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Analysis of hydrogen production from combined photovoltaics, wind energy and secondary hydroelectricity supply in Brazil
Solar Energy 78 (2005) 670–677 www.elsevier.com/locate/solener
Analysis of hydrogen production from combined photovoltaics, wind energy and secondary hydroelectricity supply in Brazil E.P. Da Silva a
a,*
, A.J. Marin Neto a, P.F.P. Ferreira a, J.C. Camargo a, F.R. Apolina´rio a, C.S. Pinto b
Hydrogen Laboratory, Universidade Estadual de Campinas, Campinas—SP, 13083-970, P.O. Box 6039, Brazil b Brazilian Reference Center for Hydrogen Energy—CENEH, Campinas—SP, 13083-970, Brazil Received 9 June 2003; received in revised form 5 May 2004; accepted 15 October 2004 Available online 4 January 2005 Communicated by: Associate Editor A.T. Raissi
Abstract In this work, the technical and economical feasibility for implementing a hypothetical electrolytic hydrogen production plant, powered by electrical energy generated by alternative renewable power sources, wind and solar, and conventional hydroelectricity, was studied mainly trough the analysis of the wind and solar energy potentials for the northeast of Brazil. The hydrogen produced would be exported to countries which do not presently have significant renewable energy sources, but are willing to introduce those sources in their energy system. Hydrogen production was evaluated to be around 56.26 · 106 m3 H2/yr at a cost of 10.3 US$/kg. 2004 Elsevier Ltd. All rights reserved. Keywords: Renewable energy; Hydrogen production; Electrolysis; Hydrogen production cost
1. Introduction Electric power demand has been increasing in Brazil as well as in the so-called developing countries. Due to this constant increment in energy demand, new supply strategies have been adopted in the short and long terms. Those strategies have to be properly planned in order to grant that the access to energy be more democratic at
* Corresponding author. Tel.: +55 19 3788 2073; fax: +55 19 3289 1860. E-mail address: lh2ennio@ifi.unicamp.br (E.P. Da Silva).
reasonable social costs and in its most convenient form, respecting the principles of sustainable development. The alternative renewable energy sources and generation systems, such as solar, wind and hydroelectric power plants, meet those principles. Thoroughly thinking, although there are different denominations for those energy power systems, the primary source of energy which makes them available is solar. That is, besides photovoltaic and thermal power generation which consists in a direct utilization of this primary form of energy, wind and hydroelectric systems are also powered by the irradiative and thermal effects of solar energy on our planet.
0038-092X/$ - see front matter 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.solener.2004.10.011
E.P. Da Silva et al. / Solar Energy 78 (2005) 670–677
671
Nomenclature Symbols capacity factor fc fd availability factor CAE monthly cost of the electricity supplied by the association of photovoltaic, wind and hydroelectric sources CW monthly wind energy cost CHyd monthly hydropower cost CPV monthly cost for the photovoltaic energy TT monthly transmission tariff TTuc energy coming from Tucuruı´ including transmission tariff CMEA monthly energy cost for the association of the power sources PTUC power supplied by Tucuruı´ (MW) PW power from wind generators (MW) PPV power from photovoltaics (MW) t hydrogen production plant operation time (h month1) CMaxC maximum unitary cost for this power supply system (US$ MWh1) P power of the electrolysis plant CH cost production of hydrogen (US$ m3) CCC capital cost (US$ yr1)
In 2002, hydroelectric power generation, including hydropower units (HU), in Brazil reached 63.8 GW, which represents about 83% of the total electricity generation. Wind power generation systems account for 22 MW and are distributed throughout Ceara´, Pernambuco, Minas Gerais, Santa Catarina and Parana´ states. Solar-photovoltaic systems are limited to small power units located in research centers and remote areas, and because of that they are not quantified in the Brazilian energy generation system (Porto, 2002). Incentive programs, such as PROINFA which is intended to increase wind, biomass and small hydropower unit generation to 3300 MW each, aim to foster the use of alternative renewable energy sources in Brazil in the next decades. Likewise, many other countries have been attempting to introduce alternative renewable power sources in their energy systems, usually motivated by environmental issues and intending to avoid or lessen the impacts caused by conventional forms of electric power generation. For these reasons, those renewable power sources will not be restricted to remote areas, their market niche in the past; they will also have an important role in the energy market. In Brazil, the generation potential from alternative renewable sources, which is very little explored at the present, would extrapolate the internal demand of energy and originate an energy production surplus. This
CO&M CI QH F OM CEl d n CE CH2 O ty CW gEl Emin
operation and maintenance cost (US$ yr1) annual cost of the inputs (US$ yr1) annual production of hydrogen (m3 yr1) capital recovery factor over 1 year annual operation and maintenance rate unitary cost of the electrolysis plant (US$ MW1) annual discount rate number of years to recover the investment capital annual costs of electricity (US$ yr1) annual costs of the water (US$ yr1) annual plant availability (h yr1) volumetric cost of water (US$ m3) efficiency of the electrolyzer for hydrogen production minimum theoretical energy necessary to produce 1 m3 of hydrogen (MWh m3)
Abbreviations PROINFA Programa de Incentivo as Fontes Alternativas de Energia Ele´trica KOH potassium hydroxide STC standard test conditions
electric power surplus may represent a new energy market characterized by the possibility of exporting this surplus through hydrogen to other countries which do not have such a significant renewable energy potential and are willing to increase the participation of renewable sources in their energy system mix in order to reduce the use of non-renewable energy. This paper presents the study of the main parameters involved in the project of a hypothetical electrolytic hydrogen plant fed by alternative and conventional electric power sources such as photovoltaic, wind and hydropower. The hydrogen plant was arbitrarily chosen to be small (30 MW, which is equivalent to power produced by wind turbines in Brazil in 2003). The electric energy produced by those sources would be transmitted through the existing high-voltage network to a single electrolytic hydrogen production plant which, in its turn, would be strategically placed the closest possible to the potential consumer markets such as the United States, Europe and Japan. An analysis indicated that the city of Fortaleza, in Ceara´ state (CE), would be the best option (Soltermman, 1999). The potential location for the alternative power units was also studied, pointing that Coremas, PB, would be the best choice for the photovoltaic power unit and Caninde´, CE, would be most indicated for the wind power turbines. As for the conventional hydropower unit, Tuc-
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uruı´, PA, was the best option. The costs were also analyzed and discussed so that it was possible to draw some conclusions on the technical and economical viability of such a project.
