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Technical and economic analysis of a power supply system based on ethanol reforming and PEMFC
Renewable Energy 45 (2012) 205e212
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Renewable Energy journal homepage: www.elsevier.com/locate/renene
Technical and economic analysis of a power supply system based on ethanol reforming and PEMFC Daniel G. Lopes c, e, E.P. da Silva b, d, e, C.S. Pinto a, b, c, *, N.P. Neves Jr. b, d, J.C. Camargo c, e, P.F.P. Ferreira c, e, A.L. Furlan a, e, Davi G. Lopes a, e a
Faculdade de Engenharia Mecânica (FEM), Universidade Estadual de Campinas (Unicamp), Campinas, São Paulo, Brazil Laboratório de Hidrogênio, Instituto de Física (IFGW), Universidade Estadual de Campinas (Unicamp), Campinas, São Paulo, Brazil Hytron e Hydrogen Technologies, Campinas, São Paulo, Brazil d CENEH e Brazilian Reference Center for Hydrogen Energy (Unicamp), Campinas, São Paulo, Brazil e NIPE e Interdisciplinary Center of Energy Planning (Unicamp), Campinas, São Paulo, Brazil b c
a r t i c l e i n f o
a b s t r a c t
Article history: Received 14 December 2011 Accepted 5 March 2012 Available online 28 March 2012
This work presents a technical and economic analysis of a power supply system based on a 5 kW Proton Exchange Membrane Fuel Cell (PEMFC) fed with hydrogen produced by the auto-thermal reforming of ethanol. The technical analysis is based on unpublished experimental data obtained from the prototype of an ethanol reformer developed by the Hydrogen Laboratory at Unicamp and by Hytron, which represents the state-of-the-art of this technology in Brazil. The results point out that the cost of the hydrogen produced by the ethanol reformer prototype is lower than the hydrogen prices in the Brazilian market, and that the cost of the electricity produced by that hydrogen in a PEMFC is lower than other alternative sources of energy, except when compared to the electricity available in grid-connected power system in Brazil. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Hydrogen Fuel cell PEMFC Ethanol reforming Technical and economical analysis Renewable and alternative energy
1. Introduction Currently, there is a great concern related to the increase of greenhouse gas emissions and its possible consequences on global warming. This factor, associated to the increasing needs for energy
Abbreviations: ATR, Auto-thermal reforming; CAEE, Annual electric energy cost [US$]; CAethanol, Annual ethanol cost [US$]; CcATR, Replacement cost of the ATR catalyst [US$]; CcLTS, Replacement cost of the LTS catalyst [US$]; CH2, Maximum hydrogen consumption per hour in the PEMFC [kg/h]; CHCaC, Total annual cost of hydrogen for electric energy generation [US$]; CmEE, Maximum consumption of electric energy per hour in the reformer [kWh]; Cmethanol, Maximum ethanol consumption per hour in the reformer [L/h]; Cptethanol, Cost of the ethanol pretreatment [US$]; Cptwater, Cost of the process water pre-treatment [US$]; CtEE, Total electric power consumption in a year [kWh]; Ctethanol, Total ethanol consumption in a year [L]; FPEE, Electric energy generation factor [kWh/kg]; FV, Future value; GEECaC, Annual generation of electricity by the fuel cell coupled to the reformer [kWh]; IRR, Internal Rate of Return; LH2-Unicamp, Hydrogen Laboratory at Universidade Estadual de Campinas; LHV, Low Heating Value [kJ/L]; LTS, Low temperature shift; NPV, Net Present Value; PEMFC, Proton Exchange Membrane Fuel Cell; PH2, Mass production of hydrogen per hour [kg/h]; PSA, Pressure Swing Adsorption; PV, Present value; STP, Standard Temperature and Pressure (273.15 K and 101,325 kPa). * Corresponding author. Laboratório de Hidrogênio, Instituto de Física (IFGW), Universidade Estadual de Campinas (Unicamp), Campinas, SP, Brazil. Tel.: þ55 19 3521 2073. E-mail address: cspinto@ifi.unicamp.br (C.S. Pinto). 0960-1481/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.renene.2012.03.006
security, increasing oil prices and increasing energy demand, mainly from developing countries, has encouraged the use of renewable sources of energy [1]. The high potential of renewable sources in the world presents an opportunity to reduce environmental impacts, such as in Brazil where the hydraulic, solar and wind potential is high. Hydroelectricity accounts with 77% of the electricity production in Brazil and almost 50% of the total energy demand comes from other renewable sources, such as bioethanol and biomass [2]. Ethanol produced from sugar cane presents a very competitive price compared to gasoline as a fuel for light vehicles. In this scenario, the use of hydrogen as an energy vector produced from bioethanol has been considered one of the most efficient and environmentally friendly ways to store and produce electricity on demand when associated to the use of PEMFCs. In Brazil, several isolated communities lack power supply from the grid although there is ethanol available at short distance. The costs to connect those communities to the grid are unviable [3]. An alternative and local distributed generation system is indicated in these cases and to avoid diesel power generators, which causes local pollution and greenhouse gas emissions [4], or PV-battery systems, whose batteries need frequent replacement [5]. Therefore, the chain bioethanol to hydrogen to power by means of a reformer and a PEMFC seems a promising technology [3].
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Accordingly, the Hydrogen Laboratory at Unicamp, in a partnership with Hytron,1 has been developing a prototype of an ethanol reformer to produce hydrogen to be used in a 5 kW PEMFC. The main objectives of this article are to present: i) the operational data of the ethanol reformer prototype; ii) a technical and economic analysis of the equipment; iii) the hydrogen cost; iv) the electricity cost produced with this hydrogen in a PEMFC for stationary and distributed generation of electricity.
Fig. 1. The proposed system to supply electricity from ethanol reforming.
consumption; ii) Electricity consumption; iii) Cost of materials replacement; iii) Capacity and availability factors; iv) Ethanol and electricity costs; v) Labor force costs.
2. Overview of the system The system to supply electricity is composed basically by 3 subsystems: the ethanol reformer, the fuel cell and the electricity conditioning system (Fig. 1). A GenCore PEMFC with nominal power of 5 kW was employed. It requires 3.7 m3/h of hydrogen with a concentration of carbon monoxide below 30 mmol/mol. Therefore, the ethanol reformer prototype should satisfy those requirements (Fig. 2). The electricity conditioning system integrated to this fuel cell is designed for off-grid stationary applications, and composed of a battery pack and an inverter. The battery pack is used as a buffer, storing electricity generated by the PEMFC and supplying power to the inverter according to the load. The battery pack is composed of 10 12 V and 45 Ah lead-acid batteries connected in series, adding up to 120 VDC. Finally, the 6 kVA/4.8 kW sine wave inverter converts the input voltage from the battery pack to 220 VAC, 60 Hz, single-phase. The ethanol reformer was designed with 4 subsystems: the fuel processing module, the reforming gas treatment module, purification module and control module (Fig. 3). 3. Economic investment analysis According to the economic analysis of investments by Souza (2003) [6], it is considered incomes and expenditures within a timeline. The applied approach is related to the present value, due to the need of a decision to be taken on the initial or “zero” moment. In this study, the total profitability of the project was analyzed, considering the income and expenses throughout a certain period of time [7]. However, it is necessary to observe that this study aims at an economic evaluation of the use of a certain technology rather than making decisions regarding distinctive financial investments (comparative analysis). 4. Economic analysis of the auto-thermal ethanol reforming system 4.1. Parameters of the auto-thermal ethanol reforming system To calculate the hydrogen cost produced by the ethanol reformer the following parameters were quantified: i) Investment cost related to the reformer purchase; ii) Operation and maintenance costs; iii) Feedstock costs. The actual investment cost is the price of the ethanol reformer informed by Hytron in May 2008, US$ 116,280.00 [1]. Table 1 presents the technical characteristics of the reformer to feed the PEMFC. In order to establish the operation and maintenance costs of the reformer the following items were assessed: i) Ethanol
1 Hytron e Hydrogen Technologies is a spin-off company of the Hydrogen Laboratory at Unicamp, established in 2004, with its headquarters in Campinas-SP. (www.hytron.com.br).
