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How do you calculate the efficiency of a wind turbine?
Mis à jour le
March 6, 2026
5
Min reading
Wind energy is one of the most promising renewable energies. Power generation from wind power plants is considered insufficient to cover global needs. Nevertheless, it remains interesting, especially for The energy mix necessary for the ecological transition in which France is committed.
Production principles, different types of wind turbines, power, annual production... SirEnergies invites you to discover the essentials about the efficiency of a wind turbine!
Some fundamental principles of wind turbine production
Wind energy: intermittent energy
Les wind turbines do not produce a constant amount of energy. Depending on the weather conditions, these windmills Modern ones generate more or less electricity. It is also possible that their production is zero, from where Intermittence wind energy.
Air mass, wind force and wind speed have a real impact on the quantity of energy produced by a wind turbine. The efficiency of this machine is also a factor to take into account. It's about its ability to convert rotation speed propellers into electricity without losing a large quantity of energy during the transformation.
Wind turbines are found in windy regions (on poorly protected plateaus) to optimize their performance. In France, Brittany, Occitanie and the PACA region are the most suitable regions for the installation of wind power plants.
How do you express the power of a wind turbine?
Power is one of the main criteria for comparing several energy sources. She is expressed in kilowatts (kW) contrary to the efficiency whose unit is kilowatt hours (kWh). La Power of a wind turbine is calculated using the following formula:
P = 1/2 x Rho x S x V
Here, P refers to the power and Rho the density of the air. The symbol “S” represents the area of the circle whose radius is equal to the length of a blade. Finally, V is the wind speed expressed in meters per second.
The efficiency of a wind turbine is the ratio of the energy usable by the device to the energy supplied to it. In other words, it is the quantity of energy that is actually produced by the device and is consumable at any time. The best returns are in the order of 65%.
What are the different types of wind turbines?
You are now familiar with calculating the power and mechanical efficiency of a wind turbine. What about the different versions of this machine and the quantity of electricity they can offer?
Horizontal wind turbine
In a horizontal wind turbine, the axis of the generator is lateral. The blades are therefore vertical, which increases their speed of rotation. It is the most common type of wind turbine.
The power of a horizontal wind turbine depends primarily on its size. The smallest models have a production capacity of around 100 kW. The largest machines, on the other hand, produce up to 7.5 MW. The average power of horizontal wind turbines therefore oscillates between 1 and 3 MW.
Vertical wind turbine
THEvertical wind turbine looks like a wing whose blades are aerodynamic. We mainly distinguish three forms:
- The Darrieus wind turbine,
- The Savonius wind turbine,
- The rotating wing wind turbine.
The first form of vertical wind turbine is designed to withstand the most violent winds. The Savonius wind turbine works even with a low rotation speed. The blades of the rotary wing wind turbine also adapt to the winds and are oriented accordingly. The power of a vertical wind turbine rarely exceeds 1 MW.
Domestic wind turbine
The home wind turbine is designed horizontally or vertically depending on the manufacturer. Its power is between 100 W and 20 kW. In terms of efficiency, a 5 kW machine can generate between 5,000 and 20,000 kWh per year if it is well maintained. THEDomestic wind turbine is therefore an energy source to be taken into account in the future!
What is the power of a wind turbine?
The amount of energy produced by a wind turbine varies from hour to hour depending on the strength of the wind. So power is not enough to choose this machine. You need to take into account the quantity of electricity produced over a large time scale: The yield.
Power calculation
We have already analyzed the formula for the power of a wind turbine. Here, we are interested in what affects the power output or performance of this device.
La Wind speed allows you to rotate the blades of a wind turbine. The minimum required varies between 10 and 15 km/h. However, the wind turbine stops when the winds exceed 90 km/h.
Wind turbines should be located in windy areas, especially if it is a wind farm. The height of the mast as well as the size of a wind turbine impact its rotation speed. The same is true for the density of the air (Rho) which varies according to the pressure, temperature and humidity of the air.
Several other elements can change the performance of a wind turbine. It is about:
- mechanical efficiency of the turbine,
- Electrical efficiency of wind turbines,
- Number of blades and inclination...
La Betz limit must be taken into account to prevent the wind from leaving the wind turbine at the same speed as that with which it enters it. However, the rotor diameter is one of the key factors in obtaining optimal performance with this device.
Rotor diameter
The rotor is the rotating zone of a wind turbine. It is located high up in order to catch strong and regular winds. Most often composed of 3 blades, it is set in motion thanks to the kinetic energy of the wind.
The rotor diameter is nothing more than twice the radius constituted by its blades. Its importance? The amount of energy generated when wind passes through this component is proportional to its surface area. In other words, wind power is generated exponentially with respect to the radius of each blade.
How to calculate the annual production of a wind turbine?
It is not possible to accurately calculate the annual production of a wind turbine, as it depends mainly on wind speed. However, you can estimate this value assuming that energy production varies practically with m³ of wind speed.
For example, a speed of 4.5 m/s at hub height allows the wind turbine to produce up to 0.5 GWh per year, or 500,000 kWh. With 9 m/s, the device can generate up to 2.4 GWh per year, or 2,400,000 kWh.
The second method to know the annual production of a wind turbine is to take into account its Capacity factor on its location site. In other words, you must relate the annual power output of the device to its maximum theoretical production over the 8,766 hours of the year.
Take the example of a 600 kW wind turbine producing 1,500,000 kWh per year. Here, the maximum theoretical output is: 365.25 x 24 x 600 = 5,259,600. The capacity factor is: 1,500,000/5,259,600 = 0.285, or 28.25%.
Wind energy is thus an intermittent energy whose efficiency depends on several factors. However, one may ask what is the most ecological source of energy.
To go further, do not hesitate to consult our article on Offshore wind.
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