Wind at Your Site
How windy is it really where you are, and what would a turbine make there? Every hour of a typical year is used: the wind speed and direction measured at 10 m, carried up to the hub, the air density from the temperature and pressure, and the turbine’s output hour by hour. See how often each wind speed blows, where the wind comes from and how the yearly energy compares with the textbook estimate.
Why the Average Wind Is Not Enough
Power grows with the cube of the wind speed, so a few stormy hours bring more energy than many calm ones. Two places with the same average wind can give very different yields, depending on how the wind is spread: a steady coastal wind or a gusty inland one. Wind engineers describe that spread with the Weibull distribution and its shape factor k; the textbook shortcut uses k = 2 (the Rayleigh distribution).
Height matters just as much: the ground slows the wind, so a hub at 120 m sees far more than a weather station at 10 m, especially over rough land. And cold, dense air carries more power than warm air at the same speed.
The Wind at Your Site, Step by Step
m/sAssumptions of This Model
| Assumption | In reality… |
|---|---|
| The wind at 10 m: the hourly values of the PVGIS typical year (from the ERA5 weather model, a grid of about 30 km) | ERA5 smooths out hills, coasts and local effects; the typical year was chosen for its sunshine and temperature, not for its wind. Checked: for Amsterdam ERA5 gives 4.4 m/s, between the measured 4.9 m/s at open Schiphol and 3.4 m/s at sheltered De Bilt (KNMI, 2005–2020). A cell on the coast can be partly sea: near Cape Town it gives a capacity factor of about 69% over farmland, far above the 35–47% of real South African wind farms |
| From 10 m to the hub with the logarithmic profile over one roughness z₀ (neutral air) | at night the air is often stable and the wind grows faster with height; a mixed landscape needs a site measurement or a mast at hub height |
| Air density each hour from the mean surface pressure of the cell, lowered for the hub height (8.4 km scale height), and the hour’s temperature; dry air | humid air is slightly lighter; pressure varies a few percent with the weather |
| The turbine gives ½ρAv³·Cₚ up to its rated power, nothing below cut-in or above cut-out; no losses | the real power curve rounds off near rated; wakes of other turbines, downtime and cables cost about 10–20%. Real Dutch onshore wind farms reach capacity factors of about 24–30% (IEA Wind, CBS), partly with older, lower turbines |
| Weibull k and A fitted from the mean and the spread of the hourly hub-height wind (method of moments) | other fitting methods give slightly different values; the energy itself is computed from the hours, not from the fit |
Key Relations
The logarithmic wind profile: the rougher the ground, the more the wind grows with height.
Ideal gas law for dry air: colder air and lower altitude mean denser air and more power.
k describes how the wind is spread (higher = steadier), A is the scale. The Rayleigh shortcut is k = 2.
The mean power per square metre of rotor in the wind, before the Betz limit and the turbine.
Sources & Verification
- PVGIS 5.2, European Commission Joint Research Centre — typical meteorological year with hourly 10-m wind speed and direction, air temperature and surface pressure (from ECMWF ERA5). PVGIS © European Union, 2001–2026.
- C. G. Justus, W. R. Hargraves, A. Mikhail & D. Graber, “Methods for estimating wind speed frequency distributions”, Journal of Applied Meteorology 17(3), 350–353 (1978) — k = (σ/v̄)−1.086.
- J. F. Manwell, J. G. McGowan & A. L. Rogers, Wind Energy Explained, 2nd ed., Wiley, 2009 — wind shear, Weibull statistics, energy production estimates.
Frequently Asked Questions
How windy is my location?
Pick your place and the calculator uses the hourly wind of a typical year at 10 m (from the ERA5 weather model via PVGIS) and carries it up to the hub. In Amsterdam the wind at 10 m averages about 4.4 m/s; at a 120 m hub over farmland that becomes about 6.8 m/s.
How much energy would a wind turbine make at my location?
Hour by hour over a typical year: a 3 MW turbine with a 112 m rotor at 120 m makes about 9.5 GWh a year in Amsterdam (capacity factor 36%), about 1.6 GWh in Madrid, where it is much calmer inland, and about 5.9 GWh near London (capacity factor 22%). Real wind farms lose another 10–20% to wakes, downtime and cables.
What is the Weibull distribution of wind speeds?
A curve for how often each wind speed blows, with a shape factor k and a scale A. Steady winds have a high k, gusty winds a low k; the textbook shortcut (Rayleigh) assumes k = 2. In Amsterdam the hourly data give k ≈ 2.2, in Madrid ≈ 1.9; using Rayleigh instead of the real hours misjudges the yearly energy by about 3% in Amsterdam and 10% in Madrid.
What is a wind rose?
A compass diagram showing how often the wind blows from each direction. Because power grows with the cube of the speed, the directions of the strong winds bring most of the energy: in Amsterdam the south-west brings about 17% of the energy in about 14% of the hours. Turbines in a wind farm are spaced furthest apart along that direction.
Why does air density matter for wind power?
The power in the wind is ½ρv³, so denser air carries more power at the same speed. Cold air is denser than warm air, and air is thinner at altitude: at Madrid's 650 m the density at the hub is about 1.13 kg/m³, against about 1.23 near sea level in Amsterdam, almost 8% less power at the same wind speed.