Unless batteries get easier to change in an EV, I am not sure that this is a good idea. It's just gonna put extra cycles on the battery chemistry which is finite to begin with.
Especially since they're not paying you what they charged you for that energy. I'd prefer they just charge you for the net energy you take out (charge-discharge), at least. It's more of a voluntary additional outlay seemingly. I think I'd just be sure to only charge my car during off-peak hours. Keep it disconnected the rest of the time. (Also why, as someone who lives where it's sunny probably 360 days per year, I'd like an EV with solar panels on it. It won't be much, but maybe enough to keep things conditioned.)