Question about SolarEdge inverter sizing and clipping

[ButchDeal]

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.

You would have to break a string in half. What optimizers do you have?

[barrye]

Can't do that.
each string is maxed out at 5760 watts.
Don't think I can put 5760w into a 3800 H inverter. And i can't add more modules to my 7600H to decrease one of the strings

[ButchDeal]

Can't do that.
each string is maxed out at 5760 watts.
Don't think I can put 5760w into a 3800 H inverter. And i can't add more modules to my 7600H to decrease one of the strings

You can break one of the two strings in half so the SE7600 has one string of 16 and one string of 8 or 8.64
and the SE3800h has one string if 8. Or 2.88kw and

or depending on the optimizers you could totally restring so that you have two strings of 11 on the SE7600 and one string of 10 on the SE3800 but that is a bit more work

[barrye]

Thanks Butch
I wish it was that easy. Unfortunately I have a ground mount system 125' from my house with 4 conductor tech cable buried.
I only have 4 wires to work with . My optimizers are p400.
In retrospect I should have wired a 240 plug and purchased a 10000 H . C'est la vie (such is life)
I am still really happy with 70kwh on sunny days

[J.P.M.]

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

Well, it's not an exact science, but yes, that's the Reader's Digest version of the story.

That 183 hrs. est./SWAG is the approx. total number of hours over a year that a shade free array's output will exceed 7.6 kW. - even by as little as 1 W, or as high as ~ 1,670 W., or anything in between, depending on how the weather and how the TMY data the model uses may match one another, again, not any more exact than the weather.

I do suspect however, that the chimney will put a bigger damper on output as the solar zenith angle increases for the winter months.

The lost production from clipping will also probably be less as the array ages due to several other reasons that will decrease max. array output and so lower the max. array power per kW irradiance input:
1.) Annual cell efficiency degradation. Roughly something like 0.2 %/yr. to 0.5 %/yr.
2.) Array fouling. No array is ever 100 % clean , at least for long. Mine fouls at a rate of ~ 0.75 %/week +/- some if it doesn't rain or I don't hose it down. Dirt will lower POA irradiance and thus lower the power input and so the power output of an array by varying amounts as f(array fouling), but expect ~ 3% or so production loss on average.
3.) Shade. Even with optimizers, that chimney will probably cause noticeable production loss in winter from lowered irradiance input. If you had a simple string inverter, that chimney would put a very serious crimp on winter production. See below.

Those 3 things and others can and will lower the input to the inverter. Some of that loss (over those 183 hrs.) will, in effect, decrease the clipping loss, so, sort of a no harm- no foul kind of thing.

On that chimney, some back of the envelope stuff:

If it's, say, 32" wide and casts say, a 7 ft. long (?) shadow over the array in winter, that's ~ 18 ft.^2 of shadow area. 30 panels cover ~ 515 ft.^2 or so. That means, as a rough guess,18/515 ~ = 3.5% of the array will be in a shadow that no optimizer or other practical scheme will be able to compensate for. With winter production usually being lower, to a rough 1st approx. the chimney might reduce annual production by a % or two or so.

If someone has a better SWAG based on better data/logic, I'd not argue with it.

[Jeff72]

Well, it's not an exact science, but yes, that's the Reader's Digest version of the story.

That 183 hrs. est./SWAG is the approx. total number of hours over a year that a shade free array's output will exceed 7.6 kW. - even by as little as 1 W, or as high as ~ 1,670 W., or anything in between, depending on how the weather and how the TMY data the model uses may match one another, again, not any more exact than the weather.

I do suspect however, that the chimney will put a bigger damper on output as the solar zenith angle increases for the winter months.