4.2. Ethanol consumption Theoretically, the auto-thermal ethanol reforming process assumes a ratio of ethanol consumption to hydrogen production equal to 0.75 L/m3 [8]. However, the reformer consumes 1.54 L of ethanol to produce 5.5 m3 of syngas. Chromatography analysis showed that the syngas contains approximately 30% mol/mol of hydrogen; then the ethanol to hydrogen production ratio is 1.03 L/ m3 or 12.51 L/kg [1]. The mass production of hydrogen per hour for a consumption of 1.54 L/h of ethanol (PH2) is 0.123 kg/h. The experimental data regarding the PEMFC reveal that for the maximum production of energy, 5.42 kWh/h, the consumption of hydrogen (CH2) is 0.35 kg/h, equivalent to 4.4 L/h of ethanol (Cmethanol). 4.3. Electric energy consumption According to experimental data, for the maximum production of hydrogen the electric consumption of the reformer, CmEE, is 2.22 kWh, where 0.22 kWh correspond to the electric consumption of the fuel processing module and the control module. The 2.00 kWh remaining correspond to the electric consumption of the syngas compressor in the purification module.
4.4. Cost of materials replacement 4.4.1. Catalysts replacement cost The reformer prototype revealed that the spatial speeds in the catalysts were 30,000 h1 for the auto-thermal bed (ATR) and 15,000 h1 for the low temperature shift bed (LTS). According to these factors, the required volumes of catalysts were determined as 840 mL for the ATR and 1148 mL for the LTS. So, the costs for to the replacement cost of the ATR and LTS catalysts are CcATR ¼ US$ 401.86 and CcLTS ¼ US$ 803.72, respectively. The reformer was not tested uninterruptedly for a long time, so it is not possible to state the real lifetime of the catalysts. Considering that the lifetime of natural gas reformer catalysts is approximately 5 years [9], we assumed a conservative approach that the replacement of ATR and LTS catalysts should occur after 1 year (8600 h). 4.4.2. Cost of the ethanol pre-treatment (Cptethanol) and process water pre-treatment (Cptwater) For the ethanol pre-treatment, passage beds are connected in series. Predicted lifetime of theses beds are 6 months (4380 h). The unit costs of these elements are, respectively, US$ 7.91 and US$ 24.19. The components of the water purification process present a lifetime of 6 months of operation (4380 h). The unitary costs of the three elements are, respectively, US$ 7.91, US$ 24.19 and US$ 21.86. Table 2 presents a summary of the annual cost of replacement material.
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Fig. 2. Electricity supply system: (a) Ethanol reformer; (b) Fuel cell, DC/AC inverter and battery pack [1].
4.5. Availability and capacity factors The availability factor is the fraction of hours in a year that the plant is under operation. A 98% availability factor allows annually shutting down the plant 22 times during 8 h. The capacity factor of a power plant is the ratio between the actual output during a certain period of time and its output operating at full capacity. Concerning the reformer prototype, and using a conservative approach, the adopted capacity and availability factors were 90%. A period of 10 years was considered for the cost analysis. The economic calculation from Net Present Value (NPV) considers that the initial investment and the costs associated to the use of the technology happened in year zero. The reformer is expected to have a 10-year lifetime. 4.6. Cost of ethanol and electric power The average price of anhydrous ethanol2 in Brazil, without freight and taxes, is 0.371 US$/L [10]. The ethanol consumption at the reformer is 4.4 L/h. Considering the capacity and availability factors, the ethanol annual consumption is Ctethanol ¼ 31,221 L. Thus, the annual ethanol cost is CAethanol ¼ US$ 11,583.00. The price of electric power for the commercial sector in the southeast of Brazil is 0.128 US$/kWh [11]. Thus, considering the capacity and availability factors, the annual electric power consumption is CtEE ¼ 15,752 kWh. Finally, the annual electric energy cost is CAEE ¼ US$ 2016.00.
The costs estimated by the cash flow analysis for the application of the reformer are values related to the Present Value (VP) of the cash flow. Thus, it is possible to determine the amount necessary if all the expenses had to be made in year zero, considering a 10-year period (Table 3). Fig. 4 shows the percentage comparison of the values presented in Table 4
4.8. Hydrogen production cost A Flow Chart Analysis was used to determine the cost of the hydrogen produced by the ethanol reformer calculating the cost that results in a Net Present Value (NPV) of US$ 0.00 in ten years (Table 5). In this case, the cost is based on the fact that the reformer’s owner has a return of investment after applying taxes equal to the capital cost (discount rate). For this analysis, the taxes related to the hydrogen sales were not considered and the price of consumables, replacement materials and labor force were considered constant throughout the reformer’s life cycle. To determine the influence of the fixed and variable costs in the composition of the hydrogen cost, each component of the fixed and variable costs was individually equaled to zero and the new cost of the hydrogen was recalculated. This new hydrogen cost was subtracted from the initial cost (14.11 US$/kg). The results are presented in Table 6.
4.7. Annual maintenance and operation costs The annual maintenance and operation costs were considered to be 12% of the annual fuel (ethanol) cost. This is considered a standard value [10].
2 Anhydrous ethanol was used in order to avoid lower quality ethanol. However, for the application in this type of reformer, it is possible to consider the use of hydrated ethanol.
Fig. 3. Subsystems of the ethanol reformer.
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Table 1 Technical characteristics of the ethanol reformer.
Table 4 Results of the hydrogen cost from ethanol. 3.5 m3/h 99% mol/mol 50 mmol/mol 4.0 barg
Hydrogen production capacity: Hydrogen minimal content: Carbon monoxide maximum content: Hydrogen pressure:
Table 2 Cost of system’s replacement material. Annual cost of material replacement (US$) Item
Month
CcATR CcLTS Cptethanol Cptwater
12
e e 32.09 54.42
401.86 803.72 32.09 54.42
Item
401.86 803.72 64.19 108.84 1378.60
Individual value (US$)
Fixed cost Reformer Variable cost Ethanol cost Electricity cost Operation and Maintenance LTS catalyst replacement ATR catalyst replacement Water purification Ethanol purification Sub-total Total
116,280.00 70,798.31 12,380.20 7409. 46 4938.52 2716.19 663.04 394.40 99,300.11 215,580.11
5. Economic analysis of the electric power produced by the ethanol reformer connected to a fuel cell 5.1. Description of the parameters for the ethanol ATR reforming system To calculate the production cost of the electric power generated by a fuel cell, the following parameters were quantified: i. Investment cost related to the purchasing value of the components; ii. Cost of the hydrogen generated by the ethanol reformer; Reformer 54.0% 3.5%
Ethanol Cost
0.3%
Electricity Cost Ethanol Purification
2.3% LTS Catalyst Replacement 0.2% ATR Catalyst Replacement
5.8%
Water Purification 32.9%
116,280.00 10% 0.371 0.128 8.40 2483 12.5 90% 90% 20,200
Annual total
6
Table 3 Total cost of the ethanol reformer according to the present value of the cash flow for a period of 10 years.
1.2%
Basic assumptions Reformer price (US$) Discount rate Ethanol price (US$/L) Electric energy price (US$/kWh) Hydrogen production (kgH2/day) Hydrogen annual production (kgH2/year) Ethanol consumption factor (L of ethanol/kg of H2) Capacity factor Availability factor LHV ethanol (kJ/L)
Operation & Maintenance
Fig. 4. Percentage comparison of the values presented in the cash flow in Table 4.
