Whole House configuration for Powerwall/Solar Install

[smigit2002]

Hey all,

I'm getting ready to take the plunge into solar and am trying to wrap my head around the exact configuration of the system. The initial quote was for a 9kW system installed with 25 360W SunPower panels utilizing a SolarEdge 10k inverter and one PowerWall with a critical load panel.
Through all my quotes, I only asked for one battery as most installers offered LGs. When an installer offered a PowerWall, I said great! When he said I could add on another, I said even better, because Maryland offers incentives for energy storage.

I reached out to my sales rep and asked about adding a second power wall, eliminating the critical load panel and going whole house. For reference, my meter and 200A main panel are separate, the largest breaker I have is a 60A for the emergency resistance strip heat, which I realize is the max load of a PW output. I was told that no, we'd still need to do a critical load panel because even the pair of PowerWalls wouldn't be able to cover everything. I figure I'd just wait for the site survey to discuss it in more depth.

I got a call today from the gentleman who will be overseeing my project. I take the opportunity to rehash the conversation I had with sales, and again, he generally implied that doing a whole home backup on two PowerWalls wouldn't work, and that I'd have to do a critical load panel OR some sort of active load shedding. He also pulled up my file, saw the 10k inverter and said "oh, a single PowerWall can't handle that, we'll need to drop that to a 7600." I asked if two PowerWalls could handle the 10k, and he responded that I'd need two inverters.

So can someone please fact check this for me? I've read as much as I can on the forums, I've read numerous Tesla documents found online, and I just keep coming back to this picture of an inverter and PowerWall feeding a main panel, feeding the gateway feeding a utility meter.

Thanks, sorry for the long-winded post. I just hope to have all my facts straight for my site survey next week.

 

[SoundDaTrumpet]

Mostly okay. Except needing two 7600W inverters for 2 PWs... can be done with 10k inverter & 2 PWs.

 

[Dan123]

I have a 200amp service, 2PWs, 38 enphase microinverters (9800kw) total.

In my case 2PWs do provide a full-house backup. I also have my largest breaker 60amp, which is that large for the heater, and if the heater kicks in, I know that the PWs will shut down.

What made the 2PWs possible in my case is that all of the other appliances (AC and electric water heater) are efficient and have a low start up surge. For example, the Locked Rotor Amps (LRA) for my AC compressor is about 22, which can be covered even by one PW.

It is true that if you have 10K inverter, 2PWs would provide a more stable installation than 1PW. If you have 1PW, it can only accept 5KW of power, so if you are off-grid and the solar inverter is producing more than 5KW, the single PW will have to shut down the solar inverter.


I think you should insist on 2PWS. Either 7600 or 10000 inverter will be fine for 2PWs. You should press them on reasons why they can't do a full-house backup with 2PWs. Try to speak with the engineering if you can. It is possible that there is one or two loads that create the problem (maybe the 60amp resistive heating, or maybe the LRA of your AC compressor is too high). In such a case, you can use your existing main panel as the backup panel, and install a small separate panel between your meter and PW gateway. The new panel will just have 2-3 large loads that can't be backed up for some reason.

 

[smigit2002]

Great, that's reassuring. I'm hoping to switch to Geothermal soon, so for all I care I'll just remove the 60A breaker so they don't have to even think about it.

I'm hoping that when they do their site survey they will actually determine in my favor, and if not, I will continue my polite insistence.

 

[Dan123]

Great, that's reassuring. I'm hoping to switch to Geothermal soon, so for all I care I'll just remove the 60A breaker so they don't have to even think about it.

I'm hoping that when they do their site survey they will actually determine in my favor, and if not, I will continue my polite insistence.

In my case, the site survey was completely virtual. They sent me a questionnaire and I had to take a bunch of pictures of everything.

 

[miimura]

To me, whole house is relative. Just leave the largest loads in the main panel not backed up. My EV charging is not backed up and I'm OK with that.

 

[DrSmile]

I have everything backed up, including two large A/C units and a 48 amp home charger with 2 Powerwalls. The most constant load I've put on the Powerwalls was just under 10KW, no problems at all. I have no critical load panel, just a breaker in the Gateway. I am curious whether I could pull something like 15KW while my 13.2 KW solar system is supplying max production, but haven't tried it. I've read posts that this should actually work.

 

[D3xDt3Reaction]

I have everything backed up, including two large A/C units and a 48 amp home charger with 2 Powerwalls. The most constant load I've put on the Powerwalls was just under 10KW, no problems at all. I have no critical load panel, just a breaker in the Gateway. I am curious whether I could pull something like 15KW while my 13.2 KW solar system is supplying max production, but haven't tried it. I've read posts that this should actually work.

I will probably end up with a setup like yours with A/C and 14-50 plug backed up by 2 Powerwalls. But with every load in the house turned on, the Powerwalls alone couldn’t keep up. Without solar, or if solar cuts out due to cloud cover, will a breaker trip to protect the house from brownout?

 

[Dan123]

I have everything backed up, including two large A/C units and a 48 amp home charger with 2 Powerwalls. The most constant load I've put on the Powerwalls was just under 10KW, no problems at all. I have no critical load panel, just a breaker in the Gateway. I am curious whether I could pull something like 15KW while my 13.2 KW solar system is supplying max production, but haven't tried it. I've read posts that this should actually work.

I have tried it. I was able to pull 16kw from 2PW and solar, for a few minutes. However, solar is unpredictable, and if a cloud comes, its output can quickly drop.

 

[Dan123]

I will probably end up with a setup like yours with A/C and 14-50 plug backed up by 2 Powerwalls. But with every load in the house turned on, the Powerwalls alone couldn’t keep up. Without solar, or if solar cuts out due to cloud cover, will a breaker trip to protect the house from brownout?

Not the breaker, the powerwall itself shuts down if the demand exceeds its capacity.

 

[arnolddeleon]

Just beware that without some automation if the power goes out at night and you have a car charging it has a good chance of emptying your powerwall before you the sun comes out you backup the whole house.

 

[boaterva]

We have 'whole house' with three PWs, and the only load not on the PWs IS the HPWC charging circuit, which makes it great since it can't deplete the PWs. If we ever have an extended outage and we have lots of sunshine, we can charge from a dryer outlet or something.

They installed a subpanel for the HPWC 100 Amp circuit and used the original 200 Amp main panel as the 'critical loads' panel. We also have a 10K inverter.

I'm not sure what the '10K inverter' and '2 PWs' have to do with each other, as in the 'can't handle it' phrase. Extra output goes to the grid, of course.

 

[Janus]

I'm not sure what the '10K inverter' and '2 PWs' have to do with each other, as in the 'can't handle it' phrase. Extra output goes to the grid, of course.

That's the exact problem. When there's a grid outage, there's no where for the extra power to go, so the whole thing may shutdown on you to prevent an overload.

 

[Joepublic]

We also are thinking about getting a powerwall to our newly installed 8.9kw 27 panel Panasonic solar system with a Solaredge 10K HD inverter now that Massachusetts has added multiple storage incentives. The sweet spot for maximizing incentives is just to install one powerwall. After doing the virtual interview, Tesla came back saying because I have a 10k inverter I have to buy two powerwalls or get a replacement smaller inverter. The most sustained output we've had is 7.6 kw, though when cloudy, I had a 8.1kw spike presumably sunshine suddenly hitting a cool array. As an aside we got the larger inverter for when we add a future string of panels.
I thought the Solaredge could be directed to generate less power, so in the event of a power outage and an extra power couldn't be dumped to the grid, it seems odd that a modern inverter can't be told to limit production. I apologize for my ignorance as I'm still climbing the learning curve.
Do I really have to buy two powerwalls with this inverter?

 

[Dan123]

We also are thinking about getting a powerwall to our newly installed 8.9kw 27 panel Panasonic solar system with a Solaredge 10K HD inverter now that Massachusetts has added multiple storage incentives. The sweet spot for maximizing incentives is just to install one powerwall. After doing the virtual interview, Tesla came back saying because I have a 10k inverter I have to buy two powerwalls or get a replacement smaller inverter. The most sustained output we've had is 7.6 kw, though when cloudy, I had a 8.1kw spike presumably sunshine suddenly hitting a cool array. As an aside we got the larger inverter for when we add a future string of panels.
I thought the Solaredge could be directed to generate less power, so in the event of a power outage and an extra power couldn't be dumped to the grid, it seems odd that a modern inverter can't be told to limit production. I apologize for my ignorance as I'm still climbing the learning curve.
Do I really have to buy two powerwalls with this inverter?

When you are connected to the grid, one powerwall would work just fine, if you need it for self-consumption or time-based modes.

However, you would have problems with off-grid mode. Basically, here is what would happen with one powerwall and 10K inverter when the power goes off.

1. Powerwall will increase the frequency, and SolarEdge will shut-down.
2. In about 5 minutes, SolarEdge would restart.
3. If it supplies more than X (where X is approximately 5KW, but may depend on the state-of-charge of the battery), then PW will again shut down the SolarEdge inverter. Also, it is possible that the Powerwall itself will shut down.
4. In 5 minutes, this will restart and the cycle will repeat.

As a result, it will be very unstable in the off-grid mode.

SolarEdge may have a way to lower its output, but I think this only works when the Powerwall is reaching its full capacity and the charge rate is below 5KW.