About the size of a AA battery, the cell uses the microscopic organism Synechocystis which photosynthesizes sunlight to generate electrical current. Although the current generated is very small, it is enough to power a microprocessor, and the system had been running continuously for a year.
The algae used in the system doesn’t need any additional food other than sunlight, and it even continues to produce power at night because it continues the process of photosynthesis for a time even when there isn’t light present. The electrical current generated by the algae is sent to an aluminum electrode from where it can be sent to the processor.