The concrete blocks are slowly hoisted upwards by motors powered with electricity from the Swiss power grid. For a few seconds they hang in the warm September air, then the steel cables holding the blocks start to unspool and they begin their slow descent to join the few dozen similar blocks stacked at the foot of the tower. This is the moment that this elaborate dance of steel and concrete has been designed for. As each block descends, the motors that lift the blocks start spinning in reverse, generating electricity that courses through the thick cables running down the side of the crane and onto the power grid. In the 30 seconds during which the blocks are descending, each one generates about one megawatt of electricity: enough to power roughly 1,000 homes.
This tower is a prototype from Switzerland-based Energy Vault, one of a number of startups finding new ways to use gravity to generate electricity. A fully-sized version of the tower might contain 7,000 bricks and provide enough electricity to power several thousand homes for eight hours. Storing energy in this way could help solve the biggest problem facing the transition to renewable electricity: finding a zero-carbon way to keep the lights on when the wind isn’t blowing and the sun isn’t shining.
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