1.1 Source of solar energy
The sun contains huge energy. It constantly emits visible light, various rays (Figure 1-1) and a lot of heat. The sun’s temperature is extremely high, and its surface temperature is enough to vaporize any object, while its internal temperature is even higher. According to the theoretical calculations of astrophysics, the central temperature of the sun reaches 15-20 million degrees Celsius. This is an indescribable high temperature, high pressure and high density environment.
Figure 1-1 Solar temperature and ray distribution
So, where does such a huge amount of energy come from? The interior of the sun is not calm. Under the action of extremely high temperature and huge pressure, countless atoms lose most or all of their extranuclear electrons. They are under intense motion and collision. , A variety of nuclear reactions are constantly undergoing. The most important one is the nuclear fusion reaction in which hydrogen turns into helium, that is, four hydrogen nuclei undergo a series of nuclear reactions to fuse into one helium atom, and the remaining mass is converted into energy to radiate into space. According to calculations, four hydrogen nuclei fuse into one helium atom through a nuclear reaction, and the mass loss is 0.7%.According to Einstein’s law of mass-energy E=mc2, it can be known that 1g of hydrogen atoms produce 6.3×1011J of energy in the thermonuclear reaction. . The sun converts more than 600 million tons of hydrogen into helium every second, losing mass of 4.27 million tons, and the converted energy is 3.9×1020MW. Although only a small amount reaches the surface of the earth, this is still hundreds of thousands of times the global power generation.
1.2 Solar energy storage method
The solar energy received on the ground is intermittent and unstable due to the influence of climate, day and night, and seasons. Therefore, solar energy storage is very necessary, especially for large-scale utilization of solar energy. Solar energy cannot be stored directly, it must be converted into other forms of energy to be stored. There are the following methods for solar energy storage.
⑴Electric energy is stored in the solar photovoltaic power generation system, and the electricity generated by solar cells is mainly stored by storage batteries. Because of its large capacity, strong impact load capacity, high reliability, and low price, lead-acid batteries are the main energy storage devices for photovoltaic power generation systems.
(2) Thermal energy storage refers to sensible heat storage. Sensible heat storage using materials is the simplest energy storage method. In practical applications, water, sand, stones, soil, etc. can be used as energy storage materials, of which water has the largest specific heat capacity. That is, even if the temperature does not rise much, it can absorb a lot of energy
(3) Latent heat storage. It refers to the use of latent heat storage energy absorbed by the material during phase change (when changing from one phase to another phase), which has a large storage energy and releases heat at the same temperature. For example, in the infinitely slow cooling process of pure iron, the temperature is constant when it changes from one phase to another. This means that when the phase changes, the latent heat released by the substance offsets part of the heat lost due to cooling. , So the temperature does not change.
(4) Chemical heat storage refers to the use of chemical reactions to store heat, with large heat storage, small size, light weight and long storage time.
(5) Solar pond heat storage Solar pond is a salt pond with a certain salt concentration gradient, which can be used to collect and store solar energy. Because of its simplicity, low cost and suitability for large-scale use, it has attracted wide attention.
(6) Hydrogen energy storage Hydrogen can be stored in large quantities and for a long time. It can be stored in the form of gas, liquid, solid (hydride) or compounds (such as nitrogen, methanol, etc.). In addition, hydrogen and oxygen input into the fuel cell can also generate electricity.
⑺Mechanical energy storage converts solar energy into electric energy, and drives the electric water pump to pump low-level water to a high level, which can store solar energy in the form of potential energy; convert solar energy into heat energy, which pushes the heat engine to compress air, and can also store solar energy.