At least with PG&E, my understanding was that those rates only applied to a net over-production over a long period of time (I believe over the course of a year)

At least with PG&E, my understanding was that those rates only applied to a net over-production over a long period of time (I believe over the course of a year). As long as your power bill is not negative, any over-production during high value times of the day is sold at the market rate and offsets low value electricity you buy at night. This is important with solar system sizing, because not only don't you want to be a net exporter of energy, the lower tiers of PG&E's energy rates are very cheap so you don't want to generate that power either. You really only want to offset the high-tier, high-demand electricity you use (or plan to use in the future). For me it didn't really matter because my energy usage is highest during the peak times of the day, but this is my understanding of how it works. I'll know for sure in a couple of months when I see my bill :)