Application of solar thermal power generation technology
Solar photovoltaic power generation has become one of the great heroes to get rid of dependence on fossil fuels, especially the negative impact of fossil fuels on the living environment while providing energy and the gradual depletion of fossil fuels. Countries all over the world are studying and exploring clean and environmentally friendly renewable energy sources, such as solar energy, wind energy and hydropower. As one of the new clean energy sources, solar energy has great potential. Although solar energy has many advantages, its development and utilization are affected by many unfavorable factors, such as its dispersion, storage difficulties and environmental impact. After intensive research by experts at home and abroad, the development of solar energy technology continues to deepen, and solar thermal power generation technology has entered the stage of commercial application.
Keywords: solar cell; Thermal power generation; Solar power generation technology
Energy has become the main factor affecting economic and social development, especially the gradual depletion of fossil fuels such as coal and oil, and there is an energy dispute in the world today. Many disturbances in local areas are caused by competition for non-renewable energy. Faced with the increase of people's energy demand and the decrease of non-renewable energy, people began to seek the development of renewable energy, such as wind energy, hydropower and solar energy. Although the proportion of solar energy in the total energy is very small at present, its future development potential is limitless. Some experts speculate that by 2 100, the energy from the sun will exceed half of the world's total energy demand.
I. Overview of Solar Thermal Power Generation Technology
As a kind of clean energy, solar energy has not been exploited for a long time because of its low density, intermittent and spatial distribution changes, which brings difficulties to the collection and utilization of solar energy. Therefore, in order to develop solar photovoltaic power generation technology, we must find an effective method to collect and utilize solar energy, which is also the key of solar thermal power generation technology. Therefore, there are four key technologies in solar photovoltaic power generation technology, namely, concentrator technology, absorber technology, tracking technology and thermal energy storage technology. Concentrator technology and absorber technology mainly study how to obtain solar light source more efficiently, and the difficulty lies in solving the characteristics of low solar thermal energy density and changeable distribution. The difficulty of thermal energy storage technology lies in how to store the collected solar light sources and reduce the loss of heat, so as to provide energy on cloudy days, rainy days and at night when there is no solar light source.
Although solar energy is a natural, clean and renewable energy source, its low density, intermittent and spatial distribution changes make its development and utilization cost high, which hinders people's development of solar heat energy. Once the initial investment (fixed investment) of solar thermal energy technology is completed, it will bring considerable economic benefits in the later period. Coupled with the negative impact of fossil fuels on the regional environment and its non-renewability, governments all over the world have turned to vigorously support the development of solar thermal energy. The core of the four technical schemes of solar thermal power generation is the research and development of new materials. At present, solar power generation technology is mainly solar photovoltaic (PV) battery technology and concentrated solar energy (CSP) technology. China has a vast territory, spanning multiple latitudes, with diverse landforms and broad prospects for solar energy development. According to the statistical data of solar power related products in the world in 2009, the industrial scale of crystalline silicon solar cells and crystalline silicon solar modules in Chinese mainland ranks first in the world, accounting for about half of the world total, and it is an important producer of solar photovoltaic cells.
Second, the common modes of solar thermal power generation and comparative analysis
Driven by the energy crisis and the continuous research of experts from all over the world, people's development of solar energy has entered a new period. At present, various forms of solar thermal power generation modes have been developed, some of which are mature and have been put into commercial operation. One of the key technologies of solar thermal power generation is solar collector. According to the different types of solar collectors, solar thermal power generation methods can also be divided into flat photovoltaic power generation system and concentrated photovoltaic power generation system.
(A) flat photovoltaic power generation system
Flat photovoltaic power generation system includes solar panels, DC protection and acquisition system, AC protection and switching system, inverter, power generation metering, infrastructure and so on. The working principle of the system is that the battery panel array is collected by the junction box (box) and directly supplies power to the DC load, and then the collected DC electric energy is converted into single-phase or three-phase alternating current with AC voltage and frequency through the inverter, and finally it is remitted to the user's power supply system. Flat photovoltaic power generation system is mainly used in large grid-connected power plants. In application, DC line, AC line and booster station need to be considered. In the process of power generation, in order to improve the utilization rate of sunlight, uniaxial or dual-axis tracker is usually used to extend the direct sunlight time and improve the power generation. Because the principle of the tracking system is to generate shadowing effect according to the rotation of the azimuth angle of the sun to drive the battery panel, the system occupies a large area. Generally speaking, the flat photovoltaic power generation system has simple structure, low technical content, convenient installation and construction, and the required silicon crystal material price and cost are reduced. It is estimated that the comprehensive investment cost of flat photovoltaic power generation system per kilowatt is about 35 ~ 40 thousand yuan. However, the system has some disadvantages, such as low power generation efficiency, inconvenient transportation and maintenance.
