Distributed photovoltaic (PV) systems are typically built on building rooftops, factory rooftops, and vegetable sheds to make the most of available space. So, what are the similarities and differences between distributed PV power generation and centralized PV power generation?
I. Similarities between Distributed Photovoltaic Power Generation and Centralized Photovoltaic Power Generation
1. The principle is the same: both utilize solar energy to convert it into electrical energy, and then connect the generated electrical energy to the grid for production and daily life.
2. The components are the same, usually using monocrystalline silicon solar panels or solar thin films.
3. The main equipment used is basically the same, including inverters, transformers, combiner boxes, etc. The function of the inverter is to convert the generated direct current (DC) into alternating current (AC). The function of the transformer is to enhance the AC power converted by the inverter. The function of the combiner box is to collect the DC power from the solar panels, then combine them into one point and send them to the inverter in a unified manner.
II. Differences between Distributed Photovoltaic Power Generation and Centralized Photovoltaic Power Generation
1. Different Installation Locations: Distributed photovoltaic (PV) systems are mainly installed on rooftops, primarily in the inhabited North and South China regions. Centralized PV systems, on the other hand, are mainly installed in the Gobi Desert and other desert areas. Typically, they are installed in relatively remote and desolate areas where land is relatively cheap. In Northwest China, this mainly includes Ningxia, Gansu, Xinjiang, and Qinghai.
2. Different Grid Connection Voltage Levels: For distributed photovoltaic (PV) systems, a 380V connection to the grid is typically used, usually with a low-voltage trip unit. The number of distributed grid connection points depends on the specific circumstances. Centralized PV power plants typically use 35KV or 110KV for grid connection. If the power plant's capacity is less than or equal to 30 MW, a main transformer is usually not required, and the grid voltage exceeding 35KV will be connected. For power plants exceeding 30 MW, a main transformer is typically installed and upgraded to 110KV before grid connection.
3. The secondary equipment used in the power station differs: Because distributed photovoltaic power stations are low-voltage 380V grid-connected equipment, they use less primary and secondary equipment. Inverters are typically wall-mounted inverters, which are relatively simple to install and small in size. Transformers are also small-sized. Commonly used microprocessor-based protection systems include power quality monitoring, anti-islanding protection devices, and fault disconnection.
Equipment and technical specifications vary depending on the region. However, anti-islanding protection devices are currently mandatory for every distributed photovoltaic (PV) system. Centralized PV power plants typically have their own substations due to their relatively high voltage levels. Inverters are usually located indoors within the substation and are relatively large. The voltage boosting function is achieved by changing the enclosure, typically up to 35kV. There are many devices within the booster station.
The main equipment includes power station transformers, switchgear, various transformers, arc suppression coils, and main transformers. Secondary equipment includes microprocessor-based protection devices, electricity meters, and dispatch data panels. The relatively complex dispatching system directly enables centralized management of the power station. Simultaneously, the station requires a power prediction system and a power control system, making it significantly more complex than a distributed photovoltaic system.
4. Different transmission distances: Distributed photovoltaic power generation generally refers to electricity generated and connected to the grid locally, with very low or virtually no line loss. It supplements local power supply for local and nearby users. Centralized photovoltaic power stations transmit electricity to higher voltage levels through high-voltage grid connection, and then transmit the high-voltage electricity to eastern regions, realizing the west-to-east power transmission project.
