A company called Energy Vault has proposed a new utility-scale battery that is both old and new at the same time. The “battery” is mechanical, rather than chemical, and stores energy much like pumped hydro does, but it does it with bricks.
If you’re not familiar with pumped hydro, it works like this.
The system pumps water from a lower elevation to a higher elevation when electricity is plentiful and cheap. When electricity becomes more expensive, operators release that water through a hydroelectric turbine to give the grid some extra juice. Similarly, Energy Vault wants to build a system of six cranes, which will electrically stack heavy bricks into a tower when electricity is cheap and plentiful. When electricity becomes more scarce and expensive, the cranes will release each brick and harvest the energy from their fall.
This system solves an important problem inherent to pumped hydro: it requires a pretty specific kind of topography and often causes environmental concerns.
Energy Vault’s “battery” offers an interesting opportunity to deliver long-term storage to grids with more and more renewable energy. Currently, chemical batteries tend to be short-duration, sending bursts of energy onto the grid to maintain frequency. These batteries are not necessarily replacing a more traditional generation source for several hours at a time. By contrast, Energy Vault says its battery can be built for long-duration applications. So it can be used to store excess electricity from renewable energy, and discharge that energy when renewable generation is low.
According to GreenTech Media, Energy Vault estimates that a standard-sized system would be able to deliver four megawatts (MW)/35 megawatt-hours(MWh) of energy at a lower cost than any other competing energy storage system for 30 to 40 years (somewhere between $200 and $250 per kilowatt-hour). Per Renewable Energy Magazine, the company has an agreement with India-based Tata Energy to build a pilot project in 2019.
GreenTechMedia notes that Energy Vault has built a 1/7-scale version in Switzerland, but a good idea and a small demo don’t necessarily translate to immediate success. Advanced Rail Energy Storage (ARES), a similar concept where a weighted train is driven up an incline so it can later be released to produce energy, received a lot of attention since its founding in 2010. But construction is only just starting and operation isn’t scheduled until 2020.
Still, Energy Vault says that its system includes a number of advantages that will actually bring this tower of bricks to fruition. It’s built on an “easy to install” foundation and relies on proprietary software to move the cranes that assures 90 percent round-trip efficiency for the bricks. Energy Vault also plans to create its bricks from waste debris, to minimize pollution from new concrete.
With any luck, the company could replicate the staid, long-lasting energy delivery of pumped hydro, without any of the water.