TL;DW: Isn't that just because the diode matches the PV array's max power point, assuming they both use the same technology (e.g., silicon)?

It seems like that depends on the diode string and PV array remaining at approximately the same temperature as heat is dumped into the diode.

> It is 100% verified fact by both myself and others (including university researchers) that diode strings can produce more heat (or watt-hours, BTU) from a given solar panel than a bare resistance element.

In some of my early experiments with little radio transmitters some 30-odd years ago I managed to burn my fingers to an astonishing degree with little plastic transistors like ZTX300s and BC548s.

I remember my late father also commenting around that time "How come a 2N3866 which is rated for a couple of watts can get so hot it melts all its legs off when it's running off a half-flat PP3 battery?", astonished as yet another 2N3866-based amp got a bit lively and melted its legs off despite only running off a half-flat PP3 battery.

So yes I can believe a string of diodes would be a more effective heater than a resistor.

Intriguing, but wouldn't it be even more efficient to just paint something black and let the sun heat it directly?

where is this 'extra' heating coming from?