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Tesla Changed Inverter Sizing @ Install

mstgkillr

Member
May 24, 2020
67
47
Cape Coral
The signed and sealed engineered drawings (and agreement) called for the following for my 17kW PV system:
  • Solar Edge SE10000H-US (10kW) inverter with 28 panels at 340W each, totaling 9.52kW, or undersized by 4.92%
  • Solar Edge SE7600H-US (7.6kW) inverter with 22 panels at 340W each, totaling 7.480kW, or undersized by 1.59%
I was supposed to get 17.6kW worth of inverters for a 17kW system, undersizing the inverters by 3.47%.

I just checked what was actually installed and found the following:
  • Solar Edge SE-3800H-US (3.4kW) inverter with a yet to be determined amount of panels. The designed was slightly changed, I still have (50) 340W panels for 17kW total, but the layout is different.
  • Solar Edge SE-11400-US (11.4kW) inverter with a yet to be determined amount of panels. The designed was slightly changed, I still have (50) 340W panels for 17kW total, but the layout is different.
It appears that I now have 15,200kW worth of inverters for a 17kW system, undersizing the inverters by 11.18%.

Is this something that I should be concerned about?

Now, my panels are grouped by the following, which may determine how many panels each inverter receives:
  • (20) 340W panels totaling 6.8kW
  • (15) 340W panels totaling 5.1kW
  • (7) 340W panels totaling 2.380kW
  • (6) 340W panels totaling 2.040kW
  • (2) 340W panels totaling 0.68kW
Any comments or advice would be greatly appreciated!
 

Vines

Active Member
Jul 20, 2018
1,903
2,242
Silicon Valley, CA
Its a bit of bait and switch, but practically will make very little difference to yearly production.

It only affects your future ability to add panels, and only then once you exceed something like 1.3 to 1.4 DC/AC stacking ratio. Your current stacking ratio of 1.11 is of no real concern at this system size.
 
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h2ofun

Active Member
Aug 11, 2020
2,658
491
auburn, ca
The signed and sealed engineered drawings (and agreement) called for the following for my 17kW PV system:
  • Solar Edge SE10000H-US (10kW) inverter with 28 panels at 340W each, totaling 9.52kW, or undersized by 4.92%
  • Solar Edge SE7600H-US (7.6kW) inverter with 22 panels at 340W each, totaling 7.480kW, or undersized by 1.59%
I was supposed to get 17.6kW worth of inverters for a 17kW system, undersizing the inverters by 3.47%.

I just checked what was actually installed and found the following:
  • Solar Edge SE-3800H-US (3.4kW) inverter with a yet to be determined amount of panels. The designed was slightly changed, I still have (50) 340W panels for 17kW total, but the layout is different.
  • Solar Edge SE-11400-US (11.4kW) inverter with a yet to be determined amount of panels. The designed was slightly changed, I still have (50) 340W panels for 17kW total, but the layout is different.
It appears that I now have 15,200kW worth of inverters for a 17kW system, undersizing the inverters by 11.18%.

Is this something that I should be concerned about?

Now, my panels are grouped by the following, which may determine how many panels each inverter receives:
  • (20) 340W panels totaling 6.8kW
  • (15) 340W panels totaling 5.1kW
  • (7) 340W panels totaling 2.380kW
  • (6) 340W panels totaling 2.040kW
  • (2) 340W panels totaling 0.68kW
Any comments or advice would be greatly appreciated!
I have 14.5K panels, 11.4K inverter. Meets the 133% max guideline. I have maybe clip a few times for an hour. Yep, you will be fine technically, but, .. I know if I split my 14.5K solar, I am going to use 2 11.4K inverters, just in case I want to add more panels in the future.
 

holeydonut

Supporting Member
Jun 27, 2020
1,845
1,223
East Bay NorCal
IMO this type of swap without informing you is the type of stuff that drives me nuts about B2C purchases. Lennox tried to job me the same way by swapping out HVAC components for cheaper options after I had a contract.

The installers will always say "but we do this all the time" ... and gaslight you into blaming you for being annoying. However that just indicates a pattern of less than ideal practice than a real defense of their actions.

