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Nevada, Sicily to find staying power in molten salt

Solar thermal plants to retain heat and produce power even on sunless days.

The state of Nevada and Sicily, Italy, will each soon be using solar thermal plants that operate with molten salt to store and release solar energy.

Nevada got approval Thursday from the state's Public Utilities Commission for the Crescent Dunes Solar Energy Project, a 100-megawatt thermal solar plant estimated to generate 480,000 megawatt hours of electricity annually once completed.

Both plants will use giant heliostats that reflect sunlight onto pipes containing a molten salt fluid consisting of sodium nitrates and potassium. The heat absorbed by the liquefied salt is used to make high-pressure steam that directly powers a turbine for producing electricity. Since molten salt retains much of the heat it absorbs, the plant can draw on its heat for up to 24 sunless hours, according to SolarReserve, who developed the technology.

Once used for its heat, the cooled salt is fed back into the system to be reheated by solar energy and reused to produce steam for powering the turbine. The system allows the thermal solar plant to continue producing electricity even in the face of thick cloud cover or night.

SolarReserve's subsidiary Tonopah Solar Energy has signed a 25-year power of purchase agreement with the utility Nevada Energy to provide energy from the power plant.

The solar thermal plant opened in the town of Priolo Gargallo in Syracuse, Sicily by European energy company Enel two weeks ago is slightly different.

Though it will still employ the same type of technology as the Nevada-based plant, the 5-megawatt thermal solar plant in Sicily will work in conjunction with an existing gas-powered electricity plant. The high-pressure steam produced from that molten salt will be used to power the existing turbine in the gas plant with gas continuing to being used as a supplement.

The Syracuse, Sicily plant will also carry with it a bit of an historical pun. The plant, which will employ parabolic mirrors to reflect solar energy, was named "Archimedes" in reference to the mythical burning mirrors that "Archimedes is said to have used to set fire to the Roman ships besieging Syracuse during the Punic War of 212 BC," according to Enel

These are not the first plants in the world to use molten salt. SolarReserve announced in November 2009 a molten salt plant in Alcazar de San Juan, Spain, a town about 110 miles south of Madrid.

You can also bet there will be several more molten salt plants in our energy future. In May it was announced that the U.S. Department of Energy is giving a total of $62 million to 13 companies developing technology for thermal solar some of which are looking at molten salt for energy reserve storage.