# Hooking up a whole Generator with Solar



## HackWork (Oct 2, 2009)

[email protected] said:


> I need a schematic for wiring a Whole House Generator with Solar does anyone out there have a wiring diagram of how to do. My concern is NOT to ruin the Solar inverter when the generator come on when I lose power. I know someone has to have done this before so I hoping that someone can forward this information to me. I am Electrical Contractor and this is on my house.
> 
> Thanks to anyone that can help


 No one can give you a wiring diagram without knowing what you currently have. How the solar is tied in, where the disconnect is in the system, etc.

If you are an EC, I think we should talk this out. Tell us about your house and how the system is currently laid out.


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## Bird dog (Oct 27, 2015)

HackWork said:


> No one can give you a wiring diagram without knowing what you currently have. How the solar is tied in, where the disconnect is in the system, etc.
> 
> If you are an EC, I think we should talk this out. Tell us about your house and how the system is currently laid out.


More like CEO...
https://www.ccbac.com/about


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## [email protected] (Apr 3, 2020)

The solar inverter is wired to a sub panel in the house. the main service is 240/120 200a single phase. There is transfer switch that came with the Generator (200A). There is NO back up batteries to worry about. The Generator is Natural Gas. The main panel (the main has no room for more breakers) and Generator are physically in the same location on the side of the house. The inverter has a sub panel that has breaker space that is located by the Generator, inverter and main panel.


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## HackWork (Oct 2, 2009)

[email protected] said:


> The solar inverter is wired to a sub panel in the house. the main service is 240/120 200a single phase. There is transfer switch that came with the Generator (200A). There is NO back up batteries to worry about. The Generator is Natural Gas. The main panel (the main has no room for more breakers) and Generator are physically in the same location on the side of the house. The inverter has a sub panel that has breaker space that is located by the Generator, inverter and main panel.


So you have a main panel that powers a sub panel. And that subpanel is backfed by the solar system? 

What type of transfer switch it is? The kind with X-amount of branch circuits or the type that switches the entire load on an existing panel?


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## [email protected] (Apr 3, 2020)

It is a 200A that switches the entire load.


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## HackWork (Oct 2, 2009)

So this could be an issue. The solar inverter will most likely turn on and sync up with the generator, which is fine in itself. But if the solar system is producing more power than your house is drawing, then it could be bad for the generator.


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## [email protected] (Apr 3, 2020)

I was thinking that I should have an automatic disconnect to Inverter; if and when the generator comes on? I was gonna use a normally open contactor that is wired to house power (coil of the contactor) so that when the generator come on it would open and disconnect the solar inverter power from the generator power. does this make sense?


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## HackWork (Oct 2, 2009)

[email protected] said:


> I was thinking that I should have an automatic disconnect to Inverter; if and when the generator comes on? I was gonna use a normally open contactor that is wired to house power (coil of the contactor) so that when the generator come on it would open and disconnect the solar inverter power from the generator power. does this make sense?


Sure, there are many ways.

Depending on your exact system you may be able to use the load shedding system on the ATS to do it.


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## dronai (Apr 11, 2011)

Couldn't he just use a ct that is on the generator feeder, and if this senses current, it opens his solar contactor ?


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## Wirenuting (Sep 12, 2010)

Why would anyone want to power a generator with solar? 
Seems silly to me. 

Did you run out of natural gas?


BTW, welcome to ET
Please finish filling out your profile.


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## [email protected] (Apr 3, 2020)

I live in California and when the wild fires hit they shut off the power to my house. The solar doesn't provide power to house when the main power is off. last year we went without power for days. All my main appliances are Natural Gas. We live on the coast so there is no need for Air Conditioning. So a Whole House Generator makes a LOT of sense.
At least to me.

I like the CT suggestions a lot. Thanks HackWork great thinking.


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## dronai (Apr 11, 2011)

The CT suggestion was mine


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## [email protected] (Apr 3, 2020)

Sorry Dronai much appreciated. All the best while we sit here with nothing to do.


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## HackWork (Oct 2, 2009)

dronai said:


> The CT suggestion was mine


 I wanted credit

:vs_mad::vs_mad::vs_mad:


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## [email protected] (Apr 3, 2020)

HackWork, so you think disconnecting the solar inverter is good idea when the generator come on? Sorry you didn't the credit so deserved!!! I don't want to screw up the inverter or the Generator by implementing this incorrectly.....Many thanks, Chuck


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## HackWork (Oct 2, 2009)

I am still not sure about your system. You haven't told us the brand and model generator. Still a lot up in the air.

I have never seen solar backfeeding into a subpanel like you describe. 

In your situation, I might rework the service to be a main panel with only the AC and solar in it, and a feed to a subpanel with everything else in the house coming out of that sub. Then the ATS between the main and subpanel. Then the solar would be on the grid side of the ATS.