2. Water electrolysis Water electrolysis is a particular electrochemical process (decomposing electrochemical process, also known as electrolytic process) in which water is split into its basic components, hydrogen and oxygen, through the use of continuous electric current. In order to assure that water electrolysis occurs through an ideal adiabatic process, the minimum potential difference between the cathode, where hydrogen is released (reduction), and the anode, where oxygen is released (oxidation), should be 1.482 V, which is called thermo-neutral potential. The electrolyzers are generally categorized into conventional or advanced models; the conventional ones may be either monopolar or bipolar as it is illustrated in Fig. 1 (Ulleberg, 2003). In all cases the electrolyzers are composed by single cells connected in parallel in the monopolar electrolyzer and in series in the bipolar type. The advanced electrolyzers are usually bipolar. The electrolytes more commonly utilized are liquid solutions which may be acidic or alkaline, the latter being more usual. Among the possible alkaline solutions, potassium hydroxide (KOH) is preferred since its ionic conductivity, together with its low power consumption, is maximized at the concentration rates of 28–30 wt.%. Another advantage of using KOH solutions is that the electrolyzers may be made of steel which is resistant to KOH corrosion (Wendt and Plzak, 1991). Solid electrolytes are also used in advanced electrolyzers which are normally based on polymer electrolytes and are then called Solid Polymer Electrolyzers. The
polymer membranes are usually composed by hydrocarbons, and those may be made of acidic–alkaline complexes, alkyl sulfonated polymers and sulfonated polymers. Among the sulfonated polymers, NAFION by DuPont, and FLE´MION and ACIPLE´X by Asahi Chemical Industry are the most commonly used in electrolyzers. Typically the operation voltage of an electrolytic cell is higher than the thermo-neutral potential (1.482 V) and the use of catalytic surfaces is made necessary so that the overpotential caused by the resistivity to electric and ionic conduction is reduced. The ratio between the thermo-neutral potential and the actual operation potential, at a normalized electric current, defines the device efficiency and thus it defines the energy necessary to produce a certain amount of hydrogen. Other technologies such as steam electrolysis are being researched. However, they face critical material problems due to high temperature operation and strongly oxidant environment (Milliken and Ruhl, 2003). In this paper the electrolysis system will be composed by bipolar alkaline electrolyzers which are commercially available and which power consumption is about 4.43 kWh/Nm3 H2, that is, devices which energy efficiency is 80% (from the ratio between lower heating value of the hydrogen produced and the electric consumption during the time length under consideration).
3. Parameters for power generation by alternative renewables This analysis is mainly founded on two assessment reports about the Brazilian solar irradiance and wind potential which are the Atlas do Potencial Eo´lico Brasileiro (MME, 2001) and the Atlas Solarime´trico do Brasil (Tiba, 2000), respectively.
Fig. 1. Monopolar (a) and bipolar (b) electrolyzer design.
The sites for installing the wind and the solar power facilities were chosen according to some criteria which were considered strategic. The first being their closeness to the hydrogen generation plant in Fortaleza and, the second, their wind and solar potential conditions over the period of 1 year. Besides that, the sites should be connected to the existing high voltage power network. Fortaleza (CE) was chosen as the site for the hydrogen generation plant because of its strategic position, one of the nearest coastal points to the USA, Europe and Japan, and its facilities, such as the seaport and power grid connection. Caninde´ (CE), which lies around 100 km from Fortaleza, has an annual average wind speed of 8.0 m/s or a power of 616 W/m2 at a height of 50 m, so it was the most suitable site for the wind turbines. Coremas (PB) presents one of the highest solar irradiance averages in Brazil, which is about 2027 kWh/m2 yr, and lies about 400 km from the hydrogen production plant. Coremas (PB) also presents a 7-h daily insolation average over the year. Those sites are shown in Fig. 2, which also represents the average wind speed and the electricity network. The averages presented for the wind power from the Atlas do Potencial Eo´lico Brasileiro were calculated on a quarterly basis, while the data about the other power sources were given on a monthly basis. For this reason it was necessary to extrapolate the wind power data to a monthly basis through a polynomial regression. Fig. 3 shows the coupling of the two alternative renewable
Monthly Energy Density Potential (kWh/m2)
E.P. Da Silva et al. / Solar Energy 78 (2005) 670–677
673
Wind Potential
900
Solar-Photovoltaic Potential
800 700 600 500 400 300 200 100 0 1
2
3
4 5 6 7 Months of the Year
8
9
10
11
12
Fig. 3. Average energy potential supplied by alternative renewable sources over the year in Caninde´ (CE) and Coremas (PB).
power sources and the total energy on a monthly basis.
4. Determining the hydrogen electrolytic production plant capacity The production capacity of the electrolytic hydrogen plant was determined on the basis of the supply profile for the wind and photovoltaic power plants. Along the
Fig. 2. Annual average wind speed at 50 m from the ground for Caninde´, CE.
