microinverter interconnection

SceneryDriver

Senior Member
Location
New York, NY
Looking for a little advice on a PV system; I'm helping a friend sort through the install proposed by his solar installer. PV is not something I've had much experience with.

Proposed system:
(18) REC REC365AA (2020) Solar panels
(18) ENPHASE IQ7PLUS-72-2-US Inverters

6.57KW DC

A few questions:
1) Any opinions on the recommended panels? They apparently come with a 25yr warranty.

2) Any opinions on the inverters? I've read generally positive opinions on Enphase here, I think.

2) How are micro inverters typically connected to the home's service? I sort of understand AC combiners, I think; pretty much a weatherproof breaker panel that combines the AC outputs of the inverters and sums them into one circuit to be connected to the service, yes? That combiner box is typically located where? The roof, under the array?

3) Whole-house generator was installed with a 200A ATS and 200A service three years ago. The installer was kind enough to leave a j-box in the basement that the service conductors pass through right after they come off the meter outside; they're spliced with 3-position Polaris blocks. The j-box is even labeled "line-side solar tap here." It's line-side of the ATS, so no issue with genny VS inverter interactions. Opinions on line-side taps? He's on the 2020 code - how is the breaker panel for a line side tap treated? Like a service; bond N to G? I know the requirements have changed a lot in recent codes.



Thanks,

SceneryDriver
 

jaggedben

Senior Member
1) REC is what might called top-tier but not premium. Panels are pretty much a commodity and a 25 year warranty is standard. People pay more for LG or Sunpower, but generally being particular about a solar panel brand is kind of like being picky about, say, circuit breaker brands.

2) Enphase is highest quality among inverters, and easiest for electricians without solar expertise to deal with. You wire up the circuits pretty much like anything else you do in premises AC wiring.

3) They're connected pretty much like any other circuit, broadly speaking, notwithstanding the special interconnection rules in 705, and the next item.

4) Still not clear. It's probably legit, and is certainly safe, to treat it completely like an additional service disconnect. The 2020 NEC finally gave more concrete guidance on many aspects (see 705.11) but they still punted the N-G bond question. Your AHJ might have a weird opinion. Some knock-down-drag-out debates have occured here on this forum in the past.
 

SceneryDriver

Senior Member
Location
New York, NY
1) REC is what might called top-tier but not premium. Panels are pretty much a commodity and a 25 year warranty is standard. People pay more for LG or Sunpower, but generally being particular about a solar panel brand is kind of like being picky about, say, circuit breaker brands.

2) Enphase is highest quality among inverters, and easiest for electricians without solar expertise to deal with. You wire up the circuits pretty much like anything else you do in premises AC wiring.

3) They're connected pretty much like any other circuit, broadly speaking, notwithstanding the special interconnection rules in 705, and the next item.

4) Still not clear. It's probably legit, and is certainly safe, to treat it completely like an additional service disconnect. The 2020 NEC finally gave more concrete guidance on many aspects (see 705.11) but they still punted the N-G bond question. Your AHJ might have a weird opinion. Some knock-down-drag-out debates have occured here on this forum in the past.
Don't tell me I'm a breaker snob for liking QO! :)

Re. your #2 answer: does that mean the solar installer will want to being (18) circuits off the roof for the (18) micro inverters? That seams silly. Isn't that what AC combiner boxes look to prevent? Do AC combiners have overcurrent protection? I'll look at 705 tomorrow; my code book is at work.

It sounds like I'll set a panel w/ a 100A main breaker in his basement, and tie into the already-there line side tap. The solar installer can land their circuit(s) there. I assume this also means I have to bring the irreversibly spliced/tapped GEC to the new PV "service" panel, and not just the normal EGC from the ground bar in the ATS?

I remember reading at least one epic thread here debating if a line side tapped PV panel was another "service." Glad to know the NEC is still clear as mud on this. I'll ask the AHJ.



Thanks,

SceneryDriver
 

wwhitney

Senior Member
Location
Berkeley, CA
Re. your #2 answer: does that mean the solar installer will want to being (18) circuits off the roof for the (18) micro inverters? That seams silly. Isn't that what AC combiner boxes look to prevent? Do AC combiners have overcurrent protection? I'll look at 705 tomorrow; my code book is at work.
If you read the datasheet and installation instructions for the inverter part number, the latter says each microinverter has to be protected by a maximum 20A circuit breaker, and the former tells you that the maximum number of inverters on a 240V 20A circuit is 13.

