Flow, the forgotten battery

Redox flow batteries have a reputation of being second best. Less energy intensive and slower to charge and discharge than their lithium-ion cousins, they fail to meet the performance requirements of snazzy, mainstream applications, such as cars and cell phones. There’s no such thing as a flow-battery Tesla. But the companies at the International Flow Battery Forum in Prague in late June were adamant that flow batteries are now cheaper, more reliable, and safer than lithium ion in a growing number of real-world stationary energy applications. Flow-battery makers say their technology—and not lithium ion—should be the first choice for capturing excess renewable energy and returning it when the sun is not out and the wind is not blowing. The flow-battery sector has met with a number of false dawns before. This time, developers and producers say, the technology is ready. “Slowly but steadily, flow batteries are gaining their place in