Isolating generator from solar system

[Gordy]

I have a customer who just had a whole house generator installed at their home where I had put solar panels a couple of years ago. The solar system backfeeds the main panel through a 40-amp breaker. The power to the house comes underground for a pedestal about 150' from the house. The electrician put the transfer switch by the pedestal and ran power down from the generator which is off in a different direction. Normally I would either tie the solar into a line-side tap on the utility side of the transfer switch or connect the solar to the main panel by way of a normally open contactor that is tied to the dry contacts in the transfer switch (when utility power fails, the contactor opens). Currently there is no way that I know of to tell where the power in the house is coming from (utility or generator) and no way to connect the solar to the transfer switch way down at the pedestal. (Apparently the conduit to the house is thought to be damaged, so pulling the main feed to the house and adding a signal wire is not possible).
Anybody got any ideas?

[Ampster]

Where is the meter in this scenerio? Is that generator installation done according to code?

[Gordy]

The meter is at the pedestal. Yes, the generator is done according to code. The only thing unusual is that the transfer switch is at the pedestal instead of at the house.

[Ampster]

The only thing I can think of is a latching relay that would open contacts in the second or two between the time the grid drops and the time it takes the generator to start.

Not an elegant solution and your customer would have to manually reset once power was restore. That reset is a weak link if some one inadvertently hit the reset while grid is down and generator is running. Is the solar inverter a more recent UL 1741 model? Is there a way to tweak the generator frequency?

[Gordy]

Where would I get a latching relay?
Would you happen to have a manufacturer who makes such a device?
This may be the best solution given the circumstances.
Maybe I could combine this with some sort of indicator light to remind them the solar is off until reset.

[bcroe]

Where would I get a latching relay?

When some power is available at the time needed, latching can be accomplished with
an electrical circuit. For complete power loss, a 9V battery powering some CMOS logic
could last the battery shelf life. Bruce Roe

[Ampster]

Where would I get a latching relay?
Would you happen to have a manufacturer who makes such a device?
This may be the best solution given the circumstances.
Maybe I could combine this with some sort of indicator light to remind them the solar is off until reset.

I found some searching for latching relay on Google, Digikey, Amazon or other electronic suppliers. You will have to find one with coils for 240 v or use two with 120 coils. I will look in my archives for a two relay combo that works electronically as a latching relay. That is a good idea of a indicator light with a warning to not push reset when generator is on.

What did you find out about the frequency specs of the generator or the inverter you installed (UL1741)? That would possible be a more foolproof method if you can tweak the generator output by a few Hz. That is just a theoretical solution from an anonymous guy on the Internet, I would get a second opinion before I tried that because you could damage the generator if not done property.

[Mike90250]

latching relays https://www.grainger.com/category/el...nd-accessories

https://www.grainger.com/category/electrical/industrial-controls-automation-and-machine-safety/relays-and-accessories?attrs=Item+-+Relay%7CLatching+Relay&filters=attrs

[SunEagle]

latching relays https://www.grainger.com/category/el...nd-accessories

https://www.grainger.com/category/el...&filters=attrs

Any latching circuit component needs to insure the "contacts" are rated for the amperage going through them.

Building a system that can switch between grid, solar and a generator really needs some engineering so I advise the OP to get some expertise if they intend to pursue this endeavor.

[Ampster]

@Gordy , did the original solar install have the usual stickers on the service entrance? If so, the generator installer would have been on notice that there was solar downstream of his installation. If your solar install was UL1741 compliant there should be no risk to your equipment. I am not suggesting that you or your customer test that assumption. Based on @SunEagle 's comment that generator installer needs to verify the engineering. It is possible the generator could be at risk if for some reason the solar inverter did backfeed the generator. You may be able to use that as leverage for your customer to force the generator installer to fix the issue.