So on the roof, the inverters are wired in parallel, up to 13 to a circuit. Since you have more a bit more than 13, you will need 2 circuits. Those circuits could go from the roof all the way to the interconnection panel. Or you could have an AC combiner box somewhere in between, which would have (2) 20A breakers, and then you'd just need one circuit from there to the interconnection panel..

The AC combiner box is also a convenient place for the Envoy to be connected for monitoring (and where it would have its own breaker). I'm not sure what the restrictions are for placing an AC combiner box, and whether the presence or absence of an Envoy in the box affects that. Of course, you could just connect the Envoy via the interconnection panel.

Hope this helps.

Cheers, Wayne
 

jaggedben

Senior Member
Don't tell me I'm a breaker snob for liking QO! :)

Re. your #2 answer: does that mean the solar installer will want to being (18) circuits off the roof for the (18) micro inverters? That seams silly. Isn't that what AC combiner boxes look to prevent? Do AC combiners have overcurrent protection? I'll look at 705 tomorrow; my code book is at work.

It sounds like I'll set a panel w/ a 100A main breaker in his basement, and tie into the already-there line side tap. The solar installer can land their circuit(s) there. ....
I lost track of that part of your question about where the AC combiner goes. It goes on the ground, for a residence. (Maybe it goes on the roof on a big flat commercial roof, but almost never on a residence). Wayne explained the circuits. The combiner does have overcurrent devices and you don't want those on a residential roof.

Are you doing the line side tap because the solar installer doesn't want to?

You might want to bring the tap to just a fused disconnect. Enphase makes its own combiner with the Envoy already contained, which can be fed from the disco. It avoids your having to worry about selecting a panelboard that satisfies 705, and possibly other AHJ questions. But ask the solar installer what he wants.

I assume this also means I have to bring the irreversibly spliced/tapped GEC to the new PV "service" panel, and not just the normal EGC from the ground bar in the ATS?

I remember reading at least one epic thread here debating if a line side tapped PV panel was another "service."
Yup that part is still somewhat debatable. But read 705.11 when you have your 2020 book handy.

Glad to know the NEC is still clear as mud on this. I'll ask the AHJ.
(y)
 
IF you need a combiner panel anyway, one option may be to, instead of calling it a line side connection, just make another set of conductors (using that existing tap point) and put another main breaker panel per 230.40 exception #2 and connect load side to that.
 

SceneryDriver

Senior Member
Location
New York, NY
If you read the datasheet and installation instructions for the inverter part number, the latter says each microinverter has to be protected by a maximum 20A circuit breaker, and the former tells you that the maximum number of inverters on a 240V 20A circuit is 13.

So on the roof, the inverters are wired in parallel, up to 13 to a circuit. Since you have more a bit more than 13, you will need 2 circuits. Those circuits could go from the roof all the way to the interconnection panel. Or you could have an AC combiner box somewhere in between, which would have (2) 20A breakers, and then you'd just need one circuit from there to the interconnection panel..

The AC combiner box is also a convenient place for the Envoy to be connected for monitoring (and where it would have its own breaker). I'm not sure what the restrictions are for placing an AC combiner box, and whether the presence or absence of an Envoy in the box affects that. Of course, you could just connect the Envoy via the interconnection panel.

Hope this helps.

Cheers, Wayne
Thanks, Wayne. I do lighting and industrial controls, and I'm learning that solar is a very different animal. I'm happy to learn, especially so I don't look like an uninformed bumpkin to my friend :)

Were it my house, I'd place the Envoy at the interconnect breaker panel in the basement. I'm a fan of having as much inside and out of the weather as possible. It sounds like a plausible design to forego an AC combiner on the roof altogether.


SceneryDriver
 

SceneryDriver

Senior Member
Location
New York, NY
I lost track of that part of your question about where the AC combiner goes. It goes on the ground, for a residence. (Maybe it goes on the roof on a big flat commercial roof, but almost never on a residence). Wayne explained the circuits. The combiner does have overcurrent devices and you don't want those on a residential roof.

Are you doing the line side tap because the solar installer doesn't want to?

You might want to bring the tap to just a fused disconnect. Enphase makes its own combiner with the Envoy already contained, which can be fed from the disco. It avoids your having to worry about selecting a panelboard that satisfies 705, and possibly other AHJ questions. But ask the solar installer what he wants.



Yup that part is still somewhat debatable. But read 705.11 when you have your 2020 book handy.



