Hot times for solar energy: utility-scale solar thermal power may be poised for the big time

World Watch, March-April, 2008 by Susan Moran, J. Thomas McKinnon

Fly into the surreal rainbow glow of the Las Vegas strip at twilight and it becomes clear why the state of Nevada has become a metaphor for the energy crossroads confronting the United States. The city's hunger for electricity, like its visitors' appetite for carnal indulgence, is insatiable; it is the seat of Clark County, the second fastest growing county in the United States. Nevada's two public utilities project that the state will hit an electricity capacity shortfall of 2,100 megawatts by 2016 if more isn't built.

The vision of a future powered by fossil fuels in one of the sunniest spots in the world strikes many people, including Harry Reid---majority leader of the U.S. Senate and a strong opponent of coal-fired plants--as ludicrous. Which is why Nevada has emerged not only as the biggest battleground over coal but the newest test bed for utility-scale solar thermal electricity. Its advocates believe it can and should become a large piece, along with other renewable-energy sources, of our energy future.

Solar thermal technology, also called concentrating (or concentrated) solar power (CSP), uses huge arrays of mirrors to focus sunlight and make steam to run a conventional turbine generator. The photovoltaic solar power systems used mostly on rooftops, in contrast, allow the energy of solar photons to create an electron flow using semiconductors. CSP provides "peak" power to feed the midday hunger for air conditioning and other loads, but with the addition of thermal storage CSP energy can also be banked for later use long past sundown. This could overcome one of the major obstacles to deploying solar power on a large scale.

Desert Opportunities

Almost as surreal as flying into Las Vegas at night is driving southeast from the sprawling city in the blazing sunlight of a typical day. As Highway 95 veers south about 50 kilometers from town, the tract-home developments have disappeared in the rearview mirror to be replaced by the sagebrush-dotted desert, and a silver-blue mirage appears shimmering in the distance. Apart from the transmission lines it is the only noticeable break in the El Dorado Valley's sepia tones. As you approach the glistening structure its body becomes more apparent--thousands of curved mirrors gazing up in unison.

Welcome to Nevada Solar One, a concentrating solar power station with 64 megawatts of generating capacity, enough to power as many as 14,000 homes. Reducing the plant to numbers--182,400 mirrors, 120 hectares, 1.2 million liters of heat transfer oil, over 3 million kilograms of recycled aluminum, 130,000 tons of avoided carbon dioxide per year, etc.--does not capture the magnificence of this technological feat. Although it is barely a tenth the size of a modern coal station, Nevada Solar One is a milestone as the first commercial CSP plant to be built in the United States in 17 years. It is a watershed moment for large-scale solar thermal energy, which had languished since Luz International, the original designer and builder of nine CSP units (total capacity: 354 megawatts) in California's Mojave Desert, went bankrupt in 1991 after struggling through years of inconsistency in state and federal subsidies and tax credits and finally their termination.

Now, thanks to a perfect storm of forces--growing public concern about coal's impact on climate, an influx of venture capital and clean-energy startups, skyrocketing oil prices, statewide renewable energy mandates, and federal tax credits--CSP appears poised to become a much larger piece of the U.S. energy mix. In doing so it could help wean the United States off carbon-based electricity and as a result, along with other options, provide a bit of "silver buckshot" to mitigate climate change.

"The world will have more and more demand for cleaner technology as economies grow. There's not enough [fossil] fuel to go around and we have a global warming issue," says Peter Duprey, chief executive officer of Acciona Energy North America, which owns Nevada Solar One.

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Other CSP proponents argue that solar thermal electricity is less of an environmental solution and more a national energy security insurance plan. "I don't want to say it's about saving the planet, but it's the right thing to do to get to energy independence," says Gilbert Cohen, senior vice president of Acciona Solar Power and manager of the Nevada facility, as he proudly guides visitors through the plant's rows of freshly washed mirrors on a crisp November day. This plant is his baby, after all. The French-born engineer helped found a company named Solargenix that started building the plant before Acciona's parent company, Acciona Energy, headquartered in Pamplona, Spain, bought a majority stake in it in 2004.

In fact, several solar projects are well under way in Europe, particularly in Germany and Spain. Another Spanish company, Abengoa SA, last spring opened Europe's first commercial concentrating solar power plant. A European research consortium is considering the prospects for powering much of Europe with arrays of CSP plants in North Africa and trans-mission lines under the Mediterranean. Several other countries, including Peru and Chile, are also strong candidates for CSP. In the United States, CSP is most suited to the Southwest, where the warm, sunny climate and pancake-flat, unpopulated desert stretches offer vast solar potential. "We have enough suitable land in the Southwest for CSP to support over 6 million megawatts of capacity," according to Mark Mehos, the CSP program manager at the National Renewable Energy Laboratory (NREL) in Golden, Colorado. NREL arrived at this value, which corresponds to a potential CSP contribution of kilowatthours equal to over four times U.S. demand, by measuring the solar radiation and subtracting all land area that was unsuitable due to its environmental sensitivity, urban location, or slope.