GREEN ISSUE: ENERGY:The biggest problem with wind as an energy source has always been its unpredictable nature. One Irish company has found a way around that

WHEN IT comes to renewable energy, the mot du jour is storage. If you can find a way to efficiently store the power from a renewable resource like wind, you can provide the energy on tap as you need to draw on it.

That's exactly what Gaelectric want to do. The Irish company uses wind-generated power to compress air and store it under the ground in a large cavern or vessel, then releases the compressed air through a gas turbine when the energy is needed.

"There are very few supply industries where you have got a customer who wants something before you can deliver any product," says Gaelectric chief executive Brendan McGrath. "Normally if somebody wants something, you took something out of stock, but in the electricity business, it's created on demand.

"Looking at the power industry, it struck us that wind energy and the price you got for wind energy was disadvantaged because it was not predictable," he says. The company started to look into compressed air energy storage (CAES) around two years ago, and found the technology exists at two sites in the world - Germany and Alabama - as a power reservoir for coal and nuclear plants. Gaelectric argues the same storage approach could work for wind.

"We have a huge challenge to maximise wind resources, our ability to put it on the grid is weak at best," says geophysicist Keith McGrane, Gaelectric's head of energy and electricity storage. "Wind in Ireland blows strongest at night, but without storage you are spilling that power."

Gaelectric have identified a site near Larne in Northern Ireland where underground salt deposits could be leached from the ground to create cavernous space for storing compressed air.

Above ground, the associated plant would have a small footprint, says McGrane, who compares its size to that of a Lidl supermarket. If their feasibility study proves successful and the project gets the green light, it could reduce reliance on fossil fuels and enable more efficient use of wind energy, he says.

Meanwhile, the company is exploring options in Europe and has established operations in the US. In particular they have trawled through almost 100 sites of old mines and gasfields in the windy and sparsely populated northwestern state of Montana and identified two potentially suitable sites for CAES.

"We formed the view that Montana was potentially something like Saudi Arabia in the 1920s - there was a huge resource there, but they didn't actually need it themselves and it was always going to be about moving power from Montana to the likes of California," says McGrath, whose brother Éamonn now heads the company's operations in the US.

As well as developing the technical side, the company is looking at the financial and societal prospects of the compressed-air approach and how it could impact power supply, he says.

"We are quietly confident - we would expect that by the middle of March we would have a model that will show us what the value of CAES would be and how it would sit in the Irish market," says McGrath.