Microinverter compatibility vs. # of cells in PV module

[Enginerd]

I'm thinking about adding a third branch to my system. I would be doing most of the work myself, leaving final hookups for a licensed electrician. I'm looking at available microinverters and panels:

• Enphase IQ-7+, compatible with 60 & 72 cell PV modules, max continuous VA 290
• Enphase IQ-7A, compatible with 60, 66 & 72 cell PV modules, max continuous VA 335

I happen to be considering some Q.PEAK DUO BLK-G6+ 335W panels online, with 6 × 20 monocrystalline Q.ANTUM solar half cells. This amounts to 120 half-cells, equivalent to 60 full cells, which should be fine with either the IQ-7+ or the IQ-7A. So far so good.

Then I notice that my existing professionally-installed system mates IQ-7+ microinverters with Q.PEAK DUO BLK ML-G9+380W panels, which have 6 × 22 monocrystalline Q.ANTUM solar half cells... 132 half-cells, equivalent to 66 full cells. Since the panels aren't 60 or 72 cells, they don't seem to be explicitly compatible with my IQ-7+ microinverters.

So the question is, what are the implications of this? Could I be getting 10% more output with properly matched micro-inverters? Are my micro-inverters ignoring 10% of the cells (rated 60 vs. 66 actual)? Would I see a difference if I upgraded my 66 cell panels to the IQ-7A, and pulled the IQ-7+ for my future branch with 60 cell panels?

I will note that my max actual production seems to be a brief 5.2 kW flat spot at high noon, where the system is rated 6.84 kW (18 x 380W panels, half facing SE, half facing SW). This seems suspiciously close to the IQ-7+ max continuous VA cap of 290 (... x 18 = 5.22 kW).

 

[el-guapin]

......So the question is, what are the implications of this? Could I be getting 10% more output with properly matched micro-inverters? Are my micro-inverters ignoring 10% of the cells (rated 60 vs. 66 actual)? Would I see a difference if I upgraded my 66 cell panels to the IQ-7A, and pulled the IQ-7+ for my future branch with 60 cell panels?.......

Do you have ESS? Will you be adding ESS? How much? Should also take into account voltage rise.

 

[charlesj]

Are your first two branches also on Enphase inverters? Do you have Tesla batteries?
Enphase is designed with a 20A circuit breaker, 16A AC production. as their power cable is only 12 ga wire unless they have upgraded it recently.
With that in mind, the IQ7+ can have 13 panels and the IQ7A will have 11 panels. In essence, no matter how you slice it, that 20A branch can only produce
about 3900 Watts. So, since you are limited to that, you may be better off with the 7+and a larger power panel.

 

[Vines]

The number of cells is not something your microinverters care about.

The microinverters need the modules to be within the voltage and amperage ranges allowed, and depending on the inverter size will clip at some number of maximum watts/VA of output.

Since the Module itself is rated at 335W STC / 313W PTC you will lose a small amount of energy with the IQ 7+ and have a small amount of extra inverter capacity if you chose the IQ 7A. Also keep in mind that after 5% loss in combined degradation/soiling, you will be down from 313 to 297W, so likely the 7+ is your value proposition, with better dollars/kWh generated ratio over the life of the system.

To harvest that extra 23W per panel you need ideal azimuth and tilt, and also to keep them clean every year at least. After 10 years of so, it won't matter either way, since degradation will have reduced the panel output to near 290 watts.

 

[Enginerd]

I do have two PW2's... the major system components are listed in my signature block.

I'm really asking about compatibility between a given panel and its microinverter: the number of cells in a panel and the ability of the micro-inverter to manage that. Not concerned about the number of panels in each branch. I have one branch of 10 panels, one branch of 8 panels, and I'm sketching out the third branch with 8 panels.

To harvest that extra 23W per panel you need ideal azimuth and tilt

FYI, I'm laying out the third branch as a ground mount with 2 axis tracking, but I probably won't be getting super high end panels for it.

Since the Module itself is rated at 335W STC / 313W PTC you will lose a small amount of energy with the IQ 7+ and have a small amount of extra inverter capacity if you chose the IQ 7A.

