How would a solar system co-exist with a whole-house generator?

[rsilvers]

I am getting a SolarEdge system and already have a whole-house generator. I showed the guy who visited from the 35-person installer-company, and asked him, because I wanted a home-side tap - and he said he may need to do a supply-side tap. I want to make sure I understand why he is right.

So if the generator kicks in, and the SolarEdge synchronizes to the generator, and the generator transfer-switch isolates the house from the grid, won't the solar system put lots of energy into my panel that has no place to go?

How is this normally handled?

[J.P.M.]

That the question is being asked kind of makes me wonder about installer quality. You went with low buck, right ?

[rsilvers]

I never found a low priced installer.

I could hire the best chef, architect, engineer, artist, or mechanic in the world and I am going to want to have my own knowledge on something in case there are two ways to do it. I would like the panels to augment the generator if possible.

Likewise, I would have to come to my own conclusion on EnPhase vs Solar Edge and not just let them decide.

[J.P.M.]

No, I went expensive. I never found a lower priced installer.

I don't see how me wanting to know something reflects on the designer who I never spoke to.

"The installer is looking into how to handle the wiring and thought he may need to do a supply-side tap" sounds like some things that might have been considered before now might have slipped by. Not being critical of your question, just seems like that's the type of thing a savvy installer would be more sure about is all. Maybe I read too much into your comment.

[rsilvers]

The first guy came to my house yesterday for the first time. It is a 35 person company. I think the point when they are sure about it is when he returns and talks to the system designer.

[J.P.M.]

The first guy came to my house yesterday for the first time. It is a 35 person company. I think the point when they are sure about it is when he returns and talks to the system designer.

Forget I brought it up.

[KidMelody]

I have a 22kw standby generator and just installed a 10kw array. Whatever you do...find out from your POCO how they want it done.

My installer connected it one way but the POCO wants it a different way with another disconnect. They also want their own generation meter installed...has held up the process for me of turning it on.

[Mike90250]

Whoa. If the installer is asking the question, dump them, they don't deserve your business, and you don't deserve the crap job they are going to leave on your roof.

The PV panels belong on the UTILITY side of the generator transfer switch. That way, they never try to overdrive the generator.
The solar inverter needs to sync to the 60.00Hz grid before they pulse the grid to test it's capacity. IF your generator ever held frequency long enough to be qualified, and the Grid Present Pulse triggered, it's likely to fry the genset. It's a full bore pulse, to insure the grid can absorb the power and not overvoltage. If it hit your local genset-house microgrid, it's likely to fry things, and if it did pass, it's quite likely the full array output could not be used locally, and the overvoltage would trigger and shut the PV inverter down, None of which would be good for your generator or appliances in use, There have been many instances reported here of installs tripping offline because of poor utility voltage regulation, and eventually your local microgrid would fail too.
If your installer has to ask this question, get another, If You are asking the question, no, it's not a way to stretch your fuel supply.

[rsilvers]

I figured it out. My confusion was that I thought that I had a whole-house generator, when in fact I have three main panels with 150 amps, 150 amps, and 100 amps. One of those 150 amp panels goes into the transfer switch, and then the transfer switch output goes to my panel labeled #3 - which are the only circuits fed by the generator.

So I can back-feed into panel #1 and panel #2 through up to 100 amp breakers on each.

[Mike90250]

I figured it out. My confusion was that I thought that I had a whole-house generator, when in fact I have three main panels with 150 amps, 150 amps, and 100 amps. One of those 150 amp panels goes into the transfer switch, and then the transfer switch output goes to my panel labeled #3 - which are the only circuits fed by the generator.

So I can back-feed into panel #1 and panel #2 through up to 100 amp breakers on each.

I'm unable to visualize how this is wired. So you are going to have to rely on the locals to sort it out for you, Or post a clear schematic. But I can't guess as to how 3 main panels and a transfer switch are going to be wired to "n" Solar PV inverters.

[rsilvers]

[ncs55]

That is complex for sure. So, #3 is the critical load panel and isolated from the grid when the genny is running? You have a 400A main? These two subpanels are wired to a 150A breaker each at the main?

[rsilvers]

#1 and #2 are main panels. #3 and #4 are sub-panels.

I have 400 amp service split into three main panels. A 150 amp (#1), another 150 amp (#2), and a 100 amp (not in this photo).

#1 and #2 are both "main" panels that have 150 amp breakers but 200 amp bus bars. That means that either one of those can take a 90 amp breaker and be back-fed with up to 72 amps each. Since Solar Edge can take up to 135% on the DC side as on the AC side, I should be able to get up to 23,328 STC into each one. That is 74 LG-315 panels into each one, but most likely only one will be used since I will run out of decent roof at around 70 panels.

Panels #1 and #2 are always on the utility side of the transfer switch, and have no power when there is an outage. #2 feeds into the transfer switch, and in the event of an outage, would be dead. The transfer switch would send generator power to panel #3, which is fine as no solar inverter would be connected to that.

[ButchDeal]

STC has nothing to do with the feed in breaker. It is all about the spec on the inverter you use. In other words if you use an SE7600 you will need a 40a breaker regardless of how much PV is behind it.

In most locations there is supposed to be a single interconnect with single disconnect, so feeding into #1 and #2 would not be valid.

[rsilvers]

Ok on the inverter and breaker. I am glad to learn that.

The number of panels that I will have will require at least two Solar Edge inverters. Of course the installer knows how to combine them, but for my own knowledge, would they both be wired into a combiner panel and then that would go through a cut-off and then into panel #1?

[ButchDeal]

That is the correct way yes. All inverters feed AC combiner, to disconnect to final interconnect. Often the AC combiner and disconnect are the same device.

[rsilvers]

Since I can only back-feed into a 90 amp breaker, it seems like two 7600s is the most it can handle. At 135%, that is 20520 STC, or 64 315 watt panels.

If it is true that there can only be one connection point, then they would need to do a utility-side tap if I wanted more than 64 panels.

Does that sound right?

And going right to 135% doesn't sound awesome either, so may as well just start with the utility-side tap.