1. It gives you power when your home loses power from the grid. This has taken more relevance lately in light of USA utilities adopting more proactive policies regarding grid shutdowns during wildfire season. The PW works like a whole-house UPS. If the power goes out, you won't know it unless you look at the app (or your neighbor's dark homes.
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2. You will probably soon be on a TOU (time of use) rate tier with your utility, if you aren't already. With PWs, you won't have to worry about not using power hungry devices (EV charging, A/C, laundry etc.) during the day when rates are way higher.
3. During a power outage, you won't lose any solar production. Without PWs, your solar panels shut down when the grid goes down.
BTW, is the $4500 labor costs? Each wall has a list price of $6700.