1.1 The transfer of solar energy
The energy generated at the core of the sun diffuses outwards, making the surface temperature of the sun reach about 6000 ℃, just like an ocean of high-temperature gas. Most of the solar energy radiates around in the form of heat and light. That is to say, the sun mainly spreads energy outwards in the form of radiation. This is what people call solar radiation, which is also the fundamental way for the earth to obtain energy.
The huge “nuclear stove” of the sun has been “burning” steadily for 5 billion years. At present, it is in its prime, and it will take another 5 billion years to burn out its nuclear fuel.
1.2 Solar energy radiation
(1) Classification of radiationSolar radiation is divided into two types: one is the light radiation emitted from the surface of the photosphere, which spreads light and heat in the form of electromagnetic waves, also called electromagnetic wave radiation, which consists of visible light and invisible light Composition; the other is particle radiation, which is a particle stream composed of positively charged protons and roughly equal amounts of negatively charged electrons and other particles. The particle radiation is very weak, and it disappears on the road before it reaches the surface. Therefore, solar radiation mainly refers to light radiation, that is, electromagnetic wave radiation.
(2) Factors affecting solar energy radiation When solar radiation passes through the earth’s atmosphere, the solar radiation reaching the ground will be significantly reduced due to various obstructions such as reflection, scattering and absorption from the atmosphere. The reflection of solar radiation by the atmosphere is a diffuse reflection, which is about 8% of the incident radiation; the reflection on the earth’s surface is 2% to 3% of the incident radiation, and the reflection of the clouds is about 25% of the incident radiation on average. The earth is a large magnet whose magnetic field can control a vast area of more than 1,000 kilometers or even hundreds of thousands of kilometers. This area is called the “magnetosphere” of the earth. Most of the solar particle radiation will be blocked by it in outer space. Even if a few particles break in, they are often captured by the magnetic field inside the magnetosphere. Although the energy radiated by the sun into the earth’s atmosphere is only one-2.2 billionth of its total radiant energy (approximately 3.75×1026W), it is already as high as 173,000 MW, which means that the sun’s energy per second on the earth is equivalent to 5 million tons of coal.
Figur 1-1 Energy flow diagram on the earth (unit: 106MW)
Figure 1-1 shows the energy flow diagram on the earth. As can be seen from the picture, wind energy, hydropower, ocean temperature difference energy, wave energy and biomass energy, and part of tidal energy on the earth are all derived from the sun; even fossil fuels on the earth (such as coal, oil, natural gas, etc.) ) Fundamentally speaking, it is also the solar energy that has been stored since ancient times, so 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 radiation energy, photoelectricity and photochemistry.