Self-Sufficient Off-Grid Energy System for a Rowhouse Using Photovoltaic Panels Combined with Hydrogen System

SELF-SUFFICIENT OFF-GRID ENERGY SYSTEM FOR A ROWHOUSE USING PHOTOVOLTAIC PANELS COMBINED WITH HYDROGEN SYSTEM

Master thesis in energy system

MAHAMED MAXAMHUD ARKAM SHANSHAL

School of Business, Society and Engineering

Course: Master thesis in energy system Supervisor: Bengt Stridh Course code: ERA403 Examiner: Amir Vadiee Subject: Energy technology Date: 2020-07-02 Credits: 30 hp E-mail: Program: Master of Science. in energy systems [email protected] [email protected]

ABSTRACT

It is known that Sweden is categorised by being one of the regions that experience low solar radiation because it is located in the northern hemisphere that has a low potential of solar radiation during the colder seasons. The government of Sweden aim to promote a more sustainable future by applying more renewable initiative in the energy sector. One of the initiatives is by applying more renewable energy where PV panels will play a greater role in our society and in the energy sector. However, the produced energy from the PV panels is unpredictable due to changes in radiation throughout the day. One great way to tackle this issue is by combining PV panels with different energy storage system. This thesis evaluates an off-grid rowhouse in Eskilstuna Sweden where the PV panels are combined with a heat pump, thermal storage tank, including batteries and hydrogen system. The yearly electrical demand is met by utilizing PV panels, battery system for short term usage and hydrogen system for long-term usage during the colder seasons. The yearly thermal demand is met by the thermal storage tank. The thermal storage tank is charged by heat losses from the hydrogen system and thermal energy from heat pump.

The calculations were simulated in Excel and MATLAB where OPTI-CE is composed with different components in the energy system. Furthermore, the off-grid household was evaluated from an economic outlook with respect to today’s market including the potential price decrease in 2030.

The results indicated that the selected household is technically practicable to produce enough energy. The PV panels produces 13 560 kWh annually where the total electrical demand reaches 6 125 kWh yearly (including required electricity for the heat pump). The annual energy demand in terms of electricity and thermal heat reaches 12 500 kWh which is covered by the simulated energy system. The overproduction is stored in the batteries and hydrogen storage for later use. The back-up diesel generator does not need to operate, indicating that energy system supplies enough energy for the off-grid household. The thermal storage tank stores enough thermal energy regarding to the thermal load and stores most of the heat during the summer when there are high heat losses due to the charge of the hydrogen system. The simulated energy system has a life cycle cost reaching approximately k$318 with a total lifetime of 25 years. A similar off-grid system has the potential to reduce the life cycle cost to k$195 if the energy system is built in 2030 with a similar lifespan. The reduction occurs due to the potential price reduction for different components utilized in the energy system.

Keywords: Off-grid, PV panels, hydrogen system, battery system, thermal storage tank, heat pump, life cycle cost, electrical load, thermal load, OPTI-CE

PREFACE

This thesis was done for RG Förvaltnings AB and were performed at Mälardalens University. It demonstrates a simulated off-grid energy system for a household located in Eskilstuna Sweden where it operates to cover the yearly energy demand in terms of electricity and heat. The life cycle cost was also evaluated regarding to today’s market and the potential price change that may occur in 2030. The focus is to understand if the selected energy system is technically feasible and how much the life cycle cost is for the simulated system. We would like to thank our supervisor Bengt Stridh at Mälardalens University for helping us with the thesis including Pietro Campana for introducing the code OPTI-CE in MATLAB. We would also like to thank Hans-Olof Nilsson for participating in the interview and answering all the questions as well as Anders Kruhsberg for providing with the needed data for the selected household in Eskilstuna.

Mahamed Maxamhud, Arkam Shanshal

Västerås, July 2020.

SAMMANFATTNING

Det är välkänt att Sverige kategoriseras som en av de länderna som upplever låg solinstrålning. Främst för att landet är beläget på norra halvklotet där man utsätts för låg solinstrålning under de kallare säsongerna. Sveriges regering försöker främja en mer hållbar framtid genom att tillämpa mer förnybart initiativ inom energisektorn. Ett av initiativen är användandet av mer förnybar energi där solceller kommer att spela en större roll i vårt samhälle och inom energisektorn. Den producerade energin från solcellerna är relativt oförutsägbar på grund av förändringar av solinstrålningen under dagarna. Ett bra sätt att hantera detta problem är genom att kombinera solceller med olika energilagringssystem. Detta arbete utvärderar ett radhus i Eskilstuna som är urkopplad från det lokala elnätet. Energisystemet utnyttjar solceller som kombineras med en värmepump, ackumulatortank, batterisystem samt ett vätgassystem. Det elektriska energibehovet tillgodoses med hjälp av solceller, batterisystem som används ur ett kortvarigt perspektiv och ett vätgassystem som används under de kallare säsongerna ur ett mer långsiktigt perspektiv. Termiska energibehovet tillgodoses med hjälp av en ackumulatortank som får sin termiska energi från värmeförlusterna som sker i vätgassystemet samt värme från värmepumpen.

Beräkningarna utfördes i Excel och MATLAB där koden OPTI-CE som består av olika filer för energisystemet. Dessutom utvärderas hushållet utifrån ett ekonomiskt perspektiv med avseende på dagens marknad inklusive den potentiella prisminskningen under 2030.

Resultatet indikerade att energisystemet kan producera tillräcklig energi. Solcellerna producerar drygt 13 560 kWh under året där det totala elektriska behovet uppnår 6 125 kWh under samma period (elektriska behovet för värmepumpen är inkluderat). Det elektriska och värmebehovet uppnår totalt 12 500 kWh som täcks av det simulerade energisystem. Överproduktionen från solcellerna lagras i batterisystemet och vätgassystemet för senare användning när behovet är hög. Dieselgeneratorn behöver inte arbeta vilket indikerar att batterisystemet och vätgassystemet producerar tillräckligt mycket energi. Ackumulatortanken lagrar tillräckligt mycket termisk energi med avseende på det termiska behovet. Komponenten lagrar främst energi under sommaren när det uppstår höga värmeförluster från vätgassystemet under laddningsperioden. Det simulerade energisystemet har en livscykelkostnad på k$318 med en livslängd på 25 år och har potentialen att sänka livscykelkostnaden till k$195 ifall energisystemet är byggt 2030. Det är främst på grund av den potentiella prisminskningen för de olika komponenter i energisystemet.

CONTENT

1 INTRODUCTION ...... 1

Background ...... 2

Purpose ...... 3 Research questions ...... 3

Delimitation ...... 3

2 METHODOLOGY ...... 4

3 LITERATURE STUDY ...... 5

Off-grid system ...... 5 Comparison between off and on-grid ...... 6

Environmental impact from the energy sector ...... 8

Heat and electricity market price ...... 9 Life cycle cost ...... 10

System components ...... 10 PV system ...... 10 3.4.1.1. PV Panels ...... 11 3.4.1.2. Inverter ...... 11 Battery ...... 12

The hydrogen energy system ...... 12 Hydrogen ...... 12 Hydrogen system ...... 13 Electrolyser ...... 14 3.5.3.1. Alkaline electrolyser ...... 14 3.5.3.2. Polymer electrolyte membrane electrolyser ...... 15 Hydrogen compressor ...... 15 Fuel cell ...... 16 3.5.5.1. Proton – exchange membrane fuel cell ...... 16 Geothermal Heat pump ...... 17

Heat storage tank ...... 18

4 CURRENT STUDY ...... 18

Practicable energy system for the off–grid household ...... 18

Simulated energy system for the off-grid household ...... 20

Power calculation and model design ...... 21 PV system ...... 21 4.3.1.1. Solar radiation calculation ...... 22 Battery ...... 23 Hydrogen system ...... 23 4.3.3.1. Heat losses from the hydrogen system ...... 24 Diesel generator ...... 25 Thermal storage tank ...... 25 Heat pump ...... 25 Life cycle cost ...... 26 System cost ...... 26 4.3.8.1. System cost in today’s scenario ...... 26 4.3.8.2. System cost in future scenario (2030) ...... 28 Operational strategy ...... 29 4.3.9.1. Electrical operational strategy ...... 29 4.3.9.2. Heat operational strategy ...... 30 Climate data in Eskilstuna ...... 31 Electrical and thermal load in the household ...... 34 Deeper look on the load and energy production during the first week of November ...... 36

Sensitivity analysis ...... 37 Sensitivity analysis for the economical aspect ...... 37 Sensitivity analysis for the energy aspect ...... 37

5 RESULTS ...... 38

The electrical power output ...... 38 The PV system ...... 38 The battery system ...... 39 The hydrogen system ...... 41 Diesel generator production ...... 43

The heat power output ...... 43 Heat losses from hydrogen system ...... 44 Heat in the thermal storage tank ...... 44 Heat from heat pump ...... 45

Load and energy production during the first week of November ...... 47 Electrical load and production ...... 47 Thermal load and production ...... 48

Life cycle cost and component capacity ...... 49

Sensitivity analysis ...... 50 Economical aspect ...... 50 Energy aspect ...... 51

6 DISCUSSION ...... 52

7 CONCLUSION ...... 56

REFERENCE ...... 58

LIST OF FIGURES

Figure 1 The practicable off-grid energy system for the household. The blue line represents the DC electricity, green lines represents the AC electricity, orange represents the heat and the grey represents hydrogen production and consumption in the energy system...... 20 Figure 2 The simulated off-grid energy system for the household. The blue line represents the DC electricity, green lines represents the AC electricity and orange represents the heat...... 21 Figure 3 Electrical operational strategy...... 30 Figure 4 Thermal operational strategy...... 31 Figure 5 Ambient temperature in Eskilstuna per hour for one year (STRÅNG, 2020)...... 32 Figure 6 Diffuse horizontal radiation in Eskilstuna per hour for one year (STRÅNG, 2020). 33 Figure 7 Global horizontal radiation in Eskilstuna per hour for one year (STRÅNG, 2020). 34 Figure 8 The electrical demand in the household per hour for one year according to RG Förvaltning...... 35 Figure 9 The thermal load in the household according to RG Förvaltning...... 36 Figure 10 Annual production from the PV panels per hour...... 39 Figure 11 Battery system SOC per hour for one year...... 40 Figure 12 Battery output per hour for one year...... 41 Figure 13 Power output per hour during one year from the hydrogen system...... 42 Figure 14 Hydrogen system SOC per hour for one year...... 43 Figure 15 Heat losses per hour taking place in the hydrogen system for one year...... 44 Figure 16 Heat in thermal storage tank per hour for one year...... 45 Figure 17 Heat pump production per hour for one year...... 46 Figure 18 Electrical load per hour during the first week in November...... 47

Figure 19 Electrical production per hour during the first week of November. The purple line corresponds to the hydrogen system output, the blue line corresponds to the PV production and the red line corresponds to the batteries output ...... 48 Figure 20 Thermal load per hour during the first week of November ...... 48 Figure 21 Thermal production per hour during the first week of November. The blue line indicates how much thermal energy that is stored in the thermal storage tank. The black line indicates the heat pump production and the red line indicates the heat losses from the hydrogen system ...... 48 Figure 22 LCC change depending on the change of the discount rate ...... 51

LIST OF TABLES

Table 1 Difference between off and on-grid systems...... 7 Table 2 PV panels specifications (Nordic Solar, 2019)...... 22 Table 3 System cost in todays scenario...... 27 Table 4 System cost in future scenario (2030)...... 28 Table 5 Life cycle cost for todays and future scenario...... 49 Table 6 Components dimensioned and chosen capacity for todays and future scenario...... 49 Table 7 The sensitivity analysis for the economical aspect including the first three scenarios...... 50

LIST OF EQUATIONS

Equation 1...... 10 Equation 2...... 11 Equation 3...... 14 Equation 4...... 14 Equation 5...... 16 Equation 6...... 16 Equation 7...... 17 Equation 8...... 17 Equation 9...... 17 Equation 10...... 22 Equation 11...... 22 Equation 12...... 22

Equation 13...... 23 Equation 14...... 23 Equation 15...... 23 Equation 16...... 23 Equation 17...... 24 Equation 18...... 24 Equation 19...... 24 Equation 20...... 25 Equation 21...... 25 Equation 22...... 25 Equation 23...... 26 Equation 24...... 26

NOMENCLATURE

Symbol Description Unit

E Energy Wh T Temperature °C P Power W η Efficiency % COP Coefficient of performance - Q Heat W SOC State of charge % NOCT Nominal operating cell temperature ˚C µ Temperature coefficient %/ ˚C t Time s A Area m2 G Solar radiation W/m2 N Lifetime years θ Angle of incidence ˚ β Tilt angle ˚ α Solar altitude ˚ σ Self-discharge rate %

ABBREVIATION

Abbreviation Description

AC Alternative Current DC Direct Current COP Coefficient of Performance GA Genetic Algorithm GHG Greenhouse Gases IC Initial Cost LCC Life cycle Cost NMC Nickel Manganese Cobalt O&M Operation & Maintenance PEM Proton Exchange Membrane PV Photovoltaic SMHI Swedish Metrological and Hydrological Institute SOC State of Charge STC Standard test condition

DEFINITIONS

Definition Description

MATLAB Programming platform designed especially for engineers and scientists. OPTI-CE Open simulation and optimization code adjusted to hybrid power system.

