Arizona Solar Plant to Generate Power After Sundown

Something new is headed for the US Southwest desert: solar power plants that can make electricity whether or not the sun is shining, The Wall Street Journal reported Friday.

Abengoa Solar Inc. expected to start construction in mid-2011 on a plant in Arizona that will store sun-generated heat to provide six extra hours a day of electric-generating capacity. The heat will create steam that can be used to turn power turbines.

Abengoa's $2 billion Solana plant is expected to be the first major stored-heat plant in the US when it enters service in 2013. Some already exist in Spain and a few more are on the drawing board for Nevada and California.

On Dec. 21, Abengoa, a unit of Spanish utility company Abengoa SA, cleared a major hurdle when it announced it received a $1.45 billion US loan guarantee for the 250-megawatt Arizona project, planned for a site 70 miles southwest of Phoenix near Gila Bend.

The Solana plant will be able to meet winter heating and lighting needs by putting electricity on the grid early in the morning -- before the sun is shining -- and help satisfy summer cooling demand by producing power after sundown. The plant, which could power up to 70,000 houses, has signed a 30-year agreement to sell electricity to utility company Arizona Public Service.

Such utility-scale solar plants use mirrors to focus the sun's rays on a liquid, contained in tubes, which can be heated to very hot temperatures. The liquid is used to boil water and create steam. By using a conventional steam turbine generator, electricity is produced.

But the twist is that the Arizona facility will have two giant salt tanks, each 122 feet in diameter and 34 feet deep, that together can hold and store 40 percent of the heat created by the plant.

Such storage technologies are expected to become more commonplace in the US at solar plants as officials try to limit the release of carbon dioxide from fossil fuel power plants and make renewable power production more dependable.