential to cause injury or illness to employees include equipment, materials, processes or work activities, and the environment.

228 Exercises

(i) Hazardous Products Quiz Choose the best answer for each question: 1) Hazardous products are ... a) Helpful to you b) Harmless to you c) Dangerous to you

2) If a label says “CAUTION”, it is ... a) A little hazardous b) Very hazardous

c) Not hazardous at all THEME 3.1.3

3) If a label says “POISON”, it is ... a) A little hazardous b) Very hazardous c) Not hazardous at all

4) If you must use a hazardous product, choose the ______hazardous product for the job. a) Most b) Worst c) Least

5) If the label has the words “harmful if inhaled”, it can harm you if... a) You breathe it in b) You eat or drink it c) You get it on your skin

6) If the label has the words “fatal if swallowed”, it can harm you if you ... a) You breathe it in b) You eat or drink it c) You get it on your skin

7) If the label has the words “harmful if absorbed through the skin”, it can harm you if you ... a) You breathe it in b) You eat or drink it c) You get it on your skin

8) Any product that is toxic can ... a) Easily burn b) Make you sick c) Burn your skin

9) Any product that is f ammable can ... a) Easily burn b) Make you sick c) Burn your skin

10) Any product that is corrosive can ... a) Easily burn b) Make you sick c) Burn your skin

229 (ii) Indicate which of the following potential hazards exist in your college classroom or training workshop: (a) Tripping hazards (b) Broken pieces of equipment (c) General clutter in work areas (d) Unknown chemical substances (e) Excessive noise (f) Spilled liquids (g) Use of f ammables near heat (h) Improper use of tools (i) Heavy lif ing (j) Contact with substances without proper protection THEME 3.1.3

Your own notes

230 (iii) Have a look at the image below and identify the various individual hazards and group them into the six categories (safety, biological, chemical, physical, ergonomic and organisational). Use the table below.

FIGURE 6: IDENTIFY THE VARIOUS INDIVIDUAL HAZARDS AND GROUP THEM INTO THE SIX CATEGORIES THEME 3.1.3

Image source: GIZ/S4GJ

# Hazard Hazard Category

231 Further information (all materials are on the resource CD)

(i) Sample Material Safety Data Sheet for a chemical product (cement) (ii) Activity Quiz: Household Hazardous Products (iii) Activity: Preventing Chemical Accidents - Hazard Mapping

Your own notes THEME 3.1.3

232 THEME 3.1.4 MINIMISING ACCIDENTS THROUGH CLEAR COMMUNICATION AND HEALTH AND SAFETY CHECKLISTS

Introduction

T e best way to reduce accidents in the workplace is to be proactive in terms of prevention and to have well-informed employees who know that safety is a major concern in the company/institution. It is not suf cient to communicate only verbally and to reiterate expectations in memos. It is better to

have a health and safety communication strategy in place, including checklists and posters, to identify THEME 3.1.4 possible safety hazards. A commitment to clear communication is essential to maintaining appropriate safety standards. Furthermore, it is important to involve all employees and formalise procedures for new suggestions about improving workplace safety. A safety coordinator is certainly helpful, but it is preferable and of en more ef ective to include all employees.

Keywords

Communication Work area arrangement Health and safety checklist

Theme Outcomes

At the end of this theme, you should be able to: (i) Explain the importance of clear and ef ective communication in the workplace. (ii) Explain how a work area is arranged to minimise accidents and injury. (iii) Design a health and safety checklist that can be used at the workplace/learning institution for accident prevention.

Deﬁ nition of Terms Communication Communication is essential to maintaining appropriate safety standards. Employees must know about the risks they face, the prevention measures being taken, and any emergency action plans. T is information should be provided in clear, non-technical language that will be easily understood by all.

233 GOOD COMMUNICATION BETWEEN THE EMPLOYER AND WORKERS INCLUDES THE FOLLOWING: (i) A list of hazardous substances used or produced is available in every workplace. (ii) Having Safety Data Sheets readily available for each classiﬁ ed hazardous chemical substance that is used. (iii) Turning information from the Safety Data Sheet into workplace instructions that give practical information on how to handle substances. (iv) Making sure that containers for hazardous substances are clearly labelled with appropriate hazard warnings relating both to the physical hazards and to health hazards.

THEME 3.1.4 (v) Communicating the results of risk assessments. (vi) Asking workers regularly about potential health and safety problems. (vii) Providing workers with all relevant information, instruction and training on the precautions they should take to protect themselves and other workers. (viii) Ensuring that all workers know how to make proper use of all the control measures provided, who they should report problems to, and what they should do in the event of an accident involving hazardous substances.

Work Area Arrangement Ef ective arrangement of the work area can eliminate some workplace hazards and help get a job done safely and properly. Poor arrangements can frequently contribute to accidents by hiding hazards that cause injuries. If the sight of paper, debris, clutter and spills is accepted as normal, then other more serious health and safety hazards may not be noticed at all.

EFFECTIVE ARRANGEMENT OF THE WORK AREA INCLUDES: (i) Good housekeeping: Keep the working environment clean and tidy, with fl oors and access routes kept clear of obstacles. Remove rubbish regularly so it does not build up. (ii) Cleaning and maintenance: Remove rubbish regularly and keep work areas clear. Cleaning methods and equipment must be suitable for the surface being treated. (iii) Good lighting levels: Position lights to ensure all fl oor areas are evenly lit and all potential hazards, obstructions and spills can be clearly seen. (iv) Floors should be checked for damage regularly and maintenance carried out when necessary. Potential hazards include holes, cracks, or loose carpets and mats. Floor surfaces should be suitable for the work carried out, for example, it may need to be resistant to oil and chemicals used in production processes. Coating or chemically treating existing fl oors can improve their slip-resistant properties. (v) Handrails on stairs, slip-resistant covers for steps, high visibility and non-slip marking of the front edges of steps and good lighting can all help to prevent slips and trips on stairs. (vi) Clean up spills immediately using an appropriate cleaning method. Use warning signs where the fl oor is wet and arrange alternative routes. (vii) Remove obstructions. If this is not possible, then suitable barriers and warning notic- es should be used.

234 Health and Safety Checklist Safety checklists are a great way to determine compliance with certain standards and to ensure consistency. Many companies use them as documentary evidence that they have a system in place to identify and control hazards and risks. T ere is no doubt that most incidents are caused by human errors, however, most checklists only check physical issues in the work environment.

Your own notes THEME 3.1.4

235 Examples

Below you can f nd a basic induction checklist which can be used as documentary evidence that new employees have been introduced to the basic health and safety regulations in a certain company or institution.

INTRODUCTION TO BASIC HEALTH AND SAFETY REGULATIONS

Manager: Site: THEME 3.1.4 Employee: Date of Induction:

Person conducting Induction:

Topic Yes No Comments

1. Introduction

2. Organisational overview and site tour

3. Outline of site rules (provide copy)

4. Discuss OHS manual

5. Emergency procedures

6. Incident reporting

7. Hazard reporting

8. First Aid

9. Use of PPE

10. Security and access arrangements

11. Copy qualiﬁcations/licences

12. Discuss training schedule

This information has been provided to me:

Name and signature of employee Date

Name and signature of person conducting induction Date

236 Below you can f nd a basic electrical hazard checklist which can be used as documentary evidence for compliance with certain standards in a work or training facility.

BASIC ELECTRICAL HAZARD CHECKLIST

Inspector: Site: Date:

Hazard category and number: THEME 3.1.4 1. Deteriorated 2. Damaged or broken 3. Unapproved 4. Missing cover(s) 5. Not working 6. Bare live parts or wires 7. Improper use

Hazard Topic Location and Comments Number(s)

Electrical panels

Electrical machines

Wiring

Outlets

Fixtures

Switches

Appliances

Others

237 Below you can f nd a general but more inclusive checklist which can be used by the company’s safety representative or inspector as documentary evidence for compliance with certain standards in a work or training facility.

SAFETY REPRESENTATIVE INSPECTION LIST THEME 3.1.4

Frequency: Monthly

Date issued: Target for comple- tion: Inspector:

Department:

Location:

Nr Topic Yes No Remarks

BUILDINGS

Clean and in good state of 1 repair?

No broken windows, doors 2 or other openings?

FLOORS

Clean and free from 3 slippery substances?

No tripping or other 4 obstruction hazards?

No holes, unevenness or 5 structural damage?

VENTILATION

Sufﬁcient natural or 6 artiﬁcial ventilation

7 All fans in working order?

Free from any dangerous 8 gases, dust, smoke etc.?

238 LIGHTING

Sufﬁcient natural or 9 artiﬁcial lighting

10 All lights in working order?

No straining glares or 11 contrasts?

12 No dark or shadowy spots?

POLLUTION

13 Adequate disposal system? THEME 3.1.4

14 No air pollution?

Complying with all 15 disposal standards and procedures?

HYGIENE

All toilets, urinals and 16 change rooms clean and hygienic?

Kitchens and eating places 17 clean and hygienic?

No eating in places not so 18 indicated?

DEMARCATION

Aisles and passageways 19 demarcated?

Access and exit routes 20 demarcated?

Fire equipment demarcat- 21 ed?

Electrical switchgear 22 demarcated?

All demarcation lines clear 23 and visible?

Your own notes

239 HOUSEKEEPING

Working area clean and 24 tidy at all times?

25 Yard tidy and clean?

26 No redundant materials?

27 Adequate storing space?

28 Safe stacking?

29 No obstruction in aisles? THEME 3.1.4 Cupboards and shelves 30 tidy and clean?

REFUSE AND WASTE

Adequate refuse bins and 31 removal system?

Separate bins for speciﬁc 32 materials as prescribed?

COLOUR CODING

All pipe work colour 33 coded?

All electrical apparatuses 34 colour coded?

Hazardous machine parts 35 colour coded?

Uniform colour-coding 36 system throughout?

MACHINE GUARDING

All hazardous machine 37 parts adequately guarded?

All guards in good state of 38 repair?

All guards in place and 39 used according to pre- scriptions?

ELECTRICAL SUPPLY AND EQUIPMENT

40 No installation defects?

Regular inspections as 41 prescribed?

42 No abuse?

240 EMERGENCIES

First Aid boxes in place, 43 demarcated, secured?

First Aid boxes contents 44 correct?

First Aiders trained with 45 valid certiﬁcates

Emergency procedure 46 understood by all and displayed? THEME 3.1.4 47 Alarm system working?

Recommendations:

Signature of representative Date

(Adapted from: http://www.labourguide.co.za/health-and-safety/861-safety-representative-inspection-list)

Exercises

(i) Have a look at the educational videos: A person called Napo is working with chemicals, including those that are irritants, f ammable, corrosive, toxic or a danger to the environment. T e videos illustrate the incorrect way of handling these substances and the serious consequences of doing so, and then move on to show the correct way of dealing with chemicals by respecting the safety instructions and by following safe working practices. T ese videos are suitable for all levels of employees in all sectors of the economy (you can f nd them on the CD) and for students in college workshops and labs.

(ii) Use one of the above health and safety checklists or part of one and design a custom-made checklist that can be used in your work and training facility at your learning institution. Carry the inspection out and discuss your results with your class.

241 Further information (all materials are on the resource CD)

(i) Educational videos: Napo http://www.napof lm.net/en/napos-f lms/multimedia-f lm-episodes-listing-view?f lm- id=napo-012-danger-chemicals&sourceid=banner&utm_source=home&utm_medi- um=banner&utm_campaign=campaign (ii) Sample Hazard Communication Programme (iii) Have Health and Safety representatives been appointed at your workplace? http://www. labour.gov.za/DOL/downloads/documents/forms/occupational-health-and-safety/ THEME 3.1.4 Your own notes

242 THEME 3.1.5 EFFECTS AND CONSEQUENCES OF ELECTRICAL ACCIDENTS ON THE HUMAN BODY AND ON PROPERTY

Introduction

T e occupational health and safety (OHS) risks associated with the installation, maintenance and decommissioning of electrical installations are complex. T e main hazards associated with small-scale solar energy applications, i.e. PV and SWH systems or small-scale wind turbine systems are handling issues, working at height, working in awkward postures for longer periods and risks related to electrical

installations. To a certain degree we have dealt with these risks and how to avoid or minimise them in THEME 3.1.5 the previous four themes. T is theme deals with electrical safety in general and, more specif cally, with the risks while working with and around small-scale solar energy applications.

Keywords

Dangers of electrical energy Electric shock (electrocution) Electrical accidents involving property Lockout/Tagout procedures

Theme Outcomes

At the end of this theme, you should be able to: (i) Explain the ef ect and consequences of electrical shock and burns on the human body. (ii) Explain the ef ect and consequences of electrical accidents on property. (iii) Explain and demonstrate the correct procedures for isolation (lockout/tagout) of electrical equipment. Deﬁ nition of Terms Dangers of Electrical Energy Some of us might have already experienced some mild form of electric shock (electrocution). If we were fortunate, the extent of that experience was limited to a simple tingling sensation or even mild pain. But when we are working with and around electric circuits capable of delivering high power to loads, electric shock becomes a much more serious issue. A typical residential PV system can provide more than suf cient current to pose a serious safety hazard. When working with such electrical installations or similar circuit assemblies, serious accidents could occur and pain is the least signif cant result of an electric shock. You, your colleague or any other victim could receive serious contact burns or even in a worst-case scenario, experience potentially fatal respiratory paralysis (suf ocation) or ventricular f brillation (heart failure/cardiac arrest). In addition, a f re resulting from wrong installations, e.g. short circuit, overheating or sparks, could damage or completely destroy residential or commercial property.

243 FIGURE 1: ELECTRICAL INSTALLATIONS AND SERIOUS ACCIDENTS THEME 3.1.5

Image source: http://de.123rf.com/photo_6365353_elektriker-auf-feuer.html?term=feuer kabelkurzschluss When working with electrical installations, serious accidents could occur. Make sure that all connected (live) parts are de-energised (disconnected) before working on or near electrical installations, and follow the required electrical safety programme.

Effects of Electric Current on the Human Body An electric charge travels along conductors, usually in the form of wires. But did you know that the human body is also a good conductor? T at means that an electric charge can easily f ow through our bodies. You might think that if you get shocked, you can pull away quickly and not get hurt - but an electric charge travels fast, almost at the speed of light, so a person has little chance of pulling away when the current is strong enough. T ere are three main ef ects of electric current on the human body:

(i) When an electric current is conducted through a material, any opposition to that current (resistance) results in dissipation of energy, usually in the form of heat. T is is the most basic ef ect of electrical energy on living tissue, i.e. skin, muscles, organs etc. If you become part of an electric circuit, your tissue acts as a resistor and consequently the tissue heats up. If the current is strong enough, the amount of heat generated can be suf cient to burn the tissue. Physiologically, the ef ect is the same as damage caused by an open f ame or any other high-temperature source of heat, except that electrical power has the ability to burn tissue well beneath your skin, meaning it can even burn internal organs. (ii) Another ef ect of an electric current on the body is electric shock (electrocution). T is is perhaps the most signif cant type of electrical hazard, as it relates to the human nervous system. T e nervous system is a network of special cells in the human body which conduct the multitude of signals responsible for the regulation of many bodily functions. Given that the nervous system is a conductor in itself, it poses very little resistance to an external electric current. If the strength of an electric current is suf cient and is conducted through your body, its ef ect will overload your nervous system and prevent you from being able to actuate your muscles appropriately. If you are triggered by an involuntary external current through your hands, this problem is especially dangerous. Your forearm muscles responsible for bending f ngers tend to be better developed than those muscles responsible for extending f ngers. If both sets of your hand and forearm muscles contract because an electric current is conducted through your arm, clenching of your f ngers into a f st is usually the result. T is will worsen the situation as you or any other

244 victim will be unable to let go of the live wire or conductor. T us, stopping the current as quickly as possible is essential. However, even when the current has been stopped, victims may not regain voluntary control over their muscles for a while, as the nervous system is still in disarray. T e muscle controlling the lungs and the heart can also be af ected by the electric current. Even relatively low currents can disrupt nerve cell signals so severely that the heart cannot beat properly, sending the heart into a condition known as f brillation. A f brillating heart f utters rather than beats, and is inef ective at pumping blood to vital organs in the body. T e consequences of this can be fatal.

Table 1 below illustrates the types of ef ects various levels of electric currents can have on the body. Please note that the various ef ects indicated in the table are given for an average healthy adult person and do not necessarily ref ect the risk electrical energy poses to all persons. Note also that body resistance is not a f xed quantity. It varies from person to person and from time to time, thus two

dif erent resistance values are given. Furthermore, the ef ects of an electric current on the human body THEME 3.1.5 are directly related to the length of time the body is exposed to an electric current and the path the current takes through the body.

TABLE 1: EFFECTS OF VARIOUS LEVELS OF ELECTRIC CURRENTS ON THE BODY

Electric Potential Potential differ- Average physiological or harmful effects after Current difference ence required and 1 sec. exposure (DC) required and assumed low body assumed high resistance 1 kΩ body resistance 100 kΩ

1 mA 100 V 1 V Threshold of feeling, tingling sensation.

5 mA 500 V 5 V Maximum harmless current (mild pain).

Pain with beginning of sustained muscular 10-100 mA 1000 V 10 V contraction also known as “Can’t let go current” or “Frozen on the circuit”.

Severe pain, ventricular ﬁbrillation, fatal if 100-300 mA 10 kV 100 V continued.

(Adapted from data provided by the Georgia State University, USA) (http://hyperphysics.phy-astr.gsu.edu/hbase/electric/shock. html#c1)

(iii) Apart from the direct ef ects an electric current can have on the body, it is important to consider that an electric shock itself could indirectly result in injury by causing you to fall from a ladder or roof or putting parts of your body into harm’s way. Indirect injury as a result of shock is particularly associated with the installation, maintenance and decommissioning of solar arrays, both PV and SWH systems on roofs, and small-scale wind turbines. Here, the main hazards are associated with working at height and include access issues, falling objects, falls, slips and trips. Preventing Electric Shock (Electrocution) An electric current is the result of charge f owing through a complete circuit. Furthermore, in order for an electric current to be conducted through a circuit, there needs to be a potential dif erence supplied by an energy source (AC or DC outlet). T ese conditions are usually present when an electric installation is energised or, in common language, when an electric installation is “live”. An electric shock can occur when the human body becomes part of a live electrical circuit. T us, to avoid harmful shocks, make sure that all live parts of the circuit are de-energised (disconnected) before working on or near them. If this is not possible or has been neglected and an electrical accident has happened, the extent of injury accompanying the shock usually depends on three factors:

(i) T e amount of current conducted through the body T e amount of current existing in a circuit depends on the potential dif erence supplied by the

245 AC or DC source and the resistance values in the circuit. While current is the crucial factor in electrical energy-related accidents, potential dif erence and resistance are important as well, as these two variables determine the strength of a current passing through the body. T e Poten- tial-Current-Resistance relationship, i.e. Ohm’s law, has been dealt with in Topic 2, and also applies in the case of electric shock.

Note Let us quickly review Ohm’s law: Current (I) is inversely proportional to the overall resistance (R) in the circuit (ampere values decrease at the same rate as the ohm values increase) and directly proportional to the electric potential dif erence impressed across the circuit (ampere values increase at the same rate as the volt values increase).

T us, while the best protection against shock is to make sure that all live parts are discon-

THEME 3.1.5 nected before working on or near electrical installations, it also makes sense to increase your own resistance values. Resistance can be added to the body through the use of insu- lated tools and appropriate electrical safety PPE for head, eye, hand and foot protection, including insulating gloves and shock resistant boots.

FIGURE 2: DURING PV SYSTEM TESTING AND COMMISSIONING, WORKERS ARE EXPOSED TO ARC FLASH HAZARDS IN COMBINER BOXES AND INVERTERS

Image source: https://solarprofessional.com/articles/design-installation/calculating-dc-arc-f ash-hazards-in-pv-systems/page/0/6 During PV system testing and commissioning, workers are exposed to arc f ash hazards in combiner boxes and inverters. It is therefore important to wear the correct safety gear to prevent injuries.

(ii) T e path of the current through the body T e path an electric current takes through the human body makes a dif erence, as current will af ect whatever body tissues are in its path. Since the heart and lungs are probably the most critical organs for a person’s survival, shock paths traversing the chest are the most dangerous.

(iii) T e length of time a person is subjected to the current If the duration of electric shock is longer than the period of the cardiac cycle, the risk of ventricular f brillation is considerably higher. Ventricular f brillation is a major cause of death due

246 to electric shock. If the normal cardiac electrical activity is suf ciently disrupted due to the external electric current, the heart rate can rise to 300 beats/min. T e heart ceases to function as a pump, blood pressure falls, there is no more oxygen supply and death occurs within minutes. Ventricular f brillation does not stop when the current that triggered it is removed. For shock durations below 100 ms and for the hands-to-feet pathway, f brillation may occur from currents above 500 mA. T is threshold decreases considerably if the current f ow is longer than one cardiac cycle. For shock durations of 1 s, the level is 50 mA and for durations longer than 3 s it drops to 40 mA. T e threshold of ventricular f brillation also depends on the physiological parameters of the human body.

