Wind energy is of the fastest-growing clean energy solutions, and wind turbines are one of the best ways to harness the unbelievable power of wind energy.
But how much energy can we extract from the wind? And how efficient are wind turbines in doing so?
According to the U.S. Wind Turbine Database, the mean turbine capacity in 2020 is 2.75 megawatts (MW). At a 42% capacity factor, an average turbine generates over 843,000 kWh per month. In other words, an average wind turbine produces enough energy to power 940 average U.S. homes! This is assuming that the average U.S. home uses 893 kilowatt-hours (kWh) of electricity per month.
If we dive into the numbers behind wind turbine energy production, we can find out just how much energy they produce and what factors affect their output.
Factors affecting the energy output of wind turbines
Some factors are related to the wind turbine itself and its components, while others have more to do with factors outside of human influence. Here are some of those factors:
Average Wind Speed
The faster the wind, the faster the rotor in the wind turbine will rotate, resulting in more energy output.
The lower the air density, the weaker the wind, and vice versa.
Weaker wind won’t generate enough lift power to rotate the blades, which means that the rotor will spin slower, and you will receive less energy output.
Wind turbines operate optimally in temperatures ranging between -20 to 50 degrees celsius.
If the temperature exceeds that range, the air density will be lower, which will result in less energy output, as we discussed earlier.
In 1919, a German physicist named Albert Betz did some calculations and concluded that the maximum energy harnessed from wind wouldn’t exceed 59.3% of the wind’s kinetic energy. This is known as the Betz limit.
In other words, the best wind turbine a man can make is capable of extracting only 59.3% of the wind’s kinetic energy (wind speed X cross-sectional area).
This limit applies to any wind turbine, no matter how big or small it is, and to this day, the best wind turbines can only achieve 70-80% of the Betz limit (i.e. 40% of the wind’s kinetic energy).
As you know, wind is much faster at higher altitudes. This means that the higher the tower, the faster the wind. In turn, the rotor will rotate faster, resulting in increased energy output.
Longer blades allow wind turbines to sweep more area and capture more wind, which results in increased energy output.
The gearbox transfers rotational energy from the rotor to a generator, producing electricity.
The more efficient the gearbox is, the less energy it will waste on heat and friction, thus increasing the energy output of the wind turbine.
The more efficient your generator is at converting the energy from motion to electric power, the more electricity you will get.
How much power does a wind turbine generate?
Wind turbines come in models and different sizes, each with unique efficiencies and blade lengths, so it can be difficult to measure the exact output of every type of wind turbine.
Using this equation, we can calculate the theoretical power output of a wind turbine with any known parameters.
P = Power output
Cp = Maximum power coefficient (0.25 to 0.45)
ρ = Air density
A = Rotor swept area
V = Wind speed
k = 0.000133
To save you the trouble, we made a list of wind turbine output for several sizes of turbines:
|Rotor Diameter/m||Tower Height/m||Rated Power/kW||Annual Production/MWh|
Note: These numbers are theoretical. They are merely here to give you an idea of what the different physical specifications will achieve in energy output.
While the numbers themselves are just theoretical, the equations used to calculate them are not. These same equations have been in use for a while now and are reliable.
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So how many wind turbines would we need to power all of the houses in the US?