Published on March 2nd, 2011 | by Susan Kraemer7
Liquid Air Tested to Store Renewable Energy in UK
Yet another innovative way to store renewable energy is being tested in the UK by a cryogenic company, Highview Power Storage, whose liquid air energy storage could be up to 70% efficient and cost just $1,000 per kilowatt.
Why the race is on to invent storage
Renewable energy without storage does not produce a convenient and steady supply of energy, just as coal, until the railroad was invented, did not. Coal requires an endless supply of mined coal trucked in via railroad to keep producing steadily. Just as coal needed the railroad for its steady supplies of fuel, renewable energy needs to invent storage for a steady supply of variable energy.
With renewables, sometimes there is too much energy for the grid, which cannot handle it. Wind is especially a problem, with some states having to give wind power away for free at night when no one can use it. People may be asleep, but the energy must go somewhere.
How this invention works
The Highview unit would use an unused excess at times of low demand to power refrigeration units to cool air to around -190 °C – which turns air into liquid nitrogen for cryogenic energy storage.
Once the refrigerators, powered by the renewable energy, have chilled the air to a liquid, it is then stored in a tank at ambient pressure – about 1 bar. When electricity is needed, the liquid air is subjected to a pressure of 70 bars and warmed in a heat exchanger.
Rewarming liquid air creates a gas to power a turbine
Just allowing the liquid air to warm again produces a high-pressure gas that can drive a turbine to generate electricity. Using just ambient air heat to warm it, the process recovers around 50% of the electricity that is fed in, but it becomes up to 70% efficient if a source of heat is available. Waste heat could be harnessed inexpensively from a nearby industrial or power plant, and used to heat the cooled air to warmer-than-air temperature for a power boost.
A 300 kilowatt cryogenic energy storage system has been tested for the last nine months, storing and supplying electricity to the UK grid. It has proved proof of concept and that the process is economical, as the supplies needed are inexpensive. Next, Highview plans to build a 3.5 MW, commercial-scale system by late 2012, building it up into an 8 to 10 megawatt storage plant by early 2014.
Till now, the company has been buying the supplies, but it has now added an on-site liquefaction plant, and will begin producing its own liquid air or cryogenic liquid nitrogen from late March, which will reduce costs.
Other ways to store renewable energy:
Techniques we’ve covered that are being tested so far include
Gravity hydro under rivers: Pump Hydro Underground to Store Wind Power
In caves: For Baseload Wind Cheaper than Fossil Fuels
In boxes: Storing Renewable Energy in Boxes of Air.
In new kinds of batteries: Metal-Air Battery With 11 Times the Energy at Half the Cost?
In hundreds of homes, using thermal energy storage: Maine Residents Get $6,000 to Store Energy as Heat
In ice storage on commercial rooftops, for use in air conditioners: Make Ice at Night to Store Wind Energy
By distributing the storage among multitudes of electric cars (promising, once we have enough electric cars)
Traditionally, energy has only been stored in pumped hydro – only useful when enough gravity-fed water is available. Water is pumped to the top by night-time cheap wind power, and when surges are needed, dropped to activate water turbines.
But as we add more clean renewable energy, additional storage will need to be invented and commercialized to go with it. This will create whole new industries to do that, the way coal created the need to build the trans-continental railroad. (Wind Storage Worth Trillions)
This is why the Obama administration funded the DOE to find and push innovation in this sector (Top ARPA-E Funding Goes to Renewable Storage in “Liquid Battery”) and why states leading the way in renewables are also leading the way in storage. (California Proposes First Renewable Energy Storage Requirements)