Testing with a 75 watt lightbulb directly hooked to the buck converter output, no dice. It works as expected. The load cannot pull the solar output down more than a few tenths away from Voc.
Trying with a 1500 watt resistance heater it is better, but still cannot get down to Vmpp, much less below to be able to scan back and forth for the Vmppt.
I'm back to the 700w inverter and an old battery. I have about 400w of load. It is very jumpy, going from 18v out of the panel to 14v very quickly. In addition the setting on the pot jumps around with any minor change in light, especially even thin clouds. It appears the panel max output is closer to the theoretical Vmpp of 16.5v +/- .5v, while the Max output of amps & watts from the buck converter into the battery is closer to 14.5-16.0 v at the panel, as observed yesterday.
Collecting more data.
Ok it has to be the varying efficiency of the buck converter. At the moment max panel output is at 16.2v +/- .1, but max amps into battery are at panel voltage of 14.8 +/- .2v. Panel temp averages 126F.
There is some loss of low light performance with this set up. In 100% building shade where all the lighting is indirect I get .42A panel direct, or 10% of panel direct full sun output. With the buck booster in the circuit and adjusted to the MPPT (14.9v) it is only getting .38A. So a 10 percent loss of available shade power, but only 1% of normal output. It would not surprise me to see a similar loss through the PWM controller though at those power levels.
Jim