The lost production from clipping will also probably be less as the array ages due to several other reasons that will decrease max. array output and so lower the max. array power per kW irradiance input:
1.) Annual cell efficiency degradation. Roughly something like 0.2 %/yr. to 0.5 %/yr.
2.) Array fouling. No array is ever 100 % clean , at least for long. Mine fouls at a rate of ~ 0.75 %/week +/- some if it doesn't rain or I don't hose it down. Dirt will lower POA irradiance and thus lower the power input and so the power output of an array by varying amounts as f(array fouling), but expect ~ 3% or so production loss on average.
3.) Shade. Even with optimizers, that chimney will probably cause noticeable production loss in winter from lowered irradiance input. If you had a simple string inverter, that chimney would put a very serious crimp on winter production. See below.

Those 3 things and others can and will lower the input to the inverter. Some of that loss (over those 183 hrs.) will, in effect, decrease the clipping loss, so, sort of a no harm- no foul kind of thing.

On that chimney, some back of the envelope stuff:

If it's, say, 32" wide and casts say, a 7 ft. long (?) shadow over the array in winter, that's ~ 18 ft.^2 of shadow area. 30 panels cover ~ 515 ft.^2 or so. That means, as a rough guess,18/515 ~ = 3.5% of the array will be in a shadow that no optimizer or other practical scheme will be able to compensate for. With winter production usually being lower, to a rough 1st approx. the chimney might reduce annual production by a % or two or so.

If someone has a better SWAG based on better data/logic, I'd not argue with it.

So, if I had to do it again, go with 10k inverter? Is there any benefit to 7600 inverter besides price?

Installer claimed 7600 inverter would begin generating earlier in day and generate later in day versus 10k inverter...does that sound right? he said due to voltage needed to start generating being less on 7600 inverter.

[ButchDeal]

So, if I had to do it again, go with 10k inverter? Is there any benefit to 7600 inverter besides price?

Installer claimed 7600 inverter would begin generating earlier in day and generate later in day versus 10k inverter...does that sound right? he said due to voltage needed to start generating being less on 7600 inverter.

Nope no truth at all.
Voltage is irrelevant as the optimizers will boost the voltage anyway, however both inverters have the SAME operating voltage.
the 10000kw inverter is ever so slightly less efficient but way less so than cliping losses
the 7600 has optional EV charger and usually doesn't require a line-side tap
10000kw usually does require a lineside tap...

line side tap being a slight added cost.

[J.P.M.]

So, if I had to do it again, go with 10k inverter? Is there any benefit to 7600 inverter besides price?

Installer claimed 7600 inverter would begin generating earlier in day and generate later in day versus 10k inverter...does that sound right? he said due to voltage needed to start generating being less on 7600 inverter.

Since you're asking, my preference, for single orientation arrays, and until I found out differently, would be to mimimize shading on the array, And KISS as a time tested (for me anyway) method to help avoid problems, and skip the more parts to fail optimizer design, and size a string inverter ~ = (STC rating of the array) * (inverter efficiency).

However, in the quest to find out differently, and keeping in mind that none of us is as smart as all of us, I'd consult with folks like Butch because he knows more about SolarEdge than I know about them and their products, and he might convince me that all the problems I seem to read about popping up around here in inordinate quantities about SolarEdge quirks, problems and crappy customer service are simply due to ignorant users.

Otherwise, see Butch's comments about the rest of your post.

[Jeff72]

Nope no truth at all.
Voltage is irrelevant as the optimizers will boost the voltage anyway, however both inverters have the SAME operating voltage.
the 10000kw inverter is ever so slightly less efficient but way less so than cliping losses
the 7600 has optional EV charger and usually doesn't require a line-side tap
10000kw usually does require a lineside tap...

line side tap being a slight added cost.

OK, on that note, and correct me if i'm wrong here, in my case with the 9,855 kW panel array, it will be worthwhile to gain the clipping loses and to go to a 10k inverter, right?

So now i'm back on the plan to asking the installer for a 10k inverter replacement. Since I have a line side tap, should the existing wiring for the 7600 inverter work for the 10k inverter? I'm not sure what gauge wire they used but I am wondering if the gauge required for 7600 inverter will work for 10k inverter also?

