Salvo wrote:
One of the myths around here is that series is better than parallel because you can use smaller cable. Going to higher voltage Vmp comes at a cost. In this case, efficiency drops by 5%. Charging current will forever be 5% lower.
The OP can use the same hardware and connect panels in parallel. The panel cable will be a little larger, but so what?
It's not a myth :).
24V in series do use a smaller cable - much smaller, like #10 vs #4. Cable cost - higher with parallel - is only one of variables. Routing a cable that thick is never easy, difficult to hide it in the room. Also, with parallel wiring you need a rooftop box, a decent one from AM solar would cost $60, and won't look awfully esthetic on the roof. Though people have come up with cheaper solutions like $5 PVC box + $20 or so terminals inside. In a hot climate with plenty of UV I wouldn't want any plastic box on the roof.
Charging current in series is 5% lower (let's pretend for simplicity here that 15-20% boost of MPPT is also a myth). On the plus side, you can increase panel wattage by 30-50% before you will need to increase the cable gauge from #10 to #8 - which is still thin and easy.
3*24V in series is below 150V limit of TS MPPT 45, no matter what wattage. Even 3*280W is below 150V - not that I recommend this with 45A.
One factor (other than cost) that favors 4*150 with PWM vs 3*235 or 3*250 with MPPT, is a better aerodynamics. I understand this is a motorhome - they tend to drive more and faster than towed rigs. Not sure this is really important though.
