The National Grid will take preliminary bids for one of the world's biggest energy storage schemes tomorrow.
Japanese, British and European companies are expected to compete for the 200 megawatts project, which will be used to plug the gap when Britain's doesn't have enough power.
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One bidder, American firm AES, said that the energy stored will be equivalent to that generated by more than a million iPhone-sized lithium-ion batteries, according to the Times.
The scheme is increasingly important given the number of coal-fired power plants that are going offline, as well as the intermittency of renewable energy sources such as wind and solar.
A spokesman for National Grid said: "It will support the UK’s energy mix in a rapidly changing market. Contracts will be announced at the end of August."