Solar photovoltaic mounting system
Application of solar photovoltaic mounting system
Application of solar photovoltaic mounting system
1. Development status and application prospects of solar photovoltaic power generation in China
1.1. Economic cost analysis of solar photovoltaic industry in China
The rise of the solar photovoltaic industry is in the ascendant in China, and the development speed is alarming, but it also faces many problems such as overcapacity, repeated construction, and insufficient domestic demand. My country's PV cell production accounts for 28% of the world's total (2008), but domestic use accounts for less than 4% of annual output, and huge capacity has not been really utilized. Among them, most of the solar demonstration projects under construction are mainly off-grid applications. The grid-connected power generation project is only 1.2MW, accounting for about 6% of the total solar photovoltaic power generation.
Because solar power generation is directly related to the intensity and time of sunlight, as well as the placement and inclination of the solar panels, the amount of electricity generated will fluctuate with time; in addition, due to the continuous aging of solar panels, the photoelectric conversion rate will also decrease year by year. In this way, if solar power and thermal power are connected to the grid, it will affect the stability of the main grid. This is the main reason why grid companies are unwilling to connect solar power plants to the grid on a technical level. On the other hand, for other power generation methods, the unit cost of solar power generation is the highest, that is, the cost of solar power generation is 3 yuan per kilowatt-hour, while the cost of thermal power generation is only 0.25 yuan. The difference between the two is 12 times. The cost of wind power generation It is 0.6 yuan, which is quite close to the cost of nuclear power. Therefore, the high cost of solar power generation has become a direct reason for restricting the development of this industry. At present, the central government proposes to build a conservation-minded society, promote a green economy and low-carbon emissions, and provide financial subsidies for solar power grid access. The unit power generation cost can be reduced to 1.5 yuan / Kwh.
According to the spirit of the Copenhagen Declaration and the Kyoto Protocol, major carbon-emitting countries have pledged to reduce their own carbon emissions, and developed countries are seeking to introduce carbon tariffs into international trade. From this perspective, solar power generation will be competitive in the future market. On the other hand, in terms of China ’s own conditions, compared with European countries, China ’s territories are vast and deserted, the central and western regions are sparsely populated, there is sufficient sunshine, more than 2/3 of the land area, and the average annual sunshine time exceeds 2200 hours, suitable for the construction of solar photovoltaic power plants . Among them, Tibet, Qinghai and other regions have less rain throughout the year, and the sunshine time exceeds 3000 hours. Therefore, solar photovoltaic power stations should be focused on.
1.2. Cost analysis of solar photovoltaic mounting system
According to German statistics, in a large-scale solar power station project, the construction and installation cost accounts for about 21% of the total investment in photovoltaic projects, while the investment in solar photovoltaic supports only accounts for about 3% of the total cost. Therefore, relative to the high investment of solar power plants, the fluctuation of the cost of brackets is not a sensitive factor. The cost of selecting high-end brackets is only increased by less than 1%. However, if the brackets selected are not suitable, the maintenance costs in the future will increase greatly. Cost-effective.
2. Products and installation of solar photovoltaic mounting system
2.1. Material of solar photovoltaic mounting system
At present, the solar photovoltaic mounting system commonly used in China is divided into three types, including concrete support, steel support and aluminum alloy support. Concrete supports are mainly used in large-scale photovoltaic power stations. Because of their self-importance, they can only be placed in the field and have a good foundation. However, they have high stability and can support huge-sized solar panels. Aluminum alloy brackets are generally used for solar applications on civil building roofs. Aluminum alloys have the characteristics of corrosion resistance, light weight, beauty and durability, but their low bearing capacity cannot be applied to solar power station projects. In addition, the price of aluminum alloy is slightly higher than that of hot-dip galvanized steel.
The steel bracket has stable performance, mature manufacturing process, high bearing capacity, and simple installation. It is widely used in civil, industrial solar photovoltaic and solar power stations. Among them, the section steel is produced by the factory, with uniform specifications, stable performance, excellent corrosion resistance, and beautiful appearance. It is worth mentioning that the combined steel support system, which is installed on site, only needs to use specially designed connectors to assemble the channel steel. The construction speed is fast and no welding is required, thus ensuring the integrity of the anticorrosion layer. The disadvantage of this kind of product is that the connecting parts have complicated craftsmanship and various types, and they have high requirements on manufacturing and design, so they are expensive.
2.2. Installation method of solar photovoltaic support
2.2.1. Components of solar photovoltaic support
Divided from the connection method, the installation of solar support can be simply divided into two types of welding and assembly. Welded brackets have low requirements on the production technology of section steel (angle steel), good connection strength, and low price. It is the commonly used bracket connection form on the market. However, the welding bracket also has some shortcomings. For example, the corrosion resistance of the connection point is difficult. If the paint is painted, the paint layer will peel off every 1 to 2 years, and it needs to be repainted. The subsequent maintenance costs are high; When it is installed in a remote area, the cost of welding electricity is high; the construction speed is slow and it is not beautiful enough. With the improvement of China's urbanization level, residents have higher and higher requirements on the aesthetics of buildings. The photovoltaic mounting system used in civil buildings is not suitable for welding brackets.
