How Winds are Created The earth’s winds are caused by pressure differences across the earth’s surface due to uneven heating Local Winds: During the day the air over the land is heated more than the air over the sea. Opposite during the night Day pattern: Wind blows from sea to land Night pattern: Wind blows from land to sea
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How Winds are Created The earth’s winds are caused by pressure differences across the earth’s surface due to uneven heating Local Winds: During the day.
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Transcript
How Winds are Created The earth’s winds are caused by pressure
differences across the earth’s surface due to uneven heating
Local Winds: During the day the air over the land is heated more than the air over the sea. Opposite during the night Day pattern: Wind blows from sea to land Night pattern: Wind blows from land to sea
How Winds are created
Global Winds: Occur due to greater heating of the air near the equator than the poles. Thus wind blows in the direction from the poles to the equator
Large ocean and land masses also affect the wind pattern
It is important to understand these wind patterns for the evaluation of potential wind sites
Wind power systems are composed of: Tower Rotor with 2 or 3 blades (fiberglass reinforced
plastics, epoxy laminates Yaw Mechanism such as a tail vane Low-speed shaft, high-speed shaft, and gearbox
(Mechanical Drive Train) Electrical generator Speed sensors and controlModern wind power systems also include: Power electronics Control electronics Batteries to improve the load availability when in
stand-alone mode Transmission link connecting to the area grid
Characteristic of Wind Turbines
Variations in wind speed causes fluctuations in the amount of power produced Short Term: Gusts and Turbulence Long Term: Seasonal Changes
WTs have a cut-in, cut-out and a peak power output for a given wind velocity
Power from the wind is proportional to the area swept by the rotors
In practice, the max power efficiency is 45%
Global Picture
Source: GWEC (Global Wind Energy Council) 2008: http://www.gwec.net/fileadmin/documents/PressReleases/PR_stats_annex_table_2nd_feb_final_final.pdf
Wind Power
Source: GWEC (Global Wind Energy Council) 2008: http://www.gwec.net/fileadmin/documents/PressReleases/PR_stats_annex_table_2nd_feb_final_final.pdf
Wind Power
Source: GWEC (Global Wind Energy Council) 2008: http://www.gwec.net/fileadmin/documents/PressReleases/PR_stats_annex_table_2nd_feb_final_final.pdf
Top 10 total installed capacity
Top 10 added capacity (2008)
Total Installed Wind Capacity
Total Installed Wind Capacity
Cost Analysis
Wind energy generation costs have dramatically decreased over the last 25 years from 40 cents/KWh to 4 cents/KWh
20 years from now wind energy is expected to be cheaper than conventional sources of energy
Advantages and Disadvantages of Wind Turbines Advantages
Clean Source of Energy Unlimited Supply Popular with the Public
Disadvantages How do wind plants impact the power system grid
(Not enough data) Very expensive to install and connect to the power
grid
Wind Turbine Power:
P = 0.5 x rho x A x Cp x V3 x Ng x Nb
P = power in watts (746 watts = 1 hp)
rho = air density (about 1.225 kg/m3 at sea level, less higher up)A = rotor swept area, exposed to the wind (m2)Cp = Coefficient of performance (.59 {Betz limit} is the maximum theoretically possible, .35 for a good design) V = wind speed in meters/sec (20 mph = 9 m/s)Ng = generator efficiency (50% for car alternator, 80% or possibly more for a permanent magnet generator or grid-connected induction generator)Nb = gearbox/bearings efficiency (depends, could be as high as 95% if good)