There are two environmental costs to this setup.

The first is that if he weren't frivolously moving electrons through his heater, there would be more to feed to the grid for other people. So there is an opportunity cost of reducing CO2-generating energy production elsewhere.

The second is that he installed a much bigger array than optimal, due to regulatory requirements, and that too has up-front environmental consequence. Since he's burning off that excess electricity rather than feeding it to the grid, there's really no redeeming value to an array that's too big.

I don’t understand this attitude at all. Your first “cost“ is like saying there’s an opportunity cost to my purchasing bubble gum and putting it on a shelf because other people can’t chew that bubble gum and I’m not chewing it yet.

Well one thing you can do is try to figure out the approx. carbon output of those extra panels and buy trees to help remove an equivalent amount from the atmosphere so you can offset the carbon output. Of course you are spending money doing this and one must consider the carbon emitted in the process of earning that money. Depending on his circumstances this could be very little or none.

True. Thanks for that.

Don't forget the embodied energy of the overbuilt solar system!

I had, thanks for reminding me.