Over the past decade, prices for solar panels and wind farms have reached all-time lows. However, the price for lithium ion batteries, the leading energy storage technology, has remained too high. So researchers are exploring other alternatives, including flow batteries, thermal batteries, and gravity-based systems. CORRECTION (March 14, 2020): At 12:53 we incorrectly identify the size of the energy storage market. Overall, the energy storage market is predicted to attract $620 billion dollars in investments by 2040.