1 INTRODUCTION

In today’s world where most energy production comes from non-renewable resources and the demand for energy is continuously rising in several industrialized and developing countries, many governments including organizations are trying to find efficient and price-effective ways to use renewable energy (Ritchie & Roser, 2020). However, Sweden has had a relative unchanged energy consumption since the late 80s (Grahn, 2019). The utmost usage of non- renewable energy sources is originally from fossil fuels and will eventually run out in the future. The non-renewable energy sources that uses different types of natural resources have various environmental damages including higher temperature and pollution of air. The earths “carbon budget” is also being more unstable and creating problems in both developing and industrialized countries due to the burning of fossil fuels. This leads to a rise in the greenhouse effects, that changes the ecosystem more rapidly than the organisms can adapt to. (Elizabeth, 2013) The development of new alternative fuels and renewable energy systems is needed in order to meet the energy demand taking place in the future. The worlds energy consumption is expected to grow by 25% by 2040 and the world population is set to grow by 1.1 billion (Swedish Cleantech , 2019). In Sweden, the residential and service sector including the industrial sector reach approximately 39% respective 38% of the annual energy usage (Grahn, Energimyndigheten, 2019). But, Sweden like most industrialized countries has been working actively the past decades to minimize the independence on fossil fuels. The Scandinavian country became the first state member in the European union to meet the renewable energy target set by the EU for 2020 and plan to reach 100% renewable electricity generation by 2040 (Swedish Cleantech , 2019).

Sweden’s initiative towards a more sustainable future is by applying more alternative sustainable initiative in the energy sector. A great alternative in renewable energy has been the solar power that contains several photovoltaic cells that converts solar energy and generates electrical energy. Solar power has the potential to play an important role in the future towards producing environmental, reliable and economic power (Saedpanah, Asrami, Sohani, & Sayyaadi, 2020).

Solar power already plays a role in today’s energy sector, from small household installations to large-scale projects. The cost of solar panels has dropped in the past decades and is considered being to be one of the cheapest sources of power station. As a result of the low greenhouse emissions, decreasing cost and being more efficient, many nations are moving towards electrification (Vattenfall, 2019). However, the generated electricity from solar panels cannot be controlled and changes throughout the day as it varies based on the time of the day and the weather conditions. One great way to handle this problem is to apply different types of storage technologies for instance, batteries and hydrogen storage. (Zhang, Lundblad, Campana, & Jinyue, 2016)

1 By using a combination of both solar power and energy storage, a new opportunity is provided to the consumer regarding being more independent from the traditional electrical and heat supply. Only few similar cases exist in Sweden, but if this scenario reaches more consumers the technical and economic aspects should be more investigated (Börling, 2018) . This thesis will be focusing on optimize and evaluating a fully self-sufficient off-grid energy system for a household in Eskilstuna, Sweden. The annual electricity and heat demand are fulfilled by using solar power combined with batteries, hydrogen energy system, storage tank, and a geothermal heat pump.

Background

If the energy from sunlight that reaches Earth in 60 minutes was converted into electricity, then it would be higher than what we consume in 12 months. (Stephen Cass, 2019). Even though the distance between the Sun and Earth is more than 149 600 000 km. (SMHI, 2019). There are many ways to use energy from the Sun, a suitable technology is photovoltaic system that is designed to supply usable solar power to the consumer or being stored in storage components. Solar panels convert the solar energy into usable electricity through a process known as the photovoltaic effect. The sunlight that strikes the semiconductors is composed of particles called photons that makes the electron more lose. This makes the electron behave in an orderly manner providing generated electricity. The generated current is known as DC and must be converted to AC by using an inverter. The conversion is necessary because Sweden’s electrical grids operates using alternating electricity and so does most electrical appliances in households (Lytle, 2019).

Not all energy is equally consumed around the world, more than 1.2 billion people around the globe have a small or no access to electricity. The electricity demand in developing countries is likely to grow at more than 6% annually over the next few decades. This could potentially have serious environmental implications for several countries and the world at large. This can be fought by increasing the supply of energy for individuals and communities with alternative energy resources (Mashable, 2017). One option is by distributing an off–grid installation in photovoltaic system. The system generates direct current and uses an inverter to convert the direct current into alternating current, while a hydrogen system and batteries is utilized to store energy when there is a surplus power from PV.

It is familiar that Sweden is characterized by being one of the regions that experience low solar radiation in the globe because it is located in the northern hemisphere that has a low potential of solar energy during different seasons. However, due to the potential of combining hydrogen energy system and battery, it has a high potential of utilizing solar power.

Sweden is one of the Scandinavian countries located in the northern Europe on the Scandinavian Peninsula. The largest part of energy being consumed in Sweden is originally from renewable energy. There are not many countries that consume more energy per capita than Sweden and the carbon emissions produced in Sweden are low compared to those other countries. The governments energy policies have also encouraged the usage of renewable

2 energy and make the production more cost efficient. Green electricity certification is one of the examples where the aim is to promote the most cost – effective production of renewable energy and gradually reducing its reliance on fossil fuels (Sweden, 2019).

Purpose

The purpose of this thesis is to evaluate and optimize with respect to life cycle cost an off– grid energy system for one family rowhouse located in Eskilstuna, Sweden. The yearly heat and electricity demand are met by using a photovoltaic system combined with a heat pump and hydrogen system where different storage systems are used. A thermal storage tank for produced hot water, a battery storage for short term usage and hydrogen system for long term usage are included. The heat losses from the charging state of the hydrogen system (corresponding to electrolyser) and discharging state of the hydrogen system (corresponding to fuel cell) is utilized in the thermal storage tank to supply with heat to the household. The energy system being applied in the given household is optimized and dimensioned to meet the annual energy demand.

Research questions

• What is the most practicable energy system (suitable components) for the household being off grid? • Is it technically sustainable for the households to be off grid regarding the energy supply being needed? • What is the life cycle cost and dimensions for the implemented energy system regarding to today’s market and 2030 if the system is implemented at that time?

Delimitation

The heat demand for the households is met by the heat losses taking place in the hydrogen system and heat from heat pump being connected to thermal storage tank. The electrical production comes mainly from photovoltaic solar cell that is connected to the household. The surplus energy from solar panels are stored in battery storage and hydrogen system. If the production from PV is not enough to cover the load then power is taken from battery in the first hand, and if the power from batteries is not enough then power from the hydrogen system is taken. The energy storage used in the energy system is considered being a hydrogen system, battery storage and a thermal storage tank. The simulated hydrogen system is performed as one component that represents the electrolyser, compressor, hydrogen storage and a fuel cell. The component operates as an extra storage component with chosen charging and discharging efficiencies. The required electricity for heat pump is considered in this project. However, required electricity for the electrolyser (in the charging state of the hydrogen system) is not considered. The renewable energy support that offers investment support to private households is not taken into consideration. The calculation for the under-

3 floor heating system, potential environmental impact from the energy system and degradation of the PV panels during its lifespan are also not considered in this project.

2 METHODOLOGY

To understand the theoretical aspect behind this kind of system, a literature survey of the state of art will be done by using various articles and an interview with Hans-Olof Nilsson the owner of the first self-sufficient house in Sweden and the founder of Nilsson Energy. Other similar studies will be presented in this section, as well as the specifications for the used components of the energy system. The interview with Hans-Olof-Nilsson took place through Microsoft Teams where several relevant questions was asked to him.

Different software is being used to decide the energy production of this system. This is done to validate if the used system is technically sustainable to provide with needed energy. Software as MATLAB including a code called Opti-CE (Opti-CE, 2016) and Excel is used in this case. The cost and the economic evaluation of this system will be done by doing calculations in Opti-CE and the information regarding the cost of the components is taken from different references.

The code Opti-CE is using genetic algorithm in MATLAB with a purpose to find the most suitable capacity for the chosen components in the renewable power system. It is beneficial for both the energy supply of renewable including how much the LCC is over the life of the project. The energy supply is optimized with the usage of Genetic Algorithm that is calculates the best scenario according to the electrical and thermal demand in the household.

The software is used to optimize the life cycle cost of the chosen energy system in order to meet the energy demand by being totally self-sufficient. The free version Opti-CE includes components as PV panels, battery system and a diesel generator (Opti-CE, 2016) .

The results from the simulation and the economical evaluation are presented in the result section. A scheme of the energy system will be presented in this section as well. A sensitivity analysis is performed in the energy system to determine how the energy output and the life cycle cost is affected in different scenarios. The investigated scenarios consider increase with 10% of the energy demand, decrease with 10% of solar radiation, increasing the lifespan of some components to match the lifespan of the project, decreasing the operation and maintenance cost with 10%. Changing the discount rate is also considered in the sensitivity analysis. Thereafter, the results that have been obtained are discussed and analysed in the discussion section. Thus, making it possible to draw different conclusion regarding the results from the simulation and economic evaluation for the energy system being applied in the household.

4 3 LITERATURE STUDY

The literature study describes the theoretical section of various subjects being studied. It defines various scientific articles that reflects and deals with similar issues in the energy section. Different aspects of off – grid energy system was investigated in order to expand the knowledge in this subject. The articles are published by both active and retired professors that is based on original research and can support a hypothesis and theory. All scientific reports were searched in search engines like Diva, Google Scholar and Primo to find the most suitable scientific articles. The scientific articles were filtered to receive a more suitable research that depend on modern specification. It also includes the components that exists in today’s market and important specification for each component. The specification of the various components being used in the energy system is covered by the design, installation, operations and efficiency among others.

Off-grid system

The use of renewable energy sources is increasing by time and the usage of them are needed to replace the convectional energy sources (International Energy Agency, 2014). Off-grid system are using renewable energy sources to meet the annual energy demand without any connection to the electrical grid. The size for the system and what components that are being used are dependent on the location and power needed (Tsiaras, Papadopoulos, Antonopoulos, G. Papadakis, & Coutelieris, 2020).

The renewable energy sources that are used in off-grid system contribute with lowest environmental impact compared with other convectional energy production sources where a diesel generator is considered. The problem with this type of system is the high initial cost since some components are expensive to use as energy storage components. (Philip, o.a., 2016).

Sandwell, Chan, Foster, Nagpal, Emmott, Candelise, Buckle, Daukes, Gambhir and Nelson (2016) continue explaining in their article that there are several factors that play a major role in the development and optimization of such a system. For instance, life cycle cost (LCC), environmental impact and renewable resources. The Life cycle cost are considered in this project as well.

According to Magnus Berg, a researcher in Vattenfall that has been interviewed by Agneta Wahlström (2019) that even though some houses in Sweden has gone off-grid, it still not an option to everyone due to its technical expensive. Berg consider that going off-grid are relatively costly in the region since it would require a large amount of capital to have no connection to the electrical grid and that would not be an option for many people today. However, the researcher consider that the price of the system has a potential to decrease in the upcoming years. He also mentioned that the production from solar panels may not meet the energy demand during various periods of the day. That occur during the wintertime, then long time storage alternatives should be used that store energy when the there is an overproduction and use it when the demand is high. In this case hydrogen system is suitable.

5 Nevertheless, Hans-Olof Nilsson the owner and the finder of Nilsson Energy built his own house in Gothenburg Sweden totally disconnected from the local grid by relying on solar energy connected with hydrogen energy system (Nilsson Energy, 2017). Nilsson Energy and Better Energy are two companies that consider that long term energy storage system as hydrogen system are needed in order to fil the gap between the production and demand between different season. It is also included that overproduction during the sunny days can be stored in form of hydrogen for later use when the energy demand is high. (Energy & Energy, Swedish housing block powered 100% off-grid by sun and hydrogen, 2019)

To understand how off-grid system works, Better energy (2018) explains the process as following: The solar panels convert the solar energy to electricity that goes through inverters in order to convert DC electricity to AC electricity. Some of the generated electricity is fed to the house for direct usage and some portions are stored in batteries that could be used when it is needed. The company also mentions that stored energy in the storage banks are used to power the electrolyser in order to split water molecules to oxygen and hydrogen. The oxygen is let out to the atmosphere and the hydrogen are stored. The hydrogen is compressed to around 300 bar and stored in storage tanks for later use. According to the company the hydrogen can be used as a fuel in a fuel cell in order to generate both electricity and heat.

