Xcel Energy has 1.1 gigawatts of wind turbines installed in Minnesota. They hope to triple that amount by 2020. Xcel, in an effort to increase the efficiency of their wind power systems, and combat the intermittent nature of wind has installed a bank of sodium-sulfur batteries capable of storing 7 megawatt-hours of electricity.
sodium-sulfur batteries are excellent batteries for storing grid energy. They are made from inexpensive, abundant materials, have a high energy density and have high efficiency charge/discharge cycles.
– from sustainabledesignupdate