Result Hydrogen cost (US$/kg) NPV
14.11 0.00
iii. Cost of the battery pack exchange; iv. Maintenance and operation cost. In order to define the investment cost, price quotations were carried out. Table 7 presents the initial investment cost with these components. 5.2. Cost of the hydrogen generated by the ethanol reformer Once the unitary cost of the hydrogen produced by the ethanol reformer is calculated (US$/kg), it is possible to determine the cost of the electric energy (US$/kWh) generated by the PEMFC. The annual production of electric power (FPEE) is given by the annual hydrogen production by the reformer, which is 2483 kg/ year, and by the fuel cell specific consumption. According to the experimental results of the fuel cell, each 0.35 kg of hydrogen generates 5.42 kWh; therefore FPEE is 15.5 kWh/kg. Using FPEE and the amount of hydrogen generated annually by the reformer, the electric energy generation capacity, GEECaC, is 38,487 kWh/year. The total cost of hydrogen consumed by the fuel cell is calculated by using the unitary cost of hydrogen generated by the reformer multiplied by the amount of hydrogen used by the fuel cell in one year (Table 5); therefore CHCaC ¼ US$ 35,035.13. 5.3. Cost of battery pack substitution The average lifetime for a battery pack in such application is around 4 years [8]. As the lifetime of the whole system is being considered as 10 years, 2 substitutions of the battery pack will be necessary. This substitution will take place in year 4 and year 8 (Table 8). 5.4. Maintenance and operation costs Considering that the components of this subsystem present a very low maintenance cost when compared to the hydrogen generation system, it was neglected [1]. Table 5 Composition of the hydrogen cost generated by the ethanol reformer (values updated by the discount rate of 10% a.a.). Cost in US$/kg of H2
ATR/LTS/PSA
H2 cost
14.11
Reformer Ethanol cost Electric power cost Operation and maintenance LTS catalyst replacement ATR catalyst replacement Water purification Ethanol purification
7.62 4.64 0.81 0.49 0.33 0.16 0.04 0.03
D.G. Lopes et al. / Renewable Energy 45 (2012) 205e212 Table 6 Cost with initial investment of the components for the generation of electric power. Item Fuel cell (5 kWa) Battery bank (12 V) Inverter (4.8 kW) Total a
Quantity (unity)
Unit price (US$)
Total cost (US$)
1 10 1
32,558.14 110.70 3255.81
32,558.14 1107.00 3255.81 36,920.95
209
Table 9 Composition of the electric energy cost. Cost in US$/kWh
CaC/B.P/Inverter
E.E.Cost
1.07
Cost with hydrogen Fuel cell Inverter Battery pack
0.91 0.13 0.01 0.01
Price of the fuel cell including import and transport taxes.
Table 7 Cost of the electric energy generation system according to the cash flow (updated values at 10% a.a.). Item
Individual value (US$)
Variable cost Hydrogen Fixed cost Initial investment: Fuel cell Inverter Battery pack Cost of two battery packs Sub-total Total
215,332.26
32,558.14 3255.81 1107.00 1272.49 38,193.45 253,525.68
Table 8 Results of the electric energy cost. Basic assumptions Initial investment (US$) Discount rate Annual cost with hydrogen (US$) Annual electric energy generated (kWh) Usage factor Availability factor
36,920.93 10% 30,035.13 38,494 90% 90%
Results Cost of generated electric energy (US$/kWh) NPV
1.07 0.00
Table 8 presents the summary of the costs determined by the cash flow analysis for the generation of electric energy, considering a 10-year lifetime. Fig. 5 shows the cost shares. 5.5. Calculation of the electric energy production cost The unitary cost of electric energy was determined by equaling the NPV to zero for the PEMFC system in ten years of operation. This leads to the cost at which the system carries out a return of investment equal to the capital cost (discount rate). The assumed values for the Flow Chart Analysis are presented in Table 9.
1.3% 0.9% Fuel Cell 12.6%
84.8%
Batteries Inverter Hydrogen Cost
In this analysis, the taxes related to the sales of electric energy were not considered and the prices of consumables and replacement materials were considered constant through the system lifetime. The influence of factors in the final cost of electric energy was calculated following the same criterion used for the cost analysis of the hydrogen produced by the ethanol reformer. After zeroing the value of each item in Table 8, the electricity cost was calculated and subtracted from the value found in the final result (1.07 US$/kWh) showed in Table 9 and Fig. 5. 6. Comparative analysis of the cost of hydrogen produced by the ethanol reformer To evaluate the cost of the hydrogen produced by the ethanol reformer under the conditions established in this study a comparative analysis was carried out with the following “products”: i) the market price of hydrogen 4.03 sold in cylinders,4 available in the region of Campinas, SP; ii) the cost of hydrogen produced by alkaline water electrolysis [12]; and iii) the production cost presented by [9]. Fig. 6 shows the comparison of the hydrogen price and costs. According to the quotation provided by a traditional gas company in May 2008, the hydrogen price available at Unicamp in Campinas, SP, was 139.02 US$/kg [1]. Fig. 6 also indicates that although the ethanol reformer is a prototype, its hydrogen production cost is competitive with the market price in the region of Campinas, SP. The market price means the production cost plus all the taxes and profits of the production and commercialization chains. Market production costs are unavailable. Regarding the alkaline water electrolysis process [12], there is a small difference of cost between these two processes despite the reformer is 17 times smaller. The cost of hydrogen generated by the ethanol reformer is still around 10% lower than the cost of hydrogen produced by water electrolysis. However, when compared to the production cost from natural gas reforming presented by [9], there is a large influence not only from the production scale of hydrogen but also from the low cost of natural gas. Even with a production around 16 times larger than the ethanol reformer, the production cost of hydrogen in this case is approximately 4.5 times lower for natural gas reforming. Evaluating the cost of hydrogen produced by ethanol reforming and the economic feasibility of selling this hydrogen to the market, in the region of Campinas, SP, a calculation of the Internal Rate of Return (IRR) and the payback period was carried out. Also, the hydrogen price and the payback period were calculated for the IRR assessment at 100%, 75%, 50% and 25% (Figs. 7 and 8). According to Fig. 7, the ethanol reformer IRR for the hydrogen market price is 273%. Analyzing the payback for this IRR, it is observed in Fig. 8 that the initial investment in the ethanol
3
Hydrogen at 99.99%mol/mol purity. Cylinder with 7.2 m3of gas, at a pressure of 16,475.17 kPa (168 kgf/cm2) and gross weight of 68.5 kg. 4
Fig. 5. Cost share presented in the cash flow of Table 8.
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160.00 139.02
140.00
120.00 Market Price of H2 (4.0 T) Cost (US$/kg)
100.00 Cost of hydrogen by electrolysis; 4,9 kg/h (FERREIRA, 2008)
80.00
Cost by Ethanol Reformer: 0,3 kg/h
60.00
Cost of prodction by NG Reformer; 4,6 kg/h (DOE 2002)
40.00 15.35
20.00
14.11 3.15
0.00
Fig. 6. Comparison of the hydrogen cost produced by the ethanol reformer.
160.00 139.02 Hydrogen Price (US$/kg)
140.00 120.00 100.00
86.51
80.00 65.58 60.00 44.19 40.00 24.19 20.00 0.00 0%
25%
50%
75% 100% 125% 150% 175% 200% 225% 250% 275% 300% IRR
Fig. 7. IRR for the hydrogen market price and the price of hydrogen produced by the ethanol reformer.
48
Payback (Months)
44 36
24 24
16 12
12
5 0 0%
25%
50%
75% 100% 125% 150% 175% 200% 225% 250% 275% 300% IRR
Fig. 8. Payback period for the IRR related to the market price of hydrogen and for the IRR at 100%, 75%, 50% and 25%.
reformer would be paid in only 5 months. On the other hand, considering the lowest IRR presented in the figure, at 25%, the hydrogen price without taxes5 would be 24.19 US$/kg and the payback 44 months.
5 It’s worth highlighting that the values considered for the IRR and payback calculation do not take into account the taxes related to the hydrogen produced by the reformer, except for the market price of hydrogen for the region of Campinas-SP-Brazil.
This comparative analysis shows that the technology for hydrogen production by ethanol reforming is promising. Although it is still a prototype with a production capacity of only 0.3 kg/h of hydrogen, the costs at 14.11 US$/kg are highly competitive, especially when compared with small electrolysis systems fed by secondary power, at about 48.70 US$/kg in Brazil [13]. Moreover, an important cost reduction is expected with an increase in the production scale, in the technology learning curve, and in the reformer’s capacity, for example, prototypes of 4.0 kg/h of hydrogen.
