4 Advice to Choose a 144 Cell Solar Panel

I am matching panels and invert to maximize utilization. please help
I am limited to 25 panel of similar size.

the decision is between Lumina1 SS9-72HD 535 panel vs Philadelphia 144-550w panel.
the inverter of interest is the SRNE-HESP thanks to @42OhmsPA guidance.

the specs are below with my newbie calculation (adjusting for low temp of -3C for my location.)
Please comment on:
1/ 72 cells vs 144 cells panel type in general and which panels would you choose .
2/ temperature calculation
3/ string and system sizing
4/ anything helpful.

thank you

Panels comparison
STDLumina I
SS8-72HD -535w bifacialPhiladelphia M144

550W-bifacialMax Power Pmax535 w 550 wVoc49..25Vmp41..19Short-circuit Isc13..69Max power current Imp12..05module eff20.71%21.3% NMOTMax Power Pmax404wVoc46.30Vmp38.80Short-circuit Isc11.05Max power current Imp10.43Open vol temp coef Voc-0.265%/C-0.22Power temp coef PMP-0.334-0.35NOCT+/-2

SRNE inverter model HESPu

Number of MPPT2'Max PV inputw/w'Max. input current25Amp + 25Amp'Max Voc550Vdc + 550 Vdc'MPPT vol range125-450Vdc/125-450Vdc'
Coldest temp in my area is -3C.
Low temp adjusted calculations and string sizing

Lumina I
SS8-72HD -535w bifacialPhiladelphia M144
550W-bifaciallow temperature adjusted56.11 v per panel55.42 v each2 strings of 6 per MPPT
336.6 V ' 27.56Amp amp over limit of 25332 V -27.4 Amp
amp over limit of 252 strings of 6 =12 modules in each MPPT12x535w = w12x550w = wtotal system: 24 modules in 4 strings W W I don't think you can go wrong with either panel choice.

Personally I would go with the Philadelphia solar since they are slightly more efficient being 144 cell.

6S2P per MPPT is the best option for 24 panels, you've already figured that out.

I wouldn't have any concerns being slightly over the "max" current input. In ideal conditions you will lose out on a little bit of power but it will be negligible in the grand scheme of things.
My MPPTs are W 22A limit.
Here's what happens you hit the max.

...nothing, the MPPT just stops taking power in.


Your math looks good to me, nice well laid out post too.


I'm sure some others will chime in soon enough. I haven't double-checked the math, but 6s2p could be 6s oriented SE or SSE and the other 6s oriented SW or SSW. Then likely no clipping at all.
It will reduce depth of cycle of battery, charges earlier in the day an keeps charged later.

Looks like from your figures, only standard test conditions might exceed 25A. NMOT does not.
is 25A max operating current, or max allowed short-circuit current? The data sheets I've found are for different model and don't clarify that.

On the other hand, if you have NEM 2.0 reservation with PG&E, then you may want to favor late afternoon production. But maybe not, since although price is 1.5x or 2x as high, production is reduced when not due South.

Panels are cheap. Batteries are more expensive, unless DIY. So I recommend over-paneling.

25 panels fit? So roof mount? I guess you will have 24 panels as 2x 6s2p.
I see the pallet of 31 is same price as 26 individual panels (It is recommended to buy a couple extra in case broken in shipping or installation.)
Not knowing how they differ, it would seem $ less is the way to go. About 3% less STC wattage rating, only 1.5% less CEC PTC rating.

If you do have 2 strings of different orientations, you may be able to parallel another 6 if you can fit them somewhere. Like vertical on a fence?

I haven't double-checked the math, but 6s2p could be 6s oriented SE or SSE and the other 6s oriented SW or SSW. Then likely no clipping at all.
It will reduce depth of cycle of battery, charges earlier in the day an keeps charged later.

Looks like from your figures, only standard test conditions might exceed 25A. NMOT does not.
is 25A max operating current, or max allowed short-circuit current? The data sheets I've found are for different model and don't clarify that.

On the other hand, if you have NEM 2.0 reservation with PG&E, then you may want to favor late afternoon production. But maybe not, since although price is 1.5x or 2x as high, production is reduced when not due South.

Panels are cheap. Batteries are more expensive, unless DIY. So I recommend over-paneling.

25 panels fit? So roof mount? I guess you will have 24 panels as 2x 6s2p.
I see the pallet of 31 is same price as 26 individual panels (It is recommended to buy a couple extra in case broken in shipping or installation.)
Not knowing how they differ, it would seem $ less is the way to go. About 3% less STC wattage rating, only 1.5% less CEC PTC rating.

If you do have 2 strings of different orientations, you may be able to parallel another 6 if you can fit them somewhere. Like vertical on a fence?

@Hedges
thank you for pointing out the the lumina is 144 cells.
Thankyou both Hedges and 42OhmsPA for commenting. I agree that 144 cell (or half cut in general) is a good safe choice. I think it's more likely to hedge against a newbie design error, than it is to confuse an MPPT. Depending on when your main power usage is, it may not really matter (IE if you mostly want to chop summer loads back, you're probably massively overproducing anyway so the half cut giving you an extra 30 min of low angle production, and 0.5% efficiency boost, isn't that much $)

I would recommend holding off on buying the inverter until you have the full inverter + battery approvals (from AHJ and POCO) in hand. With potential tariff changes, there's an argument to buy a more expensive, known quantity for California approval, inverter and battery sooner.

I found this datasheet and it says 25A max input but NO max ISC. Typo? The Euro 230V one has different specs. I don't know if there's an official way in NEC to scale from max input current to max ISC. I think it is fine but I worry about warranty and plan check




Solar panels IMO are mostly determined by how they fit your roof. They do have a different risk (IE, turned out to have missing certifications; can be really expensive to return. If the solar panel can be found in the interconnection application web app it's probably not that bad of a risk).

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This is the one I am following to see that the 12kpv gets listed, before I start my ESS interconnection application. IT covers the inverter and battery combination

I don't see SRNE on there, so it might just not be approved in this manner, or they delegated approval to a different company & it's showing up as a different name


Alternatively I might just do 18kpv, there's some followup work on my house I dream of doing, which that can help with.

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