Classification and composition of photovoltaic power generation systems
Since photovoltaic power generation technology entered the large-scale civilian field, in order to adapt to various application scenarios, it has developed into a wide variety of photovoltaic product families in various forms. According to different classification standards, there can be the following classifications:
(1) According to the output current type, it can be divided into photovoltaic power generation DC system and photovoltaic power generation AC system. The DC system is mainly used for low-power lighting loads without AC inverter and long-distance transmission. It is commonly used in various integrated solar products, such as solar street lights, solar lawn lights, solar navigation lights, solar (micropower) children’s toys, etc.
(2) According to whether it is connected to the public grid, it can be divided into grid-connected photovoltaic power generation systems and independent photovoltaic power generation systems. Independent photovoltaic power generation systems are also called off-grid photovoltaic power generation systems. They are mainly used in areas where there is no public grid power supply or the public grid power is unstable, as well as various special application scenarios. They are more common in production and life in remote rural areas, mountainous areas or islands. Electrification can solve the difficulty of using electricity for basic power such as daily lighting and water pumps.
❶ Structure characteristics of independent photovoltaic power generation system
Independent photovoltaic power generation systems generally consist of solar modules or arrays, controllers, batteries, and so on. According to the difference of specific application scenarios, the AC inverter is also an option in the system components. Generally speaking, independent photovoltaic power generation systems, as a supplement to the public grid power supply system, are generally small in scale, simple in structure, high in system integration, and relatively easy to operate and maintain.
❷ Grid-connected photovoltaic power generation system structure and classification characteristics
The grid-connected photovoltaic power generation system is mainly composed of solar energy component array, DC/AC combiner box, DC/AC power distribution cabinet, inverter, step-up transformer, primary and secondary protection equipment, photovoltaic power station monitoring system and other equipment. The inverter is very important to the entire grid-connected photovoltaic power generation system. It converts the direct current generated by the solar cell into alternating current, which is convenient to connect to the public grid and transmit it to the long-distance electric load area.
Generally speaking, a photovoltaic power station is constituted by a power generation site that is dominated by photovoltaic power generation systems and includes various auxiliary facilities such as buildings (structures), maintenance, and living. Currently, grid-connected power stations are the dominant form of photovoltaic power generation technology application. Grid-connected photovoltaic power plants can also be classified according to different standards.
(1) According to installed capacity: it can be divided into small photovoltaic power station, medium photovoltaic power station and large photovoltaic power station. Generally speaking, the installed capacity of small photovoltaic power plants is less than or equal to 1MWp, usually 0.4~10kV voltage level is connected to the grid; the installed capacity of medium-sized photovoltaic power plants is greater than 1MWp, but less than or equal to 30MWp, usually 10~35kV voltage level is connected to the grid; large photovoltaic power plants The installed capacity of the power station is greater than 30MWp, and it is usually connected to the grid with a voltage of 35kV or higher.
(2) According to the different access points and the country’s differences in grid management and electricity price subsidy policies, grid-connected photovoltaic power plants can be divided into two categories: discrete distributed photovoltaic power plants and large centralized photovoltaic power plants.
①Distributed photovoltaic power station Distributed photovoltaic power station, that is, distributed photovoltaic power generation project, mainly refers to the photovoltaic power generation that is built near the user’s site, and the operation mode is self-generated and used by the user, surplus electricity is connected to the Internet, and is balanced in the power distribution system. system. According to the difference of grid-connected management, distributed photovoltaic power plants (power generation projects) can generally be divided into three situations: one is mainly for self-use, and surplus electricity can be connected to the Internet. Generally, the grid-connected power should not exceed 50%, and it should be connected to the grid at a single point; the second is all for self-use; the third is the full grid connection, which is currently limited to distributed projects for residential use. Distributed photovoltaic power plants generally have a low grid-connected voltage level, and in most cases, they do not need to be equipped with booster stations and related distribution equipment, and do not need to be directly dispatched by the power grid management department, and the daily operation, maintenance and repair work are relatively simplified.
②Centralized photovoltaic power station Large-scale centralized photovoltaic power station refers to the use of deserts, mountains, lakes and other rich and relatively stable solar radiation resources to construct, put into operation and directly integrated into the public grid, connected to the high-voltage power transmission system to provide long-distance load Photovoltaic power generation system. Centralized photovoltaic power plants generally have a long construction period, a high investment amount, and a large area. The installed capacity is generally 20MW and above, and the grid voltage level is mostly 35kV and above.