powerwall technology that will let me run off grid
They aren't made to run off grid indefinitely. They are made to get you through a short interruption. You get a few hours off grid with a power wall. Without air conditioning, well pumps, or other large loads. And it won't play nice with a backup generator -- it will only charge from solar, and if you turn on your generator the Solar+Power Wall go offline. If there's no sun because of nearby wildfire (smoke) or storms (clouds), then you are up **** creek once the batteries run low. So yeah, it'll work fine for those times where the lights are out for a few hours because a drunk hit a light pole down the road. But when the hurricane comes and blows out your neighborhood, your house will be just as dark as the next guys.
For 95% of the folks out there - the run of the mill Generac 21kW propane generators will cost 1/2th of what a Power Wall will, will run your A/C and everything else you have, and with a small 100Gal tank run 10 times longer before needing to refuel. You ~could~ run offgrid with one, but they aren't meant for long run times -- they need an oil change about every 100 hrs (that's ... every 4 days if you tried to run completely off grid) -- there's an entirely different class of generators made to run long term, but... you will pay for it. And fuel isn't free either. If you are only running a couple of times a year, the fuel cost is negligible, but if you are really wanting to go entirely off-grid, it's a different kettle of fish.
There are much better energy storage products out there than Tesla, particularly if you are really talking about running anything off grid for more than a couple of hours at a time. There just isn't a huge market, because the grid is amazingly accessible in the US, and for most people, even as expensive as those power bills can be, it's a really large investment to go off-grid that has a fairly long payback, if any at all in many markets.
For the "virtual power plant" idea, that's fine. You don't need huge capacity - you just need a lot of units out there. The goal of a utility scale storage project is to provide enough energy to offset needing to start a higher cost, higher polluting asset. At about 13kWh per home, the Power Wall compare that to a utility scale installation is on the order of 10MWh-1,200 MWh. So you need a lot of homes signed up to have a similar impact as a single utility scale energy storage installation -- thousands, if not tens of thousands. If you know anything about the duck curve - that's usually only about the 2-4 hours right as the sun goes down before loads start to naturally diminish on their own. That length of time gets longer as more on demand power sources get knocked off line for opportunistic renewables, but that's what the energy storage is supposed to buffer and mitigate anyway.
I say this with some knowledge of the industry - I do power plants for large factories for a career. And I'm about 1/3 of the way to having enough solar at my home to just tell my utility company to eat crap. I do have a energy storage system, and it works with a standby generator (a cheapy Harbor Freight Predator, it runs about 10 hrs/year, so I won't feel bad when it craps the bed), and it's all integrated and runs together and I've had to run off grid for upwards of a week during "Wildfire Safety Shutdowns" -- so there are systems that can work, and work well together, just not the Power Wall. If I were willing to cut down a few trees I'd be closer to 1/2 the way, but the shade from the trees saves me more in avoided HVAC than it would generate in increased solar production.
