For the time being, the direct utilization of solar energy by mankind is still in its infancy, and there are mainly solar thermal collectors, solar water heating systems, solar warming, solar power generation, and other ways. Solar collectors Solar water heating units usually include solar collectors, storage tanks, pipes and pumping pumps other components. In addition, in winter, heat exchangers and expansion tanks are needed, as well as power generation devices to prepare for the power plant can not supply electricity. Solar collector (solar collector) in the solar thermal system, accept solar radiation and heat transfer to the heat transfer processor heat transfer device. According to the heat transfer medium can be divided into liquid collector and air collector. According to the way of light can be divided into concentrating type collector and heat-absorbing type collector two. There is also a vacuum collector: a good solar collector should last 20-30 years. Collectors made since about 1980 should last 40 to 50 years with little maintenance. Solar water heating systems The most widespread early application of solar energy was for heating water, and today there are millions of solar water heating installations around the world. The main components of a solar water heating system are the collector, the storage unit and the circulation lines. In addition, there may be auxiliary energy devices (e.g., electric heaters, etc.) for use when there is no sunshine, and there may also be forced circulation of water to control the water level or control the electric portion or temperature of the device, as well as the piping to the load, and so on. According to the circulation method solar water heating system can be divided into two kinds: 1, natural circulation: this type of storage tank placed above the collector. Water heated by solar radiation in the collector, the temperature rises, resulting in the collector and the storage tank in the water temperature is different and produce a density difference, thus giving rise to buoyancy, this thermosiphon image, prompting the water in addition to the tank and the collector in the natural flow. By the relationship with the density difference, water flow in the collector of solar energy absorption is proportional to the amount. This type of water circulation is not required, maintenance is very simple, it has been widely used. 2, forced circulation: hot water system using water to make water in the collector and storage tanks between the cycle. When the collector at the top of the water temperature is higher than the bottom of the storage tank water temperature a number of degrees, the control device will start the water so that the water flow. A check valve is provided at the water inlet to prevent water from flowing backwards from the collector at night, causing heat loss. The flow rate of this type of hot water system can be known (because the flow rate from the water can be known), it is easy to predict the performance, can also be projected in a number of time the amount of heated water. Under the same design conditions, it has the advantage of obtaining a higher water temperature than the natural circulation method, but because it must utilize water, there are problems with water power, maintenance (such as leaks, etc.), and the control device moves from time to time, and it is easy to damage the water. Therefore, in addition to large-scale hot water system or the need for higher water temperatures, the choice of forced circulation type, most of the general use of natural circulation type water heater. Room warming The use of solar energy for room warming in winter, in many cold regions have been used for many years. Because of the very low winter temperatures in cold regions, indoor heating equipment must be available, if you want to save a lot of fossil energy consumption, trying to apply solar radiation heat. Most solar warming houses use hot water systems, but also use hot air systems. The solar heating system consists of a solar collector, a thermal storage device, an auxiliary energy system, and an indoor heating fan system. The process is solar radiation heat transfer, thermal energy storage through the working fluid in the collector, and then supply heat to the room. As for the auxiliary heat source, it can be installed in the heat storage device, directly installed in the room or installed in the storage device and the room between different designs. Of course, it is also possible to use the heat energy directly to heat the room without the need of heat storage, or to use solar energy directly to generate electricity in the form of thermoelectricity or photovoltaic, and then to heat the room, or through the heat device of the cold and warm room for the use of the warm room. The most commonly used room warming system is the solar water heating system, which passes hot water into a heat storage device (solid, liquid or phase change heat storage system), and then uses a fan to drive the indoor or outdoor air into the heat storage device to absorb heat, and then transfers this hot air to the room; or uses another kind of liquid to flow into the heat storage device to absorb heat, and then uses the fan to blow the heated air into the room when the hot fluid flows into the room, and then achieves the effect of room warming. The effect of warming the room is achieved by using a fan to blow the heated air into the room. Solar power generation is the direct conversion of solar energy into electrical energy, which is stored in a capacitor for use when needed. Solar off-grid power generation system Solar off-grid power generation system includes 1, solar controller (photovoltaic controller and wind and solar complementary controller) on the power generated by the regulation and control, on the one hand, the adjusted energy sent to the DC load or AC load, on the other hand, the excess energy sent to the battery bank storage, when the generated electricity can not meet the needs of the load, the solar controller and the battery's electrical energy sent to the Load. After the battery is fully charged, the controller should control the battery from being overcharged. When the battery's stored electricity is discharged, the solar controller should control the battery not to be over-discharged to protect the battery. When the controller's performance is not good, it has a great impact on the service life of the battery and ultimately affects the reliability of the system.2. The task of the solar battery bank is to store energy so as to ensure that