Small wind / Buyer questions
Energy and economics
What if a site has two distinct wind-speed regimes instead of one smooth distribution?
The short answer
When a site has two distinct wind regimes, one fitted smooth distribution may conceal information relevant to energy or load matching. That does not automatically make the fit unusable. It means the analyst should test whether the simplified representation preserves the outcomes that the project decision depends on.
Inspect the structure before fitting
Plot the observed speed histogram and examine the associated direction, season and time of day where data quality permits. Distinct peaks may reflect separate weather patterns, but they can also arise from processing errors or mixed measurement configurations. Resolve those alternatives before assigning a physical explanation.
Keep sample coverage visible. A small collection of strong-weather observations should not be treated as a stable second regime without sufficient supporting evidence.
Compare the simplified and retained representations
Calculate the relevant result using the observed distribution or time series and compare it with the fitted representation under the same turbine and loss assumptions. Identify which speed regions account for any difference.
For a process active only in one season, examine that season separately. An annual fit that reproduces annual energy reasonably well may still misrepresent when the generation is available. The acceptable simplification depends on the question, not solely on the visual smoothness of the curve.
Choose a model with an explicit purpose
A preliminary annual comparison may tolerate a simplified distribution with a documented error range. A service assessment sensitive to calm persistence or operating windows generally needs chronological evidence. Avoid adding model complexity that the data cannot support.
The deliverable should retain the observed distribution, the fitted assumptions and the comparison of decision-relevant outputs. This allows a buyer to judge whether the simplification is adequate without confusing an elegant statistical fit with validated site conditions or guaranteed turbine generation.
Sources
- System Advisor Model documentation: wind-resource inputs and time-series limitations
- NREL wind-resource assessment report: measurement analysis and long-term correlation
Examples are illustrative. Confirm product-specific performance, compatibility and supply scope in the applicable documents.