Pianotuna said,
"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."
If I'm understanding the Tracer 3215BN's efficiency graph correctly, there is about a 0.5% drop in efficiency at 35v vs. 17.5v, using 280 watts. And at half power (140w), or even at quarter power (70w), less than a 1% drop.
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