Question about SolarEdge inverter sizing and clipping

[Jeff72]

Jeff72: What's your zip and what's your array azimuth and tilt ? A PVWatts run can estimate your max. possible hourly output for sunny days by hour for an approx. reference.

7.6 kW output sounds low for a 9.9 kW array, and it's probably due to the inverter being undersized, especially if the output for 4 hrs. is dead flat at 7.6 kW. Was the reduced or flat output somewhat symmetric around solar noon +/- some ?

There's a small and quite unlikely chance the low output may be due to shading, but stranger things have happened. What was the daylong output in kWh for those two sunny days ?

My zip code is 60564

Here is what I found on the design doc:
AZIMUTH 180
TILT ANGLE 25

Do new member get limited on what we can post here? This board is cutting off like 90% of what I typed here. Lost all the response to your questions....sigh

[Mike90250]

Typing is best accomplished using standard fonts. The "fancy" fonts trigger the anti-canned meat software and that truncates the post. phones, tablets and mac's are the worst offenders.

[Jeff72]

Jeff72: What's your zip and what's your array azimuth and tilt ? A PVWatts run can estimate your max. possible hourly output for sunny days by hour for an approx. reference.

7.6 kW output sounds low for a 9.9 kW array, and it's probably due to the inverter being undersized, especially if the output for 4 hrs. is dead flat at 7.6 kW. Was the reduced or flat output somewhat symmetric around solar noon +/- some ?

There's a small and quite unlikely chance the low output may be due to shading, but stranger things have happened. What was the daylong output in kWh for those two sunny days ?

Attempt #2 (copied from notepad to try to get whole posting in here)

My zip code is 60564

Here is what I found on the design doc:
AZIMUTH 180
TILT ANGLE 25

My SolarEdge 7600HD inverter does seem hard limited to 7600 AC output power. I was under the impression it could generate more, but it seems it can just take in more DC input and is limited to 7600 W AC output hard limit.

Here is the information for the two days where I saw a good amount of clipping (in my opinion):
5/22 59.44 kWh System production and 10:45am CT to 2:30pm CT clipped at 7600 W during that 3 hour 45 minute duration
5/23 46.16 kWh System production and 10:45am CT to 2:30pm CT clipped at 7600 W during that 3 hour 45 minute duration (Note: system was down during clipped time frame on 5/23 for 45 minutes due to some export/import monitoring configuration adjustments to make those functions work)

I do not think it is a shade issue for the clipping. I do have a chimney and it shades the panel on the left and right of it slightly during the day this time of year only, but not that much.

I had tried to get a 10000HD inverter installed but the installer convinced me that the 7600HD would be able to handle my system and that my clipping loss would be minimal. I'm not so sure that will be the case. I feel like June/July/August will have some nice sunny days where I lose almost 4 hours of 9.855 kW - 7.600 kW = 2.255 kW theoretically each hour (though I realize there will be loses in inverter conversion and the panels won't necessarily generate that full amount...though, they are 27 total LG 365 W panels all facing south, so I'm not sure...)

Any suggestions or comments on the above would be appreciated.

[ButchDeal]

Attempt #2 (copied from notepad to try to get whole posting in here)

My zip code is 60564

Here is what I found on the design doc:
AZIMUTH 180
TILT ANGLE 25

My SolarEdge 7600HD inverter does seem hard limited to 7600 AC output power. I was under the impression it could generate more, but it seems it can just take in more DC input and is limited to 7600 W AC output hard limit.

Here is the information for the two days where I saw a good amount of clipping (in my opinion):
5/22 59.44 kWh System production and 10:45am CT to 2:30pm CT clipped at 7600 W during that 3 hour 45 minute duration
5/23 46.16 kWh System production and 10:45am CT to 2:30pm CT clipped at 7600 W during that 3 hour 45 minute duration (Note: system was down during clipped time frame on 5/23 for 45 minutes due to some export/import monitoring configuration adjustments to make those functions work)

I do not think it is a shade issue for the clipping. I do have a chimney and it shades the panel on the left and right of it slightly during the day this time of year only, but not that much.

