Utility solar project adds molten salt for storage

SolarReserve lands deals to build concentrating solar power plants that can deliver power even with the sun isn't shining by using heated salt as storage.

Updated at 2:30 p.m. PST with additional information on PG&E deal.

SolarReserve said on Tuesday it has signed a deal to build a utility-scale solar plant in Nevada with a molten salt storage system that will let it supply power when the sun isn't shining.

The Santa Monica, Calif.-based company has a 25-year power purchase agreement with utility NV Energy to supply about 480,000 megawatt-hours of electricity a year, enough to power about 75,000 homes during peak times. The capacity of the concentrating solar system will be 100 megawatts and be located near the town of Tonopah in Nye County, Nev.

The plant will use a field of heliostats--large mirrors that track the movement of the sun--to heat molten salt held in a tower. That liquid salt is heated to over 1,000 degrees Fahrenheit and transferred to storage tanks. It is then fed into a loop where it creates steam that turns a turbine to generate electricity. The colder molten salt is recaptured and fed back into tanks to be heated again.

Click for larger image. SolarReserve

The company did not indicate how many hours of storage it intends to have at the Tonapah plant but said that the solar field will be able to deliver energy at peak times even when the sun isn't shining.

Construction of the project is expected by the end of 2010, but it still needs approval from the Nevada Public Utilities Commission.

The southwest U.S. is prime land for concentrated solar thermal technology, which needs the right sun angle and a lot of sunlight. Utilities in California and other states are pursuing large-scale solar projects to meet state mandates for renewable energy generation.

The addition of a storage system adds to the overall cost per kilowatt-hour of solar. But it allows the power producer to deliver electricity during peak times when the cost of electricity is highest.

Also on Tuesday, California utility Pacific Gas & Electric said that it has signed a contract to purchase electricity from a SolarReserve-developed project at the Rice Airfield in San Bernardino County, Calif.

The proposed Rice Solar Energy project, which has not yet been approved by state regulators, would produce 150 megawatts of electricity, or enough to power 60,000 average homes, starting in 2013, according to PG&E.

In a company blog, PG&E said that the molten salt storage technology was successfully demonstrated in the 1990s at the Solar Two power plant in California, and plants in Spain have also used the technique. "Best of all, a well-insulated storage tank for molten salt can be 99 percent efficient, so it loses heat only very gradually," company representative Jonathan Marshall wrote.