E.P. Da Silva et al. / Solar Energy 78 (2005) 670–677
year, there are periods in which the electricity supply from wind and photovoltaic stations are not sufficient to power the hydrogen plant. Coincidently, it is possible to complement the hydrogen generation plant demand with energy from Tucuruı´ hydroelectric power station. For the design analysis of the wind power station, the wind turbines adopted are the ones manufactured by the Brazilian company Wobben-Enercon. The turbine model is the E-40 whose output power is 600 kW at a wind speed of 12 m/s, and has a set of blades with a diameter of 40 m. In order to minimize turbulence effects from one turbine onto the others, they must be placed according to the prevailing wind direction and separated according to their rotor blade diameter. The wind turbines must lie at a distance equal to 10 times its rotor diameter parallel to the wind direction, and 5 times its rotor diameter in the direction perpendicular to the wind. This implies that each of the proposed wind turbines will occupy a 0.08 km2 area. The area available for installing wind turbines in Caninde´ (CE) is estimated to be about 500 km2. This study will consider an occupation of 1% of the area available, which implies in 5 km2 and a total of 62 wind turbines with nominal power of 37.2 MW. The annual average wind speed for this area is 8.0 m/s, which leads to the annual average power of 177.7 kW according to Betz relation, and to the capacity factor (fc) of 0.3. This factor is defined as the ratio between the power generated by the wind turbine, during its application, and the power that would be generated at standard conditions (12 m/s wind speed, air density of 1.225 kg/m3). Assuming that the wind power station efficiency (gu) is equal to 0.97, which is the performance associated to the aerodynamic interference among the rotors, and the availability factor (fd) is equal to 0.95, which indicates the overall operation time, the effective power delivered by the wind station will be 10.7 MW, considering the number of wind generators, and the annual energy generated will be 89.1 GWh, value based on annual average wind speed and 8322 h of operation in a period of 1 year. According to the data in the Atlas do Potencial Eo´lico Brasileiro, it is also possible to determine the maximum and minimum monthly power supplies along the period of 1 year which will be 16.2 MW (power supplied at 9.2 m/s wind speed from March to May) and 4.4 MW (supplied at 6 m/s of wind speed from September to November), respectively. For the design of the solar power plant, photovoltaic panels made by Siemens Solar Industries with CdS/CIS technology were adopted. Those panels are commercially available for some time now and have the lowest efficiency losses in the temperature range of 20–100 C (Sze, 1981). Their useful area and nominal power correspond to 0.3651 m2 and 44.3 W (rated power output at standard test conditions—STC), respectively which means that their efficiency is around 12.1%.
The annual insolation in Coremas (PB) is equal to 5.55 kWh/m2 day (related to an 8-h day). Along the year the total energy generated will be given by the annual insolation multiplied by the number of days in 1 year (365 days), the area of each panel (0.3651 m2), and the panel efficiency (12.1%). This implies that the average energy and power generated by one panel over a year are 89.5 kWh and 30.7 W. Under practical operation conditions, numerous power losses occur due to many causes and a factor that relates the available energy from the photovoltaic array and the theoretical energy provided by the same array, at STC, is useful to be defined. This factor is called derate factor and is generally found at about 0.7–0.8. In this work, we assume this factor to be equal 0.8. Then, each panel will provide 71.6 kWh and 24.6 W. The availability factor (fd) is considered to be equal to 0.95 which is the same as the wind turbine farm yields to 68.0 kWh and 23.4 W per panel over 1 year. The capacity factor for those panels is 0.17 at the conditions mentioned above. Considering that the total area of one panel is 0.5 m2 and that it is necessary to double this area in order to avoid shading effects of nearby panels, each panel will occupy an area of 1 m2. The photovoltaic power plant will be assumed to have an average final output equivalent to that of the wind power station, which is 10.7 MW. This figure was chosen in order to make it possible to observe how the two different systems would perform along the year. Therefore, it will be necessary 457,300 panels which will occupy an area of 0.46 km2. The maximum and minimum power supplies along 1 year will be 12.0 MW and 7.6 MW, which are connected to the maximum and minimum insolation. Since the total production capacity for the hydrogen plant is equivalent to 30 MW, the annual power distribution for each energy source is represented by Fig. 4.
Wind Power Solar-Photovoltaic Power Hydro Power
Installed Power (MW)
674
30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0
1
2
3
4
5
6
7
8
9
10
11
12
Months of the Year
Fig. 4. Annual distribution power supply for each source (wind, solar and hydroelectric).
E.P. Da Silva et al. / Solar Energy 78 (2005) 670–677
5. Energy cost estimation
675
12 11
C AE ¼ C W þ C Hyd þ C PV ;
ð1Þ
10
Months of the Year
The most important input for the production of electrolytic hydrogen is electricity. Therefore, the electricity cost has the highest weight over the final cost of hydrogen. Because of the seasonal characteristics involved in the power supplies (Fig. 3) presented in this work, the final costs for electricity, as well as for hydrogen, will also vary along the year. The annual cost of the energy may be determined by the monthly energy supply distribution according to Eq. (1):
9 8 7 6 5 4 3 2 1 0
where CAE is the monthly cost of the electricity supplied by the association of photovoltaic, wind and hydroelectric sources, CW is the monthly wind energy cost, CHyd is the monthly hydropower cost, and CPV is the monthly cost for the photovoltaic energy. All costs are given in US$/kWh. Because of the modular nature of the wind and solar power units, that is, the increase in the power supply depends uniquely on the upgrade of generator modules, it is possible to adopt a unitary cost for power production which does not depend on generation capacity of the power plants. In the Brazilian case the costs for those sources are presented in Table 1. Besides the energy generation costs, there is the tariff for power transmission through the high voltage network. The alternative renewable plants will both use the network which connects Paulo Afonso hydropower station to Fortaleza. For this network, the monthly transmission tariff (TT) is equal to 620 US$/MW. The energy coming from Tucuruı´ has a cost (TTuc) equal to 26.00 US$/MWh, which already includes the transmission tariff. The monthly energy cost for the association of those power sources (CMEA) can be derived from Fig. 4, which leads to: C MEA ¼ ðP Tuc t T Tuc Þ þ ðP W t C W þ P W T T Þ
C MaxC ¼
þ ðP PV t C PV þ P PV T T Þ;
ð2Þ
Max½C MEA : tP
ð3Þ
Table 1 Unitary cost for power production by wind, solar and hydroelectric sources (Porto, 2002)
Monthly operation time Tucuruı´Õs energy cost Monthly transmission tariff Wind power cost Photovoltaic power cost *
Source: Porto 2002.
Symbol
Value
Unity
t TTuc TT CW CPV
691 26 620 50* 500*
Hours US$/MWh US$/MW US$/MWh US$/MWh
1x10
6
2x106
3x106
4x106
Cost (US$)
Fig. 5. Monthly energy cost for wind, solar and hydroelectric sources.
