This board implements the schematic shown on page 1 of the LTC3105 datasheet:

https://www.analog.com/media/en/technical-documentation/data-sheets/3105fb.pdf

The header pins are positioned so as to plug easily into a 2.54mm pitch breadboard. The photovoltaic cell and battery are attached externally using the header pins.

The LTC3105 is a step-up voltage converter with a low start-up voltage of 250mv. It includes Maximum Power Point Control (MPPC), which Linear Technologies advertises as being useful in solar applications.