At present, China's photovoltaic industry has entered a stage of large-scale development, and more and more photovoltaic power plants have entered the 25-year operation period. The level of power generation during operation is a key factor affecting the economic efficiency of the power station. Therefore, how to ensure the high-efficiency power generation of photovoltaic power plants becomes the most important issue faced by operators. Before solving this problem, it is first necessary to analyze the loss of the photovoltaic power plant equipment and understand where the power plant losses occur.
Power station losses based on absorption losses and inverter losses in photovoltaic arrays
In addition to the influence of resource factors, photovoltaic power plant output is also affected by the loss of power plant production and operation equipment. The greater the loss of power plant equipment, the smaller the power generation. Photovoltaic plant equipment loss mainly includes four categories: photovoltaic array absorption loss, inverter loss, collector circuit and box loss, boost station loss.
(1) Photovoltaic array absorption loss is the power loss from the PV array through the combiner box to the DC input of the inverter, including the photovoltaic module equipment failure loss, shielding loss, angle loss, DC cable loss and bus box branch loss;
(2) The inverter loss refers to the power loss caused by the DC to AC inverter, including inverter conversion efficiency loss and MPPT maximum power tracking capability loss;
(3) The collector line and box-loss are the power losses from the inverter's AC input terminal through the box change to each branch's meter, including the inverter output loss, the box change conversion loss and the plant line loss;
(4) The booster station loss is the loss from the power meter of each branch through the booster station to the gateway table, including main transformer loss, station transformer loss, bus loss and other station line losses.
After analyzing the October data of three photovoltaic power plants with integrated efficiency of 65%~75% and installed capacity of 20MW, 30MW and 50MW respectively, the results show that the absorption losses of photovoltaic square arrays and inverter losses are the main factors affecting the power plant output. Among them, the absorption loss of the photovoltaic square array is the largest, accounting for about 20~30%, followed by the inverter loss, accounting for about 2~4%, while the collector line and the box loss and the booster station loss are relatively small, total about About 2%.
Further analysis of the above-mentioned 30MW photovoltaic power station, its construction investment is about 400 million yuan, the power loss of the power station in October is 2747600 kW • h, accounting for 34.8% of the theoretical power generation, if calculated by 1.0 yuan per hour, in October total The loss of 4,119,900 yuan has a huge impact on the economic benefits of the power station.
How to reduce the loss of photovoltaic power stations and increase the amount of power generated
Among the four types of losses in photovoltaic power station equipment, the collector lines and the box-loss and boost-station losses are usually closely related to the performance of the equipment itself, and the losses are relatively stable. However, if the equipment fails, it will cause a large power loss, so to ensure its normal and stable operation. For photovoltaic square arrays and inverters, losses can be minimized through pre-construction and later operation and maintenance. The specific analysis is as follows.
(1) Failure of PV modules and combiner equipment
There are many photovoltaic power station equipment. The 30MW photovoltaic power station in the above example has 420 junction boxes. Each junction box has 16 branches (a total of 6720 branches), and each branch has 20 panels (134,400 cells in total). Board), a huge amount of equipment. The larger the number, the higher the frequency of equipment failure and the greater the power loss. Common problems include burning of photovoltaic modules, ignition of the junction box, chipping of the battery board, welding of the lead wire, and failure of the bus box branch. In order to reduce the loss of this part, on the one hand, the inspection and acceptance of the work must be strengthened and ensured by an effective acceptance method. The power plant equipment is from the quality, including the ex-factory equipment quality, equipment installation and arrangement to the design standards, the construction quality of the power station, etc.; on the other hand, the intelligent operation level of the power station should be improved, and the operation data analysis should be performed through intelligent auxiliary means to find out in time. Sources of faults are used to perform point-to-point troubleshooting to improve the operating efficiency of O&M personnel and reduce power station losses.
(2) Blocking loss
Due to factors such as the installation angle and arrangement of PV modules, some PV modules are obstructed, affecting the power output of PV arrays and causing power loss. Therefore, during the design and construction of the power station, the PV modules should be prevented from being in shadow. At the same time, in order to reduce the damage of the PV modules caused by the hot-spot phenomenon, appropriate bypass diodes should be installed to divide the battery string into several parts, making the battery strings voltage and Proportional loss of current, reducing loss of electricity.
(3) Angle loss
The tilt angle of the PV array varies from 10° to 90° depending on the purpose, and usually the latitude at which it is placed is selected. The angle selection influences the solar radiation intensity on the one hand, and on the other hand, due to dust, snow and other factors affecting the power generation of photovoltaic modules. For example, when the angle is set at 45° or more, 20 to 30 cm thick snow can be caused to slide down depending on its own weight. Loss of power caused by snow cover. At the same time, the angle of PV modules can be controlled through intelligent auxiliary means to adapt to seasonal and weather changes and maximize the power generation of the power station.
(4) Inverter losses
The inverter losses are mainly reflected in two aspects. One is the loss caused by the inverter conversion efficiency, and the other is the loss caused by the MPPT maximum power tracking capability of the inverter. Both of these aspects are determined by the performance of the inverter itself, and the benefit of reducing inverter losses through later operation and maintenance is relatively small. Therefore, the equipment selection in the initial period of power station construction is locked down and the loss is reduced by selecting the inverter with better performance. In the later stage of operation and maintenance, the inverter operating data can be collected and analyzed through intelligent means to provide decision support for equipment selection of new power plants.
Through the above analysis, it can be seen that the loss will cause huge losses in the photovoltaic power plant. The overall efficiency of the power plant should be improved by reducing the loss in key areas first. On the one hand, it ensures the equipment and construction quality of the power station through effective acceptance tools; on the other hand, in the operation and maintenance of the power station, it is necessary to use intelligent auxiliary means to upgrade the production level of the power station and increase the power generation. (Guo Dan writes)
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