Just figured out how to do it
Your solar set up looks a bit like this Note the location of the *
Panels------*-Controller--Battery
There may (should) also be a fuse in there somewhere
The way to insure fan only runs when charging is to hook it in at the * You may need a voltage regulator (simple device) but hook it in at the * That way it only gets power from the panels as there is a diode in the controller.
if you use a 12 volt fan (you can also get 5 volt)
Here is one list of 3 terminal regulators
Mouser Electroincs
