Adding Storage and MID to Existing Solar PV System

S

solarken

NABCEP PVIP
Location
Hudson, OH, USA
Occupation
Solar Design and Installation Professional
I am adding SolarEdge batteries and Backup Interface (BUI, a Microgrid Interconnection Device (MID)) to an existing SolarEdge PV System and would like help clarifying a few things. The existing system has a 200A meter-main on the outside of an outbuilding, and the meter-main has a 100A breaker in it that feeds a subpanel inside the outbuilding, and the feed-thru lugs in the meter main feed an underground feeder to the main home about 100ft away, via 4/0 XHHW for L1 and L2 and I believe 2/0 Neutral. There is no EGC with the feeder to the house. There is a 200A loadcenter in the home. The breaker in the meter-main was downsized to 150A and a 60A backfed PV breaker was added in the initial PV installation. The inverter is inside the outbuilding.

I am planning on installing the SolarEdge batteries and the BUI inside the outbuilding, removing the house feeder connection from the feed thru lugs, and feeding the main breaker of the BUI from the feed-thru lugs of the meter main. I will run 4/0 AL XHHW from the lugs to the BUI, with a 2/0 AL Neutral and #4 copper EGC. I plan on removing the PV breaker from the meter main and relocating the connection to the PV breaker in the BUI. I plan on pulling the disconnected house feeder into a junction box inside the outbuilding, and extending the conductors to the load terminals on the BUI.

My first question concerns the 4/0 aluminum conductors, and whether there is any violation concerning ampacity, and if 310.12 permitting 83% covers the above approach and allows 4/0 AL for the 200A. I would think this is ok, especially since the main braker in the meter main was downsized to 150A.

One issue I have with the above is that the outbuilding that will house the batteries would not have power in an outage, since the 100A subpanel is fed upstream from the meter-main, before the BUI. In Ohio, our winters can get cold, so I am thinking it might be better to replace the 100A subpanel in the outbuilding with a 200A subpanel, and feed it from the BUI load terminals, and feed the house from feed-thru terminals in this new subpanel, so everything is backed up. This would permit a small heater to be powered in the battery room during a grid outage if needed.

Is there any issue if this 200A subpanel were added, again in regards to ampacity and 310.12? And since the downsizing of the meter-main breaker from 200A to 150A was done to accommodate the PV breaker and that is no longer needed, any issue with putting back in the original 200A main breaker?

I am also going to try (finally) to use a generator connected to the generator input on the BUI. Hopefully it will work.

Your feedback and suggestions are appreciated.
 
I think the success of the installation will hinge on how much of the big loads in the home are propane or natural gas. Even if you have 2 or 3 batteries, they won't last long if they have electric heat and you are trying to heat the home with battery power. My other concern is your plan to utilize the BUI's generator input terminals. I don't think they ever really got the generator support firmware ready for primetime. We tried that once, and it did not go well. I don't think the 4/0 AL wire will be an issue. The inspectors around here would not look twice at that.
 
PWDickerson said:
I think the success of the installation will hinge on how much of the big loads in the home are propane or natural gas. Even if you have 2 or 3 batteries, they won't last long if they have electric heat and you are trying to heat the home with battery power. My other concern is your plan to utilize the BUI's generator input terminals. I don't think they ever really got the generator support firmware ready for primetime. We tried that once, and it did not go well. I don't think the 4/0 AL wire will be an issue. The inspectors around here would not look twice at that.
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Thanks for response. There should not be any issues with the load. In the 2 years since I installed the solar PV system, I have never seen usage exceed 8kW, and that was brief. Generally, they use between 2 and 6 kW.
How long ago did you try the generator connection to the BUI? And can you elaborate on the issues you experienced?
 
There is no code issue with adding the 200A panel on the load side of the BUI to combine the load. But options for single phase panels that accept 200A branch breakers are limited, so either do your homework and order ahead of time or do the load calc to justify putting the home on a 125A breaker.

IMO you should not have any issues with 310.12 for the feeder to the home because it's a feeder for a dwelling. The outbuilding gives me pause regarding whether you have an issue with the service. If the installation was considered to be compliant under 310.12 beforehand, then it should still be compliant afterward, because in no case is a feeder required to be larger than the service conductors would be under 310.12. However if the outbuilding plus home means the service isn't supposed to use 310.12 then perhaps you have a problem, technically. A lot of AHJs don't seem to really know about 310.12 so unless you get 'that guy' for your inspector I would do a load calc to justify a 175A breaker, to make sure I have a backup plan. From what you've told us about the load it's obviously not a real-world issue.

That missing EGC to the house concerns me a bit more. Saftey-wise I'd just bond and ground at the house like was allowed 30 years ago, but inspection wise...
 
jaggedben said:
There is no code issue with adding the 200A panel on the load side of the BUI to combine the load. But options for single phase panels that accept 200A branch breakers are limited, so either do your homework and order ahead of time or do the load calc to justify putting the home on a 125A breaker.
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I was not going to use a branch breaker, just feeding the House from feed-thru lugs in teh new 200A Load Center. The plan is:

Grid - 150A MeterMain Breaker - MeterMain Feed Thru Lugs - SolarEdge BUI 200A Supply Breaker - BUI Load Terminals - New 200A Outbuilding Load Center - Outbuilding Load Center Feed-thru Lugs - Feeder to House 200A Load Center. Customer may want to replace the 150A MeterMain Breaker with the original 200A breaker from before the Solar Install.
 
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