The MIT research — The Impact of Renewable Electricity Futures on Water Demand — is a compilation of the water segment of the Renewable Electricity Future study. In it, the researchers find that as solar panels, wind turbines and other sources of non-thermal renewable energy replace coal, gas and similar thermal powerplants, the use of water to cool those powerplants will decrease by about half.
"The most important use of water for electricity production is for cooling," says Adam Schlosser, an author of the study and the assistant director for science research at MIT's Joint Program on the Science and Policy of Global Change. "The benefit of renewables like wind or solar is that you don't need to boil water for steam to spin the turbines, and then you don't need water to cool the steam. That cooling process is removed, saving a lot of water."
This is good news for water-stressed regions, including much of the western United States, as production of electrical power results in one of the largest uses of water in the nation. A 2005 report by the U.S. Geological Service found that about 201,000 million gallons of water each day were used to produce electricity, with much of this water going toward keeping powerplants cool.
While most Americans will use less water when powering their homes with renewable energy, the MIT researchers did find that areas that switch to thermal renewable technologies might end up using more water. Biomass energy, being produced mostly in the northwestern United States, is one strong example, the study finds.
"Biomass is obviously contributing to the carbon aspect of the overall problem," Schlosser says, "But it's actually exacerbating an already water-stressed situation because you not only need water to grow it, you also need water to cool the thermal electricity generation process."
Schlosser compares this to concentrated solar technology being used in the southwest, which typically relies on a dry cooling system where fans are used instead of water.
"Solar technology really benefits the southwest because it uses a resource that's so plentiful in that region — the sun — and doesn't use a resource that there is very little of — water," Schlosser says.
But Schlosser explains that the dry cooling technology — while an obvious choice for the drought-stricken southwestern United States because it uses 90 percent less water — is less efficient and more expensive because the electric plant would need to use electricity to run large fans that force air through the heat-exchange process. This explains why areas where water scarcity is more subtle would choose to stick to water cooling technologies in thermal electricity generation.
Along with using less water, the Renewable Electricity Future study finds that greenhouse gas emissions would be reduced by about 80 percent, potentially offering significant public health benefits. The National Research Council estimated that in 2005, air pollution emissions from coal powerplants cost $32 per megawatt of energy in public health damages, the report notes, suggesting that the health cost benefits could counterbalance the costs to build clean energy infrastructure.