Lithium ion batteries aren't just for your laptop anymore. A group of truck-size battery banks are delivering quick bursts of power to the electricity grid in upstate New York.

AES Energy Storage, a subsidiary of power generation company AES, today said that the first 8 megawatts of a planned 20-megawatt battery grid storage system are now online in Johnson City, N.Y. The full project is expected to be completed later this year.

The network of batteries is designed to keep an even balance between energy supply and demand in that portion of the New York grid. The batteries will store energy and, based on a signal from grid operators, supply power for a few seconds as needed.

This battery system supplies eight megawatts of power to the grid in upstate New York to maintain a steady frequency. It will be expanded to 20 megawatts later this year.

The electric grid requires a steady frequency--the rate with which current changes direction in the U.S. grid. Frequency regulation, as it's called in the utilty industry, is traditionally done by turning up natural gas turbines to increase power into the grid.

The advantage of a battery-based system is that it can respond quickly--in as little as one second, according to AES--and is less polluting than turning up fossil fuel plant generation.

There are already battery storage systems connected to the grid, but AES said this is the largest in the U.S. Battery maker A123 Systems, which also makes batteries and cells for cars and power tools, supplied the hardware for the storage system.

The Johnson City project received a $17.1 million loan guarantee from the Department of Energy, which has funded a number of energy storage-related projects. Another technology being tested for frequency regulation is flywheels supplied by Beacon Power, which is developing a frequency regulation service in Stephentown, N.Y.

AES Energy Storage is making revenue on the project already since it gets paid for regulating the frequency, one of a few ancillary services provided to grid operators to maintain reliability. It says it has other frequency regulation projects in its pipeline, including one for 100 megawatts of power in advanced development.

Grid energy storage for different applications has risen in importance the last few years. Using storage can make the grid more reliable and make it easier to integrate intermittent wind and solar energy sources, say experts.