Renewable energy and fuel cells
In Thomas Dickerman's letter he quotes Amory Lovins as saying we could have our present way of life with 80% less energy (OGJ, Aug. 9, 2004, p. 10). It is worth noting that Amory Lovins made this claim shortly after the 1974 energy crisis. The fact that per capita energy consumption in the US today is virtually the same as in 1974 suggests that this claim is baseless.
Mr. Dickerman asserts that we can use electric power to produce hydrogen by electrolysis of water and then use the hydrogen as a transportation fuel. He further alleges that a fuel cell system is three times as efficient as the internal combustion engine. This claim ignores the dismal efficiencies in hydrogen production.
The theoretical energy required to dissociate liquid water into hydrogen and oxygen is 39.4 kilowatt-hours (kw-hr)/kilogram (kg) of hydrogen. But the efficiency of the electrolysis process is only about 70%.1 Let's suppose the electrical energy for the electrolysis process is provided by a coal-fired electrical generating plant with an overall conversion efficiency of 40% (i.e., 40% of the thermal energy input to the plant is converted into electrical energy). Then the energy input to the boiler of the plant required to produce the kg of hydrogen is 140.8 kw-hr.
Now let's look at the fuel cell. Since the reaction that occurs in the fuel cell produces water vapor, the theoretical energy obtainable from the fuel cell is 33.4 kw-hr/kg of hydrogen. The best fuel cells operate at an efficiency of about 70%.2 So the energy actually obtained from the reaction of a kg of hydrogen in a fuel cell is 23.3 kw-hr. If hydrogen is to be used as a transportation fuel, it must be compressed to at least 4,000 psi, and this compression requires energy. After subtracting the energy needed for compression, we find the net output from the kg of hydrogen in the fuel cell is only about 17.4 kw-hr. So, an energy input to the electrical generating plant of 140.8 kw-hr produces a kg of hydrogen which yields a net electrical output from the fuel cell of 17.4 kw-hr. The overall conversion efficiency of this whole process is a dismal 12%.
Worse, Mr. Dickerman advocates the use of renewable energy to produce the electrical energy for the electrolysis. Space does not permit an analysis of all renewable energy sources for electricity generation, but let's look at the numbers for photovoltaic (PV) cells, certainly one of the favorites of the environmentalists. Doing an input-output analysis on the energy obtained from a PV array vs. the energy required to produce it is a nightmare, but some people have done these calculations, and the results suggest that the energy payback time for a PV panel is about 8 years.3-7 Energy payback time is the time required for a PV panel to generate the energy equivalent to that used to produce it, and this time depends in part upon whether the panel is a fixed panel on a roof or whether the panel is installed in a more sophisticated system at a remote site. These panels have a useful life expectancy of about 25 years. A modern PV panel operating over a period of 25 years can probably be expected to convert no more than about 12% of the incident solar radiation on the cell into electrical energy. Since we need an electrical energy input of 56.3 kw-hr to the electrolyzer to obtain 17.4 kw-hr from the fuel cells, if PV cells are used to provide this electrical energy, the efficiency of the whole process is a miniscule 4% (i.e., 4% of the energy in the incident solar radiation on the PV cells appears as electrical output from the fuel cells). This dismal conversion efficiency has two consequences:
1. The energy required to make the PV array will exceed the energy produced by the fuel cells.
2. The cost of this energy will be prohibitively expensive.
The renewable energy resources touted by Mr. Dickerman and others all have serious environmental impacts, most of which the "green" seem to prefer to ignore. Some environmentalists are now lobbying for the removal of some high-profile hydroelectric power dams. The "hydrogen economy' is a myth which would only make a bad situation worse.
References
1. Wang, M., "Hydrogen a transportation fuel," OGJ 101, Aug. 25, 2003, p. 10
2. Standing, T., "Making hydrogen," OGJ, Apr. 14, 2003, p. 10.
3. Longmuir, G., "Alternate energy," OGJ, Sept. 22, 2003. p. 10.
4. Yoder, C., "Alternative energy FAQ2," http://www.ibiblio.org/ecolandtech/alternativeenergy/faqs/Alternative.Energy.FAQ2.
5. Alsema, E. A., Frankel, P., Kato, K., "Energy pay-Back Time of Photovoltaic Energy Systems: Present Status and Prospects," Second World Conference On Photovoltaic Solar Energy Conversion, Vienna, July 6-10, 1998.
6. Knapp, K. E., and Jester,T. L., "An Empirical Perspective on the Energy Payback Time for Photovoltaic Modules," Solar 2000 Conference, Madison, Wis., June 16-21, 2000.
7. PV FAQs, DOE/GO-102004-1847, Jan. 2004, Renewable Energy Laboratory, US Dept. of Energy, Washington, DC, 20585.
