What is wind power density and how it is calculated from wind data please explain briefly.

The wind power density is a calculation of the kinetic energy (the available energy) that moving air has per square unit of wind swept area. The typical unit is Watts per square meter (W/m^2).

The total kinetic of air is described by the equation:
KE = ½*ρ*A*(V^3)
Where ρ is the air density, A is the swept area of the turbine, and V is the average velocity of the wind.

The wind power density is described by
WPD = ½*K*ρ*(V^3)
Where the only difference is that the area has been removed in order to have the proper units and K is a value that described the shape of the distribution (Rayleigh/Weibull) of the wind speeds. This is because the power output increase is not proportional to a velocity increase in the wind – it is actually larger. Follow this link for a good discussion of this principle.

The K value is generally determined by a wind resource assessment but in wind application is often somewhere in the ball park of 2. By then plugging the number for the density of the area and the average wind velocity over the period of the measurements one can obtain the data for the wind power density at a given location.

For a longer but more detailed description of the wind power density see the Danish Wind Industry Association's "Guided Tour" webpage. Danish Wind Industry Association’s “Guided Tour” webpage. Under the link for “Energy Output” on the left side you will find all you need with regards to this question and much more. [URL=www.seic.okstate.edu/owpi_old/about/Library/Lesson3_WPD_windclass.pdf ]This classroom lesson[/URL] This classroom lesson about wind power density might also be helpful.

Hopefully this was helpful.

Christopher Bassett
Windustry