By Barbara Kessler

While the country frets about which new energy sources to turn to, researchers at Virginia Tech have been sizing up fuels and power-generation methods by how much of a precious finite resource – namely, water — they consume.

The results are likely to further complicate popular conceptions about the best renewable energy sources because as it turns out, two renewable, highly touted fuels — biodiesel and ethanol — are the thirstiest, using more water per energy produced than say, coal. On the one hand, that’s no surprise. Plants used to make these fuels require irrigation. On the other hand, the research raises serious questions about what’s really “renewable.”

The message, says key researcher TamimYounos, is that water “is very critical for energy extraction and power generation” and must be factored into government policies on these matters, including the inconvenient fact that “some of the new energy initiatives, such as biodiesel and ethanol production are in conflict with protecting water resources.”

The most water-efficient energy sources are natural gas and synthetic fuels produced by coal gasification, according to the study by Younos, associate director of the Virginia Water Resources Research Center and undergraduate student Rachelle Hill.

Younos and Hill looked at 11 types of energy sources, including coal, ethanol, biodiesel, natural gas, liquefied natural gas, hydrogen and oil; and five power-generating methods — hydroelectric, fossil fuel thermoelectric, solar thermoelectric, geothermal and nuclear power. They tested each to see how much water was required to produce one BTU (British Thermal Unit), a standard measure of pure energy.

Of the power-generating methods, hydroelectric and geothermal used the least water; nuclear, the most. (Which leaves solar thermoelectric, a developing technology which many have high hopes for, somewhere in the middle.)

To put the research in more accessible terms, Hill analyzed how much water it would take to burn one 60-watt incandescent bulb for 12 hours a day for one year. She found that, depending on the source of energy at the power plant supplying the electricity, that single bulb would require 3,000 to 6,000 gallons of water. A compact fluorescent bulb, however, would save about 2,000 to 4,000 gallons of water per year.
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