SELF-SUFFICIENT OFF-GRID ENERGY SYSTEM FOR A ROWHOUSE USING PHOTOVOLTAIC PANELS COMBINED WITH HYDROGEN SYSTEM : Master thesis in energy 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 Course code: ERA403

Subject: Energy technology Credits: 30 hp

Program: Master of Science. in energy systems

Supervisor: Bengt Stridh Examiner: Amir Vadiee Date: 2020-07-02 E-mail:

mmd14005@student.mdh.se asl15002@student.mdh.se

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

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

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

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 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 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 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 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)

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

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-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.

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

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

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

block of several flats The system is connected to a big grid Energy supply Self-sufficient Relies upon the grid, but an

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

required, and maintenance cost are higher since more Components needs

maintenance

The maintenance is not required in the house that is connected to the grid, except if the house has solar panels connected to the house Complexity of the system Complex due to the variety

of components connected to the household.

The electrical grid is a complex system itself, however the household’s connections to the grid are not complex

Environmental impact Low, no CO2 emissions in

operation Higher CO2 emissions 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).

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, &

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.

𝐿𝐶𝐶 = 𝑃𝑉(𝐼𝐶) + 𝑃𝑉(𝑂&𝑀)

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

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).

𝑃𝑝𝑣 = 𝑛𝑝𝑣 ∗ 𝐴𝑝𝑣 ∗ 𝐺𝑔𝑡

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

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.

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.}

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):

2𝐻₈𝑂 + 𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐𝑖𝑡𝑦−→ 𝐻₈(𝑔) + 2𝑂𝐻A

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).

𝐻₈𝑂−→1

2𝑂8(𝑔) + 2𝐻C+ 𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐𝑖𝑡𝑦

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.

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: 𝑊_E= 𝐶_F∗𝑇H 𝜂E(J 𝑃₈ 𝑃H) KAH K − 1L 𝑚_N O

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).

𝐻8+

1

2𝑂8−→ 𝐻8𝑂

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):

Equation 7. Cathode: 2𝐻C₊H 8𝑂8+ 2𝑒A−→ 𝐻80 Equation 8. Total reaction: 𝐻₈+H 8𝑂8−→ 𝐻8𝑂 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.

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.

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.

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.

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.