I had tried to get a 10000HD inverter installed but the installer convinced me that the 7600HD would be able to handle my system and that my clipping loss would be minimal. I'm not so sure that will be the case. I feel like June/July/August will have some nice sunny days where I lose almost 4 hours of 9.855 kW - 7.600 kW = 2.255 kW theoretically each hour (though I realize there will be loses in inverter conversion and the panels won't necessarily generate that full amount...though, they are 27 total LG 365 W panels all facing south, so I'm not sure...)

Any suggestions or comments on the above would be appreciated.

You can look at your graphs on the monitoring site and see that the production ramps up and down on a parabolic curve so you would NOT EVER have a solid block of clipping.
you PV modules are NOT going to produce the full DC STC rating especially in summer.
your shadows will limit the amount of clipping as well.

So yes you will have some clipping, the amount of clipping can be modeled with PVwatts but will not be 2.255kW every hour

I am not sure why you though a 7.6kW inverter would NOT have a hard limit at 7.6kW. That is kind of what makes it a 7.6kW inverter...

[barrye]

I have 11.2kw of pv panels in southern British Columbia and a 7.6 ev inverter.
I expected to get clipping when I installed it. On a sunny day i draw a straight line at 7.6 kw from 10am till 4pm.
I installed the 7.6 strictly for the EV portion.
I am waiting for the 11.4 kw EV inverter to come out and add a third string to my existing system.
I have to say I am happy with the 70 plus KWhours i am producing on sunny days

[Jeff72]

You can look at your graphs on the monitoring site and see that the production ramps up and down on a parabolic curve so you would NOT EVER have a solid block of clipping.
you PV modules are NOT going to produce the full DC STC rating especially in summer.
your shadows will limit the amount of clipping as well.

So yes you will have some clipping, the amount of clipping can be modeled with PVwatts but will not be 2.255kW every hour

I am not sure why you though a 7.6kW inverter would NOT have a hard limit at 7.6kW. That is kind of what makes it a 7.6kW inverter...

Example of clipping on 5-22

So is this "normal" and to be expected? At what point should I request a 10 kW inverter instead of the 7.6 kW inverter?

2019-05-22 Capture.PNG

[Jeff72]

I have 11.2kw of pv panels in southern British Columbia and a 7.6 ev inverter.
I expected to get clipping when I installed it. On a sunny day i draw a straight line at 7.6 kw from 10am till 4pm.
I installed the 7.6 strictly for the EV portion.
I am waiting for the 11.4 kw EV inverter to come out and add a third string to my existing system.
I have to say I am happy with the 70 plus KWhours i am producing on sunny days

I am not sure I understand. You have 11.2 kW of panels but you also went with 7.6 kW inverter. I would think you would want a 10 kW inverter also to make use of those panels fully?

I still don't get why they undersize the inverter for a panel array that can theoretically do a bit higher like my 9.855 kW and your 11.2 kW.

[J.P.M.]

Attempt #2 (copied from notepad to try to get whole posting in here)

My zip code is 60564

Here is what I found on the design doc:
AZIMUTH 180
TILT ANGLE 25

My SolarEdge 7600HD inverter does seem hard limited to 7600 AC output power. I was under the impression it could generate more, but it seems it can just take in more DC input and is limited to 7600 W AC output hard limit.

Here is the information for the two days where I saw a good amount of clipping (in my opinion):
5/22 59.44 kWh System production and 10:45am CT to 2:30pm CT clipped at 7600 W during that 3 hour 45 minute duration
5/23 46.16 kWh System production and 10:45am CT to 2:30pm CT clipped at 7600 W during that 3 hour 45 minute duration (Note: system was down during clipped time frame on 5/23 for 45 minutes due to some export/import monitoring configuration adjustments to make those functions work)

I do not think it is a shade issue for the clipping. I do have a chimney and it shades the panel on the left and right of it slightly during the day this time of year only, but not that much.

