The inspection of photovoltaic modules is carried out according to relevant inspection standards. Here, the inspection technology of photovoltaic modules is introduced in combination with the inspection standards of photovoltaic modules.
1. Photovoltaic module electrical performance test
The electrical performance test of photovoltaic modules is mainly to test photovoltaic modules under standard test conditions (battery temperature: 25℃±2℃, irradiance: 1000W/m2, standard solar spectral irradiance distribution conforms to the provisions of GB/T6495.3) Electrical properties of load changes. The test procedure is in accordance with the method of the GB/T6495.1 standard, and the I-U characteristics of the test components are tested under the standard test conditions. If necessary, the temperature and irradiance can be corrected according to the provisions of the GB/T6495.4 standard.
2. Photovoltaic module insulation performance test
The purpose of the photovoltaic module insulation performance test is to determine whether the insulation between the current-carrying elements in the photovoltaic module and the module frame is good.
1) Test conditions
The temperature is the ambient temperature (see GB/T2421), and the relative humidity does not exceed 75%.
2) Test procedure
(1) Short-circuit the lead wires of the components and connect them to the positive pole of the DC insulation tester of the current limiting device.
(2) Connect the exposed metal part of the module to the negative pole of the insulation tester. If the module has no frame or the frame is a bad conductor, a test metal bracket can be installed for the module and connected to the negative pole of the insulation tester.
(3) Increase the voltage of the insulation tester at a rate not greater than 500V/s until it is equal to 1000V plus twice the maximum voltage of the system (ie, the open circuit voltage of the system under standard test conditions). Maintain this voltage for lmin. If the maximum voltage of the system does not exceed 50V, the applied voltage should be 500V.
(4) Reduce the voltage to zero without disassembling the component cables, and short-circuit the positive and negative poles of the insulation tester for 5 minutes.
(5) Remove the short circuit of the positive and negative poles of the insulation tester.
(6) Connect the wires according to steps (1) and (2), apply a DC voltage of not less than 500V to the components, and measure the insulation resistance.
3. Photovoltaic module hot spot durability test
The purpose of the hot spot durability test of photovoltaic modules is to evaluate the ability of photovoltaic modules to withstand the heating effect of hot spots.
The process of the hot spot durability test of photovoltaic modules includes the determination of the worst case, the 5h hot spot durability test and the diagnostic measurement after the test, which is divided into the following 4 steps;
(1) Select the worst battery.
(2) Determine the worst shading ratio.
(3) 5h hot spot durability test.
(4) Post-test diagnostic measurements.
Here, the process of hot spot durability test of photovoltaic modules is introduced by taking photovoltaic modules with solar cells connected in series as an example.
1) Worst solar cells present in selected PV modules
(1) Irradiate the non-shading component under a radiation source of not less than 700W/m2, and test its l-U characteristics and the current lMP at the maximum power.
(2) Short-circuit the components and select a battery by one of the following methods:
①The module is irradiated by a stable radiation source with an irradiance of not less than 700W/m2, and the hottest battery is measured with an appropriate temperature detector.
②Under the irradiance specified in step (1), completely block each battery in turn, and select one of them. When it is blocked, the short-circuit current decreases to the maximum. During this process, the irradiance does not change by more than 5%.
2) Determine the worst shading ratio
(1) Also at the previously specified irradiance (within ±3%), completely block the selected cell and check whether the ISC of the module is smaller than the previously determined IMP. If this does not happen, one cannot be sure whether the maximum power consumption will be generated within a battery. At this point, continue to completely block the selected battery.
(2) Gradually reduce the shading area of the selected battery until the ISC of the module is closest to the IMP, and the power consumed in the battery is the largest at this time.
Note: For a monolithic solar cell, its equivalent circuit is shown in Figure 1. When the hot spot effect occurs, the power loss of the solar cell can be given by the formula. Since the parallel resistance of the solar cell is usually much larger than the series resistance, the power consumed by the solar cell in the case of short circuit depends on the solar cell. The power dissipated by the series resistance of the battery.
P=Ps +P5h = Ps+（Ps/R5h）Ps≈Ps
When the solar cells are connected together in series and the hot spot effect occurs, as shown in Figure 2, the power consumed by the solar cells under short-circuit conditions depends on the parallel resistance of the solar cells and the short-circuit current, as shown in the formula .
Py=Isc²（R5h+Rs）≈Isc²R5h
Consider the relationship between Isc and R5h and the shaded area (or ratio Y) of the solar cell.
Under an appropriate shading ratio, the internal resistance of the Y battery and other battery strings form the best match, at this time the Y battery consumes the most power and the hot spot effect is the most significant. This can also be seen from the I-U characteristic curve of the photovoltaic module during the hot spot effect, as shown in Figure 3.
From the IU curve, the mirror image (dotted line) of the IU curve of the (S-1) battery string to the I axis, and the intersection point A (Uy, ly) of the IU curve of the Y battery, determines the power consumption of the Y battery (shaded area Uy×Iy). Obviously, the power consumed by the Y battery is not greater than the maximum output power of (S-1) battery strings, and the current reaches the maximum at Iy=IMP (S-1), that is, the maximum output power point of (S-1) battery strings. When the number of cells in the module is large, lup(S-1) is close to the maximum output power point current IMP when the module is not shaded. Therefore, by comparing the components Isc and IMP, it can be judged whether the Y battery has reached the maximum power consumption.