Comparison between off and on-grid This section presents the comparison between the off and on-grid systems as well as some advantages and disadvantages. Application area, size of the system, storage ability, energy supply, system and maintenance cost and environmental impact among other things that are presented.

According to Anil and John (2015) the biggest difference between the two energy systems is the treatment of the exceeded generated energy. They mention that the exceeded generated energy from the off-grid system can be stored in a storage system for later usage. However, the exceeded energy from the on-grid system are injected directly to the grid

Kempener, d’Ortigue, Saygin, Skeer, Vinci and Gielen (2015) primary considers two differences between the systems. The first one regarding the size of the system and the other one is the power supply. They mention that the off-grid system is small in size compared to the on-grid system since it supplies energy to a house or block of flats, meanwhile an on-grid house is considered to be a big system since it is connected to large centralized grid that can supply energy to cities and even to a whole country. The second difference that has been pointed out by the authors is the energy supply, the off-grid system generates its own energy without relying on the grid. The on-grid houses on the other hand relies on the grid when it comes to the energy supply, but these houses are capable to generate a portion of the electricity by itself if solar panels are connected to them.

In an article written by Algaddafi, Alshahrani, Hussain, Elnaddab, Diryak and Daho (2016) it is mentioned that going off-grid are requiring higher investment cost since different components are expensive to have such as fuel cell and batteries. However, by having an on- grid system minimize the investment cost since no batteries are needed. In this case these

6 costs can be avoided. However according to a study done in Tehran by Jafari, Ghadamian and Seidabadi (2019) that going off-grid benefits family households with greater net present value, lower levelized energy cost and lower annual energy production cost than having an on-grid connected system.

Hans-Olof Nilsson (2020) mentioned during an interview that an on-grid household comes with the obligation to pay the electricity network subscription that differs from various supplier where taxes for consumed energy is included. Nilsson continue saying that going off- grid means avoiding all these costs. However, it is important to have contact with an operating company that handles technical support. Algaddafi, Alshahrani, Hussain, Elnaddab, Diryak and Daho (2016) continue explaining in their article that on-grid systems which is connected to the electrical grid is affected if any outage occurs in the grid. However, an off-grid system that is self-sufficient is not affected due to its connection position. The authors also point out that an off-grid system can be the solution to generate power in isolated places where the grid connection unavailable. However, the storage system in an off- grid system requires ongoing maintenance and even replacement when the lifespan of the component has exceeded. Even though the system of an off-grid and an on-grid is different to each other, both is very complex. however due to the number of different components in the off-grid system and have it totally independent from the grid makes it more complex.

According to Hans-Olof Nilsson (2020) if something goes wrong in the energy supply for an off-grid system during the operation, it is not possible to call the local network supplier and ask for help. In contrast ongoing maintenance and service has to be done in order to avoid these issues. He mentioned also that the maintenance cost for an off-grid system are higher than it is for an on-grid system. The reason for that is because the off-grid system consists of many components that need maintenance and some of them needs even replacement after a certain time

Ghenai and Bettayeb (2019) as well as Sandwell et al (2016) are considering in their articles that off-grid systems produce clean energy and reduces the greenhouse effect (diesel generator alternative are not used) compared to the traditional energy production alternatives that the grid are using. Hans-Olof mention also, the system he is using in his house only contributed with CO2 emissions during the manufacture of the components.

However, the energy system contributes with no CO2 emissions and is producing 100% clean energy in operation.

To understand the difference between the two systems as well as the advantages and disadvantages Table 1 is created

Table 1 Difference between off and on-grid systems.

Off-Grid On-Grid Storage system Needed in the household Not needed in the household

Size of the system System for a household or a The system is connected to a block of several flats big grid

Energy supply Self-sufficient Relies upon the grid, but an on-grid house is capable to

7 generate a portion of its own energy if its combined with solar panels

Fee for used energy None Electricity network subscription and value added taxes Economy High investment cost Low investment cost. Running and fixed cost to grip operator and to electricity dealer.

Grid outage Not affected System stop working

Maintenance Ongoing maintenance is The maintenance is not required, and maintenance required in the house that is cost are higher since more connected to the grid, except Components needs if the house has solar panels maintenance connected to the house

Complexity of the system Complex due to the variety The electrical grid is a of components connected to complex system itself, the household. however the household’s connections to the grid are not complex

Environmental impact Low, no CO2 emissions in Higher CO2 emissions operation compared to off-grid

Environmental impact from the energy sector

The organisation World Bank published a statistical paper indicating that roughly 1.2 billion people have no access to the electrical grid (Ritchie & Max, Acess to Energy, 2019). Even though the percentage of access to electricity has increased since the 90s, a great increase of carbon dioxide emissions still occurred. The carbon dioxide emissions per capita was approximately 1.5 metric tons in 1980. However, it has reached a value of roughly 7.5 metric tons during 2014. This indicated the usage of fossil fuels has increased rapidly as the population has increased in a higher acceleration. (Chen, Wang, & Zhong, 2019). The increase of concentration has led to a climate change where the mean global surface temperature has increased resulted damaging changes to the crop and water resources including health. That has a severe impact on the water-energy nexus where GHG has a significant role and is significantly more evident than ever. The usage of non-renewable energy systems will eventually lead to reducing resources at a household level where the energy demand will be higher in the next 30 years as the water availability is lower. (Halvorsen, Schelly, Handler , Pischke, & Knowlton, 2016).

8 An alternative against high carbon dioxide emissions is by implementing more renewable energy in the energy sector. This type of designs and actions is important to reduce the concentrations of GHG emissions and the dependence of non-renewable energy that has an excessive effect on Earth. However, the environmental impact of the renewable energy has a different environmental impact on Earth. The energy system has a small fraction of GHG emissions during manufacturing process. However, the generated energy has no production of GHG emissions from usage of fossil fuels and decreases the pollution in the air. Including a decreased dependence on imported fuel which has an impact on the economy. Thus, the usage of renewable energy contributes to environmental improvement that indicates that the concentration of carbon emissions decreases with time. There has been different approach towards less carbon dioxide emissions that allows more renewable sources to be applied in the energy sector. A great approach was the establishment of Kyoto protocol which is an international treaty that took place between 1997 and 2014. The agreement binds the European union and 36 industrialized countries towards a decrease of greenhouse emissions that has a rough impact on Earth. Since the agreement of Kyoto protocol took place in the late 90s there has been lowering carbon dioxide emissions from the European Union by 11.8% between 1990 and 2014. (Dogan & Seker, 2016).

Heat and electricity market price

The Scandinavian countries share a common electricity market where the prices set on the electricity exchange depends on various factors. The electricity consumption in this region is relatively high compared to the rest of Europe due to the high energy consumption in the industrial section. The price of both electricity and heat are affected by different variables in the market, for instance how much electricity that can be produced along with the demand of energy. Different cases determine the electricity price in the market. For instance, the electricity price will decrease and lead to a dip of price if the weather is milder than normal. (Energimarknadsbyrån, 2020). The largest electricity market in Scandinavia is named Nord Pool and organizes different markets for electricity and heat. The market that handle daily and historical prices are called Elspot that are well integrated since the 1990s and handles trade across Scandinavian countries.

The establishment Nord Pool has gone through a few adjustments since it was fully integrated. However, it is possible to trade for future contracts that delivers up to half a dozen weeks. It also includes offers that are long-term forward contracts with delivery a few years in the future. However, there is different types of economic methods that can be used to analyse an invested project. In this case there are life cycle cost, net present value and levelized cost of energy (NordPool, 2019).

Renewable energy systems that are combined with new technologies are less popular in the market compared to more popular energy systems that is considered as a non-renewable energy. However, there is a possibility that engines that use hydrogen as fuel will have a greater efficiency than engines fuelled with gasoline in a couple of decades (Ayres, Turton, &

9 Casten, 2007). The economic growth will increase more rapidly if the energy efficiency has the same direction (Bayar & Graviletea, 2019).

Life cycle cost The methodology life cycle cost is considered an important tool for determining how to make an energy system more tough against climate change (Rodehorst. Beth, 2018). The term life cycle cost originally came from the US armed forces in the 1950s to have a better view and control of the economy (Klas. Andersson, 2008). Life cycle cost does refer to the activity from its manufacturing, usage, maintenance to its final clearance that is required to manufacture the entire energy system. The methodology uses different approaches that is conducted in different reasons. Life cycle cost are mainly used to inform the Engineers and clients about different investment scenarios. Including to assess financial benefits of the energy efficiency during its lifespan (Islam, Jollands, & Sujeeva, 2015). The formula used in life cycle are dependent on variables such as the sum of all the net present value of all cost that occur during the lifetime of the energy system.

�� = ��(��) + ��(�&�)

Equation 1.

PV(IC) describes the present value of the initial investment cost being used in the energy system. PV(O&M) describes operational and maintenance cost, and future replacement cost in the energy system (Fernando. Pacheco - Torgal, 2017).

System components

This section of the report covers the components that are included in the off-grid system. The energy system consists of PV panels where solar panels and inverters are included. A storage system that consists of battery storage units for short term usage, hydrogen system for long term usage and hot water storage tank to produce hot water. The hydrogen energy system consists of an electrolyser, compressor, a hydrogen storage tank and a fuel cell. A geothermal heat pump is also included in the system to provide both space heating and hot water.

PV system PV modules have become more and more popular during the last few decades (Saedpanah, Asrami, Sohani, & Sayyaadi, 2020). Solar panels are considered to be the most effective way to utilize sun energy. The overall cost for solar panels has decreased and the efficiency has increased making it one of the most common system in the clean energy supply with reduced

CO2 emissions. (Zander, Simpson, Mathew, Nepal, & Garnett, 2019).

There are primarily two different Photovoltaic applications. The first option is the grid connected and the other on is a stand-alone system. The grid connected PV system is used to generate electricity to the household and have the possibility to feed the grid with electricity

10 when there is an overproduction from the panels, with other word selling the overproduction. The stand-alone system is the off-grid system that is not connected to the electrical grid because of the location of the house or for environmental purpose. However, different kind of storage system should be applied to this system to meet the demand during colder periods. (Ali & Khan, 2020). A PV system for off-grid application is used in this project, since no grid connection is available in this case as mentioned before.

3.4.1.1. PV Panels Solar panels are considered being the most important component in the PV system, mainly because without them the energy from sunlight cannot be utilized. They come in many sizes and shapes. (Limited, 2013). The solar panels are built by using a certain number of solar cells to create the panel. The solar cells are used to collect and convert the sun power to electricity in the form of direct current. (Bhatia, 2014). The process calls the photoelectric conversion and occur by the movement of the electrons through the solar cells. (Michel, 2018). Bhatia (2014) mentions that the photons in the sun light increases the movement of the electrons in the solar cells and make them work in a higher state of energy. The electrons work as a producer for the direct current.

There are different types of PV cells in the market such as the c-Si cells that cover around 97% of the solar cell market, thin solar cells that is also well used in the market and the semiconductor solar cells that consist of different materials as cadmium telluride, and copper indium gallium selenide (Masson & Kaizuka, 2019). The power generated from the PV panels can be calculated by using Equation 2 taken from (Kaabeche, Belhamel, & Ibtiouen, 2011).

�� = �� ∗ �� ∗ ��

Equation 2.

Where npv is the module efficiency, Apv is the area of the used pv panels and Ggt represents the global solar radiation.

3.4.1.2. Inverter The most suitable inverters that are used to convert the direct current from renewable sources to alternate current are multi inverters (Pakdel & Jalilzadeh , 2017).This type of inverters are use as they have the ability to produce high voltage from sources with lower current output (Ounejjar, Al-Haddad, & Gregoire, 2011). There are several models of inverters that are used in this area such as cascaded H-bridge (CHB), flying capacitor (FC) and neutral point clamped (NPC) (Abu-Rub, Rodriguez, Holtz, & Ge, 2010).

But according to Pakdel and Jalilzadeh (2017) the new developed packed U cell (PUC) can be the most efficient inverter to use since these inverters don’t require the same amount of high input power and same number of capacitors as other inverters.

But in general, the, inverters are divided into two groups, the centralized inverters and the micro inverters. For the centralized inverter all the solar models are connected to the same

11 inverter. For the micro inverter every panel or every number of panels are connected to an own inverter. The cost of inverters has dropped in recent years and corresponds to approximately 10% of the total cost of the PV system. However, some of the inverters are more expensive than other. For example, the micro inverters are more expensive than the traditional centralized inverters because of using several inverters, since every module needs an own inverter. (Hong, o.a., 2016).

