The main advantages are:
1. The string inverter adopts a modular design. Each photovoltaic string corresponds to an inverter. The DC end has a maximum power tracking function. The advantage of end-to-end parallel connection to the grid is that it is not affected by module differences between strings and shadows, and at the same time reduces the mismatch between the best operating point of the photovoltaic cell module and the inverter, maximizing the power generation.
2. The string inverter MPPT voltage range is wide, generally 250-800V, and the component configuration is more flexible. On rainy days and in areas with a lot of fog, power generation takes a long time.
3. The string-type grid-connected inverter is small in size and light in weight, and is very convenient to transport and install. It does not require professional tools and equipment, nor does it require a special power distribution room. It can be used in various applications. It can simplify construction and reduce land occupation in applications, and DC line connections do not require DC combiner boxes and DC distribution cabinets. The string type also has the advantages of low self-consumption, small failure impact, and easy replacement and maintenance.
The main disadvantages are:
1. There are many electronic components, and the power devices and signal circuits are on the same board. It is difficult to design and manufacture, and the reliability is slightly poor.
2. The electrical clearance of power devices is small and is not suitable for high altitude areas. For outdoor installation, exposure to wind and sun can easily cause aging of the casing and heat sink.
3. Designed without an isolation transformer, the electrical safety is slightly poor, and it is not suitable for the negative grounding system of thin film modules. The DC component is large and has a great impact on the power grid.
4. When multiple inverters are connected in parallel, the total harmonics will be high. The THDI of a single inverter can be controlled to more than 2%. However, if more than 40 inverters are connected in parallel, the total harmonics will be superposition. And it’s harder to suppress.
5. With a large number of inverters, the total failure rate will increase, making system monitoring difficult.
6. There are no DC circuit breakers, AC circuit breakers, and DC fuses. When the system fails, it is not easy to disconnect.
7. A single inverter can realize the zero voltage ride through function, but when multiple inverters are connected in parallel, it is difficult to realize the zero voltage ride through function, reactive power regulation, active power regulation and other functions. Saw it in Hengtongyuan, Shenzhen.