Alpine PV Module Testing

^{Created by E.Ö., SUPSI, on 25.04.2025}

^{Last updated by M.L., OST, on 02.05.2025}

The article “Alpine PV Stressors” explains the particularly challenging environment of the Alps. Factors such as low temperatures, ice formation, snow accumulation, strong winds, high irradiance and high ultraviolet (UV) radiation may lead to the need for “alpine PV module design”. Furthermore, these specific challenges may require reliability tests that go beyond the requirements of established International Electrotechnical Commission (IEC) standard tests. In this article, we present a range of IEC standard tests relevant to alpine conditions, as well as various tests and test sequences developed by different actors for extreme climatic conditions.

The alpine related tests are:

Static Mechanical Load Test (IEC 61215-2:2021 and beyond)
Non-uniform Snow Load Test (IEC 62938 and beyond)
Snow Load Test Including Downhill-Slope Force
Dynamic Mechanical Load Test (IEC 61215-2:2021) and PV Modules – Dynamic Mechanical Load Test (IEC TS 62782:2016)
Non-uniform Dynamic Mechanical Load Test
Hail Impact Test (IEC 61215-2:2021), PV Modules – Qualifying guidelines for increased hail resistance (IEC TS 63397:2022) and VKF Prüfbestimmungen (ACFI Test Specifications)
Ultraviolet (UV) Test (IEC 61215-2:2021 and beyond)
Hot-spot Endurance Test (IEC 61215-2:2021 and beyond)
Bypass Diode Thermal Test (IEC 61215-2:2021 and beyond)
Thermal Cycling Test (IEC 61215:2021)
Humidity-Freeze Test (IEC 61215-2:2021)
Alpine Test Sequences

Static Mechanical Load Test (IEC 61215-2:2021 and beyond)

This test evaluates the module’s structural integrity under uniform static mechanical stress, simulating conditions such as snow loads and wind pressures. In accordance with the IEC 61215 standard, mechanical load tests are conducted at ambient temperatures (25°C) with pressures usually reaching up to 5400 Pa. In alpine conditions, however, the loads from snow and wind can be significantly higher, and temperatures can be much lower. Additionally, materials generally become more brittle at lower temperatures, which increases the risk of issues like micro-crack formation especially under mechanical stress [1–3].

To address these demanding conditions, some manufacturers produce specialized alpine modules designed to withstand static mechanical loads that exceed standard IEC requirements, such as up to +8000 Pa (design load). Fraunhofer ISE’s TestLab offers the possibility for such extended mechanical load test, with pressures up to 10’000 Pa, temperatures between -40°C and +60°C and, for dynamic tests, frequencies up to 0.2 Hz [4]. Furthermore, SUPSI also offers mechanical load test at room temperatures with pressures up to 15’000 Pa and collaborates with OFI within a project to develop a test sequence for conducting mechanical load tests following thermal cycling, which would obviate the need for low-temperature mechanical load tests – a process that poses significant challenges for many testing laboratories.

Non-uniform Snow Load Test (IEC 62938 and beyond)

In alpine regions, PV modules often experience substantial, uneven snow loads due to the rugged terrain and harsh winter conditions. This uneven snow distribution can place significant strain on the modules, potentially leading to mechanical failure. This test ensures that both the modules and their mounting systems can safely withstand non-uniform loads, thereby reducing the risk of accidents. As previously mentioned, in alpine environments, snow and wind-induced loads can be much higher, and the lower temperatures make the module materials more brittle. Conducting these non-uniform snow load tests at temperatures below 0°C provides valuable insights for applications in alpine regions. Fraunhofer ISE’s TestLab offers to perform non-uniform mechanical load test at low temperatures as mentioned above.

Snow Load Test Including Downhill-Slope Force

Standard snow load testing procedures apply pressure on horizontally mounted modules. This situation does not take into account downhill-slope forces, as can arise in the case of a frozen snow layer sticking to the module. In order to simulate snow loads on a tilted surface, SPF and SUPSI developed a test stand allowing to apply homogeneously distributed vertical and horizontal forces on a module. To do so, an airbag is used to apply pressure vertically, while the horizontal forces are applied with strongly adhesive but non-sticky tapes. The test stand allows to apply forces of up to 20 kN/m² (horizontally and vertically) on a module-area of up to roughly 15 m². Moreover, the system allows to test modules together with their mounting system and tracks the deformation in real time with sensors and cameras. This certification process is recognized by the Swiss Association of Cantonal Building Insurers. So far, there is no defined value to reach for a PV module to be sold specifically for alpine applications. There are examples of alpine modules certified for 5400 Pa, while 8000 Pa or even 13’000 Pa seem to be the goal set by actors in the field of alpine PV [3,5,6]. Of course, the required robustness depends strongly on the meteorological conditions of the location where the module is to be installed, the setup of the mounting system, and the inclination at which the module is mounted.

