Why must wind-speed bins specify which boundary values they include?

The short answer

Bin boundaries must be defined so a value exactly on an edge is neither omitted nor counted twice. A table labelled only 4–5 and 5–6 does not state where a reading of 5 belongs. The rule matters when rounded data or many repeated values concentrate at boundaries.

Write an unambiguous assignment rule

For example, a workflow can include the lower boundary and exclude the upper boundary for ordinary bins, with an explicitly handled final bin. Another consistent convention can also work. The important requirement is that every valid observation has one intended assignment.

Define how below-range, above-range and missing values are handled. A missing-data marker must not accidentally enter the lowest wind-speed class, and a value at the top edge should not disappear silently.

Test edge cases before using the full record

Create a small verification set containing values just below, exactly at and just above several boundaries. Confirm the assigned bins, the represented duration and the total count. Use the same unit and rounding stage as the production calculation.

Then reconcile the sum of bin durations with the valid source duration. A mismatch signals a processing issue to investigate before the power curve is applied. Matching totals alone is useful but does not prove every row was assigned correctly.

Keep the convention consistent across comparisons

Apply the same rule to alternative turbines, seasons and later campaign extensions unless a documented method requires a change. Otherwise an apparent resource difference may partly reflect a changed grouping convention.

Include bin definitions in the assessment handover rather than only a chart image. If an earlier calculation omitted or duplicated boundary observations, correct the affected energy outputs and retain the revision record. This preserves the distinction between a data-processing correction and a real change in the wind available to the project.