Photovoltaic System Mounted on Adjacent Building

[Geepers808]

The following is the situation I have:

1. Two buildings on adjacent but separate lots (same owner for both lots but different TMKs).
2. Each building has its own service with associated Utility meter and the electrical distribution systems are independent.
3. Contractor is proposing to install photovoltaic systems consisting of panels with micro-inverters on both roofs (approximately 150 panels).
4. One of the buildings is a warehouse so part of the photovoltaic system on this roof (approximately 80% of the output) will be fed into the electrical system of the adjacent building since it has a greater electrical load.
5. We've spoken to the local Utility Company and they have indicated that they typically do not allow photovoltaic systems to span different lots but they seem to be willing to accept this installation if it meets code.
6. The Contractor has discussed the matter with the local Building Department and they do not seem to have any objections with the arrangement.

The following are the questions I have:

1. Are there any "show stopper" issues with the above arrangement?
2. Are there any special grounding considerations that would need to addressed in the above situation? In particular, we are concerned about the grounding issues with the photovoltaic system on the warehouse roof being tied into the adjacent building.
3. Other than grounding issues are there any other code issues that would need to be addressed?
4. Anyone with a similar situation that could share their experience on the matter in regards to the Utility Company or Building Department?

Thanks you for your attention to this matter. Any insight you could provide is greatly appreciated.

 

[jaggedben]

For simplicity's sake, I would physically separate the arrays feeding the separate services, and ground each array to the service it feeds. That is, keep all metal parts attached to each system separate from each other. (I hope the warehouse doesn't have a metal roof that would make this impossible.)

One possible issue... You don't say if the buildings are physically touching each other. If they are not, and you are trenching between them, and you are on the 2008 code, and this is a DC system, you might run into problems with the requirement for an additional grounding electrode where the DC conduit comes down to the ground. If you tried to follow this requirement, you'd then need to tie the new electrode to the GES, presumably the one on that property, and a gnarly discussion could ensure over whether you are violating some part of 250 by tying together GESs on different services. This requirement was only in the 2008 code, and you might want to simply avoid doing it, and point out to the AHJ that it was taken out in 2011. Or take your chances and simply not follow it and see what happens. I think this requirement has been largely ignored in the industry in any case, at least on smaller scale systems.

If the buildings are touching each other, I would just take the shortest conduit route from the warehouse to the other property, for the system that feeds that property, and ground as your AHJ requires, as if it weren't on the other building.

Don't see any showstopper though.

 

[Marvin_Hamon]

I was involved in something like this during a residential install where the person owned two homes next to each other and he wanted part the PV on the "party house" to back feed the main house meter. The two properties were already tied together by a generator in the main house that also backed up the party house.

Since the generator system was already installed we already had access to line and neutral conductors from the main house at the party house. There was also a bonding conductor that bonded the main house grounding electrode system to the party house grounding electrode system making one big system. That seemed to me to be a good idea and I could not find anything in the NEC that prevented it.

The line and neutral conductors from the inverter at the party house were connected to the generator feeders so they had no connection to the party house when the generator was off. There were a couple of automatic transfer switches involved and much complexity but in the end with the generator off the party house inverter was able to backfeed the main house service. It's important to note that nothing interconnected the neutral conductors of the two properties as that would have created two neutral to ground bonds which is not allowed in the code.

My part of this project was designing the control system to lockout the inverter in the party house feeding the main house when the generator in the main house was on. Not a trivial matter I can tell you.