01-01-11 Solar Plant to Generate Power After Sundown

Something new is headed for the Southwest desert: solar power plants that can make electricity whether or not the sun is shining.Abengoa Solar Inc. expects 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 creates steam that is used to turn power turbines.Abengoa's $2 billion Solana plant is expected to be the first major stored-heat plant in the U.S. 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 U.S. 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 can 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% of the heat created by the plant.Such storage technologies are expected to become more commonplace in the U.S. 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.Mark Mehos,a solar program manager for the National Renewable Energy Lab in Golden,Colo.,said such molten salt storage systems add about 20% to the construction cost of solar plants but more than make up for it by boosting a plant's flexibility and productivity.Electricity from solar plants is expensive,especially at a time when natural-gas prices have plunged,making gas-generated electricity cheap by comparison.Utilities,which are under state mandates to buy more clean power,say solar power may look more economical in the future if fossil fuel prices rise or if a tax is imposed on carbon emissions by power plants.