The desire to store generated energy for use at a different time isn't limited to solar cells or other day-only sources. A similar problem is posed by the fact

The desire to store generated energy for use at a different time isn't limited to solar cells or other day-only sources. A similar problem is posed by the fact that conventional power stations have a fixed maximum throughput, but demand is much higher during the day. To balance the load and maximize revenue, a number of power producers employ a decidedly low-tech way to store energy: every night, they pump a lake of water up a mountain, and during the day they drain it through hydroelectric generators. Really! I shit you not: http://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity http://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity