Solar Thermal Energy in the Desert? Not So Hot

Source: New York Times
By TODD WOODY

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,” 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 the nation’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 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.”

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.

In California alone, plans are under way for 35 large-scale solar projects that, in bright sunshine, would generate 12,000 megawatts of electricity, equal to the output of about 10 nuclear power plants.

Their water use would vary widely. BrightSource Energy’s dry-cooled Ivanpah project in Southern California would consume an estimated 25 million gallons a year, mainly to wash mirrors. But a wet-cooled solar trough power plant barely half Ivanpah’s size proposed by the Spanish developer Abengoa Solar would draw 705 million gallons of water in an area of the Mojave Desert that receives scant rainfall.

One of the most contentious disputes is over a proposed wet-cooled trough plant that NextEra Energy Resources, a subsidiary of the utility giant FPL Group, plans to build in a dry area east of Bakersfield, Calif.

NextEra wants to tap freshwater wells to supply the 521 million gallons of cooling water the plant, the Beacon Solar Energy Project, would consume in a year, despite a state policy against the use of drinking-quality water for power plant cooling.

Mike Edminston, a city council member from nearby California City, warned at a hearing that groundwater recharge was already “not keeping up with the utilization we have.”

The fight over water has moved into the California Legislature, where a bill has been introduced to allow renewable energy power plants to use drinking water for cooling if certain conditions are met.

“By allowing projects to use fresh water, the bill would remove any incentives that developers have to use technologies that minimize water use,” said Terry O’Brien, a California Energy Commission deputy director.

NextEra has resisted using dry cooling but is considering the feasibility of piping in reclaimed water. “At some point if costs are just layered on, a project becomes uncompetitive,” said Michael O’Sullivan, a senior vice president at NextEra.

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,” Mr. Goedhart said.

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,” Mr. Kammen said, “water will be a key issue.”