Renewable. Rechargeable. Remarkable

"Renewable. Rechargeable. Remarkable.", Feature Article, September 2005:
by Mark T. Kuntz and Justin Dawe -- Mechanical Engineering magazine
"Like a fuel cell, a flow battery has a long life and is both energy-efficient and environmentally friendly. Also, like a fuel cell, the energy rating of the system is a separate design variable from the power rating. Increasing the volume of the electrolyte tanks increases the amount of energy that the system can store and release; increasing the number of cell stacks increases the power that the system can generate.

Like traditional batteries, but unlike fuel cells, flow batteries are an 'electricity in, electricity out' system. There is no external fuel source, such as hydrogen, that is added regularly to recharge the system. Instead, electric energy is supplied to the system at one time, and the system stores that electric energy in electrochemical form until it is needed later. For grid applications, this simpler arrangement avoids the need to create new fuel or distribution systems.

In addition, unlike fuel cells, flow batteries are not based on rare or valuable materials. Fuel cells typically use platinum or other expensive catalysts to speed the oxidation of their energy carrier. Instead, the material at the heart of a flow battery cell is vanadium, a plentiful, nontoxic metal."