Poly vs Mono Panels and MPPT Controller on a camper van

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miguel-d asked Apr 8, '20

Poly vs Mono Panels and MPPT Controller on a camper van

Hello,

I have a camper van with a 12V system powered by a single 150W Poly Panel (not from Victron) controlled by a MPPT 75/15. Now I want to upgrade and I'm thinking about selling the current panel and controller and get two 175W Victron solar panels (in parallel).

My first question is regarding the cell technology that I should go for. The 175W Mono and Poly Victron solar panels have the same size and the price is very similar too. I can't find anything on the datasheet regarding the efficiency but I read that the mono panels tend to work better on low light situations while poly work better in shaded conditions (scattered rays).

Should I go for one of each to have the best of both worlds? Or should I go for 2 Mono since it will give me the best performance in full sun and low light conditions (the conditions that I will have maybe 98% of the time).

My second question is regarding the new controller. The MPPT Calculator gives me the 100/20 option, but its datasheet says that the Nominal PV power at 12V is 290W and the new system would give me 350W at the peak. Is the 100/20 controller a good option? Will I be able to take full advantage of the system with it?

Thanks for the help!

MPPT Controllers Solar Panel

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spirou commented · Apr 08, 2020 at 08:27 PM

Realistically, the panels will rarely if ever produce enough to reach the 20A limit unless you're chasing sun all the time. But if you want to play it safe then get the 100/30 model (what I have with 2x160W). Poly or mono is largely irrelevant IMO. There might be a bigger difference between two panels of the same type than between different types. I know mine are terrible in winter low light when I need them most. On the previous van I also had a poly panel (1x120W) and it seemed to handle itself quite a bit better than these two now.

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miguel-d spirou commented · Apr 09, 2020 at 05:23 PM

I live in Portugal so, specially during the summer, sunny days are a constant. If I get more than the 290W with the 100/20 what happens? Does the fuse burn or it caps out the charging power at 290W? I cannot understand why the calculator suggests the 100/20 controller to a system capable of doing 350W. Am I thinking something wrong or should the calculator suggest the 100/30 instead?

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spirou miguel-d commented · Apr 10, 2020 at 04:24 AM

For some reason the web calculator is off in certain cases. Use the excel file for a more accurate result.

As far as I understand, if you go over 20A it will shed the extra as heat so make sure it's in a well ventilated space. But like I said, it might not even happen often unless you hit a certain set of conditions: low temperatures + wind to keep panels cool, very empty battery (less so with lithium), a lot of sun straight down on the panels.

In reality, even (early) morning sun is often enough to replace lost charge at least to the point where the battery becomes the limiting factor of how much current goes in (lead more than lithium). If you're using something like 30Ah per night, you might be able to recharge that much before the panels are even able to produce more than 20A.

The max I ever got on the previous van (including Portugal in summer) was 112W (120 rated) on a 75/15. The total number of days when it reached a max over 100W was 15 in 5 years. Most commonly it was in the 70-100W range and I don't expect the new system to be much different in that regard. So far (just winter), as on the old van, batteries recharge before the sun is at full power.

Anyway, if you want peace of mind and have a substantial buffer then get a 100/30.

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miguel-d spirou commented · Apr 12, 2020 at 03:22 PM

Thank you very much for your input! I've managed to get 140W from the 150W panel that I have some days ago on the 75/15. I work from the van so I consume a lot of power during day and night. I will think more about this and make a decision. I don't like the size and price of the 100/30 but I might end up going to that one just for the peace of mind and you said. Thanks again! Regards from Portugal

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Answer 1 · 2020-04-08T18:40:43Z

neoneddy answered · Apr 08, 2020 at 06:40 PM

Don't do two different types. The MPPT will track to sweet spot of the lowest performing panel. So you'll effectively have two Poly panels in performance if you do split.

I've got a larger array on my bus at 1950 watts. I find myself having partial shade quite a bit. It doesn't take much to put them in shade mode (like a grapefruit sized shadow). I'd go with whatever option lets you buy the most wattage of panel. Even adding more. You can never have too many IMHO.

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