US researchers have made an important step forward in the quest to store electricity from intermittent energy sources such as wind and solar.
A Harvard University team came up with a way to drive down the cost of flow battery technology, which is capable of storing energy on large scales - within an electrical power grid, for example.
Grid-scale storage for renewables could be a game-changer - making wind and solar more economical and reliable.
While flow battery designs are suited to storing large amounts of energy cheaply, they have previously relied on chemicals that are expensive or difficult to maintain, driving up costs.
Most previous flow batteries have chemistries based on metals. Vanadium is used in the most commercially advanced flow battery technology, but its cost is relatively high. Other variants contain precious metal catalysts such as platinum.
The researchers say their new battery already performs as well as vanadium flow batteries, but uses no precious metal catalyst and has an underlying chemistry that is metal-free, instead relying on naturally abundant, more affordable chemicals called quinones.
The amount of energy that can be stored by a flow battery is limited only by the size of the tanks and the amounts of storage chemicals that can be afforded
General Electric Global Research in New York, called the results "promising", and said the approach "may serve as the basis for a new flow-battery technology".
Electrode: Batteries contain two types of electrode where reactions take place. A reaction in one generates electrons and a reaction in the other absorbs them, yielding electrical energy
Electrolyte: Usually a liquid or gel containing an acid, base or salt. In batteries, it is the medium that allows electric charge to flow between the two electrodes
These water-soluble compounds are organic (carbon-based) and are similar to chemicals that store energy in plants and animals.