D.G. Lopes et al. / Renewable Energy 45 (2012) 205e212 1.70
PhV + Electrolysis + Fuel Cell*
3
1.60
Etanol Reformer + Fuel Cell
1.50
Electricity Cost
1.40
Discount Rate
Cost (US$/kWh)
2.5 Cost (US$/kWh)
Reformer Price
PhV + Battery*
2.73
1.95
2
211
Ethanol Cost
Capacity de Factor
1.30 1.20 1.10 1.00
1.5 0.90
1.07
0.80
1
0.70
0.5
-50%
-40%
-30%
-20%
-10%
0%
10%
20%
30%
40%
50%
Percent Variation
0
Fig. 11. Sensitivity analysis for the electric power cost. Fig. 9. Comparative analysis of the electric energy cost.
7. Comparative cost of the electricity
7.1. Sensitivity analysis
In order to contextualize the power cost from the fuel cell system, a comparative analysis was carried out between two systems: the first consisting of a set of photovoltaic panels linked to a battery pack and the second consisting of a set of photovoltaic panels linked to a water electrolyzer and a PEMFC. The choice of these two systems was due to their current niche applications, mainly in isolated areas, where the reforming system could also be employed. The electricity produced by a fuel cell system using hydrogen generated by an ethanol reformer is the lowest among the technologies that were presented [8], and the electricity cost is approximately 2.5 lower than the electricity produced by the system with photovoltaic panels, electrolyzer and fuel cell (Fig. 9). On the other hand, the electric cost from the ethanol reforming system associated with a PEMFC is very high (7.8 times higher) when compared to the sales price of electric power in the gridconnected power system for the residential segment in Brazil, which is 0.138 US$/kWh [11].
The sensitivity analysis for the cost of the hydrogen generated by the ethanol reformer and for the electricity cost were carried out based on the reformer price, ethanol cost, electricity cost, discount rate and capacity factor (Figs. 10 and 11). The capacity factor of the ethanol reformer is the component that shows the highest sensitivity for the hydrogen cost (Figs. 10 and 11). Therefore, it is necessary to make its value as close as possible to the unit, which means a system operation with very few interruptions. In the calculation of the hydrogen cost, the value of the capacity factor was assumed to be equal 0.9. However, it is necessary to carry out long trials with the ethanol reformer to obtain the actual figure. Among the other factors, the price of the ethanol reformer represents the highest contribution to the hydrogen cost. A reduction of the reformer price by 50% would reduce the hydrogen cost by 27% (from 14.11 to 10.23 US$/kg of H2) and the electricity cost by 26% (from 1.07 to 0.79 US$/kWh). Although they are less significant, the contributions of ethanol and electric energy consumption by the ethanol reformer reveals that an increase in the reformer efficiency would result in a cost reduction of the produced hydrogen and consequently of the generated electric energy.
Cost (US$/kg)
24.00 23.00
Reformer Price
22.00
Ethanol Cost
21.00
Electricity Cost
20.00
Discount Rate
19.00
Capacity de Factor
8. Conclusions
18.00 17.00 16.00 15.00 14.00 13.00 12.00 11.00 10.00 9.00 8.00 50%
40%
30%
20%
10%
0%
10%
20%
30%
40%
50%
Percent Variation Fig. 10. Sensitivity analysis for the cost of hydrogen produced by the ethanol reformer.
This study presents a technical and economic feasibility analysis of an ethanol reformer in Brazil for the production of hydrogen to feed a PEMFC. The hydrogen cost from ethanol reforming is 14.11 US$/kg, which is lower than current market prices, about 139.00 US$/kg. According to the comparative analysis, the ethanol reforming seems promising, although this system is a small prototype. Moreover, cost reductions are expected since the technology is under development. Hydrogen prices in the market vary significantly. Prices presented in this study refer to hydrogen supplied at small scale and with required quality for PEMFC. Furthermore, these values refer to current prices, which include taxes and fees, profits, etc. Therefore, ethanol reforming systems to produce hydrogen for applications around 200 kg/month can be economically viable. Regarding the power generated by a PEMFC associated to the ethanol reformer, the reference value is 1.07 US$/kWh. This is around 2.5 times lower than the electricity cost obtained by
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electrolytic hydrogen produced by photovoltaic panels. On the other hand, this reference value is almost 8 times higher than the electric energy supplied by the grid-connected power system in the southeast region of Brazil (0.138 US$/kWh). However, the present system can be competitive when compared to other alternatives that are also under development. The sensitivity analysis shows that the capacity factor of the ethanol reformer presents the highest impact on hydrogen and electricity costs. Therefore, this characteristic of the system should be prioritized, that is, its operation should be continuous with few interruptions. Ethanol reforming consists on an interesting alternative for the renewable production of hydrogen, not only as a chemical feedstock for the industry, but also for the production of electricity in selected applications using fuel cells. Acknowledgments The authors would like to acknowledge the support of the Hydrogen Laboratory at Unicamp, Hytron e Hydrogen Technologies, NIPE/Unicamp, the Brazilian Reference Center for Hydrogen Energy and CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior). * Cristiano da Silva Pinto, Phone þ55 19 3521 2073, cspinto@ifi.unicamp.br. References [1] Lopes Daniel G. Technical And Economical Analysis Of The Introduction Of The Technology Of Hydrogen Production From Ethanol Reforming For The Generation Of Electric Energy With Fuel Cells. Campinas, Faculdade de Engenharia Mecânica, Universidade Estadual de Campinas; 2009. p. 110 thesis (Doctorate).
[2] BEN, Balanço Energético Nacional. Available at: www.ben.epe.gov.br. accessed on 20.08.2008. [3] Lopes Davi G. O Impacto da Energia Elétrica Proveniente do Reformador de Etanol e Células a Combustível: Cenário para a Promoção do Desenvolvimento Socioambiental da Comunidade “Pico do Amor”/MT. Campinas, Faculdade de Engenharia Mecânica, Universidade Estadual de Campinas; 2009. p. 97 Dissertation (MSc). [4] Camargo JC. Medidas do Potencial Fotovoltaico na Região das Bacias dos Rios Piracicaba e Capivari. Campinas, Faculdade de Engenharia Mecânica, Universidade Estadual de Campinas; 2000. p. 108 Dissertation (MSc). [5] Furlan AL. Comparative analysis of photovoltaic power storage systems by means of batteries and hydrogen in remote areas of the Amazon region of Brazil. p. 116 Dissertation (MSc). FEM - UNICAMP; 2008. [6] Souza AB. de, Projetos de Investimentos de Capital: Elaboração, análise, tomada de decisão. São Paulo: Atlas; 2003. [7] Kaplan S. Energy economics e quantitative methods for energy and environmental decisions. Nova York: McGraw Hill; 1983. [8] Marim Neto AJ, Lopes DG, Camargo JC, Silva EP, Neves JR NP. Simulação do processo de reforma autotérmica de etanol para a produção de hidrogênio em unidade integrada. Article present in III WICaC. Available at: http://www.ifi. unicamp.br/ceneh/WICaC2006/PDF/11-AntonioMarin.pdf. [9] DOE (USA). Department of energy cost and performance comparison of stationary hydrogen fueling Appliances. The Hydrogen Program Office of Power Technologies e U.S Department of Energy. Available at: http://www1. eere.energy.gov/hydrogenandfuelcells/pdfs/32405b2.pdf; 2002. accessed on 12.11.2008. [10] CEPEA, Centro de Estudos Avançados em Economia Aplicada. Available at: http://www.cepea.esalq.usp.br/alcool/?id_page¼407. accessed on 22.10.2008. [11] SAD Sistema. de Apoio a Decisão e ANEEL. Período de agosto de. Available at:, http://rad.aneel.gov.br/reportserverSAD?%2fSAD_REPORTS% 2fSAMP_TarifaMedCConsumoRegiao&rs:Command¼Render; 2008. accessed on 23.10.2008. [12] Ferreira PFP. Infrastructure for Hydrogen Energy Use: Fueling Stations for Fuel Cell Vehicles. p. 148 thesis (Doctorate). FEM e UNICAMP; 2007. [13] Pinto CS, Silva EP, Neves Jr NP, Miguel M, Villasboa JWB. Itaipu hydroelectric power plant and its experimental hydrogen production unity. In: ECOS 2009-22nd international conference on efficiency, cost, optimization, simulation, and environmental impact of energy systems, 2009, Foz do Iguaçu. Proceedings of ECOS2009, vol. 1. Rio de Janeiro: Associação Brasileira de Engenharia e Ciências Mecânicas - ABCM; 2009. p. 1639e46.
