Photovoltaic Power Generation System
Aug 04, 2023
Introduce
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Photovoltaic, or photovoltaic power generation system, is a power generation system that uses the photovoltaic effect of semiconductor materials to convert solar Radiant energy into electrical energy. The energy of photovoltaic power generation systems comes from inexhaustible solar energy, which is a clean, safe, and renewable energy source. The photovoltaic power generation process does not pollute the environment or damage the ecology.
Photovoltaic power generation systems are divided into independent photovoltaic systems and grid-connected photovoltaic systems. The photovoltaic power generation system is composed of solar cell arrays, battery packs, charge and discharge controllers, inverters, AC distribution cabinets, solar tracking control systems, and other equipment.
history
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Heinrich Hertz first discovered the Photoelectric effect in 1887, and Albert Einstein explained this phenomenon in 1905. Photovoltaic (PV) systems use the Photoelectric effect of semiconductor materials to directly convert light into electrical energy. The composition of semiconductors and the intensity and wavelength of effective solar radiation received by photovoltaic devices can both affect the power generation of photovoltaic devices (Hertz, 1887; Einstein, 1905). In 1954, three researchers from Bell Labs developed the first practical "solar cell". This battery can convert 6% of incident solar energy into electrical energy (Pedin, 2004). With continuous progress in research and development, the conversion efficiency of photovoltaic devices has also improved.
classification
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Solar photovoltaic power generation systems can be divided into two categories based on their relationship with power systems: independent photovoltaic power generation systems and grid-connected photovoltaic power generation systems.
Independent photovoltaic power generation system
The independent photovoltaic power generation system is composed of a solar Photovoltaic system, storage battery, charging controller, power electronic converter (inverter), load, etc. Its working principle is that the solar radiation energy is first converted into electric energy through the Photovoltaic system, and then the load is powered by the power electronic converter after conversion. At the same time, the surplus electric energy is stored in the energy storage device in the form of Chemical energy after passing through the charging controller. In this way, when the sunlight is insufficient, the energy stored in the battery can be transformed into AC 220V, 50 Hz electrical energy for AC loads after being boosted by power electronic inverters, filters, and power frequency transformers. The characteristic of solar power generation is to generate electricity during the day, while the load is often used 24/7. Therefore, energy storage components are essential in independent photovoltaic power generation systems, and the main energy storage components used in engineering are batteries.
grid-connected PV system
Grid-connected photovoltaic power generation system consists of a Photovoltaic system, high-frequency DC/DC boost circuit, power electronic converter (inverter), and system monitoring part. Its working principle is that the solar radiation energy is converted by a Photovoltaic system, then transformed into high-voltage DC after high-frequency DC conversion, and then outputs sinusoidal AC current with the same frequency as the grid voltage to the grid after being inverted by power electronic inverter.
The biggest difference between the above two photovoltaic power generation systems is that the grid-connected photovoltaic power generation system is directly connected to the power grid, so the electricity surplus of the Photovoltaic system and the parallel grid can be complementary, eliminating the necessary energy storage elements such as batteries in the independent photovoltaic power generation system, which not only reduces the system cost but also ensures the reliability of the system. At the same time, in summer, the solar Radiant intensity is high, and the photovoltaic system generates more power, which can regulate the peak load of the grid in summer. With the large-scale application of solar photovoltaic power generation and the rapid decline in the price of solar cell modules in recent years, grid-connected systems will undoubtedly be more widely used.
advantage
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1) Reliable operation: It can supply power normally even in harsh environments and climatic conditions.
2) Long lifespan: The lifespan of crystalline silicon components is usually over 25 years, while the lifespan of amorphous silicon components is usually over 20 years.
3) Low maintenance cost: After completion, only a small number of staff are required to regularly inspect and maintain the system. Compared to conventional power stations, maintenance costs are high.
4) Natural energy: Energy is an inexhaustible source of solar energy, without the need for energy costs.