Battery A storage component is one of the essential components in the system in order to mitigate the intermittency in power from solar energy. The power from the PV panels is dependent on the sun light during the daytime, and even during the daytime there can be some gaps between the demand and the supply from the sun. (Hoppmann, Volland, Schmidt, & Hoffmann, 2014). Because of the change in the weather, time of the day that affect the power from the sun and to cover the power gaps, battery storages are used (Braff, Mueller, & Trancik, 2016).

There are different types of energy storage such as mechanical, thermal and electrochemical energy storage (Jung, Jeong, Kim, & Chang, 2020). But according to many studies as the previous one done by Jung, Jeong, Kim and Chang (2020) and the one done by Jurasz, Ceran and Orlowska (2020) the suitable storage for this kind of system is the electrochemical energy storage where lithium ion batteries are used. The cost for lithium ion chargeable batteries has dropped during the last years and even the performance of has improved. (Zhang, Campana, Lundblad, & Yan, 2017).

The battery is either charged or discharged depending on the amount of energy that is produced by the PV panels and the required demand of the house. When the demand is higher than the generation, the battery is discharged, and when the generation is higher than the demand then the battery is charged. (Kaabeche, Belhamel, & Ibtiouen, 2011).

The hydrogen energy system

Hydrogen Hydrogen is considered being an energy carrier that can store and deliver energy in usable form. The chemical element can power all commercial sectors such as buildings, transportation and industrial with the needed energy. (Eduardo I. Ortiz Rivera, 2008). The chemical element is a colourless, tasteless gas that happened to be the lightest element in the universe (Wiberg, Hollerman, & Wiberg, 2001). Hydrogen has been intensively investigated since the oil crisis that took place during the 1970s along with the high level of carbon dioxide in the atmosphere. It is mostly used for industrial purposes that could potentially play a major role in electricity and heat generation (Moliner, Lázaro, & Suelves, 2016). The element is a diatomic element that is never alone and always consist of two atoms bonded together.

12 The existence of hydrogen is often in the form of compounds that consists of a negative denoted H- That’s highly reactive with oxygen (Wiberg, Hollerman, & Wiberg, 2001). There are different techniques to produce hydrogen for instance through electrolysis of water and the treatment of thermolysis (Sherif, Barbir, & T.N.Veziroglu, 2005).

Hydrogen is used in various self-sufficient energy system. It is used in household for production of both heat and electricity. Both oxygen and hydrogen supplied approximately by 5% from water electrolysis while the 95% is mainly produced from fossil fuels. The overproduction of generated electricity is fed into batteries and hydrogen system. (Orida, Kyakuno, Hattori, & Ito, 2004).

Sherif, Barbir and Veziroglu (2005) explains that there are advanced technologies that are dependent on hydrogen as a fuel. These types of application can be applied in energy system that are not dependent to the electrical grid. The chemical element would be produced in large quantities and therefore replacing fossil fuels that has a larger environmental impact. It can be produced through electrolysis and then transporter through underground pipelines in gaseous form. Another option is by transporting hydrogen in liquid form through large tanks that can later be used in industrially sectors. That can also be applied for households that is self-sufficient and has no connection to the electrical grid. According to Evans, Strezov and Evans (2012) chemical energy storage is mostly applied to renewable energy sectors as solar energy where different types compatible batteries and fuel cells are utilized.

Hydrogen system Hydrogen system is an alternative to replace fossil fuel and can be applied in different application in the energy sector. For instance, in different types of fuel cell technologies that can be utilized in various sectors that requires electricity and heat. The chemical element is considered being an ideal fuel for future application being applied in different household. Hydrogen has an extremely low density as it is the lightest element in the periodic system. (Sinigaglia. Tiago, 2017). The storage of hydrogen consists of three main phases, it includes the production of hydrogen, storage of the element and consumption of hydrogen. There are different types of advanced storage methods being applied today. For instance, high pressured compressed hydrogen that is stored in a tank with a kept high pressure and increased density. This methodology is mostly used in storage, because it is the most understood and used methodology in modern time. Hydrogen system is mostly suitable for colder seasons for off-grid power supply. Mainly because there is less available production from the energy system (Dagdougui. Hanane, 2018).

To make it possible to use hydrogen as fuel, the physical state must be changed in order to improve the density by volume. A common technique of achieving higher storage density is by using a compressor where it is possible to achieve pressure between 200 and 700 bar. As hydrogen leaves the compressor, various characteristic properties increase which results a volumetric density between 20-50 kg/m3 including a considerably high gravimetric density. (Meng, 2006)

13 Electrolyser Even though hydrogen is considered as a common and safe fuel from a public perception, it is not an energy source that occur in nature. Hydrogen is mostly produced through different methodologies and one of them is by applying water splitting. (J.Rossmeisl, A, & Nørskov, 2005). This methodology reaches an efficiency of approximately 70 %. However, the process depends on high proportion of electricity and is considered being relatively expensive. The methodology uses two separate electrodes that are separated by a solid polymer electrolyte or an aqueous electrolyte. Thus, it is possible to produce a large quantity of hydrogen gas from water (Michalski, o.a., 2017).

The chemical reaction that takes place in the electrolyser requires energy and therefore considered being endothermic. In order to carry out the electrolysis an anode and a cathode electrode is used in the process. Reduction takes place in the cathode where hydrogen is produced. The reaction taking place in the cathode can by expressed by Equation 3 according to (Chun-Hua. Li, 2009):

2�� + ��−→ �(�) + 2��

Equation 3.

The other chemical reaction takes place in the anode, where electrons is removed from the water and enters the electrodes resulting oxidation in the water. The reaction taking place in the anode can be expressed by the following chemical reaction according to (Chun-Hua. Li, 2009).

1 � �−→ � (�) + 2� + �� 2

Equation 4.

3.5.3.1. Alkaline electrolyser Alkaline electrolyser is the most developed and mature electrolysis technology in today’s market. The technology is available in both small scale and large scale to produce hydrogen. Alkaline electrolysis consists of electrodes consisting of the metallic chemical element nickel for splitting water. The procedure has an operation temperature between 60 – 90 ˚C and the pressure does not surpass 30 bars. Even though the alkaline electrolysis is the most equipped technology, it has its limitations. This technology has a low current density and the efficiency is relatively low. However, it produces a high purity of hydrogen at approximately 99.5 – 99.9% and it is possible to reach 99.999% with the assistance of gas purification systems. (Sanchez, Amores, Abad, Lourdes, & Clemente-Jul, 2020).

The paper (2020) also includes that alkaline electrolysis needs further development in order to reach a higher current density in the conductor for a higher efficiency. These efforts are carried in different research and development (R&D) facilities dependent on the company. However, this project carried out the electrochemical process in the software Aspen Plus that doesn’t include codes but different components taking place in an Alkaline electrolysis.

14 MATLAB is one type of software that can handle this kind of process. But, due to the integrated tool called Aspen Custom Modeler it is possible to predict the productivity of hydrogen in an accurate way.

3.5.3.2. Polymer electrolyte membrane electrolyser A polymer electrolyte membrane electrolyser has different components related to an alkaline electrolyser. It consists of polymer membrane that is made from ions and produces proton due to a chemical reaction. It includes current collectors, separator plates, flow fields and porous plates that is made from metal. The catalyst is usually made from platinum that attracts the protons from separated molecular. Both protons and electrons are split from water on the anode side and the protons pass through the membrane on to the cathode. The electrons flow from the anode to the cathode through an external circuit flow with a reasonable thermoneutral voltage. (Barbir, 2005).

Hydrogen compressor After the hydrogen is produced by an electrolysis, the specific volumetric energy density of the gaseous hydrogen needs to be compressed to a high pressure. There are different types of compressor that is possible to apply in this scenario. However, it is important that the compressor have a relative high efficiency. Adiabatic process is considered being the most efficient way to compress a gas where it is compressed in different stages. (Farkhondeh. Jabari, 2016). The most common compressor for gaseous substances is mechanical compressor that are available for both low power and high-power applications. The most suitable compressor being used in this case for hydrogen production is electrochemical hydrogen compressor that has an efficiency reaching 79%. The electrochemical hydrogen compressor applies to an adiabatic process where the initial temperature changes due to the work that occurs in the compression. However, there is other characteristics will change due to the process. For instance, the pressure will be increased as the volume will decrease. The compressor is active simultaneously as the electrolyser is at work and receives its power from the PV modules (Rhandi, Trégaro, Druart, Deseure, & Marian , 2020).

In order to deliver the produced hydrogen from electrolysis to the hydrogen compression, work is required. Only pure hydrogen or hydrogen -containing mixtures is transferred to the hydrogen compressor. The hydrogen compressor aside of compromising the gas it can also be used to extract the mixtures or waste gases that is not needed before it enters the hydrogen tank storage. The gas is compromised to a pressure between 100 – 700 bars. (Kirill. Dzhus, 2008).

The compressor work in a hydrogen compressor is calculated by the following formula:

� � � = � ∗ ( ) − 1 � � �

15 Equation 5.

The specific heat capacity of the fuel (hydrogen) is represented by Cp. P2 and P1 represents the output and inlet pressure. T1 and ηc represent the state temperature in the inlet compressor and the efficiency of the compressor that varies for different products. The mass flow of the produced hydrogen is stated by mH2 and the isentropic exponent of hydrogen is stated with r.

Fuel cell Fuel cell are primary used for commercial in addition to industrial areas and are considered being a key application for enabling technology towards a higher usage and dependence of hydrogen. Fuel cells has replaced a number of internal combustion engines that is suitable for both portable and stationary power (Acar & Dincer, 2020). Even though the availability and usage of fuel cells has increased over the past decades, the history of the electrochemical device extends for over 150 years (Eduardo. I. Ortiz-Rivera, 2007). Theoretically, a fuel cell operates like a battery and consists of two electrodes that is placed besides an electrolyte (Chun-Hua. Li, 2009). Hydrogen is being used as fuel and is transported into the anode and the oxygen is entering the cathode. The oxygen allows a reaction between the oxygen ion and the hydrogen ion that is positively and negative charged resulting water. Including a reaction that takes place in the catalyst where the fuel (hydrogen) is split into an electron and a proton. The catalyst consists of different elements depending on the fuel cell being used. The proton and electrons take different directions in the fuel cell, the proton passes through the catalyst and reaches the cathode. The electron also reaches the cathode that is located beside the electrolyte. The electrons that is transported to the cathode creates direct current due to movement of them (Eduardo I. Ortiz Rivera, 2008). The total reaction that occurs in both the cathode and anode are the following (Chun-Hua. Li, 2009).

1 � + � −→ � � 2

Equation 6.

3.5.5.1. Proton – exchange membrane fuel cell Proton exchange membrane fuel cell is considered to have a good performance with an electrical efficiency between 40% and 60%. The fuel cell might be the most suitable choice for residents due to its size and fuel consumption including a similar system as polymer electrolyte membrane electrolysis. Proton exchange membrane was designed and created by the American multinational conglomerate General Electric company during the early-1960s. The fuel has an operating temperature between 40-80 degree Celsius and used the chemical element platinum as catalyst. The fuel cell uses two separate electrodes that has a solid membrane between them. The hydrogen is used as fuel and is fed into the anode and oxygen is fed to the cathode. The chemical reaction that occurs in both the cathode and anode are the following. (Chun-Hua. Li, 2009):

Anode: �−→ 2� + 2�

16 Equation 7.

Cathode: 2� + � + 2�−→ � 0

Equation 8.

Total reaction: � + � −→ � �

Equation 9.

Proton exchange membrane fuel cell is considered being a suitable option for the household because it offers various advantages. The fuel cell has a low operating temperature between 60 to 80° Celsius and have a quick start up time reaching approximately 30 seconds. (Nguyen & Shabani, 2020)

Geothermal Heat pump

A geothermal Heat pump (GHP) is one of the components that can be combined with other renewable sources in order to provide clean energy. The Idea of using a geothermal heat pump is by utilizing low grade energy from ground or air and use it for heating or cooling depending on the wanted purpose. (Abbasi, Baniasadi , & Ahmadikia, 2016). It is the most effective way to utilize the ground temperature to provide heating and cooling for the indoor temperature and even heating of water (Kubba, 2016).

Ibrahim Dincer and Marc A. Rosen (2012) mention in their book about the function of the geothermal heat pump. They mentioned that the operating fluid works as a barrier for the ground energy and heat up a refrigerant that is connected to the component. In this case the refrigerant turns into vapor that is compressed by a compressor. The compression increases the pressure and temperature. Thereafter, the compressed vapor can be used in order to heat up water pipes that are later used in the household.

