Energy Analysis of a Solid Oxide Fuel Cell (Sofc) Operated by PV System in the Residential Sector, in Highland


Master's Thesis, 2018
74 Pages, Grade: P5

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CONTENTS

1 INTRODUCTION

2 LITERATURE REVIEW
2.1 Energy generation
2.2 Technologies description

3 METHODOLOGY
3.1 Temperature and solar irradiation
3.2 Estimating energy demand
3.2.1 Electric calculation
3.2.2 Heat calculation
3.3 Photovoltaic farm
3.4 Integration Photovoltaic-Fuel cell system

4. RESULTS AND FINDINGS
4.1 Solar source and air temperature
4.1.1 Ambient temperature
4.1.2 Solar Source
4.1.3 Cell Temperature
4.1.4 Cell efficiency and output power
4.2 Energy demand
4.2.1 Electric consumption
4.2.2 Heat Consumption
4.3 Determination of PV system
4.3.1 PV modules quantity
4.3.2 Calculation of array size
4.3.3 Designing the PV facilities
4.4 PV-H2-SOFC System
4.4.1 Design of the system
4.4.2 Simulation results
4.5 Analysis: Solar source, energy demand and PV-H2-SOFC

5 ECONOMIC RESULTS
5.1 Economic simulation results
5.2 Economic analysis

6 ENVIRONMENTAL IMPACT
6.1 Environmental simulation results
6.2 Environmental analysis

7 DISCUSSION

8 CONCLUSION
8.1 Evaluation
8.2 Recommendations

9. REFERENCES

10. APPENDICES

ABSTRACT

The present report involves the study of the energy potential of a hybrid system composed of a photovoltaic farm, hydrogen and solid oxide fuel cell (SOFC), which is implemented in Highland, Scotland. The system is intended to supply the demand for electricity and heat (hot water) in a residential, that represents an annual consumption of 3880 [kWh] and 986.4 [kWh], respectively.

The first step consists of the solar farm evaluation, which is configured by 14 PV panels (monocrystalline) that represent an annual generation of 3878 [kWh]. The prevalence of solar irradiation was in the summertime, with an average of 2.5 kWh/m[2]/day]. In contrast, the during the winter season there was a shortfall in the energy production, with around 85 [%] less. This last factor involves that in winter time, the PV system can provide only a 30 [%] of the monthly consumption. Compared in the summer, which had a generation excess of almost 40 [%]

The simulation of the integration of the fuel cell into the PV system demonstrated an increase in the global efficiency of around 20 [%]. At the same time, involves the rise in the electricity generation in 58 [%] more than the solar farm, this allowed the hourly production of 53 [kW]. In the case of heat performance, was obtained an hourly potency of 29 [kW], which represent a 90 [%] higher than the daily hot water demand.

In relation to the environmental factor, the project showed a significant improvement in the GHG emission that allowed reduced over 75 [%] the emission respect to the traditional energy sources, such as grid electricity and gas.

On the other hand, the economic evaluation has predominant differences in the generation cost, mainly in the electricity that involves around 80 [%] more expensive than the traditional source. However, monetary retribution in the sale of excess energy, which improves the overall balance.

LIST OF FIGURES

Figure 1: Renewable energies available by location. Source (The Highlands Council, 2006) 13

Figure 2: Total energy consumption in Scotland. Source (Scottish Government; BEIS, 2018) 14

Figure 3: Alkaline water electrolyser. Source (Elamari, 2011) 15

Figure 4: Operating mechanism of SOFC. Source (Shearer, 2017) 15

Figure 5: Flow diagram of Module Output, Source: (Own illustration) 16

Figure 6: Flow diagram of electric demand. Source (Own illustration) 18

Figure 7: Flow diagram of heat demand. Source: (Own illustration) 19

Figure 8: Facilities design of PV farm. Source (Own illustration) 20

Figure 9: Steps of Input data for FCPower model simulation. Source (Own source) 25

Figure 10: Average of hourly temperature, Source: (Own illustration) 30

Figure 11: Average of monthly Irradiation per year. Source: (Own illustration) 31

Figure 12: Average of hourly slope Irradiation. Source: (Own illustration) 31

Figure 13: Ambient and Cell temperature per month. Source: (Own illustration) 32

Figure 14: Ambient and Cell temperature per hour. Source: (Own illustration) 33

Figure 15: Cell temperature and Efficiency. Source: (Own illustration) 34

Figure 16: Source: (Own illustration) 35

Figure 17: Electric demand and PV generation per month. Source (Own illustration) 36

Figure 18: Electric demand per hour. Source (Own illustration) 36

Figure 19: Total litres of hot water per month. Source based on (Energy Saving Trust, 2008) 37

Figure 20: Heat demand per month. Source (Own illustration) 38

Figure 21: Total litres of hot water per hour. Source (Energy Saving Trust, 2008) 38

Figure 22: Heat demand per hour. Source (Own illustration) 39

Figure 23: Monthly heating demand. Source (Own illustration) 40

Figure 24: Location of PV installation, Source: (Google earth, 2018) 43

Figure 25: Structure of PV module, Source: (Own illustration) 43

Figure 26: Distribution of solar PV farm, Source: (Own illustration) 44

Figure 27: Design of PV-H2-SOFC system. Source (Own illustration) 45

Figure 28: Hydrogen demand required monthly. Source (Own illustration) 46

Figure 29: Hydrogen demand required hourly. Source (Own illustration) 46

Figure 30: Hourly hydrogen variation. Source (Own illustration) 47

Figure 31: Dimension of hydrogen tank. Source (Own illustration) 49

Figure 32: Capacity range of hydrogen tank. Source (Yuan, et al., 2017) 49

Figure 33: Explanatory diagram of PV-H2-SOFC system. Source (Own illustration) 51

Figure 34: Efficiency of the system from FCPower model simulation. Source (D. Steward, 2013) 53

Figure 35: Economic comparison between both electrical systems. Source (Own illustration) 59

Figure 36: Economic comparison between both heat systems. Source (Own illustration) 59

Figure 37: Distribution of CO2 emission of PV-H2-SOFC, from FCPower model simulation. Source (D. Steward, 2013) 62

Figure 38: Comparison of GHG emissions between both electrical systems. Source (Own illustration) 62

Figure 39: Comparison of GHG emissions between both heat systems. Source (Own illustration) 63

Figure 40: Solar Radiation program. Source (Muneer, 2017) 71

Figure 41: Project setup, from FCPower model simulation. Source (D. Steward, 2013) 72

Figure 42: Input simulation system, from FCPower model simulation. Source (D. Steward, 2013) 73

Figure 43: Output model in the system calculation, one-hour load from FCPower model simulation. Source (D. Steward, 2013) 74

LIST OF TABLES

Table 1: Data base of PV module 21

Table 2: Data base of inverter 23

Table 3: Operational parameters of electrolyser 25

Table 4: SOFC Design parameters 26

Table 5: Operational parameters of compressor 26

Table 6: Monthly Averaged Air Temperature 29

Table 7: Summary of hourly Cell temperature per month 32

Table 8: Performance of solar module 35

Table 9: Summary of number PV module 40

Table 10: Summary of output energy of photovoltaic module 41

Table 11: Summary of voltage and current dimension 42

Table 12: Summary of string calculation 42

Table 13: Summary of sizing of PV array 42

Table 14: Monthly hydrogen variation 48

Table 15: Summary of electrical efficiency of electrolyser 50

Table 16: Hydrogen produced by the electrolyser 50

Table 17: PV-H2-SOFC Specifications 52

Table 18: Energy output of the system, from FCPower model simulation 52

Table 19:Economic description of the project, from FCPower model simulation 56

Table 20: Annual Levelized Cost of Energy, from FCPower model simulation 57

Table 21: Cost factors per season, from FCPower model simulation 57

Table 22: Breakdown of the monthly cost of electricity, from FCPower model simulation 58

