In this article from Renewable Energy World, Tildy Banyar looks at developments in large-scale battery energy storage solutions for integrating variable output renewable generation into the grid. The original article is available here: http://www.renewableenergyworld.com/rea/news/article/2011/08/batteries-for-energy-storage-new-developments-promise-grid-flexibility-and-stability?cmpid=WNL-Wednesday-August31-2011.
Balancing power supply and demand is always a complex process. When large volumes of renewables such as solar PV, wind and tidal energy, which can change abruptly with weather conditions, are integrated into the grid, this balancing process becomes even more difficult.
The issue for power plants is flexibility. "Large amounts of wind energy are being reliably and cost-effectively integrated onto the power system today," said Denise Bode, CEO of the American Wind Energy Association (AWEA), who added "Energy storage can be a valuable resource for the power system in maximising the efficient use of this resource, and add flexibility for electric utilities."
The Electric Reliability Council of Texas Inc. (ERCOT) faced the renewable power industry's most critical issue in February 2008. With a huge wind portfolio in the state the wind died down, and ERCOT declared emergency conditions after a 1200-MW drop in production. The three-hour shortfall, accompanied by increasing overall electricity loads, very nearly caused rolling blackouts. David Crane, president and CEO of New Jersey-based NRG Energy Inc., told the Houston Business Journal that "If a system can go unstable in the winter because 1500 MW of expected wind turns into 400-MW wind and then fossil has to scramble to come online - and several of our plants had to scramble to fill the gap - that's a big issue and there's going to be a big debate."
Effective energy storage can match total generation to total load precisely on a second by second basis. It can load-follow, adjusting to changes in wind and solar input over short or long time spans, as well as compensating for longterm changes. While fossil plants may take 10 minutes or more to come online, and will consume fuel even on "spinning reserve" standby, storing renewable energy for later use effectively produces no emissions.
"Grid-scale storage is here now," says Ed Cazalet of MegaWatt Storage Farms, which develops and operates large electricity storage facilities that connect directly to the wholesale electric grid. "Storage should be deployed now at the gigawatt scale...where capacity, ancillary services and energy time-shifting are clearly needed," he adds. But each power plant faces different issues, and each requires a tailored energy storage solution.
Some well-established technologies offer significant energy storage capacity but require specific geographical features and considerable infrastructure. Others can be deployed rapidly to wherever they are required, but currently offer restricted capacity, often at high cost. One technology that is now attracting considerable interest is large-scale battery storage.