How to run a 11.4kW system beyond the 7.7kW limit?

[Desola]

Hi,

I just got a new Tesla solar system with 28 panels=11.4 kW and powerwall+ installed. I don't have a PTO yet. My power output is capped at 7.7kW, it is obvious because every day the power chart stops at this mark, and I saw several threads confirming this limit. I had an online chat with a Tesla project advisor who told me that it should be possible to reach my full capacity because "Tesla overdrives the inverters up to 170%". He didn't know how exactly, though, he hinted that it might only be possible after PTO.
I'm concerned since I didn't read about anyone with >7.7kW output on a single powerwall+ inverter, could you shed some light on it? I'd like to get clarity before PTO and full payment. Maybe I don't have to pay for the panels > 7.7 kW

Thanks!

 

[Vines]

Hi,

I just got a new Tesla solar system with 28 panels=11.4 kW and powerwall+ installed. I don't have a PTO yet. My power output is capped at 7.7kW, it is obvious because every day the power chart stops at this mark, and I saw several threads confirming this limit. I had an online chat with a Tesla project advisor who told me that it should be possible to reach my full capacity because "Tesla overdrives the inverters up to 170%". He didn't know how exactly, though, he hinted that it might only be possible after PTO.
I'm concerned since I didn't read about anyone with >7.7kW output on a single powerwall+ inverter, could you shed some light on it? I'd like to get clarity before PTO and full payment. Maybe I don't have to pay for the panels > 7.7 kW

Thanks!

I have seen that this DC/AC ratio is considered acceptable by Tesla, and other users have posted that the yearly kWh production difference between this system with the 1.7 stacking ratio is approximately 1% or just over compared with a system with a lower 1.2 stacking ratio.

In effect I say you got what you paid for, the absolute most kWh for the least $$$.

 

[rando]

PVWatts shows a nearly 10% difference between a 1.7 and 1.2 DC/AC ratio in San Jose (assuming south facing and 5:12 roof slope). The production difference will be diminished if your site is less than ideal (shading, not south facing, unusual microclimate weather patterns ...). Is that enough to justify the cost of another inverter (possibly not an option for a Tesla cookie-cutter type install)? Overdriving (if possible without shortening service life) would likely be the more cost effective option.

 

[jjrandorin]

Hi,

I just got a new Tesla solar system with 28 panels=11.4 kW and powerwall+ installed. I don't have a PTO yet. My power output is capped at 7.7kW, it is obvious because every day the power chart stops at this mark, and I saw several threads confirming this limit. I had an online chat with a Tesla project advisor who told me that it should be possible to reach my full capacity because "Tesla overdrives the inverters up to 170%". He didn't know how exactly, though, he hinted that it might only be possible after PTO.
I'm concerned since I didn't read about anyone with >7.7kW output on a single powerwall+ inverter, could you shed some light on it? I'd like to get clarity before PTO and full payment. Maybe I don't have to pay for the panels > 7.7 kW

Thanks!

You are capped at inverter size. Peak production during the day is usually much less important than daily production. I would not expect that peak production number to magically go up somehow after PTO.

 

[Vines]

PVWatts shows a nearly 10% difference between a 1.7 and 1.2 DC/AC ratio in San Jose (assuming south facing and 5:12 roof slope). The production difference will be diminished if your site is less than ideal (shading, not south facing, unusual microclimate weather patterns ...). Is that enough to justify the cost of another inverter (possibly not an option for a Tesla cookie-cutter type install)? Overdriving (if possible without shortening service life) would likely be the more cost effective option.

It is interesting how much better a pure south facing roof is with a perfect azimuth. My numbers above were low if talking about the perfect roof.

 

[shred86]

It's pretty sad a Tesla solar advisor doesn't understand the 170% overdrive. It's kind of a silly phrase but all that means is the Tesla inverter is capable of allowing up to a 1.7 DC/AC ratio, meaning you can have up to a 12.92 kW system on that single 7.6 kW inverter. As it's already been mentioned, that is different than what the inverter is capable of outputting, which the max for the 7.6 kW inverter is nominally 7.6 kW but you will commonly see ~7.7 kW.

The optimal DC/AC ratio will completely depend on your setup. For example, I have an 11.2 kW system on a single 7.6 kW inverter, all east facing panels, and I'm estimated to lose less than 0.01% of annual production:

• 17,296 kWh/year with a 1.47 DC/AC ratio, or a single 7.6 kW inverter
• 17,453 kWh/year with a 0.98 DC/AC ratio, or a 7.6 & 3.8 kW inverter

I'm constantly clipping (hitting the max inverter limit). In fact, I'm estimated to clip about 393 hours a year, which seems like a lot, but having an "oversized" panel design (larger DC/AC ratio) results in more production when you're not clipping (e.g. mornings, evenings, seasons with less optimal sun angles, etc.) compared to a smaller panel design (smaller DC/AC ratio).

The only way to know how much production you're missing out on is to use something like PVWatts to do a comparison. I actually wrote a blog post about how to do it (it's simple). Once you know how much additional production you could be achieving, you then want to compare it with how much it would cost to have an additional inverter or if a smaller panel design would have been more optimal.