5) No noise pollution: The entire system has no mechanical moving parts and does not generate noise.
6) Modular: Select system capacity according to needs, flexible and convenient installation, and easy expansion.
7) Safety: There are no flammable items in the system, and the safety performance is high.
8) Autonomous power supply: It can operate off the grid, independently supply power, and is not affected by the public power grid.
9) Distributed power generation: Distributed photovoltaic power stations can be built to reduce the impact and harm on the public power grid.
10) High altitude: In areas with high altitude and strong sunlight, the output power of the system can be increased even more. (Compared with photovoltaic power generation in high altitude areas, Diesel generator efficiency, and output power are reduced due to low air pressure.
Application Scenario
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In addition to traditional solar power plants and distributed rooftop photovoltaics, photovoltaics can also be applied to various scenarios, such as architecture, agriculture, fisheries, public facilities, landscape construction, etc. These composite and cross-border models enable photovoltaic construction projects to balance economic development and ecological protection while generating clean electricity; On the other hand, this mode of efficient and intensive use of space will help new Energy development projects to obtain the land resources needed for construction.
In Zhongba County, China, all heat supply in this county is provided by solar energy. The black part on the left side of the picture is a solar collector with an area of 35000 square meters, just like the water heater we usually use, which can convert solar energy into heat. It collects the heat and stores it in the colored jar in the picture. This jar can generate heat 24 hours a day and provide heating for the county town. This is 100% solar energy, completely zero carbon.
Photovoltaic+Land Ecological Restoration
According to the statistics of the United Nations Convention to Combat Desertification, the global land area in extreme drought and drought is about 25500 Square kilometers, accounting for 17.2% of the global land surface. Moreover, the area of the desert continues to expand every year. Land Degradation Neutrality (LDN) and ecological restoration of degraded land have always been important issues facing the Earth. Although desertification land needs to be repaired, it also provides a large amount of land resources. Therefore, combining ecological restoration of desertification land with photovoltaic construction will bring various benefits. Solar panels in deserts not only provide power but also reduce the amount of sunlight radiation and water evaporation on the ground. The water sprayed during the cleaning of battery panels increases the moisture content of the soil surface and promotes the growth and restoration of vegetation. Solar power stations in the desert can promote Biological carbon fixation of soil, plant colonization, improve biodiversity and restore soil activity, which is conducive to water and soil conservation, wind and sand resistance, climate regulation, and ecological environment improvement. Landowners, after a 25-year operation cycle of photovoltaic power plants, will receive high-quality land with higher vegetation coverage, healthier soil, higher land productivity, and land lease benefits during the use period.
Currently, countries such as Pakistan and Egypt, as well as Inner Mongolia, Shanxi, Qinghai, Ningxia, and other regions in China, have such "photovoltaic+land ecological restoration" projects. Take the ecological restoration project in Qinghai Gonghe Basin as an example. The 850 MW project covers an area of 54 Square kilometers. After the construction of photovoltaic power stations, the vegetation coverage of the land under and between photovoltaic panels has increased significantly, and the vegetation coverage has increased by 15%; The vegetation coverage in photovoltaic water pump irrigation areas has also significantly improved. At 10cm, 20cm, and 40cm below the photovoltaic panel, the soil moisture content increased by 78%, 43%, and 40%, respectively. In summer, the content of Soil organic matter and nitrogen increased by 11.6 times and 11.3 times respectively compared with the previous year, and soil microorganisms increased, thus improving land productivity. Photovoltaic power generation has reduced carbon emissions by approximately 1.2 million tons, and vegetation and soil organic carbon have also formed a certain degree of carbon deposition. The power station area has a significant regulatory effect on the local climate: the wind speed inside the photovoltaic park has decreased by 40.3% compared to outside the park; The relative humidity of the air is 2.8% higher than outside the park. It also has a regulating effect on soil temperature.
