Created by E.Ö., SUPSI, on 07.06.2024
Photovoltaic (PV) panels are a popular choice for generating renewable energy in various conditions, including alpine environments (above 1500 meters above sea level (MASL)). The use of PV panels in alpine conditions offers several advantages and unique challenges. One advantage of using PV panels in alpine conditions is the abundance of sunlight. Due to the high altitude and clear skies, alpine environments receive intense sunlight, which is ideal for solar energy generation, especially in winter. Additionally, alpine environments often have lower temperatures, which can enhance the efficiency of PV panels. However, there are also unique challenges that come with using PV panels in alpine conditions. These harsh conditions depend on the microclimate as well as the macroclimate, and their types and effects may vary depending on location.
The main additional stressors in Alpine conditions are snow accumulation (static mechanical load), strong winds (static and dynamic mechanical load), ice formation, hailstorms, high irradiance, high UV radiation and low module temperature. In addition, the likelihood of extreme weather events that can damage PV modules is much higher than where conventional PV modules are generally installed.
In Switzerland, the highest amounts of yearly precipitation are found in the Alps, the Alpine foothills, the south side of the Alps, and the western peaks of the Jura (see Figure 1). These regions typically receive around 2000 mm of precipitation annually. Beginning at an altitude of 1200-1500 MASL, snow is the dominant form of precipitation during winter, resulting in a consistent layer of snow covering the area for weeks or even months at higher elevations. As depicted in Figure 1, a majority of the planned systems are situated in areas with high precipitation levels. Given that the predominant form of precipitation at elevations above 1500 MASL is snow, it is anticipated that snow accumulation will occur if appropriate preventative measures are not implemented. Depending on the orientation of their installation, snow accumulation may occur on both the front and rear sides of the modules.
In central Switzerland, the annual average wind speed is less than 10 km/h. However, higher speeds are often recorded at mountain peak weather stations (see Figure 2). When wind speeds exceed 75 km/h, there is a greater likelihood of causing damage. On average, this threshold is surpassed for fewer than 14 days each year in most areas of central Switzerland. Nevertheless, in some parts of the Alpine foothills, this occurs more than 30 days a year, and on the Alpine peaks, wind speeds typically exceed 75 km/h approximately once every six days or fewer. Strong wind gusts or turbulent wind flow on PV modules result in vibrations, module deflections and consequent mechanical stresses on the module components.
Hailstones is a natural phenomenon that can cause a lot of damage, especially during the summer months in Switzerland. Depending on the size of the hailstorm and the distance it travels, hail can be very localized or occur over larger areas. There has been an increase in hail events in recent years. The amount of damage that hailstones can cause depends not only on their size, but also on the amount of hail that falls in a particular area. Hail also occurs in the Alps, although rarely (see Figure 3).
In Figure 4, some meteorological information (irradiation, ultraviolet irradiation, ambient temperature, and relative humidity) is shared for the locations Freiburg (moderate climate), Gran Canaria (maritime climate), Negev (arid climate), Serpong (tropical climate), and Zugspitze (alpine climate, 2656 MASL) [1]. According to these measurements, in the alpine climate compared to other climates, there is:
- Higher maximum irradiation (> 1400 W/m2),
- Higher maximum ultraviolet (UV) irradiation (> 60 W/m2),
- Lower average ambient temperature (minimum < -20°C), and
- Higher average relative humidity.
M. Koehl et al. presented the measured module temperatures and daily temperature differences, which is the difference between the daily maximum and minimum temperatures, for the aforementioned locations in Figure 5.The module situated in the alpine climate had lower temperatures (minimum around -20°C) than the others due to the low ambient temperatures in that region. The variation in module temperature between day and night leads to thermomechanical stresses caused by the different thermal expansion coefficients of the module materials, such as cells, encapsulants, and metallization. Interestingly, the maximum daily temperature change of a module in alpine climate (approximately 70°C) is comparable to that of a module in moderate or arid climates.
References
[1] M. Koehl, M. Heck and S. Wiesmeier, «Categorization of weathering stresses for photovoltaic modules,» Energy Science & Engineering, 2018.
