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Economic Feasibility Study of two Renewable Energy Systems for Remote Areas in UAE
Available online at www.sciencedirect.com
ScienceDirect Energy Procedia 75 (2015) 3027 – 3035
The 7th International Conference on Applied Energy – ICAE2015
Economic Feasibility Study of Two Renewable Energy Systems for Remote Areas in UAE Zahi M. Omera, Abbas A. Fardouna, Ahmed M. Alamerib b
a Electrical Engineering Department, UAE University, P.O. Box 15551, Al-Ain, UAE Field Services Department, Alain Distributiion Company,P.O. Box 67055, Al-Ain, UAE
Abstract- Safari camps are getting great deal of attention recently due to the economical and touristy benefits. However, these camps are located in remote rural areas in UAE desert where there is no grid power supply; the installed electric source typically is diesel generators. Due to the cost of fuel supply and the impacts of the generator vibrations on desert landscape, two renewable systems have been investigated. One is a conventional renewable system consisting of PVs and battery storage. The second system is a combination of PVs and fuel cell where hydrogen is provided via water electrolysis. This economical and feasibility study aims to compare the performance of both systems (Fuel cells and Batteries) using HOMER software. System capital cost and maintenance are included in the cost study. The cost of the fuel cell system is higher than the PV/battery system by about 50%. However, lead acid batteries assumed in the study have low life span and can pose serious environmental risks if not discarded properly. © 2015 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license © 2015 The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Selection and/or peer-review of under responsibility of ICAE Peer-review under responsibility Applied Energy Innovation Institute Key words: Fuel Cell, Water Electrolysis, Hydrogen Production, Efficiency, Battery-less solar system.
1.
Introduction
Safari camps in UAE are fully powered using diesel generators due to their remote locations, but the high diesel fuel prices have a direct influence on the cost of electricity in remote communities. Also it costs about 550K AED/Km to erect power to remote areas in UAE [1]. In addition, diesel generators vibrations affect the desert landscaping [2, 3]. Municipalities are adding new regulations on generator vibrations. Additionally high operating and maintenance costs of diesel generators contribute to high electrical cost in UAE desert camps. As a result, renewable energy power supply is reasonable solution due to its environmental friendly characteristics. Also, UAE has legislated new policies to encourage the use of renewable energy. For instance, Abu Dhabi’s Economic Vision - 2030 aims at generating 7% of Abu Dhabi’s energy requirements from renewable resources. In Dubai, it is planned to generate 1% of electricity needs from renewable sources by 2020 and 5% by 2030 [4].
1876-6102 © 2015 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of Applied Energy Innovation Institute doi:10.1016/j.egypro.2015.07.617
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Fig.1: Safari camp in Alain.
Conventional renewable energy systems use batteries as a storage unit because of the intermittent nature of renewable energy sources in general, such as solar and wind sources in addition to the out-ofsynchronization nature of those generation sources with the loads. It shall be noted that batteries are a must for this solution because the bulk of safari camp power is required during night hours. However, batteries have numerous failure modes in addition to recurring cost of maintenance and replacement [5]. Moreover, defected batteries must be disposed carefully and professionally, since batteries contain various hazardous materials, including heavy metals and acids, they can pose serious environmental risks if not discarded properly. Another environmental friendly system is proposed by using a combination of PEM (Polymer Electrolyte Membrane) water electrolysis and fuel cell array to feed the load. Unlike voltaic cells (i.e. Batteries), water electrolysis convert the electrical work to power reactant favorable nonspontaneous reactions such as decomposition reaction (i.e. H2O decomposition). By using solar cells and water, electrolysis effect can be obtained. By controlling the electric field inside the electrolysis, H2O will break into Oxygen and Hydrogen in the positive and negative electrodes respectively. Hydrogen is assumed to be compressed in H2 tanks and will be used again as an input for the fuel cell. However, this approach suffers from lower system efficiency due to the additional electrolysis operation. The preliminary block diagram is illustrated in the following figure for fuel cell and battery cases in Fig.2a and Fig.2b.
(a)
(b)
Zahi M. Ome et al. / Energy Procedia 75 (2015) 3027 – 3035
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Fig.2: Proposed block diagram of (a) the system (fuel cell) and (b) PV system with battery bank.
2.
Sub-system Sizing and Efficiency Evaluation
The current load for the safari camp -application of interest- is shown in Fig 3a. It shall be noted that this profile is based on the diesel generator as a power source. Power is shut down during daytime to reduce energy cost due to low diesel generator efficiency at low load. Fig. 3b shows preferred power consumption profile by the customer based on field study. Profile can be easily achieved by renewable energy source without lower efficiency penalty as the case for diesel generator.
