Will flow batteries — large tanks of liquid batteries — be a key technology to help deliver more clean power for the grid? Flow battery startup EnerVault is getting closer to commercializing that vision; it has completed the design of its prototype battery and is counting on a demonstration project next year to help the company launch its technology into the market in 2013, EnerVault CEO Craig Horne told us. The Silicon Valley startup is developing rechargeable flow batteries that, unlike a lithium-ion battery, separate the energy storage materials and electrolyte from the cells in which the electrochemical reaction occurs. The design involves two tanks, each of which contains a different mix of energy storage material and electrolyte. EnerVault's design fills one tank of electrolyte with iron (the energy storing material) and another electrolyte tank with chromium. Pumps send the solutions from the tanks into separate chambers of a cell to generate electricity. Flow batteries can be scaled up and down easily because of the use of external storage tanks. Flow batteries are also rechargeable, the electrolytes can last a really long time, and typically use abundant materials, so can be a more affordable option.