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what is a photovoltaic system
Solar photovoltaic (PV) system is a power generation system that directly converts solar radiation into electric energy by using the photovoltaic effect of solar cells. Photovoltaic system for short. Working principle: during the day, under the condition of light, the solar cell module generates a certain electromotive force, and the solar cell array is formed through the series and parallel connection of the modules, so that the array voltage can meet the requirements of the system input voltage. Then charge the battery through the charge and discharge controller to store the electric energy converted from light energy. At night, the battery pack provides input power for the inverter. Through the function of the inverter, the DC power is converted into AC power and transmitted to the distribution cabinet, which is powered by the switching function of the distribution cabinet. The discharge of the battery pack is controlled by the controller to ensure the normal use of the battery. The photovoltaic power station system shall also be equipped with limited load protection and lightning protection devices to protect the overload operation of system equipment and lightning stroke, and maintain the safe use of system equipment. The photovoltaic system consists of: solar cell array: receiving sunlight and converting it into electric energy; battery pack: storage electric energy charge and discharge controller: intelligent overcharge and over discharge protection inverter: DC inverter into AC
What is solar power generation system
The use of solar power supply is called solar power generation system. There are two kinds of solar power generation systems: separate network and grid connection. The off network system is composed of solar cell group, solar controller and battery (Group). Large solar power generation system also needs to be equipped with lightning protection combiner box, lightning rod, etc. if the output power supply is AC 220V or 110V, it also needs to be equipped with inverter. The grid connection system consists of solar cell pack, lightning protection combiner box, lightning rod, grid connected inverter (output AC 220V or 380V) and municipal power grid connection
What are the system components of solar photovoltaic system
Module design: according to IEC: 1215:1993 standard, 36 or 72 polysilicon solar cells are connected in series to form 12V and 24V modules
What are the basic structure and characteristics of solar energy system
Take solar street lamps as an example:
Basic composition of solar street lamp system
Solar street lamp is mainly composed of the following parts: solar cell module, battery, special controller for solar street lamp, luminous body, lamp pole and lamp shell Here are their characteristics:
1. Solar panel solar panel is the core component of solar street lamp. It converts the radiant energy of the sun into electric energy and then transfers it to the battery for storage There are three kinds of practical solar panels: monocrystalline silicon solar cells, polycrystalline silicon solar cells and amorphous silicon solar cells Polycrystalline silicon solar cells are better in areas with sufficient light, monocrystalline silicon solar cells are better in areas with relatively insufficient light, and amorphous silicon solar cells are better in places with insufficient outdoor sunlight
2. The main function of storage battery is to store electric energy to make up for the unstable input energy of solar photovoltaic power generation system Batteries mainly include lead-acid batteries and Ni batteries_ H battery, Ni Cd battery
3. Solar street lamp special controller in a solar street lamp, an indispensable part is the solar controller The main function of the solar controller is to protect the battery and prevent the deep charge and discharge of the battery by limiting the charge and discharge conditions of the battery In places with large temperature difference, the solar controller also has the function of temperature compensation
4. Illuminant illuminant is an important indicator of whether solar street lamps can be used normally. Generally, the illuminants used in solar street lamps include LED, low-pressure sodium lamp, low-pressure energy-saving lamp and so on Among them, LED lamp has long service life and low working voltage At present, it is the most widely used illuminant of solar street lamp
5. The height of lamp pole and lamp shell shall be determined according to the width of the road, the illumination standard of the road and the spacing between two lamps The requirement of lamp shell is not very high, mainly energy saving and practical
Take solar water heater as an example:
Composition of solar water heating system
Solar collector
The function of the heat collecting element in the system is equivalent to the electric heating pipe in the electric water heater. Unlike electric water heaters and gas-fired water heaters, solar collectors use the radiant heat of the sun, so the heating time can only be in the day when the sun shines, so auxiliary heating is sometimes required, such as boiler, electric heating, etc