I had tried to get a 10000HD inverter installed but the installer convinced me that the 7600HD would be able to handle my system and that my clipping loss would be minimal. I'm not so sure that will be the case. I feel like June/July/August will have some nice sunny days where I lose almost 4 hours of 9.855 kW - 7.600 kW = 2.255 kW theoretically each hour (though I realize there will be loses in inverter conversion and the panels won't necessarily generate that full amount...though, they are 27 total LG 365 W panels all facing south, so I'm not sure...)

Any suggestions or comments on the above would be appreciated.

I took your info and did a PVWatts run with a 1:1 DC to AC ratio (meaning a 10 kW inverter) and took the hourly output option. Then, I sort of bastardized the intent of the model and compared the hourly output with what you provided.

1.) The max. modeled hourly output is ~ 9.27 kW.
2.) using A 1:1 DC to AC ratio, I subtracted 7.6 kW from all hourly outputs that exceeded 7.6 kW and summed the results. That result is 83.1 kWh for the year.
3.) The number of hours per year that the model thinks your system's output will exceed 7.6 kW IF you have a 10 kW inverter is 183.
4.) PVWatts modeled your shade free annual output with a 10 kW inverter at ~ 14,019 kWh/yr.
5.) PVWatts modeled your shade free annual output with a 9.855/7.6 = 1.30 DC to AC ratio (a 7.6 kW inverter) as ~ 13,957 kWh/yr. There is some rounding/quirks in the model making the 10kW inverter annual output - 7.6 kW inverter output different than I calc'd the differences. Life is not perfect and neither are models.

So, misusing the model from its tended purpose, but not terribly so, and doing so for the purpose of maybe getting some feel for the order of magnitude of what the losses from a smaller inverter might be vs. a larger inverter over a "typical" (and note as opposed to, and NOT, an "average") year, you'll lose maybe (83/14,000) kWh/yr. ~ 0.006 of the annual output according to a reasonably conservative model.

See the PVWatts model and the help/info screens therein for particulars of inputs and also see NREL for an explanation of a "Typical Meteorological Year", what it is, how it's used, and why it is NOT an "average" of weather conditions.

[ButchDeal]

Example of clipping on 5-22

So is this "normal" and to be expected? At what point should I request a 10 kW inverter instead of the 7.6 kW inverter?

2019-05-22 Capture.PNG

this does not look like that much clipping. you could look at the worst day and see but keep in mind that the production is an inverter parabola that in your case is clipped at 7.6 kw.
it is not effected (with solarEdge) anyplace else other than the part above 7.6kw. Other non-optimized systems would be effected all over the curve in different ways.
as JPM points out you are likely missing very small percentage. it would cost a bit of money to attache a system over 7.6kw as it likely would require a line-side tap, thus why a 7.6kW is so common.

[Jeff72]

I took your info and did a PVWatts run with a 1:1 DC to AC ratio (meaning a 10 kW inverter) and took the hourly output option. Then, I sort of bastardized the intent of the model and compared the hourly output with what you provided.

1.) The max. modeled hourly output is ~ 9.27 kW.
2.) using A 1:1 DC to AC ratio, I subtracted 7.6 kW from all hourly outputs that exceeded 7.6 kW and summed the results. That result is 83.1 kWh for the year.
3.) The number of hours per year that the model thinks your system's output will exceed 7.6 kW IF you have a 10 kW inverter is 183.
4.) PVWatts modeled your shade free annual output with a 10 kW inverter at ~ 14,019 kWh/yr.
5.) PVWatts modeled your shade free annual output with a 9.855/7.6 = 1.30 DC to AC ratio (a 7.6 kW inverter) as ~ 13,957 kWh/yr. There is some rounding/quirks in the model making the 10kW inverter annual output - 7.6 kW inverter output different than I calc'd the differences. Life is not perfect and neither are models.