Of course, not all batteries can achieve the best impedance matching by adjusting the shading ratio. In the case of complete shading, the I-U curves of Y cells with different characteristics are shown in Figure 4. The lower the slope, the greater the parallel resistance of the cells. Considering the “test limit” defined by the maximum output power point of (S-1) battery strings, according to the intersection of the IU curve and the “test limit”, the batteries are divided into voltage-limited (Class A) and current-limited (B) kind). The parallel resistance of type A batteries is relatively large, and the optimal impedance ratio can be achieved by reducing the shading area; the parallel resistance of type B batteries is relatively small, and complete shading is the state where the Y battery consumes the most power.
3) 5h hot spot durability test
(1) Irradiate the module with a radiation source, record the value of lc, and keep the power consumption of the module at the maximum. If necessary, readjust the shading to maintain the lsc at a specific value.
(2) After 1h, block the component from irradiation, and verify that Isc does not exceed 10% of IMP.
(3) After 30min, restore the irradiance to 1000W/m².
(4) Repeat steps (1) (2) and (3) 5 times.
4) Post-test diagnostic measurements
There are no serious appearance defects; the attenuation of the maximum output power under standard test conditions does not exceed 5% of that before the test; the insulation resistance should meet the same requirements for the initial test.
4. UV aging test of photovoltaic modules
The UV aging test of photovoltaic modules is to expose photovoltaic modules to ultraviolet radiation with a wavelength of 280~400mm to evaluate their anti-ultraviolet radiation ability.
The UV aging test process of photovoltaic modules is as follows.
1) Initial measurement
(1) Visual inspection of photovoltaic modules according to GB/T9535-1998 or GB/T18911-2002 standards.
(2) Test I-U characteristics under standard test conditions according to GB/T6495.1-1996.
(3) Insulation test according to GB/T9535-1998 or GB/T18911-2002.
2) Test steps
(1) The calibrated radiometer should measure the irradiance of the test plane of the module, and ensure that the wavelength is 280~400nm, and the test spectral irradiance does not exceed 5 times of its corresponding standard spectral irradiance. The standard AM1.5 solar irradiance The irradiance distribution is given by GB/T6495.3, which ensures that the spectral irradiance with wavelength below 280nm cannot be measured, and the uniformity of irradiance on the test plane is guaranteed to be ±15%.
(2) Install the module on the test plane, and make the UV irradiation light perpendicular to the front of the module according to the area selected in step (1).
(3) To maintain the temperature of the module within the specified range, the minimum radiation dose received by the module is as follows:
①When the wavelength range is 280~320nm, the minimum irradiation amount received by the module is 7.5kWh/m².
②When the wavelength range is 320~400mm, the minimum irradiation amount received by the module is 1.5kWh/m².
(4) Adjust the module so that the UV radiation line is perpendicular to the back of the module.
(5) Repeat step (3) so that the irradiation amount is 10% of the frontal irradiation level.
3) Final test
Repeat the following measurements:
(1) Visual inspection according to GB/T9535-1998 or GB/T18911.
(2) Measure I-U characteristics under standard test conditions according to GB/T6495.1-1996.
(3) Conduct insulation test according to GB/T9535-1998 or GB/Tl891l.
4) Test requirements
The components tested shall meet the following requirements:
(1) No serious appearance defects specified in GB/T9535-1998 or GB/T18911.
(2) Under the standard test conditions, the maximum output power attenuation is not more than 5% of the test value before the test. For thin film modules, under standard test conditions, the maximum output power shall be greater than the minimum value of the nominal power of the module provided by the manufacturer.
(3) According to the provisions of GB/T9535-1998 or GB/T18911, the insulation resistance should meet the requirements of the initial measured value.
5. Salt spray corrosion test
The purpose of the salt spray corrosion test of photovoltaic modules is to determine the ability of the modules to resist salt spray corrosion.
The process of salt spray corrosion test of photovoltaic modules is as follows.
1) Initial measurement
(1) Visual inspection.
(2) Test I-U characteristics under standard test conditions (STC) (according to GB/T6495.1-1996).
(3) Conduct insulation test according to relevant standards.
2) Test steps
According to GB/T2421-1999 and IEC60068-2-11-1981, the test shall meet the following requirements:
(1) Preprocessing: not required.
(2) Condition: The inclination angle between the upper surface of the component and the vertical direction should be 15°~30°.
(3) Test duration: 96h.
3) Final test
(1) Visual inspection of components before and after cleaning and drying.
(2) After the components are cleaned and dried, the l-U characteristics are tested under standard test conditions (STC) according to GB/T6495.1-1996.
(3) Conduct insulation test according to relevant standards.
4) Test requirements
(1) There is no mechanical damage or corrosion that seriously affects the normal working performance of the components.
(2) The reduction in electrical performance (maximum power) should not be greater than 5% of the initial value.
(3) It should meet the requirements of insulation test.