5.75kw solarsystem connected to a 100 amp Panel via combiner panel ?

[wanabefree]

I am looking over some electrical plans for my proposed solar install. The basic system is 5.75kw using 23 250watt panels and enphase 215 micrconverters. nothing out of line there so far but here is the kicker. I only have a 100 amp service panel and I was original told i would need a electrical panel upgrade to go bigger than about 4k in solar do to the 120% app restriction. (only allowed a 20 amp solar input breaker in a 100amp panel). Well the plans call for the system to be wired with 17 panels in one string and the 6 additional in a separate string. Then they would go to a 125amp combiner panel with one 20 amp breaker and another 15amp bridged to combine the outputs then connected to a 60amp lock able shut off switch. OK so far but then tied into the 100amp service panel via a 30 amp 240v new breaker. To me this seems to be not per code unless they are of the belief that my 100 amp service panel has a 125 amp buss bar. There is no markings anywhere I can find anywhere in or on the panel. The home was built in 1979 and the meter panel and service panel are side by side. I do know that the service to the meter is 200amp rated per But my service panel has a 100 amp breaker that is removable not fused in like some so it is possible the panel buss is rated higher than the 100amp main breaker ?
I am wondering if perhaps they are actually going to use a line side tap but did not show it but then again why would they put a 30 amp solar feed breaker in a 100amp service panel unless they know something I don't or are hoping to get a pass from the building inspector.
I did ask the salesperson about this and he assured me that there engineers no the local codes and would not submit something that is not acceptable and even if the city rejected it they would put what ever the city requires in at no additional cost to me.

Any comments welcome, Dave

[silversaver]

Your new solar electric system will need at least two open slots in the breaker panel for the solar feed. As a general rule, the main breaker needs to be 200 amps or larger. If your main breaker panel is 100 amps or less, has fuses instead of breakers, and is in generally in poor condition; you may need a main panel upgrade as part of you solar installation. Your solar installer will make this recommendation if needed.

[wanabefree]

Your new solar electric system will need at least two open slots in the breaker panel for the solar feed. As a general rule, the main breaker needs to be 200 amps or larger. If your main breaker panel is 100 amps or less, has fuses instead of breakers, and is in generally in poor condition; you may need a main panel upgrade as part of you solar installation. Your solar installer will make this recommendation if needed.

Not sure if it was clear but this is what the solar installer/engineer is proposing for approval to the city. My panel is in good working order and they will replace two full size breakers with half size to make room for one new 30amp 240v breaker. My main breaker is 100 amp but it is unclear if the buss is the same or not as there is no tags of markings on it I can find. I am inclined to think they are assuming it is a 125amp bus thus with a 100 amp main using the 12% rule they could theoretically put up to a 50 amp solar service feed breaker. They are showing a new 30amp solar service breaker. My concern is how would or could they determine my actual buss panel rating if it is not marked but for having a removable 100 amp main breaker.
I suppose if they submitted it this way and it was not to code the code inspector would catch it and not approve the permit.

They could also I believe use a line side tap if allowed by code.
Oh This is in Moreno Valley, Ca. SCE area if it makes a difference.

[Volusiano]

I have 200A service but when they put in my 11KW system, they had to derate my panel down to 150 (could have derated to 175 but they didn't have the 175 breaker) because they backfeed 46A into a 60A breaker on my panel.

I don't know whether the breaker size is the limiting factor or the backfeed amperage from the system is the limiting factor. If the later, then in your case, even though the breaker is 30A, if the backfeed curent is less than 20A, then maybe they think they can get away with it.

If they plan on doing the line side tap then they wouldn't have put the breaker into the panel. It's either one or the other, right? Maybe line side tap is allowed by your local code, so they're going to try the panel feed first as plan A and save the line side tap for plan B if the inspection doesn't pass?

[Naptown]

Your new solar electric system will need at least two open slots in the breaker panel for the solar feed. As a general rule, the main breaker needs to be 200 amps or larger. If your main breaker panel is 100 amps or less, has fuses instead of breakers, and is in generally in poor condition; you may need a main panel upgrade as part of you solar installation. Your solar installer will make this recommendation if needed.

Actually you are limited on a backfeed breaker to 120% of the buss bar rating.
If you can find the model # of your panel and the manufacturer you may be able to determine the buss bar ratings from them (hint look inside the panel for the label by taking the cover off)

[wanabefree]

Actually you are limited on a backfeed breaker to 120% of the buss bar rating.
If you can find the model # of your panel and the manufacturer you may be able to determine the buss bar ratings from them (hint look inside the panel for the label by taking the cover off)

I have looked inside the panel several times and not found any make model or brand information but I ma going to take a look again tomorrow. I was told by a friend that it is highly possible that the buss bar is actually a 125 amp rated as most 100 amp panels do not have removable main breakers and are fixed or fused to the bus bar. maybe that is what they are thinking also as they did do a visual inspection but at the time said that all they could go by is the main breaker rating as they did not see any labels or rating stamps either.
I kinda want them to replace the panel just because it could be beneficial in the future but it would add about $1500 cost to the system.

[dusty144]

Thanx for posting this.

I'm in the exact same position. Hopeful to avoid the 200AMP upgrade. I don't have an engineer yet but hope to do the exact same thing of attaching a 60 AMP sub panel. My service too per the electrician is 200 AMP.

My loads are so low that I'm not even sure 100 AMP is needed yet my panel too is full up. I have half a mind to eliminate the dozen or so outlets I have not used in 20 years in this house. But tracing the lines would be expensive.

Any suggestions would be appreciated.

[Volusiano]

Thanx for posting this.

