topic 2(wind resources)

7/31/2019 Topic 2(Wind Resources)

1/18

1

Renewable EnergySystems

Topic 2

The Wind Resource


2/18

2

Reminder

You are welcome to use the Discussion

Board on Blackboard to pose/discuss

questions in all components of the course

with your classmates.


3/18

3

Wind speeds

The output of a wind turbine is critically dependent onwind speed.

Power in undisturbed wind is proportional to cube ofwind speed. This can be shown with the 1st law ofthermo for a control volume. Therefore 10% increase inwind speed means 33% increase in wind power.

Proportion of power in the wind captured by wind turbinevaries with wind speed.

Typically wind turbines cut in about 5 m/s, and cut out atabout 25 m/s.

Turbulent wind is undesirable


4/18

4

Large scale wind patterns inAustralia

In southern regions (latitudes of about 30 S to 50 S),prevailing winds are westerlies

Around 40 S to 50 S, strong westerlies known as theroaring forties

Further north (< 30 S) south east trade winds Seasonal variation in latitude Near equator, south east trade winds from southern

hemisphere meet north east tradewinds fromnorthern hemisphere. These are the doldrums - low

wind potential. Very high winds are undesirable for wind power. (In

some areas, special measures taken - Exmouth,Antarctica)


5/18


6/18

6

Local effects

Coastal sea breezes are caused by temperaturedifference between land and sea. The hot air over landheats up and rises. It is replaced by cooler air from overthe sea.

Elevated ridges can cause air flow to accelerate. (Ineffect, cross sectional area is decreased, so air speedsup.)

Obstacles such as trees and buildings decrease wind

speeds and increase turbulence for a significant regionaround the obstacle. (Hence, cities are not good sites)

Wind speed varies with height due to wind shear. Profileis dependent on local terrain.


7/18

7

Finding windy sites

Wind speed regime varies significantly within small region Bureau of Meteorology wind speed records do NOT give a

good indication of wind power potential.

Permanent deformation of local foliage may not be a goodindicator (affected by salt in coastal areas).

Daily and seasonal wind speed variation.

Average wind speed can vary significantly from year toyear. (Affected by weather patterns such as El Nio)

Wind monitoring studies done in 1980s. Findings from

current wind studies generally not publicly available. Wind speed atlases now being produced.

Terrain modelling packages are available.


8/18

8

Finding windy sites

Monitor wind speeds at site for at least a year.Should correlate speed and direction data with longterm data from nearby site (e.g. Bureau ofMeteorology) to determine if typical year.

Monitor at hub height - typically 50 to 60 m. (Muchwind data is from 2 m or 10m height.)

Select site with little disturbance from obstacles(buildings, trees) in direction of prevailing winds.

Flow disturbance from obstacles typically twice theheight of obstacle and downwind distance up to 20times height of obstacle. Thus bottom of rotor shouldbe at least twice the height of nearby obstacle


9/18

9

Finding windy sites

Tops of cliffs have enhanced wind speeds. Direction ofprevailing wind should be approx perpendicular to cliffface. High turbulence near edge of cliff, so locate turbineback from edge.

Hills can enhance wind speed. Long ridges arepreferable, to ensure wind travels over hill rather thanaround it.

Valleys may be suitable for enhancing wind speed.

Should be oriented close to direction of prevailing winds,and surrounded by hills


10/18

10

Variability of wind energy

Wind speed varies significantly on all timescales.

Wind turbines are thus intermittent generators. (Somesmoothing of output with many dispersed turbines)

Electricity systems typically have no (or very little) storage,so supply and demand must always be matched.

The variable output of wind turbines must therefore bematched by other generators.

Wind power output usually does not correlate with times of

peak demand. At significant levels of wind power penetration, effect on

electricity system operation may be detrimental.


11/18

11

Winds in Victoria

Victorian wind atlas

Existing wind farms in Victoria

Wind projects in Victoria
http://www.sustainability.vic.gov.au/www/html/2111-wind.asphttp://www.sustainability.vic.gov.au/www/html/2099-operating-wind-generators-in-victoria.asphttp://new.dpi.vic.gov.au/energy/projects,-research--and--development2/wind-projectshttp://new.dpi.vic.gov.au/energy/projects,-research--and--development2/wind-projectshttp://www.sustainability.vic.gov.au/www/html/2099-operating-wind-generators-in-victoria.asphttp://www.sustainability.vic.gov.au/www/html/2111-wind.asp


12/18


13/18

13

Estimating wind speed using theBeaufort Scale

Beaufort

number

Description

Wind speedat 10mheight m/s

Wind speed at10m heightkm/h

Observable effects on land Wind Turbineperformance50m height

0 calm 00.2 < 1 Calm, smoke rises vertically None

1 light air 0.31.5 15 Smoke drift; wind vanesunaffected

None

2 lightbreeze

1.63.3 611 Wind felt on face; leavesrustle; wind vanes move

None

3 gentlebreeze

3.45.4 1219 Leaves and small moveconstantly; flags flap

0 to 20% ofcapacity

4 moderate

breeze

5.57.9 2028 Papers blow; small branchesmove

20 to 60% ofcapacity

5 freshbreeze

8.010.7 2938 Small trees sway 60 to 100% ofcapacity

6 strongbreeze

10.813.8 3949 Large branches in motion;umbrellas used with difficulty

Full capacity


14/18

14

Estimating wind speed using theBeaufort Scale

Beaufort

number

Description

Wind speedat 10mheight m/s

Wind speed at10m heightkm/h

Observable effects on land Wind Turbineperformance50m height

7 neargale

13.917.1 5061 Whole trees sway Full capacity

8 gale 17.220.7 6274 Twigs break off; walking

difficult

Full capacity

9 stronggale

20.824.4 7588 Slight structural damage Wind turbineshut down

10 storm 24.528.4 89102 Trees uprooted; muchstructural damage

Wind turbineshut down

11 violent

storm

28.532.6 103117 Widespread damage Wind turbine

may bedamaged

12 hurricane

32.7 + 118 + Severe and extensivedamage; disaster

Seriousdamageunless lowered


15/18


16/18

16

Wind Shear

Wind speed increases with height due to frictionbetween air and surface of earth

Wind speed gradient function:

Exponentdepends on terrain: 0.1 for open sea; 0.13 for low grass; 0.19 for low scrub; 0.32 for forest, urban areas

ref

ref

z

z

vv

vis wind speed at height z

vref is wind speed at height zref

is wind shear exponent


17/18

17

Wind Shear

Another method of estimating the wind speedgradient is the log law and its physical basis isthe law of the wall (Boundary Layer theory)

v = m*ln(z) +c, z=zo when v=0

Roughness length varies from 0.0002 m forsmooth water to over a metre for cities with tallbuildings.

Typical value for open agricultural land is 0.03 m

0ref

0

reflnln

lnln

zz

zz

vvz0 is called theroughness length


18/18

topic 2(wind resources)

Documents