As the core equipment of the photovoltaic power generation system, the inverter is used to convert the variable DC voltage generated by the photovoltaic modules into the alternating current of the mains frequency, which is one of the important system balances in the photovoltaic array system. At present, the common inverters on the market are mainly string inverters and micro inverters. Now, let us compare and analyze between them.
String inverter
The string inverter is based on the modular concept. Each PV string (1-5kw) has a maximum power peak tracking at the DC side through an inverter, and is connected in parallel at the AC side. The most popular inverter on the market. String inverters are mainly used in small and medium rooftop photovoltaic power generation systems and small ground power stations.
Working Principle:
The operation of string inverter technology is simple and clear. It converts the direct current (DC) generated by the panel string into alternating current (AC), which is typically used in households or businesses and fed into the public grid in the grid connected system. String inverters belong to the category of "centralized" inverters, which means they are installed separately from solar photovoltaic arrays. All direct current generated by the module is directed to the inverter. These inverters are usually integrated with batteries to store electricity for future use.
Performance:
String inverters are generally less efficient in situations where shading is present because the output of the entire string is limited by the lowest-performing panel. However, in unshaded conditions, string inverters can be equally efficient and are often more cost-effective than microinverters.
Advantages:
- The string inverter adopts a modular design, each photovoltaic string corresponds to an inverter, the DC side has the maximum power tracking function, and the AC side is connected to the grid in parallel. The influence of shading, while reducing the mismatch between the optimal operating point of the photovoltaic cell module and the inverter, maximizes the power generation.
- The string inverter MPPT voltage range is wide, generally 250-800V, the component configuration is more flexible, and the power generation time is long in rainy days and foggy areas.
- The string grid tied inverter is small in size and light in weight. It is very convenient to carry and install. It does not require professional tools and equipment, nor does it require a special power distribution room. It can simplify construction and installation in various applications. The floor space is reduced, and the DC line connection does not require DC combiner boxes and DC distribution cabinets. The string type also has the advantages of low self-consumption, small fault impact, and convenient replacement and maintenance.
Disadvantages:
- There are many electronic components, power devices and signal circuits are on the same board, which is difficult to design and manufacture, and the reliability is slightly poor.
- The electrical clearance of the power device is small, which is not suitable for high-altitude areas. Outdoor installation, wind and sun exposure can easily lead to the aging of the casing and heat sink.
- Without isolation transformer design, electrical safety is slightly poor, not suitable for the negative grounding system of thin-film modules, the DC component is large, and the impact on the power grid is large.
- When multiple inverters are connected in parallel, the total harmonic is high, and the THDI of a single inverter can be controlled to more than 2%, but if more than 40 inverters are connected in parallel, the total harmonic will be superimposed, and it is difficult to suppress.
- The number of inverters is large, the total failure rate will increase, and the system monitoring is difficult.
- There is no DC circuit breaker or AC circuit breaker, no DC fuse. When the system fails, it is not easy to disconnect.
- 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.
Micro inverter
A solar micro inverter, or simply microinverter, is a plug-and-play device used in photovoltaics, that converts direct current (DC) generated by a single solar module to alternating current (AC). Photovoltaic micro inverters can achieve maximum power point tracking at the panel level, which has advantages over central inverters. In this way, the output power of each module can be optimized to maximize the overall output power.
Working Principle:
Microinverters are devices used in solar photovoltaic systems to convert the direct current (DC) generated by individual solar panels into alternating current (AC) that can be used in homes or fed into the electrical grid. Unlike traditional string inverters, which are connected to multiple panels in a series, microinverters are typically installed on each individual panel. Each microinverter works independently, optimizing the power output of each panel regardless of shading or other factors affecting neighboring panels. When sunlight hits a solar panel, it generates DC electricity. This DC electricity is then sent to the microinverter attached to the panel.
Performance:
Micro grid inverters tend to offer higher energy yields compared to string inverters, especially in installations where shading is a concern. Because each panel operates independently, shading on one panel doesn't significantly impact the output of other panels in the system. This results in better overall system performance, particularly in partially shaded conditions.
Advantages:
- When one or more modules fail, the system can continue to provide power to the grid, with high availability. Multiple redundant modules can be selected to improve system reliability.
- Flexible configuration. In the household market, the size of photovoltaic cells can be installed according to the user's financial resources.
- Effectively reduce the impact of shadows caused by local shading on output power.
- No high-voltage electricity, safer, simple and faster installation, low maintenance and installation cost.
- Improve the power generation of each inverter power module and track the maximum power. Due to the tracking of the maximum power point of a single module, the power generation of the photovoltaic system can be greatly increased by 25%.
Disadvantages:
- Application is limited. The application of pv micro inverter is generally only suitable for roof households.
- The cost of micro inverters is higher than that of central inverters and string inverters.
Inverters of various styles can be found in Home Power Inverter, if you have the need to buy micro inverters or want to understand the relevant information, please enter our products in time to look through.