BASIC SAFETY PRECAUTIONS FOR WORKING WITH OR NEAR ELECTRIC ENERGY SYSTEMS THEME 3.1.5 (i) Do not use power tools with defective cords. (ii) Use only equipment and installation components, i.e. cables, overcurrent protection devices (OCPD) etc. that are rated for the level of current (ampere) or power (watt) required for the installation. (iii) Always use wooden ladders or other non-conductive materials, such as ﬁ breglass ladders, when working with or near electric energy systems. (iv) Keep in mind that the risk of electric shock is even greater in areas that are wet or damp. (v) Know where the distribution board is. In case of an emergency, quickly disconnect the current by putting the main circuit breaker on NEUTRAL or OFF. (vi) All circuit breakers should be labelled so that it is easy to identify which circuits they protect. (vii) Do not touch a person in the event of an electrical accident. Always disconnect the current ﬁ rst and then attend to the accident.

Property Damage: Fire Caused by Electrical Accidents A fair amount of f res in domestic and commercial environments are due to electrical accidents associated with faulty wiring or with faults in electrical devices.

Fires of electrical origin are caused by the following: (i) A spark can appear from a sudden discharge through the air between two conductors, or from one conductor to earth. T e current existing in these incidents is usually small and seldomly causes serious f res, unless explosive gases or f ammable vapours are present, or highly f ammable material is in contact with the conductor. (ii) An electric arc is a much larger and brighter discharge and the current quantity can be very high, e.g. hundreds of ampere. An arc usually arises when a circuit is broken, e.g. due to rodent damage on a PV roof-top system, leaving a narrow gap across conductors over which the electric charge continues to f ow. When an arc appears, the air in its vicinity becomes ionised (hot ionised highly conductive plasma) and forms a conductor, which may allow the charge to f ow to any nearby conducting framework. T e temperature of an electrical arc is very high, i.e. tens of thousands of degrees Celsius. Any combustible material in the vicinity could therefore lead to a serious f re.

247 FIGURE 3: DAMAGE CAUSED BY FIRE THEME 3.1.5

Image source: http://tgalsolar.com/?s=panel+f re Incorrect PV installations or faulty system components can generate arcs of considerable intensity and can start f res.

(iii) Unintentional short circuits are electrical malfunctions and are usually caused when conductor insulation breaks, resulting in a charge f owing along a dif erent path than the one intended. Short circuits, for example, may occur between two phases, between a phase and neutral or between a phase and earth (ground). A short circuit in a DC circuit typically occurs when the positive and negative terminals of a battery or a PV module are connected with a low-resistance conductor, like a too-thin wire. With low resistance in the connection, a high current exists, causing the battery or the PV cells to deliver a large amount of energy in a short time. A large current through a battery can cause the rapid build up of heat, potentially resulting in an explosion. In AC circuits, high current conditions and resulting short circuits can typically also occur with electric motor loads under stalled conditions. Such short circuits, either in AC or DC circuits, are likely to result in a very high current and can therefore quickly trigger an overcurrent protection device (OCPD) or, if such a protection mechanism is not installed, the formation of an electric arc which can easily lead to a f re. Short circuits in PV systems may occur when part of the array is shaded. Normally cells in modules are connected in series, and when several cells of the module are shaded, the current of the af ected module is reduced. T is situation can lead to irreversible cell damage and hot spot heating, resulting in unintentional short circuits which, in a worst-case scenario, can trigger a f re. Due to the fact that it is dif cult to prevent shading, PV module manufacturers typically install bypass diodes in their modules. When cells are shaded or already damaged, diodes can give the current another path, skipping the damaged or shaded cells (f nd more on bypass diodes in Topic 4).

248 FIGURE 4: DAMAGED PHOTOVOLTAIC MODULES THEME 3.1.5

Image source: http://www.lgenergy.com.au Photovoltaic modules are usually considered safe and reliable, but shading of cells can lead to hotspot development, which will damage modules and can potentially even cause f res.

Lockout/Tagout Procedures T e main aim of lockout/tagout (LOTO) procedures is to prevent accidents from occurring as a result of the unintended activation of electrical equipment. Lockout procedures usually use mechanical locks, typically padlocks that block the accidental activation of electrical equipment or power outlets, for example, an isolator switch is switched of and then locked in the “of ” position. T e procedure also requires that a tag is f xed to the locked device indicating that the machinery or equipment is not to be energised or activated. LOTO procedures can be used when working on electrical circuits, when bypassing guards or safety devices or when carrying out maintenance or repair works on machinery and jammed mechanisms.

LOTO STEPS: (i) Notify others that the equipment will be shut down. (ii) Perform a controlled shutdown to power down the equipment. (iii) Open all of the energy isolating devices identifi ed on the equipment’s specifi c LOTO procedure. (iv) Lock and tag all energy isolating devices. (v) Dissipate or restrain stored or residual energy. (vi) Verify that the equipment is completely de-energised by attempting to cycle it (veri- fi cation of isolation, see next page). (vii) Verify that the equipment is completely de-energised by testing for potential difference with a voltmeter (testing for isolation, see next page).

249 PROPER LOTO LABELLING: (i) Name of the person placing the LOTO and the date placed (ii) Details regarding the shutdown procedure for speciﬁ c equipment (iii) A list of all of the energy sources and isolating devices (iv) Labels indicating the nature and magnitude of stored potential or residual energy within the equipment

FIGURE 5: LOCKOUT/TAGOUT PROCEDURES (1) THEME 3.1.5

Image source: http://www.shutterstock.com/pic-189125360/stock-photo-electrical-breaker-box-locked-out-for-service-inspection-or-installation-lockout-tagout.html?src=Pg62903boBiVDso523piZw-1-1&ws=1 To prevent installers and facility personnel from inadvertently re-energising circuits during PV system installation or scheduled maintenance, documented lockout/tagout procedures should be diligently followed.

Veriﬁ cation of Isolation Before working on electric machines and equipment that have been locked out, and only af er ensuring that no personnel are exposed, use the operating controls to verify that the equipment or machine has been de-energised and make certain it will not switch on. Testing for Isolation Once a circuit has been isolated, it must be tested (potential dif erence testing) to make sure that it is still not energised. You can use a reliable test instrument, e.g. a multimeter, by following the prove-test-prove method. T e prove-test-prove method requires you to prove the instrument before and af er a test to ensure that it works properly.

250 THE PROVE-TEST-PROVE METHOD: (i) Prove: Test potential difference against a known live source to ensure that the multimeter is working correctly. The test instrument should read 230 V (± 10-15 %). (ii) Test: Test potential difference on the locked-out (de-energised) machine or equipment to ensure isolation. The test instrument should read 0 V. (iii) Prove: Again, test potential difference against a known live source to ensure that the multimeter is working correctly. The test instrument should read 230 V (± 10-15 %). THEME 3.1.5

Af er testing for isolation ensure that operating controls of the machine or equipment are set to ‘Neu- tral’ or ‘Of ’. T e machine or the equipment is now locked out, which needs to be indicated by a tag (see Figure 6 and 10). Servicing or maintenance may now be carried out. Removal of LOTO Devices Af er the servicing and maintenance is completed and before the lockout devices are removed and energy is restored, ensure that it is safe to remove the lockout device and communicate to all af ected persons that power will be restored to the machinery or equipment.

Your own notes

251 Examples

In some urban and rural areas small-scale solar energy applications, in rural environments usually of -grid systems, have become an integral part of our modern life. However, of en these devices are not treated with the necessary caution - people forget that DC currents can also be hazardous. T e installation, maintenance and decommissioning of such small-scale solar energy applications, for example PV systems, can present risks if the system is somehow compromised due to faulty wiring, missing grounding or OCPDs. An additional challenge while installing, maintaining or adding equipment to PV systems is that the array with its individual strings and modules is always live (energised) during the day and can usually not easily be shut of for maintenance or other work on the system if LOTO procedures have been neglected or not foreseen in the initial design of such a system. THEME 3.1.5 Please note

it is not suf cient to cover the modules with opaque cover only. Even if this necessary step has been done, measuring and testing is required to determine which parts of the system are safe to handle and which are not. T is needs to be done very carefully, since many systems have modules connected in series, resulting in a relatively low current but a high potential dif erence. Lastly, electric energy-related risks and hazards occur with the integration of PV systems to the distribution board, i.e. the circuit-breaker panel that allows you to control the dif erent circuits in a domestic or commercial environment. Important!

Such integrations are only allowed to be carried out by qualif ed persons, i.e. electricians with a wireman’s licence.

For small-scale residential and commercial PV systems, the following f ve examples of technical procedures and preventive measures illustrate important recommendations: (i) Cabling and installation of protection devices (ii) Grounding/earthing measures (iii) Lockout/tagout procedures (iv) A sample checklist for OHS aspects and work area arrangements associated with the installation, maintenance and decommissioning of small-scale solar energy applications (v) Some preventive measures associated with the installation, maintenance and decommissioning of such systems Cabling and Installation of Protection Devices (Balance of System Equipment, BoS) Like all electrical installations, PV systems must also follow the recommendations in the installation and user manuals for all components. Furthermore, it is important to select cables suitable for the system’s size, i.e. rated cables and plugs that meet the output current and potential dif erence of the system to prevent a drop in potential dif erence, and can also handle the maximum possible fault current. Suitable cable sizes for small installations (< 3 kW) usually have a diameter of 4 mm2 and 6 mm2 (see also Topic 4). T e installation of DC and AC disconnects and OCPDs is strongly recommended. On the DC side these should be DC disconnect/isolator and DC rated OCPDs (circuit breakers or fuses) for each string, DC rated OCPDs (circuit breakers or fuses) at or in the combiner box for the whole array and a DC main disconnect/isolator af er the combiner. On the AC side (af er the inverter) an AC disconnect/isolator shall be installed. Please note Common AC circuit breakers are not compatible with DC circuits and vice versa! DC fuses and circuit breakers operate very dif erently in a PV system than AC protection devices (f nd more on AC and DC protection devices in Topic 2 and 4).

252 FIGURE 6: USE CONVENIENT CABLE CONNECTORS TO CONNECT PHOTOVOLTAIC MODULES THEME 3.1.5

Image source: http://www.pv-magazine.com/archive/articles/beitrag/electrical-matrimony-_100003769/86#axzz3NNYtBYkr Use convenient cable connectors, for example Sunclix plugs, to connect photovoltaic modules, as these devices allow for quick, safe and reliable installation and maintenance.

FIGURE 7: THE INSTALLATION OF DC AND AC DISCONNECTS AND OCPDS IS STRONGLY RECOMMENDED

Image source: http://www.moeller.net/images/content/loesungen_erneuerbare_energien/eaton_schutzschalter_overview.jpg T e installation of DC and AC disconnects and OCPDs is strongly recommended. Please note that the switchgear range for the DC side of photovoltaic systems is not compatible with the AC circuits and vice versa!

253 Grounding/Earthing Measures In case of system failure, short circuits and the like, grounding, also sometimes referred as earthing, aims to prevent the conductive materials of PV module frames, mounting structures and component cases from reaching dangerous potential dif erence levels which could cause electric shock. Proper grounding will ensure that exposed conductive materials of a system are equipotential, i.e. there is no dif erence between the ground and exposed conductive materials in potential dif erence. T us, it is common practice to ground each component of a PV system separately, i.e. each string of an array and the inverter separately.

Please note

THEME 3.1.5 Lightning protection devices should also be grounded separately (f nd out more about grounding in Topic 2 and 4).

FIGURE 8: DIFFERENT TYPES OF LUGS FOR GROUNDING CONNECTIONS

Image source: www.homepower.com and http://www.greenbuildingadvisor.com/sites/default/f les/PV_array_6032_MedRes.jpg Dif erent types of lugs for grounding connections are available for PV modules and module mounting structures.

254 Illustrating Lockout/Tagout Procedures for a PV System Let us assume that a Programmable Logic Controller (PLC) unit (monitoring box) shall be installed in an already mounted and functional small-scale commercial PV system to monitor the system’s performance. T e retroactive installation of the PLC unit shall be carried out during a bright and clear day, i.e. when the sun is shining. Under these conditions the array with its individual strings and modules and all its connections is always energised (live). T e design of the system however, has not made provision that necessary LOTO procedures allow precautions to be taken when doing work on the active system. T us, it is recommended to apply LOTO procedures, i.e. locking the solar array with a padlock, which allows turning of all electrical energy sources to prevent electrical shock for the installer. T is also requires a tag be added to the lock explaining what is happening. T e key to the lock needs to be kept by the person performing the work, so that he/she can turn the equipment back on. T e latter prevents someone from inadvertently turning the power

back on and electrocuting those doing the installation work. It is further recommended that the THEME 3.1.5 above procedures be presented in written form to the building’s facility manager for approval.

THE LOTO PROCEDURES: (i) Open the AC disconnect, a switch usually next to the inverter, lock and tag. (ii) Open the DC disconnect, a switch usually next to the junction/combiner boxes or controller, lock and tag. (iii) Securely cover solar panels with an opaque tarp. (iv) Use a reliable test instrument and follow the prove-test-prove method, i.e. carry out potential difference tests on the locked-out (de-energised) PV components to ensure isolation. The test instrument should read 0 V. (v) Ensure that all relevant system components are locked out. Installation of the PLC unit may now be carried out.

Af er the installation is completed, ensure that it is safe to remove the lockout device and communicate to all af ected persons that the PV systems will be re-energised.

FOLLOW THESE STEPS: (i) Ensure the proper installation of the PLC monitoring box. (ii) Remove the tarp from the solar panels. (iii) Close the solar DC disconnect by removing the lock and tag. (iv) Close the solar AC disconnect by removing the lock and tag. (v) Check and conﬁ rm (decommission) that the PLC system is working and will provide the performance data as planned.

255 FIGURE 9: LOCKOUT/TAGOUT PROCEDURES (2) THEME 3.1.5

Image source: http://www.shutterstock.com/pic-156655979/stock-photo-man-attaching-a-lockout-tag-to-an-electrical- control-panel.html?src=Pg62903boBiVDso523piZw-1-0&ws=1 To prevent the DC and AC circuits from inadvertently re-energising during PV system installation or scheduled maintenance, documented lockout/tagout procedures should be followed both on the DC and AC side of the system.

Your own notes

256 A Sample OHS Checklist for Small-Scale Solar Energy Applications T e following sample checklist (Table 2), adapted from information from the European Agency for Safety and Health at Work (https://osha.europa.eu/) illustrates some more specif c health and safety aspects and work area arrangements associated with the installation, maintenance and decommissioning of small-scale solar energy applications. Please note that the list is by no means exhaustive. More comprehensive information is available on the resource CD.

TABLE 2: SAFETY ASPECTS ASSOCIATED WITH SMALL-SCALE SOLAR ENERGY APPLICATIONS

Sample Checklist THEME 3.1.5 Done by (Name)/Date: Location/Facility:

Yes = Satisfactory No = Unsatisfactory, needs attention

Yes No Handling issues Yes No Work organisation Is work arranged so that manual Is information on the solar system, the handling operations, such as electrical installation and the building lifting and carrying operations available to the workers so that they and repetitive manual handling can perform the work safely? of even lighter items, are avoided and, where not possible, Is training on safe working proce- reduced to the minimum? dures provided?

Have workers been trained on Is there sufﬁcient cooperation, safe manual handling tech- communication and exchange of niques? information among the different actors involved (for example building In case lifting or carrying owner, site manager and the workers) operations are necessary, in order to allow the safe perfor- including lifting tools, equipment mance of the work, especially if and material from the ground to different companies and sub-contrac- the roof and vice-versa, are tors are involved? mechanical aids provided? Are workers involved in the work- In case a crane is used, are place risk assessment? workers operating the crane properly trained? Have workplace hazards linked to the organisation of the work and work-re- Are measures in place to avoid lated stress been assessed as part of or, when not possible, to reduce the workplace risk assessment? to a minimum the need for workers to perform repetitive Are there measures in place to avoid movements or to work in a high workload and tight deadlines? strained postures? Have the speciﬁc needs and risks of Are measures in place to avoid the different worker groups (migrant or, when not possible, reduce to workers, young and older workers, a minimum the need for workers female and male workers, etc.) been to work in kneeling or squatting assessed? positions frequently or for prolonged periods of time? Are there measures in place to ensure communication of information to (e.g. Other ______migrant) workers who may not have a good command of the working language in order to allow them to perform their work safely?

Other ______

257 Yes No Working at height, slips and Yes No Electric energy-related risks (PV), trips, falls burns/scalds Can work at height in general, Are only qualiﬁed persons allowed to and in particular on slanting work on electrical equipment? roofs be avoided? During maintenance/repair activities, When work at height is neces- do workers keep a safe distance from sary, are there mobile elevating high potential difference power lines work platforms (MEWPs) and and are tools and materials kept at a scaffolding available if needed? safe distance from these power lines?

When ladders are used to reach Is the work area at the power inverter the place of work at height, has dry? the appropriate ladder been chosen and is it used safely? Are workers aware that low potential THEME 3.1.5 difference levels can cause surprise When roof work is necessary, has shocks and thereby falls? the condition of the roof been assessed to ensure that the roof Are workers aware that small is dry and free from slipping and amounts of sunlight can produce a tripping hazards such as moss, potential in the PV system and shock snow, ice, vent pipes, equipment or arc ﬂash hazards lying around, etc.? Are standard temperature and In the case of skylights or holes/ pressure values (STP) ensured, i.e. is cavities, are they safeguarded? the solar thermal collector cooled off? Other ______Are workers provided with suitable PPE when risk reduction measures at the source are not sufﬁcient

Other ______

Yes No Integration into infrastructure Yes No Other Electric energy-related risks (PV) Are only qualiﬁed persons allowed to integrate the system to the mains?

Is the local electric power company contacted to turn the power off when connecting / separating the PV system to/ from the grid or working within a certain distance of power lines with high potential difference levels?

Are workers always accompanied by at least one colleague when working on electrical systems, thereby eliminating lone working?

Are workers aware of PV modules bearing electric risks in case they are damaged e.g. during cleaning activities?

Other ______

258 Preventive Measures Associated with Small-Scale Solar Energy Applications T e list below, adapted from information from the European Agency for Safety and Health at Work (https://osha.europa.eu/) illustrates some examples of preventive measures (Table 3) associated with the installation, maintenance and decommissioning of small-scale solar energy applications. Please note that this list is by no means exhaustive. More comprehensive information is available on the CD.

TABLE 3: PREVENTIVE MEASURES ASSOCIATED WITH SMALL SCALE SOLAR ENERGY APPLICATIONS

Work organisation Ask the building/installation owners to provide the necessary information for the workers operating on the solar system to enable them to perform their work safely. THEME 3.1.5 Make sure that workers have received proper training and record. In case of missing or unclear information on the system or working procedure, instruct workers to inform their line manager/employer before performing the work, so that these can contact the relevant persons and experts for assistance and provision of the missing information. Ensure good communication and teamwork exists among building owner, all workers and site managers. Consult and involve workers in the workplace risk assessment as well as in the choice of prevention measures. Assess workplace hazards linked to the organisation of the work and work-related hazards as part of the workplace risk assessment, i.e. include aspects related to workload, deadlines and support from supervisors and colleagues. Assess workers’ workload and the feasibility of the deadlines to be met, and check that the work can be done without generating overtime. In case of too high workloads and too tight deadlines, try to re-plan and re-organise the work in consultation with workers so that workloads and deadlines are acceptable. Make sure to take into account the characteristics of all worker groups and adapt working conditions to their speciﬁc needs, taking into account gender, age, (migrant) worker’s needs for information in their native language, etc. Supply all safety information in the different languages of the workers on site as necessary.

Working at height, slips,trips and falls Try to plan and organise the work so that work at height can be avoided. When work at height cannot be avoided, ensure that a system is in place to prevent or arrest falls. Provide appropriate mobile elevating work platforms and prevent them from becoming unstable or overturning. In order to choose the adequate ladder, assess the height from the ground on which the work will be done; the surface on which the equipment will rest as well as on which the workers will work; the condition of the ground on which the equipment will rest; the weather conditions and how the working tools would be taken to the height. Ensure that the ladder is fixed safely and positioned on a stable, flat surface. Assess the condition of the roof, the types of roofing material and the roof cavity to ensure that it can be accessed safely. In case the surface is wet (in case of rain, snow, ice), try to reschedule the work so that it can be done once the surface is dry. Eliminate any tripping and slipping hazards, paying particular attention to moss, debris and tools lying around. If a tripping hazard cannot be eliminated, signs and cones should be put up to warn workers of the hazard.

259 Use rigid covers for skylights or temporary openings and holes, or safeguard them by means of protective rails or guards.

