Here is an interesting article discussing fees that various utilities in the U.S. have begun to charge solar PV home owners for hooking up to the grid so that they can buy electricity from the grid when their panels aren’t generating electricity, and sell electricity back tot he grid when they are:
The article mentions a source that says that 40-60% of a solar PV systems output goes back to the grid.
There are a lot of debates right now in this country and throughout the world trying to figure out exactly the value of solar-generated electricity.
If the costs of hooking up to the grid become too high, it will create an incentive for solar home owners to go off grid with home-scale energy storage (e.g. batteries, solar fuels).