I'm in the exact same position. Hopeful to avoid the 200AMP upgrade. I don't have an engineer yet but hope to do the exact same thing of attaching a 60 AMP sub panel. My service too per the electrician is 200 AMP.

My loads are so low that I'm not even sure 100 AMP is needed yet my panel too is full up. I have half a mind to eliminate the dozen or so outlets I have not used in 20 years in this house. But tracing the lines would be expensive.

Any suggestions would be appreciated.

Eliminating circuits and removing breakers may make room on the panels if you're out of breaker space, but that wouldn't help with the 120% rule, would it? I assume the rule has to do with the bus bar size and not the amount of breakers you have on it.

If your panel is full up, can't you replace some of the larger breakers that take 2 full slots with a half-size kind that will take only 1 slot to make room?

So from all this discussion so far, I assume that derating the service panel to 75A is not an option for 100A panels or something (since it was never mentioned here so far as an option)? Especially in your case, Dusty144, since you said your loads are so low.

[wanabefree]

Eliminating circuits and removing breakers may make room on the panels if you're out of breaker space, but that wouldn't help with the 120% rule, would it? I assume the rule has to do with the bus bar size and not the amount of breakers you have on it.

If your panel is full up, can't you replace some of the larger breakers that take 2 full slots with a half-size kind that will take only 1 slot to make room?

So from all this discussion so far, I assume that derating the service panel to 75A is not an option for 100A panels or something (since it was never mentioned here so far as an option)? Especially in your case, Dusty144, since you said your loads are so low.

I believe that derating the Panel to a 75s or 80a main breaker is technically possible but might be a little tricky selling it to the code compliance officer. A line side tap is the most feasible cost effective alternate but also not aloud by some municipal codes. I just hope in my case my Panel is actually a 125a buss but only a 100a main but without finding any markings or tags on or inside it makes it hard to verify.

I talked to my salesman again about my concerns and he told me they will submit it for approval as per there original design and if the city rejects it they will do what ever is required to make it meet cod at no additional cost to me. So i guess I just have to wait and see what happens next.

[dusty144]

Volusiano thanx for taking the time.

Sorry I should have been a bit clearer. My dryer went from Electric to Gas which is why I think my panel has quite low load. Also I have converted all my lighting to CFL including a 2400 Watt incandescent with 30+ fixtures to track light to CFL. My big load is a large A/C system upsized to cool the garage and basement, for my wife. But the A/C is fed through a separate breaker outside.

I'm fortunate that my panel definitely says 125 AMP max on a sticker inside, even though my main breaker is only 100 AMP.

[dusty144]

After some investigation turns out that I have a 125 amp panel that has already been de-rated to 100 amp main breaker.
Does this mean I can use the 25 amp panel derate + the 25 amp of the 120% rule (125 ampx.2 = 25 amp) for a total of 50 AMP.
My Electrician has been able to squeeze two more spots out of my panel by removing some breakers I don't use.
I only need to put in 2x20 amp breakers for my 2 strings. But want to get the logic correct.
So I don't need to replace my panel with 200 Amp right?

Appreciate any comments.

[Itsme]

In San Jose, with a 100 amp panel i was not able to get a system larger than 3.8KW. Something about no more than 20% of the panel load. So, i had to upgrade panel to a 200 amp, to get a 5.72 KW system installed.

You can also ask the installer to consider a line side tap....if they can; then the panel is bypassed.

Thanks

[inetdog]

After some investigation turns out that I have a 125 amp panel that has already been de-rated to 100 amp main breaker.
Does this mean I can use the 25 amp panel derate + the 25 amp of the 120% rule (125 ampx.2 = 25 amp) for a total of 50 AMP.
My Electrician has been able to squeeze two more spots out of my panel by removing some breakers I don't use.
I only need to put in 2x20 amp breakers for my 2 strings. But want to get the logic correct.
So I don't need to replace my panel with 200 Amp right?

Appreciate any comments.

According to the National Electrical Code, as long as you PV backfeed breakers are at the bottom end of the panel bus, as far as possible from the main, the PV breaker sizes can add up to (125 x 1.2) -100, or 50 Amps. In NEC revisions before [2014] that explicitly limits the breaker amperage and the actual GTI nameplate maximum output, if lower, does not help you.

However, the fact that the NEC allows it does not mean that a local inspector or power company (POCO) will not give you grief about it based on (100 x 1.2) -100.

In Los Angeles, for example, LADWP will try to tell you that even without taking PV into consideration the fact that you have a 125A panel means that you cannot have only a 100A service regardless of the size of the main breaker.

[dusty144]

Thanx for the answers folks. That makes sense. So basically the code allows it but does not mean AHJ/Utility will.
I would love to upgrade my panel but I got a quote of $1250 for a new 200 amp panel, parts+labor with a new line to the meter vs $180 for just two 20 amp breakers and the necessary wiring.

This a fair chunk of change I would like to avoid.
My average loads are well below 100 amp.

[inetdog]

Thanx for the answers folks. That makes sense. So basically the code allows it but does not mean AHJ/Utility will.
I would love to upgrade my panel but I got a quote of $1250 for a new 200 amp panel, parts+labor with a new line to the meter vs $180 for just two 20 amp breakers and the necessary wiring.

This a fair chunk of change I would like to avoid.
My average loads are well below 100 amp.

The best way to make the decision in your case will be to get an opinion in advance from the AHJ (Authority Having Jurisdiction) and your POCO instead of having an electrician do the 100A panel connection and then failing an inspection.

I do not find it at all unlikely that you could stay with a 100A service for your normal house loads.
BTW, it is not the average load but the peak load that governs the service size, but the NEC calculations always tend to overestimate the load.