The sun is a huge, long-lasting, and endless energy source. Solar energy is both a primary energy source and a renewable energy source. Solar energy is rich in resources, can be used free of charge, does not require transportation, does not pollute the environment, and has the advantages of energy saving, environmental protection, and convenience. The basic structure of the sun is a sphere of hot gas, mainly composed of hydrogen and nitrogen, of which hydrogen accounts for 80% and ammonia accounts for 19%. Solar energy is the energy produced by the continuous nuclear fusion reaction process inside the sun. The average solar radiation intensity in the earth’s orbit is 1367kW/m2. The circumference of the earth’s equator is 40,000 km, so it can be calculated that the energy obtained by the earth can reach 173,000 TW. The standard peak intensity at sea level is 1kW/m2, and the average annual radiation intensity at a certain point on the earth’s surface for 24h is 0.20kW/m2, which is equivalent to 102000TW of energy. Human beings rely on these energies for survival, including all other forms of renewable energy (except geothermal energy resources).
The conversion of solar radiation energy into thermal energy through the conversion device belongs to solar thermal utilization technology, and the use of thermal energy to generate electricity is called solar thermal power generation. The conversion of solar radiation energy into electrical energy through conversion devices belongs to solar photovoltaic power generation technology. Photoelectric conversion devices usually use the principle of photovoltaic effect of semiconductor devices for photoelectric conversion, so it is also called solar photovoltaic technology. Although the total amount of solar energy resources is equivalent to more than 10,000 times the energy used by human beings, the energy density of solar energy is low, and it varies from place to place and changes with time. This is the main problem facing the development and utilization of solar energy. These characteristics of solar energy will limit its role in the entire integrated energy system.
Wind energy, water energy, ocean temperature difference energy, wave energy, biomass energy, and part of tidal energy on the earth all come from the sun. Even the fossil fuels on the earth (such as coal, oil, natural gas, etc.) are basically solar energy stored in ancient times. Therefore, the broad sense of solar energy includes a very large range, while the narrow sense of solar energy is limited to the direct conversion of solar radiant energy, photo-thermal, photoelectric, and photochemical. China is very rich in solar energy resources. There are more than two-thirds of the country’s regions, the total annual radiation is more than 5.02 million kJ/m2, and the annual sunshine hours are more than 2000h.
The total amount of solar energy is very large. The annual solar energy received by China’s land surface is equivalent to 170 billion tons of standard coal, but it is very scattered and the energy flow density is low. The solar energy reaching the ground is only about 1000W per square meter. At the same time, the solar energy on the ground is also affected by seasons, day and night, climate, etc. It is cloudy at times, strong at times, weak at times, and unstable, which limits the effective use of solar energy.
Mankind has a long history of using solar energy. As early as the Warring States Period more than 2,000 years ago, China knew that steel four-sided mirrors were used to focus sunlight to ignite, and solar energy was used to dry agricultural and sideline products. In modern times, the use of solar energy has become increasingly widespread, including the use of solar heat, photoelectric use of solar energy, and photochemical use of solar energy. As a new energy source, solar energy has three advantages compared with conventional energy:
(1) It is the most abundant energy available to human beings. According to estimates, in the past 1.1 billion years, the sun consumed 2% of its own energy, which can be said to be inexhaustible.
(2) There is solar energy everywhere on the earth, and it can be developed and utilized on the spot. There is no transportation problem, especially in rural areas, islands and remote areas with underdeveloped transportation.
(3) Solar energy is a clean energy. When it is developed and utilized, it will not produce waste residue, waste water, exhaust gas, noise, and will not affect the ecological balance.
China’s Tibet, Qinghai, Xinjiang, Gansu, Ningxia, and Inner Mongolia Plateau have the highest total radiation and sunshine hours in the country, which is one of the regions with rich solar energy resources in the world; The Sichuan Basin, the Lianghu region, and the Qinba Mountains are areas with low solar energy resources; Eastern, southern and northeastern China are areas with medium resources.
According to the sunlight in different regions, China’s solar energy resources can be divided into: rich areas, relatively rich areas, usable areas, and poor areas. Their annual light radiation is ≥586kW/m2, ≥502~586kW/m2, ≥419~502kW/m2, <419kW/m2.
In the utilization of solar energy, solar lighting system convert sunlight directly into electrical energy to provide lighting equipment, read more about the types and applications of solar photovoltaic lighting systems.