Wind Resource and Assessment Essay

Wind Resource and
Assessment

What is the Wind?


Movement of air caused by the circulation of changing temperatures.



The uneven heating of the earths surface. Factors that Affect the
Wind










Elevation
Temperature
Obstructions
Surface Roughness
Shape and Direction of Mountains
Ridges
Temperature Inversions
Water / Land Connections
Time of day
Time of Year

Elevation

Obstructions

Surface Roughness


physical features / terrain of the surface of a wind site.



α = Exponent that varies with surface roughness.
• .14 smooth terrain
• .20 small trees, buildings, corn fields
• .25 or higher with taller trees and/or buildings
• You can determine this for each particular site.

More on this later!

Shape and Direction of
Mountain Ridges

Mountain –valley winds (page 24)
Channeling

Temperature Inversions

Water and Land Connections

Time of Day and Year





Higher winds found late in the day and evening Higher winds seen during the winter
Annual Average Wind Speed can fluctuate up to 25% from year to year.

Wind power/speed
Classifications

Wind Direction and Wind Rose

Annual Frequency and Average
Annual Wind Speed in
Sixteen Compass Directions
Potato Hill, Watauga County, NC
N

35
NNW

NNE
30

NW

NE

25

20

15

WNW

ENE

10

5

W

0

E

WSW

ESE

SW

SE

SSW

SSE
S

Wind Frequency
Wind Speed

Visual Assessment


Flagging



Page 48 in text

North Carolina Wind
Map

South Dakota Wind Resource Map

LiDAR and Sodar
Wind Assesment
LIDAR


Uses laser pulses for assessing wind speed, direction, and turbulence characteristics SODAR


Uses sounds pulses for assessing wind speed, direction, and turbulence characteristics

Wind Monitoring
Activities
 Anemometers & wind vanes
 20 – 80 meter towers
 Data collected and stored every
10 minutes
 wind speed averages and wind directions

Wind Monitoring
Activities

4 Standard Techniques


Wind Assessment Techniques
• Visual Assessment – Flagging
• Wind Maps
• Anemometer / Meteorological (Met.) tower
• LIDAR/SODAR (only for large wind installations)

Wind Speed, Power and Height
Measurements



Use Metric!, Use Metric!, Use Metric!
Or
Act like any intelligent industry and use a combination of both metric and standard • Often you must convert units




1 meter = 3.28 feet
1 meter/second = 2.24 mph

Power in the Wind
 Power
 Wind
 Air

= rate @ which energy is available

is air(fluid) in motion (we want wind speed!!!)

has mass - 1.225 Kg/m3 at sea level & 59F.

 Mass
 The

of moving air contains kinetic energy

amount of power in the wind is a function of

speed & mass
 Power

is a cubic function of wind speed

• Double the speed and power increases 8 X

Wind Speed is Key!


Probably need a site with at least 10 mph average @ 30 meters for small wind turbines
& 15 mph for large



Wind resource assessment is essential !!!!!!!!!

Importance of Wind Resource Assessment
Marginal site Vs. Good site
Example: Bergey XL.1 $6500 system



4 m/s* avg. wind site. • AEO=1920



7 m/s avg. wind site. • AEO=4800

kWh/year kWh/year • $/kWh/20yr = $.17
• $/kwh/20yrs = $.07
• Lower output
• 2.5x higher output
• 240%
• 40% in cost/kWh at good site vs.
Higherdifference
cost cost/kWh marginal site.
* 1 m/s = 2.24 mph

Power Density
(P/A in watts/m2) = ½ Density x V3



Power Density expressed in watts/m2

At sea level with a temperature of 15 C
(59 F) where air density is 1.225 kg/m3


P/A = ½ Air Density x V³
Air Density = 1.225 kg/m³
Velocity = 8m/s

P/A = (.5) (1.225 kg/m³) (8m/s)³
P/A = (.6125 kg/m³) (512m³/s³)
P/A = 313.6 W/m²

Air Density (  )


Inversely related to Temperature & Elevation



Decreases with increasing temperature & elevation



Cold and low places have higher air densities



Temperature is typically less significant and sometimes ignored (10 – 15 % yearly variation)



Elevation can be significant and a constant
(density @ 5,000’ is 15 % lower than sea level)

Air Density Changes with Elevation
Density

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