The composition and working principle of solar photovoltaic power generation system

The photovoltaic power generation system mainly includes a grid-connected system and an off-grid system. The grid-connected system transmits the electric energy generated by the photovoltaic system to the national grid in parallel. The grid-connected system is mainly composed of photovoltaic modules, inverters, power distribution box and other accessories. The off-grid system operates independently and does not need to rely on the public power grid. The off-grid system needs to be equipped with a battery with energy storage and a solar controller, which can ensure the stability of the system power and can be used when the photovoltaic system does not generate electricity or is insufficient in continuous cloudy days. power down the load.

Photovoltaic modules

Photovoltaic modules are the core part of the entire power generation system. They are composed of photovoltaic module sheets or photovoltaic modules of different specifications cut by laser cutting machines or wire cutting machines. Since the current and voltage of a single photovoltaic cell are very small, high voltage should be obtained in series first, then high current should be obtained in parallel, output through a diode, and then packaged on a stainless steel, aluminum or other non-metal frame, and installed on it The glass and the back panel on the back, filled with nitrogen, and sealed. The photovoltaic modules are combined in series and parallel to form a square array of photovoltaic modules, also called a photovoltaic array.

controller

The photovoltaic controller is an automatic control device that can automatically prevent the overcharge and overdischarge of the battery. It adopts a high-speed CPU microprocessor and a high-precision A/D analog-to-digital converter. It is a microcomputer data acquisition and monitoring control system. The current working state of the photovoltaic system, the working information of the PV station can be obtained at any time, and the historical data of the PV station can be accumulated in detail, which provides an accurate and sufficient basis for evaluating the rationality of the PV system design and inspecting the reliability of the quality of the system components. It has the function of serial communication data transmission, and can perform centralized management and remote control of multiple photovoltaic system sub-stations.

Inverter

The inverter is a device that converts the direct current generated by photovoltaic power generation into alternating current. The photovoltaic inverter is one of the important system balances in the photovoltaic array system and can be used with general AC power supply equipment. Solar inverters have special features for photovoltaic arrays, such as maximum power point tracking and islanding protection.

Solar inverters can be divided into the following three categories:

1. Independent inverter: used in independent systems, the photovoltaic array charges the battery, and the inverter uses the DC voltage of the battery as the energy source. Many independent inverters also integrate battery chargers, which can charge the battery with AC power , generally this inverter will not touch the grid, so it does not need islanding protection function.

2. Grid-connected inverter: The output voltage of the inverter can be returned to the commercial AC power supply, so the output sine wave needs to be the same as the phase, frequency and voltage of the power supply. The grid-connected inverter has a safety design, and if it is not connected to the power supply, the output will be automatically turned off. If the grid power fails, the grid-connected inverter does not have the function of backing up the power supply.

3. Backup battery inverter: a special inverter, which uses the battery as its power source, and cooperates with the battery charger to charge the battery. If there is too much power, it will be recharged to the AC power supply. This kind of inverter can provide AC power to the specified load when the grid power fails, so it needs to have the islanding effect protection function.

battery

Batteries are equipment for storing electricity in photovoltaic power generation systems. At present, there are four types of lead-acid maintenance-free batteries, ordinary lead-acid batteries, gel batteries and alkaline nickel-cadmium batteries. The widely used lead-acid maintenance-free batteries and gel batteries are widely used.

Working principle: During the daytime, sunlight shines on the photovoltaic modules to generate DC voltage, convert the light energy into electrical energy, and then transmit it to the controller. After the overcharge protection of the controller, the electrical energy from the photovoltaic modules is transported to the battery for storage. , for use when needed.