 

[Mase408]

Hi,

I just got a new Tesla solar system with 28 panels=11.4 kW and powerwall+ installed. I don't have a PTO yet. My power output is capped at 7.7kW, it is obvious because every day the power chart stops at this mark, and I saw several threads confirming this limit. I had an online chat with a Tesla project advisor who told me that it should be possible to reach my full capacity because "Tesla overdrives the inverters up to 170%". He didn't know how exactly, though, he hinted that it might only be possible after PTO.
I'm concerned since I didn't read about anyone with >7.7kW output on a single powerwall+ inverter, could you shed some light on it? I'd like to get clarity before PTO and full payment. Maybe I don't have to pay for the panels > 7.7 kW

Thanks!

I am in the same boat. I just got my 17 kWh system installed today (awaiting PTO) and it has the same issue. Capped at 7kwh. I have 1 powerwall and 2 inverters.
I brought this up before the chief technician left. He said that there is some issue in the powerwall.
And it requires the team to come back to debug/calibrate.

 

[preilly44]

I have the same issue. My 34kw system with 3 PW+ & 5 PWs are all clipping at 7.7 KW from around 9am-3:30pm. The installers said they would look into it and get back to me. I'm not holding my breath...

 

[Nmtdriver]

I am in the same boat. I just got my 17 kWh system installed today (awaiting PTO) and it has the same issue. Capped at 7kwh. I have 1 powerwall and 2 inverters.
I brought this up before the chief technician left. He said that there is some issue in the powerwall.
And it requires the team to come back to debug/calibrate.

How has it worked out for you? I have basically the same system w/ 3 powerwalls but I can't get more than 9.6kwh at peak and ~65kwh in a day. The install team had to come back to rewire something from the panel array to the inverter but were unsuccessful and wired it back. I'm quite certain 2 of 5 strings aren't connected on my system (roughly 15 of 42 panels).

 

[Mase408]

The problem is either incorrect install on the inverter/Powerwall Or CT'S not working properly which will need to be replaced.
Tesla scheduled my service/repair for next Wednesday. I will post my outcome.

 

[DrSmile]

One should consider any available energy certificates in the cost/production equation. It isn't a lot of money to install a larger inverter and this could result in enough energy certificate gain to easily offset that cost. Also a larger inverter allows you to add more panels later and see larger improvements, although this is complicated by current installation requirements. Unless there are special circumstances like shading or odd panel orientations I'd insist on a DC/AC ratio smaller than 1.4. "Overdriving inverters" is, in my opinion, a misleading term as this does not result in an increased maximum production value, only an increased daily production value.

 

[Nmtdriver]

Thanks for the update! From what I understand, the on-site electricians wired it differently than the office engineers planned. Inverters didn’t work at all when wired per engineer specs so they wired it back.

They don’t have my deposit so I’m not too concerned yet lol

 

[shred86]

It's pretty sad a Tesla solar advisor doesn't understand the 170% overdrive. It's kind of a silly phrase but all that means is the Tesla inverter is capable of allowing up to a 1.7 DC/AC ratio, meaning you can have up to a 12.92 kW system on that single 7.6 kW inverter. As it's already been mentioned, that is different than what the inverter is capable of outputting, which the max for the 7.6 kW inverter is nominally 7.6 kW but you will commonly see ~7.7 kW.

The optimal DC/AC ratio will completely depend on your setup. For example, I have an 11.2 kW system on a single 7.6 kW inverter, all east facing panels, and I'm estimated to lose less than 0.01% of annual production:

• 17,296 kWh/year with a 1.47 DC/AC ratio, or a single 7.6 kW inverter
• 17,453 kWh/year with a 0.98 DC/AC ratio, or a 7.6 & 3.8 kW inverter

I'm constantly clipping (hitting the max inverter limit). In fact, I'm estimated to clip about 393 hours a year, which seems like a lot, but having an "oversized" panel design (larger DC/AC ratio) results in more production when you're not clipping (e.g. mornings, evenings, seasons with less optimal sun angles, etc.) compared to a smaller panel design (smaller DC/AC ratio).

The only way to know how much production you're missing out on is to use something like PVWatts to do a comparison. I actually wrote a blog post about how to do it (it's simple). Once you know how much additional production you could be achieving, you then want to compare it with how much it would cost to have an additional inverter or if a smaller panel design would have been more optimal.

Correction to this - I’m estimated to lose less than 1% (0.9% to be exact or ~157 kWh/yr), not 0.01% of annual production. The point still stand, I’m just terrible with numbers apparently.

 

[Nmtdriver]

The problem is either incorrect install on the inverter/Powerwall Or CT'S not working properly which will need to be replaced.
Tesla scheduled my service/repair for next Wednesday. I will post my outcome.

How did it work out? I'm having trouble getting them to buy off on my issues. They claimed that the install supervisor is aware of the deviations on how the strings are connected but claims that it'd have no impact on performance. Still maxing out at ~9kwh / 60kwh/day on my 17kwh system...should be clearing ~90kwh/day this time of year per the pv modeling I did.

Hasn't gone thru inspection yet so they haven't requested deposit. Not sure if there's a way to leverage the inspector/the idea of the inspector failing the inspection until it's fixed or if that's a bad idea.