In a Swiss valley, an unusual multi-armed crane lifts two 35-ton concrete blocks high into the air. The blocks delicately inch their way up the blue steel frame of the crane, where they hang suspended from either side of a 66-meter-wide horizontal arm. There are three arms in total, each one housing the cables, winches, and grabbing hooks needed to hoist another pair of blocks into the sky, giving the apparatus the appearance of a giant metallic insect lifting and stacking bricks with steel webs. Although the tower is 75 meters tall, it is easily dwarfed by the forested flanks of southern Switzerland’s Lepontine Alps, which rise from the valley floor in all directions.
Thirty meters. Thirty-five. Forty. 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. “The greatest hurdle we have is getting low-cost storage,” says Robert Piconi, CEO and cofounder of Energy Vault.
Without a way to decarbonize the world’s electricity supply, we’ll never hit net zero greenhouse gas emissions by 2050. Electricity production and heat add up to a quarter of all global emissions and, since almost every activity you can imagine requires electricity, cleaning up power grids has huge knock-on effects. If our electricity gets greener, so do our homes, industries, and transport systems. This will become even more critical as more parts of our lives become electrified— particularly heating and transport, which will be difficult to decarbonize in any other way. All of this electrification is expected to double electricity production by 2050 according to the International Atomic Energy Agency. But without an easy way to store large amounts of energy and then release it when we need it, we may never undo our reliance on dirty, polluting, fossil-fuel-fired power stations.
This is where gravity energy storage comes in. Proponents of the technology argue that gravity provides a neat solution to the storage problem. Rather than relying on lithium-ion batteries, which degrade over time and require rare-earth metals that must be dug out of the ground, Piconi and his colleagues say that gravity systems could provide a cheap, plentiful, and long-lasting store of energy that we’re currently overlooking. But to prove it, they’ll need to build an entirely new way of storing electricity, and then convince an industry already going all-in on lithium-ion batteries that the future of storage involves extremely heavy weights falling from great heights.