【By TODD WOODY／張佑生譯】

AMARGOSA VALLEY, Nevada — 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 4.9 billion liters 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. “I’m worried about my well and the wells of my neighbors,” George Tucker, a retired chemical engineer, said on a blazing afternoon.

Here is an inconvenient truth about renewable energy: It can sometimes demand a huge amount of water. Many of the proposed solutions to 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.

In California, solar developers have already been forced to switch to less water-intensive technologies when local officials refused to turn on the tap. Other big solar projects are mired in disputes with state regulators over water consumption.

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, New Mexico, to San Luis Obispo, California, 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, Nevada, 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.”

Many projects involve building solar thermal plants, which use cheaper technology than the solar panels often seen on roofs. In such plants, mirrors heat 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.

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 45 million liters 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.”

【2009-11-03/聯合報/G9版/UNITEDDAILYNEWS】