Field experiences so far

^{Created by M.L., OST, on 08.04.2025}

The interviews conducted with various actors in alpine PV indicated that, so far, most interventions required on PV power plants in the Alps were due to mechanical damages. Snow drift turns out to be the biggest challenge, since it is hard to predict and can lead to huge forces. Indeed, not only does it lead to snow accumulation against the panels, but when this snow gets wet and freezes, its expansion can apply pressures much higher than the actual weight of the snow. For such cases, measurements with strain gauges would be highly interesting. Suppressing such snow drifts is the only way to avoid these damages, since withstanding forces from snow-expansion during freezing is practically impossible. This can be done by using structures to break the wind, or special plant designs, as in the case of Gondo Solar, where the spacing and geometry of the PV «trees» were designed to create wind vortexes keeping them snow free [1]. On the pilot site of Tschingel, another approach was used: the mounting structure was designed in a way that the lower part can «fold up» in the case of a 30-year event, predicted by simulations. As a result, the modules should stay intact, and the mounting structure can be repaired at minimal costs in spring [2].

Below, a few examples of field experiences are listed:

• Floating PV-installation of Lac des Toules [1]: Due to turbulences, snow accumulated between the first and second row of panels, destroying the modules and part of the mounting structure (as shown in Fig. 1).
• AlpinSolar [3]: Being the first Alpine-PV utility-scale power plant in Switzerland, some precious lessons could be learned from it:
  • In a first incident, part of the aluminum mounting structure in the lower part of the dam wall (tilted at only 51°) was destroyed, as the forces applied by snow accumulation turned out to be higher than predicted. It was replaced with steel, solving the problem.
  • In a second incident, the lower middle part of the PV installation got damaged, due to a large accumulation of snow at the feet of the dam wall. Over time, the snow got wet, compacted, and went through several freezing-melting cycles, forming a sort of mini-glacier pushing against the PV installation, destroying 270 panels and part of the mounting structure. Such extraordinary events (linked to particularly heavy snow falls in this case) have to be taken into account in the risk analysis of the project.
  • A further surprising issue was the formation of icicles hanging down form the modules, exerting torsion forces on the frames.
• Solaranlage Gries [4]: Small cracks in the glass of the modules were detected. Despite large amounts of snow regularly covering the whole installation, the cracks are most likely not linked to pressure, but to thermos-mechanical stress. To test this, the suspension of some of the modules was changed, replacing the clamps with a model featuring a rubber layer, giving the glass a bit of freedom to move during thermal expansion.
• Wind: At the site of a PV installation on a dam wall, a storm blew away several panels. The whole construction was tested to forces up to 2.7 kN/m², which should have been enough to withstand the measured wind speeds of around 200 km/h. Most likely, local effects lead to higher forces. After a cause analysis, some adaptations of the mounting structure were done.
• Avalanche: On another dam wall, part of the PV installation was damaged by an avalanche. In this case, the risk was known, but taken, in order to maximize the power output. After the incident, the concerned part of the installation was removed.
• Alpine Modellanalage Totalp [5]: Despite the possibility to heat thanks to a connection to the grid, operating moving parts in the freezing conditions of the alpine environment turned out to be very challenging. The system got stuck many times, needing on-site intervention, which themselves turned out more demanding than expected. Despite generous planning, allowing easy access to all parts of the system, doing maintenance work at -20 °C and limited space requires quite some experience and endurance. Hence, it is recommended to avoid moving parts whenever possible, and design the system even more generously, if moving parts are required.

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References

1. Cattin J, Bloch L. Interview about alpine PV: Planair, Lac des Toules 2025.
2. Knödel B, Müller-Duss S. Interview about alpine PV: BKW, Tschingel 2024.
3. Heierli C. Interview about alpine PV: AXPO, Alpin Solar (Muttsee-Staumauer) 2025.
4. Schmidhalter F. Interview about alpine PV: Enalpin 2025.
5. Strebel S. Interview about alpine PV: Test installations of ZHAW (in Davos) 2025.
6. Ramstein M, Chevillat Y. Centrale photovoltaïque flottante de démonstration au lac du barrage des Toules (VS) – Texte n.d. https://www.aramis.admin.ch/Texte/?ProjectID=44236 (accessed October 5, 2023).