I see. A single Powerwall cannot coexist with that much PV; you'll have to either isolate the Powerwall from the PV in a partial backup and let the PV shut down in an outage or use contactors or something to disconnect all but (again IIRC) 7.6kW AC of the PV so it can run off grid with a single Powerwall. You would need three Powerwalls for it all to run off grid.
A generator in the mix makes it still more complicated. Just out of curiosity, are you (as and individual or as a company) experienced at coordinating Powerwalls, PV, and generators in the same systems? Getting all to behave the way a customer wants it to can be a challenge for both the system integrator and the customer. Grid tied PV is mostly "set it and forget it", but a system like the one you are describing requires some level of understanding by the customer even after it is installed.
We have dealt with generators and PV combinations before but a Powerwall is new grounds. We'll have the Tesla certified installer to integrate it and I am beginning to see how challenging this could get. We may have to simplify this as much as possible or go with something complete different like a hybrid inverter. Although the customer is a techie this is not your average customer situation who only wants to see the magic happen.
Just be advised that incorporating a single Powerwall as a partial home backup is significantly more complicated than multiple Powerwalls as a whole home backup. How are you planning to connect the PV? The simplest approach would be to connect on the line side of the ATS so that when the grid goes down the PV shuts off and cannot backfeed the generator, but some customers will push back on that. It's good that you will have a Tesla expert to help with this.
Also be advised that if you install a single Powerwall as a partial backup and later want to install more of them to backup the whole service you will need to rewire and reconfigure the whole system. Equipment, conductors, and connectivity will all change. We get customers who want a single Powerwall now with the option of adding more later, but they do not understand how expensive the upgrade would be; the cost of the additional Powerwall is only part of the expense.
I don't see why that would have to be the case. If you know up front that ease of later full backup is a goal, then you can design the initial installation to make the later work easy to do. That may increase the cost of the initial work, but the later switch to full backup should just require adding the PWs and moving a feeder or two.
Thanks! Often times the learning happens 90% of the way into it, the other 10% happens after when I say to myself "Why did I do it that way? I could've done this way!"
Have you done this before? We have, and it has not been that simple for us.
Once only, but I've thought about these configurations a lot.
We have done it dozens of times, and most of the time adding a Powerwall and changing from a partial to whole home backup is major surgery.
Certainly likely if the original PW install was not designed with a plan for the future upgrade.
I have a dumb question. Have you done an analysis from your current electric bill to see what your average daily consumption is for the house? That really should be the starting point. You very well may need a 2nd battery but I don't see the sense in two separate Tesla systems with one battery each. Now you have an inverter with enough headroom to handle this kind of current? Is 21.56Kw its limit or can it handle more? Isn't it possible to add to the battery capacity of the already in-place system? Having two separate systems is twice the headache.
Yes, we will do an average daily usage for the house. The customer has the existing array but the original idea was for one Powerwall battery with the option to add a second to increase storage if needed. It was pointed out by jaggedben that there are many variables to consider. At the moment it looks like we will add a critical load backup panel but there is still a survey scheduled with the certified Tesla installer.
Good point. As far as I understand, the Tesla Gateway, which you should have if you're going with PW2 batteries, has a 'throughput' limit of 5Kw continuous, 7Kw surge. So aren't you limited by that, no matter how many batteries you have? Yes, a bigger array will last longer, but you cant be pulling 6Kw+ on a constant basis. So what's the actual draw with all A/C's running? The OP here seemed to indicate 21.56 was a limit but he didn't quite make it clear if that was the average house draw in Kw at any given time or the total KwH for a day, or perhaps the throughput limit of the inverter, which I'm leaning towards, but in any case that's a pretty good to big draw, indicating some big eaters of juice, like A/C's, electric water heaters, etc. Does Tesla offer Gateways that will allow more than 5Kw continuous? That's what you'd need if you want those multiple batteries to be able to supply heavier draw, right? I think dual systems with two separate controllers should be avoided at all costs. Knowing how secretive Tesla is, getting their batteries to work with some other controller/gateway or getting their gateway to work with other batteries might be an exercise in futility.
Incorrect. That's the capability of just one PW2, and for multiple PW2s those ratings add. The Gateway rating is 200A.
Interesting. I looked at the Datasheet for the Gateway and it does indeed say max AC input of 200a. So theoretically, I could open the grid circuit into the gateway, and leave it open and the system would use the grid only as necessary, and switch to the PW if the grid went down, but while it's on the grid, it could pull up to 200a AC, which is what the main breaker is marked. The 5Kw limit applies to battery ops only, it seems.
