The power of a solar cell module is proportional to the area of the solar cell, but the area of the solar cell is not exactly equal to the area of the solar cell package panel. Although some solar cell panels are large, the gaps in which the solar cells are arranged are very wide, so the power of such solar panels is not necessarily high. The output power Wp of the solar cell is under standard sunlight conditions, that is, the 101 standard defined by the European Commission, the radiation intensity is 1000W/m2, the air quality is AM1.5, and the solar cell is at a temperature of 25 ℃. This condition is about the same as that of the sun around noon on a sunny day (only close to this value in the lower reaches of the Yangtze River). This is not as some people think, as long as there is sunlight, solar cells will have rated output power, and even think that solar cells can be used normally under fluorescent lights at night. That is to say, the output power of the solar cell is random, and the output power of the same solar cell is different at different times and at different places. Calculated by area, the output power of a solar cell per square meter is about 120W, and as the conversion efficiency increases, the output power also increases accordingly. The selection of the output power of the solar cell module should be determined according to the light source power of the solar LED lighting system, the use time and the local climatic and geographical conditions.
The maximum power of the solar cell Pmax = open-circuit voltage × short-circuit current, which is its ideal power, and the rated power Pm of the solar cell is usually measured. In practical applications, the rated power is less than the maximum power, mainly because the output efficiency of solar cells is only about 70%. In use, due to the different light intensity, the power at different times is also different. According to the experimental data, the actual average power of the solar cell is P=0.7Pm. If the solar cell is to directly drive the load and make the load work stably for a long time, the rated power of the load is Pr=0.7Pm. If the power of the solar cell is selected according to the power of the load, the power of the solar cell is: Pm=1.43Pr. That is to say, the power of the solar cell is 1.43 times of the load power.
When selecting the power of the solar cell, the power consumption of the load should be reasonably selected, so as to make the generated power and the power consumption in a state of balance. However, the power generation of solar cells is also restricted by many factors such as season, climate, geographical environment and illumination time.
The economic power of the solar photovoltaic system should be below 2000Wp, and the power of the solar photovoltaic system is generally suitable for several hundred watts, especially for lighting loads, the most suitable lamps are no more than a few hundred watts. In ordinary areas of China, a watt-hour solar cell can generate nearly one kilowatt-hour of electricity a year, which is an average of 2-3Wh a day. These two values explain the characteristics of solar photovoltaic power generation. The maximum output power is used as the measurement unit of solar cells, and the annual power generation is used as the accounting basis for solar cell applications. Some misconceptions often appear in the power design scheme of solar photovoltaic systems. One is to mistake the peak watts as the installed capacity in the conventional power generation system, which leads to a serious overload of the system and an overestimation of the power generation capacity of the system several times; the other is to simply use the solar photovoltaic power supply as the mains power supply. In fact, due to the randomness of the output power of solar photovoltaic power, the applied power of solar photovoltaic power can only be designed according to statistical parameters. In addition, the attenuation of solar cell components, the reduction of battery capacity and the influence of related factors such as load changes should also be considered.
The relationship between the rated output power of the solar cell module and the input power of the lamp is about 2:1~4:1 in East China, and the specific ratio depends on the daily working time of the lamp and the lighting requirements for continuous rainy days. In addition, the output power of the solar cell is about 120W/m2. In the eastern and western regions with sufficient sunlight, it is better to use polycrystalline silicon solar cells, because the production process of polycrystalline silicon solar cells is relatively simple, and the price is lower than that of monocrystalline silicon solar cells. In the southern region where there are many rainy days and relatively insufficient sunshine, it is better to use monocrystalline silicon solar cells, because the performance parameters of monocrystalline silicon cells are relatively stable.