Table 23: Specification of GHG emission, from FCPower model simulation 61

LIST OF EQUATIONS

Equation 1: Hourly air temperature. Source (Gago, et al., 2010) 16

Equation 2: Calculation of Cell temperature, Source: (Brihmat & Mekhtoub, 2014) 17

Equation 3: Calculation of cell efficiency, Source: (Brihmat & Mekhtoub, 2014) 17

Equation 4: Calculation of Output performance, Source: (Goos, 2015) 18

Equation 5: Energy calculation of hot water. Source (ACS Chemistry for life, s.f.) 20

Equation 6: Energy of PV module, Source: (Muneer, et al., 2015) 21

Equation 7: Number of PV modules, Source: (Goos, 2015) 21

Equation 8: Voltage maximum in open circuit, Source: (Goos, 2015) 22

Equation 9: Voltage minimum in open circuit, Source: (Goos, 2015) 22

Equation 10 : Current maximum of PV module, Source: (Goos, 2015) 22

Equation 11: Maximum number of PV module per string, Source: (Goos, 2015) 23

Equation 12: Minimum number of PV module per string, Source: (Goos, 2015) 23

Equation 13: Number of modules per string, Source: (Goos, 2015) 24

Equation 14: Total number of inverters, Source: (Goos, 2015) 24

Equation 15: Hydrogen demand. Source (Kabza, 2016) 26

Equation 16: Current efficiency of electrolyser. Source (A.Ganguly, et al., 2010) 27

Equation 17: Electric efficiency of electrolyser. Source (A.Ganguly, et al., 2010) 27

Equation 18: Hydrogen produced in one hour [mol]. Source (A.Ganguly, et al., 2010) 27

Equation 19: Power of H2 consumed in a stack. Source (Kabza, 2016) 28

Equation 20: Volume hydrogen in the tank. Source (Kabza, 2016) 28

Equation 21: Required energy of hydrogen compression. Source (Saeed & Warkozek, 2015) 28

LIST OF ABBRIAVIATIONS

Abbildung in dieser Leseprobe nicht enthalten

1 INTRODUCTION

This report contemplates the technical analysis of a hybrid system composed of two renewable energies that are applied in the Highland, Scotland. Specifically, involves the integration of the photovoltaic system and the solid oxide fuel cell, in the production of electric and thermal energy. The main purpose of this study imply knows the potential of the natural sources of the zone, understand the energy demand associated to the location, test the integration of different types of renewable technologies, evaluate the performance of the system and analyse if it is possible to supply the required energy demand.

The study involves the development of different aspects, such as the determination of solar resource available in Highland and the association with the photovoltaic energy generated by the design of solar farm

Secondly, establish the relationship between the electric energy consumption by weather season and the PV energy produced. Then design the requirements of PV-H2-SOFC system, such as the database of equipment, hydrogen consumption, solar potential, size of the hydrogen tank and the respective demands. The result of the simulation allows estimating the performance of the system design, including efficiency and the hydrogen.

At the same time, it is crucial an economic and environmental evaluation which provides an estimation of electric and heat cost. Additionally, determinates the impact of CO2 in the energy generation and contributes to the declining the GHG emission in the zone.

2 LITERATURE REVIEW

2.1 Energy generation

Overall, the Highland area has a regional strategy of sustainable development by 2020, which is based on the clean energy for supply the need for energy efficiency (The Highlands Council, 2006). In a global way, Highland generates the highest proportion of Scottish renewable generation, with around a 27 [%] which represent 5,176 [GWh] of electricity (Scottish Government; BEIS, 2018). Figure 1 describes the different renewables technologies available in the zone and their potential. Particularly, Caithness located north of Highland has a rated of medium opportunity for solar energy, between 10 and 100 [MW] (The Highlands Council, 2006)

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Figure 1: Renewable energies available by location. Source (The Highlands Council, 2006)

The distribution of energy consumption, it has prevalence the heat demand with 51 [%] and third place is electricity with 24 [%], as describes Figure 2. Additionally, those proportions belong to 42 [%] domestic energy demand and a 58 [%] industrial consumption, excluding transport category. Especially, the domestic energy consumption in Highland represents 3.5-6.5 [%] of the total demand of the country (Scottish Government; BEIS, 2018). At the same time, the predominant fuels are petroleum and gas with 44 [%] and 32 [%], respectively (The Highlands Council, 2006)

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Figure 2: Total energy consumption in Scotland. Source (Scottish Government; BEIS, 2018)

2.2 Technologies description

The integration of SOFC into photovoltaic system involves two scenarios of the electrochemical process. The first one is the PV-Hydrogen electrolysis system, which is done through an electrolyser. This process water electrolysis involves electrodes used to pass electricity (from the PV system) to split into hydrogen ions and oxygen ions, which are deposit in the cathode and anode, respectively. The explanation is illustrated in Figure 3.

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Figure 3: Alkaline water electrolyser. Source (Elamari, 2011)

The second electrochemical reaction happens between the hydrogen generated by the electrolyser and the fuel cell. As Figure 4 shows the oxygen ions from the cathode travel through the solid electrolyte (YSZ) and reacts with the hydrogen gas (generated by the electrolyser) at the anode electrolyte interface to produce water and electrons. Then these electrons travel to the cathode via an external electrical circuit producing electrical power (Shearer, 2017)

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Figure 4: Operating mechanism of SOFC. Source (Shearer, 2017)

As a result, the combination of these two renewables energies can contribute to the sustainable development in Highland due to the potential of the solar source and fuel cell properties promotes a cogeneration system with a significant performance and with low CO2equivalent emission

3 METHODOLOGY

3.1 Temperature and solar irradiation

Overall, the calculation method of module output power consists of the PV modelling aspects, such as different solar irradiations [kWh/m[2]], air temperature [°C], cell temperature [°C] and PV efficiency. The detail is showed in Figure 5

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Figure 5: Flow diagram of Module Output, Source: (Own illustration)

The first step was to obtain the latitude and longitude from "Google Map", which values are 58.44 and -3.1, respectively. Then, the coordinates are the input to get the monthly average temperature [°C], monthly global horizontal irradiation [W/m[2]] and direct horizontal irradiation [W/m[2]] from the NASA website. At the same time, the hourly irradiation was got from VBA program (Muneer) and the hourly air temperature was calculated by Equation 1.

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Equation 1: Hourly air temperature. Source (Gago, et al., 2010)

Where Tmax and Tmin is the maximum and minimum temperature of each month [°C], Z corresponds to the hourly dimensionless temperature, which values were extracted from the report of Gago, et al., 2010

Once the temperature and irradiation per hour have been calculated, the data is entered into the Muneer VBA program for the calculation of the Irradiation slope [Wh / m[2]]. The next step involves obtaining cell temperature [° C], which was obtained through Equation 2

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Equation 2: Calculation of Cell temperature, Source: (Brihmat & Mekhtoub, 2014)

Where, G slope is the global slope irradiation; Gnoct corresponds to 800 [W/m2] (Brihmat & Mekhtoub, 2014); Tc, noct is the cell temperature at NOCT of 47 [°C]; Ta, noct is the air temperatures NOCT of 25 [°C]; n stc is the cell efficiency at SCT, 15.2%; Tα is the absorptivity of the module and Ta is the ambient temperature, which values are 0.8 and 2.6 [m2], respectively. (ASP-400GSM, s.f.). It is important to note that these factors belong to a monocrystalline solar module.

