Energy Bags Under the Sea to be Tested to Store Off-Shore Wind

April 18th, 2011 by Susan Kraemer

An innovative new way to store wind power has been invented by researchers at the the University of Nottingham. Literally in inflatable bags under the ocean. A university spinoff, NIMROD Energy Ltd, has been launched by Professor Seamus Garvey, based on the research. Next month a prototype is to be tested in seawater.

E.ON, a leading renewable energy company in Europe, provided a grant to the university researchers to develop the undersea Energy Bags™ in 2008.

Like pumped storage – that relies on the relentless forces of gravity to make energy when a reservoir of water is released downhill – these huge inflatable undersea bags would leverage the relentless power of compression found deep under the sea.

When excess wind power is generated, because there is no use for it on the grid – for example, at night – the energy generated would be used to pump compressed air into the bags, expanding them. Then, when needed, the natural force of the sea itself would be allowed to squeeze the compressed air out of the energy storage bags to run turbines to make electricity on demand.

Garvey believes it is possible to store energy at a cost well below $16/kWh – less than 20% of the cost for pumped hydro energy, the cheapest competing technology, and at 90% efficiency. He envisions that storage to match a third of wind power capacity will be needed by 2020.

“If you have 1MW of integrated compressed air system (including large energy stores) for every 3MW of conventional generation, then the whole set of offshore wind equipment starts to look like a very versatile power generating system which can adjust its output to match demand — notwithstanding what the wind is doing.”

According to Powermag, Garvey says that storing the equivalent of 2 GW for four days will require 7 million cubic meters of air storage. “The optimal dimensions for energy bags are around 20 meters in diameter and each has a volume (when full) of about 4,000 cubic meters,” he says. “For 7 million cubic meters, we would need 1,750 of these bags. The seabed area covered by these would be less than one square kilometer and the total surface area of bag material would be 2.2 million square meters.”

Like the best energy storage technologies, the process is simple in concept. However, it requires a new, much larger fleet of offshore wind turbines to become economic.

And that is just what is now beginning to happen around Scotland and the UK, as turbine manufacturers continue to develop ever-larger turbine sizes (try 20 megawatt wind turbines! Twenty times the size of many turbines in the US.) and ever larger wind farms off the coasts of Europe, and a gigantic North Sea grid to connect them all.

Susan Kraemer@Twitter

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