100% renewable – 100% doable
August 2020 - by Dr. Annelen Kahl, Jérôme Dujardin and Prof. Dr. Michael Lehning
The knowledge that wind power is very productive in winter and that photovoltaic (PV) installations can produce more electricity in alpine environments than in the valleys is not completely new. Yet these insights have remained little appreciated or acted upon. But with the energy transition pushing forward into a renewable future, this knowledge is of critical importance. As Switzerland is facing a substantial winter energy deficit with its nuclear power plants going offline, SCCER-SoE modelling results provide vital information as to how smart choices of installation location can help to fill this deficit with solar and wind power from the mountains.
The 2050 energy transition is not just about replacing the annual contribution of nuclear power; the real challenge is to produce enough electricity at the right time. Particularly in winter, Switzerland’s security of supply looks bleak, as high demand cannot be met by the relatively weak domestic production, and our neighboring countries might have a similar situation with increasing renewable electricity production. So, relying on imports is not only expensive but also unrealistic.
Establish optimal wind and solar power installation scenarios for Switzerland
Accordingly, it is important to align future electricity production as closely as possible with the demand. At the same time, compatibility with the existing electricity grid must be taken into account, otherwise new lines will have to be installed, and old ones expanded. When planning new solar and wind power plants, it is therefore not necessarily a question of maximizing individual annual production, but rather of achieving a production profile that adapts optimally to the temporal and spatial structure of Swiss electricity consumption and production from hydropower. We are a group of scientists from the EPFL that started the Laboratory of Cryospheric Sciences CRYOS project in the framework of the SCCER-SoE to take on this complex task of optimizing wind and (mountain) PV siting in parallel while simultaneously considering all constraints of the existing system.
With our contribution we show how Swiss electricity production can be best adapted to demand in a complex interplay between solar, wind and hydro power by adapting: 1) site selection, 2) mixing ratio of wind and solar production and 3) installation geometry of the PV modules. Controlled by a genetic algorithm, we determine optimal installation scenarios that are simultaneously compatible with the 2025 transmission grid.
We calculate the potential electricity production of the three energy sources water, wind and sun using in-house models based on detailed data sets for radiation, surface reflection, wind speed and water runoff. We represent both the varied topography of the Alps and the complex infrastructure of the Swiss hydropower system, as this is the only way to capture the spatial and temporal variability of the production. For each installation scenario, we obtain a different spatial distribution of the production with a different production profile. Using an optimal power flow model, we then determine the consequences of matching production and demand: how much electricity needs to be imported or exported and how stressed is the Swiss electricity grid as a result. The available hydroelectric power is used in a way that temporary production deficits, overproduction and possible bottlenecks in the grid are alleviated as much as possible. Constraints are considered for realistic sitings of both PV and wind installations. At the end of each analysis, the performance of the examined installation scenario is described using various metrics. We repeat this process using modified installation scenarios within the framework of an optimization procedure until we achieve maximum performance.
We use the required import as an objective function that guides the selection process and determines which solutions are most valuable. The optimization thus favors installation scenarios that minimize the import requirements and allow for maximum autonomy of the country.
Best results with 70% wind and 30% PV
The results show that the optimization achieves a 50% reduction in import with a simultaneous increase in productivity (compared to country-wide evenly distributed installations of PV and wind power). This is of key importance because it shows that high productivity and optimal timing are not mutually exclusive. It is possible to place PV and wind power installations in locations that are highly profitable and at the same time, produce electricity when it is most needed. It is even possible to do so without overloading the electricity grid. Despite the rather restrictive constraints that we apply for the possible installation locations for PV and wind power, the optimization algorithm is able to find suitable placements, without large compromises on their productivity. Best results are achieved with a mix of 70% wind and 30% PV, and the optimal locations are the Jura for wind turbines and the Alps for PV installations.
Authors
Based on her comprehensive studies of physics and the natural sciences at the University of Göttingen, the California Institute of Technology and the University of California, Dr. Annelen Kahl is working toward a better understanding of the environmental and systemic boundary conditions that enable and challenge the transition to a clean and renewable electricity production. Her current focus is on the potential of solar photovoltaic (PV) installations in alpine areas. As scientific collaborator at the EPFL and at the WSL Institute for snow and avalanche research (SLF) she contributes to the scientific foundation of Switzerland’s Energy Strategy 2050.As an entrepreneur of the EPFL spin-off SUNWELL, she aspires to actively design its implementation.
After a master’s degree in Physics at the Ecole Supérieure de Physique de Strasbourg, Jérôme Dujardin explored the R&D in the industrial sector for almost a decade. He finally decided to use his modelling skills to solve problems that our society is facing and joined the SCCER-SoE as research collaborator at EPFL in 2016. Since 2017, he works on his PhD thesis at the CRYOS laboratory and is focusing on the modelling and optimization of the Swiss electricity system and on the generation of high-resolution wind fields for wind energy applications.
Prof. Dr. Michael Lehning is the joint WSL / EPFL professor for Cryospheric Sciences and Snow Processes and heads the CRYOS and the “Snow Processes” groups at Lausanne and SLF Davos. His major research areas include: Snow - Atmosphere Interaction; Natural Hazards Forecasting; Turbulence and Boundary Layer Flows and Mountain Hydrology. Based on his modelling and measurement expertise, including remote sensing of snow, he has made significant contributions to understanding of mountain snow cover and precipitation dynamics.