Chọn Inverter cho Solar

In Vietnam, the trend of using green, clean and environmentally friendly renewable energy sources is increasing. In the forms of renewable energy such as wind energy, solar energy, geothermal energy, ..., solar energy is the energy source with the lowest investment cost. As a result, it is easily accessible to homes, manufacturing plants and, more importantly, solar power plants.

For solar power systems, the inverter (a device that converts direct current (DC) from panels to AC) is seen as the heart of the system. Therefore, choosing a quality inverter is very important. Currently for solar power plants, they are using two main technologies, which are String inverter and Central inverter. The way these two technologies work and work is very different.

Central inverter was born many years ago, also known as connection system. Multiple battery strings (20-32) will go to a DC connected cabinet, often called the DC combiner box. From this DC cabinet, the DC cable will lead directly to an inverter (Figure 1). This system has many disadvantages:

Equipped with only one MPPT (maximum power point) - that is, equipped with only 1 DC input, managing the battery chains inserted into the inverter is really difficult. The evidence is that when having problems in a chain of batteries or panels will affect the output capacity of the inverter (1-2MW), causing great damage to the owner. In addition, the fuse in the DC cabinets is a big problem for today's solar farm because it is difficult to track the status of the operation and the cause of the damage, not to mention the very time and costly replacement.

Hình 1: giải pháp Central inverter

Hình 2: giải pháp String inverter

String inverter is recently used to replace central inverter in solar power plants and is widely used in rooftop solar power systems because of its outstanding advantages. Instead of battery chains and inverter connected like central technology, string technology chooses to go differently, the battery chains will be connected directly to the inverter, if the inverter has multiple MPPT units, it means there will be many inputs more (figure 2). Normally for string inverter lines each MPPT will manage 2-4 strings. In recent years, brands have tried to limit it to 2string / 1MPPT. Grid-connected inverters need to have anti-islanding function (function against independent operation when power is lost) to ensure safe operation for equipment and people.

String inverter technology has many advantages because it is compact design, easy to replace and repair in case of problems. Thanks to the multiple MPPT (multiple inputs), it will reduce the impact of the power degradation of the panels, the faulty battery chain on the system. At the same time, the management and maintenance of the panels will be more efficient.

In general, Central Inverter and String Inverter still have certain advantages and disadvantages. The investment cost for the Central Inveter system is more economical than the String Inverter, but in return String Inverter will optimize the capacity of the system and cut down most of the costs for the operation and maintenance of the system. with Central Inverter

Refer to the samples of good String Inverter: SOLIS, SUNGROW, HUAWEI, GOODWE

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