Achieving 100 percent renewable power, as Congressional Democrats' Green New Deal and other proposals around the world envision, will require a lot of energy storage. And while the cost and availability of a storage batteries has made significant progress lately, they may not be the best solution to store renewable energy.

A new study by researchers at the Australian National University have identified 530,000 sites around the world suitable for pumped hydro storage that can store up to 22 million gigawatt hours of electricitycoincidentally about what other studies show would be needed to support a reliable electric grid powered entirely by renewable energy. 

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The storage would be needed to take full advantage of renewable wind and solar power even when consumers are not demanding peak power, and then supply that power back to the grid at times when they do.

Lithium-ion batteries similar to those made for electric cars, such as Tesla's commercial Powerpacks, are being installed on the grid around the world, including at large wind and solar farms as well as local transformer stations. Some automakers, utilities, and EV charging networks are also installing used electric-car batteries to buffer the grid on a trial basis.

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Pumped hydro storage is a much older and larger technology. It uses excess electricity produced at night to pump water uphill into reservoirs or storage tanks, then works like conventional hydro-electricity to spin turbines as the water flows back downhill during the day. Unlike conventional hydro, it doesn't generate net new power, but does improve grid reliability and enable new sources of renewable electricity to come online, according to the U.S. Energy Information Agency.

As of 2014, the latest year for which numbers are available, the U.S. had almost 24 gigawatt-hours of pumped hydro storage at 40 locations around the U.S.

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Battery storage on the grid was forecast in 2017 to grow to 1.2 gigawatt hours in 2018, according to a report by the Energy Storage Association. 

How pumped hydro works [CREDIT: EnergyAustralia]

How pumped hydro works [CREDIT: EnergyAustralia]

The Australian researchers used geographic data to identify locations that had sufficient elevation changes, water flow, and were large enough to store a sufficient amount of water, but said the sites would still need to be evaluated for the feasibility of construction and the ability to secure ownership.

Still, lead researcher Matthew Stocks told Science Alert that "Only a small fraction of the 530,000 potential sites we've identified would be needed to support a 100 percent renewable global electricity system. We identified so many potential sites that much less than the best 1 percent will be required. The perception has been there are limited sites for pumped hydro around the world, but we have found hundreds of thousands."