1. Composition of photovoltaic power generation system
Solar power generation system is a power generation system that utilizes a solar cell array to directly convert solar radiation into electrical energy. It consists of solar cell arrays, controllers, DC/AC inverters, photovoltaic power generation system ancillary facilities (DC distribution system, AC distribution system, operation monitoring and monitoring system, lightning protection and grounding system), and other components.
(1) Types of silicon solar cells
There are currently three types of commercialized silicon solar cells in the world: monocrystalline silicon solar cells, polycrystalline silicon solar cells, and amorphous silicon solar cells. The photoelectric conversion efficiency of monocrystalline silicon solar cells is relatively high, ranging from 13% to 15%, but its usage cost is relatively expensive; The photoelectric conversion efficiency of polycrystalline silicon solar cells is 11% -13%, which is currently widely used; Amorphous silicon solar cells belong to thin film batteries with low cost, but their photoelectric conversion efficiency is relatively low and their stability is not as good as crystalline silicon solar cells. Currently, they are mostly used for low light power sources, such as watches and calculators.
(2) Solar cell module
A solar cell can only generate approximately 0.5V voltage, which is much lower than the voltage required for practical applications. In order to meet the needs of practical applications, solar cells need to be connected into components. The standard number of solar cells on a component is generally 36 pieces. The physical unit sealed by a solar cell connected by wires is called a photovoltaic cell module, which has certain anti-corrosion, windproof, and rainproof capabilities. The front of this module is a glass plate, and the back is a layer of alloy sheet. The solar cell is also embedded in a layer of polymer. In this type of solar module, the battery can be directly connected to the junction box with wires, and the potential quality issues are the sealing of the edges and the junction box on the back of the module.
The output power of solar cell modules depends on solar irradiance, the distribution of solar spectrum, and the temperature of the solar cell. If the solar cell module is obstructed by other objects (such as bird droppings, tree shade, etc.) for a long time, the obstructed solar cell module will seriously heat up, which is called the “hot spot effect”. In order to prevent the battery module from being damaged due to the hot spot effect, it is necessary to parallel bypass diodes between the positive and negative poles of the battery module to avoid the energy generated by the illuminated module being consumed by the shielded module.
(3) DC/AC inverter
Inverters are devices that convert direct current into alternating current. Due to the fact that solar cells emit direct current, and ultimately the photovoltaic power generation system needs to be connected to an AC load, inverters are indispensable equipment. Inverters can be divided into independent operating inverters and grid connected inverters according to their operation mode. Independent operating inverters are used for solar power generation systems that operate independently, supplying power to independent loads. Grid connected inverters are used in photovoltaic power generation systems for grid connected operation, feeding the generated electricity into the grid for operation. The grid connected inverter converts the direct current generated by the photovoltaic array into alternating current energy in the same phase as the power grid. When the power grid fails, the inverter should stop working and disconnect the inverter load to prevent “islanding effect”.
(4) Photovoltaic box transformer
Before the photovoltaic power generation system is connected to the grid, a suitable step-up transformer is selected based on the voltage of the grid connected main line, and the 400V AC output from the inverter is boosted to the voltage level of 10kV, 35kV, or 110kV required for grid connection, meeting the conditions for grid connection.
2. Application of grid connected photovoltaic power generation system
(1) Reverse current grid connected photovoltaic power generation system
When the electricity generated by solar photovoltaic systems is abundant, they transmit electricity to the grid, commonly known as “selling electricity”; When the electricity generated by the solar photovoltaic system is insufficient, it absorbs electricity from the power grid, commonly known as “buying electricity”.
(2) Non countercurrent grid connected photovoltaic power generation system
When the solar photovoltaic power generation system has sufficient power generation, it does not supply power to the public grid, but when the solar photovoltaic system has insufficient power supply, the public grid supplies power to the load.
(3) Grid connected photovoltaic power generation system with energy storage devices
In solar photovoltaic power generation systems, there are controllers and batteries, which can store a portion of the direct current output from photovoltaic modules, improving power supply reliability; The controller is designed to limit battery over discharge, over charge, load over current, and reverse charge, and has the functions of managing battery charge and discharging and optimizing charging control.
3. Conclusion
China is very rich in solar energy resources, and the application space of the solar power generation industry is also very broad. In the northwest region, which is rich in lighting resources, if the Gobi Desert is used to install grid connected solar power generation systems, it can provide a very considerable amount of power generation. In some remote areas or islands, without the installation of a national power grid, independent photovoltaic power generation systems can be installed without the need for transmission lines, with short cycles and low overall costs, which can effectively solve the problem of difficult electricity consumption in remote areas. Due to China’s large energy consumption and uneven population distribution, the development of solar photovoltaic power generation systems is of great significance for China’s sustainable development, maintaining the independence and security of energy supply, and electricity consumption by residents in densely populated areas.