First developed by NASA, flow batteries are a potential answer to storing solar – and wind – for eight to 10 hours, far beyond what is commonly achieved today with lithium-ion. In the first of a two-part special report, Andy Colthorpe learns what the flow battery industry faces in the fight for commercialisation.

Trina BESS, the battery energy storage company originally launched alongside Chinese PV giant Trina Solar but now run as an entity in its own right, sold 1,000 residential units in the first half of this year.