More Solar for "Us"
Ok, I went off.the deep end? Bought 3 used 37watt uni-solar panels and a blue sky 2000e controller for the hefty price of $400, They were being listed as 75w panels, they are not The tested open...
Forum Discussion
pianotuna wrote:My series panels have 61' of 10 gauge wire with a voltage drop of 0.5 percent. No practical gain from larger gauge wire.
Hi CA,
MPPT benefits from larger wire size. Of course series with by pass diodes may be the best solution for MPPT.
I've never accepted that PWM requires large wire size--especially with 21 volt panels.
Parallel panels with PWM should have larger wire from the combiner box to the controller. Let's say 5x panels at 8A each. That's 40A and I would not use 10 gauge wire to the controller. Sure with 12V panels that are 21V smaller wire can be used than with 18V panels.
But look at the 21V PWM limitation. You get 8A into the battery at 14.8V. With MPPT you get 21*8 / 14.8 = 11.3A. With a 5 percent MPPT conversion loss you have 10.8A and a little less with hot panels.
PWM does not use all of the panel power (watts) just the amps. MPPT does use all of the panel watts and converts it to battery watts or amps at a given battery voltage per the above example.
Try a lower battery voltage example say 13.6V float. PWM is still 8A. MPPT is now 21*8 / 13.6*.95 = 11.7A. While the charged battery won’t accept the amps the house loads will which translates to less battery drain for MPPT when 8A is exceeded.
PWM wins for smaller systems while MPPT wins in performance for larger systems.
