Downloadable GeoJSON contains filtered NOABL wind speed data where wind speed < 5 metres / second at 45 metres about ground.
Background about NOABL wind speed database:
The Department for Business, Enterprise & Regulatory Reform's wind speed database is available from this website. It contains estimates of the annual mean wind speed throughout the UK.
The data is the result of an air flow model that estimates the effect of topography on wind speed. There is no allowance for the effect of local thermally driven winds such as sea breezes or mountain/valley breezes. The model was applied with 1km square resolution and takes no account of topography on a small scale or local surface roughness (such as tall crops, stone walls or trees), both of which may have a considerable effect on the wind speed. The data can only be used as a guide and should be followed by on-site measurements for a proper assessment.
Each value stored in the database is the estimated average for a 1km square at either 10m, 25m or 45m above ground level (agl). The database uses the Ordnance Survey grid system for Great Britain and the grid system of the Ordnance Survey of Northern Ireland.