Electric energy-related risks (PV), burns/scalds Ensure that workers who conduct the work are specifically trained on electrical risks and on the specific characteristics of solar energy systems. Perform a risk assessment of the work area, including electrical hazards from power lines. Make sure all workers are aware of the importance to strictly respect the safety distances to high power lines and check that they comply with this. Keep the inverter dry and isolate it suitably. THEME 3.1.5 Make sure that workers are aware of electric risks of PV systems and that detailed information on these systems is available. In particular, make sure that workers are informed about the risks of low potential difference levels causing surprise shocks and consequently possible falls. Prevent potential hazardous currents by using appropriate circuit interrupters. Provide information about solar thermal collectors. Note that applying fluid to a hot system can quickly turn the liquid to steam. Supply appropriate PPE (eye protectors/face shields, footwear, gloves) and ensure that it is properly maintained and that workers are trained in its use.

Your own notes

260 Exercises

(i) PV Safety and Hazard Identif cation Quiz. Choose for each question the best answer:

a) First Aid training is one of the building blocks of basic workplace safety. A. True B. False

b) You should avoid multipurpose personal protective equipment. A. True B. False

c) Which of the following is not safety equipment directly related to prevent electric THEME 3.1.5 shock hazards? A. Gloves B. Footwear C. T ermal clothing D. Goggles E. Hard hat

d) You use a voltmeter to verify the existence of current in the circuit. A. True B. False

e) You use an ammeter to verify the existence of potential dif erence in the circuit. A. True B. False

f) What kind of hazards are related to working with roof-mounted PV systems? (select more than one) A. Ultraviolet light B. Electric shock C. Chemical poisoning D. Fire E. Falls

g) Use a …………… on top of a ladder to secure the ladder. A. Rope B. Harness C. Nail D. Hammer

261 (ii) Complete the text below by using the following words: Disconnect, positively, non-conductive, exposed, hazardous, combustible, fuse, current, cords, guards, aware, access, rated, damage, immediately.

Why is it so important to work safely with or near electric energy systems? T e electrical in regular businesses and homes has enough power to cause death by electrocution. Even changing a light bulb without unplugging the lamp can be because coming in contact with the live part of the socket could kill a person.

THEME 3.1.5 What are some general safety tips for working with or near electric energy systems? Inspect tools, power cords and electrical f ttings for or wear prior to each use. Repair or replace damaged equipment . Always tape cords to walls or f oors when necessary. Nails and staples can damage causing f re and shock hazards. Use cords or equipment that is for the level of current (ampere) or power (watt) that you are using. Always use the correct . Replacing a fuse with one of a larger size can cause excessive currents in the wiring and possibly start a f re. Be that unusually warm or hot outlets may be a sign that unsafe wiring conditions exist. Unplug any cords to these outlets and do not use until a qualif ed electrician has checked the wiring. Always use ladders made of wood or other materials when working with or near electric energy systems or power lines. Place halogen lights away from materials such as cloth or curtains. Halogen lamps can become very hot and may be a f re hazard. Label all circuit breakers and fuse boxes clearly. Each switch should be identif ed as to which outlet or appliance it is for. Do not use outlets or cords that have wiring. Do not use power tools with their removed. Do not block to circuit breakers or fuse boxes. Do not touch a person or electrical apparatus in the event of an electrical accident. Always the current f rst.

262 Further information (all materials are on the resource CD)

(i) YINGLI SOLAR PV MODULES, Installation and User Manual, YINGLISOLAR.COM (ii) How to properly fuse a solar PV system, http://www.windynation.com (iii) Arc-fault Protection in PV Installations: Ensuring PV Safety and Bankability, World Re- newable Energy Forum 16 May, 2012 (iv) European Agency for Safety and Health at Work (https://osha.europa.eu/), E-Facts 68, HAZARD IDENTIFICATION CHECKLIST: OSH RISKS ASSOCIATED WITH SMALL- SCALE SOLAR ENERGY APPLICATIONS THEME 3.1.5 Your own notes

263 COMIC

264 COMIC

265 NOTES 266 Your notes own TOPIC TOPIC

Basic Principles of Photovoltaic Systems

Topic Overview

On a national and global scale interest in photovoltaic systems (PV systems) is steadily increasing. This is due to ecological factors (climate change) as well as economic factors. PV systems are proﬁ table solutions for the national energy mix and this technology will take part in shaping South Africa’s future energy supply through residential (1 – 20 kW) and commercial systems (10 – 500 kW), as well as via PV power plants (> 500 kW). As of January 2015 a total of 593 MW installed capacity by PV plants was connected to the national grid and more and more rooftop PV systems for residential and commercial users are being installed in South Africa. Consequently, it is important to know and understand this future technology better.

This topic aims to inform you on the relevant system components and their operational principles and it will offer you exciting experiments which can be carried out in your college. Thus, this last topic of the RET subject in level 2 will provide you with the foundation- al knowledge and practical skills you need when working on PV installations.

We however strongly encourage you to refer to the previous topics, i.e. Introduction to Renewable Energy, Electrical Energy and Energy Efﬁ ciency and Safe Work Practices, whenever the need arises.

267 FIGURE 1: INSTALLATIONS AND INSTALLED PV CAPACITY IN VARIOUS COUNTRIES (ADAPTED FROM IEA PHOTOVOLTAIC POWER SYSTEMS PROGRAMME [PVPS])

TOP 10 COUNTRIES IN 2014 TOP 10 COUNTRIES IN 2014

FOR ANNUAL INSTALLED CAPACITY FOR CUMULATIVE INSTALLED CAPACITY

China 10,6 GW Germany 38,2 GW

Japan 9,7 GW China 28,1 GW

USA 6,2 GW Japan 23,3 GW

UK 2,3 GW Italy 18,5 GW

Germany 1,9 GW USA 18,3 GW

France 0,9 GW France 5,7 GW

Australia 0,9 GW Spain 5,4 GW

Korea 0,9 GW UK 5,1 GW

South Africa 0,8 GW Australia 4,1 GW

India 0,6 GW Belguim 3,1 GW

Image source: GIZ/S4GJ

Topic 4 covers two units: Unit 4.1 Photovoltaic System Components and Operational Principles Unit 4.2 Photovoltaic Experiments

268 Unit 4.1 Unit

UNIT 4.1 PHOTOVOLTAIC SYSTEM COMPONENTS AND OPERATIONAL PRINCIPLES

Introduction

Photovoltaic (PV) is the direct conversion of solar radiation into electrical power with the help of semiconductor technology. In a variety of aspects, PV systems are dif erent to other renewable energy technologies and of course fossil fuel systems. One fascinating aspect of photovoltaic is that the operation of this technology is silent and that no emissions are released. Photovoltaic has a wide scope of application and centralised or decentralised use is easily feasible with power capacities from a few milliwatt to hundreds of megawatt. Subsequently, photovoltaic has developed rapidly over the past few decades.

Most areas in South Africa have an average of more than 2 500 hours of sunshine per year, as well as high average solar irradiance levels compared to Europe. T is makes South Africa’s local resource one of the most abundant in the world and thus, PV systems are a very promising energy-generating option for the country and the whole region. T is unit covers four dif erent themes which will introduce you to a wide range of relevant aspects of photovoltaic system components and operational principles. Unit Outcomes

At the end of this unit, you should be able to: (i) Describe and sketch the dif erent components of a PV system and explain their functions. (ii) State the semiconducting materials used to produce the main types of solar cells. (iii) Describe and explain the photovoltaic ef ect. (iv) Compare dif erent PV module technologies. (v) Interpret sample datasheets with reference to standards, certif cations and warranties. (vi) Identify and measure key electrical output parameters using multimeters. (vii) Explain and sketch the current-potential (I-V) curve of a PV module in a diagram. (viii) List and explain critical factors that af ect the performance of PV modules. Themes in this Unit Unit 4.1 covers four themes: T eme 4.1.1 PV System Components T eme 4.1.2 Semiconductor Materials and the Photovoltaic Ef ect T eme 4.1.3 PV Module Datasheets and Output Parameters T eme 4.1.4 Factors Af ecting the Performance of PV Modules

269 THEME 4.1.1 PV SYSTEM COMPONENTS Introduction

Both of -grid systems (sole power supply or stand-alone systems) and on-grid systems generate DC through PV modules and can thus be considered as the main components of any PV system. Apart from the PV generator, various other components are necessary for power conditioning and energy storage. Additional components called Balance of System (BoS) form part of a PV system. In this f rst theme you will be introduced to the main components of a residential (1 – 20 kW) PV system and their functions.

THEME 4.1.1 Keywords

Stand-alone Grid-connected Cell Module Array Encapsulation Standard test conditions Balance of System Inverter Maximum power point tracking Charge controller Batteries Over-current protection devices Isolators Mounting systems Roof penetrations

Theme Outcomes

At the end of this theme, you should be able to describe and sketch the dif erent components of a PV system and explain their functions.

Deﬁ nition of Terms Stand-Alone PV Systems Stand-alone or of -grid systems rely on PV generated power only. T ese systems usually comprise PV modules, batteries for energy storage and a charge regulator (see Figure 1) and are either used as back-up systems or to provide electrical energy for remote locations away from the national grid.

Grid-Connected PV Systems Grid-connected PV systems are connected to the national grid through inverters (see Figure 1) and do not require batteries for back-up storage. T ese type of systems only operate when the energy utility (Eskom) is available. In the event of power outage the system shuts down until utility power is restored.

270 FIGURE 1: SCHEMATIC ILLUSTRATION OF SOME ESSENTIAL COMPONENTS OF A GRID-CONNECTED PV SSTEM

+ - + - + - + - + -

kWh Meter THEME 4.1.1

to Grid DC disconnect Inverter AC disconnect 220 VAC

AC electrical panel to household loads

Image source: GIZ/S4GJ

PV Modules PV modules can be considered as the main components of any PV system, as they are responsible for the direct conversion of radiant solar energy into electrical energy. T e DC generated by the modules can be used either directly on-site, stored in batteries, or fed into the national grid. T e conversion of radiant energy into electrical energy takes place in PV cells, as they are made out of light-sensitive semiconductor materials. In the next theme we will give you more information about this conversion process (photovoltaic ef ect).

PV cell/module symbol used in schematic circuit diagrams

FIGURE 2: SCHEMATIC ILLUSTRATION OF A PV CELL, MODULE AND ARRAY

Cell

Module

Array

Image source: GIZ/S4GJ A schematic illustration of the progression from a single PV cell to a module to an array. T e cells are connected in series to form a module, while module strings can be connected in parallel to form an array.

271

= When manufacturing PV modules, the low individual electrical potential dif erence of solar cells (0.5 - 0.6 volt) requires that the cells are connected in series (cell stringing). T e individual cells are spaced several millimetres apart and the front contacts of each cell are soldered to the back contacts of the next cell, thereby connecting them in series. Given that an individual solar cell has a potential of between 0.5‒0.6 volt, and taking into account an expected reduction in PV module potential due to certain losses (temperature etc.), many common modules with a power rating between 10‒100 watt contain 36

solar cells in series (0.6 × 36 = 21.6). T is usually provides an open-circuit voltage (Voc, see T eme 4.1.3)

of about 21 volt and a potential dif erence at maximum power (Vmp) of between 17‒18 volt. Depending on the required power output of the module, some manufacturers string 48, 60 or 72 solar cells together. For example, many larger PV modules with a rating between 250‒300 watt have 60 or 72 cells connected

in series and a subsequent nominal potential between 36‒42 volt or a Vmp between 55‒65 volt. T us, the electrical potential (volt) of PV modules is determined by the number of solar cells stringed together, whereas the module current value depends primarily on the size of its cells and their ef ciency. THEME 4.1.1

PLEASE NOTE THAT THERE IS A LARGE VARIATION IN THE SIZE OF SOLAR CELLS USED IN PV MODULES AND THEREFORE THEIR CURRENT MAY VARY WIDELY.

FIGURE 3: SCHEMATIC ILLUSTRATION OF 36 SINGLE PV CELLS CONNECTED IN SERIES TO FORM A MODULE

Image source: GIZ/S4GJ

T e manufacturing process of PV modules requires high precision and quality control in order to produce a reliable product. T e most critical part of the module manufacturing process is the encapsulation of the cells so that these are protected from the environment. Typically, the cells are laminated (sandwiched) between a tempered safety glass layer, two transparent polymer sheets (EVA- ethyl vinyl acetate) and a plastic rear surface to keep out moisture and contaminants that could cause PV modules to fail. T e panel is framed at the end of the production process with a prof le of anodised aluminium to improve rigidity and sturdiness. A junction box at the back of the module is the interface between the module and the PV system so that it can be wired. Bypass diodes (see T eme 4.1.5) are also located here. Module warranties on quality PV modules from well-established manufacturers are usually over 20 years, indicating the robustness of the encapsulated PV modules. Usually, a typical warranty will guarantee that the module produces 90 % of its rated output for the f rst 10 years and 80 % of its rated output for up to 25 years.

272 FIGURE 4: SCHEMATIC ILLUSTRATION OF THE ENCAPSULATION OF PV CELLS BETWEEN VARIOUS LAYERS

Tempered glass

EVA

Back

cover THEME 4.1.1

Image source: GIZ/S4GJ Simplif ed schematic illustration of the encapsulation of PV cells between various layers to keep moisture out and contaminants away from the module. Standard Test Conditions (STC) T e performance of PV modules and arrays is generally rated according to their maximum DC power output (Pmax) under Standard Test Conditions (STC). STC are def ned as an operating temperature of 25o C and an incident solar irradiance level of 1000 W/m2. Since these conditions are not always typical of how PV modules operate in the f eld, actual module performance parameters are usually 85‒90 % of the STC rating.

PLEASE NOTE THAT PV MODULES VERY RARELY WORK AT RATED OPERATIONS.

Crystalline Silicon and Thin Film As there are many dif erent semiconductor materials, many dif erent types of PV modules exist. How- ever, there are two broad categories of technology, namely, crystalline silicon and thin f lm. In the next theme (T eme 4.1.2) we will give you a more detailed overview of these technologies. Balance of System (BoS) BoS represents all components and costs other than the PV modules. T us, the BoS includes: (i) T e design costs, site preparation and other related costs (sometimes even land) (ii) Support and mounting structures (iii) All other system components such as the inverter, switches/disconnects and fuses/breakers, cabling, connectors and combiner boxes, grounding hardware, batteries and controllers etc. (iv) System installation and certif cation

Inverter Inverters are electronic components necessary for the power conditioning of the PV system. T us, inverters provide not only the conversion of the DC into AC, but also control the current f ow and transformation of the entire PV system. Manufacturers design dif erent types of inverters to be used as stand-alone system inverters or as utility-interactive inverters and based on their purpose, there are dif erent types of inverter categories, e.g. grid-interactive inverters can be either string, central and/or modular (micro) inverters.

273 FIGURE 5: SCHEMATIC ILLUSTRATION OF DIFFERENT INVERTER CONFIGURATIONS

Inverter symbol used in schematic circuit diagrams = ~

= ~ THEME 4.1.1 = = ~ ~

= ~

Image source: GIZ/S4GJ Lef : single grid-interactive string. Middle: multi-string. Right: multiple inverter string.

Ef ciency averages of quality inverters from well-known manufacturers lie at about 97 % for most of their series or even more. Preference should be given to true sine wave inverters as these deliver top quality AC power. Inverters are rated according to the power they can deliver, and in the inverter data sheet you can check the inverter’s specif cations for accurate continuous power rating. When selecting inverters for a PV system, the following requirements need to be considered: (i) T e maximum open circuit voltage of the PV array shall not exceed the voltage requirements of the inverter. (ii) T e minimum voltage requirement of the inverter shall be met by the PV array. (iii) T e maximum power output of the modules shall be less than the inverter’s rating. (iv) T e maximum current at the point of operation shall be less than the inverter’s rating.

274 FIGURE 6: A 500 W GRID-INTERACTIVE INVERTER (INSIDE AND OUTSIDE VIEW) THEME 4.1.1

Image source: GIZ/S4GJ An example of a 500 W grid-interactive inverter (inside and outside view), commonly used for smaller solar power systems or for modular applications (multiple inverter strings). T ese types of inverters can be used in systems with dif erently aligned or partially shaded roofs in residential applications.

FIGURE 7: A 4 KW GRID-INTERACTIVE INVERTER (INSIDE AND OUTSIDE VIEW)

Image source: GIZ/S4GJ An example of a 4 kW grid-interactive inverter (inside and outside view), commonly used for residential grid-connected PV systems. T ese types of inverters are usually used for single or multi-string applications.

275 Maximum Power Point Tracking (MPPT) MPPT is a technique that grid-connected inverters and charge controllers use to get the maximum possible power from PV arrays at any time during its operation, thereby increasing prof tability. T is is useful because PV modules have internal impedances that vary throughout the course of the day and result in a non-linear output ef ciency which can be analysed based on the I-V curve of the module/ array (see T eme 4.1.3 and T eme 4.1.4). T e variations depend not only on the level of solar irradiance impinging on the modules, but also on their cell temperature. It is thus convenient that an MPPT circuit in the inverter or controller constantly monitors the array performance levels (I and V) and operates the system at the maximum power point of the array. T e maximum power point (MPP) is the product of the

potential dif erence (Vmp) and current (Imp) at MPP.

FIGURE 8: SIMPLIFIED DIAGRAM INDICATING THE MAXIMUM POWER POINT (MPP) OF A 75 WATT PV MODULE THEME 4.1.1

I Short circuit Maximum current 5.0 PowerPoint (MPP) 4.0 Imp 3.0

Current 2.0

1.0 Open circuit Vmp voltage

5 10 15 17 20 V Potential difference

Image source: GIZ/S4GJ A simplif ed diagram indicating the maximum power point (MPP) of a typical 75 watt PV module as the

product of the potential (Vmp) and current (Imp) at MPP, in our case at around 17 V and 4.1 A.

In many cases, the MPPT technology provides much greater system design f exibility, signif cant cost savings and higher levels of power ef ciency. Inverters without MPPT circuits would result in non-optimal operating conditions and lower ef ciency operation for the array.

PLEASE NOTE

MPPT circuits can only operate within a certain potential difference range, for example many quality inverter series with MPPT technology have a potential range between 125 V and 450 V. If the potential provided by the PV array is too low, then the system is unable to transform the current in an optimal manner due to the fact that the MPPT will not start, and if the potential difference is too high, the excess potential is lost and thus wasted. Some installations even require inverters with dual-MPPT functionality, for example arrays that are on differently aligned roofs, resulting in different solar azimuth or tilt angles. Another applica-

tion is in systems which use PV modules with different electrical parameters (Voc, Vmp etc.).

276 FIGURE 9: SCHEMATIC ILLUSTRATION OF AN INVERTER WITH DUAL- MPPT FUNCTIONALITY

M P P T = M P P ~ T THEME 4.1.1

Image source: GIZ/S4GJ Such a conf guration is used to connect two arrays from two parts of the roof (resulting in them having dif erent azimuth or tilt angles of each string), without compromising the power output of the PV system. Dual-MPPT functionality also allows strings of PV modules with dif erent electrical parameters

(Voc, Vmp etc.) to be connected. Charge Controller Charge controllers are electronic devices used in stand-alone (of -grid) systems. T eir purpose is to prevent the energy storage devices, usually batteries, from becoming overcharged. T us, a charge controller monitors the state of charge of the batteries and disconnects the array from the batteries when these become fully charged. Usually the controller will simply open the circuit between the PV array and the batteries. Charge controllers have maximum input voltage and current ratings specif ed by the manufacturer and it is required that the PV array power capacity will not exceed the charge controller’s power limits. Exceeding the power ratings of your controller can destroy it.

FIGURE 10: TWO DIFFERENT TYPES OF CHARGE CONTROLLERS WITHOUT MPPT FUNCTIONS

Image source: GIZ/S4GJ T ese controller types are commonly used for small 12 or 24 V stand-alone systems and at around ZAR 500.00 they of er reasonably priced solutions. Both controllers use PWM (pulse width modulation) as their charging mode. T e f rst controller is an industrial-grade controller fully encapsulated (IP68) to prevent corrosion and can be used in PV-Systems exposed to extreme weather conditions. T e second controller is a multi-purpose residential device with an LCD display and a user friendly interface to set various control parameters to meet application requirements.

277 Pulse Width Modulation (PWM) PWM is one of the two principal algorithms used in charge controllers for smaller stand-alone PV systems, the other being MPPT. PWM controls the average potential (V) values by turning an electronic switch between supply and load on and of at a very fast rate. T e longer the switch is on compared to the of periods, the higher the total power supplied to the load. T e result is that the potential (V) of the PV array will be pulled down to nearly that of the battery. An MPPT controller is more sophisticated but also more expensive. It will adjust its input potential (V) to harvest the maximum power from the PV array and then transform this power to supply the varying voltage requirement of the battery plus load. How- ever, PWM controllers are a good low cost solution for smaller PV systems when PV cell temperatures are moderate to high (45° C ‒ 75° C). Below is a table comparing both charging methods.

TABLE 1: COMPARISON BETWEEN PWM AND MPPT CHARGING

THEME 4.1.1 Charge Controller PWM MPPT

Potential values (volt) of PV Potential values (volt) of PV Module/array potential array and battery should array potential (V) can be match. higher than battery values. Performs well in warm Can provide boost in cold Battery climate and when the battery temperatures and when the is almost full. battery is low. Smaller systems (<200 W) System size 200 W or more to take where MPPT beneﬁts are advantage of MPPT beneﬁts. minimal. Off-grid with PV modules Larger off-grid or grid-tied Off-grid or grid-tied typically with Vmp 17–18V. PV systems. PV array size based on PV array size in watt based current (I) produced when PV on controller maximum Array sizing array is operating at battery charging current (I) × battery potential. potential (V).