The PV cell efficiency was calculated considering the efficiency at Standard Test Conditions (ɳstc) of 15.2%, hourly cell temperature (Tc),Cell temperature under standard testing conditions (Tc, stc) of 25[°C] and temperature coefficient value (αp) of -0.4 [%] (Jeffrey, et al., 2015).The detail is described in Equation 3.

Abbildung in dieser Leseprobe nicht enthalten

Equation 3: Calculation of cell efficiency, Source: (Brihmat & Mekhtoub, 2014)

The last step involves the calculation of the electrical output power by Formula 4, which factors are ɳ mod that is the electrical efficiency under Standard Test Conditions, A is the surface area of PV panel of 2.6 [m2], Gtlt consist on slope irradiation and finally, Tc is the hourly cell temperature calculated in the before step

Abbildung in dieser Leseprobe nicht enthalten

Equation 4: Calculation of Output performance, Source: (Goos, 2015)

The next steps involve the calculation of solar farm size, which calculation methodology it will explain in chapter 4.3

3.2 Estimating energy demand

3.2.1 Electric calculation

The methodology to obtain the energy data involves five steps, as Figure 6 shows. Firstly, for the electric demand, it was necessary to define the artefacts required in the home. In this case, the items selected, and their respective power are fridge-freezer 200 [W]; lights 300 [W]; oven 2000 [W]; electric kettle 2200 [W] and hob 1000 [W]. (Parry, 2015)

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Figure 6: Flow diagram of electric demand. Source (Own illustration)

The next step involves the ranges of use of each artefact. For example, the electric kettle was modulated with three intervals of use (morning, midday and evening). In addition, it was considered the seasons variable, such as the lights which was estimated with a prevalence in the wintertime and higher consumption in the morning and afternoon.

After getting the period of demand is calculated the hourly demand, which is considered the 8760 hours per year, establishing an average hour yearly. The analogous way, the monthly energy consumption is calculated as the daily summation with every five minutes of each month. Once obtained the monthly energy consumption can be compared with the air temperature (from NASA data) and define a relation between both variables

3.2.2 Heat calculation

The daily and hourly consumption of hot water was obtained from the study conducted by Energy Saving Trust. Then, the hourly demand in litres of each month was obtained. Once the global demand for hot water was obtained, it was compared with the ambient temperature. The detail of the heat demand methodology is shown in Figure 7

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Figure 7: Flow diagram of heat demand. Source: (Own illustration)

According to equation 5, the calculation of the hot water energy is given by L_day, which is the number of liters per day [L]; n ° days is the number of days of each month; T2 and T1 correspond to the required temperature of the house and the inlet temperature of the cold water, 60 and 15.2 [° C] respectively (Energy Saving Trust, 2008). In addition, it includes a factor of system efficiency, around 45 [%] (assumption efficiency) and Cp, which is the specific heat capacity of water of 4.19 [KJ/Kg k]

Equation 5: Energy calculation of hot water. Source (ACS Chemistry for life, s.f.)

When the demand energy was obtained, the thermal consumption was compared with the ambient temperature, which allows defining the monthly relationship between both variables

3.3 Photovoltaic farm

After getting, the global demand was possible to design the PV system to supply the consumption required. According to Diagram 8, three steps define the design PV farm. The first involves the energy calculation of one PV module, which is obtained by the Formula 6

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Figure 8: Facilities design of PV farm. Source (Own illustration)

It is important to note that some calculation factors were extracted from the technical specification of the monocrystalline panel (ASP-400GSM, s.f.), which is described in Table 1

Table 1: Data base of PV module

Abbildung in dieser Leseprobe nicht enthalten

Source (ASP-400GSM, s.f.)

The factors of Energy of PV module are representing by the factor showed in Equation 6, such as the useful PV surface area (Am) of 2.6 [m[2]]; ∩sys is the efficiency of the system of 15.2 [%] and Itilt is the tilted global irradiance calculated in chapter 4.1.2

Abbildung in dieser Leseprobe nicht enthalten

Equation 6: Energy of PV module, Source: (Muneer, et al., 2015)

Once obtained the yearly generation of a single module was possible to get the amount of PV panel necessary to supply the annual demand for electricity. The detail is explained in Equation 7

Equation 7: Number of PV modules, Source: (Goos, 2015)

At the same time, the array size can be designed considering voltage dimension, current module, and string calculation. Firstly, it was necessary to calculate the maximum open circuit voltage of the module, as shown in Formula 8. This involves open circuit voltage (Voc) of 59.62 [V]; temperature voltage coefficient (Tdcu, mod) of 0.4 [%/C] and the difference between the minimum ambient temperature and standard temperature (∆Tlow), which are 0.26 and 25 [C] (ASP-400GSM, s.f.), respectively.

Abbildung in dieser Leseprobe nicht enthalten

Equation 8: Voltage maximum in open circuit, Source: (Goos, 2015)

In analogous way, it can be calculated the Voltage minimum in open circuit by the Equation 9, which factors are the maximum power of the PV module (Vmpp) of 49.94 [V] (ASP-400GSM, s.f.); temperature voltage coefficient (Tdc mod) and ∆Tlow represent the difference between the Tmax, mod (15.5 [C]) and T sct

Abbildung in dieser Leseprobe nicht enthalten

Equation 9: Voltage minimum in open circuit, Source: (Goos, 2015)

The current maximum of PV module was calculated by Equation 10, considering values of short-circuit current (Isc); current temperature (Tdc, mod) and the difference between the maximum module temperature and STC temperature, represented by ∆Tmax

Abbildung in dieser Leseprobe nicht enthalten

Equation 10 : Current maximum of PV module, Source: (Goos, 2015)

The result of the voltage dimension and current is detailed in Table 1. Where the maximum and minimum open circuit voltage was 49.3 and 59.7 [V], respectively. In addition, the maximum current in the PV system is 8.42 [A]

For the following calculations, the specifications of the inverter detailed in Table 2 were considered, as well as the previously obtained results.

Table 2: Data base of inverter

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Source: (SMA Solar Technology, s.f.)

