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.