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Tonopah NV solar plant generates power at night

Crescent Dunes CSP plant, Tonopah

The Crescent Dunes Concentrated Solar Power plant 200 miles northwest of Las Vegas in Tonopah is now coming online. Unlike photovoltaic, CSP solar plants can store energy and thus generate power at night. 10,347 tracking mirrors, each about the size of a billboard, reflect the sun’s heat to the Crescent Dunes central tower to heat molten salt which powers turbines. The molten salt can also be stored and used to power the turbines for ten hours at full load at night. Thus, so long as the sun has shone that day in the Nevada desert, which it usually has, Crescent Dunes can produce electricity at night.

The Tonopah plant is next-gen CSP. Dry cooling technology minimizes water use, since the water is in a closed system, converted to steam then back to water over and over. Other CSP plants can store power, however none can do it as for as long as Crescent Dunes. This could be a game changer.

The facility still isn’t fully operational, but Painter said it is now in the final stages of startup. By early next year, he expects it to be delivering full power to NV Energy, which has agreed to buy the plant’s entire load at 13.5 cents per kilowatt hour — roughly twice the cost of power from a natural-gas fueled plant — for 25 years.

“We’re stepping through territory that’s never been stepped through,” Painter said. “We’re just being very cautious of how we bring it online.”

Solar Reserve, based in Santa Monica, explains how their molten salt system works.

Molten salt is circulated through highly specialized piping in the receiver (heat exchanger) during the day, and held in storage tanks at night – requiring no fossil fuels.

The tanks store the salt at atmospheric pressure.

Use of molten salt for both heat transfer and thermal energy storage minimizes number of storage tanks and salt volumes needed.

Molten salt is stored at 1050F until electricity is needed – day or night, whether or not the sun is shining.

As electricity is needed, molten salt is dispatched from the hot tank through a heat exchanger to create super-heated steam which then powers a conventional steam turbine.

The molten salt never needs replacing or topping up for the entire 30+ year life of the plant.

Heat loss is only 1F per day.

The salt, an environmentally friendly mixture of sodium nitrate and potassium nitrate, is able to be utilized as high grade fertilizer when the plant is eventually decommissioned.

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