623 - RENEWABLE ENERGY SOURCES AND ENERGY CONSERVATION ANSWER KEY PART-A 1. Define Renewable energy? Renewable energy is energy produced from sources that are renewed by nature again & again and their supply is not affected by the rate of consumption. The most common examples include wind, solar, geothermal, biomass, and hydropower. 2. Write any two classification of wind energy system • Based on orientation of the axis of the motor • Based on size as determined by their useful electrical power output. 3. What is a heliostat and what is its use? A heliostat is a device that includes a mirror, usually a plane mirror, which turns so as to keep reflecting sunlight toward a predetermined target, compensating for the sun's apparent motions in the sky. Heliostats are used for daylighting or for the production of concentrated solar power, usually to generate electricity. 4. List the types of solar cells. • Amorphous Silicon solar cell (a-Si) • Concentrated PV cell (CVP and HCVP) • Crystalline silicon solar cell (c-Si) • Hybrid solar cell • Monocrystalline solar cell (mono-Si) • Nanocrystal solar cell • Organic solar cell (OPV) • Photoelectrochemical cell (PEC) • Polycrystalline solar cell (multi-Si) • Solid-state solar cell • Thin-film solar cell 5. Define flood tide and Ebb tide. Flood the tidal phase during which the water level is rising and Ebb is the tidal phase during which the water level is falling Flood is the tidal phase during which the tidal current is flowing inland (flood current) and Ebb is the tidal phase during which the tidal current is flowing seaward (ebb current). 6. State the applications of biogas plant. • Gas production is cheap • Less pollution. • Waste material can be used as fertilizer. • Gas is used for cooking, lighting, as fuel. 7. Define Critical thickness. The thickness upto which heat flow increases and after which heat flow decreases is termed as critical thickness. A critical thickness is typically defined as the limit of film thickness wherein the strain is still elastically accommodated. 8. Define Cogeneration. The production of electricity using waste heat (as in steam) from an industrial process or the use of steam from electric power generation as a source of heat is called cogeneration. PART B 9. Write about the importance of renewable energy sources. Renewable energy sources are necessary and needed for the following reasons, • The demand of energy is increasing due to rapid industrialization and population growth. So the conventional energy sources will not be sufficient to meet the growing demand. • Non renewable energy, such as coal and petroleum, require costly explorations an potentially dangerous mining and drilling, and they will become more expensive as increases. • Renewable energy is reliable and plentiful and will be cheap once technology and infrastructure improves. • Renewable energy includes solar, wind, geothermal, hydropower, tidal energy and bio fuels that are grown and harvested without fossil fuels. • Conventional sources cause pollution and degrade the environment whereas Renewable energy produces only minute levels of carbon emissions and therefore helps combat climate change caused by fossil fuel usage. • The degree of civilization of any country is measured by the ability to utilize energy for human advancements and needs. 10. Compare Horizontal and vertical axis windmill. 11. What is solar collector? Classify it. A solar collector is a device that collects and/or concentrates solar radiation from the Sun. These devices are primarily used for active solar heating and allow for the heating of water for personal use. These collectors are generally mounted on the roof and must be very sturdy as they are exposed to a variety of different weather conditions. Classification: • Flat plate collectors • Evacuated collectors • Solar ponds • Stationary concentrators • Linear focus collectors • Point focus collectors • Central receivers. 12. Explain a solar water heater with neat sketch. Solar water heating (SWH) is the conversion of sunlight into heat for water heating using a solar thermal collector. A variety of configurations is available at varying cost to provide solutions in different climates and latitudes. SWHs are widely used for residential and some industrial applications. A sun-facing collector heats a working fluid that passes into a storage system for later use. SWH are active (pumped) and passive (convection-driven). They use water only, or both water and a working fluid. They are heated directly or via light-concentrating mirrors. They operate independently or as hybrids with electric or gas heaters. 13. Explain grid connected photovoltaic system. 14. Explain Environment impact and safety impact of solar system. 15. Draw a neat sketch of fixed dome type biogas plant. 16. List any four needs for energy audit. PART-C 17. (A) (i) Write the classification of energy sources. 