Created by E.Ö., SUPSI, on 12.03.2026
Gassner et al. [1] and the IEA PVPS Task 13 report [2] highlight mechanical load testing as a critical reliability assessment for PV modules deployed in Alpine environments. Both studies emphasise the effect of low temperatures, especially under mechanical load, which causes encapsulant materials to stiffen, reducing their ability to protect fragile solar cells under mechanical stress.
In the work of Gassner et al. [1], this effect was investigated by performing static mechanical load tests at +25 °C and –40 °C. The results showed that mechanical loads applied at low temperatures can induce cell cracks that do not appear at room temperature. This phenomenon was observed particularly in glass/backsheet modules with ribbon interconnections.
The study also demonstrated that thermal cycling prior to mechanical loading can initiate microcracks that are not immediately visible but may propagate under subsequent mechanical stress, producing effects similar to those observed during mechanical load tests at sub-zero temperatures. Therefore, laboratories that are not equipped to perform mechanical load tests at sub-zero temperatures may apply 50 thermal cycles (TC50) as a pre-stress before mechanical load testing to reveal comparable damage mechanisms.
To account for this effect, the modules in the present study were first subjected to TC50 before the static mechanical load tests. Static mechanical load tests were then performed with progressively increasing load levels, as illustrated in Figure 1.
Figure 1: Mechanical load test sequence (TC: Thermal cycling; MEL: Mechanical Load).
Four different module types were included in the mechanical load test sequence: three TOPCon (tunnel oxide passivated contact) modules and one BC (back-contact) module (Table 1).
One of the TOPCon modules (Module-1) represents a standard conventional design (glass/glass, EVA (ethylene-vinyl acetate) encapsulant, 2 mm / 2 mm glass thickness, standard frame design).
The other three modules are Alpine-relevant designs, featuring glass/glass design, thicker glass (2.8–3.2 mm) and reinforced frames with optimized geometries and larger frame–glass contact areas to withstand heavy mechanical loads. Regarding encapsulation materials, all three Alpine-relevant modules use EPE (EVA/POE( polyolefin elastomer)/EVA multilayer) encapsulant.
All modules were tested using the same mounting configuration.
Table 1: Summary of the tested modules. (TOPCon: Tunnel oxide passivated contact, EVA: Ethylene-vinyl acetate, POE: Polyolefin elastomer, EPE: EVA/POE/EVA multilayer).
| Module Construction | Glass Thickness | Frame | Solar Cell | Encapsulant | Number of cells | |
| Module-1 (Standard module) | Glass / Glass | 2 mm / 2 mm | 35 mm aluminum frame | TOPCon half-cell | EVA | 108 |
| Module-2 | Glass / Glass | 3.2 mm / 3.2 mm | Reinforced 40 mm aluminum frame | TOPCon half-cell | EPE | 108 |
| Module-3 | Glass / Glass | 2.8 mm / 2.8 mm | Reinforced 35 mm aluminum frame | TOPCon half-cell | EPE | 108 |
| Module-4 | Glass / Glass | 3.2 mm / 3.2 mm | Reinforced frame | Back Contact half-cell | EPE | 108 |
Test Results
Table 2 shows electroluminescence (EL) images of the modules before testing, after TC50, and after the mechanical load (MEL) cycles.
The standard module (Module-1) failed during the first mechanical load cycle (+5400 Pa / −2400 Pa) due to front glass breakage. In contrast, all Alpine-relevant modules (Module-2 to Module-4) successfully passed the full load sequence up to +8400 Pa / −2400 Pa.
Apart from the glass fracture in the standard module, the main observed effects were metallization and interconnection defects, such as damaged fingers or soldering, with varying severity among the modules.
Module-1 (Standard):
- Glass breakage during the first load cycle (+5400 Pa / −2400 Pa)
- Finger damage already visible after TC50 (Figure 2)
Module-2:
- Dark areas visible in EL images already before testing, likely caused by damaged soldering or cell fingers (Table 2)
- Formation of additional damaged fingers near the long edges of the module, with the number increasing at higher mechanical loads (Figure 3)
- No significant electrical performance change
Module-3:
- Darkened interconnection wires, small darker areas, and microcracks were observed near ribbon soldering regions on the short edges of the module, starting after TC50 (Figure 4)
- Formation of damaged fingers near the long edges, increasing with applied load (Figure 4)
- No significant electrical performance change
Module-4:
- Formation of very small and sparse dark areas in EL images after mechanical load tests (Figure 5)
- No significant electrical performance change
Overall, EL imaging shows a progressive spatial expansion of areas with reduced EL intensity, particularly near module edges. This behaviour indicates increasing mechanical stress on metallization and cell areas close to the frame. Despite these visible changes, no corresponding degradation in electrical performance parameters was measured.
Key Takeaways
- Module design strongly influences mechanical robustness. Modules with thicker glass, reinforced frames, and optimised frame geometries performed significantly better under high loads than the standard module, which failed at +5400 Pa due to glass breakage.
- The three Alpine-relevant modules successfully withstood three cycles each of +5400 Pa / −2400 Pa, +6400 Pa / −2400 Pa, +7400 Pa / −2400 Pa, and +8400 Pa / −2400 Pa after TC50 without significant performance change.
- In two Alpine-relevant modules, finger damage near the long edges was first observed at +6400 Pa / −2400 Pa and increased with higher loads, without measurable electrical impact.
- Manufacturing quality remains critical: one Alpine-relevant module type showed pre-existing metallization defects (Module-2), and two module types developed additional defects already after TC50.
Table 2: Electroluminescence images of the modules included in the mechanical load test sequence.
Figure 2: Detailed electroluminescence (EL) images of Module-1 at initial, TC50 and MEL (+5400Pa) stages.
Figure 3: Detailed electroluminescence (EL) images of Module-2 at initial and after MEL cycles.
Figure 4: Detailed electroluminescence (EL) images of Module-3 at initial, TC50 and MEL cycles.
Figure 5: Detailed electroluminescence (EL) images of Module-4 at initial, TC50 and MEL cycles.
References
[1] A. Gassner, G. C. Eder, E. Özkalay, G. Friesen, M. Feichtner and V.-M. Archodoulaki, “Enhanced mechanical load testing of photovoltaic modules for cold and snowy climates,” EES Solar, 2025.
[2] International Energy Agency Photovoltaic Power Systems Programme (IEA PVPS), “Optimisation of Photovoltaic Systems for Different Climates,” August, 2025.