Photovoltaic+Building
The largest energy consumption in Europe comes from the construction industry, which consumes about 40% of energy and emits about 36% of greenhouse gases. At present, almost 75% of buildings in the European Union are low energy efficient. If existing buildings are retrofitted with energy, it can save a lot of energy, which is expected to reduce the total energy consumption of the EU by 5% to 6% and reduce carbon dioxide emissions by 5%. Currently, Europe is promoting photovoltaic building integration projects on a large scale. Combining photovoltaic construction with buildings can reduce the consumption of land resources. European countries first estimate the available building area when constructing "photovoltaic+building" projects, in order to maximize the utilization of building area. From the results of large-scale practical deployment of photovoltaic systems in the Paris metropolitan area, it can be seen that due to covering the roof, solar panels can increase the winter heating demand of households by 3%, but in summer, this covering can reduce air conditioning energy consumption by 12%.
Liechtenstein is a very typical country that benefits from building photovoltaics. This country is located between Switzerland and Austria, with an area of only 160.5 Square kilometers and 38244 people. Liechtenstein has a small land and a sparse population, high per capita energy consumption, high per capita electricity consumption, and low energy self-sufficiency rate. However, it is the first country in the world to be allowed to be called an "energy powerhouse". From the perspective of per capita photovoltaics, in 2015, Liechtenstein surpassed Germany, which had previously ranked first (with a per capita installed capacity of 473 watts), and was awarded the title of "per capita photovoltaics champion" by the Solar Super State Association with a per capita installed capacity of 532 watts. It is worth noting that all photovoltaic projects in this country are built on buildings. Under the conditions of light resources in Liechtenstein, a modern photovoltaic system with an area of 40-50 square meters can roughly meet the electricity consumption of a family of four, and can continue to generate electricity for about 25 years, helping Liechtenstein achieve self-sufficiency in household electricity and providing a portion of electricity to industry. On May 10, 2020, Liechtenstein's domestic power generation exceeded the country's electricity load, marking the first time in its history that the country had a completely self-sufficient electricity operation without the need for any external energy. Although this is an occasional event during a special period, it also demonstrates the possibility of the country relying on building photovoltaics to achieve energy independence. The current public energy plan of the country is to achieve a per capita photovoltaic capacity of 2.2 kilowatts by 2030 and at least 4.5 kilowatts by 2050. All of these photovoltaics are still planned for construction, and the position of building photovoltaics in the country has been further consolidated.
Photovoltaic+Agriculture
'Photovoltaic+Agriculture' refers to the simultaneous development of scaffolding photovoltaic power generation and agricultural production activities on the same land. The global agricultural land area is about 500 million Square kilometers, accounting for 38% of the global land area. About one-third of it is arable land, while the remaining two-thirds are grasslands and pastures. Agricultural land occupies a large amount of land resources, and whether these lands can be used as usable areas for photovoltaic construction has always been controversial. To this end, the largest solar energy research institution in Europe, the Fraunhofer ISE in Germany, launched the agricultural and solar integrated research project APV RESOLA in 2015 to test the impact of photovoltaic panels on the yield of different crops such as winter wheat, celery, and potatoes. The Scientific control shows that the combination of photovoltaic and potato planting will increase the yield of potatoes by 3% per hectare, and agricultural land will produce 83% additional green power through photovoltaic, and the comprehensive utilization rate of land will increase by 86%. This achievement was announced at the AgriVoltaics International Agricultural Photovoltaics Conference hosted by the Fraunhofer Solar Systems Research Institute in Germany in October 2020. The "photovoltaic+agriculture" mode, which combines the cleaning of photovoltaic panels with farmland irrigation, can improve the efficiency of water resources utilization, and photovoltaic panels can also play a role in reducing the adverse impact of excessive noon light on crops and reducing water evaporation. Based on integrated agricultural and solar facilities, suitable crops can be selected for reasonable irrigation. The intelligent system of photovoltaic power supply can also ensure the agricultural production process, achieve "photovoltaic greenhouse+intelligent planting", and improve the agricultural economy and quality. The "photovoltaic+agriculture" model solves the problem of land competition between photovoltaic construction and agricultural production, and through some intervention measures in photovoltaic construction, increases crop yield while ensuring photovoltaic power generation as much as possible, achieving land composite utilization.