According to Dennemand, Perers and Furbo (2019) There is also a component called air heat pumps that is used in the energy sector. However, geothermal heat pumps GHP is significantly more efficient making it more suitable for self-sufficient households. During cold periods when the heat demand is relatively high, it is possible to extract heat from the ground that has a higher temperature than the air temperature. That is why geothermal heat pumps are considered being more attractive in the energy sector. However, a geothermal heat pump requires a larger operating space and has a higher installation price compared to an air heat pump (Emmi, Zarrella, Carli, & Galgaro, 2015).

According to Biaou and Bernier (2008) a common way to use the GHP is by connecting it to a storage tank where the heated water can be stored. The water inside the tank start to get heated when a heat exchange is occurred in a pipe that leads the cold water from the tank through the heat exchanger and back with hot water to the tank. The hot water from the tank can thereafter be transported to the household where it is used for heating.

17 Heat storage tank

As mentioned previously from the paper by Biaou and Bernier (2008) the most common way to utilize the produces heat from a GHP is by using a storage tank and it was also concluded from another research done by Li, Zhang and Ding (2020). It was also mentioned in their research that to increase the flexibility and to overcome the gap between heat produced and heat demand, a storage connected to the heat pump should be applied in the system (Li, Zhang, & Ding, 2020).

4 CURRENT STUDY

This section represents the study for the data equations that is applied in the self-sufficient rowhouse building located in Eskilstuna. The section also includes the practicable energy system and the simulated energy system for the self-sufficient household that contains different components and assists different purposes. The components are applied in both Excel and MATLAB for the most optimal solution from an economic standpoint. The total life cycle cost is calculated based on the implemented energy system in the household.

The input data for simulated energy system is inserted in Excel where the MATLAB code is being able to read it and calculate various energy output. The software MATLAB is assisted by the open source code OPTI-CE that is consisting different files. Every file corresponds to the components that is custom to the energy system from an electrical respective thermal standpoint. The relationship between every file is then used to simulate the selected energy system to get the energy and economic outlook. The optimization method genetic algorithm (GA) is implemented in MATLAB to reach the most economic scenario with the selected degree of self-sufficiency, which is in this case 100% self-sufficient. This section includes the modelling system, input parameters, operational strategy, sensitivity analysis and the equations that is used in the energy system. The obtained results are presented in the subsequent section.

Practicable energy system for the off–grid household

To decide the most practicable design system for the off-grid household it is important to model the energy system that has the capacity and right component to provide the annual energy demand in terms of heating and electricity. An interview with Hans-Olof Nilsson the founder of Nilsson Energy and owner of a self-sufficient household outside of Gothenburg has implemented a suitable energy system for off-grid household. The questions given to him was relevant where the purpose was to find the most suitable energy system for a household from both an energy and economic perspective.

18 By using the answers from the interview and information that has been collected from the literature review it was possible to decide the needed components for the off-grid system. The practicable off-grid energy system consists of different components that provide the needed power to meet both the electrical and thermal demand as it is shown in Figure 1. The system consists of PV panels, battery storage, inverters, hydrogen energy system (electrolyser, compressor, hydrogen storage and fuel cell), diesel generator, heat pump and thermal storage tank. The PV panels are used to utilize the solar radiation and generate electricity with direct current. PV panels are connected to an inverter that converts the produced DC electricity to AC electricity that is used in the household. The PV panels are also connected to batteries to store the surplus power from the panels that is not used in the house. The battery storage is used for short-term usage in terms of electricity in the household when the energy demand is higher than the produced power from PV. The chosen battery is a Lithium NMC that provides with energy in the form of electricity. There is an inverter between the batteries and the household to convert the electricity from DC to AC.

When the battery is fully charged, the surplus power is sent to the hydrogen energy system in order to produce and store hydrogen as an energy carrier and is suitable for long-term requirements. Hydrogen is also used as fuel for the fuel cell to produce electricity. The surplus electricity from the battery transports to the electrolyser that splits water into hydrogen and oxygen. The electrolyser is operated in AC electricity; thus, it is necessary to add an inverter before the electrolyser. The electrolyser is connected to a compressor that compress the produced hydrogen into a hydrogen storage tank. The hydrogen tank is then connected to a fuel cell that use the hydrogen as fuel to provide the household with the needed energy.

The fuel cell is connected to the batteries provide the household with needed electricity. An inverter is also implemented after the batteries to convert the DC electricity to AC electricity. The fuel cell and electrolyser are connected to a storage tank to utilize the heat losses that occur in the them during the operation. The geothermal heat pump is connected to the thermal storage tank to provide the tank with the needed heat. The tank is then connected to the household where heat provides to the space heating including the domestic hot water.

A diesel generator is connected to the household and operates if the production from PV, battery and hydrogen system do not cover the electric electrical demand. The diesel generator operates also if any outage of damage occurs to the system to meet the house energy demand.

Simulated energy system for the off-grid household

The simulated energy system in this project is not completely similar to the one explained in section 4.1. The difference between the simulated and the practicable energy system is the hydrogen system. The hydrogen system for the simulated energy system is assumed as one component that replaces the electrolyser, compressor, hydrogen storage and fuel cell. The discharged power from the hydrogen system is fed to the house to cover the needed electrical load. The practicable energy system is not simulated because it requires more input data and requires more analysis for each component that could not be provided. However, the simulated energy system is more suitable according to the input data. Therefore, the energy system with one component for the hydrogen system utilized in the calculations. The simulated off-grid system is illustrated in Figure 2 where every component is included. The characteristics of the hydrogen system is presented in section 4.3.3.

Figure 2 The simulated off-grid energy system for the household. The blue line represents the DC electricity, green lines represents the AC electricity and orange represents the heat.

Power calculation and model design

This section of the report presents the calculation of the power from different components that is utilized in the energy system. The assumption of the hydrogen energy system indicates that the electrolyser is considered when the hydrogen system is charged, and the fuel cell is considered when the hydrogen system is discharged. The components are needed to generate the needed energy for the household along with the PV panels, battery system and heat pump. The optimal solution for LCC was adjusted according to the decided components capacities using GA. The method GA is applied to find the needed components capacities in order to meet the load of the household by finding the optimal LCC. The results are then presented in the next section for the different components and the complete system.

PV system To calculate the produced power from the PV panels in the selected household Equation 2 from section 3.4.1.1 is used. The calculation is done for every hour during a one-year period which corresponds to 8760 hours. ηpv in Equation 2 that indicate the efficiency for the PV panels is calculated by Equation 10 which is modified by (Duffie & Beckman, 2013) .

�(�� − �) � �� − 20 �� = �, ��[1 + + ∗ ∗ 1 − �, �� ∗ ��] �, �� , �� 800

21 Equation 10.

ηpv,stc characterise the efficiency for the PV system from a standard test condition (STC). STC illustrated the fixed conditions in the energy sector where the PV panels is tested. The temperature coefficient of the power output is represented by u and is expressed by %/˚C.

The ambient temperature is represented by Ta and is collected for the given location in

Eskilstuna. Tstc represents the standard condition temperature, NOCT is the nominal temperature with the unit ˚C and �� is the global solar radiation in the plane of the PV panels.

The PV panels being used in this project is from the company Q CELLS It has a reasonable efficiency that allows the panels to produce more energy with lower number of panels. Therefore, making it well suited for converting sunlight to electrical energy. (Nordic Solar, 2019). The module is called Q.PEAK DUO BLK-G6 345 and the specifications are presented in Table 2.

Table 2 PV panels specifications (Nordic Solar, 2019).

Parameter Value Unit �, �� 19.3 % � -0.27 %/˚C � 25 ˚C �� 43 ˚C

4.3.1.1. Solar radiation calculation The total solar radiation in the PV module plane is calculated by three variables that depends on surface orientation and horizontal radiation. The different variables are represented by the diffuse radiation Gd,t, reflected radiation Gr,t and the beam radiation Gb,t. All the variables share the unit W/m2 and the total solar radiation is extracted by Equation 11.

�� = ��, � + ��, � + ��, �

Equation 11.

The beam radiation in the PV module plane Gb,t is expressed in Equation 12 taken from (Duffie & Beckman, 2013)

��, � = , , cos (θ) ()

Equation 12.

Where �, and �, is the global horizontal radiation and diffuse horizontal radiation respectively expressed in W/m2. The solar altitude is represented by a and θ represents the angle of incidence which is expressed in degrees. Equation 13 for diffuse radiation in the PV module plane is from (Duffie & Beckman, 2013).

22 1 + cos (β) ��, � = � , 2

Equation 13.

The module tilt β has the unit degrees and is inserted in Equation 14 to calculate the ground reflected radiation Gr, t (Duffie & Beckman, 2013).

1 − cos (β) � = � ∗ � , , 2

Equation 14.

The ground reflectance (albedo) for the given geographical location is expressed by ρg.

Battery The battery system for the rowhouse is chosen as an energy storage option in order to utilize the extra production from the PV panels. The batteries in the energy system is dependent on the SOC(t). The SOC(t) for the battery system is set at 20% as the lowest value and 95% as the highest value. That mean the battery cannot be charged more when its SOC is already 95% and cannot be discharged when its SOC is 20%. The selected battery is Lithium NMC. The selected battery has a roundtrip efficiency of 90% (TESVOLT).

Equation 15 and Equation 16 are taken from (Kaabeche, Belhamel, & Ibtiouen, 2011) to calculate the SOC(t) both from a charging and discharging standpoint for the selected battery bank.

�(�) ��(�) = ��(� − 1)(1 − σ) + [�(�) − ] ∗ �� ℎ��

Equation 15.

�(�) ��(�) = ��(� − 1)(1 − σ) + − �(�) ∗ �� ℎ��

Equation 16.

Where t represents the time step that is followed by every hour annually. Epro(t) indicates the produced energy from the PV system that is connected to the batteries and σ represents the self-discharge rate for the batteries. Eload(t) is the power consumption in the household which corresponds to the load in the household. ηB and ηinv represents the efficiency of the battery bank respectively inverters.

Hydrogen system In this project the hydrogen system is assumed to be as an extra storage component that works in the same way as the battery. The hydrogen system is charged when there is a surplus

23 in energy from PV and batteries and discharged when the demand in the house is higher than energy produced by the PV and batteries. The hydrogen system is similar to the battery except in the efficiency and in the SOC. The SOC in the hydrogen storage is between 0% and 100%. The equations that are used to decide the SOC are similar as the equations that are used in the battery except some changes. The equations that are used are presented in Equation 17 for charging and Equation 18 for discharging taken from (Duffie & Beckman, 2013).

�(�) ��(�) = ��(� − 1) + [�(�) − ] ∗ �� ℎ��

Equation 17.

�(�) ��(�) = ��(� − 1) + − �(�) ∗ �� ℎ��

Equation 18.

The rate of discharge (1-a) are excluded in these equations since its assumed that there are no losses when the hydrogen system is unused. In the charging and discharging process there are two different efficiencies being used. In the charging state, the electric efficiency used (��) assumed to be corresponding to the efficiency of an electrolyser and compressor together. The electrolyser and compressor efficiency assumed to be 70% and 79% respectively according to the sections 3.5.3 and 3.5.4 . In the discharging state the efficiency used (��) represents and corresponding to the efficiency for a fuel cell. �� and �� are assumed to 55% and 60% respectively. �� and �� are assumed being constant during operation. The fuel cell efficiency is chosen according to section 3.5.5.1.

4.3.3.1. Heat losses from the hydrogen system Heat losses from the hydrogen system are taken in consideration in this case, where two different heat losses are considered. Heat losses during the charge of the hydrogen system that represent the heat losses occurring in the electrolyser including heat losses during the discharge of the hydrogen system that represents the fuel cell heat losses. The losses during the charge and discharge periods are dependent on the chosen efficiencies. The heat losses during the charging periods that representing the electrolyser losses are presented in Equation 19

�� ℎ�� (��) = �ℎ�� ℎ�� ∗ (1 − �)

Equation 19.

The heat losses during the discharging period representing the fuel cell losses are presented in Equation 20.

�� ℎ�� (�� ) = ��ℎ�� ℎ�� ∗ (1 − ��)

24 Equation 20.

The heat losses from the hydrogen system are stored in a thermal storage tank in order to meet the house thermal demand. It is assumed that 70% of the heat losses are used and stored in the storage tank (Nilsson, 2020).

Diesel generator The fuel consumption from the diesel consumption is calculated by Equation 21 according to (Ismail, Moghavvemi, & Mahlia, 2013).

�� = �� + ��,

Equation 21.

Where PDG and PDG,r represent the power output from the diesel generator respective rated power output of the chosen diesel generator. The experimental coefficient of the fuel consumption curve is represented by the parameters c and d.