Contents lists available at SciVerse ScienceDirect
Renewable Energy journal homepage: www.elsevier.com/locate/renene
Technical and economic analysis of a power supply system based on ethanol reforming and PEMFC Daniel G. Lopes c, e, E.P. da Silva b, d, e, C.S. Pinto a, b, c, *, N.P. Neves Jr. b, d, J.C. Camargo c, e, P.F.P. Ferreira c, e, A.L. Furlan a, e, Davi G. Lopes a, e a
Faculdade de Engenharia Mecânica (FEM), Universidade Estadual de Campinas (Unicamp), Campinas, São Paulo, Brazil Laboratório de Hidrogênio, Instituto de Física (IFGW), Universidade Estadual de Campinas (Unicamp), Campinas, São Paulo, Brazil Hytron e Hydrogen Technologies, Campinas, São Paulo, Brazil d CENEH e Brazilian Reference Center for Hydrogen Energy (Unicamp), Campinas, São Paulo, Brazil e NIPE e Interdisciplinary Center of Energy Planning (Unicamp), Campinas, São Paulo, Brazil b c
a r t i c l e i n f o
a b s t r a c t
Article history: Received 14 December 2011 Accepted 5 March 2012 Available online 28 March 2012
This work presents a technical and economic analysis of a power supply system based on a 5 kW Proton Exchange Membrane Fuel Cell (PEMFC) fed with hydrogen produced by the auto-thermal reforming of ethanol. The technical analysis is based on unpublished experimental data obtained from the prototype of an ethanol reformer developed by the Hydrogen Laboratory at Unicamp and by Hytron, which represents the state-of-the-art of this technology in Brazil. The results point out that the cost of the hydrogen produced by the ethanol reformer prototype is lower than the hydrogen prices in the Brazilian market, and that the cost of the electricity produced by that hydrogen in a PEMFC is lower than other alternative sources of energy, except when compared to the electricity available in grid-connected power system in Brazil. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Hydrogen Fuel cell PEMFC Ethanol reforming Technical and economical analysis Renewable and alternative energy
1. Introduction Currently, there is a great concern related to the increase of greenhouse gas emissions and its possible consequences on global warming. This factor, associated to the increasing needs for energy
Abbreviations: ATR, Auto-thermal reforming; CAEE, Annual electric energy cost [US$]; CAethanol, Annual ethanol cost [US$]; CcATR, Replacement cost of the ATR catalyst [US$]; CcLTS, Replacement cost of the LTS catalyst [US$]; CH2, Maximum hydrogen consumption per hour in the PEMFC [kg/h]; CHCaC, Total annual cost of hydrogen for electric energy generation [US$]; CmEE, Maximum consumption of electric energy per hour in the reformer [kWh]; Cmethanol, Maximum ethanol consumption per hour in the reformer [L/h]; Cptethanol, Cost of the ethanol pretreatment [US$]; Cptwater, Cost of the process water pre-treatment [US$]; CtEE, Total electric power consumption in a year [kWh]; Ctethanol, Total ethanol consumption in a year [L]; FPEE, Electric energy generation factor [kWh/kg]; FV, Future value; GEECaC, Annual generation of electricity by the fuel cell coupled to the reformer [kWh]; IRR, Internal Rate of Return; LH2-Unicamp, Hydrogen Laboratory at Universidade Estadual de Campinas; LHV, Low Heating Value [kJ/L]; LTS, Low temperature shift; NPV, Net Present Value; PEMFC, Proton Exchange Membrane Fuel Cell; PH2, Mass production of hydrogen per hour [kg/h]; PSA, Pressure Swing Adsorption; PV, Present value; STP, Standard Temperature and Pressure (273.15 K and 101,325 kPa). * Corresponding author. Laboratório de Hidrogênio, Instituto de Física (IFGW), Universidade Estadual de Campinas (Unicamp), Campinas, SP, Brazil. Tel.: þ55 19 3521 2073. E-mail address: cspinto@ifi.unicamp.br (C.S. Pinto). 0960-1481/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.renene.2012.03.006
security, increasing oil prices and increasing energy demand, mainly from developing countries, has encouraged the use of renewable sources of energy [1]. The high potential of renewable sources in the world presents an opportunity to reduce environmental impacts, such as in Brazil where the hydraulic, solar and wind potential is high. Hydroelectricity accounts with 77% of the electricity production in Brazil and almost 50% of the total energy demand comes from other renewable sources, such as bioethanol and biomass [2]. Ethanol produced from sugar cane presents a very competitive price compared to gasoline as a fuel for light vehicles. In this scenario, the use of hydrogen as an energy vector produced from bioethanol has been considered one of the most efficient and environmentally friendly ways to store and produce electricity on demand when associated to the use of PEMFCs. In Brazil, several isolated communities lack power supply from the grid although there is ethanol available at short distance. The costs to connect those communities to the grid are unviable [3]. An alternative and local distributed generation system is indicated in these cases and to avoid diesel power generators, which causes local pollution and greenhouse gas emissions [4], or PV-battery systems, whose batteries need frequent replacement [5]. Therefore, the chain bioethanol to hydrogen to power by means of a reformer and a PEMFC seems a promising technology [3].
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Accordingly, the Hydrogen Laboratory at Unicamp, in a partnership with Hytron,1 has been developing a prototype of an ethanol reformer to produce hydrogen to be used in a 5 kW PEMFC. The main objectives of this article are to present: i) the operational data of the ethanol reformer prototype; ii) a technical and economic analysis of the equipment; iii) the hydrogen cost; iv) the electricity cost produced with this hydrogen in a PEMFC for stationary and distributed generation of electricity.
Fig. 1. The proposed system to supply electricity from ethanol reforming.
consumption; ii) Electricity consumption; iii) Cost of materials replacement; iii) Capacity and availability factors; iv) Ethanol and electricity costs; v) Labor force costs.
2. Overview of the system The system to supply electricity is composed basically by 3 subsystems: the ethanol reformer, the fuel cell and the electricity conditioning system (Fig. 1). A GenCore PEMFC with nominal power of 5 kW was employed. It requires 3.7 m3/h of hydrogen with a concentration of carbon monoxide below 30 mmol/mol. Therefore, the ethanol reformer prototype should satisfy those requirements (Fig. 2). The electricity conditioning system integrated to this fuel cell is designed for off-grid stationary applications, and composed of a battery pack and an inverter. The battery pack is used as a buffer, storing electricity generated by the PEMFC and supplying power to the inverter according to the load. The battery pack is composed of 10 12 V and 45 Ah lead-acid batteries connected in series, adding up to 120 VDC. Finally, the 6 kVA/4.8 kW sine wave inverter converts the input voltage from the battery pack to 220 VAC, 60 Hz, single-phase. The ethanol reformer was designed with 4 subsystems: the fuel processing module, the reforming gas treatment module, purification module and control module (Fig. 3). 3. Economic investment analysis According to the economic analysis of investments by Souza (2003) [6], it is considered incomes and expenditures within a timeline. The applied approach is related to the present value, due to the need of a decision to be taken on the initial or “zero” moment. In this study, the total profitability of the project was analyzed, considering the income and expenses throughout a certain period of time [7]. However, it is necessary to observe that this study aims at an economic evaluation of the use of a certain technology rather than making decisions regarding distinctive financial investments (comparative analysis). 4. Economic analysis of the auto-thermal ethanol reforming system 4.1. Parameters of the auto-thermal ethanol reforming system To calculate the hydrogen cost produced by the ethanol reformer the following parameters were quantified: i) Investment cost related to the reformer purchase; ii) Operation and maintenance costs; iii) Feedstock costs. The actual investment cost is the price of the ethanol reformer informed by Hytron in May 2008, US$ 116,280.00 [1]. Table 1 presents the technical characteristics of the reformer to feed the PEMFC. In order to establish the operation and maintenance costs of the reformer the following items were assessed: i) Ethanol
1 Hytron e Hydrogen Technologies is a spin-off company of the Hydrogen Laboratory at Unicamp, established in 2004, with its headquarters in Campinas-SP. (www.hytron.com.br).
