What is a good wind power density for a wind farm?

Generally, sites with WPD above 400 W/m² (NREL Class 4) are considered commercially viable for utility-scale wind. Class 5 (500–600 W/m²) and above are excellent. Class 3 (300–400 W/m²) may work for community or small commercial projects.

Why does wind speed have a cubic effect on power?

Kinetic energy is proportional to v², and power is energy per unit time, so when more air arrives per second (proportional to v), the total power scales as v × v² = v³. Doubling wind speed increases power density eightfold.

What air density should I use?

Sea level at 15 °C is 1.225 kg/m³ (standard atmosphere). Air density decreases roughly 1.1 % per 100 m of elevation and also decreases with temperature. For quick estimates use 1.225; for a real site use 1.2929 × 273.15 / (273.15 + T_celsius) × P_Pa / 101325.

How does this relate to actual turbine output?

WPD is the theoretical limit. A real turbine captures only a fraction: multiply WPD × Rotor Area × Cp (power coefficient, typically 0.35–0.45) × drivetrain efficiency. The Betz limit sets an absolute ceiling at Cp = 0.593.

What are the IEC wind speed classes?

IEC 61400-1 defines turbine design classes by reference wind speed (50 m/s for Class I, 42.5 m/s for Class II, 37.5 m/s for Class III). NREL's wind resource classes (1–7) are based on WPD at 50 m hub height and are more commonly used for site suitability ratings.

Wind Power Density Calculator

Calculate wind power density (W/m²) from wind speed and air density to classify wind resource potential.

Site Parameters

Wind Speed

Air Density (kg/m³)

Standard sea-level air at 15 °C = 1.225 kg/m³

Estimate air density from altitude & temperature

Altitude (m above sea level)

Temperature (°C)

Rotor Diameter (m) (optional)

Wind Power Density

Enter parameters and click Calculate.

NREL Wind Resource Classes (50 m hub height)

Class	WPD (W/m²)	Description
1	< 200	Poor — generally not viable
2	200–300	Marginal
3	300–400	Fair — small/community wind
4	400–500	Good — utility-scale viable
5	500–600	Excellent
6	600–800	Outstanding
7	> 800	Superb — offshore / mountain ridge

Summary

Wind power density (WPD) measures the available wind energy per unit area swept by a turbine rotor, expressed in watts per square meter (W/m²). It is calculated as P/A = ½ × ρ × v³, where ρ is air density and v is wind speed. WPD is the standard metric used by wind energy engineers to compare site quality before committing to turbine installation.

How it works

Enter the mean wind speed at hub height in meters per second (m/s) or miles per hour.
Enter the air density at the site — standard sea-level air is 1.225 kg/m³, but elevation and temperature reduce it.
The calculator applies the wind power density formula: WPD = 0.5 × ρ × v³.
The result is displayed in W/m² alongside the IEC/NREL wind resource class (Class 1–7).
Use the class rating to compare candidate sites and decide whether installation is economically viable.

Use cases

Pre-feasibility screening of onshore and offshore wind farm sites.
Comparing multiple candidate locations using the same air-density-adjusted metric.
Translating anemometer readings into energy-density figures for reports.
Teaching students and engineers the cubic relationship between wind speed and power.
Adjusting for high-altitude or tropical sites where air density differs from 1.225 kg/m³.
Estimating power available before applying turbine efficiency (Betz limit, rotor Cp).

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu