I've got solar with a Tesla inverter, and I'll say up front that my biggest regret is not putting a Powerwall 3 or similar battery in with the original install. The reason is simple: we've had unanticipated power outages in the last 18 months, and with no battery the solar does nothing for us when the grid goes down. I didn't think outages would be a real factor when I signed, and they have been.
The other piece is the daytime surplus. If you've got an EV and solar, there's a good chance you're producing more than you're using while you're at work, and without storage that just goes back to the grid. With a battery you can hold it and use it in the evening instead of importing. Depending on your import/export rates the savings per kWh may not be huge (for some setups it's around .10/kWh on whatever surplus you can store), but it's there and it adds up.
The part that really stings is the cost of doing it later. I got quotes to swap from the Tesla inverter over to a Powerwall setup and they came in around $9-10K US. Going with the Powerwall from the start would have only been an additional $3-4K US. So I'm looking at paying roughly two to three times as much to fix a decision I made at install.
So my answer to the question of what I'd do differently: if you're even leaning toward solar, price the battery in at the same time as the panels, even if you don't think you need it. Retrofitting is where they get you.
I'm curious what others have run into, especially those of you who added a battery after the fact. Did you find a way to do it for less than $9-10K? And for people who did it all at once, did the battery change how you charge the EV (daytime vs overnight), or did you mostly just use it for backup?
