The biggest chemical battery in the U.S. sits near the small town of Luverne, Minn. About the size of two tractor-trailers stacked on top of each other, the battery can power about 3,000 houses for more than an hour when discharging at its maximum rate. The battery draws its power from energy generated by a local wind farm. It helps to regulate the power production fluctuations of the wind turbines that feed energy onto the electrical grid, storing energy when the wind blows strongest and when the power demand from the grid is the lowest. This energy is eventually released to lessen the strain on the electrical grid.
The Dept. of Energy thinks massive energy storage like this will be important in making renewable sources practical. Recently it announced the first round of almost $20 million in stimulus funds targeting the development of new battery chemistries for large-scale storage. The funds are coming from a relatively new DOE agency, the Advanced Research Projects Agency-Energy -- created in 2007 in the image of the Department of Defense's DARPA.
Today's biggest batteries -- including the one in Minnesota and a device intended for emergency power in Texas -- are made by the Japanese ceramics company NGK Insulators. Incentives for renewable power offered by the island nation have led to the installation of NGK's largest battery, more than five times bigger than the Minnesota battery.
The chemistry inside these sodium-sulfur batteries is similar to that of the lead acid battery inside of a car. Instead of lead plates, the NGK batteries use molten sulfur and molten salt. A solid piece of ceramic serves as the electrolyte that lets electrons flow between the two hot liquids. This gives the batteries about a 15-year (4,500 charge and discharge cycle) lifetime, during which their efficiency at absorbing and discharging energy drops from about 92 to 75%.
But experts say such sodium-sulfur batteries are still too expensive, hence the need for new developments in this area. Physorg.com has the story: