Can solar plus powerwall run the home during extended power outage

[rw99]

You might have a rare but possible problem with 14.19kW of solar, and 2 Powerwalls. The Powerwall has a 5kw power rating (in/out). If you're producing 14.19kW from solar, and you're grid connected, then that excess 4.19kW above the combined Powerwalls rating of 10kw will go out onto the grid. No problem. But, if you're off-grid, and it's a bright sunny day, the Powerwalls will not be able to handle that power and I believe they will shut down in that situation.
They will not adjust frequency to shut down solar production like they do in high state of charge situation. At least that's what I've been told, and kind of makes sense.
Ideally you'd match the solar capacity to the Powerwall capacity.
Also, I did a week-long test of off grid and made a YouTube video on it. (CWNE88 is the channel name)

I’m very curious about this “mismatch” topic... I have a little over 10 kW solar and will be installing a single Powerwall (referral reward). You’re implying that I’d need two PW installed to prevent shutdown when the solar is generating more than 5 kW...or should this discussion be in kWh? Confused.

 

[miimura]

I’m very curious about this “mismatch” topic... I have a little over 10 kW solar and will be installing a single Powerwall (referral reward). You’re implying that I’d need two PW installed to prevent shutdown when the solar is generating more than 5 kW...or should this discussion be in kWh? Confused.

Yes, the instantaneous power, 5kW, is the limitation. kWh is energy, like how full the Powewall battery is. If you have more than one solar string inverter, then the most logical way is to put one inverter outside the Backup Gateway so that it shuts down with the grid and the other one has max power closer to the Powerwall's charge power limit.

 

[CWNE88]

I you have a constant background load to take some of the excess, then you'll be fine. ie, my house load never drops below 300w.

 

[Musterion]

I’m very curious about this “mismatch” topic... I have a little over 10 kW solar and will be installing a single Powerwall (referral reward). You’re implying that I’d need two PW installed to prevent shutdown when the solar is generating more than 5 kW...or should this discussion be in kWh? Confused.

It is not a mismatch, but just conservation of energy and is only a problem in micro-grid situation (power failure with grid disconnected) because power grid is an infinite sink. The instantaneous energy coming out of your solar needs a place to go. If it is greater than the sum of your house load and what the Powerwall can sink, there is no choice but to throttle the source, the solar. But because technology has not yet caught up, on-off control is used instead of throttling.

But if you have a referral award you probably have a Tesla vehicle. In that case you can actually use your car as an adjustable energy sink during a power failure in order to keep your solar system on-line.

 

[rw99]

Great info, thanks!

 

[gpez]

It is not a mismatch, but just conservation of energy and is only a problem in micro-grid situation (power failure with grid disconnected) because power grid is an infinite sink. The instantaneous energy coming out of your solar needs a place to go. If it is greater than the sum of your house load and what the Powerwall can sink, there is no choice but to throttle the source, the solar. But because technology has not yet caught up, on-off control is used instead of throttling.

But if you have a referral award you probably have a Tesla vehicle. In that case you can actually use your car as an adjustable energy sink during a power failure in order to keep your solar system on-line.

I have this potential issue with my 8.6kw array and 6.5kw inverters given the 5kw limitation of the Powerwall. What I found is that since I have microinverters the Powerwall is able to signal to some of them to turn off, lowering production to a level that the Powerwall can accept it. Older systems or systems with single inverters may not be able to do this.

 

[shapps47]

I saw this on Tesla's website:

Since Powerwall 2 is an AC coupled solution, it is compatible with all inverter types. To ensure reliable operation during power outages, at least one Powerwall is required for each 7.6 kW AC of solar included in the backup circuit.

Source:
Combining Systems | Powerwall Support