The ability to store power so it can be instantly converted to electricity is essential to the stability of the grid. Pumped hydro, using excess energy to pump water uphill into a storage lake where it can be released to instantly power turbines, is a reliable way to store power without using batteries. Startup ARES just got the ok to build a rail energy storage system in Nevada using the same idea. Extra power is used to send two electric locomotives and four 8,600 lb. rail cars 5.5 miles uphill. To generate electricity, the train is released and it generates power as it goes downhill.
This initial system is 50MW, which is substantial. ARES says it can scale to 1 GW, and a 500 MW system would only cost $20 more than this 50 MW project. One big advantage is there are no life cycle limits or degradation of the system because there are no batteries to wear out.
Electricity powers an electric motor in a locomotive that hauls a heavy load up hill. Sitting at the top of the hill, the rail cars store energy. When the energy is needed, the cars are released to roll down hill and the electric motor runs in reverse to generate electricity.
The same electro-mechanical principle that powers the ARES system supplies the regenerative braking power in electric vehicles like a Toyota Prius:… When an induction motor that powers a train or car is reversed, it produces electricity.