Wind Shear Profile Calculator
Estimate wind speed at any height using the power law or logarithmic model. Used by wind energy engineers and meteorologists to extrapolate anemometer readings to turbine hub height.
About this calculator
Wind speed increases with altitude due to surface friction — a phenomenon called wind shear. Two standard models describe this. The Power Law formula is: V = V_ref × (h / h_ref)^α, where V_ref is the known speed at reference height h_ref, h is the target height, and α is the shear exponent (typically 0.1–0.4 depending on terrain). The Logarithmic Law uses: V = V_ref × ln(h / z₀) / ln(h_ref / z₀), where z₀ is the surface roughness length. The power law is simpler and widely used in wind resource assessments; the log law is more physically rigorous over flat, homogeneous terrain. Choosing the right model and shear exponent is critical for accurately predicting energy yield at hub height.
How to use
Suppose a met mast measures 6 m/s at 40 m height, and you want to know the wind speed at a 100 m hub height using the power law with a shear exponent of 0.25. Enter: Reference Wind Speed = 6 m/s, Reference Height = 40 m, Target Height = 100 m, Model = Power, Shear Exponent = 0.25. Calculation: V = 6 × (100 / 40)^0.25 = 6 × (2.5)^0.25 = 6 × 1.257 ≈ 7.54 m/s. This ~25% increase in wind speed translates to roughly double the wind power density at hub height.
Frequently asked questions
What is a typical wind shear exponent for different terrain types?
The shear exponent α varies significantly with surface roughness. Over open water or flat coastal areas it is typically around 0.10–0.12, over open grassland about 0.14–0.16, over agricultural land with scattered obstacles around 0.20, and over forested or urban terrain it can reach 0.30–0.40. The IEC standard often assumes α = 0.20 as a neutral-atmosphere default for onshore sites. Using the wrong exponent can lead to significant over- or under-estimation of energy yield.
When should I use the logarithmic wind profile instead of the power law?
The logarithmic profile is preferred when you have a measured or well-estimated surface roughness length z₀ and the atmosphere is in neutral stability, which is common in moderately windy conditions. It has a stronger physical basis derived from boundary-layer theory. The power law is more convenient when you only have two-point wind measurements and want a simple empirical fit, especially for quick engineering estimates. For bankable energy assessments, many analysts run both models and compare results as a sensitivity check.
How does atmospheric stability affect wind shear calculations?
Both the power law and log law assume a neutrally stable atmosphere, where temperature decreases with height at the dry adiabatic lapse rate. In stable conditions (typically calm nights), wind shear is much stronger and α can exceed 0.4, meaning hub-height speeds are significantly higher than simple extrapolation suggests. In unstable conditions (hot sunny afternoons), turbulent mixing reduces shear and α may drop below 0.1. Ignoring stability effects can introduce errors of 5–15% in annual energy production estimates, so advanced site assessments use time-varying stability corrections.