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Renewable energy has a critical role to play inreducing greenhouse gases and leading the United States toward energyindependence. That role should soon be getting bigger: The U.S.government is pushing for a 100 percent increase in renewable energy by2012. The two biggest sources are the wind and the sun. But thevariable nature of wind and solar energy can cause problems withmatching supply to demand�problems that would be greatly eased if onlywe had a really good way of storing electricity on an industrial scale.Currently there are several storage systems vying for dominance.Compressed-Air Energy StorageAtnight, when the strongest winds blow and customers are sleeping, unusedwind-generated electricity can run giant compressors, forcing largeamounts of air into sealed underground spaces. When demand rises duringthe day, the compressed air can be used to spin turbines, turning theenergy back into electricity. A mechanical engineer at Sandia NationalLaboratories in New Mexico, says this technology can provide a lot ofpower over long periods of time at a relatively low cost. Thetechnology is also well established: Two compressed-air storage plantshave been in operation for decades. The McIntosh Unit 1 plant inMcIntosh, Alabama, went online in 1991; a similar plant in Germany hasbeen running since the 1970s. McIntosh 1 can reliably put out 110megawatts for 26 hours. (One megawatt is enough power to supply roughly600 to 1,000 typical American homes.)The compressed-air systemdoes have its drawbacks. For one, it does not completely eliminate theneed for fossil fuels, because the associated electric generators usenatural gas to supplement the energy from the stored compressed air.Compressed-air storage systems also require an airtight undergroundspace, limiting the locations where they can be installed. The twoexisting compressed-air plants use natural salt domes. Engineersflushed the domes with water to dissolve the salt, then pumped out thebrine to create a nicely sealed cavern. But salt dome formations arenot plentiful, so researchers are investigating other inexpensive waysto create storage chambers. A facility proposed for Norton, Ohio, woulduse an abandoned limestone mine. Another, in Iowa, would pump air intodrained natural aquifers. Abandoned oil wells and depleted natural gasreservoirs might also work, Peek says, as long as they are not tooremote to be hooked into the electrical grid.
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