Wind
Energy Learning Center
1. How is wind created?
Wind is actually a form of solar energy. Wind comes from temperature differences caused by differential heating of the
atmosphere by the sun. Different surfaces heat at different rates (land vs water). Hot air rises, reducing the atmospheric
pressure at the Earth's surface, cooler air replaces it creating . . . of course, WIND.
2. What is a wind turbine?
A wind turbine is a device that uses blades to catch or stop (convert) a percentage of the winds kinetic energy. The wind
flows around the blades causing lift and starting the blades to rotate. The blades are typically connected to a rotor shaft
that turns a set of magnents inside a stator. Similiar to an alternator, this rotating motion produces electricity. There are
several different wind turbine designs, but most operate on the same prinicpal.
3. What is "wind energy"?
Another way to ask that question: How much power is in the wind?
Good question. We start by discussing kinetic energy as mentioned earlier. Kinetic energy is a function of mass and
velocity.
Kinetic energy (joules) = 0.5 x m x V2
where:
m = mass (kg) (1 kg = 2.2 lbs)
v = velocity (m/sec) (meter = 3.281 ft. = 39.37 inches)
Answering the question of Wind Power (energy = power x time). We need to understand the power is the area swept by
the wind turbine rotor blades.
Wind turbine power (p) = 0.5 x rho x A x V3
where:
p = power in watts (746 watts per 1 hp) (1000 watts = 1 kilowatt (kW))
rho = air density (~ 1.225 kg/m3 at sea level, less at higher elevations)
A = rotor swept area (m2)
V = wind speed (m/s) (20 mph = 9 m/s or mph/2.4 = m/s)
We need to add one more variable to the equation. Cp = coefficient of performance = (.59 {Betz Law} or maximum
efficiency theoretically possible) We will come back to Mr. Betz later.
The new equation:
Wind turbine power (p) = 0.5 x rho x Cp x A x V3
Break Time: I'll add more soon!