Interpretation of UV Conditioning Test in IEC 61215 Standard

1 Background of the IEC 61215 standard and the differences between the two editions

1.1 IEC 61215 standard background

IEC 61215 "Crystalline silicon terrestrial photovoltaic (PV) modules — Design qualification and type approval" is a product testing method of the International Electrotechnical Commission. The solar industry is currently citing this standard extensively for testing materials or products.

1.2 Differences in UV test between the two versions of IEC 61215

So far, IEC 61215 has issued two editions, the first edition is IEC 61215:1993, and the second edition is IEC 61215:2005. The national standard GB/T 9535:1998 "Design Appraisal and Finalization of Crystalline Silicon Photovoltaic Modules for Ground Use" is equivalent to adopting the first edition of IEC 61215:1993.

The second edition has one more appendix A than the first edition. As for the UV test, the main change is that the title of Section 10.10 is changed from "UV test (UV test)" to "UV preconditioning test (UV preconditioning test)". In the part of "ultraviolet test", the first edition only stated that the purpose of the test is "determining the ability of the component to withstand ultraviolet (UV) radiation" and "the ultraviolet test is under consideration", while the second edition not only changed the purpose of the test For "Ultraviolet (UV) irradiation pretreatment before thermal cycle/wet freezing test of components to determine the UV attenuation of related materials and adhesive connections", the test equipment, test procedures and test requirements are described in detail.

In the following sections we will focus on how to set up the QUV accelerated weathering Tester to meet the requirements of Section 10.10 "UV Pretreatment Test" of IEC 61215:2005.

2 Principle of material weather resistance aging test

Before introducing section 10.10 "UV pretreatment test" in IEC 61215:2005, let's briefly understand the principle of material weather resistance aging test.

2.1 Outdoor aging factors

Aging damage is mainly caused by three factors: light, high temperature and humidity. Any one of these three factors will cause material aging, and their combined effect is greater than the harm caused by any one of them.

2.1.1 Lighting

The chemical bonds of polymer materials have different sensitivities to different wavelengths of sunlight in sunlight, generally corresponding to a threshold value. The short-wavelength ultraviolet rays of sunlight are the main reason for the aging of most polymer physical properties.

2.1.2 High temperature

The higher the temperature, the faster the chemical reaction. The aging reaction is a kind of photochemical reaction, and the temperature does not affect the photoinduced reaction speed in the photoinduced chemical reaction, but affects the subsequent chemical reaction speed. Therefore, the effect of temperature on material aging is often nonlinear.

2.1.3 Moisture

Water will directly participate in the material aging reaction. Dew, rain and humidity are the main manifestations of water in natural conditions. Studies have shown that outdoor materials are exposed to moisture for extended periods of time each day (up to 8-12 hours per day on average). Dew is the main cause of outdoor humidity. Dew is more damaging than rain because it sticks to materials longer, creating harsher moisture attacks.

2.2 UV accelerated aging test

2.2.1 Sunlight simulation

The QUV utilizes fluorescent ultraviolet lamps to simulate the threat of sunlight damage to durable materials. These lamps are electrically similar to those used for general lighting, but emit primarily ultraviolet light rather than visible or infrared light.

For different application conditions, different spectra and thus different types of lamps are required. UVA-340 lamps provide a good simulation of sunlight in the short wavelength range of ultraviolet light. The spectral power distribution (SPD) of UVA-340 matches sunlight very well from its cutoff point to approximately 360nm. UV-B lamps are also widely used in the QUV. They cause faster material aging than UV-A lamps, but their shorter wavelengths than the cut-off point of sunlight can produce impractical results for many materials.

2.2.2 Irradiance Control

In order to achieve accurate and repeatable test results, it is necessary to control the irradiance (light intensity). Most QUV models are equipped with a solar eye illuminance controller. This precise light control system provides the user with the advantage of selective irradiance control. Utilizing the solar eye's feedback loop system, irradiance is continuously and automatically controlled and accurately maintained. The solar eye automatically compensates for changes in light intensity caused by lamp aging and other factors by adjusting the power of the lamp. In just days or weeks, the QUV can simulate the damage of months or even years outdoors.

