Introduction

Abstract

Earth is the home of human beings. However, resource shortage, environmental pollution, and ecological deterioration of the earth have become the main challenges for humanity. To protect resources and the environment, people all over the world make arduous efforts. Among them, one of the main tasks is to change the energy sources of modern industries, which have seriously deteriorated earth’s environment. It is well–known that modern industries are driven chiefly by fuel–combustion power generation, hydroelectric power generation, and nuclear power generation, which conflict with environmental protection. Therefore, people are now devoted to clean and renewable energies. The sun, producing huge amounts of energy, is an important star for humanity. It is a continuous source of energy and light for people on earth, which maintains human life. While sunlight shines on earth, one part of this light is absorbed by the atmospheric layer and the other reaches the earth’s surface, which is.