How do you store electricity? Most of us would say, "With batteries." A Switzerland-based startup called Energy Vault has a different answer: "With giant concrete bricks."
Energy Vault, fresh off a $110 million investment in August by SoftBank Vision Fund, plans to build a demonstration project in northern Italy by the end of this year.
"The lack of a viable, sustainable, and scalable storage solution has been one of the most formidable challenges facing humanity as it transitions from its historic dependence on fossil fuels to renewable energy," said Energy Vault co-founder and CEO Robert Piconi.
"Energy Vault's technology solves this problem in a way that's as compassionate to the planet as it is efficient to build and operate."
The company's technology addresses intermittency. That's the big problem with wind and solar power generation, which are the fastest-growing segments of the renewable energy industry. How do you keep power flowing when the wind is calm or the sun has set?
Energy Vault's solution is a variation on pumped hydropower, using 35-ton concrete bricks instead of water. Pumped hydropower, the dominant form of utility-scale energy storage today, involves two water reservoirs, one at a higher elevation. To store energy, pumps move water to the upper reservoir. When that energy is needed, the water flows back down to the lower reservoir, spinning an electricity-generating turbine along the way.
Pumped hydro requires a lot of space and a hill. The Energy Vault technology needs neither. Instead, it calls for a tall, six-headed crane (a variation on those giant, T-shaped tower cranes that you see at construction sites) and a bunch of solid concrete slabs—like giant bricks.
When electricity is plentiful (strong winds, bright sun), software-controlled electric motors on each arm pick up the bricks and stack them into a cylindrical tower around the crane's vertical mast.
When the electric grid needs that stored energy, the crane disassembles that tower, piece by piece, lowering each brick back toward the ground. As the brick descends, the same motor that lifted it turns into a generator, releasing the stored energy. For a video showing the process, click here.
Energy Vault claims a round-trip efficiency of 80% to 90%. It offers versions with 20, 35, or 80 megawatt-hours of storage capacity, which it says are capable of supplying 4 to 8 megawatts of continuous power for 8 to 16 hours.
The company says it has agreements to build its storage units on four continents. It touts the simplicity of its basic technology, claiming that the units should be able to last 30 years with no loss of capacity or efficiency. It plans to use recycled waste material to make the concrete bricks.
It's certainly a fascinating concept—like storing energy by playing with giant Legos. We'll keep an eye out for the debut of the pilot project in Italy and let you know what happens.