Sorry for the confusion about my current and proposed branches. Currently I have high spec panels. What I'm really trying to understand here is how much I'm leaving on the table with my installed G9 380W panels with the IQ-7+. Seems like a lot (290 VA microinverter cap, 380W panel @ MPP, 290/380=76%, seemingly leaving 24% unused).

The number of cells is not something your microinverters care about.

I'd like to agree, as I'm wondering how the microinverter even knows how many cells are in a panel. I'm pretty sure each panel is only connected to the microinverter with a single positive and a single negative lead. But the documentation is very specific, especially for the IQ-7X. The number of cells even shows up in the model numbers. Isn't there some direct relevance?

IQ-7	IQ7-60-2-US	240 VA max continuous 20A overcurrent protection 48V max DC input	Pairs with most 60-cell/120 half-cell PV modules
IQ-7+	IQ7PLUS-72-2-US	290 VA max continuous 20A overcurrent protection 60V max DC input	Pairs with most 60-cell/120- half-cell and 72-cell/144 half-cell PV modules
IQ-7A	IQ7A-72-2-US	315 VA max continuous 20A overcurrent protection 58V max DC input	Pairs with most 60-cell/120- half-cell and 72-cell/144 half-cell PV modules; however, latest datasheet compatibility: 60-cell, 66-cell and 72-cell PV modules
IQ-7X	IQ7X-96-2-US	349 VA max continuous 20A overcurrent protection 79.5V max DC input	Pairs with 96-cell PV modules

 

[wwhitney]

Presumably Enphase could give you a definitive answer, but I believe the only restriction is that your panel maximum voltage (properly adjusted for minimum temperature conditions) does not exceed the microinverter maximum DC input voltage. The "pairs with" language would just be guidelines for the typical cases.

Cheers, Wayne

 

[Vines]

I do have two PW2's... the major system components are listed in my signature block.

I'm really asking about compatibility between a given panel and its microinverter: the number of cells in a panel and the ability of the micro-inverter to manage that. Not concerned about the number of panels in each branch. I have one branch of 10 panels, one branch of 8 panels, and I'm sketching out the third branch with 8 panels.

The cell counts are related to the voltage and amperage, same as the way they are cut and laid out effects the voltage/amperage relationship. The enphase information was likely created before cut cells were introduced recently, and still applies to 95% or more of the available product.

FYI, I'm laying out the third branch as a ground mount with 2 axis tracking, but I probably won't be getting super high end panels for it.


Sorry for the confusion about my current and proposed branches. Currently I have high spec panels. What I'm really trying to understand here is how much I'm leaving on the table with my installed G9 380W panels with the IQ-7+. Seems like a lot (290 VA microinverter cap, 380W panel @ MPP, 290/380=76%, seemingly leaving 24% unused).
View attachment 735831

Check the link here and understand the exact PTC of your module. While STC is how the panels are rated, this does not reflect any condition on earth. Nowhere will be 1000 watts per square meter while also being 25 degree cell temperature, at least not for very long. It is appropriate to start with the PTC, then take whatever hit for soiling, location, azimuth and angle to understand the actual losses of the module.

I'd like to agree, as I'm wondering how the microinverter even knows how many cells are in a panel. I'm pretty sure each panel is only connected to the microinverter with a single positive and a single negative lead. But the documentation is very specific, especially for the IQ-7X. The number of cells even shows up in the model numbers. Isn't there some direct relevance?

IQ-7	IQ7-60-2-US	240 VA max continuous 20A overcurrent protection 48V max DC input	Pairs with most 60-cell/120 half-cell PV modules
IQ-7+	IQ7PLUS-72-2-US	290 VA max continuous 20A overcurrent protection 60V max DC input	Pairs with most 60-cell/120- half-cell and 72-cell/144 half-cell PV modules
IQ-7A	IQ7A-72-2-US	315 VA max continuous 20A overcurrent protection 58V max DC input	Pairs with most 60-cell/120- half-cell and 72-cell/144 half-cell PV modules; however, latest datasheet compatibility: 60-cell, 66-cell and 72-cell PV modules
IQ-7X	IQ7X-96-2-US	349 VA max continuous 20A overcurrent protection 79.5V max DC input	Pairs with 96-cell PV modules

The inverter sees the voltage and amperage, it doesn't care about the cell count, except that it drives the voltage and amperage.

