Solar with a Standby Generator

[mkgrady]

I’m wiring a whole house standby that currently has a solar system. The solar circuit connects to the house service at the 200 amp mater/main breaker (load side). The connection is made with a tap splice onto the 4/0 aluminum SER. From there the SER runs to the house panel.

The 200 amp ATS will mount outside next to the meter/main. My question is about where this solar connection should be when the generator wiring is complete. If the tap remains as is the solar system will be feeding into the generator output during an outage. Is this a problem? Or will it just synch up with the generator output like it does when POCO power is being used.

These questions probably tell you how little I know about solar power. Hopefully I’m not the only one on here that can get something out of this question.

[romex jockey]

Methinks the term you want is anti-islanding......~RJ~

[texie]

I’m wiring a whole house standby that currently has a solar system. The solar circuit connects to the house service at the 200 amp mater/main breaker (load side). The connection is made with a tap splice onto the 4/0 aluminum SER. From there the SER runs to the house panel.

The 200 amp ATS will mount outside next to the meter/main. My question is about where this solar connection should be when the generator wiring is complete. If the tap remains as is the solar system will be feeding into the generator output during an outage. Is this a problem? Or will it just synch up with the generator output like it does when POCO power is being used.

These questions probably tell you how little I know about solar power. Hopefully I’m not the only one on here that can get something out of this question.

Your genset must be down stream from the solar.

[mkgrady]

Your genset must be down stream from the solar.

Are you saying the solar connection needs to remain where it is? If it stays on the load side of the main at the meter/main and upstream of the Ats the generator output will never see the solar output. That seems right to me. Is it?

[mkgrady]

Methinks the term you want is anti-islanding......~RJ~

Can’t say that I understand. Can you elaborate?

[ggunn]

Can’t say that I understand. Can you elaborate?

The solar connection needs to be outside (on the utility side) of the transfer switch. Yes, this means that the solar will not run when the grid is down, but connecting it inside the transfer switch would enable the PV to backfeed the generator when the loads are drawing less than what the PV is producing, which would be very bad for the generator.

[mkgrady]

The solar connection needs to be outside (on the utility side) of the transfer switch. Yes, this means that the solar will not run when the grid is down, but connecting it inside the transfer switch would enable the PV to backfeed the generator when the loads are drawing less than what the PV is producing, which would be very bad for the generator.

Thanks for that response. Very helpful.

[GoldDigger]

That is assuming that the generator frequency and voltage are stable and accurate enough to qualify to the inverter and that its output impedance is low enough to satisfy the anti islanding schemes. In many cases the grid tied inverter simply will not run when connected to the generator.
If the inverter had a mode that relaxes the "grid" specs to work with a generator, then you risk the problem ggunn describes.

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[electrofelon]

That is assuming that the generator frequency and voltage are stable and accurate enough to qualify to the inverter and that its output impedance is low enough to satisfy the anti islanding schemes. In many cases the grid tied inverter simply will not run when connected to the generator.


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I agree and doubt this is actually an issue. Even if it did initially synch, and then power production exceeded usage, I think voltage and or frequency would rise and the inverter would shut down then. That said, I of course wouldn't do it as a professional.

[ggunn]

Thanks for that response. Very helpful.

We have had customers who got concerned about the PV not continuing to run during an outage when they are using the generator, and it is possible to design a PV system that will, but it's expensive. If outages are relatively rare and short-lived, the contribution to their bottom line from the PV system during outages is minuscule.