Principles of solar cell power generation
Solar cells is a response to light and can convert light energy into electrical power devices. Photovoltaic effect can produce many kinds of materials, such as: silicon, polycrystalline silicon, amorphous silicon, gallium arsenide, copper indium selenium. They are basically the same principle of power generation is now crystal as an example to describe the light generation process. P-type crystalline silicon doped with phosphorus can be obtained through N-type silicon, the formation of P-N junction.
When the surface of solar cells exposed to light, the part of the photon absorbed by silicon material; photon energy transfer to the silicon atom, the electron transfer occurred in Vietnam, becoming free electrons in the P-N junction potential difference formed on both sides of gathering, when the external access through the circuit, under the effect of the voltage, current will flow through the external circuit to generate a certain output power. The essence of this process: photon energy into electrical energy process.
The sun is the nearest star from Earth is the center of the sun object, its mass accounted for 99.865 percent of total mass of the solar system. Sun is the only solar system objects in their own light, it brings light and heat the planet. If there is no exposure to sunlight, the ground temperature will quickly drop to near absolute zero. As sunlight exposure, average surface temperature will be maintained at around 14 °C, the formation of the human and the majority of biological survival. In addition to nuclear, geothermal and volcanic energy, the ground most of the energy are directly or indirectly related to the Sun.
The sun is a mainly composed of hydrogen and helium gas hot fireball with a radius of 6.96 × 105km (109 times the Earth radius), mass of about 1.99 × 1027t (33 times the Earth mass), the average density of about Earth 1 / 4. The effective temperature of the sun's surface 5762K, while the internal temperature of the central region and up to tens of millions of degrees. The sun's energy comes mainly from the hydrogen fusion reaction together into helium, there are 6.57 × 1011kg per second polymerization of hydrogen helium 6.53 × 1011kg, continuous production of 3.90 × 1023kW energy. The energy form of electromagnetic waves to 3 × 105km / s speed through space shooting in all directions. Global solar radiation the Earth receives only one half of 2.2 billion, that is 1.77 × 1014kW reach the Earth's atmosphere on the edge of the ("upper bound"), due to the attenuation through the atmosphere, the last of about 8.5 × 1013kW reach the surface, this generating capacity equivalent to the number of dozens of times around the world.
According to the current estimated rate of nuclear energy produced by the sun, hydrogen is sufficient to maintain reserves of 60 billion years, Earth's internal organization of the polymer into helium by thermonuclear reactions, it is about 50 billion years of life, so in this sense, it can be said of the sun energy is inexhaustible.
Sun's structure and energy transfer methods are briefly described below.
Great mass of the sun, the sun's own gravity, solar material gathered to the core, the core center of the high density and temperature, making the nuclear reaction can occur. The nuclear reaction is the sun's energy, the energy generated by continuous radiation to space, and control the activities of the sun. According to various indirect and direct information, that the sun can be divided from the center to the edge of the nuclear reaction zone, radiation zone, convection zone and the solar atmosphere.
(1) Nuclear reaction zone
25% of the solar radius (ie 0.25R) in the region, the core of the sun, focusing the sun more than half the quality. Here temperature is about 15 million degrees (K), atmospheric pressure is about 250 billion (1atm = 101325Pa), the density close to the 158g/cm3. This part of the total energy generated by solar energy produces 99% of the total, and radiate outward convection and radiation methods. Emit gamma-ray polymerization of hydrogen, these rays through the colder areas, energy consumption, increasing wavelength, into X-ray or ultraviolet and visible light.
(2) radiation zone
Outside of the nuclear reaction zone is the radiation zone, belongs to range from 0.25 ~ 0.8R, the temperature dropped to 13 million degrees, the density dropped to 0.079g/cm3. The energy generated in the solar core from the radiative transfer through out the region.
(3) convective zone
Outside the radiation zone is the convection zone (troposphere), belongs to range from 0.8 ~ 1.0R, the temperature dropped to 5000K, the density of 10-8g/cm3. In the convection zone, the energy spread mainly by convection. Inside the convection zone and part is invisible, they can only rely on the nature of observation consistent with the theoretical calculations to determine.
(4) solar atmosphere
Can be divided into ball of light, color ball, corona and other levels, all levels have significantly different physical properties. The lowest level of the solar atmosphere called the photosphere, the sun almost all the energy given from this level. Continuous spectrum is basically the sun's photosphere spectrum, absorption lines within the solar spectrum is basically formed within this layer. The thickness of the photosphere is about 500km. Chromosphere is the solar atmosphere of the middle, is the outward extension of the photosphere, has been extended to thousands of kilometers can be high. The outer solar atmosphere called the corona, the corona is extremely thin gas shell, can be extended to several solar radii away. Strictly speaking, the only form of stratified solar atmosphere the significance, in fact, does not exist between the layers is a clear boundary, and their temperature and density with height is continuously changing.
Visible, the sun is not a certain temperature blackbody, but the many layers of different wavelengths of radiation, the radiation body. However, in the description of the sun, the sun as the temperature is typically 6000K, 0.3 ~ 3.0µm wavelength of the black body radiation.
Recent development of solar energy utilization
Has learned from the Shanghai Science and Technology Commission, East China Normal University researchers using nano-materials in the laboratory success "recycling" chloroplasts, in a very low cost to achieve energy generation.
Chloroplast is the site of photosynthesis of plants, effective conversion of sunlight into chemical energy. The research group of plants in vitro is not "copy" of a chloroplast, but developed a similar chloroplast structure and a new battery --- dye-sensitized solar cells, convert light into electrical energy trying. In Shanghai Nano Special Fund's support, after 3 years experiment and explore, this bionic photoelectric conversion efficiency of solar cells for more than 10%, nearly 11% of the world highest level.
Project Manager, East China Normal University is satisfied with the advanced equipment Optoelectronic Integrated Engineering Research Center, Ministry of Education, Professor Sun Zhuo demonstrated a new type of solar cells, "sandwich" structure sandwiched a layer of insulating glass nano --- "sandwich", photoelectric conversion of the mystery hidden in this layer tens of microns thick composite film. Nano "sandwich" and "formula" is unique: Dye to act as "light-harvesting hand", nano titanium dioxide is a "media converter." Dyes as much as possible in order to "eat" the sun, researchers even inspired to spread the point "sauce" --- a fluorescent material by the nano-dots, so that different wavelengths of light can be on a "fishing light hand "and" appetite. " Continue to improve as long as the "recipe" nano "sandwich" of the photoelectric conversion efficiency can be improved again and again.
As a third generation solar cells, dye-sensitized cells is the biggest attraction of cheap raw materials and simple production process. It is estimated that the cost of dye-sensitized cell silicon solar panels equal to only 1 / 10. At the same time, it less demanding lighting conditions, even in the sun is not enough room, the photoelectric conversion rate can not be seriously affected. In addition, it also has many interesting uses. For example, using plastic instead of glass "plates" can be bent into flexible batteries; to make it into the monitor, you can side of the power generation side of the light, to achieve energy self-sufficiency.
Solar energy is a clean and sustainable energy, development of solar energy in the power generation process to reduce use of fossil fuels, thereby reducing air pollution and global warming.
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