Chapter 2 Wind Energy
Main Contents
2.1 Wind Energy History 2.2 Wind Energy Basics 2.3 Wind Power Technology 2.4 Wind Energy Benefits and Challenges
2.1 Wind Energy History
Wind Turbines: Power for a House or City
Savonius Wind Turbine
Dutch Windmill
American Multiblade Windmill
Darrieus Wind Turbine
Three-Blade HAWT （Horizontal-axis wind turbines）
The maximum power extractable from the wind is limited to 59% of the theoretical power (Betz Theorem).
The actual power obtained from a wind machine is a product of the actual efficiency times the Betz limit (0.59) times the theoretical power. P actual = Eff actual x 0.59 x P theoretical Where Eff actual is a product of the rotor efficiency times the gearing efficiency times the generator efficiency.
Power, kW
2 000 1 750 1 500 1 250 1 000
750 500 250
0 0 1 2 3 4 5 6 7 8 9 10 Wind speed, m/s
Since power (and energy) vary as the cube of the velocity, doubling the wind speed will give 8x the power and energy. Finding a good site and maximizing the wind speed is a critical part of making wind power economical.
A
v
l
KE 1 mv2 2
Pow(Pe) r KE1.m2v t 2t
m A.l. A.v.
tt
P(wa)t ts1A.v3
2
Theoretical formula: P = 1/2 π R2 v3
Where: P: theoretical wind power in Watts : air density in kg/m3 (e.g. 1.225 at sea level) R : blade length in meters v : inflow wind speed in m/s
Early Days
Small wind electric turbines (1890s – Denmark, U.S., etc.) Experiments with turbines of ~100 kW in U.K., Italy, Germany (1920s and 1930s)
Smith-Putnam Turbine 175 foot rotor, 1.25MW capacity Operated from late 1941 to spring of 1945 Economic failure – technological triumph Foundation footings still in place
1985 1995 2000 2003
2006
2007
Wind Turbine specifications: Electrical Power: 1.5-5.0 MW Turbine Weight: 150-500 tons Tower Height: 65-100 meters Blade Length: 34-60 meters Blade Weight: 6-23 tons ~$1.40/Watt $0.03-0.06/kWh (Cost of Energy)
Early Wind Farm Era
First Wind Farm – Crotched Mountain, New Hampshire , December 1980 (equipment failures, wind speed overestimated) California Wind Farms – December 1981
Cretan (克里特岛) windmill (1464, mechanical water pumping)
Dutch windmill (1500, mechanical water pumping, grain milling)
U.S. farm windmill (1854 , mechanical water pumping)
1978 – Second oil shock leads to: Public Utility Regulatory Policies Act of 1978
(PURPA) in USA Requires utilities to buy electricity from renewable and cogeneration facilities Energy Tax Act of 1978 Creates 15% Energy Investment Tax Credit (EITC) Added to existing 10% ITC Limited Partnership Structure -&y Basics
FD=1/2CdρAv2
FL=1/2ClρAv2
Cd : Drag Coefficient
Cl: Lift Coefficient
ρ: Air Density
V
A : Sheet Area
v : Air Velocity
FL
F
A
C
FD
i B
• Power Law