Principles of
Solar Cell Power Generation Solar cells are devices that respond to light and convert light energy into electricity. There are many kinds of materials that can produce photovoltaic effect, such as: monocrystalline silicon, polycrystalline silicon, amorphous silicon, gallium arsenide, selenium indium copper, and the like. Their power generation principle is basically the same, and the crystal power generation process is now described by taking a crystal as an example. P-type crystalline silicon is doped with phosphorus to obtain N-type silicon to form a P-N junction.
When the light illuminates the surface of the solar cell, part of the photons are absorbed by the silicon material; the energy of the photons is transferred to the silicon atoms, causing the electrons to move more and more, and the free electrons accumulate on both sides of the P-N junction to form a potential difference. When the circuit is turned on, under the action of this voltage, a current will flow through the external circuit to generate a certain output power. The essence of this process is the process of converting photon energy into electrical energy.
Introduction to the Sun The Sun is the closest star to the Earth and the central object of the Sun. Its mass accounts for 99.865% of the total mass of the Solar System. The sun is also the only celestial body in the solar system that emits light and heat to the earth. If there is no sunlight, the temperature of the ground will quickly drop to near absolute zero. Due to the illumination of the sun, the average temperature of the ground will remain at around 14 °C, forming the conditions for the survival of humans and most organisms. In addition to the energy of atomic energy, geothermal heat and volcanic eruptions, most of the energy on the ground is directly or indirectly related to the sun.
The sun is a hot gas fireball composed mainly of hydrogen and helium, with a radius of 6.96×105km (109 times the radius of the Earth), a mass of 1.99×1027t (330,000 times the mass of the Earth), and an average density of about the Earth. 1/4. The effective temperature on the surface of the sun is 5762K, while the temperature in the inner central region is as high as tens of millions of degrees. The energy of the sun is mainly derived from the fusion reaction of hydrogen polymerization into helium, and 6.57×1011 kg of hydrogen per second is polymerized to form 6.53×1011 kg of helium, which continuously produces 3.90×1023 kW of energy. These energies are transmitted in all directions in the form of electromagnetic waves at a speed of 3 × 105 km / s in all directions. The Earth only receives one-twentieth of the total solar radiation, that is, 1.77×1014 kW reaches the upper edge of the Earth's atmosphere (“upper boundaryâ€). Due to the attenuation through the atmosphere, the final 8.5×1013 kW reaches the surface of the earth. The number is equivalent to hundreds of thousands of times of the world's power generation.
According to the current nuclear energy rate generated by the sun, the hydrogen reserves are enough to maintain 60 billion years, and the internal organization of the earth is aggregated into a ruthenium due to the thermonuclear reaction. Its life span is about 5 billion years. Therefore, in this sense, it can be said that the sun Energy is inexhaustible and inexhaustible.
The structure and energy transfer patterns of the sun are briefly described below.
The mass of the sun is very large. Under the action of the sun's own gravity, the solar material collects toward the core, and the density and temperature of the core center are high, enabling nuclear reactions to occur. These nuclear reactions are the energy of the sun, and the energy produced continuously radiates into space and controls the activity of the sun. According to various indirect and direct data, it is believed that the sun can be divided into nuclear reaction zone, radiation zone, convective zone and solar atmosphere from the center to the edge.
(1) Nuclear reaction zone In the region of the solar radius of 25% (ie 0.25R), it is the core of the sun, which concentrates more than half of the mass of the sun. The temperature here is about 15 million kW (K), the pressure is about 250 billion atmospheres (1 atm = 101325 Pa), and the density is close to 158 g/cm3. This part produces 99% of the total energy produced by the Sun and radiates outward in convection and radiation. When hydrogen is polymerized, gamma rays are emitted. When the rays pass through the cooler regions, they consume energy, increase the wavelength, and become X-rays or ultraviolet rays and visible rays.
