Battery energy storage systems have a serious role to play
Energy storage is a very important part of maintaining the electric grid as it removes a lot of burden from power plants when power demand (and local renewable generation) fluctuates wildly.
To keep the production and demand in balance, which results in nearly perfect frequency of 60 Hz (50 Hz in Europe), energy storage eliminates fluctuations. The big daily or weekly changes usually rode on the shoulders of pumped-storage hydroelectricity. There are also other types like flywheel storage (kinetic energy).
The biggest new thing in the ESS are lithium-ion batteries, not because batteries weren't used before (on a limited scale), but because prices and durability of li-ion have become attractive - more so than other solutions now.
A base overview of energy storage systems was recently released by Verge Science, who talked with Tesla CTO JB Straubel.
Tesla is one of the leaders of battery energy storage on both ends of the scale - home energy storage (Powerwalls) and utility energy storage (Powerpacks).
Why Tesla is building city-sized batteries
We talked to the co-founder of Tesla, JB Straubel, about why giant batteries are crucial to the future of power grids everywhere. Batteries are becoming more useful at powering bigger things like bikes, cars, and soon, entire cities. We explore some of the zanier forms of energy storage already in use around the country.