Investors recently chipped in $15 million to fund battery startup EOS Energy Storage, a company that says its batteries could eventually compete with natural-gas power plants to provide power during times of peak demand.

Cheap energy storage is becoming increasingly important as greater numbers of wind turbines and solar panels are added to the grid. If renewable energy is to replace the fossil fuels that dominate power supplies and serve to backup wind turbines and solar panels, very large-scale, inexpensive batteries like the ones EOS is developing will be needed (see “Wind Turbines, Battery Included, Can Keep Power Supplies Stable,” “Battery Could Provide a Cheap Way to Store Solar Power,” and “A Solution to Solar Power Intermittency”).