2.2.3 UV control

Inside the QUV, the emission control system is simplified due to the inherent spectral stability of fluorescent UV lamps. As the tube ages, the output of all light sources decays. However, unlike most other types of lights, the spectrum of fluorescent lights does not change over time. This improves the reproducibility of test results and is a major advantage of testing with QUVs.

2.2.4 Temperature control

In QUV, temperature control is also important because temperature affects the rate at which materials age. The UV Test Chamber generally uses a black panel thermometer or a black standard thermometer to accurately control the surface temperature of the sample.

2.2.5 Humidity simulation

During the QUV condensation cycle, a Water Bath at the bottom of the Test Chamber is heated to generate steam. At higher temperatures, hot steam maintains 100% relative humidity in the Test Chamber. In QUV, the test sample actually forms the side wall of the Test Chamber, with the other side of the sample exposed to the ambient air in the chamber. The relatively cool air in the chamber makes the surface of the test specimen several degrees cooler than the hot steam in the Test Chamber. This temperature difference causes water in liquid form to slowly condense on the surface of the sample via a condensation cycle. In addition to standard condensation mechanisms, the QUV can also use water spray systems to simulate other damage scenarios such as thermal shock or mechanical corrosion. The user operates the QUV to generate a moisture cycle with UV light that closely mimics natural aging.

3 Interpretation of UV test in IEC 61215:2005 standard

Combined with the description of several aspects in Part 2, we analyze the requirements of the IEC 61215:2005 standard for the test conditions of the UV test from the aspects of spectrum, irradiance, temperature and humidity.

3.1 Definition of spectrum

The description in Section 10.10.2 d) of the standard is "ultraviolet radiation source, whose irradiance uniformity is ±15% on the component test plane, with no detectable radiation of wavelength less than 280nm, capable of producing required irradiance in the spectral range of interest". Figure 1 and Figure 2 below are the spectrum diagrams of UVA-340 lamp tube and UVB-313 lamp tube respectively. It can be seen from the figure that the spectrum emitted by UVA-340 lamp tube fully complies with Section 10.10.2 d) of the standard , while the spectrum emitted by the UVB-313 lamp has only a small number of spectral lines with a wavelength less than 280nm, which almost meets the d) part of Section 10.10.2 of the standard.

3.2 Irradiance setting

标准中 10.10.3 节 a) 部分的描述为“使用校准的辐射仪测量组件试验平面上的辐照度，确保波长在 280nm 到 385nm 的辐照度不超过 250W/m2 ( 约等于 5 倍自然光水平 )，且在整个测量平面上的辐照度均匀性到达 ±15%”，同时 10.10.3 节 c) 部分的描述为“使组件经受波长在 280nm 到 385nm 范围的紫外辐射为 15kWh/m2 ，其中波长为 280nm 到 320nm 的紫外辐射为 5kWh/m2 ，在试验过程中维持组件的温度在前面规定的范围”。以下我们分别对 UVA-340 灯管和 UVB-313 灯管的辐照度进行设定，并计算在设定辐照度下，运行多长时间可以达到标准中 10.10.3 节 c) 部分对辐照能的要求。

3.2.1 单独使用 UVA 灯管

当 在 340nm 设 定 辐 照 度 0.68 W/m2 时， 相 当 于 在 280- 385nm 波段的辐照度为 35.2W/m2 (小于 250W/m2 ，符合标准 10.10.3 节 a) 部分的要求)，而在 280-320nm 波段的辐照度为 3.1 W/m2 。我们假设 UVA 灯管运行 X 小时，组件经受波长在 280nm 到 385nm 范围的紫外辐射为 15kWh/m2 ，而灯管运行 Y 小时，波长为 280nm 到 320nm 的紫外辐射为 5kWh/m2 。具体计算如下：