(2) concentrating photovoltaic power generation system
Concentrated photovoltaic power generation technology is a large-scale photovoltaic power generation technology developed in recent years, which is mostly used in grid-connected solar photovoltaic power stations with MW level or above. Compared with flat photovoltaic power generation technology, concentrated photovoltaic power generation technology has the advantages of more economy, shorter construction period, convenient maintenance, small floor space and low requirements for site leveling. The concentrated photovoltaic power generation system can be divided into three categories: trough concentrated thermal power generation system, tower concentrated thermal power generation system and dish Stirling solar thermal power generation system.
1. Trough concentrating thermal power generation system. The earliest technology used in solar power generation is trough concentrating technology, which has become the most mature technology in concentrating solar energy technology. Trough-type solar thermal power generation is to focus and reflect the sunlight on the collecting heat pipe with the help of trough-shaped parabolic concentrator, and heat the water into steam through the heat carrier in the pipe to promote the steam turbine to generate electricity. Therefore, the key technologies of trough thermal power generation are solar concentrator, absorber, tracking technology and high temperature thermal energy storage technology. Trough solar thermal power station mainly includes two parts: heat collection and power generation. Different from traditional power generation, the heat collection part mainly includes parabolic trough reflector, heat collector, single-axis tracking control system and heat collector infrastructure. Trough concentrating thermal power generation system is the earliest, most mature and most economical power generation system at present.
2. Tower concentrating thermal power generation system. Tower concentrating technology focuses and distributes the sunlight reflected by the heliostat array installed around the concentrating tower through the receiver ring. The conversion of heat energy is realized in the receiver, and then the turbine is driven to drive the generator to generate electricity. Spain's PS20 is the largest tower-type thermal power plant currently under construction, with an installed capacity of 20MW and an area of about 1, 4 15 mu. If site conditions permit, the system can be matched with traditional thermal power plants to form a circulating turbine power generation system, reducing dependence on fossil fuels.
3. Dish Stirling concentrating thermal power generation system. The dish Stirling concentrated thermal power generation system is mainly composed of a rotating parabolic mirror, a heat absorber, a tracking device and a thermal energy conversion device. It is installed on a double-axis tracking support device to realize fixed object tracking and continuous power generation. Disc Stirling concentrating thermal power generation system not only retains the advantages of high concentrating ratio and large scale of tower system, but also solves the disadvantage of large heat loss of tower top absorber, and the installation and maintenance cost is low. However, the dish Stirling central thermal power generation system also has some obvious shortcomings, such as low power generation efficiency, large area and many materials used.
In view of the comprehensive comparison of the scale, operating temperature, annual capacity coefficient, peak efficiency, annual net efficiency, commercialization degree and technology development risk of the three centralized thermal power generation systems, it can be seen from various indicators that the trough system is relatively mature in commercial operation at present.
Third, the application prospect of solar thermal power generation technology
With the energy crisis and various advantages of solar energy resources, traditional companies that rely heavily on fossil fuels to obtain energy turn to develop solar power generation, especially in some developed countries with poor resources, such as Japan. The storage of solar energy is a key technology, and the enterprises involved in solar cells have formed a scale. According to the material composition, solar cells can be divided into crystal system, thin film system, multi-junction system, organic system and so on. Crystalline silicon is common in the market, and there will be a bigger market for thin film solar cells in the future. As a big energy demand country, China has made remarkable achievements in the production of crystalline silicon solar cells and crystalline silicon solar cell modules, accounting for about half of the world's total. With the efforts of all countries in the world, the technology of manufacturing new composite materials and obtaining solar energy will continue to mature and the cost will be reduced. There will be more and more large solar thermal power plants. When the cost of solar power generation is reduced to a certain extent, it will become the main force of the future power grid.
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