Roof Speed-Up Effects in Isolated and Interacting Building Setups: Implications for Energy Harvesting

This study investigates direction-dependent roof speed-up factors for both isolated and interacting building configurations and evaluates their influence on the energy-yield potential of small wind turbines (SWTs) in urban environments. A combined approach was adopted: A theoretical framework and wind-tunnel experiments were developed to establish a general understanding of the meteorological, aerodynamic, and energetic parameters governing rooftop wind energy conversion and to derive characteristic roof speed-up factors for standardized flat-roof configurations. Wind-tunnel experiments were conducted for four distinct building scenarios, differing in layout and surrounding interaction, under three representative wind directions. High-resolution velocity measurements were acquired at multiple rooftop positions and elevations to capture detailed flow-acceleration and turbulence patterns. The resulting data were then applied in a case study for a representative urban site in Aachen, Germany. The measured directional speed-up factors were combined with a Weibull wind-speed distribution and a representative SWT power curve to estimate annual energy yields. The results reveal pronounced spatial and directional variability in wind acceleration, with localized increases of up to 25%. These variations translate into substantial differences in expected turbine performance depending on mounting height, placement, and prevailing wind direction. To facilitate further research and practical use, the complete dataset is published openly as a benchmark for computational fluid dynamics (CFD) validation and as a planning resource for rooftop turbine siting. The study underscores the importance of local aerodynamic effects in urban wind-energy design and provides a methodological framework that links controlled wind-tunnel data with real-world wind statistics.