Solar & Generator

[ggunn]

That's what an automatic transfer switch is designed for. Put the ATS between the MDP and the protected loads panel with the generator on the PLP side and the solar on the other.

We recently installed an 812kW PV system on a hospital that has a big generator. The PV is connected in the MDP and there are numerous ATSs all over the hospital between the MDP and subpanels that are powered by the generator during a grid outage.

 

[shortcircuit2]

We recently installed an 812kW PV system on a hospital that has a big generator. The PV is connected in the MDP and there are numerous ATSs all over the hospital between the MDP and subpanels that are powered by the generator during a grid outage.

I am familar with this riser setup...its typical to a facility with emergency circuits.

How about a MDP with a solar connection that has only 1 ATS on the line side. Could we put some sort of voltage sensor on the utility side that triggers a relay controlling the inverter to only power up on utility?

 

[ggunn]

I am familar with this riser setup...its typical to a facility with emergency circuits.

How about a MDP with a solar connection that has only 1 ATS on the line side. Could we put some sort of voltage sensor on the utility side that triggers a relay controlling the inverter to only power up on utility?

Why would you need something like that? What circumstance could it handle that an ATS can't?

 

[GoldDigger]

Why would you need something like that? What circumstance could it handle that an ATS can't?

I think he is saying that, for whatever reason, he does not have a place to connect the PV on the downstream side of the ATS and so wants to add a separate relay to isolate the PV from the generator.
Since there is no possible interference with the operation of the ATS to isolate building wiring from POCO while on generator power, I do not see any problem with this.
If there were a place to make a supply side connection AND the AHJ and POCO allow supply side connections, that would be logically simpler.

 

[shortcircuit2]

I think he is saying that, for whatever reason, he does not have a place to connect the PV on the downstream side of the ATS and so wants to add a separate relay to isolate the PV from the generator.

Yes...thats what I want to figure out.

 

[pcanning87]

I've seen it done and approved with a relay (SEL 351A). It may not be economical for a smaller system though.


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[pcanning87]

Thanks for the feedback. I like electro7's post of using a relay. I would like to figure out how to apply that to larger systems...some way to isolate the inverter from seeing the generator at all.

One way would be to use a breaker with a shunt trip and a voltage contact wired to the line side of the main. That way if the grid goes down, the relay trips the dedicated PV breaker and the inverters can't see the generator.


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[pv_n00b]

Has anyone connected a PV System loadside to an electrical distribution system with generator so that the PV System can't operate when the system is on generator power?

If so how did you design this? With a relay or shunt trip breaker setup maybe?

I’ve done this in situations where a supply side interconnection was not reasonable. I used the aux contacts on the ATS to control a contactor that isolated the PV system when the ATS was in the Off or Generator setting. As far as I know they are still working after 6 years or so.

 

[shortcircuit2]

I’ve done this in situations where a supply side interconnection was not reasonable. I used the aux contacts on the ATS to control a contactor that isolated the PV system when the ATS was in the Off or Generator setting. As far as I know they are still working after 6 years or so.

Thanks... good idea.

 

[shortcircuit2]

One way would be to use a breaker with a shunt trip and a voltage contact wired to the line side of the main. That way if the grid goes down, the relay trips the dedicated PV breaker and the inverters can't see the generator.

Good idea...maybe better to use a UVR accessory...Under Voltage Release. Breaker trips off on Utility Power loss and needs to be reset mechanically.

 

[pcanning87]

Good idea...maybe better to use a UVR accessory...Under Voltage Release. Breaker trips off on Utility Power loss and needs to be reset mechanically.

Somehow I'd never come across UVRs before, I'm glad you mentioned it. That would definitely be a lot less expensive and work just as well, as long as there isn't a continuous backup UPS onsite.


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