basic calculation that needs to be done before calculating more detail when designing wind tubines is to calculate the power requirements and power that can be generated from wind turbine currently in design, some things that need to be considered in the calculation of wind power is
1) The power output of a wind generator is proportional to the area swept by the rotor - i.e. double the swept area and the power output will also double.
2) The power output of a wind generator is proportional to the cube of the wind speed - i.e. double the wind speed and the power output will increase by a factor of eight (2 x 2 x 2)

picture above shows the direction and also a component of the wind turbine through which the wind well or not,

The Power of Wind

Wind is made up of moving air molecules which have mass - though not a lot. Any moving object with mass carries kinetic energy in an amount which is given by the equation:

Kinetic Energy = 0.5 x Mass x Velocity2

where the mass is measured in kg, the velocity in m/s, and the energy is given in joules.

Air has a known density (around 1.23 kg/m3 at sea level), so the mass of air hitting our wind turbine (which sweeps a known area) each second is given by the following equation:

Mass/sec (kg/s) = Velocity (m/s) x Area (m2) x Density (kg/m3)

And therefore, the power (i.e. energy per second) in the wind hitting a wind turbine with a certain swept area is given by simply inserting the mass per second calculation into the standard kinetic energy equation given above resulting in the following vital equation:

Power = 0.5 x Swept Area x Air Density x Velocity3

where Power is given in Watts (i.e. joules/second), the Swept area in square metres, the Air density in kilograms per cubic metre, and the Velocity in metres per second.

However, there’s no way to harvest ALL of this available energy and turn it into electricity. In 1919 a gentleman named Betz calculated that there’s a limit to how much power a turbine blade can extract from the wind. Beyond the Betz Limit of 59.26% energy extraction, more and more air tends to go around the turbine rather than through it, with air pooling up in front. So 59.26% is the absolute maximum that can be extracted from the available power.
Simply put, if you capture 100% of the energy available in the wind, you stop the wind.  Obviously, the wind will stop flowing through such a turbine.  The opposite of that is that if you don't capture any energy in the wind, you don't need a turbine.  The wind is able to flow around any major obstruction.  The Betz limit says that essentially, if you capture 59.6% of the energy in the wind, that is the best compromise between stopping the air and forcing it to go around your machine.  You need to maintain the flow of air, that's the compromise any wind machine must make whether it is a horizontal axis (traditional style turbine) or vertical axis turbine, with many blades or few, or any such combination.  It's covered by the Betz limit.

More Detail in PDF Tutorial also available from Oklahoma University just Download Here

The design of blades attached with the rotor also contributes towards an effective wind turbine design. Apart from the shape and weight of these blades, it is also important to consider the material used for manufacturing them. As far as number of blades is concerned, two or three-blade wind turbines are the most popular ones in the industry.


  1. Industry Analysis // August 14, 2012 at 1:53 AM  

    very detail study related to calculation of wind power..very brief description provided here.It's really useful for gaining more knowledge about wind power energy..I really appreciate for your best efforts..keep updating such valuable post for us

  2. Layne // January 12, 2013 at 9:04 AM  

    This is a very detailed study of the wind turbine. I was wondering if you had any documentation on his subject.

  3. Krista Hiles // December 2, 2013 at 12:47 AM  

    This is very informative post. It enhances my knowledge about wind energy. I really appreciate your hard work. Keep posting.

    Power plant transition management

  4. WindQuest // January 30, 2015 at 3:01 AM  


    I have some questions about the wind energy calculations. I have checked this site and other sources in the past. Here is the basic formula that I know is used for turbines. And I think, it would also apply to fixed panels:

    P = 1/2 ρ A v3 cp


    P = power (W)

    ρ = density of air (kg/m3)

    A = area wind passing through perpendicular to the wind (m2)

    v = wind velocity (m/s)

    cp = efficiency (theoretical limit is 59.3 per Betz Law)

    To get the Actual Power, we need to know the actual efficiency of the turbine (which is always lower than the theoretical Betz Limit).

    What I need to confirm:

    If this formula is applicable to the fixed panels (square or rectangular shaped), then what is the actual efficiency?

    If the fixed panel now is a swinging panel (along the top edge), then how much of the wind energy is transferred to the swinging panel?

    How much does the "swinging panel" swing out (for now, assuming the panel is very light weight)?