Many are envisioning a future where renewable forms of energy supplant fossils fuels and finally give the environment relief from carbon pollutants and the threat of oil and gas eventually running out. And many investors are betting billions on renewables generating lots of financial returns in addition to energy. Witness JLL’s recent declaration that it sees investment opportunities in the “surging demand” for alternative sources of energy.

But for renewables to become dominant components of the national energy mix, more advanced forms of storage are essential. Solar excels as a daytime energy source, wind as a nighttime source. For both to be dependably accessible day and night and without incessant spikes and valleys, the energy generated must be stored in batteries and distributed for use when needed.

Currently, wind and solar — the fastest growing renewables — account for only 7 percent of worldwide power generation, though that percentage has doubled si