4.2. Ethanol consumption Theoretically, the auto-thermal ethanol reforming process assumes a ratio of ethanol consumption to hydrogen production equal to 0.75 L/m3 [8]. However, the reformer consumes 1.54 L of ethanol to produce 5.5 m3 of syngas. Chromatography analysis showed that the syngas contains approximately 30% mol/mol of hydrogen; then the ethanol to hydrogen production ratio is 1.03 L/ m3 or 12.51 L/kg [1]. The mass production of hydrogen per hour for a consumption of 1.54 L/h of ethanol (PH2) is 0.123 kg/h. The experimental data regarding the PEMFC reveal that for the maximum production of energy, 5.42 kWh/h, the consumption of hydrogen (CH2) is 0.35 kg/h, equivalent to 4.4 L/h of ethanol (Cmethanol). 4.3. Electric energy consumption According to experimental data, for the maximum production of hydrogen the electric consumption of the reformer, CmEE, is 2.22 kWh, where 0.22 kWh correspond to the electric consumption of the fuel processing module and the control module. The 2.00 kWh remaining correspond to the electric consumption of the syngas compressor in the purification module.
4.4. Cost of materials replacement 4.4.1. Catalysts replacement cost The reformer prototype revealed that the spatial speeds in the catalysts were 30,000 h1 for the auto-thermal bed (ATR) and 15,000 h1 for the low temperature shift bed (LTS). According to these factors, the required volumes of catalysts were determined as 840 mL for the ATR and 1148 mL for the LTS. So, the costs for to the replacement cost of the ATR and LTS catalysts are CcATR ¼ US$ 401.86 and CcLTS ¼ US$ 803.72, respectively. The reformer was not tested uninterruptedly for a long time, so it is not possible to state the real lifetime of the catalysts. Considering that the lifetime of natural gas reformer catalysts is approximately 5 years [9], we assumed a conservative approach that the replacement of ATR and LTS catalysts should occur after 1 year (8600 h). 4.4.2. Cost of the ethanol pre-treatment (Cptethanol) and process water pre-treatment (Cptwater) For the ethanol pre-treatment, passage beds are connected in series. Predicted lifetime of theses beds are 6 months (4380 h). The unit costs of these elements are, respectively, US$ 7.91 and US$ 24.19. The components of the water purification process present a lifetime of 6 months of operation (4380 h). The unitary costs of the three elements are, respectively, US$ 7.91, US$ 24.19 and US$ 21.86. Table 2 presents a summary of the annual cost of replacement material.
D.G. Lopes et al. / Renewable Energy 45 (2012) 205e212
207
Fig. 2. Electricity supply system: (a) Ethanol reformer; (b) Fuel cell, DC/AC inverter and battery pack [1].
4.5. Availability and capacity factors The availability factor is the fraction of hours in a year that the plant is under operation. A 98% availability factor allows annually shutting down the plant 22 times during 8 h. The capacity factor of a power plant is the ratio between the actual output during a certain period of time and its output operating at full capacity. Concerning the reformer prototype, and using a conservative approach, the adopted capacity and availability factors were 90%. A period of 10 years was considered for the cost analysis. The economic calculation from Net Present Value (NPV) considers that the initial investment and the costs associated to the use of the technology happened in year zero. The reformer is expected to have a 10-year lifetime. 4.6. Cost of ethanol and electric power The average price of anhydrous ethanol2 in Brazil, without freight and taxes, is 0.371 US$/L [10]. The ethanol consumption at the reformer is 4.4 L/h. Considering the capacity and availability factors, the ethanol annual consumption is Ctethanol ¼ 31,221 L. Thus, the annual ethanol cost is CAethanol ¼ US$ 11,583.00. The price of electric power for the commercial sector in the southeast of Brazil is 0.128 US$/kWh [11]. Thus, considering the capacity and availability factors, the annual electric power consumption is CtEE ¼ 15,752 kWh. Finally, the annual electric energy cost is CAEE ¼ US$ 2016.00.
The costs estimated by the cash flow analysis for the application of the reformer are values related to the Present Value (VP) of the cash flow. Thus, it is possible to determine the amount necessary if all the expenses had to be made in year zero, considering a 10-year period (Table 3). Fig. 4 shows the percentage comparison of the values presented in Table 4
4.8. Hydrogen production cost A Flow Chart Analysis was used to determine the cost of the hydrogen produced by the ethanol reformer calculating the cost that results in a Net Present Value (NPV) of US$ 0.00 in ten years (Table 5). In this case, the cost is based on the fact that the reformer’s owner has a return of investment after applying taxes equal to the capital cost (discount rate). For this analysis, the taxes related to the hydrogen sales were not considered and the price of consumables, replacement materials and labor force were considered constant throughout the reformer’s life cycle. To determine the influence of the fixed and variable costs in the composition of the hydrogen cost, each component of the fixed and variable costs was individually equaled to zero and the new cost of the hydrogen was recalculated. This new hydrogen cost was subtracted from the initial cost (14.11 US$/kg). The results are presented in Table 6.
4.7. Annual maintenance and operation costs The annual maintenance and operation costs were considered to be 12% of the annual fuel (ethanol) cost. This is considered a standard value [10].
2 Anhydrous ethanol was used in order to avoid lower quality ethanol. However, for the application in this type of reformer, it is possible to consider the use of hydrated ethanol.
Fig. 3. Subsystems of the ethanol reformer.
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Table 1 Technical characteristics of the ethanol reformer.
Table 4 Results of the hydrogen cost from ethanol. 3.5 m3/h 99% mol/mol 50 mmol/mol 4.0 barg
Hydrogen production capacity: Hydrogen minimal content: Carbon monoxide maximum content: Hydrogen pressure:
Table 2 Cost of system’s replacement material. Annual cost of material replacement (US$) Item
Month
CcATR CcLTS Cptethanol Cptwater
12
e e 32.09 54.42
401.86 803.72 32.09 54.42
Item
401.86 803.72 64.19 108.84 1378.60
Individual value (US$)
Fixed cost Reformer Variable cost Ethanol cost Electricity cost Operation and Maintenance LTS catalyst replacement ATR catalyst replacement Water purification Ethanol purification Sub-total Total
116,280.00 70,798.31 12,380.20 7409. 46 4938.52 2716.19 663.04 394.40 99,300.11 215,580.11
5. Economic analysis of the electric power produced by the ethanol reformer connected to a fuel cell 5.1. Description of the parameters for the ethanol ATR reforming system To calculate the production cost of the electric power generated by a fuel cell, the following parameters were quantified: i. Investment cost related to the purchasing value of the components; ii. Cost of the hydrogen generated by the ethanol reformer; Reformer 54.0% 3.5%
Ethanol Cost
0.3%
Electricity Cost Ethanol Purification
2.3% LTS Catalyst Replacement 0.2% ATR Catalyst Replacement
5.8%
Water Purification 32.9%
116,280.00 10% 0.371 0.128 8.40 2483 12.5 90% 90% 20,200
Annual total
6
Table 3 Total cost of the ethanol reformer according to the present value of the cash flow for a period of 10 years.
1.2%
Basic assumptions Reformer price (US$) Discount rate Ethanol price (US$/L) Electric energy price (US$/kWh) Hydrogen production (kgH2/day) Hydrogen annual production (kgH2/year) Ethanol consumption factor (L of ethanol/kg of H2) Capacity factor Availability factor LHV ethanol (kJ/L)
Operation & Maintenance
Fig. 4. Percentage comparison of the values presented in the cash flow in Table 4.