Your own notes

278 Rechargeable Batteries Batteries can accumulate the electrical energy originating from PV systems and store it as chemical energy, which can be converted back to electrical energy and be used at any desired time. A battery’s capacity for storing energy is rated in watt or amp-hours at a given potential, e.g. 12, 24 or 48 volt for residential installations. T ere are many dif erent rechargeable battery types available for stand-alone or mixed PV systems and preference should be given to deep-cycle type batteries. T e disadvantage of using batteries for storage is that they are sensitive to temperature and charge/discharge cycle history (age). In South Africa, battery storage for limited or total autonomy is still relatively expensive and a reasonable storage system for residential PV installation (usually based on deep-cycle lead type batteries) would probably require similar investments to the PV system itself, thus doubling the total costs. However, PV with storage is nearing its payof point in the German residential market and most sources agree that PV-connected battery storage is set to take of in residential settings.

At grid level, some renewable energy developers are also starting to investigate the potential of large- THEME 4.1.1 scale battery storage tied to renewable energy plants. In Japan, for example, a 4 MW facility from Sumi- tomo is used to smooth out wind-generated energy peaks. Another example is Primus Power, a company which is planning to build a 25 MW storage plant in California, again for grid-scale renewable energy integration. 25 MW of electrical storage is a respectable size when considering the average capacity of a concentrated solar power (CSP) plant (approximately 50 ‒100 MW). Here, lithium-ion batteries are the technology of choice for most of these early projects, but other electrical storage concepts could also become more economical in future (redox f ow batteries for example). More information on batteries for renewable energy systems and electric cars will be given in RET NQF level 4 (2017).

FIGURE 11: DIFFERENT 12 V SEALED GEL BATTERIES

Image source: GIZ/S4GJ Dif erent 12 V sealed gel batteries commonly used for small stand-alone (of -grid) systems.

279 Overcurrent Protection Devices (OCPD) T e safe construction and operation of a PV system is of great importance. For small-scale PV systems, South African standards are still being compiled and relevant documents within the municipal and national context are expected soon, e.g. Eskom’s proposed simplif ed utility connection criteria for connected generators, which def nes the maximum size PV installations that may connect to the distribution grid without requiring additional network studies. International guidelines for installation and operation of PV systems can be found in DIN VDE 0100-712 and IEC 60364-7-712 (CD). BoS components, particularly system design and the mechanical and electrical components of the system, must also comply with the respective national or even local standards and regulations. For example, as already mentioned in Topic 3 (T eme 3.1.5 p. 252-253) , the installation of DC and AC disconnects requires appropriately rated overcurrent protection devices (OCPD). Please note that common OCPDs for AC are not compatible with the DC side of photovoltaic systems and vice versa.

THEME 4.1.1 FIGURE 12: DC AND AC RATED OVERCURRENT PROTECTION DEVICES (OCPD)

Image source: GIZ/S4GJ DC and AC rated overcurrent protection devices (OCPD) commonly used for the safe construction and operation of residential PV systems (grid-connected). Lef : automatic DC rated circuit breaker (6 A). Right: automatic AC rated circuit breaker (10 A).

DC circuit breakers operate very dif erently to AC breakers. Short circuits in the DC side of the systems

are likely to result in a short-circuit current (Isc, see T eme 4.1.3, PV Module Datasheets and Output

Parameters), which is not much higher than the normal operating current (Imp) of the system’s module/ array. T is is due to the fact that PV cells/modules are current-limited sources and thus the short-circuit

current (Isc), which can appear under faulty conditions, requires a more sensitive overcurrent protection device which triggers faster than AC breakers. OCPDs for AC circuits are not sensitive enough for this task and usually function only when a very large short-circuit current occurs in the system. Isolators It is strongly recommended that residential and commercial PV systems feature suitable load-switching capacity on both the DC and AC sides of the system. Since the PV array or its individual modules generally cannot easily be disconnected under load, for example for maintenance work or in case of system faults, it is absolutely necessary that switch-of equipment is provided. DC isolators, designed with a suitable switching capacity for direct currents, enable functions such as safe disconnection under load. Of en, DC isolators are already integrated into inverters. However, DC isolators are also recommended in connection boxes to enable selective disconnection of a PV string, allowing the rest of the system to continue producing electrical power. According to most standards, isolating equipment must also be provided on the AC side of the system to safely disconnect the AC circuit under load. T us, isolators with suitable AC switching capacity are recommended.

280 Mounting Systems Almost all types of PV systems require some mounting structures to hold the PV modules securely in place. Exceptions to this rule are integrated products which blend completely into the roof structure, resulting in the PV array being an integral part of the roof. While these integrated products can considerably improve the aesthetics of the homes and of ces, they are usually far more capital intensive than conventional PV systems that require mounting structures. Mounting structures on residential roof op installations are usually f xed parallel to the roof surface and thus determine the azimuth and tilt angle of the array. It is important to mount the rack and rails in such a way that the structure is slightly above the roof for cooling purposes (wind passing under the array!), given that cell temperature is a factor that af ects the performance of PV modules (see T eme 4.1.4).

FIGURE 13: MOUNTING SYSTEM COMPONENTS THEME 4.1.1

Image source: GIZ/S4GJ Mounting system components (rail, clamps etc.) commonly used for grid-connected roof op PV systems.

281 FIGURE 14: FIXING STAINLESS STEEL HOOKS OR ROOF ANCHORS INTO THE RAFTERS OF THE ROOF CONSTRUCTION THEME 4.1.1

Image source: GIZ/S4GJ One of the f rst steps of mounting a PV array onto tiled roofs is f xing stainless steel hooks or roof anchors into the raf ers of the roof construction without damaging the tiles. Here this is done on a tiled training roof commonly used in TVET colleges.

FIGURE 15: A HOOK AND RAIL SYSTEM FOR A TILED ROOF

Image source: GIZ/S4GJ A more detailed view of a hook and rail system for a tiled roof. Once the roof hooks have all been secured, the mounting rail is attached to them. Please note: T e prof le of the rail can vary to suit dif erent roof hook designs.

282 FIGURE 16: PV MODULES BEING ATTACHED TO THE RAILS THEME 4.1.1

Image source: GIZ/S4GJ Once the mounting system has been secured, the individual PV modules are attached to the rails to form the array. Here this is done on a tiled training roof commonly used in TVET colleges. Mounting PV systems on racks and poles closer to the ground are more common in larger commercial applications. Some ground mounted systems may also have the ability to track the Sun across the sky, following its course over the day and the year (optimised azimuth angle). Sometimes ground-mounted PV modules are f xed on a suntracking system, making the system more prof table.

Your own notes

283 Examples Balance of System (BoS) Worldwide and across all PV market segments, including residential, commercial and PV plants, system costs have considerably decreased in the last years. T is trend mainly accounts for module cost reductions and less for BoS components. At present and on average, costs for BoS accounts for 50‒60 % of a residential PV system. However, the overall cost reduction trend for PV systems will most probably continue over the next few years, including the residential system market, which is the costliest PV market segment. Subsequently, today a 1.5 kW residential PV roof op system (grid-connected) can be pur- chased for around ZAR 42.000, i.e. ZAR 28/watt. Market research forecasts that system prices could fall to ZAR 24/watt within the next couple of years due to BoS innovation that will drive costs down, whilst services and other sof costs will remain at current levels. Please note that albeit these assumptions are

THEME 4.1.1 based on projections that use the best available information, they are subject to considerable uncertainty.

FIGURE 17: COST REDUCTIONS OF RESIDENTIAL PV ROOFTOP SYSTEMS IN THE USA BETWEEN 2008 AND 2012

US Dollar per watt 10 Services 9 BOS Hardware 8 Module 7 6 5 4 3 2 1 0 2008 2009 2010 2011 2012

Image source: GIZ/S4GJ Development of costs (US $ per installed capacity/watt) of residential PV roof op systems (PV modules, BoS hardware and services) in the American market between 2008 and 2012, adapted from Chakraborty and GTM Research. Roof Penetration Mounting structures on residential roof ops usually requires roof penetrations and these are of en the most dif cult part of installing a PV array. Roof penetration is when the installation process requires a modif cation to be made to the existing roof structure. T e conventional method of drilling a hole into the roof is the obvious example of roof penetration, but grinding a tile or raising a tile from its original position is also an example.

All modiﬁcations to a roof structure must be undertaken carefully, as roofs are designed to keep wind and rain out of the building. Any installation on a roof must not compromise the roof’s function and longevity. By modifying a roof during the installation process, the installer shoulders some of the responsibility for the roof’s functions, e.g. waterproofness, and can therefore be liable for leaks. Ensuring that any penetrations in a roof are appropriately sealed, secure and as long lasting as possible will help the installer to meet these requirements.

It is strongly recommended to refer to the mounting system and rooﬁng manufacturer’s guidelines and to ensure that all penetrations are suitably sealed and waterproof.

284 Corrugated and Other Metal Roofs A good method of sealing penetrations around small entries such as conduits on corrugated and other metal roofs is to use small durable rubber rings or silicon f ashing. Ensure that the seal is UV stabilised and freeze proof.

FIGURE 18: A SELF-SEALING MOUNTING BASE THEME 4.1.1

Image source: GIZ/S4GJ A more detailed view of how to screw a self-sealing mounting base onto a corrugated metal roof.

FIGURE 19: A MOUNTING SYSTEM

Image source: GIZ/S4GJ A mounting system has been f xed onto a corrugated training roof commonly used in TVET colleges.

285 Tile Roofs T e previous advice for corrugated and other metal roofs also applies to tile roofs, but installations on tile roofs typically require grinding out numerous tiles to f x the hooks onto the beams of the trusses. Sealing these holes properly can be tedious, but it is one of the most important activities in the installation process. Replacing all broken tiles with new ones or f xing large f exible metal sheets that cover the penetrated tile is the required standard.

WHAT NOT TO DO!

Simply using silicon to seal roof penetrations is not a sufficient method for sealing any roof penetration. Silicon may be easy to apply, but over the life of a PV system this material becomes hard and is unlikely to maintain a secure waterproof bond. Roof shapes THEME 4.1.1 usually change over time and hardened silicon will not flex sufficiently with the roof. This is of particular concern for corrugated and other metal roofs which are subject to thermal expansion due to diurnal temperature differences. Over time, the hardened silicon will become loose, leaving gaps for water to penetrate.

Your own notes

286 Exercises

Answer the following questions:

Question 1 What kind of material are PV cells made of?

Question 2 THEME 4.1.1 State the individual electrical potential dif erence of a typical solar cell.

Question 3 Considering the low individual electrical potential dif erence of solar cells, how are PV cells connected in a PV module to produce at higher potential, resulting in a greater amount of power?

Question 4 Describe the dif erent layers of PV modules.

Question 5 How is the electrical performance of a PV module typically rated?

Question 6 How reliable are quality PV modules and what is their lifetime/warranty?

Question 7 Explain the term Balance of System (BoS).

287 Question 8 What are the main dif erences between stand-alone and grid-connected systems?

Question 9 T e purpose of an inverter is to: THEME 4.1.1

Question 10 Sine wave inverters are recommended because:

Question 11 Explain why DC circuit breakers operate very dif erently to AC breakers.

Question 12 Why is it recommended to install suitable load-switching devices on both the DC and AC side of residential and commercial PV systems?

Question 13 Why is it important to mount the rack and rails in such a way that the structure is lif ed slightly above the roof?

Question 14 Why is it important to appropriately seal any penetrations in a roof?

288 Further Information (all materials are on the resource CD)

(i) Chakraborty (Centrosolar America) and GTM Research, http://www.greentechmedia.com/ articles/read/Its-Solar-Balance-of-System-Innovation-T at-Will-Drive-Cost-Reduction. (ii) Trinamount I for Tiled Roofs Installation (Video) https://www.youtube.com/watch?v=cwKG7Yrj3ug (iii) SunLock mounting system instructional (Video) https://www.youtube.com/watch?v=SzW5X1ZOL5w (iv) Renewable Energy Solar Panel System Components (Video) https://www.youtube.com/watch?v=zLLBJfdqPVM (v) MPPT (Video) https://www.youtube.com/watch?v=0ItjKs7aJFM

(vi) Charge Controllers (Video) THEME 4.1.1 https://www.youtube.com/watch?v=qGmEz58Ixk4 (vii) Inverters (Video) https://www.youtube.com/watch?v=sZx6qDj2EOo

Your own notes

289 THEME 4.1.2 SEMICONDUCTOR MATERIALS AND THE PHOTOVOLTAIC EFFECT

Introduction

T e following theme explains in simplif ed terms how semiconductor materials are used in solar cells and how the process of converting sunlight into electrical current works. THEME 4.1.2 Keywords

PV cell types Crystalline silicon T in f lm Conversion ef ciency Temperature coef cient Poly (multi)-crystalline Mono-crystalline Amorphous thin f lm Copper indium gallium selenide thin f lm Cadmium telluride thin f lm Semiconductors Doping P–Type N–Type P-N Junction Photovoltaic ef ect

Theme Outcome

At the end of this theme, you should be able to: (i) List the semiconducting materials used to produce the main types of solar cells/panels. (ii) Describe and explain the photovoltaic ef ect. (iii) Compare dif erent PV module technologies.

290 Deﬁ nition of Terms PV Cell and Thin Film Types T ere are two broad categories of technology used for PV modules, namely, wafer based crystalline silicon cells and thin f lm technology. T e ‘family tree’ in Figure 1 gives you an overview of the most established and commonly available technologies, and Table 1 and 2 of er a comparison regarding market share and conversion ef ciency (radiation energy to electrical energy).

FIGURE 1: THE TWO MAIN TYPES OF MATERIALS USED FOR THE CONSTRUCTION OF PV PANELS

Crystalline silicon THEME 4.1.2 (wafer-based) Thin ﬁlm

Amorphous-Si Poly-crystalline (a-Si)

CIGS Mono-crystalline (Copper Indium Gallium Selenide)

CdTe (Cadmium Telluride) ......

Image source: GIZ/S4GJ Two main types of materials used for the construction of PV panels can be dif erentiated, i.e. wafer-based crystalline silicon cells and thin f lm technologies.

TABLE 1: GLOBAL MARKET SHARE OF WAFER-BASED CRSTALLINE SILICON CELLS AND THIN FILM TECHNOLOGIES

Technology Market Share (%)

Mono-crystalline 54

Poly-crystalline 36

Amorphous silicon 6

CIGS 2

CdTe and other thin ﬁlm 2

Adapted from International Renewable Energy Agency, IEA-ETSAP and IRENA Technology Brief E11, January 2013 (see Further Information on resource CD)

291 TABLE 2: CONVERSION EFFICIENCIES (INDUSTRIAL MASS PRODUCTION) OF WAFER-BASED CRSTALLINE SILICON CELLS AND THIN FILM TECHNOLOGIES

Module efﬁciency Technology (%)

Mono-crystalline 14–20

Poly-crystalline 14–18

Amorphous silicon 8

CIGS 10–14

CdTe and other thin ﬁlm 9–12

Adapted from http://en.wikipedia.org/wiki/Crystalline_silicon

Apart from dif erent appearances and structural properties (rigid or f exible), the most obvious dif erence amongst PV technologies is their conversion ef ciency, which subsequently will result in dif erent area/space requirements for the dif erent technologies. For example, a thin f lm amorphous silicon PV array may need twice the area/space of a mono-crystalline array due to their dif erent nominal electrical capacity under Standard Test Conditions (STC). In any case, module ef ciency is a primary concern in the PV industry. Suf cient cost savings from module manufacturing can be suitable to of set reduced ef ciency in the f eld, such as the use of larger solar cell arrays compared with more compact/higher ef - ciency designs. T us, even though thin f lm technology has a lower ef ciency, it can be attractive because of the low production costs. On the other hand, modules with a higher ef ciency have the advantage of occupying less space and the issue of ef ciency versus cost is an important decision based on whether one requires a more ef cient device due to area constraints or not. Consequently, and due to their various properties, performance parameters and price per watt, each PV technology has characteristic constraints and advantages.

Another important distinction between the dif erent PV technology types is their temperature coef cient of power (Table 3 and Figure 2). Generally, PV module performance declines as module temperature rises (see module datasheets), but thin f lm technologies have a lower negative temperature coef cient compared to crystalline technologies and tend to lose less of their rated capacity as temperature rises. T us, under hot climatic conditions, thin f lm technologies will generate 5‒10 % more power per year compared to crystalline technologies.

TABLE 3: PV TECHNOLOGIES AND THEIR DIFFERENT TEMPERATURE COEFFICIENTS

Temperature Coefﬁcient Technology (% per degrees Celsius)

Crystalline silicon -0.4 – -0.5

Amorphous silicon -0.21

CIGS -0.32 – -0.36

CdTe and other thin ﬁlm -0.25

Adapted from various sources, for example Performance of Photovoltaics Under Actual Operating Conditions, G. Makrides, B. Zinsser, M. Norton and E. Georghiou, 2012 or Overview of Temperature Coef cients of Dif erent T in Film Photovoltaic Technologies, A.Virtuani*, D. Pavanello, and G. Friesen, 2010 (see Further Information on resource CD).

292 FIGURE 2: AVERAGE EFFECTS OF TECHNOLOGY SPECIFIC TEMPERATURE COEFFICIENTS OF POWER ON PV MODULE OUTPUT PERFORMANCE THEME 4.1.2

Image source: GIZ/S4GJ Adapted from Overview of Temperature Coef cients of Dif erent T in Film Photovoltaic Technologies, A.Virtuani*, D. Pavanello, and G. Friesen, 2010 (see Further Information on resource CD). T e average ef ects of technology specif c temperature coef cients of power on PV module output performance under dif erent climatic conditions (module temperature between 25° C ‒ 85° C) relative to performance under STC (25° C). Crystalline Silicon Most solar cells produced today are made from silicon (Si), the second most abundant element on Earth and the primary ingredient in sand. T e f rst distinctive process step in solar cell manufacturing is silica processing (chemical purif cation) which creates silicon chunks. T e next step focuses on the production of ingots, i.e. blocks or bars of high-purity silicon. To do this, large amounts of silicon chunks need to be crushed to a powder. T e useful electrical properties of crystalline silicon as semiconductor materials are based on extremely small amounts of impurities (see doping) added to the silicon powder. T e mixture is then heated at high temperatures and ingots are formed. T e ingots need to cool down before they are sliced into thin wafers which are usually only 0.2 mm (200 microns) thick, similar to the thickness of a piece of paper. T ese wafers are tested, inspected and processed further, including a chemical surface texturing process to reduce the ref ectivity of the wafer. Additional mechanical and chemical processes will then transform the wafer into a photovoltaic cell to which metal contacts on the front and rear surfaces are attached.

293 FIGURE 3: FROM SAND TO PV MODULES THEME 4.1.2

Image source: http://en.wikipedia.org/wiki/File:Polysilicon_compilation.jpg, http://en.wikipedia.org/wiki/Sand

T e most common constituent of sand is silica (silicon dioxide, or SiO2). Mechanical and chemical processes transform silica into the silicon wafers which are used for the production of solar cells, integrated circuits and other semiconductor devices.

Poly-crystalline (or Multi-crystalline) Poly-crystalline cells are ef ectively a slice (wafer) cut from a block of silicon (ingot), consisting of a large number of crystals which have a speckled ref ective appearance (see Figure 3). Poly-crystalline cells are slightly less ef cient (see Table 2) and less expensive compared to mono-crystalline cells and need to be mounted into a rigid frame. Mono-crystalline In appearance, mono-crystalline PV cells have a more uniform, smooth texture compared to poly-crystalline cells. Mono-crystalline cells are more ef cient but also more expensive to produce when compared to poly-crystalline. Like poly-crystalline, mono-crystalline PV cells must be mounted in a rigid frame to protect them. Amorphous/Thin Film Amorphous cells are manufactured by placing a thin f lm of amorphous, non-crystalline silicon onto a wide choice of surfaces. T ey are the most well-developed thin f lm technology to-date, but also the least ef cient (see Table 2) and least expensive silicon-based cells to produce. Due to the amorphous nature of the thin layer, the material is f exible and if manufactured on a f exible surface, the whole solar panel can be f exible. However, one inconvenient characteristic of amorphous solar cells is that their power output signif cantly reduces over time, about 10‒30 % during the f rst six months of operation (stabilisation). T us, the quoted electrical output of amorphous cells/modules should make reference to the power output af er stabilisation. Copper Indium Gallium Selenide (CIGS)/Thin Film CIGS is one of three mainstream thin f lm PV technologies and although not as ef cient as mono-crystalline silicon cells, CIGS has the benef t of lower priced material costs. CIGS has a high light absorption coef cient and requires a much thinner f lm than other thin f lm semiconductor materials.

