Steve made this 6 volt 5 watt solar charge controller project, that is available at Github:
Here is a 6 volt 5 watt solar charge controller project using a dedicated printed circuit board from dirtypcbs.com and an Arduino pro-mini.
The board uses sot-23 low RDSon P channel mosfets (Si2369). It has voltage and current sensing, and 3 configurable switched or unswitched outputs.
Additionally, using a Bus Pirate you can grab charge controller voltages, currents, and other variables at 5 times a second using a Python3/tkinter program I wrote to go with this project. This program uses uses I2C to connect to the Arduino.
Via the contact form.