17. (B) (II) Name Five wind mills with its location In India. Name Location State Capacity (MW) Muppandal windfarm Kanyakumari Tamil Nadu 1500 Jaisalmer Wind Park Jaisalmer Rajasthan 1064 Brahmanvel windfarm Dhule Maharashtra 528 Dhalgaon windfarm Sangli Maharashtra 278 Vankusawade Wind Park Sat ara District Maharashtra 259 Vaspet Vaspet Maharashtra 144 Mamatkheda Wind Park Mamatkheda Madhya Pradesh 100.5 Anantapur Wind Park Nimbagallu Andhra Pradesh 100 Damanjodi Wind Power Plant Damanjodi Odisha 99 Jath Jath Maharashtra 84 Welturi Welturi Maharashtra 75 Acciona Tuppadahalli Chitradurga District Karnataka 56.1 Dangiri Wind Farm Jaiselmer Rajasthan 54 Bercha Wind Park Ratlam Madhya Pradesh 50 17 (b) Explain with a neat sketch the working of a horizontal axis wind mill. Also, list the advantages and disadvantages of wind energy. Advantages: • Wind energy is renewable & Sustainable • It is good for the environment • It reduces for fossil fuel consumption • Wind Energy can provide power to remote locations. • Wind energy has low maintenance & Low running costs. Disadvantages: • Wind energy fluctuates and not stable all the time. • Installation of wind energy is costlier. • Wind systems are noisy. 18 (a) Explain the principle of solar pond with a neat sketch. Also, give its advantages and disadvantages The sun is the largest source of renewable energy and this energy is abundantly available in all parts of the earth. It is in fact one of the best alternatives to the non-renewable sources of energy. One way to tap solar energy is through the use of solar ponds. Solar ponds are large-scale energy collectors with integral heat storage for supplying thermal energy. It can be use for various applications, such as process heating, water desalination, refrigeration, drying and power generation. Working principle: • The solar pond works on a very simple principle. It is well-known that water or air is heated they become lighter and rise upward e.g. a hot air balloon. • Similarly, in an ordinary pond, the sun’s rays heat the water and the heated water from within the pond rises and reaches the top but loses the heat into the atmosphere. The net result is that the pond water remains at the atmospheric temperature. • The solar pond restricts this tendency by dissolving salt in the bottom layer of the pond making it too heavy to rise. A solar pond has three zones. The top zone is the surface zone, or UCZ (Upper Convective Zone), which is at atmospheric temperature and has little salt content. The bottom zone is very hot, 70°– 85° C, and is very salty. • It is this zone that collects and stores solar energy in the form of heat, and is, therefore, known as the storage zone or LCZ (Lower Convective Zone). • Separating these two zones is the important gradient zone or NCZ (Non-Convective Zone). Here the salt content increases as depth increases, thereby creating a salinity or density gradient. If we consider a particular layer in this zone, water of that layer cannot rise, as the layer of water above has less salt content and is, therefore, lighter. • Similarly, the water from this layer cannot fall as the water layer below has a higher salt content and is, therefore, heavier. This gradient zone acts as a transparent insulator permitting sunlight to reach the bottom zone but also entrapping it there. • The trapped (solar) energy is then withdrawn from the pond in the form of hot brine from the storage zone. Advantages: • The approach is particularly attractive for rural areas in developing countries. Very large area collectors can be set up for just the cost of the clay or plastic pond liner. • The accumulating salt crystals have to be removed and can be a valuable by-product and a maintenance expense • No need for a separate collector. • The extremely-large thermal mass means power is generated night and day. Disadvantages • Relatively low-temperature operation means solar energy conversion is typically less than 2%. • Due to evaporation, non-saline water is constantly required to maintain salinity gradients. 18 (b) (I) Compare flat plate and concentrating solar Collectors. 18 b) (ii) Write about Thermal Chemical Storage. • Thermal energy from the sun can be stored as chemical energy in a process called solar thermochemical energy storage (TCES). • The thermal energy is used to drive a reversible endothermic chemical reaction, storing the energy as chemical potential. • During periods of high solar insolation, an energy-consuming reaction stores the thermal energy in chemical bonds; when energy is needed, the reverse reaction recombines the chemical reactants and releases energy. 19 (a) Write the step by step procedure involved in designing a solar Home Lighting system. The step by step procedure for designing a solar home lighting system includes, 19 (b) With a neat sketch explain the closed cycle OTEC system. • Ocean Thermal Energy Conversion or OTEC uses the principle of a heat engine. It works by converting a temperature difference into energy. This means the difference in temperature between the warmer water on the surface and the cooler water in the depths of the ocean can be converted into electricity.