Solar energy utilization and solar cell

Solar and renewable energy classification

admin on August 2, 2021 0 Comments • Tags: #renewableenergy #solaractivity #sunradiation

Everything grows by the sun. The earth’s wind energy, water energy, ocean temperature difference energy, wave energy and biomass energy, and part of the tidal energy all come from the sun; even the fossil fuels on the earth (such as coal, oil, natural gas, etc.) are fundamentally speaking Solar energy stored in ancient times. The sun is a self-luminous celestial body closest to the earth. It brings light and heat to the earth. The sun’s activity comes from its central part, where the central temperature is as high as 15 million degrees Celsius, where nuclear fusion takes place. Solar energy is the energy produced by the continuous nuclear fusion reaction process inside the sun. Fusion produces energy and is released to the surface of the sun, emitting light and heat through a process of convection. It takes millions of years for the energy from the core of the sun to reach its surface, thus enabling the sun to shine. So far, the age of the sun is about 4.6 billion years, and it can continue to burn for about 5 billion years. Therefore, it can be said that solar energy is an inexhaustible and inexhaustible energy source. The total annual energy consumption in the world is only equivalent to the energy projected by the sun on 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 4X1026J, which 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 to 3.0 μm, and the distribution of radiation wavelengths ranges from the ultraviolet region to the infrared region. Although the solar radiation energy received by the earth is only one-two billionths of the total radiation energy emitted by the sun into space, the solar radiation energy reaching outside the earth’s atmosphere is between 132.8~141.8mW/cm2, which is affected by the atmosphere. After reflection, scattering and absorption, about 70% of it is projected to the ground, but it is already as high as 1.73X1015W; that is to say, the energy that the sun shines on the earth every second is equivalent to the energy of 5 million tons of coal burning, which is the global energy consumption Tens of thousands of times.

According to the characteristics of energy utilization, energy is divided into renewable energy and non-renewable energy. Renewable energy refers to energy sources whose raw materials can be regenerated, such as wind energy, bioenergy, geothermal energy, hydropower, and solar energy. Renewable energy does not have the possibility of energy exhaustion, so it is increasingly being valued by many countries, especially countries with energy shortages.

(1) Wind energy
Wind energy is the kinetic energy generated by a large amount of air movement on the earth’s surface. Due to the different temperature changes and the
The content of water vapor in the air is different, which causes the difference of air pressure in various places. In the horizontal direction, high-pressure air flows to low-pressure areas, that is, wind is formed. Wind energy resources depend on the wind energy density and the available wind energy accumulation time (hours). Wind energy density is the wind power available per unit area facing the wind, which is proportional to the power of the wind speed and the air density. It is estimated that the world’s total wind energy is about 130 billion kilowatts. Wind energy resources are greatly affected by topography, and most of the world’s wind energy resources are concentrated in the shrinking areas of coastal and open continents. In nature, wind is a renewable, non-polluting and huge reserves of energy. With the global warming and energy crisis, all countries are stepping up the development and utilization of wind power, minimizing the emission of carbon dioxide and other greenhouse gases, and protecting the earth on which we depend. There are two main forms of wind energy utilization: wind energy as power and wind power generation, of which wind power is the main form.

(2) Bioenergy
Bioenergy is a form of energy stored in organisms in the form of chemical energy from solar energy, a kind of energy with biomass as a carrier, which directly or indirectly originates from photosynthesis of plants. Photochemical reactions are different from thermochemical reactions. As long as the wavelength of light can be absorbed by the substance, it can still proceed at lower temperatures. The most common photochemical application is the photosynthesis of green plants. Through the photosynthesis of plants, solar energy synthesizes carbon dioxide and water into organic matter (biomass energy) and releases oxygen. Photosynthesis is the largest conversion of solar energy on earth. The fuel used by modern humans is Solar energy fixed by photosynthesis in ancient times and today. At present, the mechanism of photosynthesis is not fully understood, and the energy conversion efficiency is generally only a few percent. The study of its mechanism has great theoretical and practical significance.

(3) Geothermal energy
Geothermal energy is natural thermal energy extracted from the earth’s crust. This energy comes from the lava inside the earth and exists in the form of heat. It is the energy that causes volcanic eruptions and earthquakes. The temperature inside the earth is as high as 7000°C, and at a depth of 80~100km, the temperature will drop to 650~1200°C. Through the flow of groundwater and lava flow to the upper ground 1~5km of the crust, the heat is transferred closer Ground place. High-temperature lava heats nearby groundwater, and this heated water will eventually seep out of the ground. The simplest and most cost-effective way to use geothermal energy is to directly use these heat sources and extract their energy. Utilization forms of geothermal energy: ①200~400°C direct power generation and comprehensive utilization: ②150~200°C dual-cycle power generation, refrigeration, industrial drying, industrial thermal processing; ③100~150°C dual-cycle power generation, heating, cooling, industrial drying , Dehydration processing, recovery of salt, canned food: ④50~100C heating, greenhouse, domestic hot water, industrial drying; ⑤20~50°C bathing, aquaculture, livestock breeding, soil heating, dehydration processing. In order to improve the utilization rate of geothermal energy, many countries now adopt cascade development and comprehensive utilization methods, such as combined heat and power, combined heat, power and cooling, and first heating and then breeding.

