The performance parameters of silicon cells mainly include: short-circuit current, open-circuit voltage, peak current, peak voltage, peak power, fill factor, conversion efficiency, etc.
①Short-circuit current (Isc): When the positive and negative electrodes of the battery are short-circuited and U=0, the current at this time is the short-circuit current of the battery, and the unit of the short-circuit current is A (ampere). The short-circuit current changes with the change of light intensity.
②Open circuit voltage (Uoc): When the positive and negative poles of the battery are not connected to the load, and I=0, the voltage between the positive and negative poles of the solar cell is the open circuit voltage, and the unit of the open circuit voltage is V (volt). The open circuit voltage of a monolithic solar cell does not change with the increase or decrease of the cell area, generally 0.6~0.7V. When multiple cells are connected in series, a higher voltage can be obtained.
③Peak 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 is outputting the maximum power, and the unit of the peak current is A.
④Peak 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 solar cell outputs the maximum power. The unit of the peak voltage is V. The peak voltage does not change with the increase or decrease of the cell area, generally 0.5~0.55V.
⑤Peak 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 under normal working or test conditions, that is, the product of the peak current and the peak voltage: Pm=Im×Um. The unit of peak power is Wp (peak watts). The peak power of the solar cell depends on the solar irradiance, the solar spectral distribution and the operating temperature of the cell, so the measurement of the solar cell should be carried out under standard conditions. The measurement standard is European Commission No. 101 Standard, and its conditions are irradiance 1KW/m2, spectrum AM1.5, and test temperature 25°C.
⑥Filling factor (FF): The filling factor is also called the curve factor, which refers to the ratio of the rectangular area of the shaded part (lm×Um) to the rectangular area of the dashed part (Isc×Uoc) in Figure 1. That is, the ratio of the peak output power of the cell to the product of the open-circuit voltage and the short-circuit current: FF=Pm/Isc×Uoc. The fill factor is a unitless quantity and is an important parameter for evaluating and measuring the output characteristics of the battery. The higher its value, the more rectangular the output characteristics of the solar cell, and the higher the photoelectric conversion efficiency of the solar cell.
The series and parallel resistances inside the solar cell have a greater impact on the fill factor. The smaller the series resistance of the solar cell, the greater the parallel resistance, and the greater the fill factor coefficient. The coefficient of the fill factor is generally 0.7 to 0.85, and it can also be expressed as a percentage.
⑦Conversion efficiency (μ): The conversion efficiency of the cell is used to indicate the amount of light energy irradiated on the surface of the cell that is converted into electrical energy. It is generally expressed by the ratio of output energy to incident energy. It refers to the ratio of the maximum output power of the battery when exposed to light to the solar energy irradiated on the battery. which is:
μ=Pm (peak power of cell)/A (area of cell)×Pin (incident light power per unit area), where Pin=1000W/m2-=100mW/cm2.
Please refer to the previous article for the characteristics of silicon cells and the knowledge of the equivalent circuit of silicon cells in the manufacture of battery modules.