One of the biggest challenges transmission-network operators face in integrating large-scale solar and wind farms into their operations is the variability of these natural resources. A passing cloud or a lull in the wind can wreak havoc on a transmission system, as can the generation peaks that occur when the sky clears again or the wind picks up. Energy-storage equipment now coming online can help smooth out those valleys and peaks and could even help limit the need for new peak-period generating stations in the near future.

The term “energy storage” can include designs that compress air underground or pump water into storage ponds, both for later use in driving turbines. But today, the phrase most likely refers to batteries—really big batteries. Systems now range up to 32 megawatts (MW) or more in capacity, and while federal grants have helped jump-start such energy-storage efforts, the promise of the technology is attracting new players who see market success without the need for outside financing to help cover the costs.

Since September 2011, Public Service Co. of New Mexico (PNM) transmission system operators have been evaluating what they call the nation’s first solar-storage facility to be fully integrated into a utility power grid. PNM and the Electric Power Research Institute (EPRI) began collaborating on the Prosperity Energy Storage Project in 2008 (PNM began in 2006), and that early work put the team in a good position when U.S. Department of Energy stimulus funds became available in 2009.

The PNM design matches a 1 megawatt--hour (MWh) lead-acid battery system to a 500-kilowatt (kW) solar array. According to Steve Willard, P.E., PNM’s project manager and principal investigator for this installation, the batteries are helping the utility shift the solar panel’s output to better match customer-usage patterns and level the solar output during the array’s generating period.

“Our goal is to extract as much benefit from these batteries [as possible] year-round,” Willard said.

Summertime electricity demand can peak just as the sun gets closer to setting and customers return to their homes after work, so having the added battery capacity available during that time can aid overall system reliability.

“But during the rest of the year, we still have a lot we can do,” Willard said, adding that this includes using the batteries to store electricity PNM’s wind farms generate overnight, when the production may exceed system demands.

Willard sees federal incentives, such as the stimulus grant PNM received, as critical financing elements for similar battery installations elsewhere, but at least one private company sees plenty of opportunity, even where such assistance isn’t available. AES, one of the world’s largest electricity generation and utility owners, has started up AES Energy Storage to pursue such free-market opportunities. Its latest project is a 32-MW installation attached to sister subsidiary AES Wind’s 98-MW Laurel Mountain Wind Farm.

In this case, AES turned to lithium-ion batteries, the same basic power source used by laptop computers and plug-in vehicles. And, unlike the PNM project, Laurel Mountain’s batteries are intended to equalize the wind farm’s output and supplying ancillary grid-support services to the PJM Interconnection, which operates the region’s transmission system.

“This allows the wind farm to provide a service it otherwise might not be able to provide,” said John Zahurancik, vice president of deployment and operations at AES Energy Storage. He added that the batteries’ 8-MWh capacity enables them to supply a lot of electricity in short bursts to help PJM balance shortcomings throughout its system.

The Federal Energy Regulatory Commission (FERC) orders have opened the doors for a broader universe of energy suppliers to bid into energy auctions that once were closed to all but traditional generating plants. These orders allow this business model to function.

“They’re trying to bring competition from new technologies into the power market,” Zahurancik said.

AES Energy Storage has ramped up the size of its installations quickly, from its initial 1- and 2-MW pilot efforts in 2008 to the 32-MW Laurel Mountain project, which began commercial operation last fall. The company now has larger projects in mind, including a proposed 400-MW plant for the Long Island Power Authority.

“We are setting our sights on being an alternative to building a peaking power plant,” Zahurancik said, noting that, theoretically at least, developing larger battery plants is just a matter of adding more blocks to what is a very modular design.

And energy storage systems don’t have to be co-located with solar or wind plants. They can be sited wherever additional power support may be needed, charging up during low-demand periods from any available generation source. Because they produce zero emissions and run without need for cooling towers or other environmentally significant infrastructure requirements, they also are likely to face less local opposition.


ROSS is a freelance writer located in Brewster, Mass. He can be reached at chuck@chuck-ross.com.