Created by LT, ZHAW, on 19.12.2024
Photovoltaic (PV) systems installed in alpine regions are generally exposed to greater wind and snow loads compared to installations at lower altitudes, depeding on the specific location. The mounting system must withstand these loads throughout the lifespan of the system. Consequently, local conditions must be carefully evaluated. Several different prototypes and PV installations already exist in alpine and high-alpine regions, accompanied by specific legal frameworks that govern their implementation. The following article will first address the relevant legal aspects, followed by an exploration of various mounting system options demonstrated through exemplary installations for Table-Mounting, floating PV-Mounting, Wire Mounting, installations on dam walls and the unconventional Fir Trees.
Legal Framework
The relevant regulations for planning mounting systems for alpine PV installations, as outlined in the transitional provision of the Energy Act (Article 71a), stipulate an obligation to minimize environmental impact, incorporating restoration and compensatory measures. Additionally, these installations must be fully dismantled at the end of their operational life, with the site returned to its original state. [1] These requirements regulate the environmental impact of alpine PV installations, like soil sealing and environmental degradation, such as from large-scale concrete foundations.
Further information on the legal aspects related to alpine PV installations can be found at Legal aspects.
Examples
Table-Mounting
The installation of PV modules as «tables» is the most widely recognized ground-mounting method in alpine regions. In this setup, bifacial modules are typically mounted either horizontally or vertically onto a steel mounting structure. This structure is anchored to the ground with steel posts. The modules are positioned at a height that allows livestock, such as cattle, to graze undisturbed beneath them. Figure 1 illustrates a PV table that, according to the manufacturer, is particularly minimally invasive, as it requires only a limited number of steel posts.
Figure 1: Alpin Quattro Alpine® Test Installation Tschers [2]
Figure 2 shows another variation of PV table mounting with visible ground anchoring. The system depicted here represents prototypes for the planned installation SolSarine Hornberg.
Figure 2: Prototypes for the planned installation SolSarine Gstaad [3]
In general, PV tables intended for use in alpine regions are installed at a fixed tilt facing as close to south as possible. Typical tilt angles for these tables range between 59° and 90°. Most of the table systems displayed on the Map with known tilt angles are set at an angle of 60°.
Floating PV Mounting
The floating mounting of photovoltaic modules is currently implemented by installing the modules to float on water surfaces (see figure 3) [4], [5].
Figure 3: Floating PV Installation on Lac des Toules [6]
For installations floating on still water surfaces, the modules are built on buoyant elements anchored to the lake bed [7]. A local example and the highest floating installation in the world is the demonstration project Lac des Toules.
Wire Mounting
Another method of alpine PV mounting uses wire cables suspended in the air (see figure 4 and 5) [8], [9], [10]. Such constructions, built by the company Bartholet, have been designed with both single-axis and dual-axis tracking.
Mounting on wire cables allows for the spanning of large distances without ground supports, thereby eliminating the need for foundations over extended distances. Additionally, the dual-axis tracking variant provides a way to dynamically adapt to high wind loads by adjusting the angle of the «sail.» The tilt angle of individual module rows is controlled through a guiding cable, allowing adjustments to reduce wind loads and facilitate snow shedding.
Dam Walls
Installations on dam walls represent the most frequently implemented type of alpine PV systems to date. These installations benefit from the lack of competing land use and visually integrate well with the dam structure (see figure 6), reducing the likelihood of objections from local communities or administrative bodies concerning landscape protection. The modules are typically installed at a tilt angle of 70° or greater. For vertical dam walls, slight mounting adjustments are made to achieve optimal tilt.
Figure 6: PV Installation on the Albigna Dam [15]
Examples of existing installations on alpine dam walls in Switzerland can be found on the Map:
Albigna Solar AlpinSolar Lago di Lei Oberaar Staumauer Räterichsboden Stausee
Fir Trees
A highly innovative approach to vertical mounting, specifically designed for alpine PV installations, is offered by Helioplant [11], [12]. The cross-shaped design of this structure is inspired by coniferous trees. This design choice is motivated by technical considerations, such as enabling snow turbulence around the bifacial modules arranged vertically around a mast (see figure 7). This arrangement keeps the modules snow-free and creates a “snow crater” that reflects sunlight from the sides and below. Additionally, the vertical mounting provides maintenance access without requiring dedicated pathways. Visually, this mounting system is intended to blend into the mountainous landscape like clusters of fir trees.
Figure 7: Helioplant Test Installation in Sölden (AT) [13]
From an ecological perspective, these “solar trees” are designed to minimize impact on alpine environments by avoiding permanent shading of surfaces and allowing livestock to graze freely. The data sheet even suggests deploying this mounting system in avalanche starting zones, as it may potentially offer protective benefits. The ground anchoring is achieved without concrete foundations, aligning with the principles of minimally invasive construction in mountainous areas. Instead, the structure is secured with four micro-piles, which are intended to contribute to soil stability.
According to the manufacturer, this mounting method combined with bifacial modules can easily exceed the required winter yield of at least 500 kWh/kWp, as confirmed by the results from existing test installations. Currently, three installations are in operation in Austria and one in Gondo, Switzerland (see figure 8), where, as of October 2024, a 15.9 MW installation at the test site has been submitted for approval Gondosolar.
Figure 8: Test Installation in Gondo [14]
Conclusions
In conclusion, various installation options exist for alpine PV systems. A common feature among them is the higher tilt angle compared to installations in lowland regions. Additionally, extreme weather conditions in alpine environments, particularly wind and snow loads, necessitate highly stable construction and anchoring. However, federal requirements for minimal invasiveness and the ability to dismantle the installations must also be consistently ensured.
Sources and Links
[1] Energiegesetz
[2] KONSORTIUM FÜR ALPINE PHOTOVOLTAIKANLAGE
[3] „Alpine Solaranlagen – Solaranlagen in den Alpen – jetzt wird es konkret“ (SRF)
[4] Lac des Toules : projet de parc solaire flottant
[5] Solarstrom aus dem Stausee Lac des Toules | ABB
[6] „Photovoltaik: Auf Stauseen schwimmende Module in den Alpen liefern Strom“ (NZZ)
[7] Lac des Toules: Le parc de démonstration
[8] Solar Wings AG
[10] Factsheet Solar Wings (Bartholet AG)
[11] HELIOPLANT® – Innovative Photovoltaik-Anlagen für das Hochgebirge
[12] Factsheet Helioplant (Helioplant Engineering)
[13] HELIOPLANT® energy | LinkedIn
[14] Das Projekt Gondosolar | Zahlen und Fakten
[15] „Hochalpine Photovoltaik-Anlage auf der Albigna-Staumauer“ (ewz)
