How to choose a distributed photovoltaic inverter?

On January 13, the 5th Home Photovoltaic System Promotion Conference (Shijiazhuang Station) hosted by Sobi Photovoltaic Network and organized by Photovoltaic Home came to a perfect conclusion. Photovoltaic peers from all over the country gathered together to discuss the development of distributed photovoltaics. Growatt Product Manager Yuan Zhimin was invited to attend the meeting and shared with the participants how to select inverters for distributed photovoltaic systems.

Photo: Yuan Zhimin, Product Manager of Growatt

Yuan Zhimin pointed out: "With the development and reform of the photovoltaic market, the distributed photovoltaic market is developing better and better. In the past, when we talked about distributed systems, we thought of rooftop distributed systems, such as household and industrial and commercial rooftops. But now, distributed systems also include ground distributed systems such as wasteland, barren mountains, fish ponds and greenhouses. Therefore, the selection of inverters is particularly critical. When choosing inverters for distributed photovoltaic systems, we need to pay attention to the following five points: matching scenarios, efficient power generation, safety and reliability, grid-friendly, and intelligent operation and maintenance."

Five factors for selecting inverters for distributed photovoltaics

First, match the inverter based on the application scenario of distributed photovoltaics, and choose the appropriate inverter according to local conditions to play the greatest role. How to choose the inverter model? Single-phase or three-phase? These all depend on the situation of the roof. For home roofs or courtyards, the installed capacity is small, and single-phase or three-phase grid-connected string inverters are generally selected. When the roof area is too large, three-phase inverters are selected; for industrial and commercial roofs, complex mountainous and greenhouse projects, for irregular orientations, prone to local shading, large installed capacity, and low-voltage or medium-voltage multiple grid-connected voltages, three-phase string inverters are generally selected; for large ground and desert power stations in the northwest region, it is recommended to use centralized box inverters.

Second, one of the key factors in choosing an inverter is efficient power generation. To achieve efficient power generation in a photovoltaic power station, one indicator is the conversion efficiency of the inverter. The inverters that we often see have two concepts: maximum efficiency and weighted efficiency. What is the difference between these two concepts? Maximum efficiency is the best performance of the inverter under the best conditions. Weighted efficiency is the comprehensive performance of the inverter. The inverter's ability to achieve efficient power generation is a comprehensive reflection. In this way, weighted efficiency is more meaningful in manufacturing.

Another key indicator is MPPT efficiency, which has two strategies: dynamic and static. At present, the algorithm of static MPPT efficiency is not a big problem and most manufacturers can achieve it. The key is dynamic MPPT efficiency. In the actual working environment of the inverter, conditions such as light and temperature are constantly changing. The two indicators of inverter conversion efficiency and MPPT efficiency will affect the power generation of the inverter, which can extend the power generation time and thus increase the power generation.

Third, because the distributed photovoltaic system is close to the user side, safety and reliability become important factors in selecting inverters. Owners and developers hope that the power station can operate reliably and safely for 25 years. 1. Realize group string monitoring, be able to carry out refined monitoring of each group string, timely discover line faults, component faults, obstructions and other problems, and reduce fault location time. 2. The inverter has a protection function, it must be able to prevent fire, such as color steel tile roofs and mountain scenes are prone to fire; it must be able to prevent lightning strikes, such as roofs and mountains are prone to thunderstorms; it must be able to prevent PID and electric shock, such as fishing and agricultural light complementary scenes often have operation and maintenance or work personnel. 3. The heat dissipation design of the inverter, the 10 ℃ rule of electronic device life: for every 10 ℃ increase in the ambient temperature of the device, the life is reduced by half. 4. Consider the process design and period selection of the inverter. With a good design, a large number of experimental verifications are carried out, such as waterproofing, dustproofing, high and low temperature, etc. are very necessary.

Fourth, when choosing an inverter, you need to consider grid friendliness. In a photovoltaic system, the inverter is an important tool for converting light energy into electrical energy. The front is connected to light and the back is connected to the grid. There are three indicators for the grid friendliness of the inverter: power factor, current harmonics, and DC component. Under normal circumstances, the power factor PF is ideal when PF=1. The smaller the current harmonic THDi, the closer it is to sine. The smaller the DC component DCI, the better.

Fifth, intelligent operation and maintenance, select different monitoring solutions for different scenarios, including remote monitoring, online customer service, and remote operation and maintenance.

Growatt was established in 2010. By the end of 2016, the company had shipped more than 600,000 sets of inverters worldwide. Growatt is the only manufacturer with 60,000 sets of inverters running stably for more than 5 years. As China's largest exporter of home energy storage systems, Growatt is committed to becoming the world's largest user-side smart energy solution provider in the future.