(y)
I suggested using the line side tap because it already exists. The generator install contractor put it in three years ago. Apparently, it's just what they do now, "because people always want to add solar in the future, and it's a mess with the ATS in the mix."

I'll leave any combiner choices to my friend's the solar contractor, and ask what they want for a disco/panel. He just asked me too look at the quote to see what I thought, and to see if the line side tap was correct and usable.


SceneryDriver
 

jaggedben

Senior Member
I suggested using the line side tap because it already exists. The generator install contractor put it in three years ago. Apparently, it's just what they do now, "because people always want to add solar in the future, and it's a mess with the ATS in the mix."

I'll leave any combiner choices to my friend's the solar contractor, and ask what they want for a disco/panel. He just asked me too look at the quote to see what I thought, and to see if the line side tap was correct and usable.


SceneryDriver
Yes in this case your really have to use the line side tap. You can't install the solar where it will interact with the generator. There have been some recent threads on this.
 

GeorgeB

ElectroHydraulics engineer (retired)
Location
Greenville SC
Occupation
Retired
a) Any opinions on the inverters? I've read generally positive opinions on Enphase here, I think.

b) How are micro inverters typically connected to the home's service?
a)I had 4.25kW of solar installed 4 years ago. Installer used Enphase M215 and Renogy panels. I've had no trouble at all. Power was limited by roof available and reasonable panel prices. The 17 panel/inverters were the maximum with the 20A limit.

b) Enphase cable connected the 17 solar panel mounted inverters in parallel. 4 THWN-10 were run in PVC conduit from a roof j-box to a Duke Energy approved 30A disconnect, 3 pole (L1/N/L2 all disconected). 4 THWN-10 were run in PVC conduit to the "meter-main" which had available spaces in addition to the 200A main breaker (house breakers at the end of about 50 ft of feeder). I paid $25 extra for #10 vs the #12 he usually used to keep voltage drop down, an issue I'd read was sometimes a concern.

The same contractor did an installation 2 months later for a friend where there was more roof area; that customer wanted 10 kW. He installed a panel with 3 20A 2 pole breakers, then a 60A disconnect, then wiring to a 50A breaker in the meter-main. He replaced the 200A main with a 175A main.

My friend moved in a year (GREAT job change), but was very happy for the time he owned it. I don't know the buyer nor if it is still running, but ASSUME it is.
 

BandGap1.1eV

Member
Location
East Coast
The micro inverter you list is a 290Wac unit. I will 100% expect this system to clip during normal irradiance days during the summer with that 1.25 DC/AC ratio. Your buddy will kicking himself when his system peaks out at 10am in the morning, realizing he is losing out on power production.
 

GeorgeB

ElectroHydraulics engineer (retired)
Location
Greenville SC
Occupation
Retired
The micro inverter you list is a 290Wac unit. I will 100% expect this system to clip during normal irradiance days during the summer with that 1.25 DC/AC ratio.
I think you mean 190 W ...

In MY case, I'm in South Carolina, 35 degrees latitude ... so optimum mount is around that, optimizing annual production. BUT, my roof is between 50 and 55 degrees, harming summer but enhancing winter ... the first year or so, I watched my panel production numbers frequently and see no clipping even at peak production time.

In general, I 100% agree with you. If the panels were flatter, I would see clipping, and better annual production, But the small improvement wouldn't pay for a custom rack or new home <g>.

Duke was still giving their $1.00/DC Watt incentive which coupled with the Federal tax credit led me to predict a payback of 7-8 years. That still looks good. But, HONESTLY, I installed to shut up the ecological liberals who asked what I was doing to help. (Oh, SC tax credit didn't apply; we're 98% retired, and our SC taxable income is too low for the rebate. I didn't know that, but that's life.)
 

SceneryDriver

Senior Member
Location
New York, NY
The micro inverter you list is a 290Wac unit. I will 100% expect this system to clip during normal irradiance days during the summer with that 1.25 DC/AC ratio. Your buddy will kicking himself when his system peaks out at 10am in the morning, realizing he is losing out on power production.
That inverter will do 290W continuous. The panels are 345W each. That's a 1.19 : 1 DC/AC ratio. My understanding is that the inverter is quite well matched to the panel. He's in SE Wisconsin, and the roof is a bit steeper than optimal for summer production, but good for winter production according to his installer.

Can you recommend another Enphase microinverter that would be a better match to the panels? I've looked at the Enphase ecosystem, and I really like the Envoy system.