Eq. (2) represents the monthly energy cost in US$ for the association of those power sources in a monthly basis (CEA), PTuc is the power supplied by Tucuruı´ (MW), PW and PPV are respectively, the power produced by the wind power station and the solar power station (MW), and t is the hydrogen production plant operation time in hours per month. In Eq. (3), CMaxC is the maximum unitary cost for this power supply system (US$/ MWh). Fig. 5 shows the monthly energy cost for this power system (CMEA). P is the power of the electrolysis plant. According to Fig. 5, the maximum monthly cost, US$ 4,630,000.00, will occur in November, and the unitary energy cost (CMaxC) for this case will be 222.50 US$/MWh. The minimum monthly cost will occur in June, with unitary energy cost equals to 144.2 US$/MWh. 6. Hydrogen production costs The investments to build an electrolytic hydrogen production plant are generally high and include the acquisition of electrolyzers, rectifiers, peripheral control and gas purification systems, and infrastructure. These investments correspond to the capital costs, and usually depend on the production scale which is presented by Fig. 6. Besides the capital costs, there are the costs concerning the plant operation and maintenance. These costs also include the workforce, and may be calculated as a percentage of the capital costs. The cost of the inputs necessary for the production of electrolytic hydrogen mainly involves the costs of water and electricity. Other inputs, such as electrolytes and ionic resins, have very low costs which are not significant when compared to the capital, operation and maintenance costs.
Capital Investment (US$/kW)
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C W QH ; 1245
ð9Þ
1100
C H2 O ¼
1000
where CW is the volumetric cost of water (US$/m3). Then, the annual production of hydrogen will be:
900
QH ¼
800 700
P ty gEl ; Emin
ð10Þ
where gEl is the efficiency of the electrolyzer for hydrogen production and Emin is the minimum theoretical energy necessary to produce 1 m3 of hydrogen (MWh/m3). Coupling the Eqs. (8)–(10) into (7) leads to:
600 500 400 0
10
20
30
40
C I ¼ ðP ty C AE Þ þ
50
Production Capacity (1000 m3/h)
C W P ty gEl 1245:EEl
ffi 48:4 106 US$:
Fig. 6. Capital investment for implementing the hydrogen plant as a function of the production capacity.
The production cost of hydrogen is then given by the following expression: C CC þ C O&M þ C I ; ð4Þ CH ¼ QH where CH is the cost production of hydrogen (US$/m3), CCC is the capital cost (US$/yr), CO&M is the operation and maintenance cost (US$/yr), CI is the annual cost of the inputs, and QH is the annual production of hydrogen (m3/yr). The term CCC + CO&M may be written as
ð11Þ
The values assumed for the electric power of the hydrogen production plant, plant availability and electrolysis efficiency are shown in Table 2. Then, the annual hydrogen production is given by QH ¼
199; 700 56; 260; 000 m3 =yr 0:00355
56; 260; 000 6761 m3 =h Q_ ¼ 8322
ð6Þ
The unitary cost of the electrolysis plant may be calculated through the cost of hydrogen production per hour. Fig. 6 shows this cost as a function of the hydrogen plant production capacity and is based on the data provided by Bockris et al. (1981), Andreassen et al. (1993), Berry et al. (1996), Stuck (1991), Norsk hydro (1983), Ouellette et al. (1994). According to the Fig. 6, a hydrogen plant with a production capacity equal to 6761 m3/h will have a unitary cost equivalent (CEl) to 670,000 US$/MW. Therefore, considering the capital costs (CCC) and the operation
where d is the annual discount rate and n is the number of years to recover the investment capital. The annual cost of the inputs, CI, is written as
Table 2 Relevant parameters for determining the hydrogen production plant capacity and the hydrogen cost
C CC þ C O&M ¼ ðF þ OMÞ C El P
ð5Þ
where F is the capital recovery factor over 1 year, OM is the annual operation and maintenance rate, CEl is the unitary cost of the electrolysis plant (US$/MW) and P is the power of the electrolysis plant. The capital recovery factor, F, may also be described as F ¼
dð1 þ dÞn ; ð1 þ dÞn 1
C I ¼ C E þ C H2 O ;
ð7Þ
where CE and CH2 O are the annual costs of electricity and water (US$/yr). The annual cost of electricity may also be described as C E ¼ P ty C AE ;
ð8Þ
where ty is the annual plant availability (hours/yr), CAE is the unitary cost for the power supply system based on the wind, photovoltaic and hydropower units (US$/ MWh). In this case, the value of CAE will be considered as the monthly average of the unitary energy cost, 194 US$/MWh. At standard temperature and pressure conditions (25 C and 1 atm), 1 m3 of water yields to 1245 m3 of hydrogen and the annual cost of the water will be given by
Power of the electrolysis plant Plant availability Electric efficiency of the electrolyzer Minimum energy necessary to produce 1 m3 of hydrogen Annual discount rate Amortization time O&M rate Unitary cost of the electrolysis plant Electricity cost
Symbol
Value
Unity
P
30
MW
ty gEl
8300 0.8
Hours/year Dimensionless
Emin
0.00355
MWh/m3
d n OM CEL
10 20 6 670,000
%/year Year % US$/MW
CAE
223.00
US$/MWh
E.P. Da Silva et al. / Solar Energy 78 (2005) 670–677
and maintenance costs (CO&M) equal to US$ 3.568 · 106, and the final cost of hydrogen (CH) will be approximately 0.92 US$/m3 or 10.3 US$/kg.
7. Conclusion The technical and economical parameters for implementing a 30 MW electrolytic hydrogen production plant in Brazil were evaluated. The electric energy for this plant would be supplied by three different power sources: wind, photovoltaic and hydroelectric power units. The alternative renewable power units, as well as the hydrogen production plant, were strategically designed to be placed in the most favorable areas of the country. In the suggested configuration, the hydrogen plant would lead to the generation of 56.26 · 106 m3 H2/yr at a cost of 10.3 US$/kg, which is a regular cost when compared to some of the costs presented in the current literature (Iwasaki, 2003; Melaina, 2003; Direct Technologies Inc., 2002). The perspective of implementing this hydrogen production system from alternative renewable sources is very good, especially because the hydrogen generation plant considered in this case is very small. The costs tend to be much lower for larger plants and this might be a very important resource for future investments in the Hydrogen Economy. Acknowledgments The authors would like to thank the staff from Laborato´rio de Hidrogeˆnio for the support. The following authors, A.J. Marin Neto, J.C. Camargo, would like to thank CNPq (Conselho Nacional de Desenvolvimento Cientı´fico e Tecnolo´gico) for the financial support, and F.R. Apolina´rio, P.F.P. Ferreira would like to thank CAPES (Coordenac¸a˜o de Aperfeic¸oamento de Pessoal de Nı´vel Superior) for the financial support.
