The sun is the closest star to the earth and the central celestial body of the solar system. Its mass accounts for 99.865% of the total mass of the solar system. The sun is also the only celestial body in the solar system that emits light by itself. It brings light and heat to the earth. If there is no sunlight, the ground temperature will quickly drop to close to absolute zero. Due to the sunlight, the average temperature of the ground will be kept at about 14℃, which has formed the conditions for the survival of human beings and most living things. Except for nuclear energy, geothermal energy, and volcanic eruption energy, most of the energy on the ground is directly or indirectly related to the sun.
According to the estimation of the current rate of nuclear energy produced by the sun, hydrogen reserves are sufficient for 60 billion years, while the internal tissues of the earth polymerize into helium due to thermonuclear reactions, and its life span is about 5 billion years. Therefore, in this sense, it can be said that the energy of the sun It is inexhaustible and inexhaustible. Therefore, the application of solar energy is related to the key to human energy supply in the future.
The sun is a giant glowing gaseous body with a diameter of about 1.39 million km, a volume of about 1.42×1027m³ (1.3 million times that of the earth), and a mass of 1.98×1030kg (about 330,000 times that of the earth). The average density is only 1/4 of the density of the earth.
The energy of the sun comes from the thermonuclear reaction (from the fusion of 4 hydrogen nuclei to 1 ammonia nucleus) inside it. In the form of light radiation, the sun emits about 3.74×1026J of energy into space every second, that is, the auxiliary radiation power is about 3.74×1026W.
The average distance between the earth and the sun is about 1.5×108km. Due to the long distance, only about one part of 2.2 billion of the energy released by the sun is projected onto the earth. The solar radiation power reaching the upper boundary of the atmosphere is about 1.73×1017W. About 30% of it is reflected back to space by the atmosphere, and about 23% is absorbed by the atmosphere. The solar radiation power that can be projected to the ground is only about 47%, which is about 8.1×1018W. Nevertheless, the solar energy reaching the earth’s surface every year is still as high as 1.05×1018kw·h, which is equivalent to 1,300 trillion tons of standard coal, which is tens of thousands of times the contemporary global energy consumption. Enough to meet the energy consumption of human beings in the world for one year.
Since the land area only accounts for 21% of the earth’s surface, excluding deserts, forests, mountains, rivers and lakes, the actual solar radiation power reaching human settlements is 7×1015~10×1015W, accounting for the total solar radiation power reaching the earth’s atmosphere. 5%~6%. However, this is equivalent to the total power of nearly 10 million mega-kilowatt power plants.
According to the theory of stellar evolution, the sun is currently in a stable and vigorous middle age period. According to the current power radiated energy, it can last about 10 billion years. In 10 billion years, the sun will become a red giant with a peculiar light, and will eventually go out completely. 10 billion years, compared to the finite years in the history of human development (on the order of millions of years), it can be said to be “endless”.
- Advantages of solar energy
Compared with conventional energy sources such as coal, oil, natural gas, and nuclear energy, solar energy has the following advantages.
(1) Abundant reserves
The total amount of solar energy irradiated on the earth’s surface in a year is tens of thousands of times larger than the total amount of energy consumed by mankind each year. For mankind, solar energy resources are inexhaustible and inexhaustible.
(2) Maintain long-term
Compared to human history, the life of the sun is very long, so it can be considered that solar energy can be supplied for a long time.
(3) Widely distributed
Solar energy resources can be used where the sun is shining, so there is no need for people to explore and mine laboriously, and there is no need for long-distance transportation by trains or ships. The superiority of solar energy utilization is especially obvious for solving energy problems in remote areas with inconvenient transportation, deserts, islands, and mountainous areas.
(4) Clean and pollution-free
Solar energy is a clean energy. Solar energy does not produce waste gas, waste residue, waste water and any substances harmful to the human body during the use of solar energy. - Disadvantages of solar resources
Solar energy has the following disadvantages:
①The sun has a large area, low energy density and dispersiveness.
② Due to the change of the earth’s day and night, the sun does not always illuminate the earth’s surface, so the energy is discontinuous.
③The energy is unstable.
