Winter power from a dam

Thanks to the sunshine in the Glarus Alps, the photovoltaic plant on the Muttsee dam will deliver a great deal of power, especially during the winter months. Project Manager Christian Heierli explains why this winter power is so important, and why it is not yet clear whether this pioneer facility will be profitable.

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. 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. We want to prove that this is possible with the project.

What exactly will be mounted on the dam?
The projects foresees a plant with an installed capacity of 2 megawatts and an annual production of 2.7 gigawatt-hours, corresponding to the power consumption of about 600 average four-person households. We will install about 6,000 solar modules on a surface of 10,000 square metres. The plant will be installed a good meter away from the dam surface so that the wall remains accessible for maintenance and service.

Construction of the Muttsee dam was completed some time ago. Why has Axpo waited so long with the plans for the solar plant?
The Limmern pumped storage plant that is part of the Muttsee dam will be in test operation until the end of 2019. As a result, the dam will be intensively monitored up until the end of the year. This is why we waited with the solar plant project.

How complicated is it to install a photovoltaic 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 56-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.

Will the plant be profitable?
At the moment we cannot say so definitively. We can say it won't be easy. Current subsidies are modest, amounting to less than 15 per cent of the investment costs. Switzerland's subsidy programme is designed for own consumption by home-owners. In Central Switzerland this is quite attractive: Home-owners can replace more costly power from suppliers with inexpensive solar power from their roofs. The costs for the installations can be recovered in 15 to 20 years. However, we have to go to the market with our solar power – and that is more difficult. Currently, we are in negotiations with different potential customers for long-term power purchase agreements. In Portugal, Axpo was able to realise a large-scale solar plant without state subsidies with such an agreement.

Does that mean Axpo will build the plant even if it isn't profitable?
We will be able to determine that once more precise figures are available. It is a pilot project which does not yet exist in such form. What we can say: Axpo wants to build this plant. We assume that the problem of winter electricity will also become a political issue and that Alpine PV will therefore become more important. We want to be one step ahead here.

What would be necessary on a political scale to make the construction of these types of plants more attractive?
We could envision tendering processes like those taking place in France. The Federal Council's efforts are going in that direction at the moment. Switzerland is lagging behind in the expansion of renewables. Last year it was one of the weakest countries in Europe in this respect. And Switzerland does not have enough energy during the winter. We have to decide how we want to handle that. An import strategy is problematic. It makes us dependent and we don't know if there will be sufficient capacities available in the long term. As a result, the winter power problem must be addressed on a political level.