They require backup to provide continuous power. Of the clean air options, hydro isn't available everywhere, and nuclear remains controversial in part because of the problem of how to deal with spent radioactive fuel.
Energy storage may provide at least part of a solution for darkness and times of no wind.
Sens. Jeff Bingaman, D-N.M., Ron Wyden, D-Ore., and Jeanne Shaheen D-N.H., have introduced the "Storage Technology of Renewable and Green Energy Act of 2010," or S.3617, which would offer about $1.5 billion in tax credits for renewable energy storage connected to the domestic electric grid.
Bingaman said in a statement that increasing energy storage capacity "would help promote intermittent energy sources like wind and solar power while reducing energy demands during peak hours and contributing to an overall more reliable smart grid."
"Expanding our storage capacity will improve the efficiency, flexibility and reliability of our electric grid, allowing us to wring the most power out of it, while adding large amounts of new renewable energy resources like wind and solar," said Bingaman, who chairs the Senate Energy and Natural Resources Committee. "Growing our ability to store renewable energy not only promotes a more efficient use of energy resources, it makes energy sources like wind and solar just as reliable as conventional energy sources that burn fossil fuels."
Development of wind and solar on their own are driving demand. Boulder, Colo.-based Pike Research said in a study released in May, Energy Storage Systems for Ancillary Services, that demand for storage also is being driven by development of the smart grid and the expectation of households and businesses using plug-in hybrid and electric vehicles.
"Energy storage systems are being developed by technology providers in a wide range of solutions, from batteries, flywheels and mechanical storage," the study said. It also said a key emerging area includes frequency regulation, spinning reserve, voltage control and other services.
"It will be interesting to see if the STORAGE Act passes in something like its current form," said Richard T. Stuebi, a founding principal of NorTech Energy Enterprise, on Cleantechblog.com. "If it does, it could well signal the breakout of a new frontier in the cleantech space. If not, like so many things in the cleantech realm, grid storage may be an idea whose time has not yet quite come."