How to combine AC strings from the microinverters?

[jkonzelman]

Ok so I am far along on designing my 10kW system and all is comnig together nicely.

I plan to have 4 strings of 200W panels, 12 panels per string. I will be using microinverters so all will be producing 240 VAC at 0.9 amps.

I was planning on combining all the strings into on before sending it on the house panel box. Can I simply use a regular subpanel since the current is AC?

I was thinking of 4 curcuits each on a 15 amp breaker, so a 60 amp subpanel box sholuld work? and just send the output to the house and hook it up to a 60 amp breaker in the house panel.

am I missing something, or is it that eazy?

thanks in advance!

Jim

[Sunking]

Ok so I am far along on designing my 10kW system and all is comnig together nicely.

I plan to have 4 strings of 200W panels, 12 panels per string. I will be using microinverters so all will be producing 240 VAC at 0.9 amps.

I was planning on combining all the strings into on before sending it on the house panel box. Can I simply use a regular subpanel since the current is AC?

I was thinking of 4 curcuits each on a 15 amp breaker, so a 60 amp subpanel box sholuld work? and just send the output to the house and hook it up to a 60 amp breaker in the house panel.

am I missing something, or is it that eazy?

thanks in advance!

Jim

Huh? You plan to use micro-inverters right? You will not have any strings.

1 Panel = 1 Micro-inverter.

10000- watts / 200 watts-panel = 50 panels and 50 Micro-Inverters.

Back to the drawing boards. You failed your test.

[billvon]

Ok so I am far along on designing my 10kW system and all is comnig together nicely.

I plan to have 4 strings of 200W panels, 12 panels per string. I will be using microinverters so all will be producing 240 VAC at 0.9 amps.

I was planning on combining all the strings into on before sending it on the house panel box. Can I simply use a regular subpanel since the current is AC?

I was thinking of 4 curcuits each on a 15 amp breaker, so a 60 amp subpanel box sholuld work? and just send the output to the house and hook it up to a 60 amp breaker in the house panel.

am I missing something, or is it that eazy?

Pretty much. The Enphase AC interconnect cable can handle up to 14 inverters per string. The Enphase manual shows a very similar arrangement with 15A breakers; that's a good reference. (Dual 240VAC breakers for each string of course.)

[jkonzelman]

OucH!!!!

Huh? You plan to use micro-inverters right? You will not have any strings.

1 Panel = 1 Micro-inverter.

10000- watts / 200 watts-panel = 50 panels and 50 Micro-Inverters.

Back to the drawing boards. You failed your test.

FAILED !

Ok so maybe Im not up on the vernacular, but 12 panels with microinverters on the same trunk line
each panel is a schott poly 235, I expect them to produce ~ 200W so I rounded. whatever 96% of 212 is (output reported by schott)
48 panels, at 200W ( rounded on average) = 9600 W, so rounded to 10 kW
obviously I am not an engineer ( no attention to the minute details, just big picture kind of guy)

so I will have four trunk lines, each with 12 panels of approx 200 w and approx 1 amp each
so each line gets a 15 amp breaker, so hooking it up to a 60 Amp DC subpanel seems like a good option. I might actually go to an 80 Amp one so I can hook up the communications device from the same panel.

[jkonzelman]

Thanks!

Pretty much. The Enphase AC interconnect cable can handle up to 14 inverters per string. The Enphase manual shows a very similar arrangement with 15A breakers; that's a good reference. (Dual 240VAC breakers for each string of course.)

Thanks billvon, I appreciate the support! I guess I need to get one of the manuals soon!

[inetdog]

I was thinking of 4 curcuits each on a 15 amp breaker, so a 60 amp subpanel box sholuld work? and just send the output to the house and hook it up to a 60 amp breaker in the house panel.
am I missing something, or is it that eazy?
thanks in advance!
Jim

Just how, if at all, does the 120% rule apply in this situation? Does there have to be a main breaker in the subpanel? Would the subpanel busbar have to be rated at least 100A?

[Naptown]

So far everyone here is wrong.
enphase M190's you can put up to 15 on a circuit
enphase M215 you can put up to 17 on a circuit

So yes you can use the sub panel arrangement.
divide the panels by as close as you can get to the number of modules you will have not exceeding the # of modules you will have on each circuit. If you have 50 modules you could use 17,17,16 with the M215. total of 3 20A circuits
The M190 will require another circuit. Total of 4 15A circuits.

[Sunking]

So far everyone here is wrong.

My bad Rich. I misread the OP. I thought he was going to put a string of panels onto a single inverter.

