If renewable energy is going to take off, we need good ways of storing it for the times when the sun isn't shining and the wind isn't blowing

The sun does not shine at night, and the wind does not always blow; methods to store large amounts of energy for downtimes are needed to make widespread solar and wind power more practical. Some utility companies already use excess solar or wind power to pump water to uphill reservoirs, where it can later fall to turn turbines; this pumpedhydro approach could be installed in many more locations. Other viable energy storage solutions include facilities that compress air into large underground caverns, that heat fluids or molten salts that later create steam to turn turbines, or that can charge advanced batteries. These meth ods require breakthroughs to make them more efficient so they can compete on price with the cost of electricity from traditional power plants. E N E RGY