"We need a new solution for winter power"

In the summer of 2021 Switzerland’s largest alpine solar plant will be built. A pioneering project that also interests the Federal Institute of Technology Lausanne (EPFL) and the Institute for Snow and Avalanche Research (SLF). Annelen Kahl has been researching the performance of solar plants in high alpine regions for several years. In this interview she explains what opportunities she sees for the 2,-megawatt pioneering project from Axpo, IWB and Denner. 

Annelen, you have been researching solar plants in high alpine regions at the EPFL since 2015 and since 2018 you are also working at the SLF. What fascinates you about this area of research?

I'm fascinated by the diverse possibilities in this area as well as the complexity. Solar energy will be massively developed in Switzerland in the upcoming years because it is an important renewable energy form. Development often focuses on solar modules on the rooftops of single family homes and industrial buildings. That's all fine and well. But, I say: That alone is not the solution. If one looks at power production over a year, we need new solutions to produce a large portion of winter power. Here, I see great potential for alpine solar plants.

My goal as a researcher and with my company Sunwell is to point out new solutions for this problem, to mobilise companies to invest in these types of facilities, and, in doing so, make a contribution to sustainable energy production in Switzerland.

You mentioned winter power. Alpine solar plants could harness a great deal of electricity, especially in the winter. What else is special about these plants?

The higher the location, the more likely the plant is above the fog line. We are all familiar with these grey days, primarily during the winter months. That's why we like to go to the mountains and soak up the sun. The positive effect also applies to solar plants. Solar power can only be generated when the sun is shining. When there is snow next to the solar plant, production increases even more because of the light reflection. In addition, solar panels like cold temperatures: If the temperature goes down by one degree centigrade, the performance of the solar modules increases by 0.4 per cent.

With these advantages, a solar plant can deliver about half of its power production during the winter half-year. In other words, just when we need the most electricity.

The new solar plant on the wall of the Muttsee dam is at 2,500 metres above sea level. What opportunities do you see for this plant?

It is precisely these advantages that can be used at 2,500 metres above sea level. Since the dam is oriented to the south, it is optimally suited for solar panels. However, as a researcher I see even more potential with this project: The plant is a way to collect experience and data that can be used for other plants in alpine regions in the future. I am thinking, for example, of testing different types of panels, comparing different panel inclination angles on the dam, or data on wind forces and snow loads.

Speaking of snow loads: Together with your EPFL colleague Varun Sharma, with whom you manage your start-up Sunwell, you created a snow load model for the Muttsee plant. What is the purpose of the model?

Before building such a plant all risks must be minimised if possible. Snow is an important factor at this altitude. During some winters there is a lot of precipitation. Lots of snow remains on the panels and reduces production. This factor has to be taken into account in the construction of the plant. In the model, we calculated where and how much snow would remain lying on the plant and panel sections. We can then calculate the expected pressure on the panels. With this information the plant can be optimized – and costs can be saved.

And what did you find out specifically about the plant on the wall of the Muttsee dam?

We discovered a few critical areas. A lot of snow could accumulate at the bottom of the plant. In certain sections it would therefore make sense to reduce the number of panels. This would prevent them from damage. 

How do you estimate the potential of alpine solar plants and large-scale solar plants in the mountains?

Technically a great deal is possible in the mountains. In my scenarios I assume that 50 per cent of nuclear energy will be replaced by solar in the future. Based on this, I modelled how power production differs when we install these plants either on rooftops in the lowlands or at suitable locations in the mountains. The result is that winter production in the mountains is 68 per cent higher than in the lowlands. In addition we need about 20 per cent less solar surface to produce 12 TWh electricity per year.

Do you assume that these types of plants will have a strong influence on the power mix of the future?

The fact is that electricity from nuclear energy must be replaced in the upcoming years, namely with the renewable energies wind and solar. In principle, wind has large potential, especially in the winter. We also did a study for Switzerland on this: An optimal ratio would be 70/30: 70 percent wind and 30 percent solar energy. Unfortunately, there is strong opposition to wind power in Switzerland, which is why many projects have failed. Solar energy will become even more important in the future for this reason. In order to produce large volumes, large-scale solar plants should be built.