Wow! I can't believe people still read these old threads..
A long time ago, I gave up on trying to control the DC power from the PV arrays.
I just keep an eye on the water temperature, tell my wife to turn on the dishwasher,
or I just enjoy a nice extra long hot shower to regulate the water tank temp.. :)

To sum up the test results of using RF Coax to deliver DC power from solar arrays, it works.
(Has been working for almost six years).

I'm not sure what the max current limitations are, but in series configuration,
8 Amp panels put out a max current of 8 amps. (Into my 13 ohm heater loads IIRC).

Because they are buried cables (not in conduit), I regularly measure for leakage to ground and for normal power conduction.
So far, the cables have performed like new. I'm guessing their life span is in the 20+ year range.

20V gate IGBTs are pretty unusual. Most common are 10V to 15V on and 0 to -10V off, the latter being especially variable depending on application - generally high speed switching of more than a few tens of kHz is where negative gate drive makes sense.

It's also worth noting that a lot of IGBTs indeed do not like operating in a "half on" state for much more than the few microseconds it takes for them to switch off. One of my friends who does power electronics says that "a half on IGBT makes a poor imitation of Tiffany Yep" (a "hot" joke) but that's only if the IGBT doesn't just self destruct.