Electrical Design & Analysis of Large Photovoltaic Power Stations

Electrical Design & Analysis of Large Photovoltaic Power Stations


Abstract: In order to realize the good electrical design of large photovoltaic power plants, three aspects were selected for specific analysis from the main equipment of the electrical system of the photovoltaic power station, namely photovoltaic modules, inverters and combiner boxes. The configuration of the photovoltaic system and the electrical design of the photovoltaic power station were described. Easy operation, flexible operation and reliable power supply should be fully considered. It is necessary to continuously improve the design level of domestic photovoltaic power plants, give full play to the power generation performance of solar photovoltaic cells, and fundamentally solve the problem of energy consumption.
 
Solar resource
Solar energy is the most abundant permanent energy in the world. Today, with the increasingly prominent problem for energy, solar photovoltaic power generation has attracted extensive attention as new renewable energy. The solar photovoltaic power generation system is composed of storage batteries, photovoltaic cells, AC and DC inverters, controllers and other components. The battery is used to store the electricity converted from the photovoltaic cells; the photovoltaic cells are used for photoelectric conversion, and the AC DC inverter is used for AC/DC conversion to maximize the power converted by the photovoltaic cells to the grid. The controller is used to control the whole process of the whole system. Compared with biomass power generation and wind power generation, photovoltaic power generation has no noise, no depletion, and is safe, reliable, and absolutely clean. China is relatively rich in solar energy resources, and has the advantages of using solar energy for photovoltaic power generation. According to the amount of solar radiation received, there are five areas with solar resources, including the area with the most abundant solar energy resources, the area with abundant solar energy resources, the area with average solar energy resources, the area with few solar energy resources and the area with the least abundant solar energy resources.
 
Main equipment
The electrical system of photovoltaic power stations mainly includes high-voltage power distribution devices, communication devices, on-site step-up transformers, reactive compensation devices, relay protection devices, station power devices, main transformers, inverters, low-voltage power distribution devices, combiner boxes and collector circuits. PV modules, inverters and combiner boxes were specifically analyzed.
 
Photovoltaic modules: they have become an important basic raw material for the photovoltaic industry due to the low cost of silicon. Solar photovoltaic silicon materials are usually divided into the following three types: polycrystalline silicon, monocrystalline silicon, and amorphous silicon thin films. Polycrystalline silicon and monocrystalline silicon are widely used in the photovoltaic industry, and amorphous silicon thin films are almost in a stagnant state. However, these three types of silicon materials will be the main source of raw materials for the photovoltaic industry in the future, as shown in Table 1.
 
Table 2 Technical performance of polycrystalline silicon, monocrystalline silicon, and amorphous silicon thin films
Items Projects Poly silicon Monocrystalline silicon Amorphous silicon films
1 Maturity Ingot crystalline silicon technology is commonly used at present. Technology has reached a mature stage. Polysilicon and monocrystalline silicon technologies are relatively mature and have stable performance.
2 Conversion efficiency 12% to 16% for commercial battery 13% to 18% for commercial battery Monocrystalline silicon has the highest efficiency, polycrystalline silicon the second highest, and amorphous silicon film the lowest.
3 Price It has a lower production cost than monocrystalline silicon. Its price remains high. Its price is lower than monocrystalline silicon. 
4 Environmental adaptability Insufficient efficiency under high temperatures  The same as poly silicon  Good low light response and high battery output power efficiency
 
Inverters: As a new type of converter, it is the core equipment of solar photovoltaic grid-connected power generation systems. The efficiency of the inverter is directly related to the power generation of the system. Photovoltaic inverters can be divided into two categories: photovoltaic grid-connected inverters and independent photovoltaic inverters. Photovoltaic inverters can be divided into three categories: micro inverters, string inverters and centralized inverters according to the system's connection method. Photovoltaic inverters can be divided into three categories: microgrid energy storage inverters, off-grid inverters and grid-connected inverters.
 
Combiner box: As a wiring device, it can not only ensure the orderly connection of photovoltaic modules, but also ensure the wiring of the bus function. The square array connection box includes overvoltage protection, lightning strike protection, multi-channel solar square array parallel and overload protection of solar cells. When designing and selecting models, it is necessary to focus on factors such as temperature rise, display functions, safety, communication, surge, PV string overcurrent protection, box structure, lightning protection, and enclosure protection levels.
 
PV system configuration: the following factors such as string, optimal inclination angles, module performance, influencing factors, installation of photovoltaic modules, and calculation of the spacing between the front and rear rows must be fully considered to make the design of the photovoltaic system more scientific and reasonable.
 
The electrical design of the photovoltaic power station
The electrical design of the photovoltaic power station mainly includes the ground booster transformer, the power generation unit of the photovoltaic power station, the connection mode of the collector line of the photovoltaic power station and the main connection mode of the booster station. Reasonable selection of the main wiring scheme can effectively improve the safety, economy and stability of operation of power stations. The voltage level of collecting lines and the grouping connection method of power generation units should be scientifically selected when designing the collecting lines of photovoltaic power plants due to the high cost of collecting lines in photovoltaic power plants. 10kV and 35kV are generally selected. The grouping connection methods of power generation units generally include chains, rings, and stars. From the perspective of electricity costs, the investment of photovoltaic investment is not much, which hinders the further development of photovoltaic power generation to a certain extent. The cost should be reasonably controlled when the system is designed to improve the market competitiveness of photovoltaic power generation. The number of incoming and outgoing line loops and their wiring methods will vary with the system conditions connected to each side. When choosing the main electrical wiring, simple operation, flexible operation, and reliable power supply should be fully considered. Photovoltaic inverters and photovoltaic modules are the key equipment in the electrical design of photovoltaic power plants, and it is necessary to carefully calculate and analyze the main wiring scheme of photovoltaic power plants.