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Solar radiation and solar energy application

2021-07-30 18:14:22

Human activities and solar radiant energy

Everything grows by the sun. The energy required for human production and life, such as oil, coal, wind energy, ocean tidal energy, water energy, geothermal energy, biomass energy, and combustible ice, are all forms of solar radiation energy transformation on the earth. With the increase of population, due to the excessive use of fossil fuels, the carbon dioxide emitted by human beings has exceeded the absorption capacity of the earth's ecosystem. Ecological overload also leads to forest shrinkage, a decline of fishery resources, land degradation, reduction of freshwater resources, increasing loss of biodiversity, and serious air pollution. According to the statistics of WWF, in 1961, mankind only consumed about 2 / 3 of the earth's annual renewable resources. According to the earth vitality report 2012, mankind currently consumes 1.5 earth's ecological resources every year and will reach 2 by 2050. China's ecological situation is also not optimistic. Although China's per capita is lower than the global average and much lower than that of European and American countries, it is already 2.5 times its own biological carrying capacity, which means that we need 2.5 China's natural resources to meet the demand; At the same time, due to the large population base, China's total ecological footprint is the largest in the world. China's fragile ecosystem is under the dual pressure of economic development and a growing population.

By switching to clean and sufficient renewable resources (such as solar energy and wind energy), we may gradually reduce air pollution emissions to mitigate the impact of climate change on the earth. The use of atomic energy has also matured, but the dangers of the Chernobyl nuclear power plant leak and the Fukushima nuclear leak in Japan are frightening. Earthquakes, volcanic eruptions, floods, and other energy generated by crustal movement are also being recognized by people.

Solar photovoltaic power generation is the most flexible and convenient way to develop and utilize solar energy, which has developed rapidly in recent years.

Solar radiant energy

Solar radiant energy refers to the solar radiant energy reaching the upper boundary of the earth's atmosphere, also known as astronomical solar radiation, or solar energy for short. The solar radiation energy received by the earth is only 2.2 billion times the total radiation energy radiated by the sun to space.

The sun is a self-luminous celestial body nearest to the earth. It brings light and heat to the earth. The activity of the sun comes from its central part, and the central temperature is as high as 1500 × At 106 ℃, nuclear fusion takes place here. Solar energy is the energy generated by the continuous nuclear fusion reaction inside the sun. Fusion produces energy and is released to the surface of the sun, emitting light and heat through convection. It takes millions of years for the energy of the sun's core to reach its surface so that the sun can shine. Up to now, the age of the sun is about 4.6 billion years, and it can continue to burn for about 5 billion years. According to the current cosmological theory, in the final stage of the existence of the sun, the nitrogen in the sun will be transformed into heavy elements, and the volume of the sun will continue to expand until it engulfs the earth. After 100 million years of red giant phase, the sun will suddenly collapse into a white dwarf - the last stage of all-stars. After trillions of years, it will eventually cool completely. Therefore, for human beings, solar energy is inexhaustible and inexhaustible energy.

It is generally believed that the sun is a huge gas mass under high temperature and high pressure, which can be divided into six regions from the inside to the outside.

① Solar core: the diameter of the solar core is about 0.23 times of the diameter of the sun, the mass is about 0.4 times of the sun, the volume is about 0.15 times of the sun, the pressure is up to 10 ° ATM (1atm = 101325pa), and the temperature is about 107k. There is a fierce thermonuclear reaction, and 90% of the energy generated is radiated outward in the form of convection and radiation.

② Absorption layer: it is called the absorption layer from outside the solar core to about 0.8 times the diameter of the sun,

Also known as the radiation layer. When the pressure of this layer drops to 10 am, a large number of hydrogen ions produced by the thermonuclear reaction are absorbed here.

③ Troposphere: it is called the troposphere from outside the absorption layer to one time of the solar diameter, during which the temperature is about 5103k, and a large amount of convective heat transfer is carried out in this area.

④ Photosphere: within 50km outside the troposphere, there are a large number of low ionized hydrogen atoms, which is the visible solar surface, and its brightness is equivalent to 600k blackbody radiation. The photosphere is a very important layer. Most of the solar radiation is emitted from the photosphere. At the same time, some sunspots and flares have a great impact on the earth.

⑤ Chromosphere: the thickness of the chromosphere is about 2500km, most of which is composed of low laminated helium, hydrogen, and a small number of ions, also known as the sun's atmosphere.

⑥ Corona: beyond the chromosphere is a silvery-white corona extending into space. The corona is composed of various particles, including some solar dust particles, ionized particles, and electrons, with a temperature of more than 10k. Sometimes the corona can extend tens of thousands of kilometers into space, forming a solar wind, impacting the earth's atmosphere, producing magnetic storms or aurora, thus affecting the earth's magnetic field and communication.