294 Cadmium Telluride (CdTe)/Thin Film Cadmium telluride has potential problems with the high toxicity of cadmium (Cd) and the limited availability of tellurium (Te). Te production and reserves are subject to uncertainty and thus vary considerably. Tellurium is primarily used as an additive to steel and almost exclusively obtained as a by-product of copper ref ning. On the other hand, CdTe technology can ef ciently be produced and has a shorter energy payback time compared to other PV technologies. CdTe module ef ciency is similar to CIGS. Semiconductors Semiconductors are the foundation of modern electronics and the most common semiconductor materials are silicon (Si) and germanium (Ge). Most semiconductor chips and transistors are based on silicon and you may have heard the expressions ‘Silicon Valley’, a nickname for the southern portion of Northern Califor- nia’s Bay Area (USA). T e term originally referred to large numbers of silicon chip innovators and manufacturers of the bay region, but eventually was used to refer to all high-tech businesses in that area. THEME 4.1.2 FIGURE 4: INTEGRATED CIRCUIT (IC) CHIPS

Image source: http://en.wikipedia.org/wiki/File:T ree_IC_circuit_chips.JPG Similar to crystalline PV cells, most integrated circuit (IC) chips, like the three ICs in the image, are based on silicon due to its semiconductor qualities.

Semiconductors have had a massive impact on modern industrialised societies which rely on micro- processors (IC chips) and transistors. Any device that is computerised or uses radio waves depends on semiconductors. A semiconductor is a substance, usually a chemical element or a compound, with an electrical conductivity between that of a conductor, such as copper, and an insulator, such as glass (see also Topic 2, T eme 2.2.1 p.148). Semiconductors can display a range of useful properties, such as passing current more easily in one direction than in the other, showing variable resistance, and sensitivity to light or heat. Electronic and photovoltaic devices made from semiconductors can be used for amplif cation, switching, and energy conversion. Why use Silicon? Silicon is a common choice for semiconductors due to its inherent physical properties. You may recall from Topic 2 (T eme 2.2.1 p.147) that all matter is made up of fundamental building blocks known as atoms and that each atom consists of electrons, protons and neutrons. T e electrons and the protons carry a charge, and the charge of an electron is negative, while a proton carries a positive charge of the same magnitude as the electron. Electric charge, either negative or positive, is the most basic quantity in an electric circuit. T e silicon atom has 14 electrons, but their electron arrangement allows only the outer four of these 14 electrons to be used for bonds with other atoms. T ese outer four electrons, called ‘valence’ electrons, play an important role in the semiconductor properties and the photovoltaic ef ect.

295 T rough their valence electrons, large numbers of silicon (Si) atoms can bond together to form a crystal. In a crystal, each Si atom normally shares one of its four valence electrons in a bond with each of the four neighbouring Si atoms (see Figure 5). T e basic unit of the crystal structure or lattice consists of f ve Si atoms, i.e. the original Si atom plus the four other atoms with which it shares its four valence electrons. T us, in a crystal, each Si atom is bonded to four other Si atoms and each Si atom shares each of its four valence electrons with each of the four neighbouring Si atoms. In this arrangement, each Si atom has eight electrons in its outer orbit or shell and is very stable. With eight electrons in the outer orbit, silicon is an almost perfect crystal and has no free electrons and thus cannot conduct a charge.

FIGURE 5: THE SILICON (SI) ATOM THEME 4.1.2 Si Si Si

Si Si Si Si

Si Si Si

Image source: GIZ/S4GJ A silicon (Si) atom has four valence electrons and bonds together with other Si atoms in a lattice type structure, where every atom in the structure bonds with four other Si atoms. Doping T e useful electrical properties of semiconductor materials are based on very, very small amounts of impurities (dopants) added to it. T e amount of dopant added to silicon has a ratio of 1 part in 108. T is is 1 gram of dopant material to 100 metric tons of silicon. However, the ef ect is quite amazing and will change the electrical properties of silicon signif cantly. T ere are two types of impurities: P–type In P–type doping, boron (B) or gallium (Ga) is used as the dopant. Boron, for example, has three electrons in its outer shell and when a B atom takes the place of a Si atom in the lattice structure, the single impurity B atom creates a missing bond in the lattice. T e missing bond or incomplete bond is also called a ‘hole’. T us, when boron is mixed into the silicon crystal, ‘holes’ will form in the silicon lattice due to the fact that one electron per B atom is def cient or missing for perfect bonding. Consequently, and given, that a ‘hole’ can accept an electron from a neighbouring Si atom, ‘holes’ can conduct a negative charge. T e moving electron subsequently creates a new ‘hole’, resulting in another incomplete bond, thus triggering a kind of a chain reaction where electrons are moving around in the crystal and creating ‘holes’ which can accept moving electrons. Due to this ef ect, P–type silicon can conduct a negative charge and is a viable conductor.

296 FIGURE 6: A BORON (B) ATOM TAKES THE PLACE OF A SI ATOM IN THE CRYSTAL LATTICE

Si Si Si

‘Hole’or incomplete bond B Si B Si THEME 4.1.2

Si Si Si

Image source: GIZ/S4GJ When substituting a silicon (Si) atom with a boron (B) atom in the crystal lattice, the three valence electrons of the B atom can only bond with three of the four Si atom neighbours. T us, the bond with the fourth Si atom neighbour remains incomplete and a ‘hole’ appears. T e incomplete bond attracts electrons from the neighbouring Si atoms, which will move to ‘f ll the hole’. N–type In N–type doping, phosphorus (P) or arsenic (As) is added to the silicon (Si) in small quantities. Phos- phorous has f ve electrons in its outer shell and when a P atom takes the place of a Si atom in the lattice structure, an additional electron is available in the lattice structure. T us, a minute amount of either N– type or P–type doping turns a silicon crystal from a good insulator into a viable, but not great conductor, hence the name ‘semiconductor’.

FIGURE 7: A PHOSPHORUS (P) ATOM TAKES THE PLACE OF A SI ATOM IN THE CRYSTAL LATTICE

Si Si Si

Additional electron P Si P Si

Si Si Si

Image source: GIZ/S4GJ When substituting a Si atom with an phosphorus (P) atom in the crystal lattice, four of the phosphorus valence electrons form bonds with the neighbouring Si atoms. But the f f h additional phosphorus electron remains unbounded or only weakly bonded and can move around in the Si crystal and as a result, the phosphorus atom becomes positively charged (ionised).

297 FIGURE 8: ‘DOPED’ OR IMPURE (COMPOUNDED) SILICON

N-Type Additional Si Si Si electron (q-) Si Si Si

Si Si Si Si

P-Type THEME 4.1.2 Si Si Si Incomplete Si Si Si bond or ‘hole’ (q+)

Image source: GIZ/S4GJ ‘Doped’ or impure (compounded) silicon has a lattice with atoms which either contain more electrons to create negatively (q–) charged silicon (N–type) or a lattice with atoms which contain less electrons to create positively (q+) charged (P–type) silicon. P-N Junction Now you know that the N–type and P–type silicon create unique properties of semiconductors. N–type and P–type silicon are not so amazing by themselves, however, when both types are placed together, some very interesting behaviour appears at the P-N junction. We already mentioned in the above section that P‒doped semiconductors, i.e. boron doped silicon, can be conductive. T e same is true for N‒doped semiconductors, i.e. phosphorous doped silicon. T e P–N junction between them is, however, non‒conducting for the reason that the excess electrons in the N‒ type silicon layer move into the P‒type layer and eliminate each other’s charge. As N‒type silicon layers move, they leave positively charged ‘holes’ in the N‒type layer. During this process, while the charges are neutralised, a potential dif erence called built-in potential or built-in electric f eld, is created with a magnitude of approximately 0.5‒0.6 volts. T e built-in potential creates an electric f eld across the P–N junction and is the signif cant factor in the operation of a semiconductor, including PV cells, as it drives the current across the P–N junction into the N‒type layer and through an external electrical circuit.

FIGURE 9: THE DEPLETED P-N JUNCTION

+ -

N-type P-type

- + + + - - + + + - - - - + + + + + - + - - - - + + + - - - + - - - - + + + + - + - - + - + + - + - + - - + - - + + + + + - + + - - + + - - - + - - + + + + + - - - + - - - + -

Depletion Volt - - Free electrons + layer + Positiveion (P)

Potential difference - Negativeion (B) across thejunction + + Holes -

Image source: GIZ/S4GJ T e depleted P–N junction with separated (neutralised) charges has a potential dif erence called built-in potential or built-in electric f eld, with a magnitude of approximately 0.5‒0.6 volts.

298 The Photovoltaic Effect Many semiconductors can convert sunlight into electrical energy, a process called ‘photovoltaic ef ect’, and PV cells are explicitly designed and manufactured to exploit this ef ect. T e word ‘photovoltaic’ is a combination of the Greek word for light (photo = light) and the name of the Italian physicist A. A. Volta (1745–1827) who invented the f rst battery (voltaic = electrical energy). T e SI unit of electrical potential dif erence is called volt (V), in honour of Mr. Volta. T us, photovoltaic refers to the direct conversion of sunlight into electrical energy by means of semiconductor material in PV modules. The Photovoltaic Effect: A Simpliﬁ ed Explanation When sunlight is absorbed in a PV cell it transfers its energy to atoms, energises them and knocks electrons out of their orbit. T e electrons then move through the PV cell layers and create a charge f ow (a DC current).

The Photovoltaic Effect: A More Detailed Explanation THEME 4.1.2 When photons are absorbed into the atomic structure of the silicon lattice, their energy is transferred to electrons. T ese energised electrons can then move from their normal positions in the atoms of the semiconductor, triggering a negative charge f ow (current). A special electrical property of the P–N junction in the PV cell, called the built-in electric f eld, provides the force or potential dif erence necessary to drive the current across the P–N junction of the PV cell into the N‒type layer and through an external electrical circuit.

FIGURE 10: ELECTRIC CURRENT IN A PV CELL

Light energy(Photons)

Glass co verwith anti-reﬂectioncoating Current Electrode - N-type silicon q- q- P-N junction q- q- P-type silicon

+ Electrode

Current

Image source: GIZ/S4GJ When photons are absorbed in the P‒type silicon, electrons will be dislodged and a negative charge will f ow from the cathode (N-type silicon) to the anode (P-type silicon) creating an electric current in a short-circuited PV cell. The Photovoltaic Effect: An In–Depth Explanation Sunlight is composed of both particles (photons) and waves. T e photons contain various amounts of energy corresponding to the dif erent wavelengths of the solar spectrum. When photons strike a PV cell, they may either be ref ected, pass right through the cell or get absorbed into the cell’s crystal lattice. Absorption of photons can create a light‒generated current. T e generation of such light‒generated current happens inside the depletion zone of the P‒N junction, the contact area between the N-type and the P-type semiconductor. T e P-type material has incomplete bonds or ‘holes’ in their crystal lattice holes, creating a positive charge. T e N-type material has mobile negative charges, i.e. additional electrons. Near the junction, the N-type material electrons dif use across the junction, combining with ‘holes’ in P-type material. T e region of the P-type material near the junction takes on a net negative charge because of the electrons attracted. Since electrons departed the N-type region, it takes on a localised positive charge. T e thin layer of the crystal lattice between these charges, the P‒N junction, has been depleted of charges and thus becomes

299 nonconductive semiconductor material (separation of charges). In ef ect, this is almost an insulator separating the conductive P and N doped regions. Due to the separation of charges, an electric f eld (and a potential dif erence) has been established across this region. T e separation of charges at the P‒N junction, or more precisely, the built-in electric f eld, constitutes a potential barrier for charge f ow. T is barrier must be overcome by an external energy source to make the junction conduct. T us, the problem now is that an electron (negative charge) would require some extra energy to cross the depleted P‒N junction. T e formation of the P‒N junction, which causes this potential charge barrier, happens during the semiconductor manufacturing process. T e magnitude (potential dif erence) of the barrier is a function of the materials used in manufacturing, in PV cell silicon P‒N junctions approximately 0.5‒0.6 volts. Due to the depleted P–N junction, the built-in electric f eld is always present across the PV cell creating a force, or potential dif erence, and promoting only one‒directional current to f ow across the junction (barrier). In PV cells, the extra energy required by an electron to cross the charge depleted P‒N junction towards the N-type layer can be provided by photons. When a photon is absorbed by one of the atoms THEME 4.1.2 in the P‒type silicon, it will dislodge and free an electron. Due to photon absorption, the free electron now has suf cient energy to cross the depletion zone, resulting in a negative charge f owing towards and out of the N-type silicon. T us, if a circuit is established from the cathode (N-type silicon) to the anode (P-type silicon), i.e. if the PV cell is short-circuited, a negative charge will f ow through the external circuit creating an electric current.

Exercises can be found in Unit 4.2

Please carry-out: (i) Experiment 2: T e solar cell as energy converter (ii) Experiment 3: T e solar cell as energy converter and/or diode

Further Information (all materials are on the resource CD)

(i) How it’s made - Solar panel (Video) https://www.youtube.com/watch?v=BKrOZ6OogmQ (ii) From sand to silicon (Video) https://www.youtube.com/watch?v=jh2z-g7GJxE (iii) Silicon Wafer Production (Video) https://www.youtube.com/watch?v=AMgQ1-HdElM (iv) Semiconductor junction (Video) https://www.youtube.com/watch?v=oU_aTkPzaN8

300 THEME 4.1.3 PV MODULE DATASHEETS AND OUTPUT PARAMETERS Introduction

At some point everybody involved in planning, sizing and/or installing a PV system (or any other mechanical, electrical or electronic components) needs to check the datasheets of the selected system components. T is theme will introduce you to the facts of why datasheets are so important and what information you can expect to f nd in them. You may also recall that in Topic 3 (Safety) we introduced you to Material Safety Data Sheets (MSDS) which provide you with important product information. Melting or boiling points, toxicity, health ef ects, storage, disposal and handling procedures of products and materials are all important for occupational health and safety. T e same applies for the technical components of a PV system and a technical datasheet will provide you with product information required to work in a THEME 4.1.3 safe and ef cient manner.

Datasheets of similar components, say PV modules, may dif er from manufacturer to manufacturer and some may be more dif cult to read and understand than others. Manufacturers of quality components want you, the planner or installer, to have a successful experience with their components and thus try to be as helpful as possible. As a rule, if there is no or only a poor quality datasheet provided by the manufacturer, you can almost bet that the product is of poor quality as well! Quality products from established manufacturers will, for example, always provide you with a good installation- and user manual. As the saying goes: You usually get what you are paying for...

Keywords

Datasheet Standard Test Conditions (STC) Nominal Operating Cell Temperature (NOCT) Maximum power point (MPP)

Open circuit voltage (Voc)

Voltage at maximum power (Vmp) Nominal voltage

Short circuit current (Isc)

Current at maximum power (Imp)

Maximum or peak power (Pmax or kWp) Module ef ciency Maximum system voltage Series fuse rating Type of output terminal I‒V curves

Theme Outcome

At the end of this theme, you should be able to: (i) Interpret sample datasheets with reference to standards, certif cations and warranties. (ii) Identify and measure key electrical output parameters using multimeters. (iii) Explain and sketch the current-potential (I-V) curve of a PV module in a diagram.

301 Deﬁ nition of Terms Datasheets In general, a datasheet is a document that summarises the performance and other technical characteristics of an electric or mechanical machine, component or sof ware in suf cient detail, enabling a skilled worker or engineer to integrate the machine or component into a new or existing system or technical structure. Typically, a datasheet is created by the manufacturer and begins with an introduction, followed by a listing of specif c characteristics and further information on the connectivity of the device. Datasheets are published by manufacturers to help people choose the right products and to install them correctly. Where do you f nd datasheets? Nowadays you can f nd almost any datasheet from quality manufacturers on the internet, of en in PDF format for you to download.

A typical datasheet for PV system components usually contains most of the following information: THEME 4.1.3 (i) Manufacturer’s name (ii) Product number and name (iii) Drawings or images showing physical details, such as minimum/maximum dimensions, contact locations and sizes (iv) Important device properties (v) Functional description and installation instructions (vi) Absolute minimum and maximum ratings (power supply and/or consumption, input currents, temperatures for storage, operating etc.) (vii) Recommended operating conditions (as absolute minimum and maximum ratings) (viii) DC and AC specif cations (various temperatures, input/output potential and currents etc.) (ix) Safety instructions, warranties and liability disclaimer

Simply put, a well designed datasheet of a quality product will tell you everything you need to know about it and we strongly recommend reading and using this information. Many design and installation errors are due to overlooking or disregarding (deliberately or not) certain information in the datasheet. Again, consider that manufacturers want you to have a successful experience with their products. T e reason they are going to the trouble of producing a datasheet is that they are trying to be helpful. Un- fortunately they do not always succeed - some datasheets are not very user‒friendly and present a large amount of information in an incomprehensible manner. However, we advocate reading the datasheet before you buy the product. It is really worth taking the time to read it, particularly if you more or less know what you are looking for or what electrical and mechanical parameters are required. You don’t have to understand everything on a datasheet. T ere might be a lot of information that is not of any particular use to you, but the annotations that follow try to direct you to the datasheet parts and parameters of PV system components that you should pay particular attention to. PV Module Sample Datasheets A typical datasheet for PV modules usually contains the electrical output parameters under STC (Stan-

dard Test Conditions) and NOCT (Nominal Operating Cell Temperature), including peak power (Pmax),

potential (voltage) and current at open circuit (Voc and Ioc), maximum power point (Vmp and Imp) and the I-V curve etc. Other electrical parameters include module ef ciency, temperature coef cients, mechanical parameters such as dimensions, weight etc. and certif cations and warranties. We will illustrate this information on a sample datasheet and will explain some important electrical parameters in more detail in the following pages.

302 FIGURE 1: RELEVANT PARAMETERS INDICATED IN A SAMPLE DATASHEET FOR A PV MODULE

Sample Data Sheet foraPV Module Electrical Speciﬁcations Mechanical&General

2 92.25cm STC 1,000 W/m , 25°C, 1.5AM Peak power Pmax 220 watts Voltage at maxpower Vmp 29.8volts

Current at maxpower Imp 7.39 amps THEME 4.1.3 Voltage at open circuit Voc 36.8volts

Current at shortcircuit Ioc 8amps 166.37 Leads: NOCT 800 W/m,2 47,2°C, 1.5AM 101.6cm

Peak power Pmax 159 watts 99 cm 3.81 cm Voltage at maxpower Vmp 27 volts Current at maxpower Imp 5.9amps Voltage at open circuit Voc 34 volts Dimensions 166.37 x99cm 2 Current at shortcircuit Ioc 6.47 amps Area 17.7 k Thickness 3.81 cm Weight 17.96kg 10 9 Peak Power= Isc =8 STC 60 monocrystalline silicon 220 W Cells 8 Imp=7.39 7 Isc =6.47 NOCT Cell dimensions 15.24x15.24cm 6 High-transparency,low-iron, Imp=5.9 Peak Power= Glazing tampered glass with 5 159 W 4 antireﬂection treatment

Amperage 3 Backsheet Double-layer,high-perfomance 2 polyester Vmp= Vmp= Voc= Voc= 1 27 29.8 34 36.8 Ethyl vinyl acetate 0 Encapsulation 0 5 10 15 20 25 30 35 40 Frame Black anodised aluminium Voltage Connectors 12 AWG, PV Wire, Tyco connector Junction box Tyco Solarlak Other ElectricalParameters Bypass diodes 3diodes

Powertolerance Percent x3% Modules/pallet; 20 modules/pallet Pallets/container 28 pallets/40 k. container Efﬁciency Cell 15.5%

Module 13.5% 2 Design load 34.02kg/k Temperature Pmax -0.45 per °C Maximum wind speed 193.12 kph coefﬁcients Voc -0.35 per °C Vmp -0.42 per °C Isc +0.05 per °C Maximum system voltage 600 volts Certiﬁcations&Ratings Max. seriesfuse rating 15 amp Listing Ul 1703 Warranty Fire safety class 193.12 kph

90 % rated power 10 years limited 80 % rated power 25 years limited Proudly powered by the sun Workmanship 5years

Image source: GIZ/S4GJ

303 Cell Type T e type of technology used in the PV module, e.g. either mono-crystalline, poly-crystalline or thin f lm. Numbers of Cells and Connections T is parameter tells you how many PV cells are contained within the module and how they are connected (usually in series). Standard Test Conditions (STC) STC represents standardised test conditions that all PV modules are tested and rated at. STC is done at a temperature of 25° C, irradiance of 1000W/m2, and an air mass value of 1.5. Nominal Operating Cell Temperature (NOCT) NOCT is def ned as the temperature reached by open circuited cells in a module under the following conditions: THEME 4.1.3

Irradiance on cell surface = 800 W/m2, air temperature = 20° C, wind velocity = 1 m/s, mounting = open back side.

Note the somewhat lower insolation conditions compared to STC. In addition, module performance is of en measured at an operating temperature of 45° C instead of 20° C. At 45° C, NOCT is much more realistic and probably close to the cell temperature PV modules are likely to operate at. Consequently, and given that PV modules typically operate at higher temperatures and possibly at somewhat lower insolation conditions, more realistic power outputs are stated under NOCT. Maximum Power Point (MPP) T is is the point on the current-voltage (I-V) curve of a PV module where the product of current and potential is at its maximum.

