Wind Resource Assessment Calculator
Estimate the energy density of a wind site using average wind speed and the Weibull shape parameter. Use this when evaluating whether a location has sufficient wind potential for turbine installation.
Last updated: September 2026
Formula below · 2 sources (energy.gov, Wikipedia) · Updated Sep 2026
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About this calculator
Wind energy potential is not simply proportional to average wind speed — it scales with the mean of the cube of the speed, which is always larger than the cube of the mean. This calculator models the speed distribution with a Weibull distribution of shape k and scale c = v̄ / Γ(1 + 1/k), for which the mean cubed speed is: mean(v³) = c³ × Γ(1 + 3/k) = v̄³ × Γ(1 + 3/k) / Γ(1 + 1/k)³. For k = 2 (Rayleigh) the factor is 1.91, so the mean power density is almost twice what the average speed alone suggests; for steadier winds (k = 3) it is 1.40. Mean wind power density = 0.5 × ρ × mean(v³), with sea-level air density ρ = 1.225 kg/m³ (reduce it about 10% per 1,000 m of elevation). Sites above about 300–400 W/m² at hub height (NREL Class 3–4 at 50 m) are generally considered viable for utility-scale wind.
How to use
Suppose a coastal site has an average wind speed of 7 m/s and a Weibull shape parameter of 2.0 (a typical value for many sites). Step 1: Cube the wind speed: 7³ = 343. Step 2: Weibull factor for k = 2: Γ(1 + 3/2) / Γ(1 + 1/2)³ = 1.3293 / 0.8862³ = 1.910. Step 3: mean cubed speed = 343 × 1.910 ≈ 655.1 m³/s³. Step 4: power density = 0.5 × 1.225 × 655.1 ≈ 401 W/m², an NREL Class 4 (good) resource at 50 m. Using 7 m/s directly without the Weibull factor would give only 210 W/m².
Frequently asked questions
What is the Weibull shape parameter and how does it affect wind resource assessment?
The Weibull shape parameter (k) describes how concentrated or spread out the wind speed distribution is at a site. A k value of 2 is called the Rayleigh distribution and is a common approximation for many wind sites worldwide. Higher k values (above 2.5) indicate steadier winds, which generally produce more predictable and higher energy yields. Lower k values mean more variable winds: for the same mean speed they actually raise the mean power density in the air (more energy arrives in strong gusts), although a real turbine captures less of it because it caps output above rated speed and stops above cut-out.
How does average wind speed relate to wind power density at a site?
Wind power density is proportional to the cube of wind speed, not the average speed itself — this is a critical distinction. Because of this cubic relationship, a site with 8 m/s average speed has roughly twice the power potential of a 6.3 m/s site. The Weibull-corrected mean cubic speed accounts for the full distribution of speeds experienced over time, giving a more accurate picture of energy potential than average speed alone. Engineers use this metric when screening sites before committing to expensive measurements or turbine installations.
What wind resource assessment values indicate a commercially viable wind site?
A site is generally considered commercially viable when its wind power density exceeds 200–300 W/m² at hub height, corresponding to average wind speeds above roughly 6–7 m/s. Class 3 wind resources (mean speed ~6.4 m/s at 50 m) are typically the minimum threshold for utility-scale development. Sites with power densities above 400 W/m² (Class 4 and above) are considered excellent. Local terrain, turbulence intensity, and grid access also influence final viability alongside raw resource quality.