Popular Science | What factors affect the power generation of photovoltaic power plants?

For the investors of photovoltaic power plants, every additional kilowatt-hour of electricity generated by the power plant is an additional kilowatt-hour of electricity, because the power generation of the power plant is directly related to the return on investment cycle, so the investors are most concerned about the power generation of the power plant. The power generation of a photovoltaic power station will be affected by many factors, such as the quality of photovoltaic modules, inverters and cables, the installation orientation and inclination of modules, the shading of dust, the matching system scheme of photovoltaic modules and inverters, the quality of power grid, etc. Impact

of

shadow shading on power generation Among the many factors affecting the power generation of photovoltaic power generation system, shadow shading is a relatively common one. Common shading mainly includes poles, trees, guardrails, bird droppings, dust and front and rear row shading of components. In the construction process of

many power stations, it is often impossible to completely avoid the shadow, and many people will feel that the shadow area is small and will not have a great impact. In fact, if a part or a component is blocked, the whole string of components will be affected. This is the barrel effect of the series circuit. In a string of components, the current of each component is the same, and the maximum current is determined by the smallest component. Therefore, as long as one component is blocked, it will affect the output power of the whole string. Seriously, it will also lead to the hot spot effect of the module, reduce the power generation efficiency and service life of the module, and even lead to local burning of the module, which will bring some potential safety hazards. Therefore, we should not only avoid shadows in the design of power plants, but also pay attention to later operation and maintenance, and regularly clean components. Shading

of modules by

different shadows Influence

of system capacity ratio on power generation Capacity ratio refers to the ratio of installed capacity of photovoltaic system to rated capacity of inverter. If the photovoltaic system is designed according to the capacity ratio of 1:1, when the output power of the photovoltaic module can not reach the nominal power, the capacity of the inverter will be wasted. At present, over-matching design is often used to improve the comprehensive utilization rate of photovoltaic system, reduce the cost per kilowatt hour of the system and improve the income of the power station. However, this does not mean that the capacity ratio can be expanded indefinitely to save the investment of inverters, because the cost of inverters accounts for only about 5% of the whole photovoltaic system. Too much over-allocation is not only not cost-effective, but also leads to the limited operation of inverters, resulting in the loss of power generation. Therefore, the reasonable design of the system capacity ratio is conducive to improving the economy of the photovoltaic power generation system. In different types of resource areas, due to the different conditions of solar energy resources and the different characteristics of regional temperature, it is necessary to calculate according to the specific local conditions. The following is the recommended capacity ratio for different areas.

If the inverter is compared to the brain of photovoltaic power station, the cable is the nervous system of photovoltaic system, which connects photovoltaic modules, inverters, junction boxes, grid-connected cabinets and other equipment in series as a whole. Therefore, reasonable cable selection is very important for the whole photovoltaic system. Appropriate cable diameter shall be selected during

cable design and selection, especially for large photovoltaic power station, which covers a large area and has a long line. If the AC cable diameter is too thin, it will cause cable overload and heating, which will not only affect the power generation, but also cause potential safety hazards such as short circuit and fire. It should also be noted that the cross-sectional area of aluminum cables is much larger than that of copper cables with the same current carrying capacity, so it is necessary to consider whether the AC end of the inverter can be connected. The AC output side of the

inverter is designed according to the copper wire benchmark, and it is recommended to use the copper core cable. However, the use of aluminum core cables will save some investment costs compared with copper core cables, so many installers will use aluminum core cables. However, copper-aluminum wiring transition terminals that meet the standard requirements must be used, because copper-aluminum joints are prone to electrochemical corrosion, resulting in poor contact between copper and aluminum, increased resistance, and affecting the efficiency of the entire photovoltaic system. Running for a long time will cause the temperature of the joint to rise and accelerate corrosion, or even burn out.

Cable selection has a direct impact on the power generation of photovoltaic power station. Selecting the appropriate cable type and specification, as well as cables with good load capacity, weather resistance and durability, can minimize power loss, improve power generation efficiency, and ensure the normal operation of photovoltaic power plants and maximize power generation.

The

power quality of power grid includes: voltage deviation, current deviation, frequency deviation, voltage fluctuation or flicker, three-phase imbalance, temporary or transient overvoltage, waveform distortion, voltage sag and so on.

1. The voltage and frequency of the

grid are not constant and will change with the load and power flow, while the output voltage of the inverter follows the grid voltage. However, the inverter will stop working when the voltage and frequency of the grid fluctuate beyond a certain range.

2. Voltage fluctuation, flicker and harmonics

In some mechanical processing plants, there are high-power equipment such as crane, welding machine, gantry milling machine, and some electric arc furnace factories, the electric energy changes dramatically between the start-up and shutdown of the equipment, accompanied by a large number of harmonics. The harmonic and unbalanced negative sequence components in the grid will lead to the fluctuation of the output active power of the photovoltaic system, and the higher the grid voltage distortion rate is, the smaller the output active power of the photovoltaic system is; the output current distortion will also occur, and the higher the grid voltage distortion rate is, the larger the output current THD of the photovoltaic system is. When the grid voltage fluctuates sharply, the adjustment ability of the inverter is limited, which may cause the PV inverter to restart frequently. In serious cases, it may cause the overvoltage explosion of the power devices in the inverter and the overcurrent explosion of the electrolytic capacitor.

From the above points, the power generation of the PV power station depends not only on the power generation performance of the PV power station itself, but also closely related to the later operation and maintenance. Correct operation and maintenance can not only improve the power generation, but also improve the service life of the equipment and the power station.