(a)
(b) Fig.3: Electrical Load Profile A&B
2.1
PV System
There are certain aspects should be taken into consideration when sizing the PV array such as determining the panel generation factor (PGF). The PGF is the dominant key to size the PV panels, it combining the minimum solar insolation with the common possible losses in the system by the following equation: ൌ ൬
൰ ଶ Ǥ
There are common losses typically affecting the PV arrays such as: x x x x
Allowance of dirt. Losses due to sunlight not striking the panel straight on. System losses when the temperature above 25ͼ C. Allowance of aging.
The goal is to determine the percentage loss generated according to the previous causes. Determining the exact losses generated in the PV system is a challenging task due to absence of simple mathematical equations and the non-linearity relationships characteristics with a lot of parameters affecting the losses. The practical solution has been achieved by collecting the average losses specified by standards or by previous experimental results of research work and findings mentioned in [6].
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As stated earlier, there is another factor affecting the PGF which is the solar insolation. The worst case scenario has been selected to calculate the PGF. The following chart shows the monthly solar insolation in UAE in ቀ
୩୦
ቁ [7].
୫మ Ǥୢୟ୷
Fig.4: Solar radiation data for UAE.
On the other hand, the power demands will be calculated according to the load wattage. Although the maximum night time in UAE is typically thirteen hours, but to consider the worst situation, the energy should be selected to be available for more hours in case of lack of solar energy. The PV energy has been calculated according to the following equation: ൌ
ሺʹሻ
2.2
Battery Bank
A 48 V bus is assumed for the study. The KW/day required by the load of Figure 2, system autonomy and battery depth of discharge determines the battery capacity. The complexity of the battery as an electrochemical system without an absolute model to describe the internal system resulted to have difficulties in expecting the behavior of the overall performance. Losses of 10% are assumed [8]. Battery bank characteristics are shown in Table 2. Subsequently, the battery capacity (Ah) can be calculated by knowing the total energy, the internal losses and the system autonomy as shown in Eq. 3. Table 1: Battery bank characteristics Battery Bank Characteristic
Value
Depth of Discharge
50%
System autonomy
0.853/day
Expected losses
10%
Zahi M. Ome et al. / Energy Procedia 75 (2015) 3027 – 3035
3031
ൌ
ሺ͵ሻ
2.3
Water Electrolysis
Water electrolysis will be the Hydrogen generator of the system, in addition to Oxygen generation that can be used for other purposes. For a final hydrogen pressure of 30 bar, atmospheric pressure of the electrolysis with isothermal (adiabatic) compressor efficiencies of at least 40% to 50% was estimated to exceed the efficiency of pressurized electrolysis [9].The maximum voltage that can be applied on electrolysis electrodes is calculated to size the system. The voltage–current relationship is based on the following equation [9]: ܸୀ ܸ௩ǡ
భశ మ ்
ܫ ሺݏଵ ݏଶ ܶ ݏଷ ܶ ଶ ሻ ቆ
௧భ ା మ ା యమ
ܫ ͳቇ
(4)
ͶǤ ʹǣ Ǧ Parameter
Definition
Velec
Operation cell voltage for the PEM electrolysis, V
Vrev,elec
Reversible voltage for the PEM electrolysis, V
ri
Parameters for the ohmic resistance of the electrolyte of the PEM electrolyzer, i = 1,2
T
Temperature, °C
Aelec
Electrode area, m2
Ielec
Operation current for the PEM electrolyzer, A
Si
Parameters for the overvoltage at the electrodes of the PEM electrolyzer,i = 1,…3
ti
Parameters for the overvoltage at the electrodes of the PEM electrolyzer,i = 1,…3
2.4
Fuel Cells
The selected fuel cell technology is Proton Exchange Membrane Fuel Cell (PEMFC).In order to produce an electrical current out of the hydrogen fuel cells, the following reaction without stating the thermal and electrical outputs will take place: ½ O2 (g) + H2(g) ĺ H2O(l) (5)
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Zahi M. Ome et al. / Energy Procedia 75 (2015) 3027 – 3035
The change of free energy for the fuel cell reaction is indicated by the following equation: ¨G = –nFE (6)
Where, ǻG is the free energy change, n is the number of moles of electrons involved, E is the reversible potential, and F is Faraday’s constant. The enthalpy difference ǻH for a fuel cell reaction also specifies the entire heat released by the reaction at constant pressure. ǻH = –nFEt (7)
Where, Et has a value of 1.48 V for the Hydrogen/Oxygen reaction in equation (5) [10]. The efficiency of a fuel cell ideally for irreversible operation can be stated as: Ꮈ ൌ
ୋ ୌ
(8)
The voltage is determined using a polarization curve based on the reversible cell voltage, activation losses, ohmic losses and concentration losses [11, 12].The practical efficiency of a PEM's is in the range of 40–60% [13, 14]. According to the previous power profile, the efficiency can be calculated as in the following equation: Ꮈ ൌ
୭ୟୢ୭୲ୟ୪୬ୣ୰୷
୳ୣ୪୪େୣ୪୪Ꮈ୶୪ୣୡ୲୰୭୪୷ୱ୧ୱᎸ୶୍୬୴ୣ୰୲ୣ୰Ꮈ
(9)
3.
