Solar energy refers to the thermal radiant energy of the sun (see three ways of heat energy transmission: radiation). The main manifestation is the solar light. In modern times, it is generally used to generate electricity or to provide energy for water heaters. Since the birth of life on earth, it has been mainly survived by the heat radiation provided by the sun. Since ancient times, human beings have also been able to dry objects and use them as methods for making food, such as salt and salted fish. With the decline of fossil fuels, solar energy has become an important part of human energy use and has been continuously developed. The use of solar energy has two methods: photothermal conversion and photoelectric conversion. Solar power generation is an emerging renewable energy source. Solar energy in a broad sense also includes wind energy, chemical energy, and water energy on the earth.