(2) Radiation zone Outside the nuclear reaction zone is the radiation zone, which ranges from 0.25 to 0.8R, the temperature drops to 130,000 degrees, and the density decreases to 0.079 g/cm3. The energy generated at the core of the sun is transmitted by radiation through this area.
(3) Convection zone Outside the radiation zone is the convection zone (troposphere), which ranges from 0.8 to 1.0 R, the temperature drops to 5000 K, and the density is 10-8 g/cm3. In the convective zone, energy is mainly transmitted by convection. The convective zone and its parts are invisible, and their properties can only be determined by theoretical calculations consistent with the observations.
(4) The solar atmosphere can be roughly divided into light spheres, chromospheres, coronas and other layers, and the physical properties of each level are clearly different. The bottom layer of the solar atmosphere is called the light sphere, and the entire light energy of the sun is emitted almost entirely from this level. The continuous spectrum of the sun is basically the spectrum of the light sphere, and the absorption line in the solar spectrum is basically formed in this layer. The thickness of the photosphere is approximately 500km. The chromosphere is the middle layer of the solar atmosphere. It is the outward extension of the light sphere and can extend to a height of several thousand kilometers. The outermost layer of the solar atmosphere is called the corona, which is an extremely thin gas shell that can extend to a few solar radii. Strictly speaking, the above-mentioned stratification of the solar atmosphere has only a formal meaning. In fact, there is no obvious boundary between the layers, and their temperature and density change continuously with height.
It can be seen that the sun is not a black body with a certain temperature, but a radiation body that radiates and absorbs at different wavelengths. However, when describing the sun, the sun is usually regarded as a black radiator having a temperature of 6000 K and a wavelength of 0.3 to 3.0 μm.
New Solar Energy Utilization Recently, it was learned from the Shanghai Science and Technology Commission that researchers at East China Normal University successfully used nanomaterials to “recreate†chloroplasts in the laboratory to achieve photovoltaic power generation at extremely low cost.
Chloroplasts are places where plants perform photosynthesis and can effectively convert sunlight into chemical energy. Instead of "copying" a chloroplast in vitro, the research team developed a new type of battery, a dye-sensitized solar cell, similar to the chloroplast structure, in an attempt to convert light energy into electrical energy. With the support of the Shanghai Nano-Special Fund, after more than three years of experimentation and exploration, the photoelectric conversion efficiency of this bionic solar cell has exceeded 10%, close to the world's highest level of 11%.
Mr. Sun Zhuo, the project leader and director of the Engineering Research Center of the Department of Advanced Optoelectronic Integration and Advanced Equipment Education of the East China Division, demonstrated the “sandwich†structure of the new solar cell—the hollow glass sandwiched with a layer of nano-sandwich, the mystery of photoelectric conversion It is hidden in this layer of tens of microns thick composite film. The “formulation†of the nano “sandwich†is unique: the dye acts as a “light
Harvester†and the nano titanium dioxide is a “photoelectric converterâ€. In order to let the dyes "eat" the sun as much as possible, the researchers have also sifted a little "preservation" - a quantum dot made of nano-fluorescent material, so that different wavelengths of sunlight can be caught The appetite of the light hand. As long as the "recipe" is continuously improved, the photoelectric conversion efficiency of the nano "sandwich" can be improved again and again.
As a third-generation solar cell, the biggest attraction of dye-sensitized batteries is cheap raw materials and simple manufacturing processes. It is estimated that the cost of a dye-sensitized battery is only one-tenth the cost of a silicon panel. At the same time, it does not require high lighting conditions, even in indoors where sunlight is not sufficient, its photoelectric conversion rate will not be greatly affected. In addition, it has many interesting uses. For example, by replacing the glass "plywood" with plastic, a flexible flexible battery can be made; by making it a display, it can generate electricity while emitting light to achieve self-sufficiency in energy.
Solar energy is a clean and sustainable source of energy. The development of solar technology can reduce the use of fossil fuels in power generation, thereby reducing air pollution and global warming.
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