Any issues running a too big Solar Edge inverter?

[reader2580]

I am relocating my solar system soon and adding a few more panels. I had a SE3000 and an SE5000 inverter. I found an incredible deal on Ebay on a new SE11400. I replaced my SE3000 with the SE11400 last night to test that the new inverter works. Will I run into issues with an inverter three times the size I need for a month or so? I intend to run just the one SE11400 inverter once I relocate my panels.

I was fairly impressed with how easy Setapp was to use although it takes a long time for some steps. I probably spent almost as much time running through Setapp as I did replacing the inverter.

[Salts]

Most grid tied inverters achieve their greatest efficiency near the top of their power capabilities... other than that, there shouldn't be a problem.

[Ampster]

I don't know if the efficiency that @Salts mentioned is per MPPT channel or overall capacity. The string sizes vary between inverters but Solaredge has lots of tools to help you figure that out. Long term it sound like you will be running a lot more panels so efficiency may not be a long term issue if you are using more of the inverter capacity. I don't know what your plans are for total capacity but in some situations, a DC to AC ratio above 1 to 1 may have some advantages. My own system was designed by my installer with a DC to AC ratio of 1.50 to 1 which is close to the maximum allowed by Solaredge. I did get a 25 year warranty on that inverter.

Most NEM agreements contain some reference to the Inverter(s). How important that is to your energy provider, is your decision to decide. I am on my third inverter on a PTO issued in 2011 at one location and while the inverter size has increased I am still within the original capacity plus the allowed 1kW increase on the original agreement. It may depend on your energy provider. Two of those were replacements when the earlier ones failed.

[solarix]

Technically, to stay within your interconnect agreement with your local utility, you need to stay Code compliant when you upgrade a solar system. Changing to a larger inverter is not just a "repair", and they could require you to upgrade all the wiring on the AC side of the inverter as well. Plus, the inverter is larger than 7.7kW and you are exceeding the 20% of buss size backfeed rule in the Code (even though your array is too smal for this to happen, the utility doesn't see it that way). This size inverter generally needs a service upgrade to make it legal. Either a derated main breaker, a larger size service, a solar ready panel, or a line side tap. Of course, you can get away without doing any of this and the utility won't be the wiser (unless for some reason they have to come visit your house) but just so you know what the game is...

[Ampster]

Technically, to stay within your interconnect agreement with your local utility, you need to stay Code compliant when you upgrade a solar system. ............. Of course, you can get away without doing any of this and the utility won't be the wiser (unless for some reason they have to come visit your house) but just so you know what the game is...

That is very important to consider. In my case I did not increase the inverter size much but in this case those issues are important, especially regarding the service panel buss and the wire, and breaker size.

[Salts]

Plus, the inverter is larger than 7.7kW and you are exceeding the 20% of buss size backfeed rule in the Code (even though your array is too smal for this to happen, the utility doesn't see it that way). This size inverter generally needs a service upgrade to make it legal. Either a derated main breaker, a larger size service, a solar ready panel, or a line side tap. Of course, you can get away without doing any of this and the utility won't be the wiser (unless for some reason they have to come visit your house) but just so you know what the game is...

What's up with the 20% rule? While I understand the main breaker + solar current could overload the busbar because the solar input is bypassing the main breaker, why not just allow installers to put the solar breaker at the bottom of the busbar?

Seems that's the logical choice to put it anyhow.. at least that's what I did. Some of the NEC does't make sense to me.

[peakbagger]

Yup, NH utilities have to register and approve the inverter capacity. They could really care less how many panels are connected.

[PVAndy]

What's up with the 20% rule? While I understand the main breaker + solar current could overload the busbar because the solar input is bypassing the main breaker, why not just allow installers to put the solar breaker at the bottom of the busbar?

Seems that's the logical choice to put it anyhow.. at least that's what I did. Some of the NEC does't make sense to me.

To use the 120% rule, the breaker needs to be at the far end of the buss from the main breaker. The reason for tor the 120% rule iis as an example. 10kw inverter putting out 60 Amos, 200 A main. If connected load remains below 80% (continuous allowed load) there is no issue. Lets assume connected load is 260A. Grid through main can supply 200A & INverter can supply 60A so the entire 260A connected load can be supplied exceed the buss rating.

Andy

[foo1bar]

What's up with the 20% rule? While I understand the main breaker + solar current could overload the busbar because the solar input is bypassing the main breaker, why not just allow installers to put the solar breaker at the bottom of the busbar?

Seems that's the logical choice to put it anyhow.. at least that's what I did. Some of the NEC does't make sense to me.

The rule behind it being at the far end of the bus bar AND only having supplies equal to 120% of the bus-bar rating is sort of a belt-and-suspenders thing.
But there is some logic that supports it too.
Having a 200A current at one end of the bar and a 40A current at the other end of the bar (and 240A being consumed somewhere in the middle) means there's a good amount of heat being generated by those currents. Even though it's a fairly low resistance bus bar, there is still some resistance. And resistance * current * current == watts of heat. So at least some have justified the reason for the 120% rule as being that the heat from the 200A and 40A currents needs to be "OK" - not causing any warpage of the busbar, etc.
Personally, I think that the bus bar also would have to support a 200A current going from the supply to the far end. And the heat from that (normal non-PV use) has to be supported. And the heat from a PV backfeed is going to be less (at least some part of that bus is only 40A instead of 200A) - so the bus already should be capable of that amount of heat, plus some.
BUT OTOH, it is reasonable to be cautious, so I can see why they had it as far-end-of-the-busbar and max-120%-total-supply.

[reader2580]

Technically, to stay within your interconnect agreement with your local utility, you need to stay Code compliant when you upgrade a solar system. Changing to a larger inverter is not just a "repair", and they could require you to upgrade all the wiring on the AC side of the inverter as well. Plus, the inverter is larger than 7.7kW and you are exceeding the 20% of buss size backfeed rule in the Code (even though your array is too smal for this to happen, the utility doesn't see it that way). This size inverter generally needs a service upgrade to make it legal. Either a derated main breaker, a larger size service, a solar ready panel, or a line side tap. Of course, you can get away without doing any of this and the utility won't be the wiser (unless for some reason they have to come visit your house) but just so you know what the game is...

This is a temporary thing, and yes, I have a line side tap. I could easily swap the old inverter back in if it becomes an issue. I wanted to test this inverter I bought from an Ebay seller before any chance to return it passed by. I am running it off the same 20 amp breaker the old inverter was on so I won't overload the wiring. Besides, I still only have the same 3180 watts of solar panels connected.

I will be getting a building and electrical permit when I move my panels and the inverter to the new location in October. I will only have this one inverter at that point.

[reader2580]

Yes, I will have to update my interconnect agreement with the utility once I actually move my solar array, but I already talked to them a while back about it. We don't have any sort of limits on how much solar we can have. Along with the move I am planning to add 1,380 additional watts of panels.