Brief introduction of trough solar thermal power generation technology

Trough solar thermal power generation uses trough condenser to gather sunlight on a line. A tubular collector is installed on this line to absorb solar energy, heat the heat transfer working medium, and then generate electricity with the help of steam power cycle. The parabolic surface of the trough concentrator tracks the sun in one dimension. The condensing ratio is 10~100 and the temperature can reach 400 ℃. The trough solar thermal power generation technology has been developed since the mid-1980s. At present, a 354 MW trough concentrating thermal power station has been installed in California, the United States. Its working medium is heat transfer oil. The heat exchanger can make the heat transfer oil produce superheated steam close to 400 ℃ to drive the steam turbine for power generation.

Technical characteristics of trough solar thermal power generation

The most important feature of trough solar thermal power generation technology is that a large number of parabolic trough concentrators are used to collect solar radiation energy and directly convert light energy into heat energy. Water is transformed into high-temperature and high-pressure steam through heat exchangers and steam turbines are driven to generate electricity. Because solar energy is uncertain, a conventional fuel auxiliary boiler is added to the heat transfer working medium for emergency use.

The disadvantages of trough solar thermal power generation are:

(1) Although the light collection efficiency of this linear focusing system has been improved due to single axis tracking, it is difficult to achieve double axis tracking, resulting in an average annual light loss of 30% due to cosine effect.

(2) Trough solar thermal power generation system has a huge structure, which is difficult to stand in China’s windy and high sand regions.

(3) Since the surfaces of linear heat absorbers are all exposed in the light receiving space, thermal insulation treatment cannot be carried out. Although the vacuum layer is designed to reduce the loss caused by convection, the radiation loss still increases with the increase of temperature.

Trough solar thermal power generation technology collector system structure

(1) Collector tube

The collector tube is a key component of the trough solar thermal power collection system, which can convert the solar direct radiation energy gathered by the reflector into heat energy, and the temperature can reach 400 ℃. At present, the inner layer of the collector pipe is stainless steel pipe, and the outer layer is glass pipe plus metal bellows at both ends. The inner tube is coated with a selective absorption coating to achieve the maximum absorption rate of concentrated solar direct radiation and the minimum re radiation of infrared wave. The glass metal seals at both ends are connected with the metal bellows to provide high-temperature protection and keep the vacuum in the sealed internal space. Reduce the convection and conduction heat loss of gas, and apply selective absorption coating to minimize the radiation heat loss of vacuum collector tube. On the other side, the metal bellows is welded to the inner heat absorption pipe. These bellows with elastic connection function can compensate the difference of thermal expansion and cold contraction between the inner metal pipe and the outer glass pipe during the heating and cooling process of the heat absorption pipe. The focused solar direct radiation energy can be converted into heat energy on the surface of the collector tube, transmitted to the heat conducting medium, and the medium is heated to a maximum temperature of 400 ℃. The external glass tube can be used as an additional protection to prevent the infrared wavelength energy from re radiating outward, so as to reduce the heat loss. The glass tube is covered with an antireflection coating, so that the solar radiation energy can pass through the glass tube.

Since the mid-1980s, China began to develop vacuum collector tubes, which have overcome many technical difficulties and established vacuum collector tube production bases, such as Beijing Solar Energy Research Institute and Huangming solar energy group. The produced collector tubes have been tested in the laboratory and can meet the relevant technical requirements. Compared with similar international products, the operation indicators can meet the relevant technical requirements of the same industry in the world. Some technical indicators are also superior to foreign technical level. However, most of the collector tubes developed and produced in China are only used for experimental research, lacking some practical operation experience.

(2) Collector mirror

The collector mirror used in the trough solar thermal power station is made of ultra white glass, which not only ensures certain focusing accuracy, but also has good wind resistance, acid and alkali resistance, ultraviolet resistance and other properties. The mirror is made of low iron glass, which is bent, rigid, hard and strong, and can withstand the test of harsh outdoor environment and extreme weather conditions. The back of the glass is coated with a protective film to prevent aging. Due to the low iron content, this kind of glass has good solar radiation transmission.

(3) Supporting structure and control system

The supporting structure is used to fix the parabolic trough condenser, and cooperate with the control system to track the collector array in one dimension to obtain effective solar radiation energy. The design of the supporting structure needs to go through computer simulation research, wind tunnel test and actual operation, and be designed under the premise of fully considering the best mechanical, optical and mechanical properties and the minimum cost.

