My janky solar charge controller, built from scavenged parts and designed for 240W, works with a panel in the back yard.
After my dad's friend who does commercial solar donated a decommissioned panel to me, I decided to take on my first electronics project. In my tenure with the MIT Solar Electric Vehicle Team, I'd learned about MPPT charge controllers: devices which optimally deliver power from variable sources. This was my goal.
I built my device around a buck converter, with an Arduino controlling the duty cycle. It's able to support constant current, constant voltage, and perturb-and-observe maximum-power (MPPT) output modes, making it theoretically suitable for battery charging, but for now it just feeds a constant 15V into some car USB chargers to top up my family's devices.
The whole thing was built using parts pulled off old electronics and assembled on a variety of supports as I was prototyping. Notable members: a desoldered PCB where I manually cut traces to get the desired connectivity, and a segment of an electronic dartboard. The crown jewel of jankiness: a 2x3mm 5-pin(!) surface-mount differential amplifier for current sensing that I hand-soldered to wires. It ain't pretty by any means, but it's been working continuously for 3 years. I do intend for my next project to look nicer. Any ideas?