Results and Discussion
The entire hybrid system was simulated by evaluating the system cost in case of battery bank and also in case of fuel cell and solar system. HOMER software, which is a computer model that simplifies the task of designing hybrid renewable micro-grids, was used in the study. The following Figure shows the modeled block diagrams of the system.
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Zahi M. Ome et al. / Energy Procedia 75 (2015) 3027 – 3035
(a)
(b)
Fig.5: System Schematics Simulated in HOMER.
The daily energy consumption is expected to be higher during night and from the time camp’s night activity starts. During the day, the consumption is due to small fridges and negligible. The cost of fuel cells varies depending on the technology deployed [15]. Fuel cell costs vary from $3000 to $6000/kW currently and are expected to reach costs ranging from $195 to 300/kW in the near future [16-19].The following two cases were discussed by fixing the solar insolation at 4.99kWh/m2 and the fuel cell system capital multiplier fixed at 0.4 of the current cost in case I and case II for load profile b. 3.1 Case I (Battery Bank) The following system configuration was identified as the most economically feasible state as shown in table 3: 5kW PV panel, 64 H600 batteries and a 5kW power converter. The net present cost of this system, yearly operating costs, and yearly cost of energy were $140,972, $1,393, and $.763/kWh. These numbers were specifically targeted as they represent UAE’s current average solar radiation and fuel cell system costs respectively.
͵ǣ Ǥ Sources
PV (Kw)
Battery Bank Size
Disp. Strgy.
Initial Capital
Operating Cost ($/yr)
Total NPC
COE ($/kWh)
Ren. Frac.
Capacity Shortage
PV + Batteries
25
64
CC
$ 123,170
1.393/Kw
$ 140,972
0.763
1.00
0.00
3.2 Case II (Fuel Cell) With the solar radiation fixed at 4.99kWh/m2, 5kW power converter and the fuel cell system capital multiplier fixed at 0.4 of current costs the following system configuration was identified as the most economically feasible as shown in table 4: 5kW PV, 5kW fuel cell. The optimum system configuration in this scenario has replaced the diesel generator with fuel cell system and PV. The net present cost of this system, yearly operating costs, and yearly cost of energy were $243,606, $13,896, and $1.318/kWh.
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Zahi M. Ome et al. / Energy Procedia 75 (2015) 3027 – 3035
Ͷǣ Ǥ Sources
PV (Kw)
Fuel Cell Fuel Cell + PV
4.
5
FC (Kw)
Disp. Strgy.
Initial Capital
Operating Cost ($/yr)
Total NPC
COE ($/kWh)
Ren. Frac.