Taking the agricultural photovoltaic power station located on the east bank of the Yellow River in Ningxia as an example, the east bank of the Yellow River in Ningxia was once one of the most seriously desertified lands, with a Height above mean sea level of 1200 meters, the maximum annual precipitation of 273 mm, and the annual evaporation of 2722 mm. Yellow sand and dust were everywhere. The development company has carried out ecological management on 160000 acres (approximately 10666 hectares) of desertification land, constructed complementary agricultural and photovoltaic power stations, planned to build 3GWp photovoltaic power generation, and completed grid connected 1GWp photovoltaic power generation. At the same time, the green industry chain of "planting research and development processing sales" of high-quality organic goji berries has been carried out, providing employment opportunities for the local 30000 impoverished population. Photovoltaic modules reduce Radiant intensity. "Photovoltaic+agriculture" makes the flowering season of Lycium barbarum longer than that of local similar Lycium barbarum for 5 weeks, and the output increases by 29%.
Photovoltaic+Fisheries
Photovoltaic+Fisheries "refers to the construction of photovoltaic power plants with a foundation on the water surface, which generate electricity while developing fisheries under photovoltaic panels. It is a multiple-development model of spatial resource composite utilization. For aquatic products: firstly, the cooling and shading effects of photovoltaic modules can reduce the sleep temperature of aquatic products, reduce water evaporation, improve the survival rate of fish, shrimp, and crabs, and reduce algae invasion; Secondly, intelligent systems for photovoltaic energy supply can effectively control the conditions of aquaculture water bodies, such as water temperature and pH; It can also achieve water-saving circulation, pool bottom pollution discharge, sterilization and oxygenation, and remote detection, creating a better ecological environment and continuously improving the yield and quality of aquatic products. For power generation operation and energy conservation and emission reduction, photovoltaic-driven fishing has zero pollution, reducing dust, carbon dioxide, sulfur dioxide, and nitrogen oxide emissions; Surface photovoltaic power plants can also avoid damage caused by fires, animal bites on cables, and other situations. The simultaneous increase in fishing production and energy conservation and emission reduction can greatly enhance the economic value per unit area of land.
Based on the data from the Jiangsu Fishery and Light Integrated Project, the yield of grass carp ponds per mu in the Fishery and Light Integrated Project has reached 35550-39705 kg/ha, which is much higher than the average level of local conventional ponds (18750 kg/ha). Install 50% to 75% photovoltaic modules on 339 acres of aquaculture water surface, establish a 10 megawatt integrated fishing and lighting pond, generate a total of 13 million kilowatt hours of electricity per year, generate 38300-kilowatt hours of electricity per acre per year, and generate an average of 3196-kilowatt hours of electricity per acre per month. Fish and vegetable (rice) symbiosis, using rice and water spinach for biological treatment, has produced a total of 194.48 kilograms of rice and 3529 kilograms of water spinach, absorbing a total of 161.99 kilograms of nitrogen, 27.63 kilograms of phosphorus, and 202.44 kilograms of potassium, and achieving an additional output value of nearly 4000 yuan and a profit of over 3000 yuan. By utilizing the organic combination of physical, biological purification, and aquaculture technology, we have achieved the goal of "using fish to feed water and grass to clean water", effectively controlling the problem of internal and external pollution in aquaculture. The degradation rate of SS is over 80%, and the degradation rate of COD, TN, and TP is over 90%. The purified water quality meets the first level standard of "Discharge Requirements for Freshwater Pond Aquaculture Water" (SC/T9101-2007).
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