Is a default Weibull shape factor acceptable for every small-wind site?

The short answer

A default Weibull shape factor can support a clearly labelled preliminary scenario, but it is not measured evidence for every site. Two distributions with the same mean speed can allocate different time to the operating regions of a turbine curve. The assumed shape can therefore affect predicted annual generation.

Identify the distribution assumption

Record the mean speed, reference height, shape parameter and source of each value. Distinguish a parameter fitted to suitable site observations from one selected because software supplied it as a default. A familiar value does not remove uncertainty about local conditions.

Check whether the chosen distribution captures important features of the observed histogram. A smooth curve can look convincing while obscuring distinct weather regimes, directional effects or missing coverage.

Test sensitivity against the purchase decision

Hold the turbine curve, mean-speed basis and loss assumptions constant while varying the shape over a defensible range. Report how the resulting energy estimate changes and whether that change affects the preferred equipment or feasibility conclusion.

Do not select the shape that produces the most attractive payback and then present it as the site's distribution. If credible alternatives produce materially different project outcomes, better resource evidence may be more valuable than refining the quotation.

Keep annual energy and timing separate

A fitted annual distribution describes occurrence, not the chronological sequence of wind. It cannot establish how long calm events persist or whether generation coincides with a particular process schedule. Use an appropriate time series when those questions matter.

The report should identify the Weibull representation as measured, fitted or assumed, with its limitations and sensitivity results. This gives the buyer an honest screening estimate while leaving product-specific performance and site service requirements to the evidence needed for the actual project.