Hi jrnymn,
As voltage rises efficiency of the controller drops. If there is a long run from the panels to the controller some money can be saved by going to series, but there will be losses in the controller. One figure is 98% with nominal 12 volt panels, and 96% with double the voltage. I do not know how low the percentage may drop.
Series may not do well in shade. It depends on the bypass diodes. In my own case there are diodes between each cell. If the entire panel has only one diode then it would not take much shade to "knock out" the entire panel.
On a rainy day you may get 1/6 not 1/2 of the possible harvest. I get output of 3 amps in rain vs 17 amps in perfect solar conditions.
In leafy shade I get 7 amps at solar noon.
I chose series/parallel and mppt because of:
1. a #10 prewire from the factory
2. MPPT was cheaper than buying another panel (at the time $5.50 per watt).
3. MPPT overall manages to extract a bit more energy during the shoulder hours
4. the latitude where I RV has longer shoulder hours
Today it is a different ball game with sophisticated PWM controllers and ultra cheap panels. I would have maxed out my roof and gone pwm.
Most folks don't bother to tilt much less twirl panels. One study suggests that after seven times people just no longer make the effort. Panels are cheap. Get an extra panel or two ($), and do a flat fixed install. OR bite the bullet and get electric tilt motors installed. ($$$$)
jrnymn7 wrote:
Correct me if I'm wrong; if I go MPPT, which ever way I wire is irrelevant, seeing as both will result in the same power output in watts (your favorite subject). Considering temps, rainy weather, etc., it seems if I go series I would have 35v x 8a for 280w, and if I go parallel I would have 17.5v x 16a for 280w. And on a rainy day, when amperage would suffer greatly, at say half, I would have 35v x 4a, or 17.5v x 8a, for 140w, either way.
The only other thing would maybe be the issue of shading or partial obstructions; which if I understand correctly, would indicate series wiring would be best?
