Solar and Generators

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nosparks1

Member
Has anyone had any negative feedback on generator problems when a solar system is backfed on the same panel being fed by the generator and there is no load being drawn on the panel with the generator running?
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Has anyone had any negative feedback on generator problems when a solar system is backfed on the same panel being fed by the generator and there is no load being drawn on the panel with the generator running?
Doing that has a good chance of frying the control section of the generator, according to SMA tech support.
 

wyrepullr

Member
Location
NJ
Line side tap

Line side tap

to prevent any issues you should make a tap on the line side of the ATS. so both the solar and utility feed are on the same side. only the CT's for the ATS are reading the utility feeders. when utility power goes off so does the Solar inverter. the ATS will transfer and run solely on back up power.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
to prevent any issues you should make a tap on the line side of the ATS. so both the solar and utility feed are on the same side. only the CT's for the ATS are reading the utility feeders. when utility power goes off so does the Solar inverter. the ATS will transfer and run solely on back up power.
Many folks balk at doing that because they wish to keep harvesting energy from their PV system during a grid outage. It's risky, though.
 

broadgage

Senior Member
Location
London, England
Yes, in general grid tie PV inverters should only be used connected to the grid, and not to a generator.
As posted above, the grid tied PV inverter should be connected to the line side of the transfer switch, such that it is connected to the grid but not to the generator.

In most cases, the generator frequency and voltage will not be accurate enough for the inverter to function.
If however the generator output WAS accurate enough for the inverter to run, then serious harm could result at no or low load.

If the PV inverter was producing say 20KW and the load was 60KW, then the generator would supply the other 40KW and all would be well.
If however the load reduced to only 5KW, then the inverter would "try" to feed 15KW back into the generator. Serious harm might then result since unlike the grid, the generator is not designed to absorb power, only to supply it.

I have used a grid tied inverter with a generator, and it worked fine.
It was however a 650KVA generator and a 4KVA inverter, and I was satisfied that the load would never be less than 4KVA.
This was however due to a mistake by others, and I can not recomend the practice.
 

tallgirl

Senior Member
If it's an SMA setup, look at the Sunny Island.

That or get something that doesn't require an entire extra set of inverters just to keep the first set of inverters working. SMA makes good kit, but it's miserable and complicated in a backup power configuration.
 
If it's an SMA setup, look at the Sunny Island.

That or get something that doesn't require an entire extra set of inverters just to keep the first set of inverters working. SMA makes good kit, but it's miserable and complicated in a backup power configuration.
FWIW, my former instructor went on a service call for an SMA system with a Sunny Islander with all the bells and whistles. The complaint was that the batteries were not charging.

This is a 48 volt system comprised of 12 volt batteries.

The installer had the batteries arranged to get 48 volts, but not symmetrically. Since that was the only thing my instructor could see wrong, he re-wired the batteries so that they were symmetrical. IOW, four sets of three instead of one set of one, one of two, and so like the installer had them connected.

That's all it was. Once the system was turned back on and did it's thing, the batteries started charging.

So I guess they are very fussy!
 
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