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.