Capacity Shortage
FC (hrs)
7
CC
$ 45.970
13.848/kW
$222,996
1.207
0.00
0.00
4.380
7
CC
$65,970
13.896/kW
$243,606
1.318
0.00
0.00
4.380
Summary and Conclusions
An economic study targeting a safari camp as a potential application has been presented using HOMER software. Comparison of PV with energy storage versus PV and Fuel cell using electrolysis for hydrogen production has been detailed. Losses for both systems have been investigated in the study. The study takes into account the load requirement variations, capital cost (FC, PV and diesel generator cost) and running cost (Hydrogen, PV cleaning, and diesel cost). The Fuel cell/PV system capital an and KWh coat are estimated at $243,606 and $1.318/kWh, respectively. On the other hand, the PV/energy storage capital and KWh energy costs are estimated at $123,170, and $0.763/kwh, respectively. However, the cost of recurring maintenance and shut down time due to battery replacement has been ignored. Acknowledgements This research has supported in part by UAE University and JCCP under research contracts 31N169 and 21N125. References [1] Private communication, AlAin Distribution company (AADC), 2012. [2] M. Saberi (2008). “Shrinking desert poses threat to safaris”. In: GulfNews, 23 October [Online]. Retrieved June 9, 2010, from http://gulfnews.com/news/gulf/uae/leisure/shrinking-desert-poses-threat-to-safaris-1.138338 [3] Private conversation with Al-Ain municipality, May 2010. [4] Masder, Abu Dhabi: Investing In An Evolving World Energy Market, www.masdar.ae/en/media/detail/abu-dhabi-investing-inan-evolving-world-energy-market, (Accessed: 14 September 2014). [5] A. Cooper, P.T. Moseley, “Progress in Overcoming the Failure Modes Peculiar to VRLA Batteries”, Power Sources Journal, Vol. 113, PP. 200-208, 2003. [6] Travis Sarver et al, “A Comprehensive Review of the Impact of Dust on the Use of Solar Energy”, Renewable and Sustainable Energy Reviews, Vol. 22, PP. 698-733, 2013. [7] Nawabi, Abu Dhabi solar radiation, http://nawabi.de/power/solar/Abu%20Dhabi%20solar.asp, (Accessed: 1 July 2014). [8] Johannes Weniger*, Tjarko Tjaden, Volker Quaschning,” Sizing of Residential PV Battery Systems”, 8th International Renewable Energy Storage Conference and Exhibition, IRES 2013, Energy Procedia, Vol. 46, PP. 78-87, 2014.
Zahi M. Ome et al. / Energy Procedia 75 (2015) 3027 – 3035
[9] W. Winkler and P. Nehter,”Modeling Solid Oxide Fuel Cells”, Ch.2, Thermodynamics of Fuel Cells, Springer, pp. 13-50, 2008. [10] Dimitris Ipsakis, Spyros Voutetakis, Panos Seferlis, Fotis Stergiopoulos, Costas Elmasides, “Power management strategies for a stand-alone power system using renewable energy sources and hydrogen storage”, International Journal of Hydrogen Energy, Vol. 34, PP. 7081-7095, 2009. [11] U.S. Department of Energy,"Comparison of Fuel Cell Technologies", Energy Efficiency and Fuel Cell Technologies Program, February 2011, (Accessed: 4 August 2011). [12] M. Nabag, A. Fardoun, H. Hejase, and A. Al-Marzouqi, “Review of Dynamic Electric Circuit Models for PEM Fuel Cells,” The 3rd International Conference on Renewable Energy: Generation and Applications (ICREGA 2014), Al-Ain, UAE, March 2-5, 2014. [13] R. Salim, M. Nabag, H. Noura and A. Fardoun, ”Dynamic Modeling of PEM Fuel Cell Using Particle Swarm Optimization”, The 3rd International Conference on Renewable Energy: Generation and Applications (ICREGA 2014), Al-Ain, UAE, March 2-5, 2014. [14] Maimilian Schalenbach, et al,” Pressurized PEM Water Electrolysis: Efficiency and Gas Crossover”, International Journal of Hydrogen Energy, Vol.38, Issue 35, PP. 14921–14933, November 2013. [15] G. Mahar and G. Simmons, “Feasibility of Utilizing Hydrogen Fuel Cell Systems in Hybrid Energy Systems, In Stand-Alone Off-Grid Remote Northern Communities of Canada” Feb 2011. [16] Cotrell, J., Pratt, W., “Modeling the Feasibility of Using Fuel Cell and Hydrogen Internal Combustion Engines in Remote Renewable Energy Systems”. Windpower 2003, Austin, TX, May 18–21, 2003. [17] Fuel Cell Report to Congress. US DOE, ESECS EE-1973. p. 39; February 2003. URL: www.eere.energy.gov/ hydrogenandfuelcells/pdfs/fc_report_congress_feb2003.pdf [18] Simbeck, D., Chang, E., ” Hydrogen Supply: Cost Estimate For Hydrogen Pathways—Scoping Analysis”. SFA Pacific Inc. National Renewable Energy Laboratory (NREL), 2002. [19] Pratt, W., “A Preliminary Investigation of Two Small Scale, Autonomous Wind–Hydrogen System. National Renewable Energy Laboratory (NREL), National Wind Technology Center (NWTC), TRAC Program Boulder, CO, 2002
Biography Abbas Fardoun is an associate Professor at the Electrical Engineering Department, UAE University, AlAin, UAE.
