"Many of us have tunnel vision on the subject of energy storage. We think lithium-ion batteries are the beginning, middle, and end of the discussion. Largely that’s because of Elon Musk and Tesla, who have built their incredible history of success both in transportation and energy storage on lithium-ion batteries. Yet there are other types of storage solutions, many of which will begin to share the spotlight with lithium-ion batteries in 2020.
The US Department of Energy’s Advanced Research Projects Agency — ARPA-E — is funding research by 10 organizations with one common goal — creating long term energy storage systems that cost $0.05 per kilowatt hour or less. Five of the projects are scheduled for completion in 2020 and the rest in 2o21. After they are complete. ARPA-E plans to fund small scale field trials to determine which are commercially viable. According to PV Magazine, the research falls into several general categories."