A solar cell is a huge PN junction, which converts solar energy into electrical energy. For a monolithic solar cell, it is a small PN junction. In addition to being able to generate electrical energy when sunlight shines on it, it also has all the characteristics of PN junction. Under standard light conditions, his rated output voltage is 0.48V. The solar cell modules used in solar lighting fixtures are composed of multiple solar cells connected together. It has a negative temperature coefficient. When the temperature rises by one degree, the voltage drops by 2mV. In use, the solar cell will not be damaged if it is open or short-circuited. In fact, we use this feature to control the charging and discharging of the system's lithium battery.