3035
ScienceDirect Energy Procedia 75 (2015) 3027 – 3035
The 7th International Conference on Applied Energy – ICAE2015
Economic Feasibility Study of Two Renewable Energy Systems for Remote Areas in UAE Zahi M. Omera, Abbas A. Fardouna, Ahmed M. Alamerib b
a Electrical Engineering Department, UAE University, P.O. Box 15551, Al-Ain, UAE Field Services Department, Alain Distributiion Company,P.O. Box 67055, Al-Ain, UAE
Abstract- Safari camps are getting great deal of attention recently due to the economical and touristy benefits. However, these camps are located in remote rural areas in UAE desert where there is no grid power supply; the installed electric source typically is diesel generators. Due to the cost of fuel supply and the impacts of the generator vibrations on desert landscape, two renewable systems have been investigated. One is a conventional renewable system consisting of PVs and battery storage. The second system is a combination of PVs and fuel cell where hydrogen is provided via water electrolysis. This economical and feasibility study aims to compare the performance of both systems (Fuel cells and Batteries) using HOMER software. System capital cost and maintenance are included in the cost study. The cost of the fuel cell system is higher than the PV/battery system by about 50%. However, lead acid batteries assumed in the study have low life span and can pose serious environmental risks if not discarded properly. © 2015 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license © 2015 The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Selection and/or peer-review of under responsibility of ICAE Peer-review under responsibility Applied Energy Innovation Institute Key words: Fuel Cell, Water Electrolysis, Hydrogen Production, Efficiency, Battery-less solar system.
1.
Introduction
Safari camps in UAE are fully powered using diesel generators due to their remote locations, but the high diesel fuel prices have a direct influence on the cost of electricity in remote communities. Also it costs about 550K AED/Km to erect power to remote areas in UAE [1]. In addition, diesel generators vibrations affect the desert landscaping [2, 3]. Municipalities are adding new regulations on generator vibrations. Additionally high operating and maintenance costs of diesel generators contribute to high electrical cost in UAE desert camps. As a result, renewable energy power supply is reasonable solution due to its environmental friendly characteristics. Also, UAE has legislated new policies to encourage the use of renewable energy. For instance, Abu Dhabi’s Economic Vision - 2030 aims at generating 7% of Abu Dhabi’s energy requirements from renewable resources. In Dubai, it is planned to generate 1% of electricity needs from renewable sources by 2020 and 5% by 2030 [4].
1876-6102 © 2015 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of Applied Energy Innovation Institute doi:10.1016/j.egypro.2015.07.617
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Fig.1: Safari camp in Alain.
Conventional renewable energy systems use batteries as a storage unit because of the intermittent nature of renewable energy sources in general, such as solar and wind sources in addition to the out-ofsynchronization nature of those generation sources with the loads. It shall be noted that batteries are a must for this solution because the bulk of safari camp power is required during night hours. However, batteries have numerous failure modes in addition to recurring cost of maintenance and replacement [5]. Moreover, defected batteries must be disposed carefully and professionally, since batteries contain various hazardous materials, including heavy metals and acids, they can pose serious environmental risks if not discarded properly. Another environmental friendly system is proposed by using a combination of PEM (Polymer Electrolyte Membrane) water electrolysis and fuel cell array to feed the load. Unlike voltaic cells (i.e. Batteries), water electrolysis convert the electrical work to power reactant favorable nonspontaneous reactions such as decomposition reaction (i.e. H2O decomposition). By using solar cells and water, electrolysis effect can be obtained. By controlling the electric field inside the electrolysis, H2O will break into Oxygen and Hydrogen in the positive and negative electrodes respectively. Hydrogen is assumed to be compressed in H2 tanks and will be used again as an input for the fuel cell. However, this approach suffers from lower system efficiency due to the additional electrolysis operation. The preliminary block diagram is illustrated in the following figure for fuel cell and battery cases in Fig.2a and Fig.2b.
(a)
(b)
Zahi M. Ome et al. / Energy Procedia 75 (2015) 3027 – 3035
3029
Fig.2: Proposed block diagram of (a) the system (fuel cell) and (b) PV system with battery bank.
2.
Sub-system Sizing and Efficiency Evaluation
The current load for the safari camp -application of interest- is shown in Fig 3a. It shall be noted that this profile is based on the diesel generator as a power source. Power is shut down during daytime to reduce energy cost due to low diesel generator efficiency at low load. Fig. 3b shows preferred power consumption profile by the customer based on field study. Profile can be easily achieved by renewable energy source without lower efficiency penalty as the case for diesel generator.
