Solar energy, the English name solar energy, can also be called solar radiant energy. It is generally believed that solar energy is the radiant energy derived from the polymerization reaction of ammonia nuclei to form sunlight. Since the formation of the earth, organisms have mainly survived by the heat and light provided by the sun, and since ancient times, humans have also known to use the sun to dry objects and use them as a method of preserving food, such as salt production and salted fish. However, under the circumstance of the reduction of fossil fuels, people intend to further develop solar energy. There are two ways to use solar energy: passive utilization (photothermal conversion) and active utilization (photoelectric conversion).
Solar energy is both a primary energy source and a renewable energy source. Solar energy is clean and safe, and there is no waste residue or waste in the process of development and utilization; it is not only rich in resources, but also free of charge, without transportation, and will not cause any pollution to the environment. As the future energy source, solar energy is a very ideal clean energy. In recent years, due to people's increasing attention to energy and environmental issues, the application and popularization of solar energy has received more and more attention. Therefore, if solar energy is used reasonably, it will provide sufficient energy for mankind.
All things grow by the sun. If there is no sun, there will be no daylight in the world; if there is no sun, all living things in the world will perish and disappear; if there is no sun, human beings will no longer exist.
The sun is the closest star to our earth, with a magnetic field and rotation. The sun has a diameter of about 1.4 million kilometers, which is equivalent to the total diameter of 109 earths. It is the largest celestial body in the solar system and contains nearly 98% of the mass of the solar system. Its interior can accommodate more than 1.3 million earths.
The nucleus reaction of hydrogen fusion to ammonia is constantly going on inside the sun, and the fusion reaction of hydrogen fusion to helium generates huge energy. The sun continuously releases huge energy to radiate into the universe, and this radiation forms solar energy. Solar energy is the most important basic energy source, and most of the energy needed by mankind comes directly or indirectly from the sun. It is various plants that convert solar energy into chemical energy through photosynthesis and store it in the plant. Fossil fuels such as coal, oil, and natural gas are also formed by ancient animals and plants buried in the ground over a long geological age. They are essentially solar energy fixed by ancient organisms. In addition, biomass energy, wind energy, tidal energy, and water energy all come from solar energy.
The sun has an extremely high temperature and brightness. Its surface temperature is as high as 5497°C, and its center temperature is as high as 15-20 million degrees Celsius. The total brightness of the sun is about 3x 1027 cd (at this time, the influence of atmospheric absorption is corrected). Since the sun has such a high temperature and brightness, its radiant energy is also extremely huge. On average, on an area of 1 m2 facing the sun outside the earth’s atmosphere, the amount of solar energy received per second is about 1367W. Solar radiant energy passes through the atmosphere. Due to absorption, scattering and reflection, only one-third of the solar radiant energy that can directly reach the surface remains, and 70% of it is irradiated on the ocean, so only about 1.5 x 1017remains.kilowatt hours, which is about 6000 times the energy consumed by the United States in 1978. The solar radiant energy that is not absorbed or scattered but can reach the ground surface is called direct radiant energy; while the scattered radiant energy is called diffuse radiant energy, and the total solar radiant energy at each point on the surface is direct and diffuse radiation. Can be the sum of the two.
The huge energy body of the sun, the fusion reaction capacity power of hydrogen fusion into hydrogen is about 3.8 ×1023 kw, the earth only receives 1/2.2 billionth of the sun's total radiation, but it is also about 1.7 ×1014 kW. This part of the radiation is absorbed by the atmosphere, accounting for about 23%, and the solar radiation reflected back to space by atmospheric molecules and dust is about 30%, and the remaining 47% can reach the ground, which is about 8.1 x 1013 kw. This amount is equivalent to the total amount of solar radiation. Hundreds of thousands of times the world's electricity generation. The radiant energy that the sun projects on the earth every year is 6 x 1017kilowatt-hours, which is equivalent to 74 trillion tons of standard coal. Scientists have shown that the energy radiated by the sun to the earth per hour is about 180,000 megawatts, which is equivalent to the heat of burning 90 megatons of high-quality coal. According to the current mass consumption rate of the sun, the sun can last about 60 billion years, so it can be said that solar energy is an "inexhaustible and inexhaustible" energy source.
The energy of the sun is huge. Although the use of solar energy has a history of more than 3,000 years, the use of solar energy as a source of energy and power has a history of less than 400 years. Especially in the past 100 years, solar thermal utilization technology has developed rapidly. Since the beginning of the 20th century, with the development of social economy and the improvement of people's living standards, the demand for energy has continued to grow. The finiteness of fossil energy resources and their impact on the global climate and environment during the combustion process have attracted increasing attention. From the perspective of resource, environmental, and social development needs, the development and utilization of new and renewable energy is an inevitable trend. Solar energy is both a primary energy source and a renewable energy source. Solar energy is clean and safe. There are no waste residues and waste materials in the development and utilization process, and it will not cause any pollution to the environment. In the new energy and renewable energy family, with the advancement of science and the development of society, the superiority of solar energy utilization has gradually become the most eye-catching member who has carried out the most research work and is the most widely used.
So far, the ways to use solar energy as a kind of energy and power are mainly divided into the following four categories: photothermal utilization, photovoltaic utilization, photochemical utilization and photobiological utilization. Among the four types of utilization, photothermal utilization is the most basic and common solar utilization. Its basic principle is to collect solar radiant energy and convert it into heat energy through interaction with matter.
In the solar thermal utilization, we usually divide the solar thermal utilization into low temperature utilization (<200℃), medium temperature utilization (200-800℃) and high temperature utilization (>800 ℃) Three kinds.
At present, low temperature utilization mainly includes solar water heaters, solar dryers, solar distillers, solar houses, solar greenhouses, and solar air conditioning refrigeration systems. In recent years, the main research and development direction is to find lower solar collector manufacturing costs, improve operating efficiency and reliability And simplify the design and installation methods. For example, the extremely low temperature (below 45°C) heat collector used for swimming pool heating has a special structure design, and the frame of the domestic water heater and the heating flat heat collector adopts special aluminum extrusion devices. In terms of sealing technology The use of synthetic rubber gaskets solves the problems of water leakage in the cover plate and cracks of the glass due to thermal stress. These measures simplify the manufacturing process of the collector and improve the operating efficiency of the collector.
The medium-temperature utilization mainly includes solar cookers and solar industrial heat utilization, and the collectors used in the medium-temperature utilization system must have a certain degree of concentration, and the medium-temperature heat transfer medium and heat storage methods must be used. These two characteristics are also the medium-temperature utilization. The main difference with low temperature utilization. In terms of concentrating heat collectors, there are compound parabolic concentrating heat collectors, linear Fresnel projection concentrating heat collectors, rotating parabolic concentrating heat collectors, etc., but another feature is the phase of medium temperature heat storage and low temperature heat storage. Compared with that, the cost is much more expensive. At present, some organic and inorganic fluids have been developed to transmit and store solar thermal energy at 200~800℃. At the same time, the phase change heat storage method that uses latent heat capacity to store heat has been developed technically. The main problems are the cost of heat storage materials, long-term chemical stability and corrosiveness to the container device.
High-temperature utilization mainly includes high-temperature solar furnaces and high-temperature thermal power generation. Generally, the high-temperature utilization system costs a lot of money. It mainly includes two aspects, namely, a rotating parabolic concentrator and a fixed mirror field. The former uses a small heat engine, especially hot air. The machine constitutes the so-called distributed small-scale solar power generation device, which has certain development prospects when used in remote areas and transforming deserts. The latter refers to large-scale tower-type power generation devices, and the technology is still in the development stage.