The design of the solar photovoltaic power generation system is divided into the software design of the solar photovoltaic power generation system and the hardware design of the solar photovoltaic power generation system. The software design precedes the hardware design. The software design of the solar photovoltaic power generation system includes: the calculation of the load power consumption, the calculation of the radiation amount of the solar cell array, the calculation of the solar cell and battery consumption and the optimal design of the mutual matching between the two, the installation of the solar cell array inclination angle. Calculation, prediction of system operation and analysis of system economic benefits, etc. The hardware design of solar photovoltaic power generation system includes: load selection and necessary design, solar cell and battery selection, solar cell support design, inverter selection and design, and control and measurement system selection and design . For large-scale solar photovoltaic power generation systems, there are also the design of the photovoltaic cell square field, the design of the lightning protection grounding spoon, the design of the power distribution system, and the selection and design of auxiliary or backup power sources. Since the software design involves complex solar radiation, installation inclination and system optimization design calculations, it is generally done by a computer. Estimates can also be used under less stringent requirements.
The general principle of solar cell power generation system design is: on the premise of ensuring that the load power supply needs are met, determine the use of the least solar cell module power and battery capacity to minimize the initial investment. Solar photovoltaic power system designers should be aware that every decision made during the photovoltaic power generation system design process will affect the cost of construction. Due to inappropriate selection, the investment of solar photovoltaic power generation system can easily be multiplied, and it may not necessarily meet the requirements of use. After deciding to build an independent solar photovoltaic power generation system, the design can be carried out according to the following steps: calculate the load, determine the capacity of the battery, determine the number of solar cells, select the controller and inverter, consider the problem of hybrid power generation, etc.
In the design calculation, the basic data required are: the geographic location of the site, including location, latitude, longitude and altitude, etc.; the meteorological data of the installation site, including the monthly direct radiation and scattered radiation of total solar radiation, the annual average Temperature, maximum and minimum temperature, longest continuous rainy days, maximum wind speed, hail, snowfall and other special meteorological conditions. Meteorological data generally cannot make long-term predictions, and can only be based on the average value of the past 10 to 20 years. However, few independent solar photovoltaic power generation systems are built in cities with complete solar radiation data, and the solar radiation in remote areas. The data may not resemble nearby cities. Therefore, we can only use the meteorological data of a nearby city or the data recorded by meteorological observation stations in similar regions to make analogies. In the analogy, it is necessary to grasp the possible deviation factors. It should be known that the estimation of solar energy resources will directly affect the performance and cost of the solar photovoltaic power generation system.
1. Load calculation of solar photovoltaic power generation system
Estimating the load of a solar photovoltaic power generation system is one of the key factors in the design and pricing of an independent photovoltaic power generation system. The name, power requirements, rated operating voltage, and daily power usage time of all loads must generally be listed. The same is listed for both AC and DC loads, the power factor is not considered in the AC power calculation. Then, the loads are classified and grouped by operating voltage to calculate the total power requirement for each group. Next, select the system operating voltage and calculate the average ampere hour (A h) required by the entire solar photovoltaic power generation system at this voltage, that is, calculate the sum of the average daily power consumption of all loads. Regarding the selection of the system voltage, the voltage required by the maximum power load is often selected. In systems with AC loads as the mainstay, the DC system voltage should be considered compatible with the selected inverter input voltage. Usually, for an independent solar photovoltaic power generation system, the AC load works at 220V, and the DC load works at a multiple of 12V, that is, 12V, 24V or 48V, etc. In theory, the determination of the load is straightforward, but in practice the requirements of the load are often uncertain. For example, the power required by household appliances can be known from the manufacturer's data, but their working hours are not known. The daily, weekly and monthly usage time is likely to be overestimated, and the cumulative effect will be This leads to an increase in the design, capacity and cost of solar photovoltaic power generation systems. In fact, some of the higher power loads can be scheduled to be used at different times. In the strict design, we must master the load characteristics of the independent solar photovoltaic power generation system, that is, the load power at different times in 24 hours a day, especially for the centralized power supply system, after understanding the electricity consumption law, it can be controlled in a timely manner.
2. Determination of battery capacity of solar photovoltaic power generation system
The determination of the optimal value of the battery capacity in the solar photovoltaic power generation system must comprehensively consider the power of the solar cell array, the load capacity and the efficiency of the inverter. There are many ways to calculate battery capacity.
When purchasing solar cell modules, if they are used to form a square array in series or parallel in a certain way, the designer or user should propose to the manufacturer that the I-U characteristic curves of all modules must have good consistency to avoid the combination of square arrays. Efficiency is too low. Generally, the combined efficiency of photovoltaic modules should be required to be greater than 95%.
Designers and users should also have a basic understanding of the azimuth and inclination of the square matrix. In my country, which is located in the northern hemisphere, the orientation of the square array should be set in the south direction. However, as long as it is within ±20° of due south, the output power of the phalanx will not decrease much. If for some reason, the phalanx is not set due to the south, it should be within 2° of the southwest as possible, which means that the output peak of the phalanx will be sometime after noon, which can be beneficial for winter use. When the square matrix is set in a non-south direction, its power output decreases roughly according to the cosine function. Regarding the inclination angle of the square matrix, for small solar photovoltaic power generation systems, it is generally set according to an integer multiple of the local latitude. If the demand for increasing power generation in winter is to be considered, the inclination angle of the phalanx can be appropriately larger than the local latitude, generally ф=5°~15°。
Read more: Classification of solar photovoltaic power generation system