Storing the wind under water

Sensemaking / Storing the wind under water

Experimental 'energy bags' that store wind power as compressed air could make offshore wind a more reliable source of electricity.

05 Aug 2011

Experimental 'energy bags' that store wind power as compressed air could make offshore wind a more reliable source of electricity.

An underwater device to store energy from offshore wind turbines is being tested off of the Scottish coastline. The so-called ‘energy bag’ will store the turbines’ output as compressed air, which can later be released to provide electricity. If all goes to plan and the device is rolled out, the result will be wind power whatever the weather.

The development is part of a £1.1 million research programme at Nottingham University to develop a new generation of super batteries and energy storage systems, funded by E.ON. The bag will be anchored to the sea bed at a depth of 600m, where the surrounding water pressure can help to contain the compressed air, limiting the costs normally attached to high pressure storage. Measuring 20m in diameter, it will be able to store 70MWh – the equivalent of 14 hours of wind turbine production. It was developed by Thin Red Line Aerospace, which also designs stress-resistant inflatable structures for NASA.

“If for every 3MW of wind energy generated you have 1MW of compressed air storage, then offshore wind starts to look like a very versatile power-generating system which can adjust its output to match demand”, says Seamus Garvey, the University of Nottingham professor leading the project. By 2025, Garvey estimates, at least 25% of offshore wind power in the UK could be combined with a compressed air storage system.

The installation could allow energy to be stored at under £10,000/MWh, according to Garvey. That’s less than 20% of the cost of the cheapest alternative, pumped hydro, where energy is stored by pumping water up to high reservoirs when demand for electricity is low, and releasing it through turbines at peak times.

The fact that many sources of clean energy are intermittent is often cited as an obstacle to taking renewables to scale. But there are many ways of dealing with this problem, says Jim Skea, Research Director at the UK Energy Research Centre: “This [energy bag] is obviously still a bit experimental, but it could form a good part of that portfolio of options.”

Nottingham has also been investigating the possibility of using pre-existing geological formations, such as salt domes, as high pressure containers. – Ian Randall

Photo credit: Keith Thomson / Thin Red Line Aerospace

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