Israel’s Electric Fuel Energy has developed a novel Iron Flow energy storage technology that is projected to be less costly, safer, and more environmentally friendly than other large-scale battery storage solutions.  It is particularly suited for renewables and long-duration storage.

http://www.solarserver.com/solar-magazine/solar-news/current/2016/kw10/novel-israeli-iron-flow-energy-storage-solution-to-drive-down-costs-and-optimize-the-use-of-renewables.html