In order to overcome these shortcomings, finished brackets with channel steel as the main supporting structural members have appeared on the market. The most obvious advantages of assembling brackets are fast assembling and disassembling, without welding; all bracket components are factory-produced, with uniform anti-corrosion coating and good durability; fast construction and beautiful appearance. But it is not easy to achieve the above points. First of all, in order to make the connection between the channel steels convenient, different splices and fixing devices must be designed according to various connection conditions (as shown in the figure). The connection and fixing device must be able to firmly connect the assembly and the channel steel, and can be fixed and locked at any position of the channel steel, and the installation and disassembly are convenient. Secondly, the connection between the channel steels needs to be secured, for example, by engaging teeth. Finally, the on-site cutting of the entire section of channel steel needs to be as precise and convenient as possible, and the back hole cannot be cut. This requires the channel steel to add scale marks to facilitate the construction personnel to cut on site.
2.2.2. How to connect the base of solar photovoltaic support
There are four main ways to install the base of the solar photovoltaic support, namely direct embedding, connection of embedded parts, ground anchoring method and concrete block counterweight (see figure below).
Figure: Different basic forms of double-row columns
The four different foundation forms of the double-row column type bracket can be selected according to the actual situation. Among them, the method of concrete block counterweight and embedded parts is often applied to roof solar construction or reconstruction, which can effectively avoid damage to roof waterproof layer and other structures; The method and direct buried type are often used in the construction of solar power plants, and have the characteristics of stability and high reliability.
According to the European construction experience, the ground anchor method has the strongest foundation and the highest safety, but the connection between the ground anchor and the solar photovoltaic support needs to be specially customized, and the cost is very high. In contrast, the direct-buried construction is simple and convenient. It only needs to use a hole-opening machine to drill holes and pour concrete in the field. Before the concrete is solidified, the channel steel can be directly inserted into the hole. The foundation requires high self-reliance of the soil on site, and the preliminary geological survey test is required. Of course, in the case where the geological conditions are very guaranteed, it is not necessary to do preliminary geological exploration.
The arrangement of the primary and secondary beams of solar photovoltaic brackets mainly depends on the placement method of the solar panels. In general, the direct burial method is obviously superior to the ground anchor method under the premise that the electrical conditions permit.
The structural design of the solar photovoltaic support panel is rectangular, and the arrangement can be divided into horizontal arrangement and vertical arrangement. Horizontal arrangement is mostly used for projects with double-row battery panels; vertical arrangement is mostly used for projects with single-row battery panels.
The legs of the bracket are located under the main beam. If the front and rear legs are used, the bracket is a statically indeterminate structure. The front legs must bear 80% of the shear force of the bracket (mainly wind pressure). At the same time, in order to ensure the overall stability of the bracket, it is usually necessary to add diagonal braces;
(Disadvantages: unstable relative to triangular brackets; advantages: guarantee the height of the components from the ground)
If a triangular bracket is used, the front legs are replaced with MQP connectors, and there is no need to add diagonal braces, but with this design, the solar panel is closer to the ground, and weeding operations are required in grassland areas.
(Advantages: Stability; Disadvantages: Applicable to a certain height from the ground, such as cement pier foundation, steel structure foundation, there are limitations)
2.3. Technical difficulties of solar photovoltaic mounting system
In fact, the manufacturing process of the finished stent is not simple, and high-quality products often have multiple technical patents. First, high-quality section steel usually has a high level of galvanizing process. According to the requirements of national standards, the average thickness of the galvanized layer should be greater than 50 microns, and the minimum thickness should be greater than 45 microns. In fact, although the average thickness of the galvanized layer of many products can meet the requirements, the minimum thickness is less than 40 microns, and pitting corrosion often occurs in actual use. The corrosion rate of halogen to steel is very fast. Within a year, it may cause the weakening of the overall support structure and cause hidden safety hazards. Therefore, it is not easy to achieve a highly uniform galvanizing process.
Secondly, the connection of section steel is a technical difficulty. After years of research and development, some well-known international brands have formed a set of effective connection methods. This includes not only the clever conception of the connecting piece, but also the design of the channel steel back hole, the bite teeth and so on. This involves many aspects of iron and steel metallurgy technology such as stamping and casting.
In addition, double-sided channel steel used to withstand large loads must be back-to-back welded. There is a big gap between the various welding processes. Pressure laser welding can ensure that the entire cross-section is evenly connected, and the two channel steels are completely integrated into one, and they are stressed together. However, the electric welding technology can only fix the two channel steel parts together, and the force form is closer to the composite beam. In order to improve the bearing capacity, some steel bar manufacturers have added cold-rolled stiffeners to the channel steel.
In short, there are many technical difficulties in the production process of assembled steel brackets, which requires China's metallurgical engineering technicians to overcome technical barriers and further reduce their cost of use.
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