PV tie in

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blueheels2

Senior Member
Location
Raleigh, NC
Occupation
Electrical contractor
Similar to another poster I've done lots of utility scale but very little residential.

I have a customer who has an array on their roof with inverters that feeds back to a disconnect on the exterior of the house. 20 amps 4 wire. There used to be AC units (Lennox I think but don't remember) that tied into this disconnect and used the solar panels to power the HVAC units. Units were ripped out and new ones don't havre that capability. SO now they have solar power that isn't being used.

I would like to tie it into a sub panel in the basement that has plenty of room. It also already has labels etc noting pv system is in use. Can I just tie the pv disconnect into this sub panel (12/3 on a 20 amp 2pole ) and be code compliant?
 
Can't be definitively answered without more info. The sub and an equipment in series upstream has to follow article 705. That should be relatively easy with a small system like that but details matter.

If the HVAC units weren't considered an interconnected power source and the PV didn't backfeed the panel then you may need a utility interconnection agreement and additional utility requirements may come into play.

I'm a little thrown by you saying the array has inverters. That seems to me like the PV is it's own interconnected system and that being tied into the HVAC disconnect would have nothing to do with the HVAC units 'capabilities.' In which case it might already have utility approval and just need to be hooked back up. But, which is it? Need more detail to understand.
 
jaggedben said:
Can't be definitively answered without more info. The sub and an equipment in series upstream has to follow article 705. That should be relatively easy with a small system like that but details matter.

If the HVAC units weren't considered an interconnected power source and the PV didn't backfeed the panel then you may need a utility interconnection agreement and additional utility requirements may come into play.

I'm a little thrown by you saying the array has inverters. That seems to me like the PV is it's own interconnected system and that being tied into the HVAC disconnect would have nothing to do with the HVAC units 'capabilities.' In which case it might already have utility approval and just need to be hooked back up. But, which is it? Need more detail to understand.
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I was going off of customer information about the inverters on the roof. I didn't get up there but sounds like I might have to. It's a weird setup at least to me. The PV disconnect has a missing ko but I it tied directly to the HVAC units. The HVAC panel (only other power in the area is main lug and has 2 breakers that feed the units and. that's it. No missing ko,s or anything like that. So solar had to tie directly to the units. Stickers on the disconnects, panel are just generic this has 2 power sources etc. Same stickers are on the sub panel in the basement.
 
Yeah a little confusing here but it would be good to know for sure that there are inverters up there. Perhaps it was some kind of off-grid system to power DC HVAC units then you can grab a meter and check for DC voltage at the disconnect. Also often PV interconnection permits are public building permits like all others and you can check if there was ever one pulled in the past at this address, to see if this was an AC grid tied system in some way.
If there is no permit pulled and you're getting DC voltage, you could get the specs of those panels and other devices that may be on the roof and begin to design a system and select an appropriate inverter for utility interconnection.
 
I seem to remember a few years back that there was some HVAC equipment being sold that would allow the interconnection of a PV system within the HVAC gear. Never installed one, but maybe that is what was going on here. If so, it should be fairly straightforward to redirect the modest PV output circuit to the sub-panel as you suggest, but as Jaggedbed says, you will need to make sure you are following the 705 rules, and there is a utility interconnection agreement in place.
 
I did the engineering design on a couple of these systems back when they first came out. They were basic microgrid inverter based systems that connected to the HVAC branch circuits. The biggest problem I ran into was that HVAC branch circuits were often run without a neutral before the code required outlets at the HVAC and the microinverters needed a neutral. Had to get a waver from the microinverter manufacturer to connect without the neutral. All the ones I worked on had a standard utility interconnection agreement.
 
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