the loads are powered at night or on cloudy or rainy days.3. The solar inverter is responsible for converting the DC power to AC power for use by the AC loads. Solar inverter is the core component of photovoltaic wind power generation system. Due to the relative backwardness and remoteness of the area where it is used, maintenance is difficult. In order to improve the overall performance of the PV wind power generation system and to ensure the long-term stable operation of the power station, the reliability of the inverter is highly demanded. In addition, due to the high cost of new energy power generation, the efficient operation of solar inverters is also very important. Solar off-grid power generation system main product classification A, photovoltaic module B, wind turbine C, controller D, battery pack E, inverter F, wind / photovoltaic power generation control and inverter integrated power supply. Solar grid-connected power generation system Renewable energy grid-connected power generation system is a power generation system that feeds renewable energy generated by photovoltaic arrays, wind turbines, and fuel cells into the power grid directly in reverse through a grid-connected inverter without battery storage. Because the power is fed directly into the grid, eliminating the need to configure batteries and the process of battery storage and release, the power generated from renewable energy sources can be fully utilized, reducing energy loss and lowering system costs. Grid-connected power generation systems are able to utilize utility power and renewable energy sources in parallel as a power source for local AC loads, reducing the load shortage rate of the entire system. At the same time, a renewable energy grid-connected system can act as a peak shifter for the utility grid. Grid-connected power generation system is the development direction of solar wind power generation, representing the most attractive energy utilization technology in the 21st century. Solar grid-connected power generation system main product classification A, photovoltaic grid-connected inverter B, small wind turbine grid-connected inverter C, large wind turbine converter (double-fed converter, full-power converter).
[edit]Space solar power
The first space solar cell was contained in Vangtuard I, launched in 1958, with a body-mounted structure and a monocrystalline Si substrate, with an efficiency of about 10% (28°C). By the 1970s, improvements were made to the cell structure, with technologies such as BSF, photolithography, and better reflection-reducing films, which increased the cell's efficiency to 14%. During the 1970s and 1980s, terrestrial solar cells doubled their global production approximately every 5.5 years; while space solar cells improved their performance in the space environment, such as radiation resistance. Improvements in terrestrial and space solar cell performance were greatly facilitated by the rapid development of solar cell theory in the 1980s. By the 1990s, the research on thin film and III-V batteries was developing rapidly, and the concentrating array structure had become more economical, and the space solar cell market was very competitive. In the continuing research on higher performance solar cells, there are two main avenues: research on concentrator cells and multi-bandgap cells. × Main Performance of Space Solar Cells Battery Efficiency Since solar cells generally have different efficiencies under different light intensities or spectral conditions, the AM0 spectrum (1.367 KW/m2) is generally used for space solar cells, and the AM1.5 spectrum (i.e., ground-based noontime clear-sky sunlight, 1.000 KWm-2) is generally used for terrestrial applications as the standard light source for testing the cell efficiency. (The efficiency of solar cell in AM0 spectrum is generally lower than that of AM1.5 spectrum by 2 to 4 percentage points, e.g. the AM1.5 efficiency of a Si solar cell with AM0 efficiency of 16% is about 19%). ◎ 25℃, AM0 conditions solar cell efficiency Cell type Area (cm2) Efficiency (%) Cell structure General Si solar cell 64cm2 14.6 Single junction solar cell Advanced Si solar cell 4cm2 20.8 Single junction solar cell GaAs solar cell 4cm2 21.8 Single junction solar cell InP solar cell 4cm2 19.9 Single junction solar cell GaInP /GaAs 4cm2 26.9 Monolithic Stacked Double Junction Solar Cell GaInP/GaAs/Ge 4cm2 25.5 Monolithic Stacked Double Junction Solar Cell GaInP/GaAs/Ge 4cm2 27.0 Monolithic Stacked Triple Junction Solar Cell ◎ Concentrator GaAs Solar Cell 0.07 24.6 100X GaInP/GaAs 0.25 26.4 50X, monolithic stacked layer double junction solar cells GaAs/GaSb 0.05 30.5 100X, mechanically stacked solar cells Space solar cells work outside the atmosphere, the average intensity of solar irradiation is basically unchanged in near-Earth orbits, which is usually called AM0 irradiation, and its spectral distribution is close to the spectrum of the blackbody radiation of 5800 K, with an intensity of 1353 mW/cm2. Therefore, space solar cells are mostly designed and tested using the AM0 spectrum. AM0 spectrum design and testing. Space solar cells usually have high efficiency in order to obtain a specific power output under the weight and volume constraints of space launch. Especially in some specific launch missions, such as micro-satellites (weight of 50 to 100 kilograms) on the application, requires a higher specific power per unit area or per unit weight. Anti-irradiation performance Space solar cells work outside the Earth's atmosphere, will inevitably be irradiated by high-energy charged particles, causing attenuation of the battery's performance, mainly due to the electron or proton radiation so that the diffusion length of the minority carriers is reduced. The degree of attenuation of its photovoltaic parameters depends on the material and structure of the solar cell. There are also factors such as reverse bias, low temperature, and thermal effects that are important causes of cell performance degradation, especially for stacked solar cells, where cell performance degradation may be more serious due to significantly different thermal expansion coefficients. × Reliability of Space Solar Cells The reliability of the photovoltaic power supply plays a key role in the success of the overall launch mission, and the high or low cost of the solar cells/arrays is not important in comparison with ground applications, as the balance of the space power system is much more costly, and the reliability is of paramount importance. Space solar arrays must undergo a series of