Replying to myself.. there are some caveats obviously that getting days when this payment happens is presumably not guaranteed, although with temperatures tending to rise one could expect it to happen. And maybe the price is not guaranteed either beyond a certain point. In other words, maybe don't buy a PowerWall unless you need one for other reasons.. it's probably not a reliable money making idea. Just in case, on the off chance, anyone was thinking of this as a small side income, lol.