This is a major issue with wind power generation.
Xcel Energy Launches Groundbreaking Wind-to-Battery Project
Minneapolis MN (SPX) Feb 29, 2008
Xcel Energy soon will begin testing a cutting-edge technology to store wind energy in batteries. It will be the first use of the technology in the United States for direct wind energy storage.
Integrating variable wind and solar power production with the needs of the power grid is an ongoing issue for the utility industry. Xcel Energy will begin testing a...(complete article here).