 

[wwhitney]

There's also an Enphase Module Compatibility Calculator:

https://enphase.com/installers/microinverters/calculator

Cheers, Wayne

 

[Vines]

Oops forgot the link to the PTC data.
Solar Equipment Lists

 

[charlesj]

I do have two PW2's... the major system components are listed in my signature block.

I'm really asking about compatibility between a given panel and its microinverter: the number of cells in a panel and the ability of the micro-inverter to manage that. Not concerned about the number of panels in each branch. I have one branch of 10 panels, one branch of 8 panels, and I'm sketching out the third branch with 8 panels.


FYI, I'm laying out the third branch as a ground mount with 2 axis tracking, but I probably won't be getting super high end panels for it.


Sorry for the confusion about my current and proposed branches. Currently I have high spec panels. What I'm really trying to understand here is how much I'm leaving on the table with my installed G9 380W panels with the IQ-7+. Seems like a lot (290 VA microinverter cap, 380W panel @ MPP, 290/380=76%, seemingly leaving 24% unused).
View attachment 735831

I'd like to agree, as I'm wondering how the microinverter even knows how many cells are in a panel. I'm pretty sure each panel is only connected to the microinverter with a single positive and a single negative lead. But the documentation is very specific, especially for the IQ-7X. The number of cells even shows up in the model numbers. Isn't there some direct relevance?

IQ-7	IQ7-60-2-US	240 VA max continuous 20A overcurrent protection 48V max DC input	Pairs with most 60-cell/120 half-cell PV modules
IQ-7+	IQ7PLUS-72-2-US	290 VA max continuous 20A overcurrent protection 60V max DC input	Pairs with most 60-cell/120- half-cell and 72-cell/144 half-cell PV modules
IQ-7A	IQ7A-72-2-US	315 VA max continuous 20A overcurrent protection 58V max DC input	Pairs with most 60-cell/120- half-cell and 72-cell/144 half-cell PV modules; however, latest datasheet compatibility: 60-cell, 66-cell and 72-cell PV modules
IQ-7X	IQ7X-96-2-US	349 VA max continuous 20A overcurrent protection 79.5V max DC input	Pairs with 96-cell PV modules

I see that the 380W panels and 290W inverter has a 1.3 DC to Ac ratio. That is pretty good. And as explained, time will take a toll on production no matter what. Don't think you will lose out much as in the fall, winter and spring with sun lower on the solar arc, actual solar energy available is lower but with that panel you should be able to generate more over time than with a different setup.
Also note as I mentioned above, no matter which inverter you use, you are limited with the number of panels. 7+ has 13 panel limit, 7X has 12 panel limit and 7A has 11. Overall max output of about 3900W max with each. Higher ratios will serve you better over time.

 

[Will792]

I'd like to agree, as I'm wondering how the microinverter even knows how many cells are in a panel. I'm pretty sure each panel is only connected to the microinverter with a single positive and a single negative lead. But the documentation is very specific, especially for the IQ-7X. The number of cells even shows up in the model numbers. Isn't there some direct relevance?

I think Enphase was trying to oversimplify compatibility of microinverters and since there was a lot commonality for max voltage and current between different models of panels with the same numbers cells it almost worked. Now there are some 60 cell panels that are not compatible with IQ7 because of max voltage being too high. The only way to check compatibility is to use Enphase calculator for given panel and lowest location temperature.

What is missing in Enphase documentation is the description what happens with microinverter if max DC voltage is exceeded. Does it shut down or burns out?

 

[swedge]

Enphase has a white paper which points out that panels seldom and only briefly put out their maximum power. The panel dc rating, if memory serves, is based on full midday sun with the panel exactly facing the sun. So the panel orientation and roof slope conspire to limit the maximum real output. And noon is a moment in time, so for any orientation, the peak output does not last very long. So they argue that in practice undersizing the mircoinverter does not cost very much production.

Check the Enphase website or contact them for advice. Installers and sales people will of course tend to advise the more expensive option, so speak with a technical advisor.