Solar Panel Project

The solar cells wired together resting on blue foam

Yesterday was my last day at college. I spent the morning moving out and the rest of the day in the Academic Center working on the solar panel.  My goal was to build a low-cost USB solar panel that could be mounted on the top of my rear rack to charge cell phones, cameras and other electronics while we were biking.


Earlier in the week I had spent many hours soldering the individual cells together.  The top of each cell is negative charge, while the bottom is positive.  Thus, I had to string the tops and bottoms of adjoining cells to have the voltages add in series.  Each cell produces about .5 V, so the panel ideally would put out 6 volts in direct sunlight.  However, the cells are very brittle and I chipped a lot of corners in the process of wiring them, so they probably put out less than .5V each.

Each USB head has 4 pins.  Pin 1 connects to 5V and Pin 4 connects to ground.  Pins 2 and 3 are data pins, and depending on the voltage that they detect in each pin the iphone can tell if it is being plugged into the wall or the computer.  For non-apple products the data pins can usually be ignored.

After a lot of research, I ended up building a very simple circuit.  The circuit included a 5V voltage regulator, a diode and a few resistors to connect to the data pins.  Since the voltage coming in from the solar panels is variant depending on the intensity of the sun, the voltage regulator is needed to buck or amplify the voltage to make sure it is exactly 5V.  The diode makes sure current only flows one way so there is no back flow into the panels.

The Circuit and the USB connector

After building the circuit, I moved on to preparing an Altoids tin to house the wires.  I cut out a space on the side to have the female USB head exposed to make plugging in easy.

The circuit housing box with a cut-out for the USB input

Finally, I laid up carbon fiber around the edges to strengthen the panel and prevent the blue foam from shredding if it got banged around.  The carbon fiber also reinforced the brass hooks that were stuck into the foam that would be relied on to mount the panel on the bike. I rubbed epoxy on top of the cells to glue them to the foam and hopefully protect them so they didn't break as easily.

The final solar panel

Alright, so it is a bit sloppy looking and may or may not actually work.  It was raining the day I finished it so I couldn't test it.   I will update this post once I test it!

 In the meantime, I am finishing up ordering gear and finding campsites along our route.  In the next few days I will lay out all of the gear on my floor and try to pack it all....