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Analysis of hydrogen production from combined photovoltaics, wind energy and secondary hydroelectricity supply in Brazil E.P. Da Silva a
a,*
, A.J. Marin Neto a, P.F.P. Ferreira a, J.C. Camargo a, F.R. Apolina´rio a, C.S. Pinto b
Hydrogen Laboratory, Universidade Estadual de Campinas, Campinas—SP, 13083-970, P.O. Box 6039, Brazil b Brazilian Reference Center for Hydrogen Energy—CENEH, Campinas—SP, 13083-970, Brazil Received 9 June 2003; received in revised form 5 May 2004; accepted 15 October 2004 Available online 4 January 2005 Communicated by: Associate Editor A.T. Raissi
Abstract In this work, the technical and economical feasibility for implementing a hypothetical electrolytic hydrogen production plant, powered by electrical energy generated by alternative renewable power sources, wind and solar, and conventional hydroelectricity, was studied mainly trough the analysis of the wind and solar energy potentials for the northeast of Brazil. The hydrogen produced would be exported to countries which do not presently have significant renewable energy sources, but are willing to introduce those sources in their energy system. Hydrogen production was evaluated to be around 56.26 · 106 m3 H2/yr at a cost of 10.3 US$/kg. 2004 Elsevier Ltd. All rights reserved. Keywords: Renewable energy; Hydrogen production; Electrolysis; Hydrogen production cost
1. Introduction Electric power demand has been increasing in Brazil as well as in the so-called developing countries. Due to this constant increment in energy demand, new supply strategies have been adopted in the short and long terms. Those strategies have to be properly planned in order to grant that the access to energy be more democratic at
* Corresponding author. Tel.: +55 19 3788 2073; fax: +55 19 3289 1860. E-mail address: lh2ennio@ifi.unicamp.br (E.P. Da Silva).
reasonable social costs and in its most convenient form, respecting the principles of sustainable development. The alternative renewable energy sources and generation systems, such as solar, wind and hydroelectric power plants, meet those principles. Thoroughly thinking, although there are different denominations for those energy power systems, the primary source of energy which makes them available is solar. That is, besides photovoltaic and thermal power generation which consists in a direct utilization of this primary form of energy, wind and hydroelectric systems are also powered by the irradiative and thermal effects of solar energy on our planet.
0038-092X/$ - see front matter 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.solener.2004.10.011
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Nomenclature Symbols capacity factor fc fd availability factor CAE monthly cost of the electricity supplied by the association of photovoltaic, wind and hydroelectric sources CW monthly wind energy cost CHyd monthly hydropower cost CPV monthly cost for the photovoltaic energy TT monthly transmission tariff TTuc energy coming from Tucuruı´ including transmission tariff CMEA monthly energy cost for the association of the power sources PTUC power supplied by Tucuruı´ (MW) PW power from wind generators (MW) PPV power from photovoltaics (MW) t hydrogen production plant operation time (h month1) CMaxC maximum unitary cost for this power supply system (US$ MWh1) P power of the electrolysis plant CH cost production of hydrogen (US$ m3) CCC capital cost (US$ yr1)
In 2002, hydroelectric power generation, including hydropower units (HU), in Brazil reached 63.8 GW, which represents about 83% of the total electricity generation. Wind power generation systems account for 22 MW and are distributed throughout Ceara´, Pernambuco, Minas Gerais, Santa Catarina and Parana´ states. Solar-photovoltaic systems are limited to small power units located in research centers and remote areas, and because of that they are not quantified in the Brazilian energy generation system (Porto, 2002). Incentive programs, such as PROINFA which is intended to increase wind, biomass and small hydropower unit generation to 3300 MW each, aim to foster the use of alternative renewable energy sources in Brazil in the next decades. Likewise, many other countries have been attempting to introduce alternative renewable power sources in their energy systems, usually motivated by environmental issues and intending to avoid or lessen the impacts caused by conventional forms of electric power generation. For these reasons, those renewable power sources will not be restricted to remote areas, their market niche in the past; they will also have an important role in the energy market. In Brazil, the generation potential from alternative renewable sources, which is very little explored at the present, would extrapolate the internal demand of energy and originate an energy production surplus. This
CO&M CI QH F OM CEl d n CE CH2 O ty CW gEl Emin
operation and maintenance cost (US$ yr1) annual cost of the inputs (US$ yr1) annual production of hydrogen (m3 yr1) capital recovery factor over 1 year annual operation and maintenance rate unitary cost of the electrolysis plant (US$ MW1) annual discount rate number of years to recover the investment capital annual costs of electricity (US$ yr1) annual costs of the water (US$ yr1) annual plant availability (h yr1) volumetric cost of water (US$ m3) efficiency of the electrolyzer for hydrogen production minimum theoretical energy necessary to produce 1 m3 of hydrogen (MWh m3)
Abbreviations PROINFA Programa de Incentivo as Fontes Alternativas de Energia Ele´trica KOH potassium hydroxide STC standard test conditions
electric power surplus may represent a new energy market characterized by the possibility of exporting this surplus through hydrogen to other countries which do not have such a significant renewable energy potential and are willing to increase the participation of renewable sources in their energy system mix in order to reduce the use of non-renewable energy. This paper presents the study of the main parameters involved in the project of a hypothetical electrolytic hydrogen plant fed by alternative and conventional electric power sources such as photovoltaic, wind and hydropower. The hydrogen plant was arbitrarily chosen to be small (30 MW, which is equivalent to power produced by wind turbines in Brazil in 2003). The electric energy produced by those sources would be transmitted through the existing high-voltage network to a single electrolytic hydrogen production plant which, in its turn, would be strategically placed the closest possible to the potential consumer markets such as the United States, Europe and Japan. An analysis indicated that the city of Fortaleza, in Ceara´ state (CE), would be the best option (Soltermman, 1999). The potential location for the alternative power units was also studied, pointing that Coremas, PB, would be the best choice for the photovoltaic power unit and Caninde´, CE, would be most indicated for the wind power turbines. As for the conventional hydropower unit, Tuc-
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uruı´, PA, was the best option. The costs were also analyzed and discussed so that it was possible to draw some conclusions on the technical and economical viability of such a project.
