Classification and Application of Photovoltaic Power Generation System
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Photovoltaic power generation systems are power generation systems that convert solar energy into electrical energy, using photovoltaic effects. The photovoltaic power generation system is divided into an independent solar photovoltaic power generation system and a grid-connected solar photovoltaic power generation system.
Independent solar photovoltaic power generation refers to a power generation method in which solar photovoltaic power generation is not connected to a power grid. A typical characteristic is that a battery is required to store energy used at night. Independent solar photovoltaic power generation is mainly used in remote rural areas such as home systems and village-level solar photovoltaic power stations in the civilian area; it is mainly used in telecommunications, satellite broadcasting and television, and solar water pumps in industrial areas, in areas with wind power and small hydropower. It can also form hybrid power systems, such as wind power/solar power generation complementary systems.
Grid-connected solar photovoltaic power generation refers to the way that solar photovoltaic power generation is connected to the national power grid for power generation. It is a supplement to the power grid and typically requires no batteries. Civil solar photovoltaic power generation is mostly home-based, and its commercial use is mainly for power supply of enterprises, government buildings, public facilities, security facilities, night landscape lighting systems, and industrial uses such as solar farms.
Photovoltaic power generation systems can be divided into two categories, namely space applications and ground applications, depending on the location of their use.
It can be used as an independent power source on the ground, or it can be combined with a wind turbine generator or a diesel engine to form a hybrid power generation system. It can also be connected to a power grid to deliver power to the grid. Currently widely used photovoltaic power generation system is mainly used as an independent ground power supply. The general stand-alone photovoltaic power generation system is mainly composed of a solar cell array, a battery, a controller, and a blocking diode, and its functions are as follows:
1. Photovoltaic cell phalanx: The role of the phalanx is to convert solar radiant energy directly into electrical energy for use by the load. Generally, a number of solar cell modules are connected in a certain manner, and then are equipped with appropriate brackets and junction boxes.
2. Battery pack: A battery pack is an energy storage device of a solar cell array, and its role is to store the excess electric energy that the array emits during the sunshine, and to use it for the load in the evening or on rainy days. In the photovoltaic power generation system, the battery is in floating charge and discharging state, and the amount of sunshine in the summer is large. In addition to supplying electricity to the load, the battery is also charged. In winter, the amount of stored energy is gradually released, and this part of the stored energy is gradually released. On the basis of this, we must add a much smaller daily cycle. During the day, the square array charges the battery, (while the square array also supplies electricity to the load). At night, all the load power is supplied by the battery. Therefore, the self-discharge of the battery is required to be small, and the charging efficiency is high, and at the same time, it is also necessary to consider factors such as price and ease of use. Commonly used batteries include lead-acid batteries and silicone batteries, and nickel-cadmium batteries, which are relatively expensive, are also required for higher applications.
3. Controller: In different types of photovoltaic power generation systems, the controllers are different, and their functions and complexity are very different. They need to be determined according to the requirements and degree of importance of the power generation system. The controller consists of electronic components, meters, relays, switches, etc. In a simple solar battery and battery system, the role of the controller is to protect the battery and avoid overcharging and overdischarging. If the photovoltaic power station is connected to the grid, the controller needs to have various functions such as automatic monitoring, control, regulation, and conversion. If the load uses alternating current, inverters should also be provided between the load and the battery. The role of the inverter is to reverse the low voltage DC power provided by the square array and the battery to 220 volts AC, which is used by the load.
4. Blocking diodes: Also known as back-charged diodes or isolation diodes, its role is to use the unidirectional conductivity of the diode to prevent the battery from discharging through the solar cell squares when there is no sunlight. The requirement for a blocking diode is that the operating current must be greater than the maximum output current of the square array and the reverse withstand voltage is higher than the battery pack voltage. When working in the square array, there is a certain voltage drop across the blocking diode, typically 0.6V to 0.8V for silicon diodes; and about 0.3V for Schottky or germanium diodes.
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