I am experimenting with an unstabilised DC power supply (solar panel array rated at 44V open circuit) which in practise seems to fluctuate up to about 45V open circuit in operation. Could I ensure the output stays at or below 40V by connecting a suitably high power & heatsinked 40V zener diode across it? Like a DO5 stud mount type?

If so.. when the voltage rises above 40V, how would I appraise the actual power dissipation in the zener?

The panels short circuit output is listed at 15A. Would I use straightforward P=IV?

That would seem to say the diode could experience 15 x 45 = 675W above 40V

However the conduction of the diode above 40V, would start to drop the PSU's output voltage so would the actual diode dissipation under full supply output actually be lower?

The highest rating I can find for such zeners seems to be about 50W.

Should I use some form of dummy load in series with the zener, and if so, would that mean I should subtract a figure to reflect the dummy load's own voltage drop, from the value chosen for the zener? Small Bio