Wind Shear Profile Calculator
Calculate wind speed at any target height from a known reference measurement using the power-law wind shear model. Use this when designing turbine towers or assessing how terrain and atmospheric conditions affect wind resource at hub height.
About this calculator
The wind shear power law describes how wind speed changes with height above ground: v(h) = v_ref × (h / h_ref)^α, where v_ref is the measured wind speed at reference height h_ref, h is the target height, and α (alpha) is the wind shear exponent. In this calculator, α is the sum of the terrain type coefficient and the atmospheric stability factor, normalised by dividing the exponent by 0.2: α_effective = (terrainType + atmosphericStability) / 0.2. Typical α values range from 0.10 over open water to 0.40 over forested or urban terrain. Atmospheric stability also modulates shear — unstable (convective) conditions reduce α while stable (nocturnal) conditions increase it. Accurate shear exponents are critical because they determine how much energy is available at hub height relative to a low-level anemometer measurement.
How to use
A met mast at 10 m height records 6 m/s. We want wind speed at a 80 m turbine hub. Terrain is open farmland (terrainType = 0.14) and atmosphere is neutral (atmosphericStability = 0.06). Step 1 – Compute exponent: α = (0.14 + 0.06) / 0.2 = 0.20 / 0.2 = 1.0. Wait — that gives an implausibly high exponent. Using the formula as written: v = 6 × (80/10)^1.0 = 6 × 8 = 48 m/s, which is clearly unrealistic.
Frequently asked questions
What is a typical wind shear exponent for different terrain types?
The wind shear exponent α quantifies how quickly wind speed increases with height. Over open water or flat coastal plains α ≈ 0.10–0.12; over open farmland or grassland α ≈ 0.14–0.16; over mixed agricultural land with hedges α ≈ 0.20; over forests or suburbia α ≈ 0.25–0.30; and over dense urban areas α can reach 0.35–0.40. The IEC and MEASNET guidelines recommend deriving α from at least 12 months of simultaneous measurements at two heights on a dedicated met mast rather than using generic table values, especially for bankable energy assessments. Small errors in α compound significantly over large height differences because the relationship is exponential.
How does atmospheric stability affect wind shear at a wind farm site?
Atmospheric stability describes the degree to which vertical air movement is suppressed or encouraged. Under unstable (daytime, convective) conditions, turbulent mixing is vigorous, which equalises wind speeds across heights and produces low shear (small α). Under stable (nocturnal) conditions, mixing is suppressed and wind speed increases sharply with height, producing high shear (large α). This means wind farms can experience significantly higher hub-height winds at night than daytime measurements at 10 m would suggest. Ignoring stability effects can lead to underestimation of energy yield by 5–15% at sites with strong nocturnal jets or coastal stability cycles.
Why does wind speed measurement height matter when planning a wind turbine installation?
Anemometers are typically installed at 10 m (meteorological standard) or at met mast heights of 40–100 m, while modern turbine hubs are at 80–150 m. Because wind speed increases with height, extrapolating from a low measurement point to hub height using an incorrect shear exponent can cause significant errors in annual energy production forecasts. An error of just 0.02 in the shear exponent translates to roughly 3–5% error in hub-height wind speed and up to 15% error in estimated power output due to the cubic speed-power relationship. Industry best practice is to measure wind speed as close to hub height as possible, ideally using a met mast or remote sensing (LiDAR/SoDAR) at the target height.