Maintenance costs are more important than whatever minuscule percentage you add to the grid and maintenance costs are averaged out by everyone paying.

The cost of infrastructure doesn't change if you're consuming power 2h/day or 24/day.

Sure. No one is asking for that amount though. Every utility bill has the breakdown of the costs. Just pay me the per unit cost listed in the “generation” part of the utility bill. I’m pretty sure even then, I’d be at a disadvantage, assuming PG&E would have a lower cost advantage in generating electricity in bulk.