The detailed testing procedure is described in [6], that can be downloaded from SPF’s website.

Source: https://www.ost.ch/de/forschung-und-dienstleistungen/technik/erneuerbare-energien-und-umwelttechnik/spf-institut-fuer-solartechnik/testing/schneelast, downloaded on 13.03.2025. ©2025, SPF Institut für Solartechnik.

Dynamic Mechanical Load Test (IEC 61215-2:2021) and PV Modules – Dynamic Mechanical Load Test (IEC TS 62782:2016)

Alpine regions are often exposed to strong wind gusts, making it crucial for modules and their mounting systems to endure dynamic mechanical loads without sustaining damage. This test assesses the module’s structural integrity by applying uniform dynamic (cyclic) mechanical stress, simulating the impact of wind-induced cyclic loads. According to IEC TS 62872, in the test, a back-and-forth pressure of ±1,000 Pa (with a tolerance of ±100 Pa) is applied 1,000 times. The load cycles at a rate of 3 to 7 cycles per minute, with each cycle consisting of one positive and one negative load.

Non-uniform Dynamic Mechanical Load Test

Wind gusts exert irregular and non-uniform dynamic forces on PV modules [7,8]. This combination is not tested in the IEC standards, which test static (IEC 61215-2) or dynamic (IEC TS 62782) uniform loads, or static non-uniform loads (IEC 62938). Hsu and Wu defined a non-uniform mechanical load test for PV modules, adapting the reliability testing to Taiwan, where typhoons repeatedly cause damage to PV installations [7]. Since winter storms are a common phenomenon in the Alps, this test is highly relevant for alpine modules too. Performing it at low temperatures, as described above, would be even better.

Hail Impact Test (IEC 61215-2:2021), PV Modules – Qualifying guidelines for increased hail resistance (IEC TS 63397:2022) and VKF Prüfbestimmungen (ACFI Test Specifications)

Hail damages to buildings and PV installations has increased over the past years, leading to higher requirements for hail resistance in norms [9]. As indicated in the hail map of Switzerland, published in Swissolar’s Merkblatt Photovoltaik Nr. 17 – Umgang mit Hagelschäden an Solaranlagen [9], the Pre-Alps and the Jura, are particularly at risk. These regions are highly relevant for “alpine PV” too, as they benefit (to a lower extent) from similar advantages (high albedo and irradiance), but at lower building costs, as highlighted here by Solalpine.

Hail impact test simulates the impact of hailstones on PV modules to assess their resistance to physical damage. According to the IEC 61215 standard, a PV module must be able to withstand the impact of a 25 mm hailstone launched at 23 m/s. In comparison, the Swiss VKF standard requires a minimum hailstone size of 30 mm (HW 3, hail resistance class 3). For modules deployed in alpine regions, HW 4 should be the minimum. Several manufacturers offer alpine modules with hail resistance classes of HW 4, and occasionally HW 5.

Source: VKF, Hail Register (HR), ACFI Test Specifications No. 00a General Part A.

Many laboratories and institutes offer hail resistance testing services, including SUPSI, SPF-OST, TÜV and Fraunhofer ISE. It is important to note, in addition to the standard tests, SUPSI and SPF-OST also provide the possibility of tailored experiments, allowing hail stones with diameters up to 80 mm at higher speeds.

Source: https://www.ost.ch/en/research-and-consulting-services/technology/renewable-energies-and-environmental-engineering/spf-institute-for-solar-technology/testing/hail, downloaded on 14.03.2025 ©2025, SPF Institut für Solartechnik.

Ultraviolet (UV) Test (IEC 61215-2:2021 and beyond)

At higher altitudes, elevated UV radiation levels increase the risk of UV-induced degradation of both module materials and high-efficiency cell technologies. According to IEC standards, the UV test is conducted at a module temperature of 60 ± 5°C, with exposure to at least 15 kWh/m² of UV radiation in the 280 nm to 400 nm wavelength range. This test evaluates the module’s ability to withstand prolonged UV exposure. However, extended UV tests beyond 15 kWh/m² may be necessary to better understand the long-term effects of high-altitude UV radiation on PV modules. UV testing up to 120 kWh/m² helps assess the risks of material degradation and cell deterioration. Several laboratories and institutions, including SUPSI, TÜV, and Fraunhofer ISE, provide UV testing services.

Hot-spot Endurance Test (IEC 61215-2:2021 and beyond)

At higher altitudes, both irradiance and albedo can be higher. In Switzerland, irradiance levels of up to 1600 W/m² (total front and rear sides) have been observed for PV modules tilted at 60 degrees at altitudes of above 2000 meters. Additionally, many alpine PV systems are planned to be installed at steep tilts and in dense configurations to manage snow load and minimize land usage, respectively. However, this increases the risk of row-to-row shading at certain times of the year, especially in winter times when the sun is low (more direct light) and albedo is high (snow on the ground).

