California says yes to molten solar

State approves commercial-scale solar plant using molten salt to store heat energy and increase capacity for electricity generation.

The California Energy Commission has approved a permit for SolarReserve to build a 150-megawatt solar plant that uses molten salt to store energy, the company announced Wednesday.

The Santa Monica, Calif.-based start-up says its Rice Solar Energy Project will be located 30 miles from Blythe, Calif., and when running at full capacity will supply enough energy to power the equivalent of 68,000 homes annually. The project also has a 25-year power purchase agreement with Pacific Gas & Electric (PG&E).

The molten salt system will enable the solar farm to store and release solar energy so that it can continue to generate electricity for up to eight hours after sunset, according to SolarReserve.

Molten salt solar plants, which have been built in Spain by SolarReserve with additional molten solar projects underway in Nevada and Sicily, work by using molten salt to retain and release heat energy.

In the case of a molten salt solar plant, heliostats--giant rotating mirrors controlled by computers to best track and reflect sun onto a specific point--reflect sun rays onto a central tower, or a series of pipes, containing a molten salt mixture. The molten salt generally consists of sodium nitrates and potassium. The solar rays heat the liquefied salt to a temperature of up to 1,000 degrees Fahrenheit. The steam from the molten salt is then harnessed to power a generator that makes electricity. Afterward, the cooled molten salt is then piped back to the tower to be heated once again.

In the case of the proposed Rice Solar Energy Project, the heliostats will be directed to a large central tower using a molten salt system developed by Pratt & Whitney Rocketdyne. The company received more than $10 million to develop more efficient molten-salt systems, as part of a Department of Energy (DOE) project sponsoring 13 companies with funds.

However, this latest California board approval does not mean this project is full steam ahead. The Rice Solar Energy Project still needs to receive approvals from both the Bureau of Land Management and the Western Area Power Administration, according to SolarReserve.

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