mechanical, thermal, electrical and other demanding reliability tests. Si solar cells Silicon solar cells are the most commonly used satellite power supply, from the 1970s, due to the development of space technology, the power demand of various vehicles is growing, in accelerating the development of other types of batteries at the same time, the world's space technology is more developed in the U.S., Japan, and the ESA and other countries have carried out one after another the research of high-efficiency silicon solar cells. Represented by Japan's SHARP, the United States' SUNPOWER and ESA, they are leading in the research and development of space solar cells. Among them, the development of back-surface field (BSF), back-surface reflector (BSR), double-layer reflection-reducing film technology for the first generation of high-efficiency silicon solar cells, this type of battery typical efficiency can be achieved up to about 15%, and many satellites in orbit at present apply this type of battery. By the mid-1970s, the COMSAT Institute proposed a non-reflective velvet battery (to further improve the efficiency of the battery). However, the application of this type of battery is limited: first, the preparation process is complicated to avoid damage to the PN junction; second, such a surface will absorb all wavelengths of light, including those photon energy is not enough to produce the infrared radiation of electron-hole pairs, so that the temperature of the solar cell, thus offsetting the efficiency effect of the use of fleece and improved; third, the electrodes must be fabricated along the fleece surface extends, increasing the difficulty of contact, so that the cost of the Higher. In the mid-80s, in order to solve these problems, the production of high-efficiency batteries introduced some of the electronic device production process means, the use of inverted zeta suede, laser groove buried grid, selective emission junction production process, the use of these processes not only make the efficiency of the battery to further improve, but also make the application of the battery becomes possible. Especially after solving the problem such as the use of band-pass filters to eliminate the temperature rise effect, the application of such batteries has become the main protagonist of space power supply. Although many process technologies are proposed by a number of research institutes, but it is in some of the larger companies have been carried forward, such as the inverted gold tower velvet, selective emission junction and other processes in the photovoltaic research center of the University of New South Wales in Australia appeared, but Japan's SHARP and the U.S. SUNPOWER company's current level of technology for the world's first-class, and some of the technology has even been transplanted to the Mass production of solar cells for terrestrial use. In order to further reduce the impact of composite on the back of the cell, the back structure is used after the back passivation of the open hole to form a point contact, i.e., localized back field. Typical structures of these high-efficiency cells are PERC, PERL, PERT, and PERF [1], of which the cells of the former structure have already gained practical use in space. Typical high-efficiency silicon solar cells with a thickness of 100 μm, also known as NRS/BSF (with a typical efficiency of 17%) and NRS/LBSF (with a typical efficiency of 18%), are characterized by an inverted tunica fluffy selective emission structure on the front side, passivation structures on both front and back surfaces to reduce the surface composite, and a back field with either a total or a partial back field. In practice, it was also found that although the efficiency of cells with localized backfields was generally one percentage point higher than that of NRS/BSF, the irradiation resistance of localized backfields was usually poor. By the mid-1990s, space power engineers found that although the initial efficiency of this type of battery was relatively high, the terminal efficiency of the battery decreased by about 25% compared with the initial efficiency, limiting the further application of the battery, and the cost of the space power supply still could not be well reduced. In order to change this situation, research organizations led by SHARP proposed a bilateral junction battery structure, the emergence of which has effectively improved the terminal efficiency of the battery, and has gained practical application on the HES and HES-1 satellites. In addition, researchers also found that the satellite on the battery array position requirements are more demanding, if the solar battery array is not directed to the sun or poor orientation to the sun, etc. will affect the power of the satellite power supply, which to a certain extent also limits the satellite overall system configuration. For example, the space station such a complex vehicle, there are battery arrays almost can not fully guarantee its sufficient sun angle, thus it needs high efficiency battery to meet the requirements. Although conventional high-efficiency batteries have been partially applied, the high alpha absorption coefficients of the batteries, the limited space and the weight requirements make them still unable to meet the large-scale power needs of space systems. Conventional battery structures are still limited to a large extent. In this case, Russia in the study of high-efficiency silicon batteries in the early stages of the focus on improving the terminal efficiency of the battery is the main, in conjunction with the battery array research put forward the idea of a double-sided battery and has been successful, really efficient long life and low cost. × solar street light solar street light solar street light is a use of solar energy as an energy source of street lights, because it is not affected by the power supply, do not have to open the trench buried line, does not consume conventional electricity, as long as the sun is sufficient on the ground can be installed and so on, and therefore by the people's widespread concern, but also because it does not pollute the environment, and is known as a green environmental protection products. Solar street lamps can be used for town parks, roads, lawn lighting, and can be used for population distribution density is small, inconvenient economic underdevelopment, lack of conventional fuels, difficult to generate electricity from conventional energy sources, but solar energy resources are abundant in order to solve the problem of people's home lighting in these areas.
