Small wind / Buyer questions
Energy and economics
Does a wind direction record mean wind comes from or travels toward that direction?
The short answer
Meteorological wind direction normally identifies where the wind comes from. A north wind therefore arrives from the north. Some software arrows and engineering vectors instead point toward the direction of motion. Confirm the convention for each dataset and drawing before using it to decide which obstacles are upwind of a proposed turbine.
Check metadata rather than the arrow alone
Record the data provider's direction definition, angular reference and units. A map arrow may be drawn to show motion while a numeric field uses a from-direction convention. Both can be valid when labelled, but mixing them rotates the interpreted exposure.
Use an unambiguous test case in the processing notes. State which side of the proposed tower an obstacle occupies when a named direction is reported. This makes an otherwise abstract convention visible on the site plan.
Keep the geometric references consistent
Confirm whether site drawings and wind observations share the same north reference. Coordinate axes, local drawing orientation and instrument installation records may each need explanation. Do not correct a direction by an arbitrary offset just because a wind rose looks unexpected.
Separate environmental direction from nacelle heading or a control-system angle. Those signals can have their own zero positions and sign conventions. A resource dataset should not be assumed interchangeable with an equipment control variable.
Resolve the convention before assessing exposure
Overlay the interpreted incoming directions on the obstacle plan and review the sectors that matter most for useful energy. If a convention error is found, revise the affected plots and siting conclusions while retaining the original data and correction record.
The enquiry package should include a labelled wind rose, north arrow and a statement of direction convention. This avoids assessing the wrong side of a tree line or building as upwind. It also allows the supplier and site assessor to discuss orientation without inventing product-specific yaw behaviour.
Sources
- WMO Guide to Meteorological Instruments and Methods of Observation, hosted by NOAA
- U.S. DOE Small Wind Guidebook: resource and siting background
Examples are illustrative. Confirm product-specific performance, compatibility and supply scope in the applicable documents.