Solar sunroof intermittent now not working

[HPsauce]

Just opened up the roof lining and tested it.
Didn't fire up at all until there was a bit of sun, so I suspect there may be a trigger level of input. But then kept going behind cloud.
Input voltage was varying but typically somewhat over 12V and output just slightly under 3V to the fan.
If we get any "proper" sun later I'll see how those figures change.
Edit: Not working now.

[HPsauce]

Not working now.

But this cool morning in the bright sun it's whirring away happily.
But by 11:30am it's stopped - must be something thermal surely, but what?
And working again a few minutes later, though we do have intermittent clouds so it might be cooling down when shaded, very strange?

In full sun the blower is quite sprightly, the panel output (under load) measures about 12V and the controller is sending about 6V to the blower (vs 3V when overcast and running slowly).