(a)
(b) Fig.3: Electrical Load Profile A&B
2.1
PV System
There are certain aspects should be taken into consideration when sizing the PV array such as determining the panel generation factor (PGF). The PGF is the dominant key to size the PV panels, it combining the minimum solar insolation with the common possible losses in the system by the following equation: ൌ ൬
൰ ଶ Ǥ
There are common losses typically affecting the PV arrays such as: x x x x
Allowance of dirt. Losses due to sunlight not striking the panel straight on. System losses when the temperature above 25ͼ C. Allowance of aging.
The goal is to determine the percentage loss generated according to the previous causes. Determining the exact losses generated in the PV system is a challenging task due to absence of simple mathematical equations and the non-linearity relationships characteristics with a lot of parameters affecting the losses. The practical solution has been achieved by collecting the average losses specified by standards or by previous experimental results of research work and findings mentioned in [6].
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Zahi M. Ome et al. / Energy Procedia 75 (2015) 3027 – 3035
As stated earlier, there is another factor affecting the PGF which is the solar insolation. The worst case scenario has been selected to calculate the PGF. The following chart shows the monthly solar insolation in UAE in ቀ
୩୦
ቁ [7].
୫మ Ǥୢୟ୷
Fig.4: Solar radiation data for UAE.
On the other hand, the power demands will be calculated according to the load wattage. Although the maximum night time in UAE is typically thirteen hours, but to consider the worst situation, the energy should be selected to be available for more hours in case of lack of solar energy. The PV energy has been calculated according to the following equation: ൌ
ሺʹሻ
2.2
Battery Bank
A 48 V bus is assumed for the study. The KW/day required by the load of Figure 2, system autonomy and battery depth of discharge determines the battery capacity. The complexity of the battery as an electrochemical system without an absolute model to describe the internal system resulted to have difficulties in expecting the behavior of the overall performance. Losses of 10% are assumed [8]. Battery bank characteristics are shown in Table 2. Subsequently, the battery capacity (Ah) can be calculated by knowing the total energy, the internal losses and the system autonomy as shown in Eq. 3. Table 1: Battery bank characteristics Battery Bank Characteristic
Value
Depth of Discharge
50%
System autonomy
0.853/day
Expected losses
10%
Zahi M. Ome et al. / Energy Procedia 75 (2015) 3027 – 3035
3031
ൌ
ሺ͵ሻ
2.3
Water Electrolysis
Water electrolysis will be the Hydrogen generator of the system, in addition to Oxygen generation that can be used for other purposes. For a final hydrogen pressure of 30 bar, atmospheric pressure of the electrolysis with isothermal (adiabatic) compressor efficiencies of at least 40% to 50% was estimated to exceed the efficiency of pressurized electrolysis [9].The maximum voltage that can be applied on electrolysis electrodes is calculated to size the system. The voltage–current relationship is based on the following equation [9]: ܸୀ ܸ௩ǡ
భశ మ ்
ܫ ሺݏଵ ݏଶ ܶ ݏଷ ܶ ଶ ሻ ቆ
௧భ ା మ ା యమ
ܫ ͳቇ
(4)
ͶǤ ʹǣ Ǧ Parameter
Definition
Velec
Operation cell voltage for the PEM electrolysis, V
Vrev,elec
Reversible voltage for the PEM electrolysis, V
ri
Parameters for the ohmic resistance of the electrolyte of the PEM electrolyzer, i = 1,2
T
Temperature, °C
Aelec
Electrode area, m2
Ielec
Operation current for the PEM electrolyzer, A
Si
Parameters for the overvoltage at the electrodes of the PEM electrolyzer,i = 1,…3
ti
Parameters for the overvoltage at the electrodes of the PEM electrolyzer,i = 1,…3
2.4
Fuel Cells
The selected fuel cell technology is Proton Exchange Membrane Fuel Cell (PEMFC).In order to produce an electrical current out of the hydrogen fuel cells, the following reaction without stating the thermal and electrical outputs will take place: ½ O2 (g) + H2(g) ĺ H2O(l) (5)
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Zahi M. Ome et al. / Energy Procedia 75 (2015) 3027 – 3035
The change of free energy for the fuel cell reaction is indicated by the following equation: ¨G = –nFE (6)
Where, ǻG is the free energy change, n is the number of moles of electrons involved, E is the reversible potential, and F is Faraday’s constant. The enthalpy difference ǻH for a fuel cell reaction also specifies the entire heat released by the reaction at constant pressure. ǻH = –nFEt (7)
Where, Et has a value of 1.48 V for the Hydrogen/Oxygen reaction in equation (5) [10]. The efficiency of a fuel cell ideally for irreversible operation can be stated as: Ꮈ ൌ
ୋ ୌ
(8)
The voltage is determined using a polarization curve based on the reversible cell voltage, activation losses, ohmic losses and concentration losses [11, 12].The practical efficiency of a PEM's is in the range of 40–60% [13, 14]. According to the previous power profile, the efficiency can be calculated as in the following equation: Ꮈ ൌ
୭ୟୢ୭୲ୟ୪୬ୣ୰୷
୳ୣ୪୪େୣ୪୪Ꮈ୶୪ୣୡ୲୰୭୪୷ୱ୧ୱᎸ୶୍୬୴ୣ୰୲ୣ୰Ꮈ
(9)
3.