Thermal storage tank A thermal storage tank is used in the system in order to store heat in form of energy and to meet the house thermal demand. Heat losses from the hydrogen system is fed to the storage tank in order to be stored. The losses from the hydrogen system are not enough to keep the energy in the tank stable during the whole year. In this case the storage tank is connected to a heat pump that supply with heat to the tank when it is needed.

Heat pump The heat pump is used to supply the thermal storage tank with the needed energy in order to keep it stable during the whole year in purpose of meeting the heat demand of the house. Equation 22 is used for the heat pump work and is taken from (Guo, Ma, Ma, & Zhang, 2017).

�(�) � (�) = ��

Equation 22.

Where P is the power of the heat pump, Q is the heat that the heat pump produces, and COP is the coefficient of performance. The power of heat pump is dependent on time and changes with the change of the heat production. The heat pump used in this project has a constant COP value of 3.5 during the simulation. (Emmi, Zarrella, Carli, & Galgaro, 2015)

25 Life cycle cost The optimization model adjusted to the household minimized the life cycle cost for the energy system that is adjusted to the household. Equation 23 is modified from (Campbell, 2008) and is used to calculate the life cycle cost for the selected household.

� � �� = �� − �� + (1 − ��) + (1 − ��) + (1 + �) (1 + �) (1 + �) (1 + �)

Equation 23.

ICC represents the initial cost in $ for the whole system and N represents the lifetime for the project in years. The parameters n is the selected year that is referred to the system and dn is the annual depreciation for the system in $ and is consistent from year to year. an is the maintenance and operational cost of the in $. The discount rate is referred as i (%) and the tax rate is designated with tr (%). The tax rate represents the depreciation tax benefit during the projects lifespan and is considered as 0 in this project since this tax is not applied in

Sweden. R is the total number of replacements during the systems lifetime and ICCc is the investment cost of the component corresponding to the c-th replaced. Ic is the lifetime of the c-th component. The salvage value is represented by s and has the unit $.

Equation 24 represents R as a function of the lifetime for the components to be replaced.

� � = ��

Equation 24.

This equation is adjusted in MATLAB where floor represents a function that rounds a number to the next smaller integer. It takes the salvage value (s) into account which is assumed to be equal to 10% of the initial cost (Mathew, 2006).

System cost In order to perform the calculation of the life cycle cost, and to decide the cost of the system it is needed to collect and present the specific and the maintenance cost of every used component in the energy system. The lifetime of the system is presented in this section as well.

4.3.8.1. System cost in today’s scenario The values in today’s scenario is collected from the manufacture company webpages or from webpages that sell the component, but some of them are assumed as well. Table 3 represents the system cost and the needed parameters that are used in the life cycle cost calculation.

26 Table 3 System cost in todays scenario.

Parameter Value Unit Reference

Specific cost PV system 1.21 $/W (Lindahl, Stoltz, Westerberg, & Berard, 2018) Specific cost battery 0.5 $/Wh (TESVOLT) Specific cost inverter 0.33 $/W (Suministrol del sol, 2020) Specific cost diesel 0.2 $/W (DUAB-HUSET, 2020) generator Specific cost diesel 1.126 $/l (INGO, 2020) Specific cost 0.737 $/W (NREL, 2018) electrolyser Specific cost hydrogen 0.08 $/kWh (NREL, 2018) storage Specific cost fuel cell 0.507 $/W (NREL, 2018) Specific cost thermal 1572.6 $/m3 (CombiHeat, 2020) storage tank Specific cost heat pump 0.76 $/W (PolarPumpen, 2020) Maintenance rate PV 3 %/year (NREL, 2018) Maintenance rate 8 %/year (NREL, 2018) battery Maintenance rate diesel 8 %/year (DUAB-HUSET, 2020) Maintenance rate 8 %/year (NREL, 2018) electrolyser Maintenance rate 4 %/year (NREL, 2018) hydrogen storage Maintenance rate fuel 6 %/year (NREL, 2018) cell Maintenance rate heat 5 %/year (PolarPumpen, 2020) pump Maintenance rate 0.03 %/year (CombiHeat, 2020) thermal storage tank Project lifetime 25 years PV system lifetime 25 years (NREL, 2018) Battery lifetime 25 years (TESVOLT) Inverter lifetime 10 years (Suministrol del sol, 2020) Diesel generator 20 years (DUAB-HUSET, 2020) lifetime Electrolyser lifetime 20 years (NREL, 2018) Hydrogen storage 20 years (Kalinci, Hepbasli, & lifetime Dincer, 2015) Fuel cell lifetime 30 000 hours (Kalinci, Hepbasli, & Dincer, 2015) Thermal storage tank 20 years (CombiHeat, 2020) lifetime Heat pump lifetime 20 years (PolarPumpen, 2020)

Tax rate 0 % Assumed

27 Discount rate 2 % Assumed

The average discount rate was 1,9 between 2017-2019 according to Central Bureau of Statistics in Sweden (SCB, 2020). However, a discount rate at 2% is considered a reasonable value in today economy and accepted in the calculation by RG Förvaltning.

4.3.8.2. System cost in future scenario (2030) The life cycle cost is even calculated using future expected component values. The future scenario is performed using expected changed values in 2030. The expected values that are used in this scenario are also collected from the manufacture webpages, but some input parameters are assumed as well.

Table 4 System cost in future scenario (2030).

Parameter Value Unit Reference

Specific cost PV system 0.48 $/W (Iene, 2020) Specific cost battery 0.2 $/Wh (BNEF, 2020) Specific cost inverter 0.28 $/W (Magazine, 2018) Specific cost diesel 0.2 $/W (DUAB-HUSET, generator 2020) Specific cost diesel 1.726 $/l (Bytbil, 2019) Specific cost electrolyser 0.232 $/W (NREL, 2018) Specific cost hydrogen 0.08 $/kWh (NREL, 2018) storage Specific cost fuel cell 0.237 $/W (NREL, 2018) Specific cost thermal 1572.6 $/m3 (CombiHeat, 2020) storage tank Specific cost heat pump 0.76 $/W (PolarPumpen, 2020) Maintenance rate PV 3 %/year (NREL, 2018) Maintenance rate battery 8 %/year (NREL, 2018) Maintenance rate diesel 8 %/year (DUAB-HUSET, 2020) Maintenance rate 9 %/year (NREL, 2018) electrolyser Maintenance rate 4 %/year (NREL, 2018) hydrogen storage Maintenance rate fuel cell 6 %/year (NREL, 2018) Maintenance rate heat 5 %/year (PolarPumpen, pump 2020) Maintenance rate thermal 0.03 %/year (CombiHeat, 2020) storage tank Project lifetime 25 years PV system lifetime 25 years (NREL, 2018) Battery lifetime 25 years (TESVOLT) Inverter lifetime 10 years (Suministrol del sol, 2020)

28 Diesel generator lifetime 20 years (DUAB-HUSET, 2020) Electrolyser lifetime 20 years (NREL, 2018) Hydrogen storage lifetime 20 years (Kalinci, Hepbasli, & Dincer, 2015) Fuel cell lifetime 30 000 hours (Kalinci, Hepbasli, & Dincer, 2015) Thermal storage tank 20 years (CombiHeat, 2020) lifetime Heat pump lifetime 20 years (PolarPumpen, 2020) Tax rate 0 % Assumed Discount rate 2 % Assumed

Operational strategy The operational strategy explains how the system is working in order to meet the demand. The operational strategy is obtained in the MATLAB code where the electrical strategy is adjusted to the electrical load in the household including the various components. The heating operational strategy is adjusted to the thermal load including the different components that serves the heating. The electrical operational strategy consists of the electric load, PV panels, batteries, hydrogen system and diesel generator. The heating operational strategy consists of the thermal load, heat losses from the hydrogen system, thermal storage tank and heat pump.

4.3.9.1. Electrical operational strategy The electrical operational strategy illustrated how the components that cover the electrical load operate. When there is an overproduction from PV panels it is possible to charge the batteries that is connected to it. If there is an overproduction from the PV panels and the batteries is fully charged it is possible to transport the overproduction to the hydrogen system. If the production from the PV panels is lower than the electrical load, then will the batteries be discharged. If the battery reaches the minimum state of charge of 20%, then will the hydrogen system discharge in order to meet the electrical load. However, if there is not enough energy from the batteries including the hydrogen system then will diesel generator start to operate to compensate the electrical load. The electrical operation strategy is illustrated according to Figure 3.

Figure 3 Electrical operational strategy.

4.3.9.2. Heat operational strategy The operational strategy for heating is adjusted to the thermal load in the selected household. The heating consists of the losses from the hydrogen system, heat from heat pump and thermal storage tank. The thermal load is met by the energy in the storage tank, that is why it is important to keep the energy in the storage tank higher than the thermal needed. The heat losses from the hydrogen system is fed to the storage tank, and when extra heat is needed then energy will be taken from the heat pump. When the needed energy from the storage tank at time t is lower than the energy in the storage tank at the same time then the storage tank is discharged. When the needed energy at time t is higher than the energy in the tank at the same time then the heat pump will operate and increase the storage tank energy to up to 20% of the maximum tank capacity (lower bound). When there is no thermal load at time t and the storage tank energy at the same time is higher than 20% of the maximum tank capacity (lower bound) then the tank will be charged with the heat losses from the hydrogen system only, if losses exists. When the thermal load does not exist at time t and the energy in the storage tank at the same time is lower than the lower bound, the heat losses from the hydrogen system (if existed) will charge the tank. If heat losses do not exist, the heat from heat pump will increase the energy in the tank up to the lower bound. The operational strategy for the heat is illustrated in Figure 4 where different components are included.

Figure 4 Thermal operational strategy.

Climate data in Eskilstuna This section describes the meteorological data for the selected household in Eskilstuna where all data is collected from STRÅNG that is from SMHI. The collected data are presented during the time interval of 8760 hours that is corresponding to 2019. The climate data is referred as input parameters for the upcoming calculations that is needed in the power output for the PV system. The data corresponds to the geographical location in western Eskilstuna. The data is represented by the ambient temperature, global horizontal radiation and diffuse horizontal radiations. The ambient temperature is used to calculate npv in Equation 10. The radiations are used for solar radiation calculation that is necessary for the hourly simulation of the PV system. The diffuse horizontal radiation is used in Equation 13., and the global horizontal radiation is used in Equation 14.

Figure 5 illustrates the temperature in degree Celsius that occurs in the location. The temperature is between -18 and 29 degree Celsius which is reasonable values for the geographical location.

Figure 5 Ambient temperature in Eskilstuna per hour for one year (STRÅNG, 2020).

The total amount of shortwave radiation received from the sun is illustrated in Figure 6. It is quite reasonable that the diffuse horizontal radiation reaches relatively high values during the summer when the PV panels is exposed to much sun light compared to the remaining seasons. The global horizontal radiation has the same characteristics as the ambient temperature where it reaches relatively low values during the winter and fall. These values are indicating that the batteries including the hydrogen system is most suitable in these periods.

Figure 6 Diffuse horizontal radiation in Eskilstuna per hour for one year (STRÅNG, 2020).

Figure 7 show similar characteristics as the ambient temperature reaching highest values during the summer and relatively lower values during the colder seasons. It reaches approximately 900W/m2 during the summer and 100 W/m2 during the colder seasons according to Figure 7. The power production should also be relatively high during the summer and low during the colder seasons.

Figure 7 Global horizontal radiation in Eskilstuna per hour for one year (STRÅNG, 2020).

Electrical and thermal load in the household Figure 8 illustrates the annual electrical demand in the referred household in Wh. The off- grid household requires more energy during colder seasons when the temperature reaches low values. The maximum electrical demand reaches values that reaches approximately 2.9 kWh during the winter. However, the electrical demand is low during the summer and reaches higher values during the colder seasons. The data is given by RG Förvaltning and according to the company, some values during the year are assumed and specially during the summer. The assumptions are done since the house is not constructed yet and the actual electrical demand is not known. According to the company the straight line in Figure 8 during the summer is related to some errors in the estimations.

Figure 8 The electrical demand in the household per hour for one year according to RG Förvaltning.

The thermal load has almost a similar structure compared to the electrical load. During the winter the demand reaches relatively high values that needs to be compensated by the energy system, and during the summer the demand reaches lower values compared to the colder seasons. However, the thermal load is still quite high and requires energy from the system. Figure 9 illustrate that the thermal demand reaches approximately up to 2.8 kWh during the winter. According to the company in order to create a thermal load profile some assumptions are done, and that can specially be seen during the summer according to Figure 9. The load during the summer is fixed by using constants values (seen as straight lines) with different heights. The variation in the heights of the lines are done to make a variety in the thermal load profile during the desired period.

