Surplus electricity? The heavy blocks go up. When power is needed later, they descend and drive generators. A huge installation in Rudong, China, stores energy this way: in raised mass rather than a chemical battery.
The system is called EVx and was developed by Energy Vault. It stands next to a wind farm in Jiangsu province. The project information lists an energy storage capacity of 100 megawatt-hours and a power output of 25 megawatts. The installation is therefore designed to deliver that output for four hours.
Up goes the surplus
Think of placing a heavy object on a shelf. Lifting it requires energy. Let it fall and that energy is released. The installation, of course, lowers its blocks in a controlled way: the descending mass makes the drive system work as a generator.
When charging, the lifting mechanisms use electricity to raise the blocks within the structure. During discharge, the flow of energy is reversed. This shifts electricity through time: the moment when wind or solar produces plenty of power need not be the moment when that power is used.
How much electricity can it hold?
The two figures mean different things. Megawatts indicate how quickly the installation can deliver electricity. Megawatt-hours describe how much energy it can store in total. One hundred megawatt-hours divided by 25 megawatts gives four hours. At a lower output, that supply can last longer.
That makes this different from a power station that keeps generating new electricity. Power must first go in. Energy is also lost through lifting, the drive system and conversion. Energy Vault quotes an expected round-trip efficiency of more than 80 percent for the project; this is the manufacturer’s expectation.
A big building for a simple principle of physics
The scale is striking. While a home battery hangs on a wall, this form of storage requires a tall structure and plenty of heavy mass. The energy stored depends on weight and the difference in height. More capacity therefore also means more material, space or height.
This is not a newly announced idea. Energy Vault reported successful charging and discharging tests and commissioning by China Tianying in May 2024. The current project page describes the installation as connected to the grid and tested with the local grid authorities.
What is interesting is how familiar the technology behind that large building really is: lifting, holding and controlled lowering. The challenge lies in coordinating those movements on a large scale, turning a stock of blocks into a useful electricity reserve.