If there's a change order or a material changing to the understanding of your original contract, the customer needs to sign off before the change is made. Even if the change actually benefits the customer, in one manner, that doesn't make up for uniformed harm in another area.

Tesla going ahead with a modification of the contract without your input should not cause you any harm whatsoever. Since there is now potentially more clipping, you are suffering damage (even if it's minor).

I think it's too late for you to just abandon the install and ask them to take everything off. But I think it's fair for you to be compensated.

Since you have a contract or purchase order with the original equipment, I think you should contact Tesla and tell them you want the difference in the equipment costs refunded to you. This may not offset the loss of production, but it does make things "right" assuming you're ok with the revised layout. Of course, if they overloaded the SolarEdge 3800 with way too many panels you may want a different tactic.

Please note I just pulled these prices after a quick search. You should confirm the part numbers and prices on your own:

What you got:
SE3800H-US is $1,414.48
SE11400H-US is $2,801.50
= $4,215.98

What you initially agreed to pay for:
SE10000H-US is $2,637.96
SE7600H-US is $2,083.00
= $4,720.96

Difference is $504.98. So in my mind, Tesla can make this right by refunding you $504.98. After all, they did a change order without consulting you, and you are receiving diminished value as the result.

Assuming you get through to them, They'll still make you sign some paperwork if you accept such an agreement. Watch out to make sure their lawyers don't back-door some BS language in there about how your "settlement" for a $504.98 discount invalidates your warranty or reduces your rights to any post-purchase service.

I am not a laywer; and I accept no responsibility for you listing to random internet advice haha.
 
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mstgkillr

Member
May 24, 2020
67
47
Cape Coral
This is probably a dumb question, but I'm going to ask it anyways... considering how my panels are laid out, I assume the load from the arrays have to be balanced between the two inverters?

It appears, from my drone photos and novice interpretation of the layout, that they are combining the 20 and 15 panel array in one conduit, the 7 and 6 array into other, which eventually combine into a single conduit back to the inverters. Not sure what they are doing with the 2 panel array.

I'm missing 5 panels, which they are coming back tomorrow to install.

DJI_0124.JPG
 

Vines

Active Member
Jul 20, 2018
1,903
2,242
Silicon Valley, CA
IMO this type of swap without informing you is the type of stuff that drives me nuts about B2C purchases. Lennox tried to job me the same way by swapping out HVAC components for cheaper options after I had a contract.

The installers will always say "but we do this all the time" ... and gaslight you into blaming you for being annoying. However that just indicates a pattern of less than ideal practice than a real defense of their actions.

If there's a change order or a material changing to the understanding of your original contract, the customer needs to sign off before the change is made. Even if the change actually benefits the customer, in one manner, that doesn't make up for uniformed harm in another area.

Tesla going ahead with a modification of the contract without your input should not cause you any harm whatsoever. Since there is now potentially more clipping, you are suffering damage (even if it's minor).

I think it's too late for you to just abandon the install and ask them to take everything off. But I think it's fair for you to be compensated.

Since you have a contract or purchase order with the original equipment, I think you should contact Tesla and tell them you want the difference in the equipment costs refunded to you. This may not offset the loss of production, but it does make things "right" assuming you're ok with the revised layout. Of course, if they overloaded the SolarEdge 3800 with way too many panels you may want a different tactic.

Please note I just pulled these prices after a quick search. You should confirm the part numbers and prices on your own:

What you got:
SE3800H-US is $1,414.48
SE11400H-US is $2,801.50
= $4,215.98

What you initially agreed to pay for:
SE10000H-US is $2,637.96
SE7600H-US is $2,083.00
= $4,720.96

Difference is $504.98. So in my mind, Tesla can make this right by refunding you $504.98. After all, they did a change order without consulting you, and you are receiving diminished value as the result.

Assuming you get through to them, They'll still make you sign some paperwork if you accept such an agreement. Watch out to make sure their lawyers don't back-door some BS language in there about how your "settlement" for a $504.98 discount invalidates your warranty or reduces your rights to any post-purchase service.

