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The main task of the inverter is to convert the direct current generated by the photovoltaic modules into alternating current that meets the requirements of the grid, which is the core of the photovoltaic system.
In the field of distributed pv system, there are two main types of inverters that we often hear about. This article focuses on string inverter vs micro inverter.
1. Difference between string inverter vs micro inverter in working principle
Microinverters are able to track the maximum power point of each or more PV modules to ensure that each module performs at its best. It can also fine tune and monitor the output power of each module, which is a "one-to-one" service that allows each module to be maximized.
It is enough to track the maximum power point of each or more photovoltaic modules, and after inverting, they are integrated into the AC power grid to finely adjust and monitor the output power of each photovoltaic module. And its power is generally less than 4kW, small and delicate.
String inverters act as a "leader" and can track the maximum power point of one or more strings of PV modules individually. It has a relatively wide power range, generally between 1.5kW and 500kW, which can meet the needs of larger-scale photovoltaic systems.
2. Circuit design in string inverter vs micro inverter
Differences in topology and circuit design between microinverters and string inverters are also a major difference. The input design of the microinverter adopts the method of single component independence or parallel connection of components, which makes it have unique performance in terms of operating voltage, system overall efficiency, operation and maintenance mode, etc.
The input design of the string inverter adopts the method of multi-component series connection, which makes it more advantageous in terms of voltage and power output.
However, it should be noted that due to the serial connection between modules, once a problem occurs in one module, it may affect the power generation of the entire string of modules.
Therefore, there is a certain difference between the two inverters in terms of system efficiency. Especially when shading or individual differences occur in the module after a period of operation, the system efficiency of the microinverter will be significantly better than that of the string inverter system.
3. Operating voltage in string inverter vs micro inverter
In terms of operating voltage, the photovoltaic modules in the microinverter system are connected in parallel, so there is no voltage superposition between the modules during system operation, and the DC voltage is low, not exceeding 120V, which is safer.
In terms of overall system efficiency, microinverters can independently track each PV module because each module has an independent MPPT (maximum power point tracking), and accurately track to the maximum power output point, thus avoiding the "short board effect" and making the system more efficient.
The string inverter system is a series circuit, and the cumulative voltage of the whole string line can reach 600V~1000V, so special attention needs to be paid to safe operation.
String inverters, on the other hand, track the entire string of modules, and if a module fails, it will affect the power generation of the entire string of modules.
4. Installation in string inverter vs micro inverter
In terms of O&M, the solar microinverter has a module-level control function, which can accurately view the power generation status and other information of each module, making O&M more convenient and efficient.
In terms of installation location, the microinverter adopts a modular design, is small in size and light in weight, and can be installed directly on the photovoltaic bracket to achieve plug-and-play without taking up additional space.
On the other hand, the string inverter controls the entire string of modules, and only the power generation of the entire string of modules can be seen during operation and maintenance, which is relatively general. Installed below or near a wall of a string of components, requiring a fixed bracket or hoop mounting.
5. How to choose the right one
Both inverter products have their own suitable subdivision application scenarios and application advantages, and the appropriate type of inverter should be selected according to local conditions when selecting inverters.
String inverters have become the main choice in the distributed PV market due to their mature and reliable technology and low cost advantages.Thanks to technological progress, the cost per watt of microinverters is also decreasing.
With higher requirements for the safety, system efficiency and intelligent operation and maintenance of photovoltaic power plants, microinverters will be more widely used.
6. Conclusion
Microinverters and string inverters each have their own characteristics and advantages. Microinverters perform well in O&M accuracy, system efficiency, and safety, and are suitable for scenarios that have high requirements for PV power plant safety, system efficiency, and intelligent O&M.
String inverters have become the mainstream choice in the distributed PV market due to their mature and reliable technology and low cost advantages. When choosing an inverter, we should choose the most suitable type of inverter according to the actual situation and specific needs.
It is believed that with the continuous progress of photovoltaic technology and the continuous development of the market, microinverters and string inverters will usher in broader application prospects.
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