Reliable and highly resolved information about onshore wind energy potential (WEP) is essential for expanding renewable energy to eventually achieve carbon neutrality. In this pilot study, simulated 60 m wind speeds (ws60m) from a km-scale, convection-permitting 3.3 km-resolution ICON-LAM simulation and often-used 31 km-resolution ERA5 reanalysis are evaluated at 18 weather masts. The estimated ICON-LAM and ERA5 WEPs are compared using an innovative approach with 1.8 million eligible wind turbine placements over southern Africa. Results show ERA5 underestimates ws60m with a Mean Error (ME) of -1.8 m s-1 (-27%). In contrast, ICON-LAM shows a ME of -0.1 m s-1 (-1.8%), resulting in a much higher average WEP by 48% compared to ERA5. A combined Global Wind Atlas-ERA5 product reduces the ws60m underestimation of ERA5 to -0.3 m s-1 (-4.7%), but shows a similar average WEP compared to ERA5 resulting from the WEP spatial heterogeneity.