Adding solar array/system to outbuilding with (subpanel)400 ft from main panel/and array/system

[pretzelboy]

Hi all,

I currently have a home with a functioning but inadequate roof mounted grid tied 4.2 kw system.

I have an outbuilding that is 200 ft from main house and is fed by a subpanel with underground wiring from a 60 amp breaker in the main.

The subpanel itself 100 amps (main breaker that it came with), its draw is limited by the 60 amp breaker in house/main panel

Feeder cable is 1-1-1

I would like to add a complete array/system to this barn roof (which has excellent unobstructed sunlight) that would feed into the subpanel.
no battery just grid tied but feeding (back) to the main house/panel.

Is this possible? practical? could someone give advice on methods for interconnect-I've read that AC powerline/trunk (after the inverter/microinverters) you would wire into a smaller breaker on the panel ( which sounds...weird) wouldnt you wire directly into the sub panel's main breaker sharing with the feeder cable from house?

Also if someone could explain any limitations so I can size the system correctly

Thx
G

 

[Hedges]

You should be able to just install a microinverter system or string inverter system. If everything is grid tied, no off-grid or battery backup operation, it is pretty simple.

You are supposed to comply with 120% rule for any breaker panels that also have PV backfeeding them. Not hard to do when 10)A panel is fed by 60A breaker. Have to consider busbar and main breaker in panel that contains 60A breaker, and the 60A breaker ought to be at far end of busbar away from main breaker. It would comply with 120% rule if 200A busbar and 175A main breaker, or 225A busbar and 200A main breaker.

 

[pretzelboy]

You should be able to just install a microinverter system or string inverter system. If everything is grid tied, no off-grid or battery backup operation, it is pretty simple.

You are supposed to comply with 120% rule for any breaker panels that also have PV backfeeding them. Not hard to do when 10)A panel is fed by 60A breaker. Have to consider busbar and main breaker in panel that contains 60A breaker, and the 60A breaker ought to be at far end of busbar away from main breaker. It would comply with 120% rule if 200A busbar and 175A main breaker, or 225A busbar and 200A main breaker.

Hi

I think I'm following - my main panel at house is 100 amp (I know but small house no HVAC, etc)
the current 4.2 kw roof system with inverter feeds into that panel along with the drop from main utility.
60 amp breaker to 111 cable 200 ft undrground, to subpanel with 100 amp main (and busbars id assume)

I saw this (from you) back in november
...But also not uncommon to have a breaker (main or the branch feeding from upstream panel) larger than panel rating.
e.g. a 60A panel allowed 72A by 120% rule, if fed with 50A breaker, could have 22A PV breaker (round down to 20A which is available). 80% of rating for continuous current, 16A from inverter at 240V is 3.8kW inverter allowed.

So given that additional info i would likely wire the infeed (AC) from the new array to a 20 amp breaker on the oppoiste end of the busbar from the subpanels main breaker?

and my limitation on the solar array is approx 3.8 kw?

Thanks again, G

 

[Hedges]

Hi

I think I'm following - my main panel at house is 100 amp (I know but small house no HVAC, etc)
the current 4.2 kw roof system with inverter feeds into that panel along with the drop from main utility.


and my limitation on the solar array is approx 3.8 kw?

Sounds like you already have 4.2 kW on a panel limited to 3.8 kW by 120% rule (assuming 100A busbar, 100A main breaker.)

Line side tap, replace panel with higher amperage, or add a main breaker only panel fed by meter, branching out to a fused disconnect for existing PV system, also to existing main panel (which then feeds outbuilding.) Could feed outbuilding from the same fan-out, but I think OCP required at near end for long run, if wires limited to 60A ampacity.

You can probably fit a lot of panels on the outbuilding/barn?
Replacing both panels with 200A but small main breakers might be good.

 

[pretzelboy]

Sh*t you completely lost me there... sorry

could I do what I described? Im trying to add solar capacity without scrapping/replacing my house array
I also would like to avoid the 3K expense of putting a new 200 amp main service panel in.

10 or so 300 watt solar panels on the barn would likely get me back to zero utility bills again (the 4.2 system on house roof was only adequate when brand new and home was used part time)

 

[Hedges]

What is main panel breaker amperage? Busbar amperage? How many kW of PV already feeding that panel? (sounds to me like slight above NEC limits already, not that I'm terribly worried.)

A sketch with meter, panels, breaker ratings, wire gauge would make it visual.

