Integrating Generator with Solar PV System

[Cassinian]

We installed a 14.7 kW solar PV system and are now installing a 22 kW whole house backup generator. The solar panels and SolarEdge inverter are on our barn, because its roof had the best sun exposure. The panels on roof of the barn connect to the inverted inside the barn, which connects to a 100A sub-panel also inside the barn, which is then connected to the main panel in the house on a 100A breaker. So far, this has worked fine. But, we then installed a 22 kW whole house NG backup generator, which connects at the service entrance. In the event of a power failure, the generator will kick in automatically, but because of the way the PV system is connected, the generator will feed power to the inverter (and if the sun is out the inverter will push power back to the generator). My concern is that either the generator or the inverter will suffer damage. I can manually disconnect the inverter at the barn, but that's only an option if I leave the generator in manual mode (it's designed to self-start and self-test, so I'd prefer not keeping it shut off).

The only solution I can think is to add some type of module that would disconnect the barn in the event of a power failure, or automatically disconnect the inverter. Even when the generator is working in automatic mode, there is an approximate 40 second window before the generator restores power; during that 40 seconds, all power is out (and the inverter at that point is shut down). I can envision something as simple as a relay that is tripped when power is lost, and remains so until manually reset. If such a relay was installed between the inverter and the sub-panel, it would disconnect the inverter as soon as power was lost (and stay disconnected); the inverter would never come back on and would never tangle with the generator.

Does something like this exist? Has anyone encountered a similar situation as ours? Any help would be most appreciated. Thanks!

 

[mvas-sti]

Yes, they make relays / contactors that can disconnect a GTI
When the generator is ON, then energize the relay / contactor and disconnect the GTI from the Main Panel.
When the generator is OFF, then the GTI will reconnected to the Main Panel.

 

[Cassinian]

Thanks for the quick response! And yes, just to be sure, this is a grid-tied system. So, a couple of questions just to clarify.. the GTI is in the barn, and connects to the sub-panel in the barn. Several other circuits run off this same sub-panel, including interior and exterior lights, fans and heaters (the barn has five horse stalls). Optimally, I'd want to disconnect the GTI from the sub-panel, but keep the sub-panel connected to the main panel in the house. That way, if power was out and the generator was running, the barn would be powered up as well. Right now I have a manual disconnect between the GTI and the sub-panel that disconnects just the GTI (as per regs), so what I'm hoping to find is an automatic disconnect that I can install inline with the manual disconnect.

I only need the automatic disconnect to disconnect.. it does not need to automatically reconnect. I can manually reset it to reconnect the GTI once power from ComEd is restored. I did look at one potential solution, which was a 50A module that is used to delay startup of high-load systems like A/C. These modules work in tandem with the Generac generator, but there were two problems with that solution: first, is was only available at 50A max, and the wire lugs were too narrow to tie into the 100A breaker; and second, it would cut power to the sub-panel in the barn. I want to keep barn powered up from the generator, and just disconnect the GTI.

What I'm envisioning is a relay disconnect switch powered from the sub-panel, and with a manual reset. As soon as power is lost at the sub-panel, the relay would trip and disconnect the GTI. The GTI would remain disconnected until power was restored and the relay was manually reset. In this way, the sub-panel stays connected to the main panel, and only the GTI is disconnected.

Does that make sense? Thanks!

 

[James]

What you are looking for is technically possible.
I see no reason to disconnect the Pv inverter when you are running from backup generator instead of grid supply.
It should sync to the new “grid as it sees it”
However, you need to avoid the circumstances where the pv inverter is trying to push more electricity into the system than the loads are drawing.
Worst case would be in the middle of the day when the pv array is generating 14kw and your load is low, 2kw?
So you need to have a control system that can switch in loads in say 3kw segments to dissipate the solar generation up to the whole 14kw.

 

[Cassinian]

Right, so that was my first thought. The GTI would sync to the generator. But the technician who was out when we did the final inspection with the county (which just by chance was the same day the backup generator was being installed) said the generator could damage the SolarEdge inverter. He said he had seen it happen a few other times, although he did not know specific circumstances. The electrician installing the generator thought the inverter would sync, but then a second technician said the generator could be damaged by the inverter. After some additional research, the general consensus seems to be that the safest solution is to disconnect the GTI from the sub-panel, so that it's never connected when the generator is running. And I can do that easy enough with the manual disconnect switch. I just want to find an automatic disconnect I can put inline with the manual disconnect, so I don't need to worry about if the generator kicks on in the middle of the night, or in the middle of a storm.

 

[David Prosser]

try Deep Sea Electronics, not sure if they are available in the US though.

 

[dmxtothemax]

Nearly all invertors have an "anti-islanding" feature to prevent this from happening,
the minute the invertor senses the grid is not present ( when the generator kicks in ) then the invertor will shut down to prevent any problems, as far as I know such features are usually manditory.

 

[Cassinian]

Nearly all invertors have an "anti-islanding" feature to prevent this from happening,
the minute the invertor senses the grid is not present ( when the generator kicks in ) then the invertor will shut down to prevent any problems, as far as I know such features are usually manditory.

Correct, the GTI has an anti-islanding feature to shut it down in the event of a power outage. However, because it's connected to the house via the sub-panel in our barn (the roof of which being where the panels are physically located) the inverter will receive power from the generator when the Generac kicks in. According to the solar tech who installed the GTI, at that point the inverter will recognize power from the generator as power being restored and will come back up (potentially damaging itself or the Generac).

The Generac is connected via an ATS that prevents it from feeding power back to the grid, but it will still feed to the inverter, and the inverter will feed to it unless the inverter is disconnected.

Normally this would not have been a problem if the GTI and the generator ATS where both located in the house at the service entrance; the inverter would have been cut out of the system by the ATS (and the anti-islanding feature would have worked as intended). If I were to move the inverter from the barn to the house, and trench a DC connection from the barn to the house (which I do not want to do) I could fix this problem. But to me, a simpler (and much less expensive) option would be an automatic disconnect for the GTI that would disconnect it in the event of a power failure, and remain disconnected until manually reset.

Unfortunately, I have yet to find such a thing.

 

[David Prosser]

Unfortunately, I have yet to find such a thing.

Have tried Deep Sea Electronics then ?

 

[Cassinian]

Unfortunately, I have yet to find such a thing.

Have tried Deep Sea Electronics then ?

Yes, I did visit their site. I found a DSE P100 decoupling relay, but it's a lot more sophisticated in design than I was expecting. Seems to do a lot more than what I need, although it could work.

It does give me hope that I might find a simpler solution, but if not it could be a way to go. I appreciate the recommendation.