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BrightSource to use salt – storage for its solar thermal PPAs with SCE

In August of this year, BrightSource Energy, a VC-funded CSP firm with gigawatts of PPAs in its pipeline, announced a power tower CSP system that includes two-tank molten-salt storage.

This week, BrightSource Energy announced that it has added storage capabilities to three of its power purchase agreements with Southern California Edison. BrightSource claims that adding storage allows utilities to "avoid the hidden costs associated with integrating intermittent resources that require fossil fuel back-up."

The advantages of molten-salt storage includes increased capacity factor. Extended production of electricity into later parts of the day and after the sun sets Greater operational flexibility to shape production to meet changing utility customer demand Added balancing and shaping capabilities, as well as ancillary services to support a reliable grid BrightSource’s power tower solar thermal system uses a field of software-controlled mirrors called heliostats to reflect the sun’s energy onto a boiler atop a tower to produce high temperature and high pressure steam. The steam is used to turn a conventional steam turbine to produce electricity. When paired with storage, the steam is directed to a heat exchanger, where molten salts are further heated to a higher temperature, storing the heat energy for future use.

Later, when the energy in storage is needed, the heat stored in the molten salts is used to generate steam to run the steam turbine. BrightSource claims to have efficiency and cost advantages over competing parabolic trough solar thermal technologies because of the power tower’s ability to reach higher temperatures and higher pressures during operation. According to the BrightSource S-1, the firm has at least three patent applications covering storage.

Today, molten salt storage is used widely in solar thermal plants in Spain from Abengoa and others. The “solar salts” are composed of 60 percent sodium nitrate (NaNO3) and 40 percent potassium nitrate (KNO3) -- commonly available materials.

Another entrant in the CSP with molten salt storage field is Santa Monica, Calif.-based SolarReserve, which is building a 110-megawatt solar thermal plant in Nevada with help from a $737 million DOE loan guarantee. SolarReserve CEO Kevin Smith told us back at Intersolar that it could produce power for close to 12.5 cents per kilowatt-hour, a figure that will drop to 7.5 cents in a few years.