Equations 11 and 12 establish regarding the calculation of the maximum and minimum of PV module per string. Where Vdc_max_inv and Vdc_max_inv is the maximum and minimum voltage of the inverter. Additionally, the V dc_max_mod and V dc_min_mod is the voltage maximum and minimum of the PV module

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Equation 11: Maximum number of PV module per string, Source: (Goos, 2015)

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Equation 12: Minimum number of PV module per string, Source: (Goos, 2015)

The determination of PV array is defined by the module per string, which is calculated with Equation 13. Where the ∩str is the maximum number of PV module per string and the n_mod_str represents the number of strings. At the same time, the inverter quantity depends on the number of PV modules (∩mod) and the module per strings (∩array), which shown in Formula 14

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Equation 13: Number of modules per string, Source: (Goos, 2015)

Abbildung in dieser Leseprobe nicht enthalten

Equation 14: Total number of inverters, Source: (Goos, 2015)

3.4 Integration Photovoltaic-Fuel cell system

The fuel cell operates by the photovoltaic system was simulated with FCPower model (D. Steward, 2013). Considering the data necessaries to make the simulation and the definition of the system is possible to get the output electric and heat generation, carbon dioxide emission and economic values. Particularly, the simulation of the system involved seven steps described in Figure 9

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Figure 9: Steps of Input data for FCPower model simulation. Source (Own source)

Firstly, the was established the components of the system, considering the fuel cell, the electrolyser, compressor and the solar energy. Then was necessary to define the parameter of the equipment, for example, the efficiency of the photovoltaic panel, fuel cell capacity, compressor and electrolyser size. It's important to note that this data was extracted from the values showed in Tables 3 and 4

Table 3: Operational parameters of electrolyser

Abbildung in dieser Leseprobe nicht enthalten

Source (El-Maaty, 2005)

An electrolyser has the finality of hydrogen production. According to the datasheet of the electrolyser showed, consist of an alkaline electrolyser that reacts by the anode and cathode producing electrolysis. Also, it has a diaphragm for preventing the mix of hydrogen and oxygen (Guan, et al., 2004)

Table 4: SOFC Design parameters

Abbildung in dieser Leseprobe nicht enthalten

Source: (Battelle Memorial Institute, 2016)

The simulation was included a compressor, which takes care of compress the gas hydrogen and increases the mass density before the pass to the hydrogen tank (A.Ganguly, et al., 2010). The specification of the compressor is detailed in Table 5

Table 5: Operational parameters of compressor

Abbildung in dieser Leseprobe nicht enthalten

Source (A.Ganguly, et al., 2010).

The next step involves the calculation of hydrogen required, which was obtained throughout Formula 14. It was considered the total demand, electric and heat (E_demand [kWh]), the efficiency of the system of 45 [%] (D. Steward, 2013) and the Higher Heating Value (HHV) of 39.39 [kWh/kg] (Kabza, 2016)

Abbildung in dieser Leseprobe nicht enthalten

Equation 15: Hydrogen demand. Source (Kabza, 2016)

Then the solar source, hydrogen, electric and heat demand are the last input of the simulation, which was calculated as hourly consumption of the entire year, obtaining a total of 8760 values in each category. However, the economic factors weren’t modified due was considered the values existing in the program FCPower model

The electric efficiency of the electrolyser was calculated by Formula 17, which factors are Current efficiency (ni) of 95 [%], which was obtained from the Equation 16 where the ielec represented the current of the electrolyser of 60 [A]. The voltage efficiency (nvolt) of 88 [%]. This last value was extracted from the datasheet electrolyser

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Equation 16: Current efficiency of electrolyser. Source (A.Ganguly, et al., 2010)

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Equation 17: Electric efficiency of electrolyser. Source (A.Ganguly, et al., 2010)

With the previous calculations and the Formula 18 is possible to get the amount of hydrogen produced where Nelec, is the number of cells (30 cells) and the F, is Faraday’s value, which is a constant of 96487 [C/mol]

Abbildung in dieser Leseprobe nicht enthalten

Equation 18: Hydrogen produced in one hour [mol]. Source (A.Ganguly, et al., 2010)

The power of hydrogen consumed in the stack was determined by the Equation 19, which involves the operational current (I) of 166 [A]; the number of cells per stack (N) of 259 and the nominal stack open circuit (V) of 285 [V]. These values belong to the fuel cell datasheet

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Equation 19: Power of H2 consumed in a stack. Source (Kabza, 2016)

The determination of the volume of hydrogen storage was gotten by the Boyle Equation (shown in Formula 20), where the P1 is the pressure of the electrolyser of 30 [bar]; V1 is the volume of hydrogen produced by the electrolyser of 610 [m3] and P2 is the pressure of the compressor of 200 [bar]

Abbildung in dieser Leseprobe nicht enthalten

Equation 20: Volume hydrogen in the tank. Source (Kabza, 2016)

The energy required to compress the daily hydrogen demanded was obtained by Equation 21, which 1.931 [kWh/kg] represents the energy required to compress 1 [kg] of hydrogen and the H2_required is the amount of hydrogen consumption in 24 hours

Equation 21: Required energy of hydrogen compression. Source (Saeed & Warkozek, 2015)

4. RESULTS AND FINDINGS

4.1 Solar source and air temperature

4.1.1 Ambient temperature

According to the location and base data from NASA (Prediction of Worldwide Energy Resource) was possible to get, the monthly average of ambient temperature corresponds to the year 2017. The detail is showed by Table 7

Table 6: Monthly Averaged Air Temperature

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Source (NASA database. Prediction of Worldwide Energy Resource, 2017)

The Table of the monthly ambient temperature describes the higher temperatures is between the months June and September, during the summer season. In contrast, the lowest temperatures are in the months of December, January and February. Furthermore, considering Formula 1 and the monthly average temperature data was calculated the hourly temperature, which is shown in Figure 10

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Figure 10: Average of hourly temperature, Source: (Own illustration)

Figure 10 establishes the higher range of temperature during the afternoon, between midday and 6 pm. In addition, the period with lower temperature is in the morning, with around 6 [°C]

4.1.2 Solar Source

The monthly global horizontal irradiation [W/m[2]] and direct horizontal irradiation [W/m[2]] had got them from the NASA website. As Figure 11 shows, the highest irradiation is during the summertime, with around 4.5 [kWh/m[2]] in May 2017. However, the lower values of GHI and DHI was between 0.2 and 0.5 [kWh/m[2]], corresponding to December and January

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Figure 11: Average of monthly Irradiation per year. Source: (Own illustration)

On the other hand, the hourly slope irradiation gotten from the VBA program (Muneer) showed that irradiation is concentrated at midday with approximately 300 [Wh/m[2]]. Further, the minimum value obtained was almost 10 [Wh/m[2]] on wintertime. The results obtained are described in Figure 12

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Figure 12: Average of hourly slope Irradiation. Source: (Own illustration)

4.1.3 Cell Temperature

After of calculation of hourly temperature and irradiation, it was calculated the cell temperature considering the formula and factors detailed in chapter 3.1. Figure 13 shows the higher performance of cell temperature, which was above 15 [°C] in August. In the same month, the air temperature was over 13 [°C].

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Figure 13: Ambient and Cell temperature per month. Source: (Own illustration)

The detail of the cell temperature values is in Table 8, which establishes the monthly average, maximum and minimum cell temperature

Table 7: Summary of hourly Cell temperature per month

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Source: (Own illustration)

The analogous way, it was obtained the hourly average of cell temperature, which is described by Figure 14. Overall, the curve between cell temperature and ambient temperature are similar, but the exception in the interval of time10 and 20 hours.

