Flow batteries finding niche support for grid stability

New Scientist : Several companies are producing new designs of a type of high-performance battery that up to now has been both expensive and difficult to maintain. The so-called flow battery uses two aqueous electrolytes that are stored separately when the battery is idle. To generate electricity, the electrolytes are pumped into the two sides of a single chamber that is divided by a thin membrane across which an electron-producing chemical reaction occurs. To store energy in the battery, an external current is applied to the membrane to reverse the reaction. When the battery is added to a local power grid, that external current can be provided by either the incoming power flow or local electrical production. Flow batteries can be very large, producing several hundred kilowatts of power over several hours, and they are safer than lithium-ion batteries, which can be prone to thermal runaway. Those qualities make them very useful for supplementing local electricity during peak usage periods or providing backup when external power service is interrupted. Flow batteries are now being installed as part of grids at large farms and military bases.