Solar Costs - MPPT vs PWM

CA Traveler wrote:
MPPT has no way to detect panel wattage. Power is the product of volts and amps and the controller searches for the point on the IR curve where it can maximize that product and convert the power to battery voltage and amps. That's how you can get 40A to charge the 12V batteries from 8A panels for example.

Voc is not a factor since the panel is producing amps so it's not operating open circuit and the panel voltage will be less than Voc. Voc or any input voltage to the controller is a factor due to electronic limitations.

At 60A the MS-MPPT-60 will start derating at 140V input down to 0A at 150V. 150V is the stated maximum voltage.

ISTR one way MPPT works is by fiddling with its R to keep panel voltage at where the MPPT experiences highest wattage using feedback on the wattage changes. EDIT--one way but there are others--see below link.

I think the buck converter 24 to 12 then takes that max wattage in and puts it out at battery voltage and whatever amps that comes to

AFAIK with PWM, the controller passes through the actual panel amps (same amps as its Isc at the time, which is a variable) The amps the panel does depends on panel voltage per the IV curve but that is in the panel, and the controller could care less about that, it just gets those amps in and starts controlling when battery voltage reaches the high set-point.

So it seems to me that PWM uses actual panel amps while MPPT is independent from panel amps and makes its own amps regardless of panel amps.

So MPPT on a 12v panel does not take the panel amps and then add some amps. It starts from scratch and gets it own amps, which might be higher or lower than panel amps (depending on panel temperature mostly)

http://en.wikipedia.org/wiki/Maximum_power_point_tracking