Estimate electrical power at a specified wind speed and, with rated power or wind-distribution data, daily and annual energy. Compare HAWT or VAWT scenarios in metric or US units; all calculations stay in your browser.
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Worked wind turbine examples
Small residential HAWT — metric
Assume D = 2.8 m, v = 6.5 m/s, ρ = 1.225 kg/m³, Cp = 0.40, generator efficiency = 90%, rated power = 1 kW, and capacity factor = 25%.
Swept area: A = π × (2.8 ÷ 2)² = 6.16 m².
Available wind power: ½ × 1.225 × 6.16 × 6.5³ = 1,035 W.
Rotor mechanical power: 1,035 × 0.40 = 414 W.
Generator output: 414 × 0.90 = 373 W at that operating point.
This is a screening example. A real purchase decision should use measured hub-height wind and the specific manufacturer's certified power curve.
How to use and check the calculation
Choosing inputs
Use rotor diameter for a HAWT, not one blade's length. For a VAWT, enter both projected rotor width and height. Use wind measured at hub height when possible; otherwise, the advanced height correction provides a screening estimate.
Formula and variables
Pwind = ½ρAv³ Protor = Pwind × Cp Pdelivered = Protor × η × site multipliers
ρ is air density, A is swept area, v is hub-height wind speed, Cp is rotor aerodynamic performance, and η is drivetrain/generator efficiency.
Power versus energy
W, kW, and MW are instantaneous power. Wh and kWh are accumulated energy. Capacity-factor mode always uses rated kW × 8,760 × capacity factor. Distribution mode calculates expected average power across wind bins and then annual energy.
Manufacturer power curves
Prefer a curve measured for the exact turbine under a recognized standard such as IEC 61400-12-1. Paste speed/output pairs in distribution mode; the calculator interpolates between them and applies cut-in and cut-out. Check whether the published curve is gross electrical, net electrical, or corrected to a reference air density.
Why an annual mean cannot be cubed
The average of v³ is not the cube of average v. A year containing calm periods and strong winds therefore cannot be represented by inserting one annual mean into the cubic formula. Rated clipping and cut-out shutdown make the mismatch larger.
Realistic assumptions and mistakes
Do not confuse Cp with capacity factor.
Do not apply losses twice if a capacity factor or curve is already net.
Keep cut-in < rated < cut-out.
Do not assume the cubic curve continues above rated output.
Account for obstacles, turbulence, downtime, wiring, icing, and long-term variation.
Wind turbine calculator FAQ
What is the difference between wind turbine power and energy?
Power is the instantaneous rate of output in W or kW. Energy is power accumulated over time in kWh. Annual energy requires a rated-power capacity factor or a wind-speed distribution combined with a power curve.
Is rotor diameter the same as blade length?
No. Rotor diameter spans the full circle swept by the blades and is approximately twice the blade radius on a HAWT.
What are typical Cp and capacity factor values?
Cp is an operating-point aerodynamic coefficient and is often about 0.25 to 0.45 for small wind calculations. Capacity factor is annual energy divided by rated power times 8,760 hours and depends strongly on the turbine and site.
What is the Betz limit?
The Betz limit is the theoretical maximum fraction of wind power an ideal rotor can capture: 16/27, or about 59.3 percent.
What do cut-in, rated, and cut-out wind speeds mean?
Cut-in is where generation begins, rated speed is where the turbine first reaches nameplate output, and cut-out is where it shuts down for protection.
Can annual average wind speed be cubed to estimate annual energy?
No. Because power is nonlinear and turbines have control limits, cubing one annual mean loses the frequency of low, high, and shutdown winds. Use a distribution and power curve.
How do HAWT and VAWT swept areas differ?
A horizontal-axis turbine uses circular area π × diameter² ÷ 4. A vertical-axis turbine commonly uses projected area equal to rotor diameter × rotor height.
How much energy may a 1 kW wind turbine generate?
At a 20 percent capacity factor, a 1 kW turbine produces about 1,752 kWh per year before any losses not already represented in that capacity factor.
What size wind turbine could support a home?
Divide annual household use by the site's expected annual kWh per rated kW, then confirm with measured hub-height wind data and manufacturer energy estimates. Site quality can matter as much as nameplate size.
Why does actual wind production differ from this estimate?
Turbulence, wakes, icing, downtime, electrical losses, air density, control behavior, wind direction, long-term variability, and differences between an assumed and certified power curve all affect production.
Methodology, review, and limitations
Author: Starlight Tools Editorial Team (technical calculator documentation)Technical reviewer: Starlight Robotics Technical Review (engineering-model and software QA)Published: 14 July 2026Reviewed: 14 July 2026
The operating-point model follows the standard kinetic wind-power relationship. The annual distribution model converts the entered mean to a Weibull scale parameter, finds the probability mass in 0.25 m/s bins, evaluates the calculated or pasted power curve at each midpoint, and sums expected output. Rayleigh is Weibull with k = 2. Capacity-factor mode is deliberately independent of the one-speed result.
Sources: The US Department of Energy's Small Wind Guidebook covers Cp, air density, wind shear, Rayleigh energy curves, turbulence losses, and why annual estimates use a turbine curve plus a wind-frequency distribution. NREL's Annual Technology Baseline describes Weibull distributions combined with turbine power curves for AEP. IEC 61400-12-1:2022 defines power-performance measurement procedures and uncertainty assessment.
Limitations: This is a deterministic screening estimate, not a certified yield assessment, structural design, or financial recommendation. Rayleigh/Weibull may not fit a complex site; pasted curves are not density-corrected; directional effects and uncertainty are not modeled. Select turbines using measured long-term hub-height data, certified manufacturer curves, and a qualified site assessment.
