Wind Speed and Power Relations

we can make a relation using equation of energy kinetic, The kinetic energy in air of mass (M) ・moving with speed V is given by the following equation in SI units :



The power in moving air is the flow rate of kinetic energy per second Therefore:


Which :

P = mechanical power in the moving air
rho = air density, kg/m3
A = area swept by the rotor blades, m2
V = velocity of the air, m/s
then, the volumetric flow rate is A.V, the mass flow rate of the air in kilogramsper second is rho.A.V, and the power is given by the following:



Two potential wind sites are compared in terms of the specific wind power expressed in watts per square meter of area swept by the rotating blades. It is also referred to as the power density of the site, and is given by the following expression:

This is the power in the upstream wind. It varies linearly with the density of the air sweeping the blades, and with the cube of the wind speed.