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In the renewable energy field, wind turbines have played an important step, but today the future of wind energy may come from the underground. The compressed-air energy storage plants could be the solution. Air is pumped into large underground formations where it can be used later to deliver the large amount of energy that it previously received.

1. Transmission Developers would provide electricity transmission in underwater cables (previous story this week), that can be lain in aqueducts, riverbeds and lakes, or down ocean coastlines – clearing the one big hindrance to the development of renewable energy, which is the new transmission needed, and the NIMBYism that succeeds in prevents that from being built, because these would be out of sight. 2. The other,  Riverbank Power – an equally innovative breakthrough, would provide a complete solution to storing wind power (previous story)  effectively making it dispatchable base-load power.

This is why Highview has been testing its 300-kilowatt pilot plant for the past nine months, supplying electricity to the UK's National Grid. The process stores excess energy at times of low demand by using it to cool air to around -190 °C. Excess electricity powers refrigerators that chill the air, and the resulting liquid air, or cryogen, is then stored in a tank at ambient pressure (1 bar). When electricity is needed, the cryogen is subjected to a pressure of 70 bars and warmed in a heat exchanger. This produces a high-pressure gas that drives a turbine to generate electricity. The cold air emerging from the turbine is captured and reused to make more cryogen. Using ambient heat to warm it, the process recovers around 50 per cent of the electricity that is fed in, says Highview's chief executive Gareth Brett. The efficiency rises to around 70 per cent if you harness waste heat from a nearby industrial or power plant to heat the cryogen to a higher than ambient temperature, which increases the turbine's force, he says. Unlike pumped-storage hydropower, which requires large reservoirs, the cryogen plants can be located anywhere, says Brett. Batteries under development in Japan have efficiencies of around 80 to 90 per cent, but cost around $4000 per kilowatt of generating capacity. Cryogenic storage would cost just $1000 per kilowatt because it requires fewer expensive materials, claims Brett.