2. Water electrolysis Water electrolysis is a particular electrochemical process (decomposing electrochemical process, also known as electrolytic process) in which water is split into its basic components, hydrogen and oxygen, through the use of continuous electric current. In order to assure that water electrolysis occurs through an ideal adiabatic process, the minimum potential difference between the cathode, where hydrogen is released (reduction), and the anode, where oxygen is released (oxidation), should be 1.482 V, which is called thermo-neutral potential. The electrolyzers are generally categorized into conventional or advanced models; the conventional ones may be either monopolar or bipolar as it is illustrated in Fig. 1 (Ulleberg, 2003). In all cases the electrolyzers are composed by single cells connected in parallel in the monopolar electrolyzer and in series in the bipolar type. The advanced electrolyzers are usually bipolar. The electrolytes more commonly utilized are liquid solutions which may be acidic or alkaline, the latter being more usual. Among the possible alkaline solutions, potassium hydroxide (KOH) is preferred since its ionic conductivity, together with its low power consumption, is maximized at the concentration rates of 28–30 wt.%. Another advantage of using KOH solutions is that the electrolyzers may be made of steel which is resistant to KOH corrosion (Wendt and Plzak, 1991). Solid electrolytes are also used in advanced electrolyzers which are normally based on polymer electrolytes and are then called Solid Polymer Electrolyzers. The
polymer membranes are usually composed by hydrocarbons, and those may be made of acidic–alkaline complexes, alkyl sulfonated polymers and sulfonated polymers. Among the sulfonated polymers, NAFION by DuPont, and FLE´MION and ACIPLE´X by Asahi Chemical Industry are the most commonly used in electrolyzers. Typically the operation voltage of an electrolytic cell is higher than the thermo-neutral potential (1.482 V) and the use of catalytic surfaces is made necessary so that the overpotential caused by the resistivity to electric and ionic conduction is reduced. The ratio between the thermo-neutral potential and the actual operation potential, at a normalized electric current, defines the device efficiency and thus it defines the energy necessary to produce a certain amount of hydrogen. Other technologies such as steam electrolysis are being researched. However, they face critical material problems due to high temperature operation and strongly oxidant environment (Milliken and Ruhl, 2003). In this paper the electrolysis system will be composed by bipolar alkaline electrolyzers which are commercially available and which power consumption is about 4.43 kWh/Nm3 H2, that is, devices which energy efficiency is 80% (from the ratio between lower heating value of the hydrogen produced and the electric consumption during the time length under consideration).
3. Parameters for power generation by alternative renewables This analysis is mainly founded on two assessment reports about the Brazilian solar irradiance and wind potential which are the Atlas do Potencial Eo´lico Brasileiro (MME, 2001) and the Atlas Solarime´trico do Brasil (Tiba, 2000), respectively.
Fig. 1. Monopolar (a) and bipolar (b) electrolyzer design.
The sites for installing the wind and the solar power facilities were chosen according to some criteria which were considered strategic. The first being their closeness to the hydrogen generation plant in Fortaleza and, the second, their wind and solar potential conditions over the period of 1 year. Besides that, the sites should be connected to the existing high voltage power network. Fortaleza (CE) was chosen as the site for the hydrogen generation plant because of its strategic position, one of the nearest coastal points to the USA, Europe and Japan, and its facilities, such as the seaport and power grid connection. Caninde´ (CE), which lies around 100 km from Fortaleza, has an annual average wind speed of 8.0 m/s or a power of 616 W/m2 at a height of 50 m, so it was the most suitable site for the wind turbines. Coremas (PB) presents one of the highest solar irradiance averages in Brazil, which is about 2027 kWh/m2 yr, and lies about 400 km from the hydrogen production plant. Coremas (PB) also presents a 7-h daily insolation average over the year. Those sites are shown in Fig. 2, which also represents the average wind speed and the electricity network. The averages presented for the wind power from the Atlas do Potencial Eo´lico Brasileiro were calculated on a quarterly basis, while the data about the other power sources were given on a monthly basis. For this reason it was necessary to extrapolate the wind power data to a monthly basis through a polynomial regression. Fig. 3 shows the coupling of the two alternative renewable
Monthly Energy Density Potential (kWh/m2)
E.P. Da Silva et al. / Solar Energy 78 (2005) 670–677
673
Wind Potential
900
Solar-Photovoltaic Potential
800 700 600 500 400 300 200 100 0 1
2
3
4 5 6 7 Months of the Year
8
9
10
11
12
Fig. 3. Average energy potential supplied by alternative renewable sources over the year in Caninde´ (CE) and Coremas (PB).
power sources and the total energy on a monthly basis.
4. Determining the hydrogen electrolytic production plant capacity The production capacity of the electrolytic hydrogen plant was determined on the basis of the supply profile for the wind and photovoltaic power plants. Along the
Fig. 2. Annual average wind speed at 50 m from the ground for Caninde´, CE.
E.P. Da Silva et al. / Solar Energy 78 (2005) 670–677
year, there are periods in which the electricity supply from wind and photovoltaic stations are not sufficient to power the hydrogen plant. Coincidently, it is possible to complement the hydrogen generation plant demand with energy from Tucuruı´ hydroelectric power station. For the design analysis of the wind power station, the wind turbines adopted are the ones manufactured by the Brazilian company Wobben-Enercon. The turbine model is the E-40 whose output power is 600 kW at a wind speed of 12 m/s, and has a set of blades with a diameter of 40 m. In order to minimize turbulence effects from one turbine onto the others, they must be placed according to the prevailing wind direction and separated according to their rotor blade diameter. The wind turbines must lie at a distance equal to 10 times its rotor diameter parallel to the wind direction, and 5 times its rotor diameter in the direction perpendicular to the wind. This implies that each of the proposed wind turbines will occupy a 0.08 km2 area. The area available for installing wind turbines in Caninde´ (CE) is estimated to be about 500 km2. This study will consider an occupation of 1% of the area available, which implies in 5 km2 and a total of 62 wind turbines with nominal power of 37.2 MW. The annual average wind speed for this area is 8.0 m/s, which leads to the annual average power of 177.7 kW according to Betz relation, and to the capacity factor (fc) of 0.3. This factor is defined as the ratio between the power generated by the wind turbine, during its application, and the power that would be generated at standard conditions (12 m/s wind speed, air density of 1.225 kg/m3). Assuming that the wind power station efficiency (gu) is equal to 0.97, which is the performance associated to the aerodynamic interference among the rotors, and the availability factor (fd) is equal to 0.95, which indicates the overall operation time, the effective power delivered by the wind station will be 10.7 MW, considering the number of wind generators, and the annual energy generated will be 89.1 GWh, value based on annual average wind speed and 8322 h of operation in a period of 1 year. According to the data in the Atlas do Potencial Eo´lico Brasileiro, it is also possible to determine the maximum and minimum monthly power supplies along the period of 1 year which will be 16.2 MW (power supplied at 9.2 m/s wind speed from March to May) and 4.4 MW (supplied at 6 m/s of wind speed from September to November), respectively. For the design of the solar power plant, photovoltaic panels made by Siemens Solar Industries with CdS/CIS technology were adopted. Those panels are commercially available for some time now and have the lowest efficiency losses in the temperature range of 20–100 C (Sze, 1981). Their useful area and nominal power correspond to 0.3651 m2 and 44.3 W (rated power output at standard test conditions—STC), respectively which means that their efficiency is around 12.1%.
