Solar power from the mountains

Photovoltaics requires space - whether on roofs, for example, or on hillsides, lakes or dams. Solar power from alpine regions may seem strange at first. However, it is practical for several reasons.

Producing solar power high up in the mountains is a relatively new idea. But it is a promising approach, especially for Switzerland. First this, you need to look at the big picture, i.e. the 1.5-degree target and the global emissions budget calculated by the Intergovernmental Panel on Climate Change (IPCC). With its “Energy Perspectives 2050+”, Switzerland has committed to the goal of reaching net zero emissions status by 2050. The decarbonisation of the energy sector can only be achieved by its electrification. This requires the complete transformation of the system and the rapid expansion of renewable electricity production by water, wind or solar power. The potential for hydroelectric power in Switzerland, however, is largely exhausted and will tend to decrease due to melting glaciers. For wind power plants, on the other hand, there is a lack of productive locations. This leaves photovoltaics, which currently supplies around 3 TWh a year to the power grid. To reach the net-zero target, however, its contribution would have to increase to at least 39 TWh a year, and not just by 2050. This should preferably take place by 2035, if the emissions budget is not to be exceeded, as Jürgen Rohrer from the Zurich University of Applied Sciences ZHAW in Wädenswil calculated.


Rohrer, Professor for Ecological Engineering, calculated an even higher value. For example, there is sufficient roof space in Switzerland to generate as much as 54 TWh of solar power a year. However, to make use of these spaces, a clear legal photovoltaic obligation would be necessary. Even if this were politically feasible, small-scale construction would not be efficient enough or sufficiently fast. The search for alternative spaces for large-scale solar power plants is therefore well under way - in addition to roofed motorways or car parks, fields, lakes and, most recently, mountains are also being considered by planners. All of these spaces have disadvantages, such as competition with food production, costs or the landscape protection. Nevertheless, there has been enormous momentum recently, especially in the mountains.


Alpine photovoltaics, as Rohrer has been assessing since 2017 with a test installation at an altitude of 2500 metres in Davos Totalp, is an interesting option for several reasons. First, the expansion of the photovoltaic electricity share could be accelerated by the necessary factor of six thanks to the plant sizes. Second, the efficiency of the photovoltaic cells is higher in the cooler alpine regions and can be further increased using so-called bifacial cells - i.e. with active front and rear sides. Solar radiation is higher, snow reflects the light more intensely and there are fewer foggy days than in Central Plateau. As a result, the annual yield in the mountains is much higher than in the lowlands, especially in winter. This means, according to Rohrer, that the output is up to four times as high as in the Central Plateau - thus closing the otherwise problematic photovoltaic winter gap. Studies concerning the effects on the local fauna and flora are still in the early stages. Landscape protection is at least being taken into account to the extent that the installations will not be noticeably visible from the inhabited valley.


Meanwhile, the federal government has also taken action. According to current legislation, photovoltaic systems outside regular building zones could generally not be granted a permit to date. Since November 2022, obtaining such permits has been made easier by the federal law entitled “Urgent measures for the short-term provision of a secure power supply in winter”.

The effects were quick to materialise: in Valais in particular, major projects are now being considered, with different players in the background and different concepts. For example, Alpiq is planning a solar park at Combe de Prafleuri together with the municipality of Hérémence with a capacity of 30-40 MW and an output of up to 50 GWh per year. 45 per cent of this is to be electricity generated in winter. This large installation would have space in a former quarry facing the south, and a test installation is already being prepared. Solar power is planned in Grengiols, 2000 metres above the Saflisch valley. The annual 2 TWh from plant with the size of 700 football pitches could supply three per cent of Switzerland's electricity. An interesting aspect of this project is the construction of a water reservoir as a buffer for solar power.


Incidentally, experiences have already been made with photovoltaic systems in alpine altitudes. More than 4800 solar modules with an output of 2.2 MW have been installed on the Muttsee dam with a height of 2500 metres in the canton of Glarus. Solar power has been flowing here since late summer 2022 - 50 per cent of the output is generated in winter. A floating photovoltaic system is in operation at an altitude of 1810 metres at the reservoir near Bourg-Saint-Pierre. Compared to the current projects, this is a small plant that only produces around 800,000 kWh and is therefore to be expanded. It seems that the mountains are currently being rediscovered. In any case, the space is there.

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