The performance of the photovoltaic module is mainly the output characteristic of the module, which is called the I-U characteristic, that is, the current-voltage characteristic. It is an important parameter to test the performance of the module and an important indicator to measure the conversion efficiency of light energy into electric energy. Its characteristics are shown in Figure 1. The graph reflects the output voltage and output current of the photovoltaic module when the module is exposed to sunlight. And the relationship between output power.
Several important performance parameters of photovoltaic modules:
1) Short-circuit current (Isc): When the positive and negative electrodes of the solar cell module are short-circuited to make U=0V, the current at this time is the short-circuit current of the solar cell module. The unit of the short-circuit current is A, and the short-circuit current increases with the light intensity. The change changes.
2) Open circuit voltage (Uoc): When the positive and negative poles of the battery module are not connected to the load, the electric limit between the positive and negative poles of the module is the open circuit voltage, and the unit of the open circuit voltage is V.
3) Peak current (Im): The peak current is also called the maximum working current or the best working current. The peak current refers to the working current when the solar cell module outputs the maximum power, and the unit of the peak current is A.
4) Peak voltage (Um): The peak voltage is also called the maximum working voltage or the best working voltage. The peak voltage refers to the working voltage when the maximum power of the battery module is output. The unit of the peak voltage is V. The peak voltage of the module changes with the increase or decrease of the number of cells. The peak voltage of the module with 36 cells in series is 17~ 17.5V.
5) Peak power (Pm): Peak power is also called maximum output power or optimal output power. The peak power refers to the maximum output power of the solar cell module under normal working or test conditions, that is, the multiplication of the peak current and the peak voltage Pm=ImUm. The unit of peak power is W.
The peak power of the solar cell module depends on the solar irradiance, the solar spectral distribution and the working temperature of the module. Therefore, the measurement of the solar cell module should be carried out under standard conditions. The measurement standard is the European Commission’s No. 101 Standard, and its conditions: Irradiation The temperature is 1000w/㎡, the air quality is AM1.5, and the test temperature is 25℃.
6) Fill factor (FF): The fill factor is also called the curve factor, which refers to the ratio of the maximum power of the solar cell module to the product of the open circuit voltage and short circuit current. The fill factor is
FF=Pm/UocIsc
The fill factor is an important parameter for evaluating the output characteristics of the solar cell modules. The higher the value, the more rectangular the output characteristics of the solar cell modules and the higher the photoelectric conversion efficiency of the solar cell modules. The value of the fill factor FF of the solar cell module is always less than 1, generally between 0.5 and 0.8.
FF can be given by empirical formula
FF=[Uoc﹣ln(Uoc＋0.72V)/Uoc＋1V]
7) Conversion efficiency (η): Conversion efficiency refers to the ratio of the maximum output power of the solar cell module when exposed to light to the solar radiation power incident on the component. which is
η=Pm/Pin=FF·(UocIsc/Pin)
In the formula, Pin is the incident power of the sun (kW). For solar cells used on the ground, the solar radiation power is 1000W/㎡ (sea level), and for space batteries, the solar radiation power is 1367W/㎡.