Step 1: Components Needed
1. Duct tape.
2. 12v battery, rechargeable. (I salvaged one from an old electric dirt bike)
3. Scrap wire (that can handle 12v)
4. bits of metal for the clips.
5. 12v Solar panel with fuse, clips, and blocking diode. (AutoZone, $23)
6. Female car socket with alligator clips.
7. 12v thermistor relay switch. (eBay.com, $5-$7 USD.)
8. wire stripper tool.
9. A container that would work as a water resistant casing.
10. 12v car fan
11. small Phillips screwdriver
Step 2: Wire circuit as shown in diagram
I just stripped the ends of the scrap wires and wrapped them around the metal bits with the other ends screwed into the thermal switch fasteners.
Warning: the circuit is "Floating" so you can could potentially get shocked even when your fan or other device is not running!
(Sorry for the poorly drawn diagram)
Step 3: Tape it together.
Fasten the wiring and thermal switch board to the battery. (I would recommend encasing the whole setup in a water resistant box!)
Step 4: Tune the thermal switch.
There's a small potentiometer on the board, using a screwdriver you should tune this to your desired temperature that the fan would power on at.
Step 5: Video + Further Innovation Goals
Later I would like to add a rain resistant casing to the project, a blocking diode immediately before the socket adapter, a secondary socket that does not go through the thermal switch (to charge mobile devices and rechargeable flashlights via a USB car charger adapter), and a more powerful solar panel.
If you're having trouble viewing the video on your device like I am, this might work also: Off Grid Smart Tent Prototype v1