The annual insolation in Coremas (PB) is equal to 5.55 kWh/m2 day (related to an 8-h day). Along the year the total energy generated will be given by the annual insolation multiplied by the number of days in 1 year (365 days), the area of each panel (0.3651 m2), and the panel efficiency (12.1%). This implies that the average energy and power generated by one panel over a year are 89.5 kWh and 30.7 W. Under practical operation conditions, numerous power losses occur due to many causes and a factor that relates the available energy from the photovoltaic array and the theoretical energy provided by the same array, at STC, is useful to be defined. This factor is called derate factor and is generally found at about 0.7–0.8. In this work, we assume this factor to be equal 0.8. Then, each panel will provide 71.6 kWh and 24.6 W. The availability factor (fd) is considered to be equal to 0.95 which is the same as the wind turbine farm yields to 68.0 kWh and 23.4 W per panel over 1 year. The capacity factor for those panels is 0.17 at the conditions mentioned above. Considering that the total area of one panel is 0.5 m2 and that it is necessary to double this area in order to avoid shading effects of nearby panels, each panel will occupy an area of 1 m2. The photovoltaic power plant will be assumed to have an average final output equivalent to that of the wind power station, which is 10.7 MW. This figure was chosen in order to make it possible to observe how the two different systems would perform along the year. Therefore, it will be necessary 457,300 panels which will occupy an area of 0.46 km2. The maximum and minimum power supplies along 1 year will be 12.0 MW and 7.6 MW, which are connected to the maximum and minimum insolation. Since the total production capacity for the hydrogen plant is equivalent to 30 MW, the annual power distribution for each energy source is represented by Fig. 4.
Wind Power Solar-Photovoltaic Power Hydro Power
Installed Power (MW)
674
30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0
1
2
3
4
5
6
7
8
9
10
11
12
Months of the Year
Fig. 4. Annual distribution power supply for each source (wind, solar and hydroelectric).
E.P. Da Silva et al. / Solar Energy 78 (2005) 670–677
5. Energy cost estimation
675
12 11
C AE ¼ C W þ C Hyd þ C PV ;
ð1Þ
10
Months of the Year
The most important input for the production of electrolytic hydrogen is electricity. Therefore, the electricity cost has the highest weight over the final cost of hydrogen. Because of the seasonal characteristics involved in the power supplies (Fig. 3) presented in this work, the final costs for electricity, as well as for hydrogen, will also vary along the year. The annual cost of the energy may be determined by the monthly energy supply distribution according to Eq. (1):
9 8 7 6 5 4 3 2 1 0
where CAE is the monthly cost of the electricity supplied by the association of photovoltaic, wind and hydroelectric sources, CW is the monthly wind energy cost, CHyd is the monthly hydropower cost, and CPV is the monthly cost for the photovoltaic energy. All costs are given in US$/kWh. Because of the modular nature of the wind and solar power units, that is, the increase in the power supply depends uniquely on the upgrade of generator modules, it is possible to adopt a unitary cost for power production which does not depend on generation capacity of the power plants. In the Brazilian case the costs for those sources are presented in Table 1. Besides the energy generation costs, there is the tariff for power transmission through the high voltage network. The alternative renewable plants will both use the network which connects Paulo Afonso hydropower station to Fortaleza. For this network, the monthly transmission tariff (TT) is equal to 620 US$/MW. The energy coming from Tucuruı´ has a cost (TTuc) equal to 26.00 US$/MWh, which already includes the transmission tariff. The monthly energy cost for the association of those power sources (CMEA) can be derived from Fig. 4, which leads to: C MEA ¼ ðP Tuc t T Tuc Þ þ ðP W t C W þ P W T T Þ
C MaxC ¼
þ ðP PV t C PV þ P PV T T Þ;
ð2Þ
Max½C MEA : tP
ð3Þ
Table 1 Unitary cost for power production by wind, solar and hydroelectric sources (Porto, 2002)
Monthly operation time Tucuruı´Õs energy cost Monthly transmission tariff Wind power cost Photovoltaic power cost *
Source: Porto 2002.
Symbol
Value
Unity
t TTuc TT CW CPV
691 26 620 50* 500*
Hours US$/MWh US$/MW US$/MWh US$/MWh
1x10
6
2x106
3x106
4x106
Cost (US$)
Fig. 5. Monthly energy cost for wind, solar and hydroelectric sources.
