North Sea Rocks Could Store Months Of Renewable Energy

The power generated from these turbines when winds are strong could be stored in rocks beneath them for winter when demand is greatest. PORNPIPAT CHAROENTHAI/Shutterstock

Already the site of the world's mightiest wind turbines, and following its bonanza of oil and gas, the bed of the North Sea may offer a third way to power Britain. Rocks beneath its waters have been shown to have the potential to store months' worth of energy, allowing the UK, and possibly nearby nations, to run on renewable energy year-round.

Dr Julien Mouli-Castillo, of the University of Edinburgh, has examined North Sea geological records and noted the region is rich in porous sandstone aquifers that could hold enough compressed air to power the country for months.

The cheaper solar and wind power get, the more attention turns to how to store the energy they produce for periods of low production. As batteries come down in price, the challenge of storing a nation's power overnight looks increasingly achievable. Northern Europe, however, has the greatest demand for electricity in winter, when solar power at high latitudes is of little use and wind alone may not be enough. A way needs to be found to store power for months at a time.

Compressed air could be the answer. The air is placed under high pressure when electricity is cheap, and is released to drive turbines when demand outstrips supply. Naturally, the system is much more affordable if the storage container comes pre-provided. Germany and the US have turned caverns within salt deposits to this purpose. They work well, but the supply is limited close to where the power is produced or consumed.

In Nature Energy, Mouli-Castillo notes large areas of the North Sea rest on porous rocks. The geology of the area is exceptionally well known because so much of it has been drilled for oil and gas. Drawing on a database of the 11,000 drilling operations in Britain's offshore zone, Mouli-Castillo calculates there are enough suitable sites to store 77-96 terawatt hours, 10 times the capacity of Britain's salt caverns.

This is equivalent to 160 percent of the electricity the UK uses in January and February each year, aquifers filled with compressed air throughout the year using electricity from wind turbines located nearby could provide secure power all winter. The efficiency of storage is low compared to some alternatives. The paper estimates just 54-59 percent of the energy produced would eventually find its way to the grid. By contrast, pumped hydro often has an efficiency of 80 percent and batteries over 90 percent, but the UK is too flat to support much hydropower.

As always the problem is money. Moulid-Castillo estimates the price of storing a kilowatt hour to be $0.42-4.71, around 10 times the cost of onshore storage. Nevertheless, if other options are insufficient, offshore storage may be competitive with nuclear power, and certainly cheaper than climate change.

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