Result Hydrogen cost (US$/kg) NPV
14.11 0.00
iii. Cost of the battery pack exchange; iv. Maintenance and operation cost. In order to define the investment cost, price quotations were carried out. Table 7 presents the initial investment cost with these components. 5.2. Cost of the hydrogen generated by the ethanol reformer Once the unitary cost of the hydrogen produced by the ethanol reformer is calculated (US$/kg), it is possible to determine the cost of the electric energy (US$/kWh) generated by the PEMFC. The annual production of electric power (FPEE) is given by the annual hydrogen production by the reformer, which is 2483 kg/ year, and by the fuel cell specific consumption. According to the experimental results of the fuel cell, each 0.35 kg of hydrogen generates 5.42 kWh; therefore FPEE is 15.5 kWh/kg. Using FPEE and the amount of hydrogen generated annually by the reformer, the electric energy generation capacity, GEECaC, is 38,487 kWh/year. The total cost of hydrogen consumed by the fuel cell is calculated by using the unitary cost of hydrogen generated by the reformer multiplied by the amount of hydrogen used by the fuel cell in one year (Table 5); therefore CHCaC ¼ US$ 35,035.13. 5.3. Cost of battery pack substitution The average lifetime for a battery pack in such application is around 4 years [8]. As the lifetime of the whole system is being considered as 10 years, 2 substitutions of the battery pack will be necessary. This substitution will take place in year 4 and year 8 (Table 8). 5.4. Maintenance and operation costs Considering that the components of this subsystem present a very low maintenance cost when compared to the hydrogen generation system, it was neglected [1]. Table 5 Composition of the hydrogen cost generated by the ethanol reformer (values updated by the discount rate of 10% a.a.). Cost in US$/kg of H2
ATR/LTS/PSA
H2 cost
14.11
Reformer Ethanol cost Electric power cost Operation and maintenance LTS catalyst replacement ATR catalyst replacement Water purification Ethanol purification
7.62 4.64 0.81 0.49 0.33 0.16 0.04 0.03
D.G. Lopes et al. / Renewable Energy 45 (2012) 205e212 Table 6 Cost with initial investment of the components for the generation of electric power. Item Fuel cell (5 kWa) Battery bank (12 V) Inverter (4.8 kW) Total a
Quantity (unity)
Unit price (US$)
Total cost (US$)
1 10 1
32,558.14 110.70 3255.81
32,558.14 1107.00 3255.81 36,920.95
209
Table 9 Composition of the electric energy cost. Cost in US$/kWh
CaC/B.P/Inverter
E.E.Cost
1.07
Cost with hydrogen Fuel cell Inverter Battery pack
0.91 0.13 0.01 0.01
Price of the fuel cell including import and transport taxes.
Table 7 Cost of the electric energy generation system according to the cash flow (updated values at 10% a.a.). Item
Individual value (US$)
Variable cost Hydrogen Fixed cost Initial investment: Fuel cell Inverter Battery pack Cost of two battery packs Sub-total Total
215,332.26
32,558.14 3255.81 1107.00 1272.49 38,193.45 253,525.68
Table 8 Results of the electric energy cost. Basic assumptions Initial investment (US$) Discount rate Annual cost with hydrogen (US$) Annual electric energy generated (kWh) Usage factor Availability factor
36,920.93 10% 30,035.13 38,494 90% 90%
Results Cost of generated electric energy (US$/kWh) NPV
1.07 0.00
Table 8 presents the summary of the costs determined by the cash flow analysis for the generation of electric energy, considering a 10-year lifetime. Fig. 5 shows the cost shares. 5.5. Calculation of the electric energy production cost The unitary cost of electric energy was determined by equaling the NPV to zero for the PEMFC system in ten years of operation. This leads to the cost at which the system carries out a return of investment equal to the capital cost (discount rate). The assumed values for the Flow Chart Analysis are presented in Table 9.
1.3% 0.9% Fuel Cell 12.6%
84.8%
Batteries Inverter Hydrogen Cost
In this analysis, the taxes related to the sales of electric energy were not considered and the prices of consumables and replacement materials were considered constant through the system lifetime. The influence of factors in the final cost of electric energy was calculated following the same criterion used for the cost analysis of the hydrogen produced by the ethanol reformer. After zeroing the value of each item in Table 8, the electricity cost was calculated and subtracted from the value found in the final result (1.07 US$/kWh) showed in Table 9 and Fig. 5. 6. Comparative analysis of the cost of hydrogen produced by the ethanol reformer To evaluate the cost of the hydrogen produced by the ethanol reformer under the conditions established in this study a comparative analysis was carried out with the following “products”: i) the market price of hydrogen 4.03 sold in cylinders,4 available in the region of Campinas, SP; ii) the cost of hydrogen produced by alkaline water electrolysis [12]; and iii) the production cost presented by [9]. Fig. 6 shows the comparison of the hydrogen price and costs. According to the quotation provided by a traditional gas company in May 2008, the hydrogen price available at Unicamp in Campinas, SP, was 139.02 US$/kg [1]. Fig. 6 also indicates that although the ethanol reformer is a prototype, its hydrogen production cost is competitive with the market price in the region of Campinas, SP. The market price means the production cost plus all the taxes and profits of the production and commercialization chains. Market production costs are unavailable. Regarding the alkaline water electrolysis process [12], there is a small difference of cost between these two processes despite the reformer is 17 times smaller. The cost of hydrogen generated by the ethanol reformer is still around 10% lower than the cost of hydrogen produced by water electrolysis. However, when compared to the production cost from natural gas reforming presented by [9], there is a large influence not only from the production scale of hydrogen but also from the low cost of natural gas. Even with a production around 16 times larger than the ethanol reformer, the production cost of hydrogen in this case is approximately 4.5 times lower for natural gas reforming. Evaluating the cost of hydrogen produced by ethanol reforming and the economic feasibility of selling this hydrogen to the market, in the region of Campinas, SP, a calculation of the Internal Rate of Return (IRR) and the payback period was carried out. Also, the hydrogen price and the payback period were calculated for the IRR assessment at 100%, 75%, 50% and 25% (Figs. 7 and 8). According to Fig. 7, the ethanol reformer IRR for the hydrogen market price is 273%. Analyzing the payback for this IRR, it is observed in Fig. 8 that the initial investment in the ethanol
3
Hydrogen at 99.99%mol/mol purity. Cylinder with 7.2 m3of gas, at a pressure of 16,475.17 kPa (168 kgf/cm2) and gross weight of 68.5 kg. 4
Fig. 5. Cost share presented in the cash flow of Table 8.
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160.00 139.02
140.00
120.00 Market Price of H2 (4.0 T) Cost (US$/kg)
100.00 Cost of hydrogen by electrolysis; 4,9 kg/h (FERREIRA, 2008)
80.00
Cost by Ethanol Reformer: 0,3 kg/h
60.00
Cost of prodction by NG Reformer; 4,6 kg/h (DOE 2002)
40.00 15.35
20.00
14.11 3.15
0.00
Fig. 6. Comparison of the hydrogen cost produced by the ethanol reformer.
160.00 139.02 Hydrogen Price (US$/kg)
140.00 120.00 100.00
86.51
80.00 65.58 60.00 44.19 40.00 24.19 20.00 0.00 0%
25%
50%
75% 100% 125% 150% 175% 200% 225% 250% 275% 300% IRR
Fig. 7. IRR for the hydrogen market price and the price of hydrogen produced by the ethanol reformer.
48
Payback (Months)
44 36
24 24
16 12
12
5 0 0%
25%
50%
75% 100% 125% 150% 175% 200% 225% 250% 275% 300% IRR
Fig. 8. Payback period for the IRR related to the market price of hydrogen and for the IRR at 100%, 75%, 50% and 25%.
reformer would be paid in only 5 months. On the other hand, considering the lowest IRR presented in the figure, at 25%, the hydrogen price without taxes5 would be 24.19 US$/kg and the payback 44 months.
5 It’s worth highlighting that the values considered for the IRR and payback calculation do not take into account the taxes related to the hydrogen produced by the reformer, except for the market price of hydrogen for the region of Campinas-SP-Brazil.
This comparative analysis shows that the technology for hydrogen production by ethanol reforming is promising. Although it is still a prototype with a production capacity of only 0.3 kg/h of hydrogen, the costs at 14.11 US$/kg are highly competitive, especially when compared with small electrolysis systems fed by secondary power, at about 48.70 US$/kg in Brazil [13]. Moreover, an important cost reduction is expected with an increase in the production scale, in the technology learning curve, and in the reformer’s capacity, for example, prototypes of 4.0 kg/h of hydrogen.