I am not a laywer; and I accept no responsibility for you listing to random internet advice haha.

I totally agree, and I hope Tesla has no pushback on this solution. I will be interested to hear how they resolve this.
 

Laketime

Member
Dec 13, 2020
150
101
LI NY
I'm guessing the other 'array' on the roof is a solar hot water system for the pool? It also looks like that was installed on the best roof for solar output. Just based on shading and the different facing mini arrays you would never be at max production so you are quite a bit under the max ratio for panel/inverter. On my install I did hear the installer mention something about needing to make sure the right strings were going to the right inverter. He said having too much inverter vs panels will impact me negatively during lower output times. I didn't quite get the reasoning though.
 

CrazyRabbit

Member
Apr 21, 2020
415
126
Fort Worth TX
@mstgkillr,
when i was considering tesla i actually asked for a ac/dc of 1.4 on my east-west array, which would never resulted in clipping. now if all your panels are the same orientation it is a bit different. but 1.1 to 1.4 ac/dc ratios are still normal. you can run it thru PVwatts, click the advance parameters and play with the ac/dc ratio and see how it affects your production.
when your inverters are pegged they have the highest efficiency (name plate), you probably lose 1-2% efficiency at 80 percent load, which PVwatts will not show.
with my Enphase inverters, i can calculate my efficiency and can see what i have described above.
Now PVwatts can't do east-south-west orientations on one string, you would need to do some trigonometry your self to see if you would get clipping. depending on your roof pitch, mine is 32 degrees, my production on a east or west array is 60% with the sun directly overhead.
 
Last edited:

h2ofun

Active Member
Aug 11, 2020
2,658
491
auburn, ca
I'm guessing the other 'array' on the roof is a solar hot water system for the pool? It also looks like that was installed on the best roof for solar output. Just based on shading and the different facing mini arrays you would never be at max production so you are quite a bit under the max ratio for panel/inverter. On my install I did hear the installer mention something about needing to make sure the right strings were going to the right inverter. He said having too much inverter vs panels will impact me negatively during lower output times. I didn't quite get the reasoning though.
I would love to know more about your comment of too much inverter vs panels. imipacting negative. That is basically what I was planning to do, but assumed no negatives other than cost.
 

Laketime

Member
Dec 13, 2020
150
101
LI NY
I would love to know more about your comment of too much inverter vs panels. imipacting negative. That is basically what I was planning to do, but assumed no negatives other than cost.
I believe part of it has to do with the efficiency of the units- they are most efficient when running close to max. But he also mentioned something about the inverter not turning on if there was not enough solar output which would happen more if they are too oversized. That part I am more fuzzy about though (we went over a lot that day).
 
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h2ofun

Active Member
Aug 11, 2020
2,658
491
auburn, ca
I believe part of it has to do with the efficiency of the units- they are most efficient when running close to max. But he also mentioned something about the inverter not turning on if there was not enough solar output which would happen more if they are too oversized. That part I am more fuzzy about though (we went over a lot that day).
How To Size an Inverter: Solar Inverter Sizing Fully Explained

Boy, this totally changes my approach. No one had told me that too large of an inverter is not good, but the articles do not lie. Any more thoughts? I just wrote in installer engineer asking their thoughts.
 

Vines

Active Member
Jul 20, 2018
1,903
2,242
Silicon Valley, CA
How To Size an Inverter: Solar Inverter Sizing Fully Explained

Boy, this totally changes my approach. No one had told me that too large of an inverter is not good, but the articles do not lie. Any more thoughts? I just wrote in installer engineer asking their thoughts.

That article is pretty old. Most inverters are better than 95% efficient, even when lightly loaded (above 0.7 dc/ac)

I do have a 20 year old Xantrex SW4048 inverter, which is only about 30% efficient at less than half loaded.
 
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holeydonut

Supporting Member
Jun 27, 2020
1,845
1,223
East Bay NorCal
How To Size an Inverter: Solar Inverter Sizing Fully Explained

Boy, this totally changes my approach. No one had told me that too large of an inverter is not good, but the articles do not lie. Any more thoughts? I just wrote in installer engineer asking their thoughts.


