The source of the power is irrelevant: you could be selling that electricity to the grid, or offsetting the cost of your home's usage. Buying a solar panel may eliminate the middle man, but there's still lost opportunity cost.
The source of power may be irrelevant to you, but not to me. Where I live net metering is capped at 30% of my utility costs. So if I produce more than 30% of what I use the utility company sucks up the excess that I produce and keeps it for free.