[edit]Solar Cells
Solar Cell Power Generation Principle A solar cell is a pair of light responsive and able to convert light energy into electricity devices. Can produce photovoltaic effect of many kinds of materials, such as: monocrystalline silicon, polycrystalline silicon, amorphous silicon, gallium arsenide, indium copper selenide and so on. Their power generation principle is basically the same, now take crystal as an example to describe the process of photovoltaic power generation. p-type crystalline silicon after doping phosphorus can be obtained n-type silicon, the formation of p-n junction. When the light irradiation solar cell surface, part of the photons are absorbed by the silicon material; photon energy transferred to the silicon atoms, so that the electrons have been relocated to become free electrons in the P-N junction on both sides of the formation of the potential difference between the collection, when the external circuit, the role of the voltage, there will be a current flowing through the external circuit to produce a certain output power. The essence of this process is: photon energy is converted into electrical energy. Introduction to the Sun The Sun is the closest star to the Earth, but also the center of the solar system, its mass accounts for 99.865% of the total mass of the solar system. The Sun is also the only object in our solar system that emits its own light, bringing light and heat to the Earth. Without sunlight, the temperature of the ground would quickly drop to near absolute zero. Thanks to the sun's rays, the average temperature of the ground is maintained at about 14 degrees Celsius, forming the conditions for the survival of human beings and the vast majority of living creatures. In addition to atomic energy, geothermal and volcanic energy, 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, radius of 6.96 × 105km (109 times the radius of the earth), the mass of about 1.99 × 1027t (330,000 times the mass of the earth), the average density of the earth's 1/4. The sun's surface temperature of the effective 5762K, and the internal center of the region of the temperature is as high as tens of millions of degrees. The energy of the sun mainly comes from the fusion reaction of hydrogen into helium, with 6.57×1011kg of hydrogen polymerizing to form 6.53×1011kg of helium per second, generating 3.90×1023kW of energy continuously. This energy is in the form of electromagnetic waves that travel through space at a speed of 3×105km/s in all directions. The Earth receives only one twenty-two billionth of the total solar radiation, i.e., 1.77×1014kW reaches the upper edge of the Earth's atmosphere ("upper boundary"), and due to the attenuation when it crosses the atmosphere, the last about 8.5×1013kW reaches the Earth's surface, which is equivalent to hundreds of thousands of times of the world's power generation capacity. According to the current rate of nuclear energy generated by the sun, hydrogen reserves are estimated to be sufficient to last for 60 billion years, and the life span of helium, which is polymerized into helium in the internal tissues of the earth as a result of thermonuclear reactions, is about 5 billion years, so it can be said that the sun's energy is inexhaustible in this sense. The structure of the Sun and the method of energy transfer are briefly described below. The mass of the sun is very large, and under the action of the sun's own gravity, solar material gathers in the core, and the density and temperature in the center of the core are very high, making it possible for atomic nuclear reactions to occur. These nuclear reactions are the energy source of the Sun, and the resulting energy is continuously radiated into space and controls the activity of the Sun. Based on a variety of indirect and direct information, it is believed that the sun can be divided into a nuclear reaction zone, a radiation zone, a convection zone and a solar atmosphere from the center to the edge. (1) the nuclear reaction zone in the solar radius of 25% (i.e., 0.25R) of the region, is the core of the sun, concentrating more than half of the mass of the sun. Here the temperature is about 15 million degrees (K), the pressure is about 250 billion atmospheres (1 atm = 101325Pa), the density is close to 158g/cm3. This part of the energy generated by the sun accounted for 99% of the total energy generated, and convection and radiation to the outside. Gamma rays are emitted when hydrogen polymerization occurs, and when such rays pass through the colder regions, they consume energy, increase wavelength, and become X-rays or ultraviolet rays and visible light. (2) Radiation zone Outside the nuclear reaction zone is the radiation zone, belonging to the range from 0.25 to 0.8 R, the temperature drops to 130,000 degrees, the density drops to 0.079 g/cm3. The energy generated in the core of the sun is transmitted by radiation