Obviously, the sun goes down, but the problem is not insurmountable for several reasons as several Arizona users have demonstrated.  Moreover, PVs will provide their electricity just about when we need it in our homes, off-setting some traditional generation without additional power plant construction.  Any time they are not producing enough to meet demand, the normal grid-tied system can take over.  If the solar arrays are large and constructed near an existing power plant (coal, hydro) they can firm up the solar.

Local solar firms have been putting in PV systems for the last 30 years with 5 sunless days of battery storage.  The batteries cost $1 per pound, last 6 or 7 years and are 100% recycled. This is less than a pound of food that only lasts one meal.

Not a problem for grid-tied systems until we get into the hundreds or maybe 1000s of Megawatts.  One option is to site solar at existing generating facilities, like a gas-fired or coal-fired power plant.  If the solar backs off due to weather or storms, the fossil-fueled portion of the plant can ramp up to keep the power output steady.  This is a variation on the hydro-dam idea I mentioned last night. There are merchant gas plants considering this right now – and it’s not a bad deal considering wholesale gas plants are selling power to the grid at $100 / MWH ($0.10 / kWh).