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Figure 14: Ambient and Cell temperature per hour. Source: (Own illustration)

4.1.4 Cell efficiency and output power

The relation between the cell temperature and the efficiency is described in Figure 15, which shows an inverse relationship. For example, when the cell gets the highest temperature of 16 [°C], the performance decrease to 6 [%]

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Figure 15: Cell temperature and Efficiency. Source: (Own illustration)

The generated power per hour calculated by Equation 4 is represented in Figure 16. It describes the peak of output performance happens between 12 and 13 hours, with around 260 [W]. The hourly power increases in the summer months, with six more hours of daily power. For example, the daily average of each month shows that the highest performance was in May with 102 [W]

Table 8: Performance of solar module

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Figure 16: Source: (Own illustration)

4.2 Energy demand

4.2.1 Electric consumption

The total energy demand calculated was of 3883 [kWh]. Figure 17 describes the monthly average of electric consumption and the generation provided from PV system, which was obtained in chapter 4.3.1. Where the highest rated was in January with 383 [kWh]. In contrast, the solar generation is inverse to the electric energy consumption, especially in winter time

Abbildung in dieser Leseprobe nicht enthalten

Figure 17: Electric demand and PV generation per month. Source (Own illustration)

The analogues way, it was obtained the average hourly electricity consumption showed by Figure 18, where the demand is concentrated between the hours 12 and 13, with around 1.6 [kW]. During the rest of the day shows a similar consumption with a maximum power at night and morning of 0.5 [kW]. In contrast, the minimum performance was in the early morning with 0.2 [kW], which supply the fridge-freezer during this period

Abbildung in dieser Leseprobe nicht enthalten

Figure 18: Electric demand per hour. Source (Own illustration)

4.2.2 Heat Consumption

Based on the report of Energy Saving Trust (Energy Saving Trust, 2008) was extracted the monthly sum of litres of hot water, which is detail in Figure 19. The highest consumption was in December with 4000 litres, which means around 133 litres per day. In addition, between the months of January and June showed similar consumption with around 3500 litres monthly and 120 litres per day

Abbildung in dieser Leseprobe nicht enthalten

Figure 19: Total litres of hot water per month. Source based on (Energy Saving Trust, 2008)

According with the data reviewed previously and the Formula described in Chapter 3.2.2 was possible to get the monthly energy demand of house. Figure 20 shows the comparison between the ambient temperature and the energy demand. In general, the peak of consumption was in January and December with over 80 [kWh]. Which is opposite to the air temperature in those months due shows the lowest rated, with less of 6 [°C]

Abbildung in dieser Leseprobe nicht enthalten

Figure 20: Heat demand per month. Source (Own illustration)

At the same time, the hourly demand of hot water was obtained by the report of Energy Saving Trust (Energy Saving Trust, 2008), which is explained in Figure 21 the different ranges of consumption during the day. For example, the peak in demand is in the morning at 8 am with 10 litres. Then the consumption starts to increase again in the afternoon with above 8 litres. The average hot water consumption is around 4.7 per hourly

Abbildung in dieser Leseprobe nicht enthalten

Figure 21: Total litres of hot water per hour. Source (Energy Saving Trust, 2008)

In a comparative way, the energy demand and the air temperature are inversely proportional during the morning. For example, the highest demand is concentrated at 8 am with around 0.24 [kWh] but the air temperature is the lower at approximately 8 [°C]. However, the lowest demand is between the 2 and 3 pm with around 0.1 [kWh]. The description of the data is showed in Figure 22

Abbildung in dieser Leseprobe nicht enthalten

Figure 22: Heat demand per hour. Source (Own illustration)

In the case of heating demand, it was not considered in the study due that it will be supply by gas. This assumption is based on the report of domestic properties of The Highland Council’s (The Highland Council’s, 2012) that it establishes the main fuel of heating is gas. However, it was estimated the heating monthly consumption, which is shown in Figure 23. Where describes the highest rates are between the winter months with over 550 [kWh]. Also, the total annual heating demand was of 4822 [kWh]

Abbildung in dieser Leseprobe nicht enthalten

Figure 23: Monthly heating demand. Source (Own illustration)

4.3 Determination of PV system

4.3.1 PV modules quantity

Based on the methodology of the Chapter 4.2, is described in Table 10 the total energy module supplied of 275.12[kWh/year], the energy of a single PV module of 0.754 [kWh/day] and total consumption of 3880 [kWh/year], calculating a total of 14 PV modules

Table 9: Summary of number PV module

Abbildung in dieser Leseprobe nicht enthalten

Source: (Own source)

Additionally, the breakdown of power generation is detailed in Table 11. The highest output energy is May with a total of 476 [kWh] considering 14 PV panels. Between the months of June and October the generation it stays in similar values, above 350 [kWh]. Nonetheless, the lowest was in December with 71 [kWh]. Obtaining a total of yearly energy generation of 3978 [kWh]

Table 10: Summary of output energy of photovoltaic module

Abbildung in dieser Leseprobe nicht enthalten

Source: (Own source)

4.3.2 Calculation of array size

The result of the voltage dimension and current is detailed in Table 12. Where the maximum and minimum open circuit voltage was 49.3 and 59.7 [V], respectively. In addition, the maximum current in the PV system is 8.42 [A]

Abbildung in dieser Leseprobe nicht enthalten

Table 11: Summary of voltage and current dimension

Source: (Own source)

The next step was to calculate the string configurations which is based on data from PV panels described in Chapter 3.3. Table 13 shows the detail of the number of maximums a minimum of PV module per string, which range is between 10 to 5

Table 12: Summary of string calculation

Abbildung in dieser Leseprobe nicht enthalten

Source: (Own source)

According to the Formulas described in Chapter 3.3 and the previous results was calculated the size of the photovoltaic farm. As Table 14 shows, the total of module per string are 21 and is just necessarily have one inverter for the connection system

Table 13: Summary of sizing of PV array

Abbildung in dieser Leseprobe nicht enthalten

Source: (Own source)

4.3.3 Designing the PV facilities

The location belongs to Wick, Highlands with the geographic coordinates of latitude 58.43 and longitude -3.09. As Figure 24 shown, the solar field is installed in the residential ground, with a dimension of 47.13 [m] width and 81.83 [m] long. As consequence, the available area is around 3878.74 [m[2]]

Image was removed due to copyright issues

Figure 24: Location of PV installation, Source: (Google earth, 2018)

In this case, around 2% of the useful area is occupied by the PV facilities of 47.32 [m[2]], which was included a 30% of the surface is left unoccupied to allow the maintenance between PV panels, with approximate 11 [m2]. The detail of PV farm has represented in the right of Figure 26. Additionally, the installation of PV module must consider a 45° inclination and orientate towards the south. The detail of the PV module inclination is explained in Figure 25

Abbildung in dieser Leseprobe nicht enthalten

Figure 25: Structure of PV module, Source: (Own illustration)

Regarding the calculation done it in the chapters 4.3.1 and 4.3.2, was obtained a PV farm of 2 rows and 7 columns, which make a total of 14 PV panels. Furthermore, involves 7 PV module per string, that is connected in series. The equivalent way, the system integrated one inverter with a maximum of voltage and current per string of 600 [V] and 18 [A], respectively. Additionally, the distance calculated between rows of PV panels is 13 [m], this is to reduce the probability of shadow. The installation system is described in Figure 26

Abbildung in dieser Leseprobe nicht enthalten

Figure 26: Distribution of solar PV farm, Source: (Own illustration)

4.4 PV-H2-SOFC System

4.4.1 Design of the system

There are two types of system configuration, which is showed in Figure 27. The first one (blue line), is when the PV generation is higher than the energy demand. In this case, involves the following order:

- Solar generation; PV farm; Boost converter; Buck converter; electrolyser; compressor (It is necessary to increase the mass density and reduce the size of the storage tank); fuel cell; converter; inverter and load demand

The second model (red line) is when the PV generation is not enough to supply the hydrogen consumption of the electrolyser. As a result, the is necessary to follow the red line described in the illustration, which steps are:

