JiminDenver wrote:
The plan is to wire for parallel and run test in both. In parallel I gain the advantages of tolerance if shade is on one panel, better efficiency from a lower Voc to 12v and less heat at the controller. Switching to series in extended lower light situations may prove better then.
It would be good to have a parallel/serial comparison.
My take is different. For 2 panels one in shade parallel may/may not be better than serial. Parallel loses power from unused voltage while serial loses power from bypass diodes in one panel and controller efficiency. When the shadow allows 1/3 or 2/3 of the second panel to conduct there is no contest. Serial wins hands down. This was demonstrated in my rather unscientific observations when my rig was in storage and posted on these boards. Another post when I was parked next to a tree clearly shows the bypass diode effect.
You might be surprised at the efficiency of better designed controllers. I'm quite pleased with my setup with 3x250W and MPPT60 controller. I'm running 105V+ panel input and 12V batteries. On 3/3/15 on a clear day in Phoenix with flat mounted panels sloped 4 degrees to the west I got 600W for about 1.5 hours. Ambient was about 70F and panel temps unknown. While I'm not expecting a huge increase with summer time sun elevations it will be interesting to see what the system can produce.
Costs last fall for my system was about $100+ more than an equivalent PWM system. PWM involves more panels and mounting hardware, wire and combiner costs. From what I've seen there is probable little difference today except smaller systems may favor PWM but I haven't done the comparison on the current low cost MPPT controllers.
