THE future of energy storage has taken root on an onion farm in southern California.

Seeking to offset its electricity bills, Gills Onions in Oxnard has installed a flow battery. When electricity prices from the grid peak, the farm can tap stores of energy created by processing agricultural waste. The battery can supply 600 kilowatts of electricity over six hours to run farm machinery for a fraction of the usual cost.

Flow batteries are centred around two aqueous electrolytes, which are held in separate tanks when the battery is idle. To get electricity from it, the liquids are pumped into a chamber separated by a membrane, sparking an electron-producing chemical reaction across the membrane. To store energy, an external current is applied across the membrane and the process works in reverse.