Winter power from a dam

Thanks to the sunshine in the Glarus Alps, the solar plant on the Muttsee dam, which will be built in summer 2021, will deliver a great deal of power, especially during the winter months. Project Manager Christian Heierli explains why this winter power is so important.

Christian, why does it make sense to install a solar plant on the Muttsee dam?

Because the dam is exceptionally well-suited for such an undertaking. We already have existing, developed infrastructure and will not need to build on any new areas. The dam has a southern exposure and gets optimal sunlight. The plant will generate a major portion of its production during the winter months – double the volume of a comparable facility located in Central Switzerland. The plant is situated at an altitude of 2500 metres above sea level. At this height, there is less fog and higher production thanks to reflecting snow effects, as well as increased efficiency owing to low temperatures.

Why is it important to produce power during the winter months?

Switzerland consumes more power than it produces during the winter. This situation will intensify in the upcoming years when large-scale power plants are taken off grid here and abroad. There are various scenarios to resolve power shortages during the winter. If available, we can turn to imports, we can increase our seasonal storage, or we can build power plants that are not dependent on weather conditions. An important approach from Axpo's perspective is the development of alpine photovoltaics. We want to prove that this is possible with this plant.

The plant on the Muttsee dam will deliver a large portion of its production during the winter – but in comparison to the large-scale power plants that will be shut down will this really make a difference?

Solar plants in Switzerland are comparatively small depending on their locations. However, the nationwide proportion of solar power has strong development potential. It's true: The plant on the Muttsee dam alone will not make a significant contribution. More such plants need to be built in non-protected areas where the required infrastructure is already in place. For example in ski resorts or like here on dams. We want to prove that this is possible with the project.

What exactly will be mounted on the dam wall?

The projects foresees a plant with an installed capacity of 2.2 megawatts and an annual production of 3.3  gigawatt-hours, corresponding to the yearly power consumption of about 740 average four-person households. We will install about 5,000 solar modules on a surface of 10,000 square metres. 

How complicated is it to install a solar plant on a dam?

Logistically it’s quite complex. The dam is not accessible by road. Although there are tunnels from the pumped storage plant to the dam, they are used for maintenance and are unsuitable for transporting construction material. The material is delivered to Tierfehd and then transported to the dam area by helicopter. The time window for the work is very narrow – the plant has to be built during the alpine summer. That's a period of only three months – that’s about as long as construction takes.

And the large volumes of snow aren't a problem for plant operation?

Of course, we have to consider snow volumes. The solar plant will be mounted to the dam at a 65 respectively 51 -degree angle – steep enough for the snow to slide off. Because of the high snow volumes during the winter, we decided not to install modules on the lowest section of the dam. As a matter of fact, the snow is also helpful. Thanks to the reflection effects it has a positive impact on solar power production.