See below for response... "But there is an important gain to be had here that has not been discussed, that is that by using these controllers when the voltage of the (loaded) solar panel would fall below what could charge the battery, the controller can boost the voltage to a level that will result in the battery being charged, so that even though there is some loss through the controllers, the gains made by being able to store this power that is otherwise unavailable can far outweigh these losses and add a significant amount of stored power that would otherwise be unavailable." Response... If the solar panel is putting out less than 14V there likely is very little power available anyway, and the MPPT controllers don't seem to function there anyway, as their internal losses may be more than the small amounts available. You speak of switch mode, not sure if we are thinking of the same thing. I see switch mode as a DC to high freq AC converter useful in very efficient power supplies that can adjust voltage and current, which I guess is the same impedance matching that you refer to. Correct me if I am wrong, but the way I read design on the MPPT controllers is that it runs the panels at a higher voltage which will still give the same current which results in more wattage, which is then more (output) current at a lower voltage. HOW?? The internal switch mode circuits convert the DC to AC to DC and match the solar panel's maximum output wattage point to the charging voltage needed. In theory this might gain 25% but only if the voltage difference is great, ie. very low battery charge. Also, quite a lot of heat is made in the controller circuits and this is lost energy. With my use, my Blue Sky 50A controller probably gains 5-7%. Possibly worth the $500, due to the much higher current gain when the batteries might be very low, but, not sure this has ever happened. If I had bought the Xantrex pulse modulation style controller for ~$200, it would have come with a shunt connection that could go to a 12V water heater element. It would send any available excess current automatically there. I hope this was clearer than mud. Lee Haefele
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