Saving wind power for later

Start-up General Compression looks to commercialize concept for storing electricity generated by wind turbines using compressed air. Image: Pumping wind power underground

Martin LaMonica Former Staff writer, CNET News
Martin LaMonica is a senior writer covering green tech and cutting-edge technologies. He joined CNET in 2002 to cover enterprise IT and Web development and was previously executive editor of IT publication InfoWorld.
Martin LaMonica
5 min read
A start-up says it's devised a system to produce electricity from wind turbines even when there is no wind, taking on the major challenge of storing wind-generated power.

General Compression, based in Attleboro, Mass., last week said it received a $5 million round of seed funding to commercialize a wind-power storage system that uses compressed air.

Wind turbines typically have an onboard power generator that sends electricity down the tower and onto the grid. General Compression plans to break with that basic design and place an air compressor in the nacelle, the housing on a turbine where the generator usually sits.

Its plan calls for sending highly compressed air down the tower and into underground storage, such as caves or depleted gas wells, or through pipelines. The pressurized air can be released when needed to power an electricity generator, even if wind is not spinning the turbine's blades.

General Compression is one of a wave of companies trying to meet a growing demand for clean sources of power. Like others, the company is trying to commercialize concepts that have been around for decades but not fully pursued because they were considered too expensive or technically difficult. Now, with higher prices of energy forecast, these ideas are being applied to the clean-energy market.

Company executives argue that a compressed-air energy storage system will allow wind farm operators to charge more for their product.

Rather than get paid for electricity only when the wind is blowing, they can now make wind-generated power available when the demand--and price--is highest, say company executives.

"The problem with wind is intermittency," said company president Michael Marcus. "It does not garner high prices from power purchasers because it is not schedulable...(but) you can get a higher price if it's available on demand."

For example, if the wind is blowing hardest at 11 at night, a wind farm operator could store the energy generated from the wind and release it at 10 o'clock the next morning when demand for power starts spiking up.

The compressor was designed by Mechanology, a compressor research and development firm which spun off General Compressor in 2005 and remains a shareholder.

The company now has a prototype device and plans to build a large-scale version of put it through testing later this year. The plan is to test the "compressor array" in a turbine in the field next year, Marcus said.

Iowa's stored-energy park
Although General Compression's design is a radical change from existing turbines, the compressed-air energy storage (CAES) idea has already been implemented.

There are two existing compressed-air storage facilities in operation, one in Germany and one in Alabama. But neither is fueled by wind turbines.

A more recent development is the Iowa Stored Energy Park, which recently chose a site for a CAES operation with wind power in mind.

Projected to cost $200 million and funded primarily by municipalities, the Iowa Stored Energy Park will store compressed air in an underground aquifer in central Iowa, said Kent Holst, the project's development director.

In large part, the gear required for the operation is already available because they intend to modify equipment used to store natural gas underground, he said. "The most difficult part was finding a usable geologic structure. Several are already being used for natural gas storage," Holst said.

Compressed-air energy storage

In the Iowa project, set to be online in 2011, the wind turbines will not be on site, but the motors to power the compressor are expected to be generated from wind electricity.

The economic reasoning behind the operation is to store wind power when the resource is available and sell it on the market at peak demand times, Holst said.

Wind power--an industry that is seeing a boom in turbine construction--already operates in a cost-effective manner even though utilities can't rely on wind turbines at all times, said Josh Magee, senior wind analyst at Emerging Energy Research.

But if utilities were able to count on wind power to boost the capacity they need to meet their highest demand, such as the middle of a hot summer day, it would make wind power far more attractive, he said.

"If you could figure out a way to do it cost effectively and show (utilities) you can be very profitable at it...then you would have the ability to rapidly scale wind power," he said. "If all of the sudden you had capacity, you can make a bigger dent in climate change, energy security and make a significant contribution to peak demand."

For years, government research efforts have explored the idea of "firming up" wind power--that is, make it available during peak times--by storing electricity in fuel cells or batteries, but there have been few significant attempts, Magee said.

The 'Saudi Arabia of wind'
Compressed-air energy storage is promising, but Magee said General Compression itself faces a number of challenges.

The company has a substantial engineering task ahead of it, and it has to prove that the resulting equipment will be financially interesting to wind farm investors, he said.

Also, finding appropriate sites for General Compression's turbines would be even more complex than typical wind farms because some sort of geological formation, such as depleted gas fields or mines, would be required for storage in many cases.

Executives at General Compression, however, see a number of applications where on-site storage makes sense.

Its planned customers are utilities or energy-intensive industries, such as aluminum or fertilizer makers. The compressed air also can be used for carbon dioxide sequestration or to make hydrocarbon fuels like methane or methanol, Marcus said. U.S. government agencies have expressed interest in wind-powered military bases that would not be dependent on the electric grid.

In the case where there isn't a geologic formation available, underground pipelines--now used for natural gas--could store between 6 and 12 hours of a wind farm's power generation.

Marcus and his brother David, who is company CEO, have been working in the wind industry for about four five years. In trips to the Dakotas, Marcus said he feels he's standing in the "Saudi Arabia of wind power," although no one has yet to put a drill in the ground.

He predicts that if deployed widely, wind could make up over half of the U.S. power generation--a far cry from today. The total amount of power generated by wind turbines is growing rapidly worldwide, but it represents a tiny fraction of total electricity generation in the U.S., according to the Department of Energy.

"You're never going to change the fact that wind is intermittent, but there's so much energy there to be grabbed," Marcus said. "The equipment doesn't need to get better. The price for the energy needs to change."