Figure 9 The thermal load in the household according to RG Förvaltning.

Deeper look on the load and energy production during the first week of November In order to understand how the electrical and thermal load are covered by the different components that are used in the household a deeper look on the load and production is done. It is suitable to investigate the energy system during the colder seasons as the electrical and thermal demand are relatively high. This period is investigated to see how all the components operate relating to the electrical and thermal load. Taking a period during the summer would not show how all the components operates since the hydrogen system does not have any output during this period. Thus, the first week of November are chosen to be investigated where the electrical and thermal load are being compared with the electrical and thermal production during the same period.

36 Sensitivity analysis

A sensitivity analysis was performed on the energy system and that is done to see how the change in some parameters can affect both the energy output and economy outlook. Five scenarios are investigated, where three covers the economical aspect and two cover the energy aspect.

Sensitivity analysis for the economical aspect four scenarios are done for the economical aspect to see how the change in some parameters in every scenario could affect the life cycle cost of the system. The first scenario includes an increase of the lifespan of the used components to be the same as the lifetime of the project which is 25 years. That mean that all the components except the inverter and fuel cell have a lifespan on 25 years. The second scenario includes a decrease with 10% of the operational and maintenance cost of the system. The third scenario includes the previous two scenarios, with other words changing the lifespan of the components and decrease the operational and maintenance cost of the system with 10%. The fourth scenario consider a change of the discount rate to see how an increase and decrease in the discount rate can affect the LCC of the energy system.

Sensitivity analysis for the energy aspect Two scenarios for the energy aspect are done to see how the change in some parameters could affect the energy outlook of the system. The first scenario is including a 10% increase of the electrical and thermal load in the household. The second scenario includes a 10% decrease of the solar radiation.

37 5 RESULTS

This section presents the results from the simulated energy system for the off-grid household located in Eskilstuna. The results are presented in both electricity and heating in form of energy that is utilized in the household. The output parameters from the storage system is illustrated with figures and tables. The economic analysis LCC for the optimized house is also included with respect to the project’s lifetime. The LCC are presented in two scenarios, the first one is considering today’s market price, and the second one is considering the future market price in 2030.Results from sensitivity analysis are presented as well. As a key result it can be mentioned that the energy system produces enough of sufficient energy to cover both the electrical and thermal demand of the household. More about the results are concluded in the upcoming section.

The electrical power output

This section presents how much power that is produced from the system including how much the storage components are charged with. The power output is simulated every hour during the period of one year. As a key result it can be said that the energy system produces enough electricity

The PV system Results from the PV production is shown in this section. Figure 10 demonstrates how much energy the chosen PV panels are producing during the period of one year. The investigated rowhouse has a roof area of 89 m2 where 40 PV panels are placed on. The PV panels that are adjusted to the roof top are suitable with the tilt and azimuth angle of the roof equal to 52 degrees respectively 33 degrees east. It is also important to mention that the simulation does not consider that the PV panels can be covered by snow during wintertime.

Figure 10 Annual production from the PV panels per hour.

Figure 10 shows that the PV panels have a high production during the summer. However, the production is not high during the colder seasons due to the less access to the sun light. The solar panels produce 13 560 kWh yearly which is higher than the total annual household electric consumption at 6 124 kWh (required electricity for heat pump is included in the total electrical load). The surplus power is stored in in the household storage systems for later use. The PV panels does not contribute any electricity to the household during night since the sun is not available.

The battery system This part of the results is presenting the state of charge of the battery and how much is required from it in order to meet the electric demand. Figure 11 illustrates the SOC(t) for the battery system during the whole year. The figure shows that the battery is mostly reaching the max capacity during summer. The battery system reaches a maximum value of 85 kWh during the summer when there is a surplus of energy from the PV panels. When the battery system reaches a fully charged value, it transfers the surplus energy to the hydrogen system that is connected to it. Figure 11 shows that the battery system is also charged during colder seasons even though the electrical demand is high. This is due to the lower production from

39 the PV panels indicating that the battery system and the hydrogen system is operating to cover the energy load in the household. The system has an initial SOC(t) rate at 95%, but it is decreasing due to the low production from the PV system. The battery system does not reach a value that is lower than 20% of the battery capacity, because the simulation does not allow the battery system to operate at a lower capacity. However, if there is any power needed in the household and the battery has reached its lower capacity, then power from the hydrogen system will be used in order to meet the required electrical demand.

Figure 11 Battery system SOC per hour for one year.

Figure 12 illustrates the power output from the battery. The power required from the battery is not high during the summer compared to the colder season. This is because the PV system works enough to prevent the battery system to fully operate. However, during the afternoon and over night when there is no production from PV panels, the battery system operates to cover the demand. The negative values indicate that the battery system is charging.

Figure 12 Battery output per hour for one year.

The hydrogen system The power output of the hydrogen system and the SOC(t) are presented in this section. It is charged when there is a surplus in energy from the PV panels and batteries are fully charged. The hydrogen system is discharged when the power from PV and batteries are lower than the electrical demand.

Figure 13 shows how much power is required from the hydrogen system annually. The power from the hydrogen system is required during the colder seasons when the production from both PV panels and batteries are not covering the demand. The negative values during the warmer seasons indicates that the hydrogen system is charged with the surplus energy that comes from the batteries, and no power is required from the hydrogen system during this period. The hydrogen system will produce electricity when the system is discharged which happens mostly during the colder seasons. The discharge of the hydrogen system (representing fuel cell) occurs 2 350 hours which happens during the colder season. The charge of the hydrogen system (representing the electrolyser) occurs 2 307 hours during the warmer periods.

Figure 13 Power output per hour during one year from the hydrogen system.

Figure 14 indicates the annual SOC(t) for the hydrogen storage which is dependent on the production from the PV panels and the battery system. The initial SOC(t) is set at 50% of the max capacity indicating that the hydrogen storage has enough hydrogen to produce electricity to the household when it starts to operate. The hydrogen storage is discharged during the beginning of the year when the electrical demand is relatively high and is charged throughout the warmer season when there is a surplus of energy from PV panels and batteries are fully charged. Thereafter, the hydrogen starts to discharge during the colder season indicating that the hydrogen system will produce power to the household when the batteries do not cover the demand. The capacity of the hydrogen storage is optimized to have a capacity of 6 572kWh. Figure 14 shows that the hydrogen system has more energy at the end of the year than what it started with, indicating there will be enough energy to cover the load in the upcoming year if the load is assumed the same.

Figure 14 Hydrogen system SOC per hour for one year.

Diesel generator production The diesel generator does not operate during the year because both the battery and hydrogen system produce enough energy to the household when the electrical demand is higher than the production from the PV panels. However, the diesel generator will start to operate if the energy demand is not met for any reason.

The heat power output

The heat power output shows how much heat that is produced by the hydrogen system in form of heat losses during the charge and discharge period, heat pump production and the thermal energy in the thermal storage tank.

43 Heat losses from hydrogen system Figure 15 shows the heat losses from the hydrogen system during the charging period (corresponding to the electrolyser losses) and discharging period (corresponding to the fuel cell losses). The figure shows that the heat losses takes mostly place during the summer i.e. during the charging period of the hydrogen system and reaches maximum value of 6.5 kWh. However, there is also heat losses during the colder period when the hydrogen system is discharging.

Figure 15 Heat losses per hour taking place in the hydrogen system for one year.

Heat in the thermal storage tank Figure 16 demonstrates the heat in the thermal storage tank. The tank is storing the heat losses from the hydrogen system and the produced heat from the heat pump. During the summer, the stored heat in the storage tank is increasing due to the high heat losses from the hydrogen system that is fed to the storage tank. However, during the other periods the storage tank is storing enough energy to meet the heat demand. The thermal energy in the storage tank are decided according to the heat operation strategy in section 4.3.9.2.

Figure 16 Heat in thermal storage tank per hour for one year.

Heat from heat pump Figure 17 demonstrates how much heat the heat pump is producing depending on how much heat there is in the storage tank. The produced heat from the heat pump occurs during the colder season when the thermal need is relatively high and heat losses from the hydrogen system is low. The heat pump has no production during the summer since the thermal load is low during that period and the heat losses from the hydrogen system is relatively high. However, the heat pump is producing enough heat to keep the energy in the thermal storage tank stable during the colder periods. The annual electricity demand for the heat pump is also covered by the energy system.

Figure 17 Heat pump production per hour for one year.

46 Load and energy production during the first week of November

This section illustrates the correlation between the energy load and production. The figures in this section show how the load is covered by using the different components in the energy system.

Electrical load and production Figure 18 and Figure 19 demonstrates the electrical load respective production during the first week of November. This section demonstrates that the electrical demand is relatively high while the PV panels do not produce much energy.

Electrical load during the first week of November 3000

2500

2000

1500

1000

Electrical load (Wh) 500

0 2 7 12 17 22 27 32 37 42 47 52 57 62 67 72 77 82 87 92 97 102 107 112 117 122 127 132 137 142 147 152 157 162 167 Time (hour)

Figure 18 Electrical load per hour during the first week in November.

Figure 19 shows the power production from the different components in the energy system and how the supply is divided between the PV panels, batteries and hydrogen system. The figure shows that the hydrogen system operates mostly during this period. This is due to the electrical load being higher than the production from the PV panels.

Electrical production during the first week of November 3500 3000 2500 2000 1500 1000 500 Electrical production (Wh) 0 1 6 11 16 21 26 31 36 41 46 51 56 61 66 71 76 81 86 91 96 101 106 111 116 121 126 131 136 141 146 151 156 161 166 Time (hour) PV Battery Hydrogen system

47 Figure 19 Electrical production per hour during the first week of November. The purple line corresponds to the hydrogen system output, the blue line corresponds to the PV production and the red line corresponds to the batteries output

Thermal load and production Fel! Hittar inte referenskälla. and Figure 21 illustrates the thermal load and production during the first week of November. The thermal load is relatively high during this period as different components compensate for the needed energy.

2500 Thermal load during the first week of November

2000

1500

1000

500 Thermal Thermal load (Wh)

0 1 6 11 16 21 26 31 36 41 46 51 56 61 66 71 76 81 86 91 96 101 106 111 116 121 126 131 136 141 146 151 156 161 166 Time (hour)

Figure 20 Thermal load per hour during the first week of November

Figure 21 demonstrates how much thermal energy is produced from each component during the first week of November. It is important to point out that the heat losses from the hydrogen system and the thermal energy from heat pump are utilized in the thermal storage tank in order to be stored and used to cover the thermal demand.

Thermal production during the first week of November 7000 6000 5000 4000 3000 2000 1000 0 Thermal Thermal production (Wh) 1 6 11 16 21 26 31 36 41 46 51 56 61 66 71 76 81 86 91 96 101 106 111 116 121 126 131 136 141 146 151 156 161 166 Time (hour) storage tank heat losses heat pump

Figure 21 Thermal production per hour during the first week of November. The blue line indicates how much thermal energy that is stored in the thermal storage tank. The black line

48 indicates the heat pump production and the red line indicates the heat losses from the hydrogen system

Life cycle cost and component capacity

This section presents the life cycle cost of the energy system using both todays and future market cost. The dimension of the capacity for the components are shown in this section as well. Table 5 presents the life cycle cost for the system with today’s market costs and the life cycle cost for the system if it is built in 2030 instead. The calculation shows that the life cycle cost reaches k$318 regarding to today’s market. However, the energy system reaches a value of k$195 if it is built in 2030 instead.

Table 5 Life cycle cost for todays and future scenario.

Life cycle cost for today’s k$318 scenario Life cycle cost for future k$195 scenario

Table 6 shows the dimension for the components that are required to meet the needed electrical and thermal demand, where the capacity of PV panels, battery and hydrogen system is dimensioned according to the optimized LCC for both todays and future scenario. However, the capacity of the thermal storage tank is set to cover the thermal load of the household that is 6 461 kWh. The dimensioned components are sized to meet the total electrical demand of 6 125 kWh (required electricity for heat pump is included in the total electrical load). Table 6 illustrates that the capacities for PV and thermal storage tank are the same for both scenarios. However, the capacities for the battery system and hydrogen system do change. The capacity for the battery system increases from 85 kWh in today’s scenario to 93 kWh in the future scenario, and the hydrogen system capacity decreases from 6 572 kWh in today’s scenario to 6 425 kWh in future scenario.

Table 6 Components dimensioned and chosen capacity for todays and future scenario.