Results and Discussion
The entire hybrid system was simulated by evaluating the system cost in case of battery bank and also in case of fuel cell and solar system. HOMER software, which is a computer model that simplifies the task of designing hybrid renewable micro-grids, was used in the study. The following Figure shows the modeled block diagrams of the system.
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Zahi M. Ome et al. / Energy Procedia 75 (2015) 3027 – 3035
(a)
(b)
Fig.5: System Schematics Simulated in HOMER.
The daily energy consumption is expected to be higher during night and from the time camp’s night activity starts. During the day, the consumption is due to small fridges and negligible. The cost of fuel cells varies depending on the technology deployed [15]. Fuel cell costs vary from $3000 to $6000/kW currently and are expected to reach costs ranging from $195 to 300/kW in the near future [16-19].The following two cases were discussed by fixing the solar insolation at 4.99kWh/m2 and the fuel cell system capital multiplier fixed at 0.4 of the current cost in case I and case II for load profile b. 3.1 Case I (Battery Bank) The following system configuration was identified as the most economically feasible state as shown in table 3: 5kW PV panel, 64 H600 batteries and a 5kW power converter. The net present cost of this system, yearly operating costs, and yearly cost of energy were $140,972, $1,393, and $.763/kWh. These numbers were specifically targeted as they represent UAE’s current average solar radiation and fuel cell system costs respectively.
͵ǣ Ǥ Sources
PV (Kw)
Battery Bank Size
Disp. Strgy.
Initial Capital
Operating Cost ($/yr)
Total NPC
COE ($/kWh)
Ren. Frac.
Capacity Shortage
PV + Batteries
25
64
CC
$ 123,170
1.393/Kw
$ 140,972
0.763
1.00
0.00
3.2 Case II (Fuel Cell) With the solar radiation fixed at 4.99kWh/m2, 5kW power converter and the fuel cell system capital multiplier fixed at 0.4 of current costs the following system configuration was identified as the most economically feasible as shown in table 4: 5kW PV, 5kW fuel cell. The optimum system configuration in this scenario has replaced the diesel generator with fuel cell system and PV. The net present cost of this system, yearly operating costs, and yearly cost of energy were $243,606, $13,896, and $1.318/kWh.
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Ͷǣ Ǥ Sources
PV (Kw)
Fuel Cell Fuel Cell + PV
4.
5
FC (Kw)
Disp. Strgy.
Initial Capital
Operating Cost ($/yr)
Total NPC
COE ($/kWh)
Ren. Frac.
