Solar Off Grid

W@ttson

W@ttson

Senior Member
Location
NJ-USA
Occupation
PE
Hello all,

I have a quick question regarding solar off grid installs that I can't wrap my head around.

Some people setup remote cabins/houses such that they are off grid and only utilize solar panels. I have recently heard of a setup where the solar panels are connected to a charge controller/inverter unit. This unit would charge onsite batteries. A local generator would be connected to this charge controller/maintainer. In the event that there was not enough sun to charge the batteries, the generator would be used to charge the batteries. Then the unit would send the power to the electrical panel and feed all of the normal 120/240V loads.

The question is, is the generator a separately derived system? There is no utility. The N-G occurs at the main panel where all of the 120/240V loads are located.
 
For an NEC-compliant system, if there is only one N-G bond in the entire system, there are no SDSs. Each SDS would have its own N-G bond. With only one N-G bond, the generator's grounded conductor needs to be directly connected to the grounded conductor from the inverter(s) in the charge controller/inverter, so neither source is an SDS.

Cheers, Wayne
 
The few that I have done were not SDS. It had a main panel just as if it was utility fed, and power went through the charge controller/inverter to the panel.

Sometimes the battery was being charged from the solar array, and sometimes from the generator. But the system remained unchanged.
 
I believe most if not all such systems are non-separately derived. (I've worked on a couple.) Typically the inverter/charger has an internal contactor that connects or disconnects only the ungrounded conductors from the generator as needed.

For such systems you need a generator that allows ground and neutral to be isolated at the generator.
 
Thanks everyone. I guess where I was getting tripped up is the fact that the generator was being directly wired into that electronic device (the charge controller/inverter unit). I didn't know how the neutral was being handled in there. Kind of became a bit of a black box to me.

Thanks again for clearing it up.
 
I've worked on hundreds. They are often DIY and the N-G bond could be anywhere, or nowhere.

Generally, there will be a main panel of some sort right next to the main inverter(s). That is where it makes the most sense to put the N-G bond.

The generator feeds through the inverter. It is usually located somewhere remote to cut down on noise. Therefore, it is usually a 4 wire feed.

Some of them are from the times before a 4 wire feed was required for remote buildings. Often a 3 wire feed in that case, bonded at the generator (shack) and bonded at the main.

In any case, there is never any provision for a switched neutral. In fact, on the old ones, the inverter never switches out. It is a bunch of transistors and can transmit power either direction, so once the generator comes on line they close a relay and parallel the generator and the inverter. Then the inverter transistors run in reverse to charge the batteries.
 
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