AMARGOSA VALLEY, Nev. — In a rural corner of Nevada reeling from the recession, a bit of salvation seemed to arrive last year. A German developer, Solar Millennium, announced plans to build two large solar farms here that would harness the sun to generate electricity, creating hundreds of jobs.
But then things got messy. The company revealed that its preferred method of cooling the power plants would consume 1.3 billion gallons of water a year, about 20 percent of this desert valley's available water.
Now Solar Millennium finds itself in the midst of a new-age version of a Western water war. The public is divided, pitting some people who hope to make money selling water rights to the company against others concerned about the project's impact on the community and the environment.
"I'm worried about my well and the wells of my neighbors," said George Tucker, a retired chemical engineer.
Here is an inconvenient truth about renewable energy: It can sometimes demand a huge amount of water. Many of the proposed solutions to America's energy problems, from certain types of solar farms to biofuel refineries to cleaner coal plants, could consume billions of gallons of water every year.
"When push comes to shove, water could become the real throttle on renewable energy," said Michael E. Webber, an assistant professor at the University of Texas in Austin who studies the relationship between energy and water.
Conflicts over water could shape the future of many energy technologies. The most water-efficient renewable technologies are not necessarily the most economical, but water shortages could give them a competitive edge.
In California, solar developers have already been forced to switch to less water-intensive technologies when local officials have refused to turn on the tap. Other big solar projects are mired in disputes with state regulators over water consumption.
To date, the flashpoint for such conflicts has been the Southwest, where dozens of multibillion-dollar solar power plants are planned for thousands of acres of desert. While most forms of energy production consume water, its availability is especially limited in the sunny areas that are otherwise well suited for solar farms.
At public hearings from Albuquerque, N.M., to San Luis Obispo, Calif., local residents have sounded alarms over the impact that this industrialization will have on wildlife, their desert solitude and, most of all, their water.
Joni Eastley, chairwoman of the county commission in Nye County, Nev., which includes Amargosa Valley, said at one hearing that her area had been "inundated" with requests from renewable energy developers that "far exceed the amount of available water."
While water is particularly scarce in the West, it is becoming a problem all over the country as the population grows. Daniel M. Kammen, director of the Renewable and Appropriate Energy Laboratory at the University of California, Berkeley, predicted that as intensive renewable energy development spreads, water issues will follow.
"When we start getting 20 percent, 30 percent or 40 percent of our power from renewables," Kammen said, "water will be a key issue."
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Many projects involve building solar thermal plants, which use cheaper technology than the solar panels often seen on roofs. In such plants, mirrors heat a liquid to create steam that drives an electricity-generating turbine. As in a fossil fuel power plant, that steam must be condensed back to water and cooled for reuse.
The conventional method is called wet cooling. Hot water flows through a cooling tower where the excess heat evaporates along with some of the water, which must be replenished constantly. An alternative, dry cooling, uses fans and heat exchangers, much like a car's radiator. Far less water is consumed, but dry cooling adds costs and reduces efficiency — and profits.
The efficiency problem is especially acute with the most tried-and-proven technique, using mirrors arrayed in long troughs. "Trough technology has been more financeable, but now trough presents a separate risk — water," said Nathaniel Bullard, a solar analyst with New Energy Finance, a London research firm.
That could provide opportunities for developers of photovoltaic power plants, which take the type of solar panels found on residential rooftops and mount them on the ground in huge arrays. They are typically more expensive and less efficient than solar thermal farms but require a relatively small amount of water, mainly to wash the panels.
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Water disputes forced Solar Millennium to abandon wet cooling for a proposed solar trough power plant in Ridgecrest, Calif., after the water district refused to supply the 815 million gallons of water a year the project would need. The company subsequently proposed to dry cool two other massive Southern California solar trough farms it wants to build in the Mojave Desert.
"We will not do any wet cooling in California," said Rainer Aringhoff, president of Solar Millennium's American operations. "There are simply no plants being permitted here with wet cooling."
One solar developer, BrightSource Energy, hopes to capitalize on the water problem with a technology that focuses mirrors on a tower, producing higher-temperature steam than trough systems. The system can use dry cooling without suffering a prohibitive decline in power output, said Tom Doyle, an executive vice president at BrightSource.
The greater water efficiency was one factor that led VantagePoint Venture Partners, a Silicon Valley venture capital firm, to invest in BrightSource. "Our approach is high sensitivity to water use," said Alan E. Salzman, VantagePoint's chief executive. "We thought that was going to be huge differentiator."
Even solar projects with low water consumption face hurdles, however. Tessera Solar is planning a large project in the California desert that would use only 12 million gallons annually, mostly to wash mirrors. But because it would draw upon a severely depleted aquifer, Tessera may have to buy rights to 10 times that amount of water and then retire the pumping rights to the water it does not use. For a second big solar farm, Tessera has agreed to fund improvements to a local irrigation district in exchange for access to reclaimed water.
"We have a challenge in finding water even though we're low water use," said Sean Gallagher, a Tessera executive. "It forces you to do some creative deals."
In the Amargosa Valley, Solar Millennium may have to negotiate access to water with scores of individuals and companies who own the right to stick a straw in the aquifer, so to speak, and withdraw a prescribed amount of water each year.
"There are a lot of people out here for whom their water rights are their life savings, their retirement," said Ed Goedhart, a local farmer and state legislator, as he drove past pockets of sun-beaten mobile homes and luminescent patches of irrigated alfalfa. Farmers will be growing less of the crop, he said, if they decide to sell their water rights to Solar Millennium.
"We'll be growing megawatts instead of alfalfa," Goedhart said.