Electrical Code or APS (arizona power service) question

[nscottsdale]

I have an accessory building on my property 2k sqft workshop that has a sub panel with 90 amp breaker and 2-2-2-4 AL MHF going to my main panel at my house.

Arizona Power Service (APS) caps out the max system size you can have if you are going to grid tie. Based on my bills / usage (and a failed Tesla solar purchase) i know max for grid tie allowed by APS is 10.2 kW.

If i place solar panels on my accessory building , and get a 10kw grid tie inverter as part of a DIY permit/install, can I do it all at my accessory building panel - or for some reason must the inverter be on my house next to the meter and main panel? Teh solar will be on that accessory building roof.

Backstory on Tesla was that they don't have a panel fastener to go on my style of accessory building steel roof - they only do standing seam mounts.

Thanks in advance for any tips.

 

[BentleyJ]

I believe the 120% rule applies. Usually the largest grid-tie solar breaker that can be installed in a panel is 20% of the the bus bar rating. If your subpanel is a typical 100A or 125A model then your solar array would be limited to a 20A breaker which should have a maximum of 16A of continuous load. 16A x 240V = 3,840W. If your main panel is 200A then it would support up to 40A of additional solar breakers.

 

[nscottsdale]

That is disappointing. But thanks.

 

[MarkSolar]

You could run high voltage DC from the panels on the barn up to the inverter at the house, that would minimize the size wire you need. You could also run 240v AC but that would require larger wire. If your panel is 200A you could use a 40A breaker to backfeed but only run 32A through it because NEC considers solar a continuous load. That means max inverter output would be 7.7kW. But since you have to run a cable up to the house anyway, it's not much money to install a line side tap which would allow you to run a 10kW inverter, or more if the power company ever changes their mind.

It looks like you have a very large place, it's hard to understand the rationale for such a limitation on solar. Do you know your annual consumption? By us the power company allows us to install 110% of our average consumption.

 

[400bird]

The 120% rule has been slightly miss represented above.
Your main and PV breakers added together can't exceed 120% of the bus bar rating (typically the same as your main breaker rating)

However, you can downsize your main breaker.
This allows you to put a 60 amp PV breaker into a 100 amp panel by downsizing the main to 60 amps (60 + 60 = 120)

To answer your actual question, you can run either DC or AC power up to the main building. If you already have AC out at the workshop, or want AC out at the workshop, that would make the decision for me.

 

[MarkSolar]

However, you can downsize your main breaker.
This allows you to put a 60 amp PV breaker into a 100 amp panel by downsizing the main to 60 amps (60 + 60 = 120)

The subpanel and the service panel in the house would both need to be modified. Assuming it's a 200A panel in the house with a 200A bus, it can only support 40A PV on the bus, but that needs to be downgraded to 32A because of the 125% continuous duty rule. So a 200A main panel typically restricts the inverter to 7.7kW. Some of the newer 200A panels have a 225A bus, that would allow a 70A backfed breaker downsized to 58A for continuous duty. That would allow a 14kW inverter.

 

[400bird]

The subpanel and the service panel in the house would both need to be modified. Assuming it's a 200A panel in the house with a 200A bus, it can only support 40A PV on the bus, but that needs to be downgraded to 32A because of the 125% continuous duty rule. So a 200A main panel typically restricts the inverter to 7.7kW. Some of the newer 200A panels have a 225A bus, that would allow a 70A backfed breaker downsized to 58A for continuous duty. That would allow a 14kW inverter.

Um no, you aren't limited to a 40 amp breaker on a 200 amp panel (at least in the US under NEC)

The derating for continuous load is correct.


My 200 amp panel (200 amp bus bars), with a 150 amp main breaker and 60 amp PV breaker. Is 100% within NEC guidelines and is approved by codes and inspection.
With a 150 amp main, I could go up to a 90 amp PV breaker (150 + 90 = 200 * 1.2)

 

[EZ Generator Switch]

Why not get a separate feed to the back building and keep it stand alone?

 

[nscottsdale]

Yes on off grid - submitted plans to city last week.