Open Circuit Voltage (Voc) T is is the potential measured at the module terminals when no load is applied. In other words, the

circuit is ‘open’ and not connected to any load. Voc is the maximum possible potential across a photovoltaic cell or module.

Voltage at Maximum Power (Vmp) T is is the potential dif erence magnitude of a given device, usually a PV module, at its maximum power point. Nominal Voltage Nominal voltage refers to the voltage of the battery that the module is best suited to charge; this is a lef over term from the days when solar modules were only used to charge batteries. T e actual voltage output of the module changes as lighting, temperature and load conditions change, so there is never one specif c voltage at which the module operates. Nominal voltage allows users to, at a glance, make sure the module is compatible with a given system.

Short Circuit Current (Isc)

T is is the current ( I) that f ows through the module terminals at short circuit. Isc is the maximum amount of current that the solar panel can provide.

Current at Maximum Power (Imp) T is is the amount of current of a given device, usually a PV module, at its maximum power point.

Maximum or Peak Power (Pmax or kWp)

Pmax is the amount of power (P) that can be produced under standard test conditions (STC). For ex-

ample, a Pmax rating of 315 W = 0.315 kW. DC output power of PV modules typically ranges from 10 to

400 watt. Pmax is calculated by multiplying open-circuit voltage by short-circuit current (Voc × Isc). Module Efﬁ ciency Ef ciency is the most commonly used parameter to compare the performance of one PV module to another. Ef ciency is def ned as the ratio of energy output from the solar cell to input energy from the

304 Sun. In other words, if the solar irradiance is 1000W/m2, and the panel is a square meter, a 13.74 % ef ciency would give a module output of 137.4 W. T e ef ciency of a module also determines the area of a module given the same rated output. For example, a 230 watt module with only 8 percent ef ciency will require twice the area of a 230 watt module with 16 % ef ciency. Maximum System Voltage T is is a parameter used to determine how many modules of the same type can be connected together in series. If your maximum system voltage is, for example, 600 V and you connect 10 modules with an individual Voc (each module) of 36.6 V in series, a string voltage of 366 V would result, which would still be under the limit of 600 V. Series Fuse Rating T is parameter gives the appropriate fuse/breaker size for each string.

Type of Output Terminal THEME 4.1.3 T e output terminal describes the type of electrical connector installed on the back of the module. I–V Curves T e I‒V (current-voltage) curve of a PV module describes its energy conversion capability at the existing conditions of irradiance and temperature. Conceptually, the curve represents the combinations of current and potential dif erence at which the module operates, if the irradiance and cell temperature could be held constant. In other words, I‒V curves are used to indicate the performance of a module allowing determination of the maximum power point (MPP). Referring to the I-V curve in Figure 2, you will notice that the curve ranges from the short-circuit current (Isc) at zero volt to zero current at the open-circuit voltage (Voc). T e maximum power point

(MPP = Imp × Vmp), the point at which the module generates its maximum electrical power, is usually at the ‘knee’ of a normal I-V curve. In an operating PV system, one of the jobs of the inverter with MPPT is to constantly adjust the load, seeking out the particular point on the I-V curve at which the module or array as a whole yields the greatest DC power.

FIGURE 2: DIAGRAM INDICATING THE MAXIMUM POWER POINT (MPP) OF A TYPICAL 75 WATT PV MODULE

I Short circuit Maximum current 5.0 PowerPoint (MPP) 4.0 Imp 3.0

urrent

C 2.0

1.0 Open circuit Vmp voltage

5 10 15 17 20 V Potential difference

Image source: GIZ/S4GJ A simplif ed diagram indicating the maximum power point (MPP) of a typical 75 watt PV module as the product of the potential (Vmp) and current (Imp), in our case at around 17 V and 4.1 A.

305 FIGURE 3: DIAGRAM WITH AN I-V AND P-V CURVE PLOTTED TOGETHER

Maximum power P Current vs. voltage max

Isc

Imp

Maximum

THEME 4.1.3 PowerPoint (MPP)

urrent

owe

C Power vs. voltage P

Potential difference Vmp Voc

Image source: GIZ/S4GJ Sometimes you f nd diagrams where the I-V and the P-V curve of a module are plotted together. T e P-V curve is calculated from the measured I-V curve. How is an I-V Curve for a Module obtained An I-V curve represents an inf nite number of current-potential operating points. T ese current-poten-

tial operating points are plotted between the short-circuit current point (Isc) where the module pro-

duces maximum current and zero potential, and the open-circuit voltage point (Voc) where the module produces maximum potential and zero current. T e point at which a PV device delivers its maximum

power output and operates at its highest ef ciency is referred to as its maximum power point (Pmax). T e potential and current values at the maximum power point are referred to as the maximum power voltage

(Vmp) and the maximum power current (Imp), respectively.

Considering the above, one can say that the I-V characteristic of a module is the basic descriptor of its performance. T us, well designed datasheets indicate the I-V characteristic of a module und various irradiance and temperature conditions, usually 5 irradiance levels ranging from 1000 W/m2 to 200 W/m2 (see Figure 4) and three temperature levels ranging from 75° C to 25° C (see Figure 5). Obviously, dif erent irradiation and cell temperature levels will alter a module’s performance. Increased irradiance levels will increase current but will not alter potential and vice versa. Increased cell temperature will lower potential and vice versa, but has little ef ect on current.

306 FIGURE 4: I-V CURVES OF A PV MODULE

3.5 MaximumPowerPoints

3.0 G=1,000 W/m2

2.5 G=800 W/m2 2.0 G=600 W/m2 1.5

urrent G=400 W/m

C 1.0 THEME 4.1.3

2 0.5 G=200 W/m

0.0 0 5 10 15 20 25 Potential difference Range

Image source: GIZ/S4GJ T e f ve I-V curves of a PV module clearly indicate that current will dramatically change between around 0.5 and 3 A as irradiance varies, but potential remains relatively constant at around 20 V.

FIGURE 5: I-V CURVES OF A PV MODULE

75°C

urrent 50°C

25°C

Potential difference

Image source: GIZ/S4GJ T e three I-V curves of a PV module clearly indicate that potential will dramatically change as temperature varies, but current remains relatively constant.

307 Examples

Apply your knowledge!

Question: Does a PV module with a rated power (Pmax) of 190 W really produce 190 W when it is on your roof? T e simple answer is: No!

Let us look into the matter step by step: 1. T e maximum power the module is rated at (190 W) is based on the power output measured under Standard Test Conditions (STC) and these are, unfortunately, in most cases a long way from real operating conditions. 2. Under STC, the solar panel is subject to an irradiance level of 1000 W/m2. T at in itself is not a problem, as irradiance levels in most parts of South Africa are even higher. T e problem is that the STC power rating is based on a panel temperature of 25° C and an air THEME 4.1.3 mass of 1.5. T ink about that for a second and consider particularly the temperature that a module will have when it is on your roof. Remember, temperature is critical because all modules lose ef ciency at high cell temperatures (potential will dramatically decrease as temperature rises, but current will remain relatively constant). Realistically, cell temperature will generally be between 45° C ‒ 60° C and thus, the real maximum power output of your module will dif er from the rated power value. 3. So unless you install a module in a very sunny and cold place, like Antarctica, you are never going to get the rated power indicated by the manufacturer. T us, let us work out the real maximum power of the 190 W module by using some information from the datasheet. T e section that contains the temperature characteristics, the Nominal Operating Cell

Temperature (NOCT) and the temperature coef cient of Pmax will assist us.

FIGURE 6: A SECTION FROM THE DATASHEET CONTAINS THE TEMPERATURE CHARACTERISTICS OF THE MODULE

Temperature Pmax -0.45 per °C coefficients Voc -0.35 per °C Vmp -0.42 per °C Isc +0.05 per °C

Image source: GIZ/S4GJ A relevant section from the datasheet contains the temperature characteristics of the module,

including the Nominal Operating Cell Temperature (NOCT) and temperature coef cients (Isc, Voc

and Pmax).

As indicated in an earlier section, NOCT is a much more realistic measure of the temperature that your panels are likely to operate at. In our case, NOCT is set at 45 °C ± 2 °C. T e temperature

coef cient of Pmax indicates how much power is lost for every degree Celsius above 25 °C (STC). Our 190 W module will lose 0.45 % of its maximum power for every degree above 25 °C. NOCT indicates a typical 45 °C and power loss at this temperature can be calculated as follows:

(45 °C ‒ 25 °C) × (‒ 0.45%) = 20 × ‒ 0.45% = ‒ 9%

308 T us, the real maximum power output of the module will be 9 % lower at a cell temperature of 45 °C than the module rated power. Our module was rated at 190 W which equals 100 %:

100% ‒ 9% = 91%.

Consequently, the real maximum power output of the module at a cell temperature of 45 °C would be approximately:

91% × 190 W = 172.9 W

However, please consider that there will be a number of additional power losses due to wiring, fuses, switches and inverters, and total losses can of en reach 25 %. T us, system designers of en oversize the PV system to ensure reliability. How much the system needs to be oversized is THEME 4.1.3 determined by the relative safety margin required and the amount of information available on solar insolation for the site. A 25 % margin is recommended, although a site with well documented solar insolation and well known system components might require only a 15 % margin.

Exercises can be found in Unit 4.2

Please carry out the following: (i) Experiment 6: T e of -load voltage and the short-circuit current at dif erent irradiance values (ii) Experiment 11:Voltage-current curve of a solar cell (iii) Experiment 12: Ef ciency determination/MPP

Further Information (all materials are on the resource CD)

(i) Guide To Interpreting I-V Curve Measurements of PV Arrays, Solmetric Corporation, 2010 (ii) PV Modules I (Video) https://www.youtube.com/watch?v=8-U7_sWu63g (iii) PV Modules II (Video) https://www.youtube.com/watch?v=v8nbwvC8aBg

309 Your own notes THEME 4.1.3

310 THEME 4.1.4 FACTORS AFFECTING THE PERFORMANCE OF PV MODULES

Introduction

Electrical energy produced by a PV system depends on several external and internal factors. External factors, such as the amount of solar radiation (irradiation/insolation), depend on the local climatic conditions and can only be inf uenced via optimal site selection. However, usually f exibility regarding selection of sites is limited in most projects, for example for residential roof op systems. Here the setting is by default predetermined (roof arrangements etc.). Other factors such as load resistance, module ef ciency,

array direction and tilt, cell temperature, shading, module mismatch and inverter conversion losses can, THEME 4.1.4 at least to a certain degree, be considered and attended to. Any of these factors can have a major impact on the PV system’s performance (power output). In this theme we will focus on the ef ects of series and parallel circuits, shading and partial shading of modules, as well as module direction and tilt, as these factors can have dramatic output ef ects.

Keywords

Series and parallel connections Module circuit design Array circuit design Shading Bypass diodes Theme Outcome

At the end of this theme, you should be able to: (i) List and explain critical factors that can af ect the performance of PV modules.

311 Deﬁ nition of Terms Series and Parallel In Topic 2 T eme 2.3.1 (Simple DC Circuits) we introduced you to testing and measuring of electrical quantities and illustrated the two main types of electric circuits, i.e. the series or the parallel circuit and the ef ects they have on electrical quantities such as electric current, potential and resistance. T e understanding of these topics now comes in handy and we strongly recommend consulting Topic 2 to recall certain facts.

Let us brief y repeat the main f ndings from Topic 2 below: Series Connection When PV cells or modules are connected in series, the nominal potential of the PV system is increased and cur-

THEME 4.1.4 rent remains constant. You have a series connection if you connect positive (+) leads to negative (-) leads (PV circuits in series). Usually the sequence in which PV cells are arranged in a PV module is in a series circuit.

In a series circuit, the three resistors appear as a single equivalent resistance with the value of Req. Simply

put, when resistors are connected in series, the total resistance (Req) is equal to the sum of resistance of the individual resistors. T erefore, let us conclude that in a series circuit the:

Total resistance (Req) = R1 + R2 + R3

Which can read as: T e sum of the three resistors R1, R2 and R3 is equal to the total resistance (Req).

Total potential (VT) = V1 + V2 + V3

Which can read as: T e sum of potential drops V1, V2, and V3 is equal to the total potential in the circuit

current (IT). T us, we can determine total potential (VT) as:

VT = I × Req

Current remains: I = constant,

and can be expressed as: I = V / Req

Based on the above, we can f nally describe resistor loads connected in series as potential dividers, due to

the fact that the total potential (VT) divides among resistors. T is is called the principle of potential division in a series circuit.

Application: We can conclude from these results, that when PV cells or PV modules are connected in series and the circuit has a constant resistance (R), the potential of each cell or module is added together, but current remains the same.

Parallel Connection When PV cells or modules are connected in parallel, the nominal current in the PV system is increased and potential remains constant. Connect positive leads (+) to positive (+) leads and negative leads (-) to negative (-) leads to wire the PV circuits in parallel.

Let us recall the equation for equivalent resistance (Req) in parallel circuits and conclude that in a parallel circuit: 1 1 1 1 Total resistance (Req) is: = + + Req R1 R2 R3

Which can read as: T e equivalent resistance (Req) is less than that of the smallest of the resistors.

Total current (IT) is: IT = I1 + I2 + I3

Which can read as: T e sum of the current I1, I2, and I3 is equal to the total circuit current (IT). T us, by

substituting the above equation, we can determine the total circuit current (IT) as:

IT = V × Req

Potential (V) remains: V = constant,

312 We declare two or more circuit elements (resistor loads) to be combined in parallel if an identical potential (V) acts across each circuit element. T us, in a parallel circuit potential values remain constant, whereas current (I) will divide when passing through a resistor. Based on the above, we can describe resistor loads connected in parallel as current dividers, due to the fact that the total current (IT) divides while passing through the resistors. T is is called the principle of current division in a parallel circuit.

Application: We can conclude from these results, that when PV cells or modules are connected in parallel, and the circuit has a constant resistance (R), the potential of each cell or module remains the same, but the current of each cell or module is added together.

T ese two principles for connecting PV cells or modules are used to build modules from individual PV cells and arrays from individual modules. T e PV cells in a module can be wired to any desired poten-

tial and current, and modules can then be connected with each other to create PV arrays to any desired THEME 4.1.4 potential and current. Module Circuit Design While the voltage from the PV module is determined by the number of solar cells, the current from the module depends primarily on the size of the solar cells and also on their ef ciency. If all the solar cells in a module have identical electrical characteristics and they all experience the same insolation and temperature, then all the cells will be operating at exactly the same current and potential. In this case, the I-V curve of the PV module has the same shape as that of the individual cells, except that the potential and current are increased.

FIGURE 1: SCHEMATIC ILLUSTRATION OF 36 SINGLE PV CELLS CONNECTED IN SERIES TO FORM A MODULE

Image source: GIZ/S4GJ

T e total current of such a module is the current of an individual cell multiplied by the number of cells in parallel. T e total potential of such a module is the potential of an individual cell multiplied by the number of cells in series. To conclude:

Module Isc = Cell Isc × number of cells in parallel

Module Imp = Cell Imp × number of cells in parallel

Module Voc = Voc × number of cells in series

Module Vmp = Vmp × number of cells in series Array Circuit Design Individual PV modules are connected both in series and parallel to form arrays. A series-connected set of solar cells or modules is called a ‘string’. When PV modules are connected in series, the potential

313 of each module is added together, but current remains the same. When PV modules are connected in parallel, the potential of each module remains the same, but the current of each module is added together. Let us illustrate this by using a typical module with a power rating of 75 watt containing 36 cells in

series (0.6 × 36 = 21.6). T is usually provides an open-circuit voltage (Voc) of about 21 volt and a potential

dif erence at maximum power (Vmp) of 17.5 V and current at maximum power (Imp) of 5 A.

FIGURE 2: TWO IDENTICAL MODULES CONNECTED IN SERIES

- - THEME 4.1.4

+ +

Image source: GIZ/S4GJ

Two identical modules with Vmp =17.5 V and Imp = 5 A connected in series will result in VT = Vmp1 + Vmp2

(17.5 V + 17.5 V = 35 V) and IT = Imp (5 A).

FIGURE 3: TWO IDENTICAL MODULES CONNECTED IN SERIES

Module 1 Module1+Module 2

Image source: GIZ/S4GJ

Two identical modules connected in series will result in VT = Vmp1 + Vmp2 and IT = Imp, i.e. the potential of each module is added together, but current remains the same.

FIGURE 4: FOUR IDENTICAL MODULES CONNECTED IN SERIES

- - - -

+ + + +

Image source: GIZ/S4GJ

Four identical modules with Vmp =17.5 V and Imp = 5 A connected in series will result in VT = Vmp1 + Vmp2

+ Vmp3 + Vmp4 (17.5 V + 17.5 V + 17.5 V + 17.5 V = 70 V) and IT = Imp (5 A).

314 FIGURE 5: TWO IDENTICAL MODULES CONNECTED IN PARALLEL + + + THEME 4.1.4 - - -

Image source: GIZ/S4GJ

Two identical modules with Vmp =17.5 V and Imp = 5 A connected in parallel will result in VT = Vmp (17.5

V) and IT = Imp1 + Imp2 (5 A + 5 A = 10 A).

FIGURE 6: TWO IDENTICAL MODULES CONNECTED IN PARALLEL

Module 1 Module 2 parallel

Module 1

Image source: GIZ/S4GJ

Two identical modules connected in parallel will result in VT = Vmp and IT = Imp1 + Imp2, i.e. the potential of each module remains the same, but the current of each module is added together.

315 FIGURE 7: FOUR IDENTICAL MODULES CONNECTED IN PARALLEL

+ + + + +

THEME 4.1.4 - - - - - Parallel circuit (4 solar panels)

Image source: GIZ/S4GJ

Four identical modules with Vmp =17.5 V and Imp = 5 A connected in parallel will result in

VT = Vmp (17.5 V) and IT = Imp1 + Imp2 + Imp3 + Imp4 (5 A + 5 A + 5 A + 5 A = 20 A).

FIGURE 8: EIGHT IDENTICAL MODULES CONNECTED IN SERIES- PARALLEL

+ + + + +

- - - - + + + +

- - - - -

Image source: GIZ/S4GJ

Eight identical modules with Vmp =17.5 V and Imp = 5 A connected in series-parallel will result in

VT = Vmp1 + Vmp2 (17.5 V + 17.5 V = 35 V) and IT = Imp1 + Imp2 + Imp3 + Imp4 (5 A + 5 A + 5 A + 5 A = 20 A).

316 Shading and Bypass Diodes Shading of PV modules, even partial shading or covering, can be a serious problem since shading of just one cell in the module can compromise the power output of the entire system. T e reduction of the power output caused by partial module or array shading may not be proportional to the portion of the surface in shadow, but might be much higher. If shading was uniform over the whole system, for example due to a cloud, then everything would be simple, as the current of all PV modules would drop by the same proportion and power loss would be proportional to the shading.

FIGURE 9: A SHADOW CAST ON A ROOFTOP PV SYSTEM THEME 4.1.4

Image source: http://www.shutterstock.com/s/photovoltaic+installation/search.html?page=1&thumb_size=mosaic&in- line=251921545 In this image the roof casts a shadow on the roof op PV system. T is will af ect the performance of the whole system, as the shadow intercepts a large quantity of a module series.

FIGURE 10: UNIFORM AND PARTIAL SHADING

Uniform shading Single substring shading

Examples of partial cell shading that will reduceasolar electric panel’s powerby up to 50%

Image source: GIZ/S4GJ Dif erent types of shading (uniform and partial) that will potentially compromise a module’s or array’s power output by up to 50 %.

317 Let us look into the ef ect of partial shading, where dif erent panels experience dif erent illumination due to shading. Figure 11 is a diagram with two dif erent P-I curves indicating the characteristics for a sample module at two illumination levels, i.e. fully exposed to sunlight and 25 % (partially) shaded. In

this example, the fully illuminated module (red line) has a maximum current (Isc) of 11 A and achieves

its highest maximum power (Pmax = 300 W) at an Imp of 9 A (see T eme 4.1.3). T e partial (25 % shaded)

illuminated module has a maximum current (Isc) of around 9 A and achieves its highest maximum power

(Pmax = 225 W) at an Imp of 7 A.

FIGURE 11: P-I CURVES INDICATING TWO ILLUMINATION LEVELS THEME 4.1.4

Image source: GIZ/S4GJ T e diagram shows two dif erent P-I curves indicating the characteristics for a sample module at two illumination levels, i.e. fully exposed to sunlight and 25 % (partially) shaded.

Let us assume that we have a string of such modules connected in series, which has only one shaded

module with partial (25 % shaded) illumination, resulting in Pmax = 225 W at Imp = 7 A. T us, this shaded

module only achieves around 75 % of the current that the other modules need for Pmax. Given that the modules are connected in series, they share the same current and consequently the whole string will

operate at Pmax of around 75 %, resulting in a 25 % power loss just because of one shaded module. When all modules in a string are connected in series, the module with the lowest current (due to shading or otherwise) will reduce the power output of the whole string.

