Concerning controller efficiencies, it seems to me,
With 280w (2x 140w) of 12v panels in series/mppt, if the mpp of the panels was found to be at 8a and 17v, that's 8a x 34v = 272w input. At 96% eff., that's 261w output. If the bank was at 12v ocv, and charging began at say 13v, that would produce 20a of charge current (261w / 13v).
With 280w parallel/pwm, if Isc was 8.5a, and panel voltage was pulled down to 13v, that would produce 17a of charge current (2x Isc); so 3a less than with mppt. Assuming the pwm operates with 100% eff., the input and output would both be 221w (17a x 13v). 221w / 272w of available power = 81.25% eff.
In hot conditions, as Vmp goes down, pwm efficiency would go up in comparison; and vice-versa.
