Solar-Powered USB Charger

This was a project to build a USB charger that runs entirely off solar power. It uses a small solar panel to charge a lithium battery, and a DC-DC converter to make sure whatever comes out is a steady 5 volts, since phones don't like it when the voltage isn't consistent. I spent a lot of time actually testing the solar cell — measuring its I-V curve so I could figure out where it puts out the most power, and testing how efficient the converter actually was with a multimeter and some load resistors. I also added a diode so current couldn't accidentally flow backward into the panel and damage it. It's a simple idea but there's more to getting it actually reliable than I expected, especially once the sun isn't directly hitting the panel.