Numerical assessment of urban wind energy micro-generation potential: a comparison between two Swiss cities
Authors: Brandi Aldo , Manoli Gabriele 
Published: March 2024

In June 2023 Swiss people voted a new climate law that set a net-zero emission goal to be reached by 2050 via a full energetic transition from fossil fuels to renewables. The country&#8217;s Energy Strategy estimates that 7% (4.3 TWh) of future total renewable energy will be supplied by wind turbines, which requires an increase in the number of installed devices from the 37 currently operating to 760. Such an objective presents numerous challenges as available space is limited by technical restrictions, the country&#8217;s complex terrain, and competition with other types of land use.Thanks to qualities like small size and weight, low noise emission levels, and the ability to operate with winds blowing from any direction at relatively low speed (> 2 m/s), vertical axis wind turbines (VAWTs) installed in urban areas are an attractive alternative to overcome the issues associated with large wind farms. Despite this, the potential for wind energy micro-generation in complex urban settings remains largely unexplored.Private households use one third of all energy consumed in Switzerland, and residential renewable energy generation currently consists almost exclusively of photovoltaic (PV) panels which, in 2021, represented 78% of all solar systems operating in the country. No similar statistics are available for residential wind energy generation. Even in the scientific literature, current understanding of the interaction between wind and urban areas is limited, and the knowledge about urban wind resources is markedly inadequate to address the challenges posed by climate change to both local and global energy sectors.Here we use use the Weather Research and Forecast (WRF) model to simulate mean near-surface wind speed over the cities of Lausanne and Geneva to assess the potential for wind energy generation. We perform simulations at 300 m grid spacing and across 85 vertical model levels, with hourly output interval throughout one entire year to identify diurnal and seasonal wind speed trends. We then use power curves of select VAWTs to translate mean wind speed data into potential electrical output maps and time series, over all model cells classified as urban. &#160;Our results show that mean wind speed is generally higher in Lausanne than in Geneva, especially at nighttime. Diurnal cycles evolve markedly differently between the two cities, although differences are at times minimized due to seasonal changes. The average potential for wind energy harvesting using VAWTs in urban environments varies with turbine size and geographical area. The average daily total energy generation potential is one order of magnitude greater in Lausanne compared to Geneva. In Lausanne, top generation is expected during the nighttime across most months, allowing for a good integration of photovoltaic generation. The opposite happens in Geneva where already lower peak wind speed, and associated energy generation, always culminate during the afternoon.This research highlights the potential for urban wind energy micro-generation, drawing attention to the role of regional differences and the need and the importance of numerical simulations for quantitative assessments at the city and regional scales.