New rays of hope for solar power’s future

High cost of fossil fuel and advanced technology improve this energy source’s prospects.

Mark Clayton
Acciona Solar Power’s Dan Kabel (left) and plant manager Robert Cable inspect a mirror array.

From five miles away, the Nevada Solar One power plant seems a mirage, a silver lake amid waves of 110 degree F. desert heat. Driving nearer, the rippling image morphs into a sea of mirrors angled to the sun.

As the first commercial “concentrating solar power” or CSP plant built in 17 years, Nevada Solar One marks the reemergence and updating of a decades-old technology that could play a large new role in US power production, many observers say.

“Concentrating solar is pretty hot right now,” says Mark Mehos, program manager for CSP at the National Renewable Energy Laboratory in Golden, Co. “Costs look pretty good compared to natural gas [power]. Public policy, climate concern, and new technology are driving it, too.”

Spread in military rows across 300 acres of sun-baked earth, Nevada Solar One’s trough-shaped parabolic mirrors are the core of this CSP plant – also called a “solar thermal” plant. The mirrors focus sunlight onto receiver tubes, heating a fluid that, at 735 degrees F., flows through a heat exchanger to a steam generator that supplies 64 megawatts of electricity to 14,000 Las Vegas homes.

Today the United States has 420 megawatts of solar-thermal capacity across three installations – including Nevada Solar One. That’s just a tiny fraction (less than 1 percent) of US grid capacity. But Nevada Solar One could signal the start of a CSP building boom.

Efforts to generate another 4,500 megawatts of solar thermal power are now in development across California, Nevada, Arizona, and New Mexico – all of which have the flat, near-cloudless skies most desirable for solar thermal, the Solar Electric Industries Association reports.

Photovoltaic panels that produce electricity directly from the sun’s rays work well on rooftops, but are still too costly for utility-scale power generation. Solar thermal, however, is nearing the cost of a natural gas-fired turbine power plant – making it a winner with several power companies that have signed long-term contracts to purchase solar-thermal power.

Desert land lures developers
In fact, there’s a land rush at the federal Bureau of Land Management. As of July, the BLM reported more than 125 applications to build solar power on about 1 million acres of desert, up from just a handful of proposals a few years ago.

“We think there’s a good market there,” says Travis Bradford, an expert at the Prometheus Institute, a Boston-based solar-energy market research firm. His firm sees 12,000 megawatts (12 gigawatts) of solar thermal installed by 2020 and maybe 20 times that in coming decades.

Dr. Mehos says perhaps 100,000 megawatts (100 gigawatts) could be built across the US Southwest over the next 30 years.

“You could supply the entire US with the sun power here in a little piece of the Southwest,” says Dan Kabel as he strolls beneath a row of trough-shaped mirrors. Mr. Kabel is chief executive of Acciona Solar Power, which owns the $266 million Nevada Solar One project. “As fossil fuel costs rise, this plant is unaffected. “If America doesn’t do this, if we don’t install many more of these clean solar-power systems, we’ll just end up seeing a lot more fossil-fuel plants instead.”

Still, the cost of power remains critical. Commercial CSP systems emerged in the late 1990s, only to be squashed by falling natural gas prices.

Today, as natural gas prices rise along with concerns about carbon emissions and global warming, the stable, predictable costs of carbon-free solar thermal is increasingly comforting to utilities.

“What’s different now from the ’80s and ’90s is that we have much higher natural gas prices than back then,” Mehos says. “I don’t think people foresee a serious drop in natural gas prices now. Even if they fell 30 percent, CSP would look attractive.”

The importance of tax credits
Concentrating solar technology produces electricity for about 17 cents per kilowatt hour (kWh), Mehos estimates. But subsidies remain critical to solar thermal development in both the US and Spain, two global hotbeds of CSP development. With the federal investment tax credit, or ITC, costs drop to about 15 cents per kWh – low enough to compete with natural gas.

A key feature of solar thermal is its potential to use heat-storage technology to generate power after the sun sets. Nevada Solar One is considering adding a molten-salt or similar system to allow it to supply power for several hours after sundown.

With such storage systems, solar thermal becomes even more attractive to utilities, experts say. Arizona Public Service is contracting with Abengoa to build a 280-megawatt solar thermal plant near Phoenix that will cost more than $1 billion and have molten-salt heat storage.
“Arizona Public Service really does want to put this [solar thermal] plant in because in the future this really could replace natural gas,” says Reese Tisdale, an analyst at Emerging Energy Research, a market-research firm in Boston. “They’re the first to say that once this plant is installed, the fuel is free.”

So far, US development of solar thermal is dominated by a handful of big overseas companies, including Abengoa and Acciona (Spain), as well as Solel Solar Systems (Israel), Solar Millenium (Germany), and Ausra (Australia), now headquartered in Palo Alto, Calif.

To stimulate development, Spain has deployed hefty, long-term feed-in tariffs. But in the US market, solar thermal is hanging by a thread. The investment tax credit, which covers 30 percent of a CSP facility’s cost, will expire at year’s end unless renewed by Congress. But bills to renew the ITC have been blocked eight times this year by Senate Republicans.

“What we’re seeing with all these companies lining up for solar thermal is hugely promising,” says Monique Hanis, spokeswoman for the SEIA. “But without the ITC, all of these solar thermal plants will be put on hold.”

That would pour cold water on a raft of potential breakthrough solar-thermal technologies promoted by US companies. So far this year, five US-based start-up CSP companies have gotten $419 million in private funding for their technologies, Emerging Energy Research reports.

BrightSource Energy, Stirling Energy Systems, eSolar, Skyfuel, and Infinia Corp. are start-up US companies pursuing refinements of existing technologies – and major new ones – and the funding to prove them. One of the key goals is to make mirrors and receivers more efficient in order to achieve higher temperatures – which tend to make for greater efficiency and lower cost.

BrightSource Energy, funded by Google and others, received $100 million in May to proceed with its advanced “central receiver” approach. It has refined 1990s technology to develop simpler, cheaper to manufacture mirrors that focus the sun’s rays on a tower receiver, heating water to nearly 1,000 degrees F.

By contrast, Stirling Energy Systems in April received $100 million to further develop its “SunCatcher” approach – a relatively small system in which a 38-foot dish supporting 82 curved glass mirrors automatically tracks the sun. The solar heat is focused onto a high-efficiency four-cylinder reciprocating Stirling engine. The Stirling engine uses solar heat to expand (not burn) hydrogen gas to move its pistons, which spin an electric motor with no fuel cost or pollution.

Each SunCatcher dish generates about 25,000 watts, turning about 30 percent of the sun power that strikes it into electricity, compared with about 20 percent for parabolic-mirror systems.

Although the technology has yet to be proven on a commercial scale, Stirling Energy Systems announced in June that it had applied for permits to build a 750-megawatt “Solar Two” facility on 6,500 acres of desert in California’s Imperial Valley about 100 miles east of San Diego. When complete, the plant could supply power for about 500,000 homes.

Another technology called “linear fresnel” is being pursued by Ausra, which has opened a factory in Las Vegas to build inexpensive mirrors mounted on rolling platforms. Though operating at lower temperatures, the technology could operate at costs well below current levels, some observers say.

Back at Nevada Solar One, Mr. Kabel looks out across the desert to a hulking building on the horizon – a natural gas fired turbine power plant – an arch rival power producer. But maybe not for too much longer.

“The way things are going, with our costs coming down, this valley is going to see a lot more of these,” he says, gesturing to the rows of mirrors. “Fossil fuel generation is headed one way – like the dinosaurs.”

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