Solar System Size vs Number of Powerwalls

[CrazyRabbit]

When running off grid you usually don’t want more solar production then what the powerwalls can charge on. So not so to few powerwalls. I suspect with Powerwall 2+ that solar can curtail under control of the TEG, since the inverter is on the CAN bus. But I’m not sure.
I do know that the solar can be set to soft curtail when appropriate grid profile has been set, 20% increments. Take a call to Tesla to get this setup, and in my case changing the grid profile my self on enphase system.

 

[CrazyRabbit]

Personally I suspect your 10-11KW of solar is a on the low side, but if it's all your roof can fit...

For 10-11KW in SC, I suspect Tesla might try and get away with a single 7.6KW of inverter on a PowerWall+, which would throw away some peaks during the very highest production time of may/june range, but not a huge amount of production.

I would try to see if you can get closer to 14-16KW of panels, two 7.6KW inverters, and IMHO 3 power walls is the right choice.

We have 23.5KW of panel, 20KW of inverter, and 3x powerwall 2, and are also in Tucson AZ like ArizonaJon.

I have a 40% reserve for backup, as we are hitting summer storms, and to the most part 40% will get us thru to solar the next day, I may adjust that to 50 or 60% as it is a bit tight with the amount of Air conditioning use during the night. Last night from power wall output stop to solar take over we used 26.5KWh from the grid, and 3x power walls is basically 40.5KWh, so 40% is about 16KWh, which would not have been enough to cover all of the grid usage.

I did not have any major car charging yesterday (We have a Model X 90D, Model 3LR, and a Model Y AWD LR)...

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The last 7 days are looking good:

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-Harry

What happens when you go off grid around noon and no loads? Your three powerwalls can only accept 15kw of power. Curious here. First go self powered to drain 10-20 out of you powerwalls some how so you have room to charge. Perhaps super cool your house, charge your car and roast a turkey all while self powered. Then go off grid and turn off you big loads and see what happens.

 

[hmcgregoraz]

What happens when you go off grid around noon and no loads? Your three powerwalls can only accept 15kw of power. Curious here. First go self powered to drain 10-20 out of you powerwalls some how so you have room to charge. Perhaps super cool your house, charge your car and roast a turkey all while self powered. Then go off grid and turn off you big loads and see what happens.

My solar production is currently at about 18.5KW, and the house load is running about 6KW.

With the heat in Tucson right now, I don't see getting the load under 3.5KW during the mid day heat, even under 4.5KW would be difficult.

Which means that I can't really keep the load under the spread between the 15KW the power walls can charge from.

I know the powerwall gateway can control the inverters by changing the frequency.

Tesla has a requirement of at least one powerwall per ~7KW of inverter capacity, and I am under that.

-Harry

 

[Matt-FL]

See picture below of house roof. I don't think I can fit more than 3 rows of 9 panels each or 27 panels total, which is approx 11 kW. I also have some piping on the roof which will likely knock me back down a panel or two to 10 kW. As the rear of my house faces almost directly south, panels on the front of the house are useless and my wife doesn't want any there anyways even if it was viable.

Tesla will for sure only give me one 7.6kW inverter with a 10-11 kW setup. I've read on here and Reddit you need to get to 13 kW or so before they will give you another inverter (above 1.7 DC/AC ratio). I'm ok with that though as like you said I shouldn't peak shave too much. Per PVWatts around 1.25 DC/AC is optimal for my location, but 1.3 or 1.4 doesn't change total output that much.

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Why not also utilize the lower porch roof? You could probably fit another 6 or so panels there.

You can always request to speak with your Tesla designer, they will typically allow you to customize (for a price).

 

[Jeremy3292]

Why not also utilize the lower porch roof? You could probably fit another 6 or so panels there.

You can always request to speak with your Tesla designer, they will typically allow you to customize (for a price).

Potentially an option, but behind the fence line are fairly tall trees which do shade the main roof in the morning. Not sure how useful it would be on the porch bc of the shade except at peak sun time. But maybe that’s something I should look into also. Thanks

 

[GregBallantyne]

Potentially an option, but behind the fence line are fairly tall trees which do shade the main roof in the morning. Not sure how useful it would be on the porch bc of the shade except at peak sun time. But maybe that’s something I should look into also. Thanks

I've got trees all around. My roof makes maybe 9-12 kwh by noon, maybe 5-6 kwh after 3:30, and 30-40 kwh between on a decent day. That's the peak sun time you're referring to.... it ain't all that bad if that's "all" you get. You don't make a lot otherwise. But I have Tesla Solar Roof, which is more forgiving of shade than panels. But all the same, peak sun hours are where the significant majority of your production will be, early and late shade notwithstanding.

Edit: I just made a financial plan for next year to add a fourth Powerwall after reading that the IRA has no prohibition for taking the 30% home battery storage 30% tax credit more than once. For whole home backup, and therefore self powering, two PW is bare minimum, three is decently across the threshold, and I think four will approach comfortable.