 

[pretzelboy]

Main panel is 40 yr old square D 100 amp panel (100 amp main breaker) dont know the busbar amperage
4.2 kw somewhat age degraded 13 yr old solar array that after inverter and pv breaker feeds into main breaker right next to/with utility feed from meter.
panel has (4) 15 amp breakers (2) 30 amp breakers (hot water and electric stove)
60 amp breaker added that goes to 100 amp sub panel in barn 200 ft from house/main panel.

sub panel has 100 amp main breaker (used only as a disconnect) and (2) 20 amp breakers for lights/hand tools in use.

So if im vioolating the 120% rule because of the PV load to main house panel, I cant put an additional 3-4 KW of panels on the barn and feed the inverted AC output to a breaker in that panel?

Probably going to just need to bite the bullet and upgrade my panel for the 21st century needs (car, eventual heat pump)

Again im sorry if I'm slow but Im learning hard

 

[Hedges]

The Square D panels I'm familiar with that have a main breaker are 125A panels, and breaker can be 125A, 100A, or 70A. (There are smaller panels with 6 or 8 slots for branch breakers that are 100A.)

125A x 120% = 150A
150A - 100A main breaker = 50A backfed PV breaker allowed.
50A x 80% = 40A continuous. 40A x 240V = 9600W allowed.

That panel could support two, 4800A systems or some other split.
But 60A breaker feeding remote sub-panel would not be allowed to backfeed. (Unless the rules now use the rating of PV breaker in remote panels instead?)

What gauge wire does the 60A breaker feed?
I'm wondering if 60A breaker could be changed to 50A, and it could feed remote panel and a breaker for the 4.2 kW system. (That would have 50A breaker + 25A breaker both able to supply current to the wire.)

Got it: 50A breaker feeds a (125A busbar) panel with 50A (or 60A) breaker going to sub panel, and a 25A breaker for 4.2 kW system. Then you can have up to 5.4kW on the remote panel.

Assuming your existing main panel has 125A busbar.

 

[timselectric]

and pv breaker feeds into main breaker right next to/with utility feed from meter.

This doesn't sound like the PV breaker is at the opposite end of the bus bar, from the main breaker.
Unless I am reading it wrong.
Also, if you turn your sub panel breaker into a PV backfeed. It must also be at the opposite end.

This is in addition to the information provided above.

 

[teal95]

At 200' your 1-1-1 cable (if copper) is good for 100 amps. (I know this because that's basically what I have.)

I would plan on replacing your house breaker box with a 200 amp panel.

I have a SolArk 15k in my barn with 20kW of panels on the roof (poorly aimed as the peak is N-S so will probably never even make 15 kW) that feeds a panel in the barn that then feeds through a 100 amp breaker to a critical loads panel in the house.

 

[pretzelboy]

I will have to get back to you tomorrow to confirm, but I believe the PV AC feed that enters my main panel seems to be coming in the "top" of the 100 amp Square D panel along with and alongside the main feed from the utility after the meter. There are those insulated multitap connectors that allow 2 wires into 1 (PV and utility) that then go to the 100 amp main breaker. I never noticed but I'm guessing that the original solar install in 2010 has a separate PV breaker upstream from the main panel? All was done to by installer to code and inspected back in 2010 (NY state)

Anyhow, my comment on the 20 amp PV breaker (or 25 as you suggested) at the barn subpanel would be literally at the opposite end of the panel from the main breaker. That breaker is currently the 100 amp that came preinstalled.

So I change out the 60 amp breaker (to a 50 amp) in the main panel, that feeds the 1-1-1 (aluminum not copper) direct burial cable to my barn subpanel. I swap out the 100 amp main breaker on that subpanel for a 50 or 60 amp main breaker.

My solar array there for back feed would be limited to no more that 5400 watts, and 20 or 25 amps (depending on the PV breaker installed at opposite end of the panel bus from the main).

Appreciate the continued feedback on this exercise. I am thinking of saving and shopping for a reasonable 200 amp panel installation

 

[Hedges]

Sounds like a "Line side tap". Maybe something like Polaris. Do you find breakers between that and the inverter?

In this case,
1) Confirm this is a 125A Square D panel with 100A main breaker.
2) Change 60A breaker to 50A and relocate to far end of busbar away from main breaker.
3) Use up to 50A PV breaker in sub-panel, and up to 9600W of PV.