(4) Hydropower
Hydropower is a kind of renewable energy and clean energy, which refers to energy resources such as kinetic energy, potential energy and pressure energy of water bodies. In a broad sense, hydropower resources include river hydropower, tidal hydropower, wave energy, ocean current energy and other energy resources; in a narrow sense, hydropower resources refer to river hydropower resources. Not only can water be used directly by humans, it is also a carrier of energy. Solar energy drives the water cycle on the earth and keeps it going. The flow of surface water is an important part. In areas with large drops and large flows, hydropower resources are abundant. With the decline of fossil fuels, hydropower is a very important and promising alternative resource. At present, hydroelectric power generation in the world is still in its infancy. Water movements such as rivers, tides, waves and swells can all be used to generate electricity.

(5) Solar
The solar energy received on the ground includes direct radiant energy and scattered radiant energy. The solar radiation directly received without changing its direction is called direct solar radiation; the solar radiation whose direction changes after being reflected and scattered by the atmosphere is called scattered radiation. In order to describe solar energy quantitatively, some concepts need to be introduced. When the earth is at the average distance between the sun and the earth, the total energy of the full spectrum of solar radiation received by the unit area of ​​the upper boundary of the earth’s atmosphere perpendicular to the sun’s rays per 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 of the atmosphere on the surface of the earth receiving sunlight is defined as atmospheric mass (AM). Atmospheric quality is a dimensionless quantity. It is the ratio of the path of the sun’s rays through the earth’s atmosphere to the path of the sun’s rays passing through the atmosphere at the zenith angle. The vertical path of sunlight on the plane is 1. The AM value is different, the solar spectrum will have different changes. When the solar radiation intensity is the solar constant, the air quality is recorded as AMO, and the AMO spectrum is suitable for the situation on artificial satellites and spacecraft. The spectrum of air quality AM1 corresponds to the spectrum of the sun directly hitting the earth’s surface (its light power is 925W/cm2). Figure 1 is the solar spectrum under the two conditions of AM0 and AM1. The difference between them is caused by the attenuation caused by the absorption of sunlight by the atmosphere, mainly from the absorption of ultraviolet light by the ozone layer and the absorption of infrared light by water vapor, and Scattering of dust and suspended matter in the air. In the figure, the solar spectral irradiance Eλ= dE/dλ, where E is the solar irradiance per unit wavelength interval, given the wavelength λ. These characteristics of the solar spectrum are a very important factor for the selection of solar cell materials.

Figure 1 AM0 and AM1 solar spectrum

Solar activity is closely related to some phenomena on the earth. Now, people have found that solar activity has a significant impact on the earth in the following aspects. The solar flares and sunspots have significant geophysical effects on the ionosphere, magnetic field, and polar regions of the earth, which affect the terrestrial short-wave radio communication, even short-term interruption, which is called “sudden ionospheric disturbance.” These reflections appeared almost simultaneously with the outbreak of the large flare. The magnetic field descends along the lines of magnetic force and collides with the gas of the chromosphere layer, causing the heel parts of the magnetic lines of force on both sides of the neutral line to glow and become a flare that people see. The flares themselves are the result of unstable magnetic fields. It is precisely because of the non-equilibrium state of the magnetic field that the flare erupts to achieve a new balance of the magnetic field. The flare eruption process is also a process of releasing a large amount of energy. Larger flares have an explosion temperature of tens of millions of degrees or even hundreds of millions of degrees, and they emit strong X-rays, ultraviolet rays, and high-energy protons. These strong radiation rays increase the pressure of hydrogen atoms, causing hydrogen atoms, ions and other particles to be ejected at a speed of more than 1000km/s and become the sun’s particle radiation. The phenomenon of “magnetic storm” shows that the entire earth is a large magnetic field, and the surroundings of the earth are full of magnetic field lines. When a flare appears, high-energy particles are emitted from its vicinity, and a magnetic field is generated when the charged particle moves. When it reaches the earth, it disturbs the original magnetic field and causes changes in the geomagnetism. When a magnetic storm occurs, the intensity of the magnetic field changes greatly, which will have a great impact on human activities, especially work related to geomagnetism. The phenomenon of the sun affecting the earth is also the phenomenon of aurora: in the north and south latitudes of the earth, at night or even in the daytime, light green, red, pink bands or arcs of light can often be seen in the sky, called aurora. This is because when the stream of charged high-energy particles from solar activity reaches the earth, they rush towards the polar region under the action of a magnetic field, which excites or ionizes molecules or atoms in the upper atmosphere of the polar region to produce light. The sun’s far ultraviolet and solar wind will affect the density of the atmosphere. The change cycle of atmospheric density is 11 years, which is obviously related to solar activity. Solar activity may also affect atmospheric temperature and the ozone layer, which in turn affects the yield of crops and the balance of natural ecosystems. Because solar activity has an impact on humans, especially in aerospace, radio communications, meteorology, etc., studying solar activities, especially the law of solar flares, and trying to predict, is of great value to the use of solar energy.

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