In medium and large-scale industrial and commercial photovoltaic power plants, it is generally recommended to use high-power inverters as much as possible, because the higher the inverter power, the cheaper the single-watt price, and the later AC power distribution cabinets and AC cables will be less, but not inverse The greater the stand-alone power of the transformer, the lower the system cost, the higher the power generation of the system, and the more convenient the operation and maintenance. This is not inevitable, but it must be considered from all aspects.
In the photovoltaic system, the factors that affect the cost are components, brackets, DC cables, inverters, AC cables, AC power distribution cabinets, transformers, manual installation and other factors. If you only choose inverters with different powers, the components, brackets, transformers, manual installation, etc. are almost the same. The accessories such as DC cables, inverters, AC cables, and AC power distribution cabinets are slightly different.
The following is a 300kW industrial and commercial power station with a color steel tile roof and an area of ​​about 3600 square meters. Five 60kW inverters and three 100kW inverters are used to compare the economics of these two schemes.
1 DC cable
The DC cable refers to the cable from the photovoltaic module to the inverter, which can save the cost of the cable and the power distribution cabinet, but it also needs to control the length of the DC cable. The DC cable from the module to the inverter generates power for the system The influence of the quantity is very large. The longer the cable, the higher the loss. The DC cable is controlled within 50 meters, and the DC cable loss can be reduced to 0.2%. The higher the inverter power, the further away the remote components are from the inverter, and the longer the cables used.
As shown in the figure above, using five 60kW inverter solutions, the square matrix of each inverter is about 720 square, the inverter has 10 groups of inputs, and the length of each group of cables is about 30 to 50 meters, with an average of 40 meters. , Then the length of the DC cable required by each inverter is 400 meters, and the total length of the DC cable of the 300kW system is 2000 meters;
If three 100kW inverter solutions are used, the square matrix of each inverter is about 1200 square meters, the inverter has 18 groups of inputs, and the cable length of each group is about 30 meters to 60 meters, with an average of 45 meters, then each The length of the DC cable required by the inverter is 810 meters, and the total length of the DC cable in the 300kW system is 2430 meters; therefore, the use of five 60kW inverter solutions will save more than 20% of the photovoltaic DC cable.
2 AC cable
The AC cable is divided into two sections, one section is the cable from the inverter to the AC combiner box, and the other section is the cable from the AC combiner box to the grid connection box. The inverters with different powers are used, only the former is different, 60kW reverse The maximum output current of the converter is 87A, the design uses 3 * 35 + 1 * 16 square copper core cable or 3 * 50 + 1 * 25 aluminum alloy core cable, 100kW inverter, the maximum output current is 145A, the design uses 3 * 70 + 1 * 35 square copper core cables or 3 * 120 + 1 * 70 aluminum alloy core cables, we assume that the distance of the 60kW inverter from the AC combiner box is 100 meters, and 5 inverters require 500 meters of cable. Assuming that the distance of the 100kW inverter from the AC combiner box is 80 meters, three inverters require 240 meters of cable.
As can be seen from the table above, if the aluminum alloy core cable is used, the cable cost of the 60kW inverter solution is lower, and if the copper core cable is used, the cable cost of the 100kW inverter solution is lower, but they are not much different.
3 AC junction box
The AC bus is divided into two parts. The first part is the switch of the inverter. There is a difference in this part. The second part is the total switch after the bus. This part is the same. The 60kW inverter has a maximum output current of 87A. The design uses 100A The molded case circuit breaker, 100kW inverter, the maximum output current is 145A, the design uses 160A molded case circuit breaker, all use CHNT Zhengtai Kunlun 3P molded case circuit breaker air switch, the price of 100A is about 136 yuan, 5 total The price is 680 yuan, the price of 160A is about 180 yuan, the total price of the three is about 540 yuan, and the difference is about 140 yuan. In fact, the AC combiner box is generally quoted according to the total power and configuration. Has little effect.
4 Inverter efficiency
Inverters range from 10kW to 60kW. If they are of the same generation type, you can see that the higher the power of the inverter, the higher the efficiency. This is determined by the power devices in the inverter. The higher the power, the greater the loss The lower the efficiency, the higher the efficiency, but after 60kW, the efficiency of the inverter has not increased much. This is because the power module growth is limited. After 60kW, generally multiple modules are used in parallel, so the efficiency growth is limited.
5 Weight and volume
For example: Gurawat MAC60kW inverter with a volume of 0.68 * 0.508 * 0.281 and a weight of 52 kg. An adult with a little more strength can move it, and a 100kW inverter with a volume of 1.051 * 0.66 * 0.362, the weight is 85 kg, it is difficult to carry by one person, and professional lifting tools are needed. If the roof is very complex, it may not be convenient to use a machine for lifting, and it is more dangerous to lift manually, so it is recommended to choose a light-weight inverter Device.
to sum up
In summary, for large-scale industrial and commercial photovoltaic power stations, which inverter is selected from more than 60kW power, the cost and efficiency of the system are not much different. You can choose according to the actual situation of the project terrain and installation method. (Liu Xiaohe)
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