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Inverter size when maximum system is 11.56 kW (34 panels)

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In Georgia to qualify for Georgia Power's monthly net metering the maximum system size is 10 kW AC. Tesla tells me that they will do a 34 panel, 11.56 kW system which will qualify. They have also said they will install a 7.6 kW Tesla inverter.
  • Will a 7.6 kW inverter limit the production that the panels would be capable of producing with a larger inverter?
  • Georgia Power 's tariff states the limitation as:"....residential applications with a peak generating capacity of less than or equal to 10 kW AC." and "The system’s AC peak generating capacity is determined by the aggregate nameplate capacity of the inverter(s) at the service point.".
  • Is Tesla's 7.6 kW inverter actually 7.6 or would the 'nameplate capacity' be less?
 
Two things to think about:

Is a larger inverter (e.g., Solar Edge 10 kW) available? It would be a shame to waste all that extra power in the summer...

Can you go with fewer panels, so you don't have to pay for what you're not going to use? Granted, there is a balance between cost of more panels and optimizing production capacity for off-peak sun hours, but have you done that yet?
 

nwdiver

Well-Known Member
Feb 17, 2013
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Two things to think about:

Is a larger inverter (e.g., Solar Edge 10 kW) available? It would be a shame to waste all that extra power in the summer...

Can you go with fewer panels, so you don't have to pay for what you're not going to use? Granted, there is a balance between cost of more panels and optimizing production capacity for off-peak sun hours, but have you done that yet?

The difference isn't as much as you would think. With a 7.6kW inverter and an oversize ratio of 1.5 the system will produce ~16,264kWh/yr. With a 10kW inverter you only gain ~200kWh/yr. With a smaller system size to reduce the oversize ratio to 1.2 with a 7.6kW inverter you lose ~3,000kWh/yr. Seems like a 7.6kW inverter oversized by 1.5 is just fine. Since Tesla is only going to have a 3.8 and 7.6kW inverter this is going to get A LOT more common. It will be interesting to see where they go from 3.8 to 7.6. 5kW? 6?.... 7?

I've installed 2 systems oversized by 50%. The annual saturation losses are < 5%.
 
The difference isn't as much as you would think. With a 7.6kW inverter and an oversize ratio of 1.5 the system will produce ~16,264kWh/yr. With a 10kW inverter you only gain ~200kWh/yr. With a smaller system size to reduce the oversize ratio to 1.2 with a 7.6kW inverter you lose ~3,000kWh/yr. Seems like a 7.6kW inverter oversized by 1.5 is just fine. Since Tesla is only going to have a 3.8 and 7.6kW inverter this is going to get A LOT more common. It will be interesting to see where they go from 3.8 to 7.6. 5kW? 6?.... 7?

I've installed 2 systems oversized by 50%. The annual saturation losses are < 5%.
I agree and found an article from 2016 that fully supports what you wrote. Why Oversizing Solar Panel Arrays Is A Smart Move
After reading your reply and this article I ran my proposed system on PVWatts with a 1.52 DC to AC ratio vs. the 1.156 if I had a 10.0 Solar Edge inverter. The 10.0 inverter only generates 536 kWh more for the whole year at my location which is similar to your numbers.
 

nwdiver

Well-Known Member
Feb 17, 2013
8,856
12,943
United States
I agree and found an article from 2016 that fully supports what you wrote. Why Oversizing Solar Panel Arrays Is A Smart Move
After reading your reply and this article I ran my proposed system on PVWatts with a 1.52 DC to AC ratio vs. the 1.156 if I had a 10.0 Solar Edge inverter. The 10.0 inverter only generates 536 kWh more for the whole year at my location which is similar to your numbers.

Is your system ground mount or roof mount? PV Watts defaults to 'open rack' for some reason. Roof mount is ~200kWh/yr lower.
 
In Georgia to qualify for Georgia Power's monthly net metering the maximum system size is 10 kW AC. Tesla tells me that they will do a 34 panel, 11.56 kW system which will qualify. They have also said they will install a 7.6 kW Tesla inverter.
  • Will a 7.6 kW inverter limit the production that the panels would be capable of producing with a larger inverter?
  • Georgia Power 's tariff states the limitation as:"....residential applications with a peak generating capacity of less than or equal to 10 kW AC." and "The system’s AC peak generating capacity is determined by the aggregate nameplate capacity of the inverter(s) at the service point.".
  • Is Tesla's 7.6 kW inverter actually 7.6 or would the 'nameplate capacity' be less?

