The working environment of the solar power generation system is relatively complex. Severe environments such as high temperatures, high temperatures, high humidity, salt fog, and large sandstorms impose very stringent requirements on the reliability and environmental adaptability of the system. In recent years, more and more photovoltaic power stations have been built on beaches, fish ponds and coastal areas. Within 2-3 years after the power station was built and operated, we discovered that due to the salty fog and high humidity environment, the normal operation of the equipment in the power station, especially the inverter, has brought about a very serious impact. This article on salt fog and high The influence of the wet environment on the operation of the inverter was analyzed in depth, and the solution was proposed, which could be used for reference and discussion in the industry.
A salt spray, high humidity environment analysis
1. Salt fog effect mechanism
In salt spray and high humidity environments, the main sources of pollution are salt fog and wet dust. Centralized inverters are generally placed inside a brick house or a container. Because of their large heat output and concentration, the direct air ventilation ducts are generally used for forced air cooling. Air is drawn directly from the outside into the inverter room and then through the inverter. Radiating air duct (outlet) is discharged outside.
In this case, the external salt mist particles and moisture will be sucked into the inverter and accumulated on internal components such as circuit boards, connectors, IGBT modules, distribution switches, and copper cables. Chloride ions play a major role in the salt fog corrosion damage process. Chloride ions easily penetrate the oxide and protective layers on the metal surface and electrochemically react with the internal metal. At the same time, the chloride ion contains a certain amount of hydration energy, which is easily adsorbed on the pores and cracks on the surface of the metal, displaces and replaces the oxygen in the chloride layer, turns the insoluble oxide into soluble chloride, and turns the passive state surface into a lively one. The surface, which reduces the insulating ability of the device and the electrical conductivity of the connection surface, causes the product to fail.
In addition, during the day when the inverter works, the temperature is relatively high and the work is stopped at night. The difference between the air temperature and the inverter temperature causes the condensation of water droplets on the inverter. After the temperature rises the next day, the water vapor evaporates, but the salt spray particles Condensate corrodes on bronze.
The harm of moist air is very great. If the power station is built near fish ponds, coastal areas, and beaches, and the surrounding air is humid, the direct ventilation of moisture into the inverter room will easily cause condensation inside the control equipment, causing creepage and flashover accidents.
For a centralized inverter room with IP54 protection and direct ventilation, the air filter in the equipment room and equipment can only filter part of the dust with a large diameter, and there is no filter protection for salt fog and moisture. Inside the inverter, ordinary protective coatings (such as copper plating, chassis plating) and protective paints (such as PCB anti-paint) cannot fully protect salt fog and wet dust.
The above cases can be seen, if you want to meet the photovoltaic power plant more than 20 years of power generation life requirements in the salt-and-moisture environment, from the design of the program to the selection of equipment need to do a good job in response measures, otherwise the consequences could be disastrous. The main components of photovoltaic power plants: components, supports, cables, inverters, AC/DC power distribution equipment, etc. need to be considered in all aspects. The inverter as the core of the photovoltaic power plant has high value, reliability has a great impact on power generation, and reasonable selection and protection are the most important considerations of the program.
From the above failure mechanism analysis and case study, the conventional container or assembly room (protection level IP55) cannot solve the problem of salt spray and high humidity. For IP20 inverters and other power distribution equipment, if used in salt spray and humid environments, the key to protection is to achieve isolation of electrical and external moist salt spray air, thus eliminating hidden troubles and ensuring long-term reliability. There are different solutions for centralized inverters and string inverters.
The protective measures of the centralized inverter solution are through the enclosed machine room protection, without gas exchange with the outside world. The following is a case of protection for photovoltaic power plants in Japan:
Most parts of Japan are close to the sea and there are relatively high requirements for salt fog protection. The following figure shows an example of a fish pond power station near Tokyo, Japan. The inverter room is a fully-enclosed structure and has no air exchange with the outside. The inverter has an IP20 degree of protection. The heat is dissipated through the high-power air-conditioning indoor unit-outdoor unit. , to achieve protection of salt spray and moisture.
The disadvantages of this solution are also very obvious: First, the additional costs brought by industrial-grade air-conditioning; second, the increase in air-conditioning maintenance workload and the number of points of failure; third, in the summer and at high-intensity irradiation, continuous operation of air-conditioning consumes a lot of Electricity affects the yield of power generation. Therefore, this scheme is suitable for scenarios where the price of electricity is higher and the initial investment is more abundant.
If a string solution is selected, the application of low-level equipment such as DC distribution cabinets (IP20) and centralized inverters (IP20) is reduced, and high-grade electrical equipment including string inverters is replaced by them. The IP65, AC bus box, communication cabinets and other equipment are all protected by IP55.
At present, string inverters of some domestic manufacturers have been able to achieve IP65 degree of protection (the external fan part of the protection level is slightly lower IP55). To further enhance salt spray resistance, the author proposes that the string inverter body adopts an all-aluminum one-piece enclosed housing (including cover plate, chassis, radiator, and better airtightness), and no external fan design (this is very The key point is that the external fan is one of the most likely to fail and be corroded in the inverter. At the same time, the outer shell of the inverter needs to be sprayed with high weatherproof outdoor type coating protection, the radiator adopts thick anodizing oxidation process, and all installations. The parts are made of stainless steel and other corrosion-resistant materials, truly IP65 protection, to meet the application in salt spray and high humidity environments. The following is the actual test scenario of the offshore field test field. After a long-term test of nearly 3 years, the inverter still maintains a stable operation without any signs of rust.
Salt fog and high-humidity environment, the corrosion of electrical facilities, has seriously affected the safety and reliability of the power plant as well as long-term operation, and it needs to pay sufficient attention to the feasibility of the power plant and the design of the project. String solution Because the system-wide equipment has a high degree of protection, there is no need to add extra cost, maintenance and fault replacement are convenient, and the responsibility interface is clear. It is the best choice for the establishment of a station plan in salt and high humidity areas. At the same time, choosing partners with high credit rating and high quality inverter products will not only achieve the best power generation performance and system reliability, reduce operation and maintenance risks and costs, but also be able to achieve better future power plant refinancing market. Valuation forms a virtuous cycle of business.
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