SceneryDriver
 
Last edited:
The micro inverter you list is a 290Wac unit. I will 100% expect this system to clip during normal irradiance days during the summer with that 1.25 DC/AC ratio. Your buddy will kicking himself when his system peaks out at 10am in the morning, realizing he is losing out on power production.

That inverter will do 290W continuous. The panels are 345W each. That's a 1.19 : 1 DC/AC ratio. My understanding is that the inverter is quite well matched to the panel. He's in SE Wisconsin, and the roof is a bit steeper than optimal for summer production, but good for winter production according to his installer.

Can you recommend another Enphase microinverter that would be a better match to the panels? I've looked at the Enphase ecosystem, and I really like the Envoy system.


SceneryDriver
I agree 1.2 DC/AC ratio is not necessarily too high. I usually shoot for between 1.1 and 1.2. Clipping is typically more likely in the winter. Many variables of course and hard to make blanket statements.
 

jaggedben

Senior Member
Enphase has an IQ7A inverter that is higher power for 60-cell type modules. It will lessen clipping. It may or may not be cost effective, since real world performance is often around 10% under nameplate. I have some older 255W panels paired with 240W microinverters and my inverters never get to 240W, they top out around 230. I agree that DC/AC up to 1.2 is not a reason to upsize inverters.
 

SceneryDriver

Senior Member
Location
New York, NY
Yes in this case your really have to use the line side tap. You can't install the solar where it will interact with the generator. There have been some recent threads on this.
Since a tap location on the line-side of the ATS exists, my plan is to set a 100A panel in the basement next to the existing panel, and use it for the solar interconnect; the solar installer can connect there. Based on what I've read, they'll need (2) 20A 2P breakers for the inverter circuits, and (1) 15A 2P breaker for the Envoy module. I plan on visiting him in WI this fall to do the work and make sure the solar installer doesn't do a hack job of things, virus permitting of course.

Since this is Schrodinger's breaker panel, and both is and isn't another service at the same time, will I have to run a GEC back to the Ufer ground connection and irreversibly splice there? I'm told there's apparently a ground bar in the j-box where the line-side tap is intended to go. Can I grab the ground wire there? I was planning on removing the green screw in the new panel. Thoughts? Ask the AHJ?


Thanks,

SceneryDriver
 

jaggedben

Senior Member
Since a tap location on the line-side of the ATS exists, my plan is to set a 100A panel in the basement next to the existing panel, and use it for the solar interconnect; the solar installer can connect there. Based on what I've read, they'll need (2) 20A 2P breakers for the inverter circuits, and (1) 15A 2P breaker for the Envoy module. I plan on visiting him in WI this fall to do the work and make sure the solar installer doesn't do a hack job of things, virus permitting of course.

Since this is Schrodinger's breaker panel, and both is and isn't another service at the same time, will I have to run a GEC back to the Ufer ground connection and irreversibly splice there? I'm told there's apparently a ground bar in the j-box where the line-side tap is intended to go. Can I grab the ground wire there? I was planning on removing the green screw in the new panel. Thoughts? Ask the AHJ?


Thanks,

SceneryDriver
Ask the AHJ on the grounding. This is one of those still unanswered questions. Propose the way you'd like to do it and have a reason in your head as to why.

Keep in mind that the NEC allows other grounding methods for multiple service disconnects besides a tap to each one. So part of the answer depends on where the GEC connection is currently made.
 

SceneryDriver

Senior Member
Location
New York, NY
Ask the AHJ on the grounding. This is one of those still unanswered questions. Propose the way you'd like to do it and have a reason in your head as to why.

Keep in mind that the NEC allows other grounding methods for multiple service disconnects besides a tap to each one. So part of the answer depends on where the GEC connection is currently made.
The house has a Ufer ground, and the GEC runs to the ATS; neutral and ground are bonded there. It was a bare #4 that came out of the slab and ran into the bottom of the panel. It was re-routed and extended with an irreversible splice and lands in the ATS now.

The breaker panel was rewired to serve as a subpanel with neutrals and grounds separate when the ATS was installed. There's also a #4 that runs to the cold water line from the ground bar in the ATS; I'm not counting that as a grounding electrode since the Ufer exists.

I really want to get the ground from the ground bar that exists in the line-side tap j-box, since it's easier. I'll ask the AHJ what they want to see if solar ends up getting installed.


SceneryDriver
 
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