D.G. Lopes et al. / Renewable Energy 45 (2012) 205e212 1.70
PhV + Electrolysis + Fuel Cell*
3
1.60
Etanol Reformer + Fuel Cell
1.50
Electricity Cost
1.40
Discount Rate
Cost (US$/kWh)
2.5 Cost (US$/kWh)
Reformer Price
PhV + Battery*
2.73
1.95
2
211
Ethanol Cost
Capacity de Factor
1.30 1.20 1.10 1.00
1.5 0.90
1.07
0.80
1
0.70
0.5
-50%
-40%
-30%
-20%
-10%
0%
10%
20%
30%
40%
50%
Percent Variation
0
Fig. 11. Sensitivity analysis for the electric power cost. Fig. 9. Comparative analysis of the electric energy cost.
7. Comparative cost of the electricity
7.1. Sensitivity analysis
In order to contextualize the power cost from the fuel cell system, a comparative analysis was carried out between two systems: the first consisting of a set of photovoltaic panels linked to a battery pack and the second consisting of a set of photovoltaic panels linked to a water electrolyzer and a PEMFC. The choice of these two systems was due to their current niche applications, mainly in isolated areas, where the reforming system could also be employed. The electricity produced by a fuel cell system using hydrogen generated by an ethanol reformer is the lowest among the technologies that were presented [8], and the electricity cost is approximately 2.5 lower than the electricity produced by the system with photovoltaic panels, electrolyzer and fuel cell (Fig. 9). On the other hand, the electric cost from the ethanol reforming system associated with a PEMFC is very high (7.8 times higher) when compared to the sales price of electric power in the gridconnected power system for the residential segment in Brazil, which is 0.138 US$/kWh [11].
The sensitivity analysis for the cost of the hydrogen generated by the ethanol reformer and for the electricity cost were carried out based on the reformer price, ethanol cost, electricity cost, discount rate and capacity factor (Figs. 10 and 11). The capacity factor of the ethanol reformer is the component that shows the highest sensitivity for the hydrogen cost (Figs. 10 and 11). Therefore, it is necessary to make its value as close as possible to the unit, which means a system operation with very few interruptions. In the calculation of the hydrogen cost, the value of the capacity factor was assumed to be equal 0.9. However, it is necessary to carry out long trials with the ethanol reformer to obtain the actual figure. Among the other factors, the price of the ethanol reformer represents the highest contribution to the hydrogen cost. A reduction of the reformer price by 50% would reduce the hydrogen cost by 27% (from 14.11 to 10.23 US$/kg of H2) and the electricity cost by 26% (from 1.07 to 0.79 US$/kWh). Although they are less significant, the contributions of ethanol and electric energy consumption by the ethanol reformer reveals that an increase in the reformer efficiency would result in a cost reduction of the produced hydrogen and consequently of the generated electric energy.
Cost (US$/kg)
24.00 23.00
Reformer Price
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Ethanol Cost
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Capacity de Factor
8. Conclusions
18.00 17.00 16.00 15.00 14.00 13.00 12.00 11.00 10.00 9.00 8.00 50%
40%
30%
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10%
0%
10%
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30%
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Percent Variation Fig. 10. Sensitivity analysis for the cost of hydrogen produced by the ethanol reformer.
This study presents a technical and economic feasibility analysis of an ethanol reformer in Brazil for the production of hydrogen to feed a PEMFC. The hydrogen cost from ethanol reforming is 14.11 US$/kg, which is lower than current market prices, about 139.00 US$/kg. According to the comparative analysis, the ethanol reforming seems promising, although this system is a small prototype. Moreover, cost reductions are expected since the technology is under development. Hydrogen prices in the market vary significantly. Prices presented in this study refer to hydrogen supplied at small scale and with required quality for PEMFC. Furthermore, these values refer to current prices, which include taxes and fees, profits, etc. Therefore, ethanol reforming systems to produce hydrogen for applications around 200 kg/month can be economically viable. Regarding the power generated by a PEMFC associated to the ethanol reformer, the reference value is 1.07 US$/kWh. This is around 2.5 times lower than the electricity cost obtained by
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electrolytic hydrogen produced by photovoltaic panels. On the other hand, this reference value is almost 8 times higher than the electric energy supplied by the grid-connected power system in the southeast region of Brazil (0.138 US$/kWh). However, the present system can be competitive when compared to other alternatives that are also under development. The sensitivity analysis shows that the capacity factor of the ethanol reformer presents the highest impact on hydrogen and electricity costs. Therefore, this characteristic of the system should be prioritized, that is, its operation should be continuous with few interruptions. Ethanol reforming consists on an interesting alternative for the renewable production of hydrogen, not only as a chemical feedstock for the industry, but also for the production of electricity in selected applications using fuel cells. Acknowledgments The authors would like to acknowledge the support of the Hydrogen Laboratory at Unicamp, Hytron e Hydrogen Technologies, NIPE/Unicamp, the Brazilian Reference Center for Hydrogen Energy and CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior). * Cristiano da Silva Pinto, Phone þ55 19 3521 2073, cspinto@ifi.unicamp.br. References [1] Lopes Daniel G. Technical And Economical Analysis Of The Introduction Of The Technology Of Hydrogen Production From Ethanol Reforming For The Generation Of Electric Energy With Fuel Cells. Campinas, Faculdade de Engenharia Mecânica, Universidade Estadual de Campinas; 2009. p. 110 thesis (Doctorate).
[2] BEN, Balanço Energético Nacional. Available at: www.ben.epe.gov.br. accessed on 20.08.2008. [3] Lopes Davi G. O Impacto da Energia Elétrica Proveniente do Reformador de Etanol e Células a Combustível: Cenário para a Promoção do Desenvolvimento Socioambiental da Comunidade “Pico do Amor”/MT. Campinas, Faculdade de Engenharia Mecânica, Universidade Estadual de Campinas; 2009. p. 97 Dissertation (MSc). [4] Camargo JC. Medidas do Potencial Fotovoltaico na Região das Bacias dos Rios Piracicaba e Capivari. Campinas, Faculdade de Engenharia Mecânica, Universidade Estadual de Campinas; 2000. p. 108 Dissertation (MSc). [5] Furlan AL. Comparative analysis of photovoltaic power storage systems by means of batteries and hydrogen in remote areas of the Amazon region of Brazil. p. 116 Dissertation (MSc). FEM - UNICAMP; 2008. [6] Souza AB. de, Projetos de Investimentos de Capital: Elaboração, análise, tomada de decisão. São Paulo: Atlas; 2003. [7] Kaplan S. Energy economics e quantitative methods for energy and environmental decisions. Nova York: McGraw Hill; 1983. [8] Marim Neto AJ, Lopes DG, Camargo JC, Silva EP, Neves JR NP. Simulação do processo de reforma autotérmica de etanol para a produção de hidrogênio em unidade integrada. Article present in III WICaC. Available at: http://www.ifi. unicamp.br/ceneh/WICaC2006/PDF/11-AntonioMarin.pdf. [9] DOE (USA). Department of energy cost and performance comparison of stationary hydrogen fueling Appliances. The Hydrogen Program Office of Power Technologies e U.S Department of Energy. Available at: http://www1. eere.energy.gov/hydrogenandfuelcells/pdfs/32405b2.pdf; 2002. accessed on 12.11.2008. [10] CEPEA, Centro de Estudos Avançados em Economia Aplicada. Available at: http://www.cepea.esalq.usp.br/alcool/?id_page¼407. accessed on 22.10.2008. [11] SAD Sistema. de Apoio a Decisão e ANEEL. Período de agosto de. Available at:, http://rad.aneel.gov.br/reportserverSAD?%2fSAD_REPORTS% 2fSAMP_TarifaMedCConsumoRegiao&rs:Command¼Render; 2008. accessed on 23.10.2008. [12] Ferreira PFP. Infrastructure for Hydrogen Energy Use: Fueling Stations for Fuel Cell Vehicles. p. 148 thesis (Doctorate). FEM e UNICAMP; 2007. [13] Pinto CS, Silva EP, Neves Jr NP, Miguel M, Villasboa JWB. Itaipu hydroelectric power plant and its experimental hydrogen production unity. In: ECOS 2009-22nd international conference on efficiency, cost, optimization, simulation, and environmental impact of energy systems, 2009, Foz do Iguaçu. Proceedings of ECOS2009, vol. 1. Rio de Janeiro: Associação Brasileira de Engenharia e Ciências Mecânicas - ABCM; 2009. p. 1639e46.