(4) Heat storage system

Renewable energy. Energy storage technology has always been an urgent problem to be solved. However, solar thermal power generation has a very mature energy storage technology solution, which is also the biggest advantage that solar thermal power generation is expected to catch up with wind power, optoelectronics and other new energy in the future. Using heat storage technology can realize the energy storage of large-scale solar thermal power stations.

  Status and progress of trough solar thermal power generation technology

Current status of trough solar thermal power generation technology

Development status abroad

The solar thermal power industry has experienced several ups and downs for various reasons. As early as the early 20th century, there was research on solar thermal power generation. However, due to the outbreak of the Second World War and the discovery of oil in the Near East, the utilization of solar energy developed slowly. Among them, the backward technology, low efficiency and high production cost of solar thermal power are also important reasons that hinder its development. Until the oil crisis in the 1970s, the solar thermal power industry was aroused again.

With the development of solar thermal power generation technology and scale, solar thermal power generation will have potential advantages in competition with conventional energy power generation. However, at present, this technology is not very complete, and it is not competitive economically. Therefore, to promote this technology, it is necessary to further reduce the power generation cost, improve the system efficiency, realize the automation of power station operation, and reduce the operation cost from the current 3 cents /kwh to 0.8 cents /kwh. Therefore, the future research focus of trough solar power generation technology is:

1. Strengthen the research on solar energy resources at the project site;

2. Developing heat energy storage technology of direct vaporization system;

3. Increase the working temperature of heat carrier;

4. Develop high-efficiency coating technology for heat absorption tubes to improve the temperature of the collector surface to 550-600 C.

Domestic development status

In China, the research on solar thermal power generation technology started relatively late, and some basic research was not started until the 1970s. During the “Seventh Five Year Plan” period, Xiangtan electric machinery plant cooperated with American space power company to develop two groups of 5 kW parabolic focusing solar thermal generators. However, due to the high price, and the fundamental solution of process, materials, components and related technologies, it failed to be popularized and used. National “Eighth Five Year Plan” It is planned to arrange key projects for small parts and materials, and build a small parabolic trough vacuum tube high-temperature heat collection device in the Institute of electrical engineering, Chinese Academy of Sciences. The successful operation of Luz trough solar thermal power station in California has aroused widespread concern in China, and it is planned to introduce such units to build a 35 MW ll Z trough solar thermal power station in Lhasa, Tibet. At that time, according to the feasibility assessment, the power cost of the power station was estimated to be about 1.1 yuan /kwh, and the operating cost was 0.1 yuan /kwh, which still has a certain advantage compared with the power cost of 0.8 yuan /kwh of coal-fired power stations in Lhasa.

In general, the research on solar thermal power in China is still relatively backward. The research level in the 1980s is only equivalent to that in the 1960s abroad. Although China has paid considerable attention to the research of solar thermal power technology in recent years, and has also achieved certain development. For example, the first domestic solar thermal power generation demonstration power station (with a capacity of 7 kW) built in Jiangning District, Nanjing in 2005 is far from the international development level. To this end, the state has allocated billions of funds in the eleventh five year plan to develop solar thermal power generation technology. Considering the current technical status of our country, we can give priority to the development of trough solar thermal power generation system, or combine solar power generation with small hydropower, solar power generation with wind power generation to form various joint systems, or adopt some energy storage equipment to reduce the dependence on climate conditions.

Development of trough solar thermal power generation technology

In order to further improve the development of trough solar thermal power generation technology and enhance its competitiveness, the following measures can be taken:

1、 It is an advanced designed concentrator. The structural form has developed from an axial unit to a truss unit. The single row length of the concentrator has increased from 100 m to 150 m. in this way, a set of driving mechanism can drive a longer concentrator array. At the same time, the material and glass thickness of the condenser lens are continuously optimized to minimize the weight of the whole machine.

2、 Taking full account of the influence of azimuth and altitude angle, the polar axis tracking technology is adopted to change the horizontal placement of the concentrating collector array from the original north-south direction to the North-South inclined axis (the inclined angle is related to latitude), so as to receive solar radiation more effectively.

3、 Is to develop high-performance high-temperature vacuum tube receiver.

4、 It is a new type of trough power generation technology with direct water as the medium. With this technology, a large number of heat exchangers can be replaced, and the purpose of simplifying the system, improving efficiency and reducing cost can be realized.

5、 It is to strengthen the reliability research, comprehensively consider the temperature, pressure, sealing and other related factors, and improve the sealing connection between the two ends of the condenser array and the heat transfer oil pipeline arranged on the ground.

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