[Jeff72]

Since you're asking, my preference, for single orientation arrays, and until I found out differently, would be to mimimize shading on the array, And KISS as a time tested (for me anyway) method to help avoid problems, and skip the more parts to fail optimizer design, and size a string inverter ~ = (STC rating of the array) * (inverter efficiency).

However, in the quest to find out differently, and keeping in mind that none of us is as smart as all of us, I'd consult with folks like Butch because he knows more about SolarEdge than I know about them and their products, and he might convince me that all the problems I seem to read about popping up around here in inordinate quantities about SolarEdge quirks, problems and crappy customer service are simply due to ignorant users.

Otherwise, see Butch's comments about the rest of your post.

I do have that chimney so I kind of need the Optimizers. I was originally going for microinverters but chose the Optimizer route for a variety of reasons.

[ButchDeal]

OK, on that note, and correct me if i'm wrong here, in my case with the 9,855 kW panel array, it will be worthwhile to gain the clipping loses and to go to a 10k inverter, right?

So now i'm back on the plan to asking the installer for a 10k inverter replacement. Since I have a line side tap, should the existing wiring for the 7600 inverter work for the 10k inverter? I'm not sure what gauge wire they used but I am wondering if the gauge required for 7600 inverter will work for 10k inverter also?

I didn't say that...

You ask if there was truth in the installers statements.

from what we are seeing and from JPMs calculations you are seeing pretty little clipping and you would lose the EV charger if you changed.
You can use PVWatts to calculate the production with a 1:1 inverter to DC ratio and see the difference as he has done

[J.P.M.]

I do have that chimney so I kind of need the Optimizers. I was originally going for microinverters but chose the Optimizer route for a variety of reasons.

Yes, I see that. Understood. I appreciate your predicament. But you asked what I'd do.

I'm aware I mouth off a lot. Folks accuse me of telling them how to build a watch if/when they ask me what time it is. In rereading my reply, I now realize that in an attempt at concise brevity, I gave an incomplete answer.

Bottom line for what I'd do: A lot of use reduction and conservation upfront and see what that does to my load. Then, a serious cost analysis as part of a preliminary design that addresses whether or not PV makes sense from a life cycle cost standpoint at all, including the effect that obstruction has on system cost effectiveness and also system design and overall project goals.

What I left out was that, for me only, after safe design, a major design goal among others including serviceability, is the lowest long term cost means of providing reliable power to a residence by using the most cost effective mix of use reduction, conservation measures, grid power and PV - and probably in that loose order. So, and again since you ask, I'd do it differently than you appear to have done it.

To your question, if I had your situation, after setting goals and doing the other, more cost effective stuff first, I'd first spend some time estimating the effect on system design and complexity, and the effect on the cost effectiveness of the system of a big obstruction in just about the worst possible location relative to the array as well as what complications and other impacts that obstruction would have on the rest of the design.

If it was my situation, since one of my goals is the least long term cost of providing electricity rather than PV as the first and maybe only line of defense against high and mostly self inflicted electric bills, I might still do PV. But if I did, I wouldn't be surprised to find out the best system for my money would be smaller. It would probably, and reluctantly (because of what I see as more complexity and more failure points from that added complexity), include optimizers because life is not perfect and is usually a set of compromises. But in this case, if I was doing it that way, if I did PV at all - which is not a slam dunk BTW - I'd consult with someone like Butch who, even though we probably disagree on their worth and efficacy, knows more about optimizer systems than I do.

Take what you want of the above. Scrap the rest.

[discodanman45]

So, if I had to do it again, go with 10k inverter? Is there any benefit to 7600 inverter besides price?

Installer claimed 7600 inverter would begin generating earlier in day and generate later in day versus 10k inverter...does that sound right? he said due to voltage needed to start generating being less on 7600 inverter.