Solar radiation and solar energy application 1

The total annual energy consumption of the world is only equivalent to the energy projected by the sun onto the earth's surface within 40 minutes. The solar radiant energy comes from its internal thermonuclear reaction, and the energy converted per second is about 4 × 1026j is basically emitted in the form of electromagnetic radiation. The sun is usually regarded as a radiator with a temperature of 6000K and a wavelength of 0.3 ~ 3.0gm. The distribution of radiation wavelength ranges from the ultraviolet region to the infrared region. Although the solar radiation energy received by the earth is only 2.2 billion times of the total radiation energy radiated by the sun to space, the solar radiation energy outside the earth's atmosphere is 132.8 ~ 141.8mw/cm2, and about 70% is projected to the ground after being reflected, scattered and absorbed by the atmosphere, it has reached as high as 1.73 × That is, the energy consumption of 10.15 million tons of coal per second is equivalent to that of the earth. The solar radiation received on the ground includes direct radiation and scattered radiation. Direct radiation is called direct radiation when it directly receives solar radiation that does not change direction; The solar radiation whose direction is changed after being reflected and scattered by the atmosphere is called scattered radiation.

To describe solar energy quantitatively, some concepts need to be introduced. When the earth is located at the average distance between the sun and the earth, the total energy of the full spectrum of solar radiation is received by the unit area of the upper boundary of the earth's atmosphere perpendicular to the solar light in unit time is called the solar constant. The value of the solar constant is 1353w / m2, and the common unit is w / m2. The influence degree of the atmosphere on the sunlight received by the earth's surface is defined as atmospheric quality (AM). Atmospheric quality is a dimensionless quantity, which is the ratio of the path of the sun's light passing through the earth's atmosphere to the path of the sun's light passing through the atmosphere in the zenith angle direction. It is assumed that the path of the sun's vertical incidence on the sea level is 1 at the standard atmospheric pressure (101325pa) and air temperature of 0 ℃. The solar spectrum will change with different am values. When the solar radiation intensity is the solar constant, the atmospheric mass is recorded as AM0. The AM0 spectrum is suitable for the situation on man-made satellites and Zizhou spacecraft. The spectrum of the atmospheric mass AM1 corresponds to the solar spectrum directly onto the earth's surface (it's incident light power is 925w / cm2). Figure 1-2 shows the solar spectra under AM0 and AM1 conditions. The difference between them is caused by the attenuation caused by the absorption of sunlight by the atmosphere, mainly from the absorption of ultraviolet rays by the ozone layer, the absorption of infrared rays by water vapor, and the scattering of dust and suspended solids in the air. In the figure, the solar spectral irradiance EA = de / D, where e is the solar radiance per unit wavelength interval. These characteristics of the solar spectrum at a given wavelength are a very important factor for the selection of solar cell materials.

Solar radiation is a kind of electromagnetic radiation, which has both fluctuation and particle. The wavelength radiation range of the sun is shown in Figure 1-3. The main wavelength range of its spectrum is 0.15 ~ 4m, while the main wavelength range of ground and atmospheric radiation is 3 ~ 120m. In meteorology, solar radiation is usually called short wave radiation, and ground and atmospheric radiation are called longwave radiation. The wavelength distribution of solar energy can be simulated by blackbody radiation with a temperature of 6000. The solar wavelength is distributed in ultraviolet (< 0.4m), visible (0.40.75m) and infrared (> 0.75m). These bands are affected by atmospheric attenuation to varying degrees. Most of the visible radiation reaches the ground, but ozone in the upper atmosphere absorbs most of the ultraviolet radiation. Due to the thinning of the ozone layer, especially in the Antarctic and Arctic regions, more and more ultraviolet radiation reaches the ground. Part of the incident infrared radiation is absorbed by carbon dioxide, water vapor, and other gases, while most of the longer-wavelength infrared radiation from the earth's surface at night is transmitted to outer space. The accumulation of these greenhouse gases in the upper atmosphere may increase the atmospheric absorption capacity, resulting in global warming and cloudy weather. Although the reduction of ozone has little impact on solar energy absorption, the greenhouse effect may increase scattered radiation and may seriously affect solar energy absorption.

Solar radiation and solar energy application 2

The included angle between the incident direction of sunlight and the ground plane, that is, the included angle between the sunlight of a certain place and the surface tangent perpendicular to the earth's center is called the solar altitude angle, which is referred to as the solar altitude for short. It has diurnal and annual changes. When the solar altitude angle is 90 °, in the solar spectrum, infrared accounts for 50%, visible light accounts for 46%, and ultraviolet accounts for 4%. When the solar altitude angle is 5 °, infrared accounts for 72%, visible light accounts for 28% and ultraviolet is almost 0. The sun's altitude angle is constantly changing throughout the day; At the same time, it is also changing throughout the year. For a certain ground plane, when the solar altitude angle is low, the distance of light passing through the atmosphere is longer, and the radiant energy is attenuated much. At the same time, because the light is projected on the ground plane at a small angle, the energy reaching the ground plane is less, on the contrary, it is more.

