Solar panels seem like simple devices: light in and electricity out, right? If you don’t care about efficiency, it might be that simple, but generally you do care about efficiency. If you are, say, charging a battery, you’d like to get every watt out of the panel. The problem is that the battery may not draw all the available current, basically leaving capacity on the table.
The solution is a technique called MPPT (Maximum Power Point Tracking). Despite sounding like a Microsoft presentation add on, MPPT uses a DC to DC converter to present a maximum load to the solar cell while providing the desired current and voltage to the load. MPPT is what [Abid Jamal] implemented to manage his solar charger.
In addition to the solar panel and DC to DC converter, [Abid’s] project uses an Arduino, an LCD, some indicator LEDs, and some discrete components. He even included an ESP8266 to provide wireless data logging. The finished project resides on perf board and lives in an acrylic case.
There’s a similar MPPT project in the Hackaday prize competition (in fact, the video below is from the creator of that project), and we’ve seen other MPPT builds, too. It might be interesting to contrast the different designs.