So, misusing the model form iots in tended purpose but not terribly so, and doing so for the purpose of maybe getting some feel for the order of magnitude of what the losses from a smaller inverter might be vs. a larger inverter over a "typical" (and note as opposed to, and NOT, an "average") year, you'll lose maybe (83/14,000) kWh/yr. ~ 0.006 of the annual output according to a reasonably conservative model.

See the PVWatts model and the help/info screens therein for particulars of inputs and also see NREL for an explanation of a "Typical Meteorological Year", what it is, how it's used, and why it is NOT an "average" of weather conditions.

ok, so if I understand you correctly:

Theoretically, my system could gain an estimate of 183 hours of extra generation with a 10 kW inverter per year.
But, the difference is really only 14,019 kWh/yr - 13,957 kWh/yr = 62 kWh/yr lost by going with a 7600 W inverter versus a 10,000 W inverter? So 0.4% lost, I guess that doesn't sound too bad.

Is that right?

Also the chimney goes right up the far south side of my south facing roof. There is a gap behind it without panels to take into consideration some shading and very minor gap on the left and right side the chimney. However, the chimnney will shade more in the winter months due to the sun being further south and casting more chimney shade on my roof, so that will affect things more in the winter too.

2019-05-23 12.36.59_old.jpg

[Jeff72]

this does not look like that much clipping. you could look at the worst day and see but keep in mind that the production is an inverter parabola that in your case is clipped at 7.6 kw.
it is not effected (with solarEdge) anyplace else other than the part above 7.6kw. Other non-optimized systems would be effected all over the curve in different ways.
as JPM points out you are likely missing very small percentage. it would cost a bit of money to attache a system over 7.6kw as it likely would require a line-side tap, thus why a 7.6kW is so common.

I think I am already a line-side tap. They connected the inverter power lines to new lugs just below where my utility meter outside connects outside the house. Everything is outside the house except the cat5 for monitoring going into the house and the main feed that goes into the house after the inverter connection outside the house.

[foo1bar]

I still don't get why they undersize the inverter for a panel array that can theoretically do a bit higher like my 9.855 kW and your 11.2 kW.

One reason can be cost.
If the max DC power from my array is just slightly above the inverter size I don't lose much energy due to clipping. BUT I may save a bunch of upfront costs because of the smaller inverter size.
It's also possible with an array that isn't pointing in optimal direction - or an array that has multiple directions that the panels are pointing - that the theoretical/nameplate max DC power output is much less than the actual DC max seen in that installation.

Here are some of the upfront costs that can be increased by increasing the inverter size:
inverter cost itself (probably only $100-$300)
Larger wire sizes needed on AC side (<$100)
Larger breaker size needed on AC side
Replacing main service panel ($1500-$5000) or switching from using main panel to doing lineside tap ($1k?)

So anywhere from $100 to $5k+ in extra costs.
And then you compare that to the other side - you have the benefit of not having to pay the POCO for the energy that would be lost to clipping.
If the clipping is fairly small (ex. 2kwh/day average for 2 months) then the financial benefit of not having clipping is fairly small. (ex: 2kwh/day * 60 days * $.25/kwh = $30/yr)
So - is that $30/year benefit (which will shrink as the modules age and become less efficient) worth the extra $1k or whatever in upfront costs?
If it's $30/year vs. $1k I'd say no.
But if it's $50/year vs. $150 iniital cost I'd say yes.

[barrye]

I used a 7.6 kw inverter because it was the largest inverter with an integrated EV charger.
when solaredge comes out with a larger integrated EV inverter I will upgrade and add more panels.
11.2 kw is the max I can connect to a 7.6 kw inverter

[ButchDeal]

I used a 7.6 kw inverter because it was the largest inverter with an integrated EV charger.
when solaredge comes out with a larger integrated EV inverter I will upgrade and add more panels.
11.2 kw is the max I can connect to a 7.6 kw inverter

you could easily connect TWO inverters. One option would be the SE7600H and SE3800H both with EV chargers....

[barrye]

Butch I have been trying to figure out how to accomplish that.
I have tried looking for a line diagram so I can do the wiring.
I have two strings of 16 panels.