- Hydrogen tank supply; fuel cell; converter; inverter and load demand

Abbildung in dieser Leseprobe nicht enthalten

Figure 27: Design of PV-H2-SOFC system. Source (Own illustration)

After defining the equipment’s parameters, it was obtained the hydrogen consumption and the deficit of hydrogen in the months with low PV generation (January, February, November and December) which is described in Figure 28. According to the calculation of hydrogen necessary to supply the energy is shown in Figures 28 and 29. Where the first illustration shows the comparison between the total monthly hydrogen required and the energy consumption, which establishes maximum demand in January with 292 [m[3]] of hydrogen. The second graph describes the hourly hydrogen required and the peak demand, which is the period of 12 and 13 hours with around 1.5 [m[3]]

Abbildung in dieser Leseprobe nicht enthalten

Figure 28: Hydrogen demand required monthly. Source (Own illustration)

In relation to the hourly hydrogen, consumption result was used in the simulation of FCPower model with total of 0.75 [kg] per day

Abbildung in dieser Leseprobe nicht enthalten

Figure 29: Hydrogen demand required hourly. Source (Own illustration)

Additionally, it was calculated the deficit of hydrogen, considering the difference between the solar energy generation and the energy demand. For example, Figure 30 shows the comparison between the hourly shortfall of hydrogen and the energy supplied. The maximum hydrogen deficit was of 0.5 [m3] and the highest hydrogen generation was over 0.6 [m3] at 11 am, when is the peak of energy supplied with 1.7 [kWh]

Abbildung in dieser Leseprobe nicht enthalten

Figure 30: Hourly hydrogen variation. Source (Own illustration)

The comparable way the monthly shortfall was calculated, which values are represented in Table 15. As a result, the total monthly hydrogen is 772 [m[3]]. The highest and lowest deficit was in December and March with 243 and 9.9 [m[3]], respectively. This data was used to design the hydrogen tank size, specifically was considered the excess of hydrogen (between months April and September) and the shortfall produced, obtaining the hydrogen balance

Table 14: Monthly hydrogen variation

Source (Own source)

The hydrogen is stored as a gas in cylinder tank, composed by aluminium inner liner (6 [mm] thick), aramid fibre and epoxy resin (Saeed & Warkozek, 2015). The size of the tank has a direct relationship with the hydrogen shortfall.

The electrolysis is carried out at 80 [°C] and with a pressure of 30 [bar] (as shown in the parameter of electrolyser). In addition, the hydrogen volume generated is of 610 [m3] and the hydrogen storage was achieved under a pressure of 200 bar (shown in the parameter of the compressor). As a result, the volume of hydrogen pressurised was of 91.5 [m3], which was calculated by Equation 20

The dimension of the tank is described in Figure 31 where the diameter is 2 [m] and a long of 7 [m]. On the other hand, the location of the tank is underground due to safety reason and decrease the excessive temperature fluctuations

Abbildung in dieser Leseprobe nicht enthalten

Figure 31: Dimension of hydrogen tank. Source (Own illustration)

In this case, the tank was configured with a 10 [%] more of volume (Yuan, et al., 2017), which represent the safe maximum of gaseous hydrogen into the tank of 100.65 [m[3]]. The safe proportions are described in Figure 32. At the same time, the power of hydrogen consumed in a stack was calculated by the Formula 19, which of 18103 [kW]

Abbildung in dieser Leseprobe nicht enthalten

Figure 32: Capacity range of hydrogen tank. Source (Yuan, et al., 2017)

Furthermore, was calculated the energy required to compress the hydrogen. Particularly was obtained by the Formula 21, considering the highest amount of hydrogen generated during the year. In this case, the highest rated was of 0.75 [kg/day], resulting 1.49 [kWh]

According to the Equation shown in Chapter 3.4 was calculated the design parameter of the electrolyser, such as the electric current; current efficiency; voltage efficiency and hydrogen produced, which amount per hour as of 0.04 [kg]. The explication of the calculation is described in Tables 16 and 17

Table 15: Summary of electrical efficiency of electrolyser

Abbildung in dieser Leseprobe nicht enthalten

Source (Own source)

Table 16: Hydrogen produced by the electrolyser

Abbildung in dieser Leseprobe nicht enthalten

Source (Own source)

A relevant point is that the battery is not included in the system due the elevated cost, which is based on the report "Sizing optimization of a stand-alone street lighting system powered by a hybrid system using fuel cell, PV and battery". It establishes that the battery represents around 30% of the total cost in a hybrid system, with a factor of 170 [€/kWh] (Lagorse, et al., 2008). In addition, a battery involves a low power conversion due to the energy capacity is reduced while the load capacity increase, reducing the efficiency to 30% (Ro & Rahman, 1997). At the same time, the batteries have an environmental issue associated, such as operational and of disposal way.

4.4.2 Simulation results

Firstly, the complete system is described on Figure 33, where explain the location and the configuration of each one of the components of the PV-H2-SOFC system. For example, the hydrogen storage is located under the ground, and the before this is used a compressor. Additionally, it shows the supply of the electric energy by photovoltaic system, which could be used directly to the load

Abbildung in dieser Leseprobe nicht enthalten

Figure 33: Explanatory diagram of PV-H2-SOFC system. Source (Own illustration)

Based on the FCPower Model hourly energy model was extracted the PV-H2-SOFC system energy balance, that is described in Table 18. The electricity generated is of 53.3 [kW] which represents five times more than the daily electric consumption demanded (10.66 [kW]). This means that the SOFC increased the output power of the system, as system compensation. In the case of heat output power was obtained throughout the combined heat and power resulting in 29.3 [kW] which is equal to eleven times more than daily heat consumption demanded (3 [kW]). In relation with the power used for the heat and power process was of 131 [kW] and a maximum H2 production ability of 17 [kW]. This last value is the fractional increase in the total amount of hydrogen required for the fuel cell at rated power generation (Wu, et al., 2017)

Table 17: PV-H2-SOFC Specifications

Abbildung in dieser Leseprobe nicht enthalten

Source (D. Steward, 2013)

The similar way was obtained power factors that are shown in Table 19. Where the electrical and heat power delivered was of 0.277 [kWh/kWh] and 0.072 [kWh/kWh], respectively. Additionally, the hydrogen delivered by the system was 0.652 [kWh/kWh]. Finally, the total yearly energy supplied was of 499,475 [kWh] and the total energy demand (heat and electric) is of 4866.4 [kWh/year]. As a result, there is 94,609 [kWh] extra per year, which could be used to supply the heating system or more electric artefacts

Table 18: Energy output of the system, from FCPower model simulation

Abbildung in dieser Leseprobe nicht enthalten

Source (D. Steward, 2013)

Overall, the FCPower Model includes three waste energy streams are accounted for, such as Fixed heat loss (unrecoverable energy); Unusable heat and Inverter loss, which is the energy loss associated with power electronics (D. Steward, 2013). According to the diagram provided by the FCPower Model (Figure 34), shows the AC efficiency, which represents the electricity efficiency, which had a maximum performance of approximately 40% between the 25 [%] and 100 [%] of system operating power.

