Supplying clean power is easier than storing it

IT SOUNDS SIMPLE: lift heavy blocks with a crane, then capture the power generated from dropping them. This is not an experiment designed by a ten-year-old, but the premise of Energy Vault, which has raised $110m from SoftBank, a big Japanese tech investor. The idea has competition. A cluster of billionaires including Bill Gates, Jack Ma, Ray Dalio and SoftBank’s Masayoshi Son are backing other schemes to capture power. A firm incubated at Alphabet, Google’s parent company, wants to store electricity in molten salt. Such plans hint at one of the power business’s hardest tasks. Generating clean power is now relatively straightforward. Storing it is far trickier.

Solar and wind last year produced 7% of the world’s electricity. By 2040, that share could grow by over five times, according to the International Energy Agency, an intergovernmental forecaster. The trouble is, a lull in the wind leaves a turbine listless. Clouds have a habit of blocking the sun. That means that solar and wind cannot, on their own, replace coal and gas plants, which produce continual power reliably.

One answer is to store power in batteries, which promise to gather clean electricity when the sun and wind produce more than is required and dispatch it later, as it is needed. In 2018 some 3.5 gigawatts of storage was installed, about twice the...