Pretty much what you said. Except no PV feeding main panel yet, so more could be added at sub-panel. Unless utility objects to so much, don't know the policy on having line side tap plus regular.

Don't think there is any need to change 100A breaker on sub panel to anything smaller. Is that a regular main breaker, or a backfed branch breaker? I think the main breakers are 70A, 100A, 125A. But if it is a smaller 6 or 8 slot panel then it might use branch breaker as main breaker. And has lower amperage busbar.


Alternatively, put a hybrid before the sub-panel and it can provide battery or batteryless backup to that panel.

 

[zanydroid]

This is way too complicated for me to follow/engage with efficiently without at least one schematic or picture. Preferably multiple.

Starting from the MSP down and showing all breaker positions.

 

[pretzelboy]

Tomorrow:
Will confirm if main house panel is 125amp busbar (definitely 100amp main breaker)
Will confirm separate PV breaker in line after inverter, before "side tap" into house/main panel

60 amp breaker feeding cable to the barn is currently at last "bottom" of main panel bus location/slot, with 100 amp main at "top"

100 amp Square D panel (subpanel) at barn is a regular 100 amp "main" breaker (preinstalled) service panel.

have only 3 breakers currently on subpanel: (2) 20 amp for lights and one 50 amp for a 14-50 NEMA outlet

I'll try and upload a photo or two

Cheers and goodnight - G

 

[Hedges]

I currently have a home with a functioning but inadequate roof mounted grid tied 4.2 kw system.

By the way, depending on available roof orientations, you might be able to increase PV panel wattage of that array 40% or so for increased kWh/day, within its 4.2kW limit.

Describe that system, inverter, PV panels, series/parallel arrangement so we can determine what could be added. Also roof slopes and orientations.

 

[pretzelboy]

Good evening,

Ive had a chance to take some photos and draw a diagram that looks like an 8 year old did it ( sorry )

I think you will see that the solar array feeds into a 50 amp breaker at bottom right of main service panel- I earlier noted the two wires that also went to the polaris couplers at the top with the feed from the utility/meter.

I did notice that this is a QO series panel and that those breakers are only rated at 80% That might be an issue, and the final straw of upgrading the panel, which is also full.

Thx- G

 

[zanydroid]

Good evening,

Ive had a chance to take some photos and draw a diagram that looks like an 8 year old did it ( sorry )

I think you will see that the solar array feeds into a 50 amp breaker at bottom right of main service panel- I earlier noted the two wires that also went to the polaris couplers at the top with the feed from the utility/meter.

I did notice that this is a QO series panel and that those breakers are only rated at 80% That might be an issue, and the final straw of upgrading the panel, which is also full.

Thx- G

OK with the solar coming in from the top as a line side tap, there is no extra load on the 100A busbar from that one. We can simply look at the contribution from the new solar. If you feed from the bottom, you can do 100 * 1.2 - 100 = 20A (adjust up if it's actually 125A), without derating the main. So 3.8kW. That main panel is in an unfinished wall so replacing it or moving out all the breakers should be easier than for recessed panel in siding or in drywall.

If you move ALL breakers out of the main panel to a new 200A or 225A subpanel, and feed only the 200A subpanel from a 100A breaker on the main panel, you can backfeed 100A. This is less neat than replacing main panel with 200A or 225A panel, but it can be DIY'ed a bit at a time instead of hiring out. Unless you are allowed to pull meter yourself and do main panel swaps at your leisure. If you are swapping main panel spring for a 225A for max flexibility.

Barn subpanel at 60A feeder breaker can easily handle up to 60A of backfeed breakers even with 100A busbar.

What do you mean by 80% rating? How is that different from normal breakers?

 

[pretzelboy]

I read that the qo series breakers (an older style of plug on breakers) rated at 80 percent not 100 like other types.

 

[zanydroid]

I read that the qo series breakers (an older style of plug on breakers) rated at 80 percent not 100 like other types.

There are fanboys that say QO is the most robust ?. QO "scales up" to more high end use cases than Homeline.

80% should be normal. IIRC it means if you load it for more than 3 hours it can only carry 80% of the rating.

Very few people are using 100% breakers here. They're more expensive too and probably not available for any of the residential brands (or in residential breaker sizes)

 

[timselectric]

I don't use Homeline , ever.
If I purchase Square D , it's only QO.

And yes, the 80% rule is for all breakers. When they are used for a "continuous load". (3 or more hour duty cycle)