In a comparative way, the total efficiency involves the total load obtained included the losses of the complete system. The maximum efficiency obtained was of over 75 [%] between the 45 [%] and 100 [%] of system operating power. In general, these losses depend on the fuel cell exhaust temperature due to heat-recovery. This is the main reason for the low electrical performance (efficiency) compared with the total efficiency

Abbildung in dieser Leseprobe nicht enthalten

Figure 34: Efficiency of the system from FCPower model simulation. Source (D. Steward, 2013)

4.5 Analysis: Solar source, energy demand and PV-H2-SOFC

In general, the results demonstrated that the temperature and Irradiation have a direct relationship. As Figure 11 shows the maximum level of radiations are in the season with elevated temperature, corresponding to the months between June and September, with maximum average values of global radiation over the 4.5 [kWh/m[2]], this represents a 49 [%] more than the annual average global irradiation. A similar case is between the ambient temperature and the cell temperature, which presented the highest variation in the month of March with a 29 [%] higher in PV cell temperature. However, there is an inverse relationship between the cell temperature and their efficiency due to the cell efficiency decrease in a 2 [%] when the PV panel get the higher average temperature of 15.5 [°C].

In an analogous way, the monthly of heat and electric demand had an inverse relationship with the weather season due to during the winter time the heat consumption had a significant rise, for example in December the consumption of hot water increase 18 [%] (96.7 [kWh]) but is the lower air temperature of 5 [°C]. A similar case the monthly electric consumption, which had the highest variation in January with 16 [%] more. The hourly demand for heat energy had prevalence in the morning (at 8 am) with around 53 [%] higher and the lowest was estimated at early morning with a decrease of 44 [%]. However, the highest electric demand was in the afternoon (at 13 hours) with a rise of 79 [%]

According to the demand for heat and electric was established the amount of 14 PV modules that provides 3878 [kWh] per year. In addition, the sizing of PV array involves one inverter, and 2 rows and 7 columns of PV modules located at 13 [m] between rows and with a 45°inclination (respect to the floor) and south orientation.

At the same time, the relation between the energy demand and the amount of hydrogen consumed by the system was direct due to the highest hydrogen demand was when the total energy consumption gets the peak. Particularly, it happens in December when the hydrogen demand had a leap of 11 [%]. Furthermore, the hourly hydrogen demand showed a higher concentration at midday with around 75 [%] more consumption. In relation with the deficit of hydrogen was calculated that is necessary a 57 [%] more of hydrogen production to supply the demand required

The integration of PV-H2-SOFC system showed an increase of electric power in a 54 [%] (compared with the PV generation). Additionally, this represents a higher supply able to generate a 79 [%] more than the demand required. The comparable way, the hourly heat energy generates 89 [%] more than hot water demand. Moreover, the total energy supply by this system involves a variation above the 80 [%] compared with the energy demanded. However, the electric efficiency represented a 66 [%] lower than the system efficiency. This last is when it had over 65 [%] of system operating power.

5 ECONOMIC RESULTS

5.1 Economic simulation results

Agreed to the simulations carried out by the program the economic analysis was obtained. Overall, all the economic factors were extracted by the same model, as consequence, all the economics indexes are in American dollars including the taxes and inflations belong to the project. For example, Table 20 shows the economic specification of the project design, such as the assumption of Inflation rate (0.001 [%]); plant life (20 years); equity financing [1%] and the total tax rate of 0.389[%]

Table 19:Economic description of the project, from FCPower model simulation

Abbildung in dieser Leseprobe nicht enthalten

Source (D. Steward, 2013)

Moreover, was obtained the Levelized Cost of Energy per year which is described in Table 21. Where the system factors of energy-cost of electric and heat is of respective way 6.5 [USD$/kWh] and 0.124 [USD$/kWh]. As a result, the annual cost of electric energy was of 25589 [USD$] and heat demand value was of 126 [USD$], with a total cost of 25715 [USD$]

Table 20: Annual Levelized Cost of Energy, from FCPower model simulation

Abbildung in dieser Leseprobe nicht enthalten

Source (D. Steward, 2013)

At the same time, was obtained the electricity costs per month, which were established the relationship between the energy demand by season (winter and summer) with the tariff associated. Described in Table 23. For example, the total demand charges were of 26,303 [USD$/year], considering the partial peak and the peak of each season; the monthly maximum charges and the cost factors. These last values are explained in Table 22

Table 21: Cost factors per season, from FCPower model simulation

Abbildung in dieser Leseprobe nicht enthalten

Source (D. Steward, 2013)

Table 22: Breakdown of the monthly cost of electricity, from FCPower model simulation

Abbildung in dieser Leseprobe nicht enthalten

Source (D. Steward, 2013)

Nevertheless, the system has an excess of energy production of 485,289 [kWh], whose sale value to the grid electricity is of 0.0401 [USD $/kWh] (estimated in FCPower model simulation), which represents a total revenue of 19460 [USD] per year.

In an equivalent way, the report “Investigation of a Renewable Energy-Based Integrated System for Baseload Power Generation” of Hosseini, et al., s.f shows the cost of different hybrid systems. Particularly, the factor for PV-H2-SOFC system is around 2.55 [USD$/kWh] (17 [¢/kWh] (Hosseini, et al., s.f.)). Therefore, considering the total demand of 4866.4 [kWh] (electric and heating) was obtained an annual total of 16545 [kWh], which a 64% lower. At the same time, the factor of Wind-SOFC system has a cost of 1.4 [USD$/kWh] (7 [¢/kWh], (Hosseini, et al., s.f.)) that represent a 41 [%] less

Moreover, the cost of traditional energy sources in the UK corresponds 3.19 [p/kWh] (0.0319 [USD$/kWh]) for gas and 11.46 [p/kWh] (0.1146 [USD$/kWh]) for the grid electricity ( Business Juice, 2017). Therefore, the annual cost associated with each demand is of 31.5 [USD$] for heat demand and 444.648 [USD$] for electricity. The comparative ranges are described in Figures 35 and 36

Abbildung in dieser Leseprobe nicht enthalten

Figure 35: Economic comparison between both electrical systems. Source (Own illustration)

Abbildung in dieser Leseprobe nicht enthalten

Figure 36: Economic comparison between both heat systems. Source (Own illustration)

5.2 Economic analysis

According to the results of energy cost, the electricity production represents an over 95 [%] of the total cost in the energy generation (electric and heat). This is due to the electricity tariff depends on the peak of demand and the season. For example, the electricity is provided by the PV system, however, the generation is relative to the irradiation (weather seasons), therefore the values cost is different as well. The variation between winter seasons and summer is an 11 [%] higher.

Regarding the remuneration of income from the sale of excess energy, it was 19460 [USD$/yr], which means a decrease of 76 [%] in the Levelized Cost of Energy (annual), assuming a total cost of 6255 [USD $] per year.

The perceptual variation between the electricity produced by the PV-H2-SOFC system and the grid electricity is of 98 [%], this involves that the unconventional system is 25,144 [USD$/yr] more expensive than the grid electricity. In the case of heat generation, the production cost of PV-H2-SOFC is 75 [%] higher than gas, which involves 95 [USD$/yr] of difference.

