olar cells are spectral selective devices, and their photoelectric response characteristics change with the change of spectral distribution. The spectral distribution of natural sunlight is different all over the world, and the total irradiance of natural sunlight has been changing and cannot be adjusted, which will affect the repeatability of test results. In order to make the test results of ground solar cells (modules) comparable and reflect the performance of solar cells (modules) in normal outdoor use, international organizations have formulated standard test conditions for ground photovoltaic devices (STC): solar radiation intensity 1000w/m2, ambient temperature 25 ℃, air quality am1.5g.
At present, the classification standards of solar simulators for Photovoltaic Testing mainly include iec60904 and astme927-
10 and jisc8912. According to the international standard iec60904-9, the spectral matching level of the solar simulator is mainly determined by three parameters: spectral matching, spectral spatial heterogeneity and irradiation instability (these three parameters are divided into short-term performance and long-term performance). According to the accuracy of these three parameters, the simulator is divided into three levels: A, B and C.
- Spectral matching
In view of the corresponding characteristics of the solar cell spectrum known at present, the current iec60904-3 standard recommends using six bands to match the spectrum of simulated sunlight. If the standard deviation of the ratio of the irradiation value of each band to the total irradiation of the corresponding band of am1.5g is within ± 25%, it can be evaluated that it has reached the class a standard. At present, most equipment manufacturers can achieve a+ level, and a few manufacturers can achieve a range fluctuation of ± 5% by using the steady-state simulator, but the manufacturing cost has also increased sharply, which is not suitable for mass production.
The irradiance distribution specified in astme927-10 and jisc8912 standards is consistent with iec60904-9.
Astme927-10 also stipulates the spectral distribution of am1.5d and amo for ground concentrating photovoltaic devices.
In addition, due to the expansion of the response range of the high-efficiency battery and components to the solar spectrum in the infrared and ultraviolet bands, the current spectral evaluation range of the simulator can no longer cover the spectral response range of the high-efficiency battery. IEC extended the evaluation range of the simulator to 300~1200nm in the revised standard iec60904-4.
- Irradiation uniformity
The irradiation uniformity in the designated test area of the test plane is an important index of the solar simulator, which is expressed by the irradiation nonuniformity. In the optical system of the solar simulator, the purpose of designing the homogenizing system and the collimating system is to improve the irradiation uniformity of the light, but the absolute uniformity is difficult to achieve. According to iec60904-9 standard, the whole test plane is divided into no less than 64 areas for testing, and the test area of each area is no more than 400mm2. The calculation method of irradiation nonuniformity is as follows:
Where u – irradiation nonuniformity,%;
Gmax – the maximum value of irradiance in the test area;
Gmin – the minimum value of irradiance in the test area.
For example, the test irradiation area is 2000mm × For 1200mm simulator, a single 125mm or 156mm battery is generally used for calibration test. Taking 156mm battery as an example, the whole test area is divided into 2000/156=12.8 areas along the length direction, rounded up to 13, and 1200/156=7.69 areas along the width direction, rounded up to 8, a total of 13 × 8 = 104 areas. By testing the irradiance of these 104 areas, the irradiance nonuniformity is finally calculated.
- Irradiation stability
The irradiance should have a certain stability during the whole data acquisition period. The relationship between the irradiance of a point on the test plane over a period of time is defined as the irradiance instability, and the calculation method is:
Where δ—— Irradiation instability,%;
Gmax – the maximum value of irradiance in the whole test process;
Gmin – the minimum value of irradiance during the whole test process.
Irradiation instability is divided into long-term instability and short-term instability.
The grade judgment principle of the solar simulator is to locate the final grade of the equipment with the worst of the three indexes of spectral matching, irradiation uniformity and irradiation stability. As shown in table 4-6, the comprehensive judgment of a tester is made, and the final grade is grade C.
Iec61215-2:2016 stipulates that if the spectral response of the tester used to test the power of components is consistent, the tester only needs to reach BBA level; The simulator used for light aging test only needs to reach CCC level.