Enphase also published some findings:
Technical Brief: Why Is My PV Module Rating Larger Than My Inverter Rating? (EN-US)

Since Enphase probably has an interest in people over-sizing their inverters (make more money selling oversized gear), it's notable that they instead show how a 1.2 to 1.4 DC/AC ratio is still optimal.
 

h2ofun

Active Member
Aug 11, 2020
2,658
491
auburn, ca
That article is pretty old. Most inverters are better than 95% efficient, even when lightly loaded (above 0.7 dc/ac)

I do have a 20 year old Xantrex SW4048 inverter, which is only about 30% efficient at less than half loaded.
I have an existing 11.4K solar edge inverter wired to my 14.5K solar. I will be splitting the solar to drive 2 gateways. It would be cheaper
to leaven the 11.4k inverter than replace and rewire. Would you think it would be okay to use another 11.4K for my new one since I was just wanting them to be the same, even if a little less efficient.?
 

FlJay

Member
Aug 24, 2020
32
8
West Volusia County
I am waiting for an install similar to the OP. The drawing for my 17kw system calls for the following:

(1) Solar Edge SE7600H-US (7.6kW) inverter with 26 panels at 340W each
(1) Solar Edge SE7600H-US (7.6kW) inverter with 24 panels at 340W each

All panels are facing east and it should be no problem changing the number of panels per inverter. I do have some tree shading issues so most of the time I will not be getting max sun all day long depending on the season.

Is this the best configuration? I was thinking that it might be better to use the next size up inverter (SE-11400-US) with maybe 28 panels and the (SE7600H-US) with 22 panels. If there is a better configuration I'd like to make the change now while it's still in permitting. Thanks for any ideas.
 

h2ofun

Active Member
Aug 11, 2020
2,658
491
auburn, ca
I am waiting for an install similar to the OP. The drawing for my 17kw system calls for the following:

(1) Solar Edge SE7600H-US (7.6kW) inverter with 26 panels at 340W each
(1) Solar Edge SE7600H-US (7.6kW) inverter with 24 panels at 340W each

All panels are facing east and it should be no problem changing the number of panels per inverter. I do have some tree shading issues so most of the time I will not be getting max sun all day long depending on the season.

Is this the best configuration? I was thinking that it might be better to use the next size up inverter (SE-11400-US) with maybe 28 panels and the (SE7600H-US) with 22 panels. If there is a better configuration I'd like to make the change now while it's still in permitting. Thanks for any ideas.
I have 47 305 panels. If I split, still trying to understand what is the actual negative to using 2 11.4k in case I have want to add more, or larger performance panels.
 

Vines

Active Member
Jul 20, 2018
1,903
2,242
Silicon Valley, CA
I have 47 305 panels. If I split, still trying to understand what is the actual negative to using 2 11.4k in case I have want to add more, or larger performance panels.

The losses are tiny when oversizing inverter compared with PV here's some reference material to research for yourself.
https://www.solaredge.com/sites/default/files/application_note_solaredge_inverters_efficiency.pdf

Most every split phase residential inverter from Solar Edge is 97% or better efficient above 2500W.
 

arnolddeleon

Supporting Member
Jul 21, 2012
838
909
SF Bay Area
I believe part of it has to do with the efficiency of the units- they are most efficient when running close to max. But he also mentioned something about the inverter not turning on if there was not enough solar output which would happen more if they are too oversized. That part I am more fuzzy about though (we went over a lot that day).

^^^ is directionally correct. The efficiency of an inverter is not a single number. They're usually at peak efficiency somewhere near the top (but not at the top) of their rating. I'm having trouble quickly finding one as an example (edit: I see @Vines posted the SolarEdge curves I was looking for). Bigger isn't always better. @nwdiver probably has the answers at his fingertips. It easy to see the "clipping" at the peak, it is not easy to see the losses at edges of production curves.
 
Last edited:

h2ofun

Active Member
Aug 11, 2020
2,658
491
auburn, ca
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