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## [email protected] (Apr 3, 2020)

The Generator is a Kohler 200A 240/120VAC single phase. It came with a 200A ATS. the solar company had no choice (because there weren't any breaker spaces at the main) but to feed the sub panel with solar instead of the main. I was thinking that since the back and forth wiring is to the sub panel form the solar inverter that I would hook up the generator to sub panel (which would be easy to connect because of the solar sub panel) and disconnect the inverter when the generator comes on because all the wiring is right there and easy to connect too??? Your thoughts please.


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## dronai (Apr 11, 2011)

I know you're are working with Hacks, but a couple questions here

The Solar invertor will disconnect on it's own when it detects an outage. 
Are you are worried that when the generator comes on, the solar will come back on, and the generator will detect voltage and turn off, and a repeated cycle ?


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## nrp3 (Jan 24, 2009)

It seems that the solar setups I've seen, not off grid, but most have connections on the utility side of the main, and when an outage occurs, the inverter shuts off as well. Ordinarily, we'd inject the 200 amp transfer switch before the main of the existing panel and gets wired as a sub panel, ie grounds and neutrals get separated. We'd need to move the utility side feed to the 200 amp switch and if there's solar move it as well so it stays ahead of the transfer mechanism so there's no sense of generator power when it becomes available in the event of an outage. If this solar tie in is somewhere down stream and just backfeeds through the existing system, as Hack and others said, you'll need to have some sort of contactor to disconnect the solar connection. Sometimes there are auxiliary contacts on the transfer mechanism that can be used to open a contactor when the transfer switch moves to the generator position or can be added to it.


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## HackWork (Oct 2, 2009)

dronai said:


> I know you're are working with Hacks, but a couple questions here
> 
> The Solar invertor will disconnect on it's own when it detects an outage.
> Are you are worried that when the generator comes on, the solar will come back on, and the generator will detect voltage and turn off, and a repeated cycle ?


No, that won’t be an issue because the ATS will only switch back if power is on the grid side. 

The problem is if the solar array produces more power than his house uses, it would be sending that power to the generator which could destroy it.

So he either has to wire it up so that the solar back feeds on the grid side of the ATS. Or wire up some type of contactor to shut off the solar when the generator is on.


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## dronai (Apr 11, 2011)

I did one job, that had both, Solar, and back up Generator by me. The Solar installer, said he had a contact for disconnecting the solar when the Generator kicked on. I didn't see what he did, but I would think there is a simple solution


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## nrp3 (Jan 24, 2009)

Maybe there’s a connection at the inverter for a dry contact, that I don’t know.


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## Jerome208 (May 10, 2013)

Shaft contact mounted on the transfer switch feeding a contactor that opens when powered.


Or feed the solar into something on the utility line side of the transfer switch.

The generator and solar cannot be allowed to push against each other. The solar will certainly come online after 5 minutes when it sees generator power and push power into the generator.


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## HertzHound (Jan 22, 2019)

[email protected] said:


> The solar inverter is wired to a sub panel in the house. the main service is 240/120 200a single phase. There is transfer switch that came with the Generator (200A). There is NO back up batteries to worry about. The Generator is Natural Gas. The main panel (the main has no room for more breakers) and Generator are physically in the same location on the side of the house. The inverter has a sub panel that has breaker space that is located by the Generator, inverter and main panel.





"The solar inverter is wired to a sub panel in the house"

"The main panel (the main has no room for more breakers) and Generator are physically in the same location on the side of the house"

"The inverter has a sub panel that has breaker space that is located by the Generator, inverter and main panel."


A little confusing which panel you want to tie the transfer switch into. With only a few posts, you probably can't hand draw a one line and snap a picture to upload.


So the inverter has a sub panel outside the house and is tied into a sub panel in the house? Is there more than one inverter outside the house? If so this "outside sub panel" could be an AC combiner. I'm pretty sure if it's part of the solar equipment it should be labeled as to what it is. Is it an AC combiner, an AC disconnect for the inverter or a rapid shut down for the solar? Who knows? I wouldn't tie a generator into it.


As far as connecting a generator into a grid tie solar, I don't see it as a safety issue. It's brought up here often, and most people say not to do it. I would probably try to avoid it, but I don't think it's a big issue. 



The Inverter has a UL listing that it will not harm the utility or anything connected to it. It should shut down before it harms the generator. It will probably never run with the generator. It knows the difference between the utility and the generator and shouldn't run anyhow. Even the posts that say an inverter generator can fool it into turning on a grid-tie inverter, I don't 100% believe. The first time a load like a refrigerator kicks in, will cause enough line disturbance to kick off a grid-tie inverter. 



