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Large scale energy storage

01 November 2011

Over the coming months energy teams from the UK’s Department of Energy and Climate Change, grid operators and utilities from UK, Europe and further afield are visiting a small site adjoining Scottish & Southern Energy’s biomass power plant on Slough trading estate west of London.

This is the world’s first pilot plant of a liquid air energy storage system, owned and operated by Highview Power Storage. It could be the answer to the big problem many power grids are facing – what do we do about wrong-time wind energy? Electricity grids need long duration, large scale energy storage to support the deployment of renewable - but intermittent - generation.

Highview Power Storage's system uses liquid air as the storage medium and can be scaled to 100MWs/GWhs of storage, similar to medium scale pumped hydro. But liquid air can easily be stored in the same low pressure tanks as used by the LNG industry - it is hundreds of times more energy dense than water (therefore taking up far less space) - and the process does not need large mountains or lakes, like some pumped storage systems. There are four core processes:

Charge - The system operates by using electrical energy (excess or off-peak) to drive an air liquefier. Similar equipment is widely deployed for the production of bulk liquid LNG, nitrogen, oxygen or argon.

Storage - The liquid air is stored in an insulated tank at low pressure, which functions as the energy store. Again, such equipment is widely deployed as bulk liquid LNG, nitrogen, oxygen or argon storage, and millions of tonnes of liquefied gases are commercially stored and transported around the world.

Regasification/Power Recovery - When power is required, liquid air is drawn from the tank and pumped to high pressure. Ambient (or above ambient waste*) heat is applied to the liquid air via heat exchangers resulting in a phase change from liquid air to a high pressure gas which is then used to drive a turbine and generator.

Cold Recycling - During the power recovery, very cold gas is exhausted, which is then recycled back into the liquefaction process (the charge stage) reducing the energy demands for producing liquid air and thereby increasing the overall round-trip efficiency.

The technology is competitive when compared with other commercially used energy storage technologies in terms of capital cost, efficiency and scalability; and it produces no harmful emissions.


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