Power plants use a stunning amount of water. In 2005, thermoelectric power (e.g. coal, natural gas) accounted for half of all water use in the United States. Across the country and particularly in the arid West, the water savings from renewable energy are as important as the pollution-free energy.
That makes the distinction in water use between centralized solar and decentralized solar a big deal, especially since centralized solar is only planned for the dry Southwest.
The following graphic illustrates water consumption for common types of power generation per MWh of electricity produced (additional reference here):
Traditional power generators are water hogs. For example, a nuclear power plant consumes 720 gallons of water for each megawatt-hour of electricity produced. Powering a single 75-watt incandescent light bulb for an two hours on nuclear-generated electricity would consume 14 ounces of water (more than a can of pop).
While most of that water is returned to the environment, this report by the Alliance for Water Efficiency and ACEEE notes that it’s not undamaged:
Water is returned to its original source, even though its qualities have changed, especially temperature and pollutant levels.
Nuclear and coal may be big offenders, but wet-cooled concentrating solar power uses even more water per MWh of electricity generated. Dry-cooled CSP cuts water consumption significantly, but it’s still far more than solar power from photovoltaics (or wind power).
If it were solely a question of cost, CSP and PV come out relatively close (see updated chart below) despite the former’s frequent need for transmission access.
But if the tradeoff is significant water consumption versus none, then decentralized PV may make more sense everywhere, including the sunny Southwest.
Photo credit: Flickr user Shovelling Son