# Variation Law of Photovoltaic Characteristics

Variation Law of Photovoltaic Characteristics
The process and main results of the numerical simulation of the change law of photovoltaic characteristics are as follows:
(1) Mathematical model establishment and numerical simulation.
According to the aforementioned equivalent circuit and U-I relational formula, a mathematical model can be established as shown in Figure 1. Using this model to simulate the photovoltaic characteristics of 300W solar panels, the results are shown in Figure 2.

(2) The influence of light intensity and ambient temperature on U-I and P-U
It can be seen from Figure 2(a) that when T, n, and i are all standard values ​​and G=1000W/m², the peak power of the photovoltaic cell used is 300W, the peak current is about 8.3A, and the voltage when the peak power is reached It is 36V, which is very close to the technical parameters provided by the manufacturer, which verifies the accuracy of the constructed test model. At the same time, both the output power and working current decrease with the decrease of light intensity (G), but the open-circuit voltage and short-circuit current remain unchanged. It can be seen from Figure 2(b) that within the nominal operating condition of 30V/10A, the temperature effect is minimal. As T increases, the short-circuit current does not change, and the open circuit voltage, operating voltage, operating current and output power decrease very little. . It can be seen that the influence of light intensity on the output characteristics of photovoltaic cells is much greater than that of ambient temperature.

(3) The influence of diode factor and series resistance on P-U among material factors.
In the test, the material structure parameters that affect the performance of photovoltaic cells are called material influencing factors, which mainly include diode factor A and equivalent series resistance. The simulation results are shown in Figure 3 (a) and (b). From the figure, it can be seen that changing the equivalent series resistance has a significant effect on the output power, while A has little effect on the output power.

(4) The influence of different incident angle and refractive index on U-I and P-U.
The influence of different incident angles and refractive indices on U-I and P-U is shown in Figure 4. It can be seen from the figure that the change of the incident angle has a great influence on the power and working current, while the influence of the refractive index is much smaller; and the incident angle and the refractive index have little influence on the working voltage.

(5) Timely tracking module.
Taking the horizontal fixed installation of solar panels as an example, the actual light angle will continuously shift with time. The light intensity G, incident angle i, and temperature T are constantly changing at time t. Therefore, only in a specific environment, the surface of the photovoltaic cell The model of actual equivalent light intensity Gt can simulate its output state more accurately, and quickly assess the potential of photovoltaic power generation in the area. Take Chengdu City, Sichuan Province as an example, set G=1000W/m², t=12, and the changes in photovoltaic cell output power P from 8 am to 16:00 pm with time t and load voltage U measured by the real-time tracking model are shown in Figure 5. Show. It can be seen from the figure that due to the simultaneous changes of light intensity and incident angle, the photoelectric conversion of horizontally fixed photovoltaic cells is basically concentrated at 10 to 14 o’clock, and the output power is closely related to the load voltage. When the load voltage is 35V, the output power is roughly equal to 300W, and the maximum current Imax35v=8.62A, which is very close to the reference peak voltage of 36V and the peak current of 8.33A provided by the manufacturer, and the deviation is less than 0.05. This set of data further verifies the performance of our test model. Accuracy. If the load voltage deviates from the peak voltage, regardless of whether the load voltage is increased or decreased, the output power of the photovoltaic cell will decrease. When the load voltage is higher than the peak voltage, the output power drops significantly. When the load voltage is 42V, the output power is only the peak value. 1/4 of the power, and when the load voltage is 43.5V, the output power approaches 0, which is consistent with the standard open circuit voltage. This result shows that when the load voltage is equal to the rated voltage of the photovoltaic cell square array, the photovoltaic cell square array has the highest working efficiency. The amount of power generation can also be determined based on the change in the measured voltage. In order to obtain the ideal power generation efficiency, it is best to adjust the angle of the photovoltaic cells to the sun in a timely manner. This also provides theoretical support and technical parameters for our development of solar panels and solar devices.

(6) Calculation of power generation.
According to the results of the timely tracking test in Figure 5, integration can be used to estimate the total daily average power generation of the panel under different load voltages. The formula is as follows
W single block=∫240Po(W)dt≈0.8kW·h
If a total of 34 battery panels of the same type are installed on a construction vehicle, the average daily power generation capacity is about 27.2kW·h.