Briefly Noted: H2 Economy Impact on Water Supplies
Hydrogen supporters generally assume that water supplies for a future hydrogen economy are virtually limitless, in part because of the belief that hydrogen will recycle through the environment, returning time and again as rain, for example. But a new study says producing hydrogen electrolytically from water may in fact have a large impact on water resources. Writing in the September issue of the year-old Environmental Research Letters, Michael F. Webber, of the Center for International Energy and Environmental Policy at the University of Texas at Austin, reports that even for a transitional hydrogen economy that may get underway 30 years from now, the added demand for water represents a significant impact on water withdrawals that have remained steady for decades. Such a transitional hydrogen economy would require the production of around 60 billion kg of hydrogen annually in the United States, a figure Webber quotes from the 2004 report by the National Academy of Sciences (After 2050, demand for a full-blown hydrogen economy might exceed 100 billion kg, according to the NAS study). Webber calculates that producing 60 billion kg of hydrogen by thermoelectrically-powered electrolysis would require up to 143 billion gallons annually of water as feedstock; total consumption, including evaporation of cooling water at power plants, could range from 0.5 to 1.7 trillion gallons annually. Water use for thermoelectric cooling alone, which currently stands at 195 billion gallons/day (most of it is not consumed) is expected to increase by anywhere between 27 and 97 %,Webber writes. The water demand for electrolysisalone is not that different from whats needed now for the production of gasoline, Webber says, but the real impact would be indirect: a steep increase in water usage as coolant for thermoelectric power plants, which presumably includes both fossil-fueled and nuclear power plants. On a per-unit basis, thermoelectric plants will on average withdraw about 1,100 gallons of cooling water plus 27 gallons of water as feedstock and coolant to produce one kg of hydrogen with a 75% efficient electrolyzer, Webber reports. This, says Webber, represents a serious technical and public policy problem. If electrolysis becomes the preferred hydrogen production method, almost all electricity will have to come from non-thermoelectric, non-hydroelectric and non-irrigated renewable sources such as wind or solar, or effective water-free cooling, such as air cooling, Webber concludes.
Source: Environmental Research Letters, http://www.iop.org/EJ/erl; Michael Webber, email@example.com.