How to Wire DC Motor to Solar Panel and Battery to Only turn on at Night?
I would use a relay such that when the panel is producing power it holds the relay open and the motor is not powered.

Once the panel fails to produce sufficient energy the relay contacts close switching on the motor.

Of course, fuses etc should be fitted as necessary.
I find it helpful to think of the "charging" side, the "load" side and the relay which is the link between the two sides. So the two wires from the panel to the charge controller also need to connect to the coil on the relay.



As for what is available in your local hardware store - I have no clue. But a car headlamp relay for example may well be suitable.