Capacity Shortage
FC (hrs)
7
CC
$ 45.970
13.848/kW
$222,996
1.207
0.00
0.00
4.380
7
CC
$65,970
13.896/kW
$243,606
1.318
0.00
0.00
4.380
Summary and Conclusions
An economic study targeting a safari camp as a potential application has been presented using HOMER software. Comparison of PV with energy storage versus PV and Fuel cell using electrolysis for hydrogen production has been detailed. Losses for both systems have been investigated in the study. The study takes into account the load requirement variations, capital cost (FC, PV and diesel generator cost) and running cost (Hydrogen, PV cleaning, and diesel cost). The Fuel cell/PV system capital an and KWh coat are estimated at $243,606 and $1.318/kWh, respectively. On the other hand, the PV/energy storage capital and KWh energy costs are estimated at $123,170, and $0.763/kwh, respectively. However, the cost of recurring maintenance and shut down time due to battery replacement has been ignored. Acknowledgements This research has supported in part by UAE University and JCCP under research contracts 31N169 and 21N125. References [1] Private communication, AlAin Distribution company (AADC), 2012. [2] M. Saberi (2008). “Shrinking desert poses threat to safaris”. In: GulfNews, 23 October [Online]. Retrieved June 9, 2010, from http://gulfnews.com/news/gulf/uae/leisure/shrinking-desert-poses-threat-to-safaris-1.138338 [3] Private conversation with Al-Ain municipality, May 2010. [4] Masder, Abu Dhabi: Investing In An Evolving World Energy Market, www.masdar.ae/en/media/detail/abu-dhabi-investing-inan-evolving-world-energy-market, (Accessed: 14 September 2014). [5] A. Cooper, P.T. Moseley, “Progress in Overcoming the Failure Modes Peculiar to VRLA Batteries”, Power Sources Journal, Vol. 113, PP. 200-208, 2003. [6] Travis Sarver et al, “A Comprehensive Review of the Impact of Dust on the Use of Solar Energy”, Renewable and Sustainable Energy Reviews, Vol. 22, PP. 698-733, 2013. [7] Nawabi, Abu Dhabi solar radiation, http://nawabi.de/power/solar/Abu%20Dhabi%20solar.asp, (Accessed: 1 July 2014). [8] Johannes Weniger*, Tjarko Tjaden, Volker Quaschning,” Sizing of Residential PV Battery Systems”, 8th International Renewable Energy Storage Conference and Exhibition, IRES 2013, Energy Procedia, Vol. 46, PP. 78-87, 2014.
Zahi M. Ome et al. / Energy Procedia 75 (2015) 3027 – 3035
[9] W. Winkler and P. Nehter,”Modeling Solid Oxide Fuel Cells”, Ch.2, Thermodynamics of Fuel Cells, Springer, pp. 13-50, 2008. [10] Dimitris Ipsakis, Spyros Voutetakis, Panos Seferlis, Fotis Stergiopoulos, Costas Elmasides, “Power management strategies for a stand-alone power system using renewable energy sources and hydrogen storage”, International Journal of Hydrogen Energy, Vol. 34, PP. 7081-7095, 2009. [11] U.S. Department of Energy,"Comparison of Fuel Cell Technologies", Energy Efficiency and Fuel Cell Technologies Program, February 2011, (Accessed: 4 August 2011). [12] M. Nabag, A. Fardoun, H. Hejase, and A. Al-Marzouqi, “Review of Dynamic Electric Circuit Models for PEM Fuel Cells,” The 3rd International Conference on Renewable Energy: Generation and Applications (ICREGA 2014), Al-Ain, UAE, March 2-5, 2014. [13] R. Salim, M. Nabag, H. Noura and A. Fardoun, ”Dynamic Modeling of PEM Fuel Cell Using Particle Swarm Optimization”, The 3rd International Conference on Renewable Energy: Generation and Applications (ICREGA 2014), Al-Ain, UAE, March 2-5, 2014. [14] Maimilian Schalenbach, et al,” Pressurized PEM Water Electrolysis: Efficiency and Gas Crossover”, International Journal of Hydrogen Energy, Vol.38, Issue 35, PP. 14921–14933, November 2013. [15] G. Mahar and G. Simmons, “Feasibility of Utilizing Hydrogen Fuel Cell Systems in Hybrid Energy Systems, In Stand-Alone Off-Grid Remote Northern Communities of Canada” Feb 2011. [16] Cotrell, J., Pratt, W., “Modeling the Feasibility of Using Fuel Cell and Hydrogen Internal Combustion Engines in Remote Renewable Energy Systems”. Windpower 2003, Austin, TX, May 18–21, 2003. [17] Fuel Cell Report to Congress. US DOE, ESECS EE-1973. p. 39; February 2003. URL: www.eere.energy.gov/ hydrogenandfuelcells/pdfs/fc_report_congress_feb2003.pdf [18] Simbeck, D., Chang, E., ” Hydrogen Supply: Cost Estimate For Hydrogen Pathways—Scoping Analysis”. SFA Pacific Inc. National Renewable Energy Laboratory (NREL), 2002. [19] Pratt, W., “A Preliminary Investigation of Two Small Scale, Autonomous Wind–Hydrogen System. National Renewable Energy Laboratory (NREL), National Wind Technology Center (NWTC), TRAC Program Boulder, CO, 2002
Biography Abbas Fardoun is an associate Professor at the Electrical Engineering Department, UAE University, AlAin, UAE.
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