35.2 W/m2 x “X” hours = 15000 Wh/m2 X = 426小时

3.1 W/m2 x “Y” hours = 5000 Wh/m2 Y= 1613 小时

由以上计算可知，当在 340nm 设定辐照度 0.68 W/m2 时，因为波长从 280nm 到 320nm 上的辐照度较小，所以需要 1613 小时，紫外辐射才能达到 5kWh/m2 。也就是说，使用 UVA 灯管时，运行1613小时才达到标准中10.10.3节c)部分对辐照能的要求，比较费时。

3.2.2 单独使用 UVB 灯管

当 在 310nm 设 定 辐 照 度 0.68 W/m2 时， 相 当 于 在 280- 385nm 波段的辐照度为 31.3W/m2 (小于 250W/m2 ，符合标准 10.10.3 节 a) 部分的要求)，而在 280-320nm 波段的辐照度为 18.8 W/m2 。我们假设 UVB 灯管运行 X 小时，组件经受波长在 280nm 到 385nm 范围的紫外辐射为 15kWh/m2 ，而灯管运行 Y 小时，波长为 280nm 到 320nm 的紫外辐射为 5kWh/m2。具体计算如下：

31.3 W/m2 x “X” hours = 15000 Wh/m2 X = 479小时

18.8 W/m2 x “Y” hours = 5000 Wh/m2 Y = 266 小时

由以上计算可知，当在 310nm 设定辐照度 0.68 W/m2 时，只需 266 小时组件经受波长在 280nm 到 320nm 的紫外辐射为 5kWh/m2 。而在 280nm 到 385nm 波段，需要 479 小时，组件经受的紫外辐射为 15kWh/m2 。也就是说，使用 UVB 灯管时，运行479小时可以达到标准中10.10.3节c)部分对辐照能的要求，比 UVA 灯管快很多。

3.2.3 共同使用 UVA 和 UVB 灯管

尽管使用 UVB 灯管可以缩短试验时间，但是如同本文 3.1 节中所述，UVB 灯管发出的光谱还有极少一部分的波长小于 280nm，也就说不完全符合 IEC 61215:2005 标准对紫外光谱的要求。但是如果单独使用 UVA 灯管，则测试时间过长。所以可以将两种灯管结合起来使用。如先使用 UVB 灯管，假设运行时间为 X 小时，再使用 UVA 灯管，假设运行时间为 Y 小时，具体计算如下：

18.8 W/m2 x “X” hours + 3.1 W/m2 x “Y” hours = 5000 Wh/m2

31.3 W/m2 x “X” hours + 35.2 W/m2 x “Y” hours = 15000 Wh/m2

The above two formulas are calculated: X = 229 hours, Y = 222 hours, that is, run the UVB lamp for 229 hours first, and then run the UVA lamp for 222 hours, which can reach the part of the radiation energy in Section 10.10.3 c) of the standard requirements. Both lamps run for a total of 451 hours, which is faster than using UVB lamps alone. In general, we recommend this method.

3.3 Temperature control

Section 10.10.2 a) of the standard is described as "equipment that can control the temperature of components when subjected to ultraviolet radiation, and the temperature range of components needs to be within 60 °C ± 5 °C". However, this temperature requirement is completely within the temperature range of the QUV. During the test, it is only necessary to set the temperature of the black panel to 60°C ± 5°C.

3.4 Humidity Control

There is no humidity requirement in the standard, so no condensation or water spray cycles are required for the test.

4 Conclusions and recommendations

The IEC 61215:2005 standard is widely used in the solar industry. When using the QUV ultraviolet accelerated aging Tester to implement this standard, you can first run the UVB lamp for 229 hours and set the irradiance to 0.68 W/m2, then run the UVA lamp for 222 hours and set the irradiance to 0.68 W/m2 . The temperature of the black panel was set at 60°C ± 5°C throughout the test.

Although humidity is not currently required in standards, many UV standards now include UV light and condensation or water spray cycles. So we suggest that when the standard is revised in the future, condensation or water spray cycle can be added.