Eq. (2) represents the monthly energy cost in US$ for the association of those power sources in a monthly basis (CEA), PTuc is the power supplied by Tucuruı´ (MW), PW and PPV are respectively, the power produced by the wind power station and the solar power station (MW), and t is the hydrogen production plant operation time in hours per month. In Eq. (3), CMaxC is the maximum unitary cost for this power supply system (US$/ MWh). Fig. 5 shows the monthly energy cost for this power system (CMEA). P is the power of the electrolysis plant. According to Fig. 5, the maximum monthly cost, US$ 4,630,000.00, will occur in November, and the unitary energy cost (CMaxC) for this case will be 222.50 US$/MWh. The minimum monthly cost will occur in June, with unitary energy cost equals to 144.2 US$/MWh. 6. Hydrogen production costs The investments to build an electrolytic hydrogen production plant are generally high and include the acquisition of electrolyzers, rectifiers, peripheral control and gas purification systems, and infrastructure. These investments correspond to the capital costs, and usually depend on the production scale which is presented by Fig. 6. Besides the capital costs, there are the costs concerning the plant operation and maintenance. These costs also include the workforce, and may be calculated as a percentage of the capital costs. The cost of the inputs necessary for the production of electrolytic hydrogen mainly involves the costs of water and electricity. Other inputs, such as electrolytes and ionic resins, have very low costs which are not significant when compared to the capital, operation and maintenance costs.
Capital Investment (US$/kW)
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E.P. Da Silva et al. / Solar Energy 78 (2005) 670–677
C W QH ; 1245
ð9Þ
1100
C H2 O ¼
1000
where CW is the volumetric cost of water (US$/m3). Then, the annual production of hydrogen will be:
900
QH ¼
800 700
P ty gEl ; Emin
ð10Þ
where gEl is the efficiency of the electrolyzer for hydrogen production and Emin is the minimum theoretical energy necessary to produce 1 m3 of hydrogen (MWh/m3). Coupling the Eqs. (8)–(10) into (7) leads to:
600 500 400 0
10
20
30
40
C I ¼ ðP ty C AE Þ þ
50
Production Capacity (1000 m3/h)
C W P ty gEl 1245:EEl
ffi 48:4 106 US$:
Fig. 6. Capital investment for implementing the hydrogen plant as a function of the production capacity.
The production cost of hydrogen is then given by the following expression: C CC þ C O&M þ C I ; ð4Þ CH ¼ QH where CH is the cost production of hydrogen (US$/m3), CCC is the capital cost (US$/yr), CO&M is the operation and maintenance cost (US$/yr), CI is the annual cost of the inputs, and QH is the annual production of hydrogen (m3/yr). The term CCC + CO&M may be written as
ð11Þ
The values assumed for the electric power of the hydrogen production plant, plant availability and electrolysis efficiency are shown in Table 2. Then, the annual hydrogen production is given by QH ¼
199; 700 56; 260; 000 m3 =yr 0:00355
56; 260; 000 6761 m3 =h Q_ ¼ 8322
ð6Þ
The unitary cost of the electrolysis plant may be calculated through the cost of hydrogen production per hour. Fig. 6 shows this cost as a function of the hydrogen plant production capacity and is based on the data provided by Bockris et al. (1981), Andreassen et al. (1993), Berry et al. (1996), Stuck (1991), Norsk hydro (1983), Ouellette et al. (1994). According to the Fig. 6, a hydrogen plant with a production capacity equal to 6761 m3/h will have a unitary cost equivalent (CEl) to 670,000 US$/MW. Therefore, considering the capital costs (CCC) and the operation
where d is the annual discount rate and n is the number of years to recover the investment capital. The annual cost of the inputs, CI, is written as
Table 2 Relevant parameters for determining the hydrogen production plant capacity and the hydrogen cost
C CC þ C O&M ¼ ðF þ OMÞ C El P
ð5Þ
where F is the capital recovery factor over 1 year, OM is the annual operation and maintenance rate, CEl is the unitary cost of the electrolysis plant (US$/MW) and P is the power of the electrolysis plant. The capital recovery factor, F, may also be described as F ¼
dð1 þ dÞn ; ð1 þ dÞn 1
C I ¼ C E þ C H2 O ;
ð7Þ
where CE and CH2 O are the annual costs of electricity and water (US$/yr). The annual cost of electricity may also be described as C E ¼ P ty C AE ;
ð8Þ
where ty is the annual plant availability (hours/yr), CAE is the unitary cost for the power supply system based on the wind, photovoltaic and hydropower units (US$/ MWh). In this case, the value of CAE will be considered as the monthly average of the unitary energy cost, 194 US$/MWh. At standard temperature and pressure conditions (25 C and 1 atm), 1 m3 of water yields to 1245 m3 of hydrogen and the annual cost of the water will be given by
Power of the electrolysis plant Plant availability Electric efficiency of the electrolyzer Minimum energy necessary to produce 1 m3 of hydrogen Annual discount rate Amortization time O&M rate Unitary cost of the electrolysis plant Electricity cost
Symbol
Value
Unity
P
30
MW
ty gEl
8300 0.8
Hours/year Dimensionless
Emin
0.00355
MWh/m3
d n OM CEL
10 20 6 670,000
%/year Year % US$/MW
CAE
223.00
US$/MWh
E.P. Da Silva et al. / Solar Energy 78 (2005) 670–677
and maintenance costs (CO&M) equal to US$ 3.568 · 106, and the final cost of hydrogen (CH) will be approximately 0.92 US$/m3 or 10.3 US$/kg.
7. Conclusion The technical and economical parameters for implementing a 30 MW electrolytic hydrogen production plant in Brazil were evaluated. The electric energy for this plant would be supplied by three different power sources: wind, photovoltaic and hydroelectric power units. The alternative renewable power units, as well as the hydrogen production plant, were strategically designed to be placed in the most favorable areas of the country. In the suggested configuration, the hydrogen plant would lead to the generation of 56.26 · 106 m3 H2/yr at a cost of 10.3 US$/kg, which is a regular cost when compared to some of the costs presented in the current literature (Iwasaki, 2003; Melaina, 2003; Direct Technologies Inc., 2002). The perspective of implementing this hydrogen production system from alternative renewable sources is very good, especially because the hydrogen generation plant considered in this case is very small. The costs tend to be much lower for larger plants and this might be a very important resource for future investments in the Hydrogen Economy. Acknowledgments The authors would like to thank the staff from Laborato´rio de Hidrogeˆnio for the support. The following authors, A.J. Marin Neto, J.C. Camargo, would like to thank CNPq (Conselho Nacional de Desenvolvimento Cientı´fico e Tecnolo´gico) for the financial support, and F.R. Apolina´rio, P.F.P. Ferreira would like to thank CAPES (Coordenac¸a˜o de Aperfeic¸oamento de Pessoal de Nı´vel Superior) for the financial support.
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