I also have an 34 Panel 11.56 system installed in December 2020. The gave me the default 10kW SolarEdge. If they're selling you 11.56 you should at least have the option to use as much of it as possible. ~200kWh/yr may not be a lot, but why not get as much as what you are paying for?
 
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nwdiver

Well-Known Member
Feb 17, 2013
8,856
12,943
United States
I also have an 34 Panel 11.56 system installed in December 2020. The gave me the default 10kW SolarEdge. If they're selling you 11.56 you should at least have the option to use as much of it as possible. ~200kWh/yr may not be a lot, but why not get as much as what you are paying for?

Because the cost of upgrading to a 10kW SE inverter is ~$2,000 plus you'd need to do a line-side-tap since most distribution panels can only accept 40A (7.68kW) of solar. Even at $2k.... is $2k worth getting another ~$30/yr in production?

Why not flip it? You paid for a 7.68kW inverter... should you not get the most out of it? ;) If it's only producing 6kW that's 1.68kW of inverter you paid for but you're not using.... max that baby out :)
 
Last edited:
I also have an 34 Panel 11.56 system installed in December 2020. The gave me the default 10kW SolarEdge. If they're selling you 11.56 you should at least have the option to use as much of it as possible. ~200kWh/yr may not be a lot, but why not get as much as what you are paying for?
From other posts it seems like they are no longer providing anything but the Tesla inverters...but I can ask. The Tesla inverter specs say it's 97.5% efficient while the SolarEdge spec sheet says theirs is 99.2%. Does that efficiency delta show up in real world results?
 

nwdiver

Well-Known Member
Feb 17, 2013
8,856
12,943
United States
From other posts it seems like they are no longer providing anything but the Tesla inverters...but I can ask. The Tesla inverter specs say it's 97.5% efficient while the SolarEdge spec sheet says theirs is 99.2%. Does that efficiency delta show up in real world results?

The inverter is ~99.2% but the optimizers are also ~99% (0.99)(0.992) = 98.2% so the difference is really negligible.

I'm really surprised they offered SE for as long as they did. Tesla is the lowest $/w installer and SE is among the highest $/w inverters at ~$0.40/w. I wouldn't be surprised of the Tesla inverters are <$0.10/w. That's a YUGE difference.
 
Because the cost of upgrading to a 10kW SE inverter is ~$2,000 plus you'd need to do a line-side-tap since most distribution panels can only accept 40A (7.68kW) of solar. Even at $2k.... is $2k worth getting another ~$30/yr in production?

Why not flip it? You paid for a 7.68kW inverter... should you not get the most out of it? ;) If it's only producing 6kW that's 1.68kW of inverter you paid for but you're not using.... max that baby out :)

For me I'd ask tesla to give me the big and the little inverter. Or drop some panels.
 
I'm getting a 35kw system and Tesla is trying to give me 3 of their 7.6kw inverters and one 3.8kw (for a total of 26.6). I'm not going to accept that.
If money is your limiting resource, then that's not an efficient choice. Go with the smaller inverters.

If roof space is your limiting resource, and money is not an issue, then going for more inverters (lower DC/AC) is a good choice.

If roof space is not your limiting resource, and you want more energy produced than you'll get from a 35 kW DC / 26.6 kW AC system, it's not clear whether you are better off adding more panels, or bumping up the inverter size. Probably more panels, but a more detailed analysis is required.

Cheers, Wayne
 

Two-rocks

New England IPA
Jan 18, 2021
304
400
gone
Inverters are more efficient at the upper ranges of their output.
You want a certain amount clipping, as it only happens at very limited times.
The net result is more output from the 'system' without needless spending.
The same nameplate company also sells FSD, and if you bought that you need to ask if you really care about a few cents here and there. :cool:
 

nwdiver

Well-Known Member
Feb 17, 2013
8,856
12,943
United States
I'm getting a 35kw system and Tesla is trying to give me 3 of their 7.6kw inverters and one 3.8kw (for a total of 26.6). I'm not going to accept that. I want as little clipping as possible. At a very minimum, I want 4 7.6 inverters but I think I'd prefer four 7.6 and one 3.8.

With an oversize ratio of 1.32 for your location.... PV watts estimates saturation losses of 57kWh/yr..... that's 0.1%. Maybe you can ask for a 0.1% discount for all the energy you're gonna lose to saturation losses. ;)

Also keep in mind that not all kWh are created equal. A kWh in TX during a blizzard is apparently worth $9... and there probably wasn't any inverter saturation occurring. A kWh produced between 11 and 3 on a nice sunny day in Maryland is probably worth ~$0... and that trend is increasing. Soon it will be worth less than $0.
 
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