The standard hot-spot endurance test is conducted at a module temperature of 55°C with an irradiance of 1000 W/m² for durations either 1 hour or 5 hours (if the hot-spot temperature is not stabilized). Given the high irradiance levels and the potential for frequent row-to-row shading in alpine environments, it is worth considering performing hot-spot endurance tests at higher irradiance levels (>1000 W/m²) and extended durations (longer than 5 hours). SUPSI has potential to perform customized hot-spot endurance tests (higher irradiance, higher temperatures and longer durations).

Bypass Diode Thermal Test (IEC 61215-2:2021 and beyond)

As mentioned previously, higher altitudes experience higher irradiance levels, and depending on the design of the PV system, frequent row-to-row shading can occur under these high irradiance conditions. When bypass diodes begin to conduct current due to partial shading, a high current can flow through the diode. This test assesses whether the bypass diodes, which provide partial protection against shading and hot spots, function properly under the elevated irradiance levels commonly found in alpine climates. Following the initial characterization of the diodes according to IEC 61215, 1.25 times the short-circuit current of the module under test is applied to a diode for 1 hour. The applied current level may be adjusted, and the test duration extended to better simulate the specific conditions of alpine environments.

Thermal Cycling Test (IEC 61215:2021)

Thermal cycling test is necessary for PV modules in alpine conditions because these areas experience significant temperature fluctuations. The test simulates rapid changes in temperature to assess how the module handles stress, preventing damage like solder bond damage, cell cracking or delamination. This ensures the module can withstand thermal changes and continue to perform reliably. It also helps verify the long-term durability and efficiency of the module in harsh alpine environments.

Humidity-Freeze Test (IEC 61215-2:2021)

The humidity freeze test is essential for PV modules in alpine conditions due to the frequent exposure to freezing temperatures and high humidity. This test simulates the freezing and thawing cycles, assessing how well the module can handle these extreme conditions. It helps identify potential issues like delamination or corrosion, ensuring the module’s materials can withstand repeated freeze-thaw cycles without degradation. The test ensures the module’s long-term performance and reliability, even in areas with high humidity and freezing temperatures. Conducting this test improves the confidence on the module’s durability in alpine environments.

Alpine Test Sequences

Performing all the tests described above would be time consuming and requires a large infrastructure. To address this issues, determine the most relevant tests and efficient ways of performing them, OFI, SUPSI, and Sonnenkraft Energy GmbH combined their expertise within the framework of the PVDetect project. A test matrix for Alpine PV modules is being developed and first recommendations have already been published:

This testing sequence provide a state-of-the-art method to assess the reliability of PV modules destined for alpine applications.

Other institutes are specialized in testing PV modules for alpine applications, but their exact testing sequence could not be found online:

References

Schneller EJ, Seigneur H, Lincoln J, Gabor AM. The Impact of Cold Temperature Exposure in Mechanical Durability Testing of PV Modules. 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC), Chicago, IL, USA: IEEE; 2019, p. 1521–4. https://doi.org/10.1109/PVSC40753.2019.8980533.
Seigneur H, Schneller E, Lincoln J, Ebrahimi H, Ghosh R, Gabor AM, et al. Microcrack Formation in Silicon Solar Cells during Cold Temperatures. 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC), Chicago, IL, USA: IEEE; 2019, p. 1–6. https://doi.org/10.1109/PVSC40753.2019.9198968.
Gassner A. Alpine PV: Stressors and module testing strategies 2025.
Additional Testing Equipment – Fraunhofer ISE. Fraunhofer Institute for Solar Energy Systems ISE n.d. https://www.ise.fraunhofer.de/en/rd-infrastructure/accredited-labs/testlab-pv-modules/additional-testing-equipment.html (accessed March 14, 2025).
Hügli A. Interview about alpine PV: REECH 2024.
Schneelast, SPF – SUPSI Prüfvorschrift Nr. 46 2021.
Hsu S-T, Wu T-C. Simulated Wind Action on Photovoltaic Module by Non-uniform Dynamic Mechanical Load and Mean Extended Wind Load. Energy Procedia 2017;130:94–101. https://doi.org/10.1016/j.egypro.2017.09.401.
Hasler S. Anforderungen an PV-Module in alpinen Regionen. OST (SPF); 2024.
Swissolar. Merkblatt Photovoltaik Nr. 17 – Umgang mit Hagelschäden an Solaranlagen 2022.

Further sources:

IEC: Provides guidelines on testing the performance and reliability of PV modules under various environmental conditions.
Swiss VKF Standards: Set specific requirements for PV modules to withstand environmental stresses such as hail impact, which are relevant for ensuring module durability in Alpine regions.