[Naptown]

Just how, if at all, does the 120% rule apply in this situation? Does there have to be a main breaker in the subpanel? Would the subpanel busbar have to be rated at least 100A?

the 125% rule applies from the sub panel to the main panel for wire size as this is considered a continuous load.
No additional overcurrent protection is required at that point it will be handled at the main panel.
The 120% rule would apply if he is backfeeding a panel through a breaker.
If he has a 200A service he will be forced to do a line tap connection which means the connection will be between the meter and the main circuit breaker and not on the buss bars. this will also require an additional disconnect near the main panel so all the services can be turned off at the same location.
We generally put the sub panel out by the meter for utility requirements and a separate breaker or fused disconnect enclosure next to the panel.

[Naptown]

My bad Rich. I misread the OP. I thought he was going to put a string of panels onto a single inverter.

It is somewhat confusing as a circuit of enphase inverters is commonly called a string even though they are in parallel

[Sunking]

It is somewhat confusing as a circuit of enphase inverters is commonly called a string even though they are in parallel

Yeah well you know I am not much of a GTI designer or a big fan of Enphase. But I am learning and warming up to Micro-Inverters. Economics are looking better for Micros.

[jkonzelman]

Ouch again!

So far everyone here is wrong.
enphase M190's you can put up to 15 on a circuit
enphase M215 you can put up to 17 on a circuit

So yes you can use the sub panel arrangement.
divide the panels by as close as you can get to the number of modules you will have not exceeding the # of modules you will have on each circuit. If you have 50 modules you could use 17,17,16 with the M215. total of 3 20A circuits
The M190 will require another circuit. Total of 4 15A circuits.

We are all wrong! boy you guys are tough!

I do plan to use the enphase M215, and yes you can have up to 17 panels on each trunk line, but for optimal mounting purposes, I plan to have 2 separate racks, each 4 x 6 = 24 per rack, total of 48 panels. Since enphase recomends tapping into the trunk line at the middle, rather than three 'strings", I was planning on four, each with 12 panels, and have six on each side of the wire going to the subpanel, less voltage loss this way I think. Each trunk line will run the full lenght of the rack, and then I can tie two together right on the end, before going to the subpanel. and I dont have to bother with connecting one set of panels on one rack to the other rack a few feet away. so it will be nice an symmetric, and I love symmetry.

Thanks for the discussion! I sure hope I am not wrong, and I certainly don't want to fail another test.

Jim

[Naptown]

We are all wrong! boy you guys are tough!

I do plan to use the enphase M215, and yes you can have up to 17 panels on each trunk line, but for optimal mounting purposes, I plan to have 2 separate racks, each 4 x 6 = 24 per rack, total of 48 panels. Since enphase recomends tapping into the trunk line at the middle, rather than three 'strings", I was planning on four, each with 12 panels, and have six on each side of the wire going to the subpanel, less voltage loss this way I think. Each trunk line will run the full lenght of the rack, and then I can tie two together right on the end, before going to the subpanel. and I dont have to bother with connecting one set of panels on one rack to the other rack a few feet away. so it will be nice an symmetric, and I love symmetry.

Thanks for the discussion! I sure hope I am not wrong, and I certainly don't want to fail another test.

Jim

Line losses wont be much either way but I agree with the way you are doing it.
The big advantages to how you are doing it are you aren't wasting connections on the Engage cable and the communications with the Envoy will be better (This is really sensitive to cable length)

[jkonzelman]

line tap? uh owh!

the 125% rule applies from the sub panel to the main panel for wire size as this is considered a continuous load.
No additional overcurrent protection is required at that point it will be handled at the main panel.
The 120% rule would apply if he is backfeeding a panel through a breaker.
If he has a 200A service he will be forced to do a line tap connection which means the connection will be between the meter and the main circuit breaker and not on the buss bars. this will also require an additional disconnect near the main panel so all the services can be turned off at the same location.
We generally put the sub panel out by the meter for utility requirements and a separate breaker or fused disconnect enclosure next to the panel.

Rich,

I was planning on feeding the solar array through the main service panel, you mention that I will be forced to do a line tap. I have no idea what that means

or why it would be necessary. would you mind elaborating a bit more?

My local power compnay requires that I install a manual disconnect "lever" style within 8 feet of the meter. so I was planning on running from the subpanel at the solar array, to the disconnect, then on to the main service panel.

Jim

[jkonzelman]

Glad to have some valildation!

Line losses wont be much either way but I agree with the way you are doing it.
The big advantages to how you are doing it are you aren't wasting connections on the Engage cable and the communications with the Envoy will be better (This is really sensitive to cable length)

Thanks! that is good news, to hear that you think it will work!