This is a simple hack, re-packaging a solar garden light. All you need is a deodorant stick, a solar light, and some silicone.
This is great for people who bike to work and park outside. Free renewable energy from the sun!
Step 1: Get yer bits together
Now you've got an empty chassis into which you can insert the battery and circuit board from your solar light.
Disassemble the solar light. It should just be a solar cell wired to a circuit board, and a battery pack.
Keep an eye out for the light sensor. A little cadmium cell that is usually somewhere near the solar panel. The cadmium cell acts as a switch, so the light turns on in darkness and stays off in light while the battery charges. I chose not to wire an on/off switch since the battery usually stays charged until at least midnight after a day in the sun and I wanted to keep this light simple.
You could wire in a switch (and use the spinny bit on the deodorant stick for a weatherproof switch actuator.) if you like late night (early morning) bike rides...
Step 2: Cut a hole for the solar cell
The easiest was to do this would be to just drill a hole and run the wires through it. But that's not as slick as sinking the solar panel into the body of the deodorant stick. (And not as aerodynamic)