In a city roughly an hour south of Milan, Italy, a huge tall tower made of massive, 35-metric-ton bricks will soon rise from the ground. It’s a full-size commercial demonstration of new technology that could be a key part of helping wind and solar power scale up around the world by storing energy differently: Instead of batteries, which are still relatively expensive and can cause environmental challenges, the system uses gravity to store energy as it raises and lowers the bricks.
“Now you can couple PV and low-cost wind with our storage and for the first time replace fossil fuels with renewables 24 hours a day,” says Robert Piconi, cofounder and chief executive officer of Energy Vault, the Switzerland-based startup that designed the new system. The company is the winner of Fast Company’s 2019 World Changing Ideas Awards in the Energy category.
Running a wind or solar farm is now cheaper than many old coal plants, but the economics of storing energy is still an issue for the renewables industry. The cost of batteries continues to fall, but when a utility needs to store electricity for more than a few hours, it’s still hard for the cost of that storage to compete with fossil fuels. “For the longer-duration utility scale, we’ve got a much more environmentally friendly and economic solution,” says Piconi. “That’s what so exciting for us, because it’s going to change the economic equation.”
When a solar farm produces extra electricity during the day, giant cranes use that energy to lift and stack the bricks, storing energy through the elevation gain. When the energy is later needed, software tells the system to lower the bricks, and that spins generators to send electricity back into the grid. The system can respond within a millisecond.
India’s Tata Power is the company’s first announced customer, with a tower that will be constructed later this year. But Energy Vault is in talks with other customers about more than 1,200 potential towers. Each tower can be erected quickly; the cranes can be delivered within months and erected within weeks, without the huge investment of a battery factory. The bricks themselves can be made on-site from materials such as concrete construction debris–which would otherwise go to a landfill–or soil. At a coal plant that plans to close and reopen renewable energy on-site, the bricks could be made from coal ash that companies would otherwise have to spend money to clean up.
Even as batteries become cheaper, the towers will still have advantages. For lithium-ion batteries, “the process to actually attain the chemicals themselves is not a not a clean process,” Piconi says. “Secondly, it requires huge investment in … manufacturing plants to make them. Thirdly, batteries start to degrade from the time you install them.” And, for now, the cost difference is large: The cost of storage over the lifetime of the new system is seven times cheaper than lithium batteries. With the cheap cost of renewables–some utilities are now signing deals for solar power for around 2 cents per kilowatt hour–and the new towers, which store energy for around a few cents per kilowatt hour, the cost of renewable electricity is lower than it has ever been.