Due to the fact that it is dif cult to prevent shading, PV module manufacturers typically install diodes in their modules. What is the function of these diodes? When cells or modules are shaded (or damaged), diodes can give the current another path, skipping the shaded (or damaged) cell or module. How does this work? T is can best be illustrated by examining how a diode functions.

318 FIGURE 12: THE DIODE

electrons holes NP

- + N-type P-type (not pointing) (pointing)

cathode anode

depletion{ region electrons holes electrons holes THEME 4.1.4 NP- - + + + NP- - + - + + + - - - - + + - - + - + + + + - - - - + + + + - - - + - + + + + - - - - - + + + - - - + - + + +

- + + - (a) Forward (b)Reverse

Image source: GIZ/S4GJ A diode is the simplest possible semiconductor device. It allows current to f ow in one direction but not the other. T e N-type and P-type silicon create these unique properties in a diode.

Lef -hand side of Figure 12: In this arrangement, the diode conducts charge as the additional electrons (negative charge) in the N-type silicon are repelled by the negative terminal of the battery (similar charges repel each other) and pass through the junction between the N-type and P-type silicon (‘electrons f lling the holes’) with the ef ect that current f ows through the junction.

Right-hand side of Figure 12: N-type and P-type silicon are both viable conductors, but the circuit shown on the right-hand side of Figure 12 does not conduct any charge. T e negative electrons in the N-type silicon get attracted to the positive terminal of the battery and the positive charge in the P-type silicon gets attracted to the negative terminal of the battery. T is is due to the fact that opposite charges (positive-negative) attract each other (see Topic 2, T eme 2.2.1). Subsequently, no or very little current f ows across the P-N junction, since the negative and positive charges in the diode are moving away from each other and towards the battery.

To conclude, the P-N junction acts like a one-way path that allows current to only f ow in one direction. T e advantage of this is that diodes can be used to block or bypass the f ow of current from other parts of an electrical circuit. T us, and in practice, bypass diodes in PV modules are connected in parallel to shunt the current around it, whereas blocking diodes are connected in series with the PV module to prevent current from f owing back into them. Blocking diodes are therefore dif erent to bypass diodes, although in most cases the diode is physically the same - they are however installed dif erently to serve a dif erent purpose.

319 Consider the arrangement in Figure 13, where the green diodes are bypass diodes, one in parallel with each solar module to provide a low resistance path (short-circuit current). T e two red diodes are referred to as ‘blocking’ diodes, one in series with each series branch. Blocking diodes are dif erent to bypass diodes, not physically, but rather in the way they are installed, because they serve a dif erent purpose. T e blocking diodes, also called series diodes or isolation diodes, ensure that the electrical current only f ows in one direction, i.e. out of the series array to the external load (controller or batteries).

FIGURE 13: DIFFERENT TYPES OF DIODES IN A PV ARRAY

I I=I+I A TAB + Blocking

diodes IB THEME 4.1.4 + +

- -

Bypass diodes + +

- - -

Image source: GIZ/S4GJ Bypass diodes, one in parallel with each solar module to provide a low resistance path, are indicated in green. Blocking diodes, one in series with each series branch, are indicated in red.

320 Shading and the Function of Bypass Diodes We already discussed earlier that it is dif cult to prevent shading - this is why PV module manufacturers install bypass diodes in their modules. We already know that: (i) When part of a PV cell or module is shaded, the shaded cells or module will not be able to produce as much current as the unshaded cells or unshaded modules in an array. (ii) If all cells in a module or modules in an array are connected in series, the same amount of current must f ow through every cell and every module. (iii) If the unshaded cells in the module force the shaded cells to operate at a current higher than their short circuit current, the shaded cells will cause a net potential loss in the system. In addition, the shaded cells will dissipate power as heat and can cause so-called ‘hot spots’. T is situation can lead to irreversible cell damage, resulting in unintentional short circuits which, in a worst-case scenario, can trigger a f re. (iv) One way to minimise the shading ef ect and potential module damage is to use bypass diodes

in the junction box of the modules. Bypass diodes allow current to pass around shaded cells THEME 4.1.4 or modules and thereby reduce potential loss through the shaded module. When a module becomes shaded, its bypass diode becomes forward biased and begins to conduct current through itself. All the current greater than the shaded module’s short-circuit current is bypassed through the diode, thus drastically reducing the amount of heat dissipation at the shaded module area.

FIGURE 14: THE FUNCTION OF BYPASS DIODES IN A STRING

Image source: GIZ/S4GJ T e arrangement on the lef -hand side of the image indicates a normal functioning solar array with unshaded modules and a uniform Imp. T e arrangement on the right-hand side of the image with the top module being (partly) shaded indicates a bypass mode where the bypass diode of the shaded module becomes forward biased and begins to conduct current through itself (green arrows indicate current f ow).

321 Exercises can be found in Unit 4.2

Please carry out the following: Experiment 4: T e of -load voltage of a solar cell/shading Experiment 5: T e short-circuit current of a solar cell/shading Experiment 8: Series connection of solar cells/shading Experiment 9: Series connection of solar cells/shading with bypass diode Experiment 10: Parallel connection of solar cells/shading Experiment 14: Charging a GoldCap capacitor / accumulator with a solar cell THEME 4.1.4 Further Information (all materials are on the resource CD)

(i) PN Juction And Diodes (Video) https://www.youtube.com/watch?v=W6QUEq0nUH8 (ii) T e PN Junction. How Diodes Work (Video) https://www.youtube.com/watch?v=JBtEckh3L9Q (iii) Critical Factors that Af ecting Ef ciency of Solar Cells, Furkan Dinçer, Mehmet Emin Meral, 2010

Your own notes

322 UNIT 4.2 Unit 4.2 Unit

UNIT 4.2 PHOTOVOLTAIC EXPERIMENTS

Introduction

For training to be truly ef ective, it is necessary to practically apply your knowledge in hands-on experiments or real world installations. Given that the latter is of en dif cult to realise in some TVET colleges, we recommend certain resources and equipment for practical photovoltaic experiments. Commercially available equipment for use in practical activities ranges from low-cost components such as PV cells, motors, leads, turbine blades, etc., to kits and laboratory apparatuses and vocational training versions of ‘real’ PV training systems. We suggest using the latter as low-cost components, as ‘hobby’ kits are rather more appropriate for use in primary and secondary schools. T ere are a number of manufacturers who of er well-designed training sets suitable for all experiments set under this unit. T e training set Solartrainer Junior, for example, includes modular experiments designed to demonstrate all the aspects of PV systems covered in this textbook, albeit on a miniature scale.

323 FIGURE 1: THE TRAINING SET SOLARTRAINER JUNIOR UNIT 4.2

Image source: GIZ/S4GJ

Your own notes

324 EXPERIMENT 1 Measurement of the irradiance of different sources of light Information T e dif erent sources of light mainly dif er in the irradiance of the colour (wavelength) of the light. T e wavelength of visible light is in the range of 400 nm (blue) to 800 nm (red). For example, sunlight is far whiter due to the high share of blue light when compared to the light of an incandescent bulb, which is yellowish due to the high share of red.

EXPERIMENT 1 SET-UP UNIT 4.2

DC OFF DC Spotlight V A (Halogen)

Volt (U) Ampere (I) Irradiation sensor Multimeter COM Adjust irradianceto different levels!

WIRING DIAGRAM

325 ASSIGNMENT

Determine the irradiance of dif erent sources of light, such as those listed in the table below. T e output jacks of the sensor are connected to a multimeter as voltmeter, the range selector is switched to position DC 2000 mV as shown in the wiring diagram. T e sensor face must be held in the direction of the source of light in such a way that the maximum measured value results. T e sensor face and the solar cell of the sensor must not be shaded during the measurement. Display will be directly in W/m2. T e sensor reacts at an irradiance of more than approx. 15 W/m2.

Irradiance (W/m2) Irradiance (W/m2) Irradiance (W/m2) Source of light at distance at distance at distance

Spotlight (level 10)

Torch UNIT 4.2

Room lighting

Sun

Sun (overcast sky)

Now take the measurements at dif erent distances from the artif cial sources of light. What are the dif erences of dif erent sources of light regarding their performance? Which observations can be made?

326 EXPERIMENT 2 The solar cell as energy converter Information A solar cell converts light energy into electrical energy.

Solar cell Light energy as energy Electrical energy converter

EXPERIMENT 2 SET-UP Cell inclination 90°! UNIT 4.2

Spotlight M (Halogen)

Motor (Load) Adjust irradianceto different levels!

WIRING DIAGRAM M

327 ASSIGNMENT

Set up the experiment according to the diagram shown. T e lamp arm is in the South position, the brightness controller is on level 10.

1: What happens when the connecting cables on the solar cell are commutated?

2: Set dif erent irradiance values on the brightness controller and observe the electric motor while

UNIT 4.2 doing so.

3: Specify the energy conversions within the solar cell and the electric motor.

328 EXPERIMENT 3 The solar cell as energy converter and/or diode Information A non-shaded solar cell converts radiation energy to electrical energy. If the solar cell is shaded completely, it loses its active role and will behave like a normal diode with P-N transition. A diode is an electronic semiconductor component, the conductivity of which depends on the current direction. T erefore, the electrical current can only f ow through the diode in one direction.

EXPERIMENT 3 SET-UP

Cell inclination 90°! UNIT 4.2

Spotlight M (Halogen)

Motor (Load)

DC OFF DC V A

Volt (U) Ampere (I) Multimeter COM Accumulator

Cell inclination 90°!

Spotlight (Halogen)

DC OFF DC V A M

Volt (U) Ampere (I) Multimeter COM Accumulator Motor (Load)

329 WIRING DIAGRAMS FOR EXPERIMENT 3

A M A M UNIT 4.2

Diagram A Diagram B

A M A M

module shaded module shaded

Diagram C Diagram D

330 ASSIGNMENT

Set up the experiment according to the diagrams shown. T e range selector switch of the multimeter as ammeter must be set to position DC 2000 mA (1 A = 1000 mA). Charge the accumulator via the solar cell with brightness controller level 10.

Diagram A T e solar cell is initially operated without a shading plate (lamp in South position, brightness controller at level 10). Which observation can be made?

Diagram B UNIT 4.2 Switch the connections to the solar cell af erwards. Which observation can be made?

Diagram C and D Do the two experiments again, but with the shading plate and without irradiation. Which observations can be made now?

331 EXPERIMENT 4 The off-load voltage of a solar cell/shading Information Crystalline silicon solar cells consist of two layers of semiconductors with positive and negative charge. If light energy reaches the cell, some of the photons will be absorbed by the semiconductor. In this way, electrons in the negative layer are released and f ow from the semiconductor to the positive layer via an external circuit (see also diagram for Experiment 3). At no-load condition,

potential can be measured on the outer contacts, the of -load potential VL.

To which extent does the of -load potential depend on the irradiated solar cell surface area?

UNIT 4.2 Irradiated surface area of 0 ½ ¾ 1/1 the solar cell

Off-load potential (mV)

EXPERIMENT 4 SET-UP

Cell inclination 90°!

Spotlight (Halogen)

DC OFF DC V A

Volt (U) Ampere (I) Multimeter COM

332 WIRING DIAGRAMS FOR EXPERIMENT 4

V V

module shaded UNIT 4.2

Diagram A Diagram B

333 ASSIGNMENT

Set up the experiment according to the diagram shown. T e lamp is in the South position, the brightness controller is on the highest level 10. T e range selector switch of the multimeter as voltmeter must be set to position DC 2000 mV (1V = 1000 mV).

Completely cover the solar cell with the 1/1 shading plate (set controller to 0 temporarily for this shading), measure the of -load potential, and enter the value into the graph. Continue with controller setting 10, with ½ shading, with ¼ shading, and without shading, and measure the potential in each case. Record the measured values in the graph and connect the measuring points by means of lines.

Off-load potential of a solar cell/shading

600 UNIT 4.2

500

400

300

Off-load potential (mV) 200

100

0 0 1/2 3/4 1/1

Relative surface area of the solar cell

Which f nding can be obtained from the measurement?

334 EXPERIMENT 5 The short-circuit current of a solar cell/shading Information Crystalline silicon solar cells consist of two layers of semiconductors with positive and negative charge. If light energy reaches the cell, some of the photons will be absorbed by the semiconductor. In this way, electrons in the negative layer are released and f ow from the semiconductor to the positive layer via an external circuit (see also diagram for Experiment 3). At no-load condition, a potential can be measured on the outer contacts, the of -load potential (which is approx. 0.5 V). If the outer contacts are connected directly to a conductor, the maximum possible current will f ow, the short-circuit current IK.

To which extent does the short-circuit current depend on the irradiated solar cell surface area? UNIT 4.2

Irradiated surface area of 0 ½ ¾ 1/1 the solar cell

Short-circuit current (mA)

EXPERIMENT 5 SET-UP

Cell inclination 90°!

Spotlight (Halogen)

DC OFF DC V A

Volt (U) Ampere (I) Multimeter COM

335 WIRING DIAGRAMS FOR EXPERIMENT 5

A A

module shaded UNIT 4.2

Diagram A Diagram B

336 ASSIGNMENT

Set up the experiment according to the diagrams shown. T e lamp is in the South position, the brightness controller is on the highest level. T e range selector switch of the multimeter as ammeter must be set to position DC 2000 mA.

Completely cover the solar cell with the 1/1 shading plate, measure the of -load potential and enter the value into the graph. Continue with ½ shading, with ¼ shading and without shading, and measure the current in each case. Enter the measured values into the graph and connect the measuring points by means of lines.

Short-circuit current of a solar cell/shading

300 UNIT 4.2 250

200

150

100 Short-circuit current (mA)

0 0 1/2 3/4 1/1

Relative surface area of the solar cell

Which f nding can be obtained from the measurement?

337 EXPERIMENT 6 The off-load potential and the short-circuit current at different irradiance values Information When using solar cells as energy converters, the level of irradiation is of importance. However, this depends on the time of day, the season and the weather conditions.

To which extent do of -load potential and short-circuit current depend on the irradiance?

Irradiance 0 20 30 40 60 80 100 120 160 200 (W/m2)

Off-load potential (mV) UNIT 4.2 Short-circuit current (mA)

EXPERIMENT 6 SET-UP

Cell inclination 90°!

DC OFF DC Spotlight V A (Halogen)

Volt (U) Ampere (I) COM Adjust irradianceto Multimeter different levels!

DC OFF DC V A

Volt (U) Ampere (I) Irradiationsensor Multimeter COM

338 Cell inclination 90°!

DC OFF DC Spotlight V A (Halogen)

Volt (U) Ampere (I) COM Adjust irradianceto Multimeter different levels!

DC OFF DC V A UNIT 4.2

Volt (U) Ampere (I) Irradiationsensor Multimeter COM

WIRING DIAGRAMS FOR EXPERIMENT 6

V V

Diagram A

V A

Diagram B

339 ASSIGNMENT

Set up the experiment according to the diagrams shown. Parallel connection of two solar cells is selected due to the improved resolution at higher currents, but shows the same result as for an individual cell. Initially, a multimeter is connected as voltmeter to the solar cells, the range selector is switched to position DC 2000 mV. T e lamp is in the South position.

In order to determine the irradiance, connect the jacks of the sensor to a multimeter as voltmeter. T e range selector is switched to position DC 2000 mV. Hold the back of the sensor directly to the centre of the surface of the connected solar cells. T e sensor face and the solar cell of the sensor must not be shaded during measurement. Display will be directly in W/m2. T e solar cell of the sensor serves as the power supply of an internal storage capacitor, which is why it makes sense to run the experiments from high to low irradiance.

Diagram A Set dif erent irradiance values on the brightness controller from 10 – 0 and enter the related poten-

UNIT 4.2 tial values into the table above.

Diagram B Af erwards, connect the multimeter as ammeter according to the f gure, range selector switched to position DC 2000 mA. Set the same irradiance values again and enter the related current value into the table above.

Please enter the values from the table into the graph below and connect the measuring points by means of lines.

Which statement can be made?

Off-load potential short circuit current / irradiance 600 600

500 500

400 400

300 300

200 200 Short-circuit current (mA) Off-load potential (mV)

100 100

0 20 40 60 80 100 120 140 160 180 200 0 Irradiance (W/m2)

Potential Current

340 EXPERIMENT 7

The short-circuit current of a solar cell at different angles of irradiation Information T e angle of incidence of the sunlight in relation to the Earth changes depending on the time of day and on the season. T erefore, in the morning the rays of sunshine fall onto a stationary solar cell at a dif erent angle than in the af ernoon.

What is the relation between the angle of incidence of the light to the solar cell and the short-circuit current intensity?

EXPERIMENT 7 SET-UP

Adjust cell inclination from 0t°°o90! UNIT 4.2

DC OFF DC Spotlight V A (Halogen)

Volt (U) Ampere (I) Multimeter COM

WIRING DIAGRAM FOR EXPERIMENT 7

341 ASSIGNMENT

Set up the experiment according to the diagram shown. Connect the multimeter as ammeter. T e range selector switch must be set to position DC 2000 mA. T e lamp is in the South position, the brightness controller is set on the highest level.

Initially set the solar cell housing to position 90°, measure the short-circuit current, and enter the values into the table. Now, rotate the solar cell housing in increments of 15° to position 0° and enter each of these values into the table below.

Angle 90 75 60 45 30 15 0 dimension (°) Short-circuit current (mA)

UNIT 4.2 Enter the values from the table into the graph and connect the measuring points by means of lines.

Short-circuit current/angle of irradiation

300

250

200

150

100 Short-circuit current (mA)

0 15 30 45 60 75 90

Angle dimension (°)

Which coherences between the angle of incidence of the light onto the solar cell and the short-circuit current intensity can be derived from the aforementioned?

342 EXPERIMENT 8

Series connection of solar cells/shading Information For many electrical consumers, the required potential is higher than the potential delivered by an individual solar cell with approx. 0.5V. T erefore, several solar cells are connected in series. What is the behaviour of a series connection of solar cells regarding the of -load potential and the short-circuit current? What ef ect does a shadow have on a solar cell?

EXPERIMENT 8.1 SET-UP

Cell inclination 90°! UNIT 4.2

DC OFF DC Spotlight V A (Halogen)

Volt (U) Ampere (I) Multimeter COM

WIRING DIAGRAM FOR EXPERIMENT 8.1

343 EXPERIMENT 8.2 SET-UP

Cell inclination 90°!

DC OFF DC Spotlight V A (Halogen)

Volt (U)

UNIT 4.2 Ampere (I) Multimeter COM

WIRING DIAGRAM FOR EXPERIMENT 8.2

344 EXPERIMENT 8.3 SET-UP

Cell inclination 90°!

DC OFF DC Spotlight V A (Halogen)

Volt (U) UNIT 4.2 Ampere (I) Multimeter COM

WIRING DIAGRAMS FOR EXPERIMENT 8.3

V V

Diagram 8.3A Diagram 8.3B

V V

Diagram 8.3C Diagram 8.3D

345 EXPERIMENT 8.4 SET-UP

Cell inclination 90°!

DC OFF DC Spotlight V A (Halogen)

Volt (U) UNIT 4.2 Ampere (I) Multimeter COM

WIRING DIAGRAMS FOR EXPERIMENT 8.4

A A

Diagram 8.4A Diagram 8.4B

A A

Diagram 8.4C Diagram 8.4D

346 ASSIGNMENT

Set up the experiment according to Diagrams 8.1, 8.2, 8.3 and 8.4. T e lamp arm is in the South position, the brightness controller is on the highest level.

Experiment 8.1 Connect a multimeter as voltmeter according to Set-up 8.1. T e range selector switch must be set to position DC 20 V. Measure the of -load potential for solar cells 1-4 and enter the values into Table 1.

Experiment 8.2 Connect a second multimeter as ammeter according to Set-up 8.2. T e range selector switch must be set to position DC 2000 mV. Measure the short-circuit current for solar cells 1-4 and enter the values into Table 1.

TABLE 1 UNIT 4.2 Solar cell 1 Solar cell 2 Solar cell 3 Solar cell 4

Off-load potential (V)

Short-circuit current (mA)

Experiment 8.3 and 8.4 Connect the solar cells (1 and 2), (1, 2, and 3), as well as all four solar cells in series according to Set-up 8.3 and 8.4 and measure both the of -load potential and the short-circuit current of the array with the same multimeter settings. Enter the respective values for potential and current into Table 2.

TABLE 2

Series connec- Series connec- Series connec- Solar cell 1 tion solar cell tion solar cell tion solar cell 1+2 1+2+3 1+2+3+4

Off-load potential (V)

Short-circuit current (mA)

Experiment 8.5 Use the set-up of Experiment 8.3 and 8.4 and gradually shade the solar cell with the lowest short-circuit current when all four solar cells are connected in series and enter the current and potential values into Table 3.

