I got the powerwalls for my home and I thought I’d only use them as a backup. After a little while I realized how much power I was buying at night because I had them setup as a backup. I did the math, resale rates are about 1/3 of purchase rates. I was using between 10 kW and 20 kW depending on the time of year. Assuming that’s $0.08 per kW I’m saving, let’s call that $1.50/day (it’s not actually that much). That’s $550/year I’m saving. The reality is probably closer to $300-$350. That said, it’s not trivial. It is using the battery, so I’m not sure if that is going to wear it out faster. But I already bought the battery for the emergency backup purpose, I might as well save a few hundred per year.