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November 23, 2014

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Storing the sun’s heat

Nevada, Arizona race to be the first to use emerging technology

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Photo courtesy of Nevada Renewable Energy Laboratory

Solar Two in Barstow, Calif., showed that molten salt could be stored at high temperatures for days without losing more than a couple degrees of heat. This allows solar plants to create energy virtually on demand, even after the sun sets.

The U.S. solar energy industry is poised for a major technological breakthrough, and Nevada is in a race with Arizona to be the first to take advantage of it.

The nation’s first commercial solar electricity generator using the holy grail of solar technology, particularly for the Southwest, will either be in Gila Bend, Ariz., or near Tonopah.

This is about more than a new source of electricity; it’s an economically viable heat storage capability that enables solar plants to produce power at night. If the Silver State wins the race to premiere a commercial solar heat storage plant, it would be another renewable energy “first” to crow about. It could help cement Nevada’s place as a world leader in the increasingly important industry.

The state is home to the nation’s first modern solar thermal plant, Nevada Solar One outside Boulder City, and the nation’s largest commercial-scale photovoltaic plant, Nellis Air Force Base’s 14-megawatt array. By the end of 2010, the state is expected to be home to the largest photovoltaic “thin film” array, Sempra’s Copper Mountain solar power plant outside Boulder City.

But competition for the next wave of solar plants is fierce, and every state wants its projects to outshine the rest. That’s because a reputation as a solar leader is expected to attract not only new large-scale solar development for a state, but also the more economically beneficial solar manufacturing sector. Manufacturing for the renewable energy industry has the potential to provide many more long-term jobs than construction and operation of renewable energy plants do. Most of the manufacturing is in California and Arizona.

The Crescent Dunes plant outside Tonopah would be another step toward more manufacturers setting up shop in Southern Nevada.

The introduction of the technology to be used at Crescent Dunes has the added significance of being more likely to produce energy that actually stays in Nevada. Exporting electricity from solar plants is controversial in a state that has little to gain from the industry other than short-term construction jobs.

Crescent Dunes is to be a cutting-edge operation, making electricity with Nevada’s solar resources for Nevadans. The plant is planned by California-based developer SolarReserve, which announced a deal this month to sell its 100 megawatts to NV Energy.

It will use giant mirrors to boil a saline mixture. The saline then turns to gas, turning a steam turbine that creates electricity. Excess molten saline is stored in heavily insulated tanks to generate more electricity later.

Thermal heat storage for solar plants was first tested in 1996 at an Energy Department and Southern California Edison project, Solar Two, in Barstow, Calif.

Solar Two showed that molten salt could be stored at high temperatures for days without losing more than a couple of degrees of heat. This allows solar plants to create energy virtually on demand, even after the sun sets, making them more attractive to utilities such as NV Energy that need reliable, consistent power through peak energy demand periods.

Most power from renewable energy is off and on. Wind turbines need wind, and solar power needs sunshine, with little to no clouds.

“You never know when they’re going to provide power,” says Tom Fair, renewable energy executive for NV Energy. “With storage you can run consistently at a certain level. For planning and working it into the grid, that’s important. Demand and supply for energy have to be balanced. With this technology, we won’t have to bring in another power supply as soon as the sun goes down.”

The technology is more useful to NV Energy and other Southwestern power companies than it is to those in other parts of the nation.

“Take California’s Pacific Gas & Electric — their customers have cooling breezes in the evening and may not need electrical cooling at night,” says Fred Morse, the Solar Energy Industry Association’s Concentrating Solar Power Division chairman, who also serves as the U.S. senior policy adviser to Abengoa Solar, the company that has a 280-megawatt solar heat storage project, Solana, planned for Gila Bend.

In parts of Arizona, as is true in Southern Nevada, air conditioners run through the hot summer nights. The peak energy use times are midday through late evening in summer and late evening through early morning in winter, making the areas well suited for the heat storage technology.

Like Crescent Dunes, Solana is scheduled for completion in 2013. Which plant will be finished first is hard to say.

The Crescent Dunes plant just completed the scoping process with the Bureau of Land Management, and plans for the plant are undergoing environmental evaluation. The plant is one of three solar projects in the state that the BLM granted “fast track” processing this week, but it could still take several months to complete the environmental impact statement.

Once that is completed, the environmental report must be made available to the public for 30 days for comment before the BLM decides whether to allow it. It would then take several months to build.

The Arizona plant is larger and expected to take longer to build, but the developers have permits. Construction could have begun, but the recession affected the developers’ ability to get financing.

“Everything is moving forward with Solana,” said Jenna Henry, spokeswoman for Arizona Power Service, a partner with Abengoa on the Solana project. “We expect to break ground in the first half of 2010. We’re just finalizing the financing, and we’ll get the ball rolling.”

NV Energy still has a few hurdles to clear before it could use Crescent Dunes power in Southern Nevada. The power purchase agreement with NV Energy has yet to be approved by the Public Utilities Commission, but the company will submit the contract for PUC review soon, Fair said.

There’s also the issue of actually getting the power from Crescent Dunes to Southern Nevada homes and businesses. The plant will be at the southern end of the Northern Nevada electrical grid. The state’s southern and northern grids don’t touch, so the only way to get the power between the two is to run it hundreds of miles through either California or Utah.

NV Energy’s vision of lighting the Strip with solar energy may hinge on the PUC signing off on the utility’s controversial plan to build a cross-state transmission line.

The OneNevada transmission line would allow renewable energy from the north’s geothermal, wind and solar plants to flow south to Las Vegas when demand is highest. And solar and natural gas-fired power can be sent north in winter, when Reno experiences higher demand.

The line is only controversial because a second privately funded line is planned for the same route. NV Energy’s line would cost more than $500 million and be funded by ratepayers.

If the PUC OKs it, NV Energy expects construction to be completed by the end of 2012, ahead of the anticipated completion of the Crescent Dunes plant.

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