# question

## 150/35 or 100/20 MPPT controller ?

Hello,

I'm going to build an off-grid system for a cabin in italian alps composed as follows:

- 48 v battery voltage (a series of 4 12v 140ah FLA batteries)

- Multiplus 1200/48

- maybe a BMV 700

- a raspberry with VenusOS and relative usb interfaces

I'm a bit unsure about what charge controller to choose. I've space for max 8 60 cells solar panels, positioned on ground south oriented with more or less 75° inclination. I've calculated power consumption is satisfated with min. 500w pv power but I want to oversize a bit the pv side. Here the dilemma:

- Use a 100/20 48v controller, with 2 series and 2 parallel 270w 24v panel . 1080Wp total.
- use a 150/35 controller, with 3 270w 24v panel in series. 810wp total

On the cost side, these 2 solutions are roughly the same.

From what I can understant, there is a potential problem with 100/20 : simulating with excel mppt size calcualtor, if temperature of panels rise too much min. pv voltage @ max temperature falls near 55v; this voltage is potentialy below the threshold (vbat + 5v) where controller cannot charge. Is this a real risk ?

I understand also there is a slight advantage using 150/35 controller (aside the potential pv wire size reduction): with more pv voltage I can have potentally more charge chance when the light is suboptimal (cloudy days, sunrise/sunset); but I find difficult to sum these advantages.

At end, a future consideration: with 150/35 i can potentialy have a max. of 6 panels (3 series and 2 parallel) for a total of 1620wp, but with 100/20 i can potentialy have 8 panels for 2160wp (2 series and 2 parallel with 2 controllers)

Any input will be appreciated

Thank you all.

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Sounds right, Indeed good if you can upgrade to 3 more panels.

I'd only opt for a MultiPlus-II 48/3000 (or multigrid II if you can find it) as this is only a little bit more expensive, and a 1200 can be insufficient in some cases (very user dependent, like what coffee machine ;)

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·

Yes this would be a very good idea if the budget can streach, you wont regret it

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Paul B ·

i've checked MultiPlus-II multiples times but is a bit over-budget (however i'd love more Amps in charger mode).

From what I learned in the past, if you have a large inverter, there'll be large consumpion (for sure when the sun doesn't shine) thus pushing for a larger battery-pv system. With great inveter power comes great responsibility :)

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dsolar ·

Yes that's true your batteries also wouldn't like it.
But it's only €200 plus VAT more expensive ;)

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