A few years ago, [Lukas Fässler] needed a solar charge controller and made his own, which he has been improving ever since. The design is now mature, and the High Efficiency MPPT Solar Charger ...

This analog MPPT, or Maximum Power Point Tracker, is used for optimizing the draw of a power cell in correspondence to the output of solar panels on the 10cm x 10cm satellite. In a nutshell ...