TABLE 3

Complete No shading ¼ shading ½ shading shading

Off-load potential (V)

Short-circuit current (mA)

347 Which f ndings are obtained from the analysis of the individual tables? UNIT 4.2

348 EXPERIMENT 9

Series connection of solar cells/shading with bypass diode Information For many electrical loads, a higher potential than a single solar cell (about 0.5 V) can supply is required. For this purpose, several solar cells are connected in series. What are the ef ects of series connection of solar cells with respect to the open circuit potential, the short-circuit current and the ef ect of a shadow, with and without a bypass diode?

EXPERIMENT 9 SET-UP

Solar cell Cell inclination 90°! U UNIT 4.2

Potentiometer

Spotlight (Halogen)

½ shade Capacitor GoldCap

DC OFF DC DC OFF DC V A V A

Volt (U) Volt (U) Ampere (I) Ampere (I) COM Multimeter Multimeter COM

349 WIRING DIAGRAMS FOR EXPERIMENT 9

A A

V V UNIT 4.2 Diagram A Diagram B

ASSIGNMENT

Set up the experiment according to the diagrams shown above, with shading size ½ and without a bypass diode. T e lamp arm is in the South position, the brightness controller is on the highest level.

Diagram A Turn the knob from the consumer (load 2) to the right (the largest resistance). Set the rotary knob to the f rst current value given in Table 1 and enter the missing potential value into the table. Now set the rotary knob to the next given value to obtain the missing value in the table. Continue until all values (potential and current) are entered into the table. Using the measured values, draw a curve into the graph provided.

TABLE 1: SET-UP WITHOUT BPASS DIODE

Potential 1,50 1,00 0,90 0,70 0,65 0,60 0,30 (V) Current 22 55 80 100 120 (mA)

Diagram B Use the ½ shading and the bypass diode. Turn the knob from the consumer (load 2) to the right (the largest resistance). Set the rotary knob to the f rst current value given in Table 2. Set and enter the missing potential value. Now enter the next given value to obtain the missing value in the table. Continue until all values (potential and current) are entered. Use the measured values to plot a curve into the graph.

TABLE 2: SET-UP WITH BPASS DIODE

Potential 1,50 1,00 0,90 0,70 0,65 0,60 0,30 (V) Current 20 50 80 100 120 (mA)

350 I-V curve

260 240 220 200 180 160 140 120 100 Current (mA)

80 UNIT 4.2 60 40 20

0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

Potential (V)

With bypass diode Without bypass diode

Which f ndings are obtained from the analysis of the two I-V curves (with and without bypass diodes)?

351 EXPERIMENT 10

Parallel connection of solar cells/shading Information For many electrical consumers the required current is higher than the current delivered by an individual solar cell. Several solar cells are thus connected in parallel to achieve a higher current. What is the behaviour of a parallel connection of solar cells regarding the of -load potential and the short-circuit current? What is the ef ect of a shadow on a solar cell?

EXPERIMENT 10.1 AND 10.2

Use the set-up of Experiment 8.1 and 8.2 and repeat these two experiments or accept the results obtained from Experiments 8.1 and 8.2 and copy them into Table 1 below.

TABLE 1 (SET-UP SIMILAR TO EPERIMENTS 8.1 AND 8.2) UNIT 4.2

Solar cell 1 Solar cell 2 Solar cell 3 Solar cell 4

Off-load potential (V)

Short-circuit current (mA)

EXPERIMENT 10.3 SET-UP

Cell inclination 90°!

DC OFF DC Spotlight V A (Halogen)

Volt (U) Ampere (I) Multimeter COM

352 WIRING DIAGRAM FOR EXPERIMENT 10.3

module shaded

module shaded UNIT 4.2

EXPERIMENT 10.4 SET-UP

Cell inclination 90°!

DC OFF DC Spotlight V A (Halogen)

Volt (U) Ampere (I) Multimeter COM

353 WIRING DIAGRAM FOR EXPERIMENT 10.4

module shaded

module shaded UNIT 4.2 module shaded

ASSIGNMENT

Set up the experiment according to the diagram shown above (Experiment 10.3 and 10.4, parallel connections). T e lamp arm is in the South position, the brightness controller is on the highest level.

Experiment 10.3 and 10.4 Connect the solar cells (1 and 2), (1, 2, and 3), as well as all four solar cells in parallel according to set-up 10.3 and 10.4 and measure both the of -load potential and the short-circuit current of the array with the same multimeter settings. Enter the respective values for potential and current into Table 2.

TABLE 2

Parallel Parallel Parallel connection Solar cell 1 connection connection solar cell solar cell 1+2 solar cell 1+2+3 1+2+3+4

Off-load potential (V)

Short-circuit current (mA)

354 Experiment 10.5 Use the set-up of Experiment 10.3 and 10.4. Use the shading plates and gradually shade the solar cell with the highest short-circuit current when all four solar cells are connected in parallel and enter the current and potential values into Table 3.

TABLE 3

Complete No shading ¼ shading ½ shading shading

Off-load potential (V)

Short-circuit current (mA) UNIT 4.2 Which f ndings can be obtained from the analysis of the individual tables?

355 EXPERIMENT 11

I-V curve of a solar cell Information If a consumer (load resistance) is connected to a solar cell, voltage and current will adopt certain values. How do voltage and current change for dif erent consumers?

EXPERIMENT 11 SET-UP

Cell inclination 90°!

Solar cell

UNIT 4.2 U

Spotlight (Halogen) Potentiometer

DC OFF DC DC OFF DC V A V A

Volt (U) Volt (U) Ampere (I) Ampere (I) COM Multimeter Multimeter COM

356 WIRING DIAGRAM FOR EXPERIMENT 11

V UNIT 4.2

ASSIGNMENT

Set up the experiment according to the diagram shown above. Due to the better resolution, the measurement is taken in series connection. However, the course of the curve in the graph basi- cally shows the same course as for the measurement of an individual cell. Connect a multimeter as voltmeter to load 2 according to the diagram. T e range selector switch must be set to position DC 20 V. Connect the other multimeter as ammeter according to the diagram. T e range selector switch must be set to position DC 2000 mA. T e lamp area is in the South position, the solar cells in position 90°.

Two measurement series will be documented:

1. Brightness controller is set to the highest level. Rotate the knob of the consumer (load 2) to its lef most position (lowest resistance).Use the knob to set the f rst current value in Table 1 and enter the missing potential value. Now, set the next specif ed value and enter the missing value into the table. Continue until all values have been entered.

TABLE 1 HIGH IRRADIANCE

Potential 1.60 1.00 0.50 0.20 (V) Current 20 40 60 80 90 100 105 110 (mA)

357 2. Brightness controller is set to level 8. Rotate the knob of the consumer (load 2) to its lef most position (lowest resistance). Use the knob to set the f rst current value in Table 2 and enter the missing potential value. Now, set the next specif ed value and enter the missing value into the table. Continue until all values have been entered.

TABLE 2 LOWER IRRADIANCE

Potential 1.50 1.00 0.50 0.20 (V) Current 20 40 60 80 90 100 105 110 (mA)

Now, enter the table values of Tables 1 and 2 into the graph and connect the related measuring points. UNIT 4.2

Potential-Current curve

240

220

200

180

160

140

120

100 Current (mA) 80

0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4

Potential (mV)

High irradiance Low irradiance

Which f ndings are obtained from the analysis of the graph?

358 EXPERIMENT 12

Efﬁ ciency determinationMPP Information T e current/potential value pairs mentioned in Experiment 11 can be used to calculate the electrical output P = V × l (please observe: 1 V × 1 A = 1 W and 1 mV × 1 mA = 0.001 mW).

How large must the load resistance be for a maximum power drain from the solar cell?

EXPERIMENT 12 SET-UP

Cell inclination 90°!

Solar cell UNIT 4.2

Spotlight (Halogen) Potentiometer

DC OFF DC DC OFF DC DC OFF DC V A V A V A

Volt (U) Volt (U) Volt (U) Ampere (I) Ampere (I) Ampere (I) COM COM Multimeter Multimeter Multimeter COM

Irradiationsensor

359 WIRING DIAGRAM FOR EXPERIMENT 12

V V UNIT 4.2

ASSIGNMENT

Repeat Experiment 11, the measurement of series 1 f rst. Now calculate the electrical output from the current/potential value pairs and enter the results into the table below. Af erwards, enter the current/potential value pairs and the output/potential value pairs into the graph and connect the measuring points. Highlight the point of maximum output!

Point of maximum output (maximum power point – MPP)

Potential 1.60 1.00 0.50 0.20 (V)

Current 20 50 80 110 130 140 150 170 (mA)

Calculated output (mW)

360 Efﬁciency determinationMPP

260

240 300

220

200 250

180

160 200

140

120 150 Current (mA) Output (mW)

100 UNIT 4.2

80 100

40 50

0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.8 2.0 2.2 2.4 0

Potential (V) I-V curve Output

Ef ciency determination of a solar cell

Ef ciency is def ned as follows:

Total output power Ef ciency = Total input power T e total output power is the maximum calculated output of the solar cell (MPP). T e total input power is obtained by multiplying the irradiance value with the overall surface area of the four solar cells. In order to determine the irradiance, connect the jacks of the sensor to a multimeter as voltmeter, as shown above. Set the range selector switch to position DC 2000 mV. Hold the sensor directly with the back side to the centre of the surface of the solar cells. T e sensor face and the solar cell of the sensor must not be shaded during the measurement. Display will show W/m2. T e dimensions of a solar cell are 5 x 10 cm.

Maximum calculated output of the solar cell in the MPP:

Measured irradiance:

Overall surface area of the 4 solar cells:

Impinging irradiation output upon the overall solar cell surface area:

Ef ciency = = x 100% = %

361 EXPERIMENT 13

Emulation of a diurnal variation Information T e angle at which the sunlight reaches a stationary solar cell on the Earth’s surface changes from sunrise to sunset. Depending on the location (latitude) of the solar cell, the angle additionally depends on the season. T erefore, the orientation according to the cardinal direction on the one hand, and the horizontal work angle on the other hand, are decisive for the maximum possible energy yield of a stationary solar cell. Since the Sun’s orbit visible from the Earth changes on a daily basis for a specif c location, it is important to f nd the orientation of the solar cell which results in the maximum yield over the entire year.

EXPERIMENT 13 SET-UP UNIT 4.2 E ENE Cell inclination 90°! 0° 22.5° NE 45° NNE 67.5°

N DC OFF DC Spotlight V A 90° (Halogen)

Volt (U) NNW Ampere (I) COM 112° Multimeter EW 135° EWE W 157.5° 180°

362 WIRING DIAGRAM FOR EXPERIMENT 13

A UNIT 4.2

ASSIGNMENT

Set up the experiment according to the diagram shown above. T e two solar cells in the middle are connected in parallel. Connect the multimeter as ammeter, the range selector switch must be set to DC 2000 mA, the brightness controller must be set to the highest level. Place the lamp arm into the East position and enter the short-circuit current value into the table below. Gradually bring the lamp arm to the West position and document the values of the short-circuit current in each case. Af erwards, enter the current values for each cardinal direction into the graph.

South- South- East ESE SSE South SSW WSW West east west

Short- circuit current (mA)

363 Emulation of a diurnal variation

600

500

400

300 UNIT 4.2

Current (mA) 200

100

E ESE SE SSE S SSW SW WSW W

Cardinal direction

1. Which f ndings are obtained from the analysis of the graph? (see also Experiment 7)

2. At which location is the Sun’s visible orbit always the same from sunrise to sunset, regardless of the season?

3. Which horizontal work angle of the solar cell must be selected for this location for maximum energy yield?

4. What must be taken into consideration for your location?

364 EXPERIMENT 14

Charging a GoldCap capacitor / accumulator with a solar cell Information A solar cell will only provide electrical energy when it is irradiated. If a consumer is to be operated in darkness as well, a part of the electrical energy generated by the irradiation must be accumulated. Traditionally, an accumulator or, for consumers with very low energy consumption, a GoldCap capacitor is used for this purpose.

EXPERIMENT 14.1 SET-UP

Cell inclination 90°! UNIT 4.2

Capacitor Spotlight GoldCap (Halogen)

DC OFF DC DC OFF DC V A V A

Volt (U) Volt (U) Ampere (I) Ampere (I) COM Multimeter Multimeter COM

365 WIRING DIAGRAM FOR EXPERIMENT 14.1

V UNIT 4.2

ASSIGNMENT

Experiment 14.1 Connect the solar cells in series and connect them to the two upper jacks of the GoldCap using a multimeter as ammeter. T e range selector must be switched to the DC 2000 mA position. Connect the other multimeter as voltmeter to the upper contacts; range selector must be switched to position DC 20 V. Bring the brightness controller to level 10 and the lamp arm into the South position. Ensure that the GoldCap is discharged (with incandescent lamp). Charge the GoldCap until only a very low current (approx. 4-5 mA) is f owing.

What is the potential now present on the GoldCap?

366 EXPERIMENT 14.2 SET-UP

Cell inclination 90°!

Capacitor Spotlight GoldCap (Halogen) UNIT 4.2

Full shade

DC OFF DC DC OFF DC V A V A

Volt (U) Volt (U) Ampere (I) Ampere (I) COM Multimeter Multimeter COM

367 WIRING DIAGRAM FOR EXPERIMENT 14.2

module shaded module shaded module shaded module shaded UNIT 4.2

ASSIGNMENT

Experiment 14.2 Switch of the halogen spotlight and shade the solar cells completely with a folder (night situation). Observe the ammeter. What happens?

368 EXPERIMENT 14.3 SET-UP

Cell inclination 90°!

Capacitor GoldCap Spotlight (Halogen) UNIT 4.2

LED (Load)

DC OFF DC DC OFF DC V A V A

Volt (U) Volt (U) Ampere (I) Ampere (I) COM Multimeter Multimeter COM

WIRING DIAGRAM FOR EXPERIMENT 14.3

369 ASSIGNMENT

Experiment 14.3 Completely discharge the GoldCap (potential 0 V) by additionally connecting the incandescent lamp as a consumer (load 1) to the upper connections of the GoldCap, and then disconnect the incandescent lamp.

EXPERIMENT 14.4 SET-UP UNIT 4.2 Cell inclination 90°!

Capacitor Spotlight GoldCap (Halogen)

DC OFF DC DC OFF DC V A V A

Volt (U) Volt (U) Ampere (I) Ampere (I) COM Multimeter Multimeter COM

370 WIRING DIAGRAM FOR EXPERIMENT 14.4

V UNIT 4.2

ASSIGNMENT

Experiment 14.4 Now insert the cables of the solar cells into the two lower jacks of the GoldCap (with diode). T e voltmeter remains connected to the upper jacks. Charge the GoldCap until only a very low current (approx. 4-5 mA) is f owing.

371 EXPERIMENT 14.5 SET-UP

Cell inclination 90°!

Capacitor Spotlight GoldCap (Halogen) UNIT 4.2

Full shade

DC OFF DC DC OFF DC V A V A

Volt (U) Volt (U) Ampere (I) Ampere (I) COM Multimeter Multimeter COM

372 WIRING DIAGRAM FOR EXPERIMENT 14.5

module shaded module shaded module shaded module shaded UNIT 4.2

ASSIGNMENT

Experiment 14.5 Repeat Experiment 14.2. Observe the ammeter. What happens? What is the potential now present on the GoldCap? What is the function of the diode within the circuit?

373 EXPERIMENT 14.6 SET-UP

Cell inclination 90°!

Capacitor Spotlight GoldCap (Halogen) UNIT 4.2

DC OFF DC DC OFF DC V A V A

Volt (U) Volt (U) Ampere (I) Ampere (I) COM Multimeter Multimeter COM

374 WIRING DIAGRAM FOR EXPERIMENT 14.6

V UNIT 4.2

ASSIGNMENT

Experiment 14.6 Discharge the GoldCap completely (see Experiment 14.3). Charge the GoldCap, document potential and current at the time intervals in the table. T en transfer the values into the graph and connect the related measuring points.

Time 10 20 30 60 90 120 150 180 210 240 300 360 (sec)

Potential (V)

Current (mA)

375 Charging a GoldCap

2.2 220

2.0 200

1.8 180

1.6 160

1.4 140

1.2 120

1.0 100 Potential (V) Current (mA) 0.8 80

UNIT 4.2 0.6 60

0.4 40

0.2 20

0 60 120 180 240 300 360 0

Time (sec)

Which f ndings can be derived from the graph?

376 EXPERIMENT 15

Charging a GoldCap capacitor / accumulator Information How does a GoldCap capacitor behave when it is loaded with a consumer?

EXPERIMENT 15.1 SET-UP

M UNIT 4.2

Capacitor GoldCap Motor (Load)

DC OFF DC DC OFF DC V A V A

Volt (U) Volt (U) Ampere (I) Ampere (I) COM Multimeter Multimeter COM

WIRING DIAGRAM FOR EXPERIMENT 15.1

M A

377 EXPERIMENT 15.2 SET-UP

Capacitor LED (Load) GoldCap UNIT 4.2

DC OFF DC DC OFF DC V A V A

Volt (U) Volt (U) Ampere (I) Ampere (I) COM Multimeter Multimeter COM

WIRING DIAGRAM FOR EXPERIMENT 15.2

378 ASSIGNMENT

Initially, charge the GoldCap as described in Experiment 14 (using the diode).

Experiment 15.1 Set up the experiment according to Diagram 15.1 (with motor). Connect the electric motor as load via a multimeter as ammeter to the upper jacks of the GoldCap; the range selector must be switched to position DC 2000 mA. Do not establish the positive connection on the electric motor yet. Connect the other multimeter as voltmeter to the GoldCap as shown; the range selector must be switched to position DC 2000 mV. Discharge the GoldCap using the electric motor (insert positive cable). Observe potential and current during the discharging procedure and enter the values into Table 1 at the specif ed time intervals.

Experiment 15.2 Again charge the GoldCap as described in Experiment 14 (via the diode). Repeat the previous instructions of Experiment 15.1, but use the incandescent lamp as load according to Diagram 15.2. UNIT 4.2 Enter the values into Table 2, transfer the values into the graph and connect the related measuring points. Which f ndings can be derived from the graph?

Table 1: Electric motor as load Table 2: Incandescent lamp as load

Potential Potential Time (min) Current (mA) Time (min) Current (mA) (mV) (mV)

0 0

1 1

2 2

3 3

4 4

5 5

6 6

7 7

8 8

9 9

10 10

379 Discharging a GoldCap with electric motor

2200 22

2000 20

1800 18

1600 16

1400 14

1200 12

1000 10 Current (mA) Potential (mV) 800 8

UNIT 4.2 600 6

400 4

200 2

0 1 2 3 4 5 6 7 8 9 10 0

Time (min)

Discharging a GoldCap with incandescent lamp

2200

2000 100

1800

1600 80

1400

1200 60

1000 Current (mA) Potential (mV) 800 40

600

400 20

200

0 1 2 3 4 5 6 7 8 9 10 0

Time (min)

Potential Current

380 For which type of applications is the tested storage unit (GoldCap) most suitable? UNIT 4.2

381 EXPERIMENT 16

Design of the island network Information If a solar cell is connected to an energy storage unit and a consumer, it is an island network of the simplest form. Depending on the irradiance, the charging condition of the storage unit and the operation of the consumers, dif erent current f ows and current intensities result within the system.

EXPERIMENT 16.1 SET-UP

Cell inclination 90°! UNIT 4.2

Capacitor GoldCap Spotlight (Halogen)

Motor(Load)

DC OFF DC DC OFF DC V A V A

Volt (U) Volt (U) Ampere (I) Ampere (I) COM Multimeter Multimeter COM

382 WIRING DIAGRAM FOR EXPERIMENT 16.1

A UNIT 4.2

ASSIGNMENT

Experiment 16.1 According to the wiring diagram, the solar cells are connected in series and are connected within the circuit to the GoldCap via a multimeter as ammeter using the two lower jacks. T e range selector must be switched to position DC 2000 mA. Bring the brightness controller to the highest level and the lamp arm into the South position. Charge the GoldCap until current is no longer f owing. Connect the electric motor via the second multimeter as ammeter to the upper jacks of the Gold- Cap within the circuit; switch the range selector to position DC 2000 mA. T e halogen spotlight is switched of . Let the electric motor run for 3 minutes.

What can be observed?

383 EXPERIMENT 16.2 SET-UP

Cell inclination 90°!

LED(Load) Capacitor GoldCap Spotlight (Halogen) UNIT 4.2

Motor(Load)

DC OFF DC DC OFF DC V A V A

Volt (U) Volt (U) Ampere (I) Ampere (I) COM Multimeter Multimeter COM

384 WIRING DIAGRAM FOR EXPERIMENT 16.2

A UNIT 4.2

ASSIGNMENT

Experiment 16.2 Connect the incandescent lamp in parallel to the electric motor as additional load until the Gold- Cap is completely discharged. Observe the ammeters. What happens?

Now, re-activate the halogen spotlight; set the brightness controller to position 10. Observe the voltmeters. What happens?

Document the current f ow directions with arrows in the two wiring diagrams (16.1 and 16.2).

385 Your own notes NOTES

386 Your own notes NOTES

387 Your own notes NOTES

388

Skills for Green Jobs (S4GJ)

Department of Higher Education and Training (DHET)