Deploying small vertical axis wind turbines on urban rooftops — A parametric, dynamic, and hybrid life cycle energy and greenhouse gas emissions analysis

• We test 163 700 scenarios for life cycle energy and emissions of a vertical-axis wind turbine • We model wind flow around 5 193 Brussels buildings using CFD and machine learning • Results show embodied energy and emissions of wind turbines are underestimated by over 50% • Energy and emissions return on investment vary widely across the city • Tall buildings should be prioritized for wind turbines, but their potential must be checked . Deploying small wind turbines in urban areas can reduce electricity transmission losses and provide nighttime generation electricity generation. However, despite a growing recognition of the potential benefits of small urban wind turbines, uncertainties in environmental effects and life cycle environmental performance still hinder widespread adoption. This paper conducts a comprehensive parametric analysis and quantifies: (1) the life cycle energy and greenhouse gas emissions performance of a small urban vertical-axis wind turbine using a hybrid life cycle inventory approach and across 163 170 scenarios, and (2) the large-scale deployment of such turbines across 5 193 urban rooftops, using Brussels, Belgium as a case study. Key findings highlight that 1) Process-based life cycle analysis underestimates embodied energy and greenhouse gas emissions by 61% and 52%, respectively, highlighting the need to use hybrid life cycle approaches; 2) The wind energy resource is significantly variable when measured across the urban rooftop canopy; 3) The greenhouse gas emissions return on investment depends on the displaced energy source; 4) The energy return on investment is variable across all rooftop heights, but higher-yield tall buildings with favourable wind conditions should be a priority for urban deployment; and 5) Small urban wind turbines are a viable renewable energy source, offering seasonal and nighttime generation that reduces battery storage needs and associated emissions.