Renewable energy has a critical role to play in reducing greenhouse gases and leading the United States toward energy independence. That role should soon be getting bigger: The U.S. government is pushing for a 100 percent increase in renewable energy by 2012. The two biggest sources are the wind and the sun. But the variable nature of wind and solar energy can cause problems with matching supply to demand—problems that would be greatly eased if only we had a really good way of storing electricity on an industrial scale. Currently there are several storage systems vying for dominance.
Compressed-Air Energy Storage At night, when the strongest winds blow and customers are sleeping, unused wind-generated electricity can run giant compressors, forcing large amounts of air into sealed underground spaces. When demand rises during the day, the compressed air can be used to spin turbines, turning the energy back into electricity. Georgianne Peek, a mechanical engineer at Sandia National Laboratories in New Mexico, says this technology can provide a lot of power over long periods of time at a relatively low cost. The technology is also well established: Two compressed-air storage plants have been in operation for decades. The McIntosh Unit 1 plant in McIntosh, Alabama, went online in 1991; a similar plant in Germany has been running since the 1970s. McIntosh 1 can reliably put out 110 megawatts for 26 hours. (One megawatt is enough power to supply roughly 600 to 1,000 typical American homes.)
The compressed-air system does have its drawbacks. For one, it does not completely eliminate the need for fossil fuels, because the associated electric generators use natural gas to supplement the energy from the stored compressed air. Compressed-air storage systems also require an airtight underground space, limiting the locations where they can be installed. The two existing compressed-air plants use natural salt domes. Engineers flushed the domes with water to dissolve the salt, then pumped out the brine to create a nicely sealed cavern. But salt dome formations are not plentiful, so researchers are investigating other inexpensive ways to create storage chambers. A facility proposed for Norton, Ohio, would use an abandoned limestone mine. Another, in Iowa, would pump air into drained natural aquifers. Abandoned oil wells and depleted natural gas reservoirs might also work, Peek says, as long as they are not too remote to be hooked into the electrical grid.
