The Wind Resource is generally catagorized in Seven Wind Zones. Wind zone one is weakest, wind zone seven is strongest, or highest in annual average wind speed. Wind speeds (zone) depend on local environments, this micro-climate can be very different from what's reported by a wind map. Onsite inspection (measurement) is recommended.
The Power in the wind increases as the Cube of the wind speed. This is the key element for the power of wind generators. Double the wind speed and increase the power available 8-fold.
Wind Zones are defined by class:
Class Wind Speed (m/s) Power Density
(sampled at 50 meter height)
Wind Zone 1 0 – 4.4 m/s 200 watts/m2
Wind Zone 2 4.4 – 5.1 m/s 300 watts/m2
Wind Zone 3 5.1 – 5.6 m/s 400 watts/m2
Wind Zone 4 5.6 – 6.0 m/s 500 watts/m2
Wind Zone 5 6.0 – 6.4 m/s 600 watts/m2
Wind Zone 6 6.4 – 7.0 m/s 800 watts/m2
Wind Zone 7 7.0 – 9.4 m/s 2,000 watts/m2
The wind is always changing. As a natural system this variation must be considered for your wind project.
All wind generators are able to adjust to the changing direction of the wind. This Yaw motion positions the working surfaces (blades) to be at a perpendicular angle (for propeller-type wind generators). The size of the blades of a wind generator defines the Swept Area.
The Power and Energy therefore, extractable at any given site is a function of your wind resource, and the Swept Area of your Wind Energy Conversion System (WECS).
The wind changes for any given location in cycles. The diurnal (daily) variation occurs as areas heat-up during the day. The deserts in Las Vegas bring diurnal onshore flow as the heat of the day causes air to rise “pulling” in cooler denser air over the ocean. Your specific site will have its own characteristics.
Power in the Wind
The Power in the Wind increases as the “cube” of the velocity. This means that a wind speed of 25 m/s has 125 times more power than a wind speed of 5 m/s.
Double the wind speed and the Power increases by 8-Fold! This is why in high winds, like a Katrina event, buildings are destroyed. The fact is, wind moving at high speeds, contain enormous power.
The chart below demonstrates the Power Density of different wind speeds in terms of Kilowatts/Square Meter (Kw/m2). Note how rapidly the Power increases as you increase wind speed:
Wind Speed (m/s) Power (Kw/m2)
0 m/s, 0
5 m/s, 0.06
10 m/s, 0.50
15 m/s, 1.68
20 m/s, 4.00
25 m/s, 7.81
30 m/s, 13.50
The Power Density in the Wind is Enormous increasing 800% with each doubling of wind speed.