Meteorological mast

A meteorological mast, universally a met mast, is an instrumented tower carrying anemometers, wind vanes, and temperature and pressure sensors at several heights. Before a wind farm is built it is the primary source of the resource measurement behind an energy yield estimate and its P50 and P90 figures. After construction it is the reference against which turbine performance can be independently checked.

It matters because it is not attached to a turbine. A mast in undisturbed flow measures the wind the machines are actually offered, rather than the wind a nacelle anemometer sees after the rotor has taken energy out of it. That independence is what makes a warranted power curve test under IEC 61400-12 meaningful.

Masts are expensive to build and maintain, so many operating sites have one at most, and some have decommissioned theirs after the resource campaign ended. Ground-based remote sensing using lidar or sodar is increasingly used in their place and is accepted under the current standard for many purposes, with the advantage that a unit can be moved between positions.

For a fleet with no reference measurement at all, the practical substitute is the fleet itself. Neighboring turbines experiencing the same weather provide a relative reference that is good enough to detect a drifting sensor or a machine losing output, even where no absolute measurement exists - which is the situation most operating portfolios are actually in.