Component Capacity in today’s Capacity in future scenario scenario PV 13.5 kW 13.5 kW Battery system 85 kWh 93 kW Hydrogen system 6 572 kWh 6 425 kWh Thermal storage tank 25 kWh 25 kWh

49 Sensitivity analysis

This section presents the obtained results from the sensitivity analysis for the scenarios that cover the economical and energy outlook.

Economical aspect The first scenario from an economical aspect includes the change of the life span for the implemented components (except inverter and fuel cell) to be equal to the lifespan of the project. The change resulted a reduction for the life cycle cost with k$36 (from k$318 to k$282). The second scenario where a decrease with 10 % for the operational and maintenance cost is included, a reduction in life cycle cost with approximately k$14 occurred. The lifespan for the components including decreasing the operational and maintenance cost with 10% was taken into consideration in the third scenario resulting in a reduction with k$50.

Table 7 shows how much the life cycle cost is decreased considering the different parameters in the first three scenarios.

Table 7 The sensitivity analysis for the economical aspect including the first three scenarios.

Changes LCC reduction

Components lifespan equal to 25 years k$36 Operational and maintenance cost k$14 decreased with 10% Components lifespan equal to 25 years k$50 including operational and maintenance cost being decreased with 10%

The fourth scenario includes a change in the discount rate in order to see how the LCC is changed depending on the variation of the discount rate as it is shown in Figure 22. A lower discount rate gives a higher LCC value and higher discount rate gives lower LCC value.

LCC depending on the change of the discount rate 450

400

350

300

LCC (k$) LCC 250

200

150 0% 1% 2% 3% 4% 5% 6% 7% 8% 9% 10% Discount rate (%)

50 Figure 22 LCC change depending on the change of the discount rate

Energy aspect The energy outlook was taken into two different scenarios. The first scenario presents if the electrical and thermal load are increased with 10%. This scenario showed that the simulated energy system does cover the electrical load for the whole year. But the energy system will not be able to cover the electrical load after the second year if the electrical load continues with the same 10% increase for remaining years. That means during the third-year backup energy from the diesel generator is needed to cover the electrical load during the colder season. More power from the diesel generator is needed during the fourth year compared to the third year, and even more is needed during the fifth year. However, the generated power from the diesel generator will continue at similar rate for the remaining years.

The second scenario considers a decrease in solar radiation with 10%. This scenario shares similar characteristics as the first scenario. Power from diesel generator is needed from the third year, in case the decrease of radiation continues for several years. More power from the diesel generator are needed during the fourth and fifth year before the generated power from the diesel generator stabilizes and continues at a similar rate for the remaining years. The two scenarios show that the energy system does not manage to cover the electrical demand after the second year if a 10% increase in load and decrease in solar radiation continued for several years. However, the system does cover the thermal load every year for both first and second scenario.

51 6 DISCUSSION

The aim with this thesis is to utilize an off-grid household that produces enough energy for the selected household with compatible components. The selected household manage to produce enough energy from the PV panels that produces almost twice as much as the needed electricity in the household including the heat pump. The PV panels that are used on the roof has a high PV rated power that makes the panels have a potential to produce enough electricity for direct use and utilize the surplus power to store for later use. However, the electrical and thermal demand of the household that correspond together to approximately 12 500 kWh is covered by the PV energy production of 13 560 kWh as a main source including the energy conversion from the other components in the energy system.

The battery system that is adjusted to this household operates every season and is well adjusted to the household from a short-term perspective. As Kaabeche, Belhamel, & Ibtiouen explained in their article about the function of the battery, the battery in this project works in the same way. It is important to point out that the capacity for the battery system is the most optimized case for this household according to the GA that was integrated in the optimization part. The characteristics from the battery system that are presented in Figure 12 is reasonable because the battery is mostly discharged during the colder periods when the demand is high. However, it operates less during the summer when the electric load is low.

The hydrogen system that is dependent on the operating PV panels and battery system has a similar characteristic as the batteries when it comes to operation. The hydrogen system is discharged during the colder seasons when PV and batteries do not cover the load and charged during the warmer seasons when there is a surplus power that the batteries cannot store. Figure 13 shows that there is no power required from the hydrogen system during the summer, because the production from the PV panels and batteries are enough to meet the load. However, the hydrogen storage is charged during the summer due to the surplus power from the PV when the batteries are fully charged. It is also possible to see that the diesel generator is not operating due to the over generated energy from PV panels, batteries and hydrogen system.

Figure 16 that displays the thermal energy stored in the thermal storage tank is adjusted to the production from heat pump including the heat losses that occurs in the hydrogen system. The capacity of the storage tank is chosen to utilize most of the heat losses from the hydrogen system. It is also possible to understand that the heat pump stabilizes the energy in the thermal storage tank in order to meet the needed heat from the tank.

Figure 19 and Figure 21 shows in detail how both the electrical and thermal production are divided between the different components in the energy system during the first week of November. It can be seen from Figure 19 that the hydrogen system is working more than the PV panels and battery system. That is because of the low PV production due to the little solar radiation in November and the low charge of the battery. Figure 21 shows that the heat pump operates only when the thermal load is higher than the thermal energy in the storage tank and when the thermal energy is lower than 20% of the storage tank capacity

52 As Ghenai and Bettayeb (2019) considered in their article the overall energy system does not contribute any carbon dioxide when it operates. Therefore, the selected energy system is fully emissions free in operation. However, it is important to point out that the energy system does contribute to a certain proportion of emissions when it is constructed and manufactured. The emissions from the manufacture and construction part is not included in this report.

Hans-Olof Nilsson was a good help for modelling a suitable energy system for the household. Mainly because, he has constructed a similar off-grid household and had the energy system operating in his household since 2015. However, Nilsson pointed out that the energy system requires services from appropriate companies that handles the components from time to time to prevent problems in the operation. However, the energy system is suitable for off-grid households. Therefore, the energy system should operate and produce energy to the household if we do not consider any malfunction occurring in the energy system. In case any malfunctions occur, then a backup energy source should be applied in the system to generate the needed energy. In the case of this work a diesel generator is applied.

As previous studies as the one done by Sandwell et al considering the importance of evaluating the system life cycle cost, the LCC is evaluated for this project as well. It is important to indicate that the simulation for this system showed high life cycle cost using the values from today’s market corresponding to k$318. Magnus Berg, a researcher in Vattenfall considered that the system can reach a lower value during the upcoming years, because different components that is adjusted to the energy system have the potential to reach a lower value within the next years. However according to the price reductions that is considered in the project and expected to happen in 2030 the life cycle cost will decrease to k$195 if the system is built at that time. The life cycle cost has the potential to reach a price reduction of k$123 which corresponds to 1 230 kSEK during the period of 10 years, using an exchange rate of 10 SEK for each dollar. It is also important to point out that the life cycle cost is only adjusted to one household. The life cycle cost for a similar energy system varies in different cases. That is because the life cycle cost considers different factors and has the potential to reduce or increase its value because it depends on which producer that supplies the components or during which period the project is implemented.

The capacity of the battery system and the hydrogen system are not the same in todays and future scenario. It can be seen from Table 6 that the capacity for the battery system increases in the future scenario as the capacity for the hydrogen system decreases. That is decided by the GA while doing the optimization of the system. The change in capacity depends on the price reduction of the different components. The new capacities for battery and hydrogen systems in the future scenario are chosen to find the cheapest LCC. This change may happen because it is more economical profitable to increase the battery system capacity and decrease the hydrogen system capacity.

The sensitivity analysis showed that the highest reduction on LCC occur if the lifespan of all components (except inverter and fuel cell) was changed to be equal to the lifespan of the project (25 years) and to reduce the operational and maintenance cost with 10%. The sensitivity analysis according to the change of the discount rate showed also a big change on the LCC. It could be seen from Figure 22 that a high discount rate leads to lower value of LCC

53 which may be due to the lifespan of the components in the energy system. According to a report from the energy authority in Sweden (2017) a higher discount rate with short lifetime of system and components result in higher LCC, but a higher discount rate with long lifetime of system and components results in lower LCC. Most of the components in the simulated energy system has a lifetime between 20-25 years. That might be a reason why LCC decreases with higher discount rate. However, the system price change from the future scenario is considered as the one resulting the biggest change on LCC.

The sensitivity analysis showed also if the energy demand (both electrical and thermal) increased with 10% and the solar radiation decreased with 10% for several years for the both cases then the diesel generator will start operating from the third year. It occurs in both cases because the produced power from the energy system is not enough during that period to meet the electrical demand. It is important to point out that the diesel generator will operate from the third year and continue operating the remaining years if the solar radiation and energy demand have a similar structure.

The results from the system indicate that the chosen energy system is feasible and technically possible today. The energy system has a great potential to be more attractive in the future from both an economic and technical viewpoint. But it is important to consider many factors to understand how the market will look like in the future. However, the price for different components need to be reduced in order to make the energy system being more implanted in society. The idea of having this kind of system should be backed by the government as well, and that can be done by giving renewable energy support that offers investments support to the companies and private household that want to invest in similar projects.

One important indicator is also how much the components will change in the future. Various components will most likely have a greater overall efficiency and be significantly cheaper in the future. A battery system has decreased its specific cost for the past 5 years and a PEM fuel cell has potential to be more efficient and cheaper in the upcoming 10 years. Which could make this type of energy system more attractive for different contractors, investors including ordinary citizen to contribute with emission free produced energy.

There is an assumption for the economic evaluation that could make the price different with reality. The used discount rate at 2% is reasonable according to today’s market values. It is difficult to understand how high the discount rate can be in 2030, because it depends on how the economy will look like in the future, that is why 2% is assumed in the future scenario as well. According to RG Förvaltning the household is owned by the residents and a discount rate at 2% is a reasonable rate in this project.

The diagrams that are presented in section 5 of this project showed that the energy system works as expected by covering the needed load as it would do in the reality. However, the values for the energy system would differ from the reality. That is because the hydrogen system in this project is assumed to be an extra storage component with different charging and discharging efficiencies representing electrolysis, compressor and fuel cell efficiencies. That mean the calculation for the hydrogen system is performed for one component that represent the electrolyser, compressor, hydrogen storage tank and fuel cell. Electrolyser reaching an efficiency at 70% and the compressor reaching an efficiency at 79% are assumed

54 as the charging efficiencies of the system corresponding to 55% as the used charging efficiency of the hydrogen system. The fuel cell efficiency is at 60% and assumed as the discharging efficiency of the hydrogen system. To receive more accurate results, it is important to consider the performance for electrolyser, compressor, hydrogen storage and fuel cell in a more detailed manner.

The used data for the electrical and thermal load were not perfectly calculated and estimated by RG Förvaltning. Some assumptions on the load were done especially during the summer resulting strange lines on Figure 8 and Figure 9. This is performed because the given household is not built yet and the real demand is not fully known. This indicates a margin of error in the simulation. Because the simulated energy system and the dimensioned capacities are based on the energy demand in terms of the electrical and thermal load. It would be possible to receive better results if more accurate data from an existing household with a similar structure was implemented in the project.

55 7 CONCLUSION

The selected off-grid energy system is technically practicable to produce enough energy. The household with a total electrical load at 6 125 kWh (including required electricity to the heat pump) and a thermal load at 6 461 kWh requires an off-grid energy system dimensioned according to the lowest LCC with a capacity of 13.5 kW for PV panels, 85 kWh for battery system, 6 572 kWh for hydrogen system and a chosen capacity at 25 kWh (0,43 m3) for thermal storage tank. The electricity is supplied by the PV panels, batteries and hydrogen system that operates codependently with each other. The overproduction from the PV panels is stored in batteries and if the batteries are fully charged then the overproduction is stored in the hydrogen system. This indicates that the energy system can operate during the colder seasons when the PV panels does not produce a high amount of energy. The diesel generator does not operate in the energy system because there is enough energy produced from the previous mentioned components. This resulted a reliability of 8 760 hours annually indicating that the renewable components fully operate annually and does not contribute to any emissions during operation. However, the diesel generator starts to operate if the energy system does not manage to cover the needed energy in case if anything goes wrong, for instants a damage in one or several components. The thermal load is covered by energy from a thermal storage tank that is charged with heat from the heat pump and utilized heat losses that occurs in the hydrogen system due to the charging and discharging. The storage tank stores most of the heat losses during the summer when there are high heat losses from the hydrogen system. The storage tank is chosen with a reasonable capacity to utilize almost all the heat losses during the year and to meet the needed thermal load.

The evaluated energy system that is adjusted in the off-grid household reaches a total cost at k$311 during its lifespan. However according to the price reductions that is expected to happen in 2030 the life cycle cost will decrease to k$195. This is mainly because of the price reduction of the various components especially the batteries and PV panels. The calculation of the future scenario showed that the off-grid energy system has the potential to be more attractive in the future due to the price reduction that can occur.

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