Batteries at a Wind Farm Help Control Output

Source: Matthew L. Wald • Posted: Saturday, October 29, 2011

ELKINS, W.Va. — Another wind farm opened on another windy ridge in West Virginia this week, 61 turbines stretched across 12 miles, generating up to 98 megawatts of electricity. But the novel element is a cluster of big steel boxes in the middle, the largest battery installation attached to the power grid in the continental United States.

The purpose of the 1.3 million batteries is to tame the wind, but only slightly, according to the AES Corporation of Arlington, Va., which developed both the wind farm, known as Laurel Mountain, and the battery project.

The installation is far too small to store a night’s wind production and give it back during the day when it is needed, or to supply power when the wind farm is calm for more than a few minutes. Instead, AES says, the battery will be a shock absorber of sorts, making variations in wind energy production a little less jagged and the farm’s output more useful to the grid.

The technology is young, and the finances are challenging. But the task of smoothing output, and the more ambitious one of storing many hours of electricity generated by wind production, seem likely to become ever more important as states require that a rising percentage of their electricity come from renewable sources.

The 13-state regional power grid that includes West Virginia, for example, has a capacity of 4,800 megawatts of electricity from the wind. But that number would grow eightfold if all of the states involved reached their renewable targets.

Power systems have always faced fluctuations in demand. As they incorporate more wind into the mix, they will have to cope with supply fluctuations as well.

Predicting wind output can be a challenge. “If you blow your forecast, you’re in a heap of hurt,” said one storage expert, David L. Hawkins, a senior consultant at KEMA, a consulting firm.

Other power sources, mostly natural gas plants, can be called on as replacements, but such plants take longer to ramp up — or ramp down — than a wind farm or a field of solar panels, a problem that is becoming more widely recognized across the country. This year, two big manufacturers of gas-fired power plants, Siemens and General Electric, promoted new models that could change output faster, but system operators say that even these may not be nimble enough.

“That’s the challenge you have in running the power system,” said Mark T. Osborn, an executive at Portland General Electric in Oregon who is working on a similar installation in the Pacific Northwest. “Storage has been thought about for years, but the costs have always been too high. Now when you’re trying to integrate more renewable resources, storage becomes more necessary.”

Already, in periods of low energy demand on windy nights, wind production is so strong that electricity prices on the grid can decline to zero or even go negative. When they are negative, grid operators bill wind suppliers to put power into the system.

In theory, the assumption would be that the operators of the batteries here would charge them at night and release the energy during peak periods in the daytime.

But the batteries are so small — somewhere between C and D batteries in size — that the wind farm, at full power, would fully charge them in about 15 minutes. Even at a peak demand time, the energy stored would only be worth a few hundred dollars.

The economics can be likened to storing tap water in a solid gold vessel. While AES did not disclose the price of the wind farm or the battery installation, a company executive gave a nod when presented with an industry estimate that the batteries and related electronics cost in the range of $25 million. The supplier, A123 Systems, of Westborough, Mass., says future installations will use batteries developed for electric cars and will cost less.

Yet the batteries perform two other tasks that the company hopes will turn a profit and pave the way for even bigger projects.

Rather than store power on a daily basis, said John M. Zahurancik, vice president for operations and deployment at AES Energy Storage, the installation will earn its keep by storing energy for minutes at a time, over and over again.

In the space of an hour, the output from the wind farm could go from 98 megawatts to zero. “In any short couple-minute interval, it could vary 20 or 30 or 40 percent,” Mr. Zahurancik said.

The batteries will smooth out the changes so the rest of the grid can catch up, he said, making the electricity sold more valuable.

The battery installation will also assist with a different kind of grid stabilization: trying to keep the alternating current system correctly synchronized. To keep the system as close to 60 cycles as possible, the regional grid operator, the PJM Interconnection, sends a signal every four seconds, asking for power to be added or withdrawn.

Experts foresee other roles as the grid evolves. For example, PJM operates a real-time market in which electricity is priced in five-minute blocks. At a given location, the price from one block to the next can vary significantly.

Mr. Hawkins of Kema said that a big battery array could make money in that market.

“It’s kind of like being a day trader on Wall Street,” he said. “If you see a $30 price spread, you can make some interesting trades doing it over and over in the course of a day.”