My own house I have a portable generator that back feeds my panel and grid-tie solar. I usually don't shut off the solar breaker when I'm running the generator. The solar never turns on with the generator. The one time I shut off the solar breaker, I forgot to turn it back on, when I turned the main back on. I'm a dumb ass, because it took two months of a higher electric bill to realize I never turned the breaker back on after an outage. After the second bill I started to sweat that there was a costly problem. I was staring at the inverter display, thinking of what a pain in the ass it was going to be to start pulling panels off the roof, looking for a short or something. "line disturbance"? Then a light went off in my head as I looked over at my panel!:vs_mad::vs_laugh:


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## dronai (Apr 11, 2011)

HertzHound said:


> My own house I have a portable generator that back feeds my panel and grid-tie solar. *I usually don't shut off the solar breaker when I'm running the generator. The solar never turns on with the generator. *The one time I shut off the solar breaker, I forgot to turn it back on, when I turned the main back on. I'm a dumb ass, because it took two months of a higher electric bill to realize I never turned the breaker back on after an outage. After the second bill I started to sweat that there was a costly problem. I was staring at the inverter display, thinking of what a pain in the ass it was going to be to start pulling panels off the roof, looking for a short or something. "line disturbance"? Then a light went off in my head as I looked over at my panel!:vs_mad::vs_laugh:


There we go 

Hacks: The typical solar array I see in residential is only 5KW, and a typical generator install for me is 20kw


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## gpop (May 14, 2018)

dronai said:


> There we go
> 
> Hacks: The typical solar array I see in residential is only 5KW, and a typical generator install for me is 20kw


Solar shouldn't turn on unless it see's a stable hertz signal. 

So you could be relying on the generator cycling up and down due to load changes as a way to stop the solar panels backfeeding the generator. 

Im not 100% sure what would happen when the inverter and the generator voltage regulator start messing with each other so its easier to disconnect the inverter.


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## Jerome208 (May 10, 2013)

I've seen it happen. Modern generators run at 60.00 Hz same a the poco. Solar will connect to the generator and start to feed into it. This makes the generator a motor and it goes faster. 



It depends on the inverter. 



It will either smoothly spin faster until frequency is out of range for the inverter and then the inverter will drop and wait x number of minutes on grid disturbance, or the inverter will refuse to increase its frequency and so the generator will be slightly sped up/drop back down/throttle opening and closing/weird noises happening.


If the customer is consuming more power than the solar makes then there "should" be no problem but...


I would not want to make any bets on what is happening with the wave forms/power factor of what the inverter is pushing into the generator/customer system.


Just do it right, we are professionals and our job is to do it right or walk.


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## ppsh (Jan 2, 2014)

I have seen many installs here of standby generators feeding the same panel the grid tie solar is feeding. All 22kw or smaller. Most all have seen 4+ days of summer usage with PG&Es outages. 

I have a hard time believing a typical 2-pole 3600rpm generac with its sub-liter lawnmower engine is going to produce a clean enough sine wave or keep a steady enough frequency for an inverter to lock on to. If the inverter does somehow manage to lock onto the generators output, and the generator starts to speed up, frequency will rise, and quickly exceed the inverters parameters for utility voltage. If the inverter doesn't kick out first, the generator should stop on an overspeed alarm.

I would be concerned of doing the same with the 80KW+ commercial units, especially ones with modern engine management,


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## HertzHound (Jan 22, 2019)

If all of this is such an issue, what’s the code article requiring an interlock between the two sources?


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## farmantenna (Nov 22, 2012)

call technical support for the manufacturer of the inverter will get you valid answers.I don't think the generator's sine wave is pure enough to fool the inverter to go back on line.


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## Jerome208 (May 10, 2013)

Inverters don't care if the sine wave is clean or not. If it is 60 Hz or near enough they will accept it and then push power. Remember the poco is not always 60.00 either. They drift a fair bit.



Yes the frequency will quickly rise and the inverter will disconnect. Then the frequency will go back to 60.0 and 5 minutes later it will reconnect and do it all over again. And again. And again.


Some inverters (SMA) will log a permanent error and need Authorized Support if they get the same error over and over again like this.


Bottom line is it is just bad design. Two generators pushing against each other, one of them (solar) just wants to push as much power as possible.


Don't do it. The only conceivable reason for doing it would be to save the customer a few bucks having to do it right. We are the professionals. We do it the right way.


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## nrp3 (Jan 24, 2009)

Even if you post the brand of inverter, I'd like to look this up. Generators are a big part of my business. Haven't had to face this problem yet, but someone will ask me or I'll have to figure it out. Be nice to know if there is a couple of terminals for that purpose.


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## HackWork (Oct 2, 2009)

Jerome208 said:


> Inverters don't care if the sine wave is clean or not. If it is 60 Hz or near enough they will accept it and then push power. Remember the poco is not always 60.00 either. They drift a fair bit.
> 
> 
> 
> ...


It seems like people are trying to justify doing it the wrong way, not sure why.


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