Parallel grid tied inverters

MarkC · October 2016

I believe this has been confirmed, but wanted to verify;

I will have two SMA SunnyBoy US models operating in parallel soon (240 VAC split phase). Both GT inverters will feed into the same sub-panel with L1, L2, N, and ground. The L1 and L2 legs are identified in each GT circuit and can be tied into the respective L1 and L2 terminals on the GT inverters - and the same L1, L2 phases at the sub-panel - if necessary. Is this really necessary, or will each GT inverter "sense" the proper phases (180 degrees apart) and come on-line and operate properly - regardless of the "matching" of L1 and L2?

solar_dave · October 2016

MarkC said:

I believe this has been confirmed, but wanted to verify;

I will have two SMA SunnyBoy US models operating in parallel soon (240 VAC split phase). Both GT inverters will feed into the same sub-panel with L1, L2, N, and ground. The L1 and L2 legs are identified in each GT circuit and can be tied into the respective L1 and L2 terminals on the GT inverters - and the same L1, L2 phases at the sub-panel - if necessary. Is this really necessary, or will each GT inverter "sense" the proper phases (180 degrees apart) and come on-line and operate properly - regardless of the "matching" of L1 and L2?

When my dual grid tie setup was complete is had a AC "combiner" prior to the run to the main panel where a double size breaker at the bottom of the panel was the attachment point

MarkC · October 2016

My "sub-panel" is essentially the same as your "combiner". As my inverters are in a remote location (solar shed), I draw some local power for lights, etc, so I have some extra breakers in the "sub-panel". My question is do I need to keep track of the two 120 volt phases from the inverters so that they are both to the same L1, L2, designations on the inverter AC connections, or do these inverters "find" the correct phases to feed power back to the grid?

BB. · October 2016

There is no reason to keep track of the L1 vs L2 connections in terms of the GT inverter. You are correct, the GT inverter simply follows the phase of the attached wires. And invert 1 does not "care" about the operation of inverter 2.

Of course, L1 and L2 should be kept straight through the house wiring (in US, Black and Red) as the various lines are carried throughout the home's wiring (i.e., if you accident mix up L1 and L2 in the wiring, you will not get 240 VAC between L1 and L1 at a 240 VAC load/inverter).

The neutral connection will not carry and significant current--It is just there for a "wiring check". If the inverter senses something other than 120 VAC between "hot" and neutral, it will fault and shut down. My older GT inverter does not even sense the neutral connection (that was added requirement for safety--To determine if there was a "broken" neutral).

-Bill

MarkC · October 2016

As always, thanks Bill. You may have told me this before, but I could not find the post. I have not modified any of the wiring in the cabin/garage, but I understand your concern about trying to obtain 240 VAC from two L1 or two L2 wires - just won't get much!!

BB. · October 2016

No problem asking again.

You will get a lot of current from Lx to neutral/ground though... Always be careful.

-Bill

solar_dave · November 2016

Just as an FYI, my AHJ (code guys) strictly stated that no loads to be attached to the "combiner".

I am a bit confused, do you have two 240V inverters, if you pass L1 and L2 straight through to the Main Grid Panel you should be good.

MarkC · November 2016

Yes - two SMA Sunny Boy US's. They both will feed thru individual disconnects and meters to the same solar sub-panel in my remote solar shed. The sub-panel has individual (dual) breakers appropriately sized for each inverter. The main issue is keeping track of the L1,L2 phases so they match at the sub-panel. I can do this, but not concerned if the SMAs don't care (as Bill has stated). It does appear to me that your "combiner" provides the same function as my local sub-panel. Can you provide some information on the "code" that does not allow any loads at this sub-panel/combiner? All local "loads" are protected by circuit breakers (15 amp outlet circuits) as are the wires to the main panel at the house (about 100 yards from the solar shed).
Thanks for any info.

solar_dave · November 2016

I don't know about the specific code but they had me label the sub-panel as such.

MarkC · November 2016

I'll do some checking and post results - I do know that one article stated that "normally no loads are added to the (combiner) panel". I'd not say my installation is "normal" as the inverters are so remote from the main panel - and that loads are needed at this remote location. I'm not too worried as every wiring system is connected by the proper sized breaker - but not being a code expert I certainly could miss a subtlety that must be adhered to.

drichlowe · July 2019

I am preparing to install a system with two Sunny Boy inverters in parallel and I am very happy I found this discussion. If MarcC and solar_dave still check these posts I would be so very grateful for comments about my system, particularly regarding the AC Combiner and AC Disconnect considering code changes since 2016.

Image: https://us.v-cdn.net/6024911/uploads/editor/0m/pkn1jvcgk64a.jpg

solar_dave · July 2019

The only issue I see is the AC disconnect should be near the main AC panel for the fire department, the code guys require it to be labeled accordingly. Check with your utility, mine required a separate solar only meter be installed as well. Also before you move ahead take this drawing to your code department and get there take.

If you are doing a DIY then the code guys may require a licensed electrician at least sticker and approve of the wiring.

Mine was more complex, I had to actually replace the whole service panel setup, the code guys would not let me derate the main because of the loads present. They required a 200->400 Amp upgrade of the service from the transformer (dual 200 amp panels). I got lucky and the utility the existing conduit (underground service) to pull the heavier wire, and it was only $300 to get it to the main meter. It was probably the right thing to do at the time because I knew that I would want a 100-125 amp service for shop building.

Parallel grid tied inverters

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