Five Ways Companies Can Store Renewable Energy for the Grid

(Bloomberg Businessweek) -- Even the best lithium-ion batteries stink at storing the large amounts of electricity a massive wind or solar installation is capable of generating. They’re expensive and hold, at most, about four hours’ worth of that grid-scale juice. Here are five potentially less costly—if somewhat Rube Goldberg-y—methods companies are trying to store power as potential energy in other forms, smoothing out renewable energy’s peaks and valleys.

Compressed Air

Hydrostor Inc. in Toronto expends grid power to compress air, which it pumps underground for storage, with a column of water keeping it compressed. Abating the pressure allows the air to decompress, releasing its energy to drive turbines on the surface for 24 hours or more. Hydrostor has two demo plants in Canada and others slated for development in the U.S., Chile, and Australia. Chief Executive Officer Curtis VanWalleghem says Hydrostor has raised $30 million and expects to double that this year.

Liquid Air

London’s Highview Power feeds wind- and solar-generated electricity into a set of off-the-shelf components that liquefy air by cooling it. To send power back into the grid, Highview heats the liquid, expanding it to drive turbines that generate electricity for at least 12 hours. CEO Javier Cavada says the company has raised about $50 million; it’s built two small-scale plants in the U.K. and is finalizing a deal for a commercial plant in the U.S.

Mine Shafts

Edinburgh’s Gravitricity Ltd. stores gravitational energy by using power from renewables to lift a weight of as much as 3,000 tons in a mine shaft. Letting the weight fall releases the energy, generating enough electricity to deliver power for as much as eight hours. The system’s winches and cables have a working life of 50 years or more, says Managing Director Charlie Blair. The company, which has raised about $1.7 million from the U.K. government and private investors, is at work on a 50-ton demo.

Pressurized Water

Gravity Power LLC in Goleta, Calif., plans to store energy by pressurizing water with a steel-jacketed, rock-and-concrete piston weighing as much as 8.5 million tons. A pump pushes the hydraulic fluid under the piston to lift it; releasing the pressure unleashes the stored energy to drive a turbine that generates electricity for a maximum of 16 hours. The company has raised $5.5 million and is seeking more for a demo plant.

IRL Jenga

Energy Vault in Lugano, Switzerland, plans to use a robotic crane to stack thousands of 38-ton blocks into a tower as high as 500 feet. This is essentially a more complex version of Gravitricity’s model: The blocks’ weight will drive generators as the crane plucks them off the tower and lowers them to the ground. CEO Robert Piconi says the system can deliver as much as 80 megawatt-hours of power, enough to cover about 60,000 homes for up to 16 hours. The company’s first commercial-scale unit will go up near Milan this year in partnership with Italian energy company Enel Group.

To contact the editor responsible for this story: Jeff Muskus at jmuskus@bloomberg.net, Jeremy Keehn

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