Ginaelectric
My customer has a solar array on his roof and now due to the recent storm want to install a 20 KW to backup his house. Does anyone have any experiance in this and do I need to shed the breaker for the solar panels so that it does not back up into the generator or does the inverter see trhe genset come on line and know not to backfeed into the generator. I am not educated in solar arrays.
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techntrek
Many grid-tie inverters will not sync up with a genset, between the voltage and frequency swings. But it is still possible.
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ohmslaw
The safe method would be to connect the solar before the transfer switch.
A line side tap.
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Ginaelectric
Well I cannot use a service rated TS and put a breaker before it so that idea is out. Will an inverter shut down when it sees a generator waveform and stay off until transfer back to utility power? Or should I install a relay to shut down the inverter during standby?
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techntrek
Since its possible the inverter will come online it would be best to design the overall system so the inverter is either removed from the system as you said, or never able to "see" the generator as ohmslaw said. That is the safe route.

That said, some have intentionally designed their system to allow sharing of loads between a genset and grid-tie inverter. But I believe there are risks to doing this. You might want to check in with the Wind Sun solar electric forum to get more input.
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ohmslaw
Ginaelectric;10387 wrote:
Well I cannot use a service rated TS and put a breaker before it so that idea is out. Will an inverter shut down when it sees a generator waveform and stay off until transfer back to utility power? Or should I install a relay to shut down the inverter during standby?


You only need to attach the solar array on the line side of the switch. Not necessarily after the service breaker.
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Ginaelectric
ohmslaw;10408 wrote:
You only need to attach the solar array on the line side of the switch. Not necessarily after the service breaker.


But the POCO does not allow line side taps. It would have to be after the main breaker and so it would really be easier to install a small relay and shed the solar circuit while under generator power. I just dont know enough about solar inverters to understand their full capabilities. How would you live off grid with solar if you did not have a generator for backup? It would seem neccessary to have one for nightime and sunless days.
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Skip Douglas SkipD
Ginaelectric;10411 wrote:
But the POCO does not allow line side taps. It would have to be after the main breaker and so it would really be easier to install a small relay and shed the solar circuit while under generator power. I just dont know enough about solar inverters to understand their full capabilities. How would you live off grid with solar if you did not have a generator for backup? It would seem neccessary to have one for nightime and sunless days.
Just a guess - batteries to store energy from the solar panels?
Skip Douglas
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techntrek
Ginaelectric;10411 wrote:
How would you live off grid with solar if you did not have a generator for backup? It would seem neccessary to have one for nightime and sunless days.


Most off-grid systems do have a generator. Often the system will be sized to handle 2-3 days of low/no sun, then on day 3 or 4 they'll fire it up to put a bulk charge on the battery to get them through until the sun comes back. This isn't always true, some oversize their system to handle long stretches w/o sun (very expensive), or they'll size it like normal but cut out any extra loads on dark days. These systems always have a battery for night time and low-sun days.

People with grid-tie systems that also want to use the solar array during an outage either have to install a specialty inverter like the Xantrex XW that can do both, use a specialty charge controller that can handle the high string voltages that grid-tie systems usually have, or install two separate systems.
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