An Irish wind power company with offices in Great Falls has outlined a new technology that could make wind energy more marketable: "compressed air" power plants.

Keith McGrane, head of offshore energy and electricity storage for Gaelectric, said the compressed-air plant offers a way to use cheap wind power at night and then reproduce additional power in the day, to fill in the inevitable gaps when the wind isn't blowing.

"The wind can blow stronger at night than it does during the day," he said.

Gaelectric, which is based in Dublin and is looking at potential wind power sites in Montana, has identified two spots in the state that could serve as compressed-air power plants.

But more tests have to occur before the company knows whether a compressed-air plant will work as planned and provide the power needed to augment power coming from a wind farm, McGrane said.

A compressed-air energy storage (CAES) system would use low-cost, "off-peak" power, such as wind power generated at night, to operate motor-driven compressors, which compress air into large, underground storage caverns.

During times of high electricity use in the daytime, the air is withdrawn and combines with natural gas to fire a turbine, which produces electricity. The relatively low-cost power can be used to balance an electrical system that has intermittent wind, thus making wind a better fit for the system.

McGrane said the company isn't revealing the exact location of the two Montana sites, but geologist Mike King said they are in the eastern two-thirds of the state. Each site needs an underground storage cavern or formation that can hold 5 billion cubic feet of air, King said.

The plant itself is fairly small, covering only a few acres, King said. A CAES plant would cost about $105 million for a 140-megawatt plant, McGrane estimated.

A wind power developer like Gaelectric could use power from the plant to augment its wind projects, offering "firmed up" or steady power to a utility, instead of intermittent wind that has to be augmented with power from another source, he said.

Gaelectric, which is developing some wind power projects in Ireland, is looking for partners in financing the expensive process of finding and assessing sites for CAES plants, he said. Any financial incentives from the state would be helpful, he said.