Like the insulated water tank of electric water heater, it is a container for storing hot water. Because the solar water heater can only work during the day, and people usually use hot water at night, the hot water produced by the collector during the day must be stored through the insulated water tank. Volume is the sum of the amount of hot water used every night. The water tank is made of porcelain, with good heat preservation effect and corrosion resistance for more than 20 years
The channel for conveying hot water from the heat collector to the insulated water tank and cold water from the insulated water tank to the heat collector, so that the whole system forms a closed loop. A properly designed and correctly connected circulating pipeline is very important for the solar system to achieve the best working state. Hot water pipes must be insulated. The pipeline must have high quality and ensure a service life of more than 20 years
The difference between solar water heating system and ordinary solar water heater is the control center. As a system, the control center is responsible for the monitoring, operation, regulation and other functions of the whole system. The current technology can remotely control the normal operation of the system through the Internet
The control center of solar hot water system is mainly composed of computer software, substation and circulating pump
Plate shell type all welded heat exchanger absorbs the advantages of high efficiency and compactness of removable plate heat exchanger, and makes up for the disadvantages of low heat exchange efficiency and large land occupation of shell and tube heat exchanger. The heat transfer plate of the plate and shell heat exchanger is wavy and oval. Compared with the current circular plate, it increases the heat length and greatly improves the heat transfer performance. It is widely used in heat exchange conditions under high temperature and high pressure
Basic features:
1. Environmental benefits – compared with using fossil fuels to produce hot water, it can reduce environmental pollution and the generation of greenhouse gas carbon dioxide
2. Save energy – solar energy belongs to everyone. As long as there is space and equipment, anyone can use it free of charge
3. Safety – unlike the danger of explosion or poisoning in the use of gas, the fear of explosion in the use of fuel oil boilers, or the possibility of electric leakage in the use of electricity
4. No space occupation – automatic operation without special personnel. In addition, the solar water heater is installed on the roof and will not occupy any indoor space
5. Economic benefits – a normal solar water heater is not easy to damage, and its service life is at least ten years or even 20 years. Because the basic heat source is free solar energy, it is very cost-effective to use it
Reference network solar energy is a kind of radiant energy, which is real-time. It must be immediately converted into other forms of energy before it can be used and stored. The conversion of solar energy into different forms of energy requires different energy converters. The collector can convert solar energy into heat energy through the absorption surface, solar cells can convert solar energy into electric energy through photovoltaic effect, plants can convert solar energy into biomass energy through photosynthesis, and so on. In principle, solar energy can be directly or indirectly converted into any form of energy, but the more times of conversion, the lower the efficiency of solar energy conversion
Solar thermal energy conversion
The black absorption surface absorbs solar radiation and can convert solar energy into heat energy. Its absorption performance is good, but the radiant heat loss is large, so the black absorption surface is not an ideal solar absorption surface. The selective absorption mask has high solar absorption ratio and low emission ratio. It has good performance of absorbing solar radiation and small radiant heat loss. It is an ideal solar absorption surface. This absorbing surface is made of selective absorbing material, which is called selective coating for short. It was proposed in the 1940s and met the practical requirements in 1955. After the 1970s, many new selective coatings were developed and mass produced and popularized. At present, hundreds of selective coatings have been developed. Selective coatings have been developed in China since the 1970s, and many achievements have been made. They have been widely used in solar collectors with remarkable results
Solar electric energy conversion
Electric energy is a kind of high-grade energy, which is convenient for utilization, transmission and distribution. Converting solar energy into electric energy is an important technical basis for large-scale utilization of solar energy. Countries all over the world attach great importance to it. There are many ways of conversion, including direct photoelectric conversion, indirect photoelectric thermoelectric conversion and so on. This paper focuses on the photoelectric direct converter – solar cell. In the world, reports on silicon solar cells appeared in 1941, and monocrystalline silicon with an effective rate of 6% was developed in 1954
