mppt vs pwm

jrnymn7 wrote:
"I'm seeing two 150w panels in series only producing a few amps more than my 245w panel. On a better controller I know of a 960w system using 160w panels in pairs for mid 40's producing 48a while I would expect 60a from four 250w 24v panels."

That sure seems counter-intuative. One would think the 12v's in series, having a higher combined Voc, would result in even more wattage being used by the controller. I can see if the mppt was rated for 50v, and you threw 46 volts at it, but most buck converters boast ~98% efficiency, when operated within their duty cycle.

Does it perhaps have to do with the 12v 160w panels being in series, and thus their output would become 160w / 44v = 3.6a, as opposed to ~9a Isc?

Not counterintuitive at all. You guys need to start thinking in watts instead of amps and Isc. 300 watts is more than 245 watts. At 13.5 v output it means 4 amps difference.

Panels in series has nothing to do with it except it reduces line losses and allows one to make use of the advantages that the MPPT controller offers.

I don't know about other controllers, but Rogue's published efficiency curves show that at a 20 amp output, 17-volt panels to a 12-volt system are about .2% more efficient than 34-volt panels, both right at 96%. At a 10 amp output, 17-volt panel input is about 1.2% more efficient. So at 20 amps 34-v panels "lose" 4 mA more than 12-v panels. At 10 amps the difference is 120 mA. Line losses for bringing 12-v power to the controller are certainly much greater than that.