We can see that piezoelectric is very expensive. One-unit costs 40 dollars and produces around 352.61 microwatts. Then photodiodes cost approximately 1.3 dollars each, and we need about ten photodiodes to produce approximately 11.3 microwatts.

Photodiodes are much smaller, they have more room for flexibility and adaptability, so we made the design scale more significant than the design of the piezoelectric.

The decision matrix was used to decide which charging method would be used for our design process. Taking a closer look at the decision matrix table below, we can see those photodiodes have a higher score than piezoelectric, not to mention those photodiodes produce a more constant charge than the other charging method.

The basic principle of solar power generation is quite complex. Sunlight shines on the semiconductor p-n junction, forming a new hole-electron pair, and under the action of the electric field built into the p-n junction, holes flow from the n-zone to the p-zone, and electrons flow from the p-zone to the n-zone, forming an electric current when the circuit is connected.

Our first test in the design process was done with the BPW34 photodiode. First, we tested the power generation efficiency of the photodiode under different lighting conditions, including a well-lit room, a poorly lit room, and sunny outside. The measurement consisted of a single photodiode and 10 photodiodes connected in series.