  Wind, as a clean and sustainable source of energy, has witnessed significant
growth in recent years. However, with a growing number of wind farms
authorised, constructed and commissioned, the wake effect (the reduced wind
speed caused by upstream wind farms) is emerging as a pressing concern for both
farm owners and policymakers. Here, to systematically and comprehensively
investigate the wake effects in real-world wind farms, we analyse the wind
speed retrieved from 7122 Sentinel 1A/B SAR images spanning over three years,
encompassing more than 60 large-scale wind farms across Europe and Asia. Our
study reveals that long-distance wakes can propagate more than 100 km.
Additionally, we identify that wake effects lead to, on average, a 1.204 m/s
(or 12.4%) speed reduction for downstream wake-affected areas. We envisage that
our quantitative findings can provide vital support to wake-related planning
and legislation for future wind energy projects where wind power plants are
expected to be in close proximity.