through this zone. (3) Convection zone Outside the radiation zone is the convection zone (troposphere), belonging to the range from 0.8 to 1.0 R, the temperature drops to 5,000 K, the density of 10-8 g/cm3. In the convection zone, the energy is mainly transmitted by convection. In the convection zone, the energy is mainly transmitted by convection. The convection zone and its inner parts are invisible, and their properties can only be determined by theoretical calculations consistent with observations. (4) The solar atmosphere can be roughly divided into photosphere, chromosphere, corona and other levels, and the physical properties of each level are clearly different. The bottom layer of the solar atmosphere is called the photosphere, and almost all of the sun's light energy is emitted from this layer. The continuous spectrum of the sun is basically the spectrum of the photosphere, and the absorption lines in the solar spectrum are basically formed in this layer. The photosphere is about 500km thick, and the chromosphere, the middle layer of the solar atmosphere, is the outward extension of the photosphere, extending up to an altitude of several thousand kilometers. The outermost layer of the solar atmosphere is called the corona, which is an extremely thin shell of gas that extends to several solar radii. Strictly speaking, the above layers of the solar atmosphere have only formal significance, in fact, there is no clear boundary between the layers, their temperature, density and height is continuously changing. It can be seen that the sun is not a black body with a certain temperature, but many layers of radiation emitted and absorbed at different wavelengths. However, when describing the sun, the sun is usually regarded as a black radiating body with a temperature of 6000K and a wavelength of 0.3-3.0μm. Solar energy utilization of the new exhibition has been internationally from crystalline silicon, thin film solar cell development into the organic molecular batteries, biomolecular screening and even synthetic biology and photosynthesis biotechnology development of bio-energy solar energy technology in new areas. Recently from the Shanghai Municipal Science and Technology Commission was informed that the East China Normal University researchers use nanomaterials in the laboratory to successfully "re-create" chloroplasts to achieve light energy generation at extremely low cost. Chloroplasts are the site of photosynthesis in plants, which can effectively convert the sun's light energy into chemical energy. The group is not "copy" a chloroplast outside the plant body, but developed a new type of battery similar to the structure of chloroplasts --- dye-sensitized solar cells, trying to convert light energy into electricity. Supported by the Shanghai Nano Special Fund, after more than 3 years of experimentation and exploration, the photoelectric conversion efficiency of this bionic solar cell has exceeded 10%, close to 11% of the world's highest level. Project leader, East China Normal University nano-optoelectronic integration and advanced equipment, director of the Ministry of Education Engineering Research Center, Professor Sun Zhuo showed the new solar cell "sandwich" structure --- hollow glass sandwiched by a layer of nano-The "sandwich" is a new type of solar cell, which can be used in a variety of applications. "Sandwich", photovoltaic conversion of the mystery hidden in this layer of tens of microns thick composite film. Nano "sandwich" of the "formula" is very unique: the dye acts as a "light catcher", titanium dioxide is a "photoelectric converter ". In order to let the dye as much as possible "eat" sunlight, the researchers have also been a unique sprinkle of "spices" - a fluorescent nanomaterials made from Made of nanofluorescent material quantum dots, so that different wavelengths of sunlight can be on the "light catcher" of the "appetite". As long as the "recipe" is continuously improved, the photoelectric conversion efficiency of the nano "sandwich" can be improved again and again. As the third generation of solar cells, dye-sensitized batteries, the biggest attraction is the cheap raw materials and simple production process. It is estimated that the cost of dye-sensitized battery is only equivalent to silicon panels 1 / 10 At the same time, it is not demanding light conditions, even in the less sunny indoors, its photoelectric conversion rate will not be too affected. In addition, it has many interesting uses. For example, with plastic instead of glass "plywood", can be made into a flexible battery can be bent; will be made into a display, you can generate electricity while glowing, to achieve energy self-sufficiency. Solar energy is a clean and sustainable energy source, and the development of solar technology can reduce the use of fossil fuels in the power generation process, thereby reducing air pollution and global warming.