In the plane perpendicular to the upper boundary of the atmosphere and light, the solar irradiance is basically a constant, but on the earth's surface, the solar irradiance changes frequently. This is mainly caused by the transparency of the atmosphere. The degree of atmospheric transparency is a parameter representing the degree of atmospheric transmission to solar light. In clear and cloudless weather, the atmospheric transparency is the best, and there is more solar radiation reaching the ground; When there are many clouds or sandstorms in the sky, the atmospheric transparency is low and the solar radiation energy reaching the ground is low.

Sunshine time is also an important factor affecting ground solar irradiance. If there is 14h in a day in a certain area, if the cloudy day time is ≥ 6h and the sun time is ≤ 8h, it can be said that the sunshine time of this day in this area is 8h. The longer the sunshine, the more total solar radiation the ground receives.

In addition, the higher the altitude, the better the atmospheric transparency, and the higher the direct radiation of the sun. In China's Qinghai Plateau, due to the average altitude of more than 4000m, clean atmosphere, dry air, and low latitude, the total solar radiation is mostly between 6000 ~ 8000mj / m2 direct radiation ratio is significant. In addition, solar-terrestrial distance, topography, and topography also have a certain impact on solar irradiance. At the same latitude, the temperature in the basin is higher than that in Pingchuan, and the temperature on the sunny slope is higher than that on the shady slope.

Law of solar-terrestrial motion: the earth's orbit around the sun is elliptical, and the sun is in one of the two focal points of its elliptical orbit. This elliptical orbit is called the ecliptic in astronomy. In the ecliptic plane, the distance between the sun and the earth is not a fixed value. The shortest distance between sun and earth (1.47) × 108km), i.e. perihelion; the Farthest distance between sun and earth (1.52) × 108km), i.e. aphelion. The difference is 5 × 106KM, accounting for about 1 / 30 of the average distance between day and earth.

The light intensity of the sun on the earth depends on the following four aspects: the distance between the sun and the earth, the relative position of the sun on the earth at a certain time, the attenuation of solar radiation entering the atmosphere, and the orientation and inclination of the solar receiving surface. Due to the different positions of the earth in orbit, the position of the sun is different based on the observer's ground plane on the earth. The specific situation is related to the geographical latitude. However, the position of the sun at the zenith can be seen at noon in different seasons.

Solar radiation and solar energy application 3

Solar activity is closely related to some phenomena on the earth. Now, people have found that solar activity significantly impacts the earth in the following aspects. Flares and sunspots in solar activity have significant geophysical effects on the earth's ionosphere, magnetic field, and polar region, affecting the ground radio short wave communication, and even short-term interruption, which is called "sudden ionospheric disturbance". These reactions occur almost simultaneously with the outbreak of large flares. The magnetic field comes down along the magnetic line of force and collides with the chromospheric gas, making the heel of the magnetic line of force on both sides of the neutral line shine, becoming a flare seen by people. The flare itself is the result of magnetic field instability. Because of magnetism

The field's non-equilibrium state leads to the flare's eruption to achieve a new balance of the magnetic field. The eruption process of the flare is also a process of massive energy release. The larger flare explosion is not only due to the thermal movement of hydrogen atoms, the temperature can reach tens of millions of degrees or even hundreds of millions of degrees, but also has strong X-ray, ultraviolet, and high-energy protons. These intense radiation rays increase the pressure of hydrogen atoms and make hydrogen atoms, ions, and other particles throw out at a speed of more than 100m / s, becoming the particulate radiation of the sun“ The phenomenon of "magnetic storm" shows that the whole earth is a large magnetic field, and the earth is full of magnetic lines of force. When the flare appears, high-energy particles are emitted from its vicinity. When the charged particles move, they produce a magnetic field. When it reaches the earth, it will disturb the original magnetic field and cause geomagnetic changes. When a magnetic storm occurs, the magnetic field intensity changes greatly, which will have a great impact on human activities, especially the work related to geomagnetism. Another phenomenon that the sun affectsos the earth is the aurora phenomenon: in the north and south poles of the earth, light bands or arcs of light green, red and pink can often be seen in the sky at night or even during the day, which is called aurora. This is because when the charged high-energy particle flow from solar activity reaches the earth, it runs to the polar region under the action of the magnetic field, which excites or ionizes the upper atmospheric molecules or atoms in the polar region to produce light. The solar far ultraviolet and solar wind will affect the atmospheric density. The variation cycle of atmospheric density is 11 years, which is obviously related to solar activity. Solar activity may also affect the atmospheric temperature and ozone layer, and then affect the yield of crops and the balance of natural ecosystems. Because solar activities have a significant impact on human beings, especially on aerospace, radio communication, and meteorology, it is of great value to study solar activities, especially the occurrence law of solar flares, and try to predict them.

 

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