USING GRAVITY TO STORE ENERGY

Using gravity to store energy

Say the grid temporarily has more renewable energy than it needs — the wind is blowing, the sun is shining, and there's not enough demand to make use of it.

Advanced rail energy storage (thus "ARES") can absorb that excess energy, using it to power electric trains that pull giant slabs of concrete up a gentle slope. In effect, the trains convert the excess electricity to potential energy.

When the grid needs that energy, the same rail cars carry the giant slabs downhill, converting the potential energy back into electricity. (Thanks, gravity!)

The conversions are done by an electric motor. When it goes uphill, it consumes electricity. When it goes downhill, it runs in reverse, generating electricity (similar to how "regenerative braking" works in cars).

The company claims the process, end to end, is 86 percent efficient, i.e., 86 percent of the energy that's put into storage can be gotten back out. It hopes to improve that number as it dials in the technology.