That is nonsense. Below is a graph typically used to justify clipping. This may have been true 15 years ago, but now with high efficiency inverters it is simply not true.

My installer put 11.25 kW on a SE7600 inverter and I clipped 4 to 5 hours almost every day from March until October. Below are two of my graphs from this year after my installer admitted that they were way too aggressive with the oversizing. My inverter would also overheat and did derate a few times as well. The day I got over 76 kWh is interesting. I peaked at 11.34 kW with a 11.25 kW system on three separate facing arrays. If I only had the SE7600 inverter for that day, I would have maybe produced 60 kWh.

[Jeff72]

Yes, I see that. Understood. I appreciate your predicament. But you asked what I'd do.

I'm aware I mouth off a lot. Folks accuse me of telling them how to build a watch if/when they ask me what time it is. In rereading my reply, I now realize that in an attempt at concise brevity, I gave an incomplete answer.

Bottom line for what I'd do: A lot of use reduction and conservation upfront and see what that does to my load. Then, a serious cost analysis as part of a preliminary design that addresses whether or not PV makes sense from a life cycle cost standpoint at all, including the effect that obstruction has on system cost effectiveness and also system design and overall project goals.

What I left out was that, for me only, after safe design, a major design goal among others including serviceability, is the lowest long term cost means of providing reliable power to a residence by using the most cost effective mix of use reduction, conservation measures, grid power and PV - and probably in that loose order. So, and again since you ask, I'd do it differently than you appear to have done it.

To your question, if I had your situation, after setting goals and doing the other, more cost effective stuff first, I'd first spend some time estimating the effect on system design and complexity, and the effect on the cost effectiveness of the system of a big obstruction in just about the worst possible location relative to the array as well as what complications and other impacts that obstruction would have on the rest of the design.

If it was my situation, since one of my goals is the least long term cost of providing electricity rather than PV as the first and maybe only line of defense against high and mostly self inflicted electric bills, I might still do PV. But if I did, I wouldn't be surprised to find out the best system for my money would be smaller. It would probably, and reluctantly (because of what I see as more complexity and more failure points from that added complexity), include optimizers because life is not perfect and is usually a set of compromises. But in this case, if I was doing it that way, if I did PV at all - which is not a slam dunk BTW - I'd consult with someone like Butch who, even though we probably disagree on their worth and efficacy, knows more about optimizer systems than I do.

Take what you want of the above. Scrap the rest.

Thanks, I appreciate your info. I have done many things already like use LED bulbs in the house and add insulation in the attic and spray foam around the box area in the basement and such. Solar has always been an interest of mine so I finally made the decision. I wanted to maximize my south facing two roofs solar generation for current house usage plus a possible future electric car or even two eventually. I feel that we did what we could with the roof and the 27 LG 365 panels in an arrangement that could do the best we can with what we had. I just feel limited now by the inverter. I originally though the 7600 would oversupply on the AC side, but that is not the case. I feel that I should get closer to the DC side 9855 W generation I would think if I get a 10,000 W inverter instead of the 7,600 W inverter and maximize the solar generation I can get.

[Jeff72]

That is nonsense. Below is a graph typically used to justify clipping. This may have been true 15 years ago, but now with high efficiency inverters it is simply not true.

My installer put 11.25 kW on a SE7600 inverter and I clipped 4 to 5 hours almost every day from March until October. Below are two of my graphs from this year after my installer admitted that they were way too aggressive with the oversizing. My inverter would also overheat and did derate a few times as well. The day I got over 76 kWh is interesting. I peaked at 11.34 kW with a 11.25 kW system on three separate facing arrays. If I only had the SE7600 inverter for that day, I would have maybe produced 60 kWh.

Thanks. Yes, that is what I am thinking. I think my installers are going by old traditional methods of design and am now under the impression that I would mostly see benefits if I swap the inverter from 7,600 to 10,000 inverter.