Solar cell, which was applied to satellite power supply in 1958. Before the 1970s, solar cells were mainly used in space because of their low efficiency and high price. After the 1970s, extensive research on solar cell materials, structures and processes has been carried out, great progress has been made in improving efficiency and reducing costs, and the scale of ground application has gradually expanded. However, in terms of large-scale utilization of solar energy, the cost is still high compared with conventional power generation
At present, the highest efficiency of solar power laboratory in the world is: monocrystalline silicon cell 24% (4cm2), polycrystalline silicon cell 18.6% (4cm2), InGaP / GaAs double junction cell 30.28% (AM1), amorphous silicon cell 14.5% (initial), 12.8 (stable), cadmium telluride cell 15.8%, silicon ribbon cell 14.6%, titanium dioxide organic nano cell 10.96%
China began the research of solar cells in 1958 and has made many achievements in the past 40 years. At present, the highest efficiency level of solar power laboratory in China is 20.4% (2cm) monocrystalline silicon battery × 2cm), polycrystalline silicon battery 14.5% (2cm) × 2cm）、12％（10cm × 10cm), GaAs battery 20.1% (LCM) × Cm), GaAs / Ge battery 19.5% (AM0), CulnSe battery 9% (LCM) × 1cm), polycrystalline silicon thin film battery 13.6% (LCM) × 1cm, inactive silicon substrate), amorphous silicon battery 8.6% (10cm) × 10cm）、7．9％（20cm × 20cm）、6．2％（30cm × 30cm), titanium dioxide nano organic battery 10% (1cm) × 1cm）。
Solar hydrogen energy conversion
Hydrogen energy is a kind of high-grade energy. Solar energy can be converted into hydrogen energy by decomposing water or other ways, that is, solar hydrogen production. The main methods are as follows:
1. Hydrogen production by solar electrolysis of water. Hydrogen production by electrolyzing water is a widely used and mature method at present, with high efficiency (75% – 85%), but it consumes a lot of electricity. Using conventional electricity to produce hydrogen is not worth the loss in terms of energy utilization. Therefore, only when the cost of solar power generation decreases significantly can large-scale hydrogen production from electrolytic water be realized
2. Solar thermal decomposition of water to produce hydrogen. When water or steam is heated to more than 3000K, hydrogen and oxygen in water can be decomposed. This method has high hydrogen production efficiency, but it requires a high-power concentrator to obtain such a high temperature. Generally, this method is not used for hydrogen production
Solar biomass energy conversion
Through the photosynthesis of plants, solar energy synthesizes carbon dioxide and water into organic matter (biomass energy) and releases oxygen. Photosynthesis is the largest process of converting solar energy on earth. The fuel used by modern humans is the fixed solar energy of photosynthesis in ancient times and today. At present, the mechanism of photosynthesis is not completely clear, and the energy conversion efficiency is generally only a few percent. The research on its mechanism in the future has great theoretical and practical significance
Solar mechanical energy conversion
In the early 20th century, Russian physicists proved that light has pressure. In the 1920s, physicists of the former Soviet Union proposed that the huge solar sail solar panel racks in space could push the spacecraft forward under the pressure of sunlight and directly convert solar energy into mechanical energy. Scientists estimate that the solar sail idea can be realized in the next 10-20 years. Usually, the conversion of solar energy into mechanical energy requires indirect conversion through an intermediate process
Solar energy is a kind of green renewable energy that converts sunlight into electric energy. Compared with other conventional energy sources, it has the following characteristics:
1、 Solar energy is inexhaustible. It is estimated that the energy of solar energy projected to the earth in a year is equivalent to the heat generated by 137 trillion tons of standard coal, which is about 20000 times the energy generated by various energy sources in the world in a year
2、 In the process of solar energy conversion, there will be no pollution endangering the environment
3、 Solar energy resources are all over the world and can be exploited in a decentralized and regional manner. About 2 / 3 of China’s regions can make better use of solar energy resources
4、 Photovoltaic power generation is intermittent, only when there is sunlight, and the power generation is directly proportional to the intensity of sunlight
5、 Photovoltaic power generation is a static operation with no moving parts, long service life and no or little maintenance
6、 The modularization of photovoltaic system can be installed close to the power consumption and far away from the power grid, which can reduce the cost of transmission and distribution and increase the reliability of power supply facilities
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