6 ENVIRONMENTAL IMPACT

6.1 Environmental simulation results

Accordant with the simulation results was established the Greenhouse Gas (GHG) emission of the system by category, which is described in Table 24. The estimation of GHG emission for electrical energy is of 194 [kg CO2eq/year]. In the case of the heat demand had a GHG impact of 51 [kg CO2eq/year]. The hydrogen produces 10,513 [kg] of CO2 equivalent per year. This value is highest due to consider the emission of "Electricity Usage for Equivalent Hydrogen Supply" (40 [kg CO2eq/year]) and the "Fuel Usage for Equivalent Hydrogen Supply" (9,882 [kg CO2eq/year]). The total emission of Greenhouse Gas per year is of 10,167 [kg]

Table 23: Specification of GHG emission, from FCPower model simulation

Abbildung in dieser Leseprobe nicht enthalten

Source (D. Steward, 2013)

Based on the previous results is described the process of the Greenhouse Gas emission in Figure 37. Particularly, explain the relation between the energy demanded and the kg CO2equivalent generated per year. For example, 3,883 [kWh/year] of electricity produces 194 [kg CO2eq/year]. Similarly, the hydrogen production, which has a delivered of 9,243 [kWh/year] generating 9,922 [kg CO2eq/year]. The hot water demand of 1,016 [kWh/year] has an annual impact of CO2equivalent of 51 [kg]

Abbildung in dieser Leseprobe nicht enthalten

Figure 37: Distribution of CO2 emission of PV-H2-SOFC, from FCPower model simulation. Source (D. Steward, 2013)

On the other hand, the comparison between the CO2eq emissions of PV-H2-SOFC system and the conventional energy sources is detailed in Figures 38 and 39. The factors of GHG emission associated with the gas and grid electricity are of 0.21 [kg CO2eq/kWh] and 0.367 [kg CO2eq/kWh] (Hill & Watson, 2016), respectively. As a result, the annual CO2eq emission is of 1631 [kg CO2eq] between both demands.

Abbildung in dieser Leseprobe nicht enthalten

Figure 38: Comparison of GHG emissions between both electrical systems. Source (Own illustration)

Abbildung in dieser Leseprobe nicht enthalten

Figure 39: Comparison of GHG emissions between both heat systems. Source (Own illustration)

6.2 Environmental analysis

In relation to the GHG analysis, was calculated the impact on the production of hydrogen, electricity and heat, which is 98 [%], 2 [%] and 1 [%], respectively of [kg CO2eq/year]. The hydrogen had a higher prevalence due to the integration of 93 [%] of "Fuel Usage for Equivalent Hydrogen Supply" and 7 [%] "Electricity Usage for Equivalent Hydrogen Supply". This is generated because the required hydrogen is greater than the amount of hydrogen produced, so the program model calculates the missing hydrogen with a higher emission factor, a variation of 93 [%] between both.

At the same time, there is a significant difference between the generation with conventional energy sources and the PV-H2-SOFC system. For example, GHG emission of PV-H2-SOFC system is an 86 [%] lower than grid electricity. In an analogous way, the CO2eq emission generated by gas is a 75 [%] higher than the hybrid system, which involves 156 [kg CO2eq] more per year.

7 DISCUSSION

Based on the energy analysis, is possible establishes that the PV system can supply only the 30 [%] of electricity demand in the winter time and during the summer there is an excess of electric generation of 40 [%]. Therefore, the solar farm has an energy variation over 80 [%] between both seasons. Despite this, the PV-H2-SOFC system manages to satisfy the required demand due to an increase in the energy generation (89 [%] higher) and the global efficiency (over 60 [%]), which was produced by the integration of the fuel cell into PV system. Additionally, the hybrid system has the capacity to supply the total hot water demand, obtaining more than 26 [kW] of daily extra heat power.

In the configuration of the system was not necessary the integration of an electric battery due to through of the water electrolysis can solve the irregularity of the solar availability. This type of solution involves the generation of energy by an electrochemical reaction. Additionally, help to decrease the operational cost of the system and avoid the environmental issues associated with its use

According to the financial results, the project showed an economic disadvantage compared with the conventional energy resources (grid electricity and gas) due to the energy cost of the PV-H2-SOFC system is 75 [%] and 98 [%] higher for the heat and electricity generation, respectively. However, there is an economic retribution for the sale of the excess energy that improves the energy cost balance (a 76 [%] less). In addition, the system can supply a greater demand for the same cost, considering for example the consumption of heating.

Regarding the environmental impact, the PV-H2-SOFC system presented low GHG emissions in the generation of electrical energy, which is 1229.96 [kgCO2eq/year] less than grid electricity. In a similar way, the heat generation produced annual 156 [kgCO2eq/year] less than the gas. This is due to the fuel cell as it has a low emission of CO2eq in comparison with another type of hybrid system. However, this analysis excludes the environmental impact of the extra supply of hydrogen, which considerably increases the emission of GHG in the system.

8 CONCLUSION

8.1 Evaluation

As for the technical study of the project, it is possible to establish that the hybrid system improves the performance, increasing the generation of energy by 54 [%]. This happens because SOFC operates as an auxiliary power source that compensates the difference between the load demand and the actual power of the photovoltaic array. Increasing the output power of the system

The generation of solar energy produced in Highland manages to partially provide the required hydrogen demand due to in the winter months there is a decrease of 93 [%] in the PV energy production. Therefore, an evaluation in the configuration of the system could optimize the generation of hydrogen. This implies, alternative sources of hydrogen supply.

One of the main challenges is the economic factor in the application technology due to the fuel cell is not massively commercialized (less technological development), which makes its price higher. Additionally, fuel (hydrogen) in the fuel cell is expensive to produce. However, it has the advantage of having great efficiency, which allows obtaining energy excess to be sold to the electricity grid and generate income.

Finally, from the environmental point of view, the PV-H2-SOFC system provides a lower impact due to the integration of the fuel cell transforms the CO produced into CO2 at a high operating temperature, decreasing drastically the emissions. Achieving being more environmentally feasible than conventional energy resources, with 86 [%] and 75 [%] less of GHG emission for the electricity and heat demand, respectively.

8.2 Recommendations

According to the technical analysis of the hybrid system, it is proposed to increase the energy load with the integration of heating or the addition of more electrical devices. At the same time, an optimization in the supply of hydrogen in the months with low solar energy. For example, increasing the amount of PV panels or replace it with another type of renewable energy.

Given that some of the results were obtained by means of assumptions, such as electrical efficiency of the electrolyser, energy consumption, hydrogen produced by the electrolyser, hydrogen demand, etcetera. It is advisable has experimental data in the laboratory to test the hybrid system. Especially in the integration of the fuel cell due to allows a greater certainty of the data. This excludes the simulation program of the PV-H2-SOFC system, which used factors of the model.

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10. APPENDICES

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Figure 40: Solar Radiation program. Source (Muneer, 2017)

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Figure 41: Project setup, from FCPower model simulation. Source (D. Steward, 2013)

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Figure 42: Input simulation system, from FCPower model simulation. Source (D. Steward, 2013)

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Figure 43: Output model in the system calculation, one-hour load from FCPower model simulation. Source (D. Steward, 2013)

[...]

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Details

Title
Energy Analysis of a Solid Oxide Fuel Cell (Sofc) Operated by PV System in the Residential Sector, in Highland
College
Edinburgh Napier University
Grade
P5
Author
Year
2018
Pages
74
Catalog Number
V458731
ISBN (Book)
9783668912885
Language
English
Tags
energy, analysis, solid, oxide, fuel, cell, sofc, operated, system, residential, sector, highland
Quote paper
Scarlett Allende (Author), 2018, Energy Analysis of a Solid Oxide Fuel Cell (Sofc) Operated by PV System in the Residential Sector, in Highland, Munich, GRIN Verlag, https://www.grin.com/document/458731

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