THE WIND POWER BOOK

Article Tools

Image Gallery

Print

E-mail

Comments

RSS

10,000

KWH 3, 413

3,413

Rarely is it a simple task to estimate the wind energy available at a particular site ...the windspeed is constantly changing. During one minute, 300 watts of power may be generated by a windmill, or 300 watt-minutes of energy (which equals 5 WH). During the next minute the wind may die, and you get absolutely no energy or power from the machine. The power output is constantly changing with the windspeed, and the accumulated wind energy is increasing with time. The wind energy extracted by the machine is the summation or total of all the minute-by-minute (or whatever other time interval you care to use) energy contributions. For example, if there are 30 minutes during a particular hour when the windmill is generating 5 WH and another 30 minutes when there is no energy generated, then the machine generates 150 WH (5 X 30 = 150) of wind energy. If there are 24 such hours a day, then 3,600 WH or 3.6 KWH are generated that day.

WIND ENERGY AND WIND POWER

Energy and power are derived from the wind by making use of the force it exerts on solid objects, pushing them along. Buildings designed to stand still against this force extract very little energy from the wind. But windmill blades are designed to move in response to this force, and wind machines can extract a substantial portion of the energy and power available.

The wind energy available in a unit volume (one cubic foot or one cubic meter) of air depends only upon the air density p (Greek "rho") and the instantaneous windspeed V. This "kinetic energy" of the air in motion is given by the formula

Kinetic Energ y

= 1/g X p X V'

Unit Volume

To find the kinetic energy in a particular volume of air, you just multiply by that volume. The volume of air that passes through an imaginary surface —say the disk swept out by a horizontal-axis windmill oriented at right angles to the wind direction is equal to

Volume- A X V X t

where t is the elapsed time (in seconds) and A is the area (in square feet or square meters) of the surface in question. Thus, the wind energy that flows through the surface during time t is just

Available Energy = 1/2 X p X V 3 X A X t

Wind power is the amount of energy which flows through the surface per unit time, and is calculated by dividing the wind energy by the elapsed time t. the fraction of the wind power avail Thus, the wind power available under able that is actually delivered to a load the same conditions as above is given or to a storage device by the formula

RSS | Comments | E-mail | Print