WIND RESOURCE
ASSESSMENT TECHNIQUES
Dr.S.Gomathinayagam
Executive Director
Centre for Wind Energy Technology
Chennai
ed@cwet.res.in
K.Boopathi
Scientist & Wind Resource Assessment
Unit Chief,WRA
Wind Resource Assessment
Centre for Wind Energy Technology
Chennai
boopathi@cwet.res.in
WIND
 Air in motion i.e. motion of air relative to the earth’s
surface.
 Free, clean and inexhaustible energy
 It is intermittent source
 One day it calm, howling next
 It will vary place to place and time to time
WIND RESOURCE-GLOBAL WIND SYSTEM
 All renewable energy (except tidal and geothermal power), and
even the energy in fossil fuels, ultimately comes from the sun.
About 1–2% of the energy coming from the sun is converted into
wind energy

The region around equator at 0 deg latitude are heated
more by the sun than the rest of the globe. Due to this
flow of air takes place from the cold regions to hot
regions.
Wind speed characteristics
Horizontal and Inter annual Variability
Vertical Wind Variability
Temporal and Inter annual Variability
Atmospheric boundary layer and Vertical wind profile
Vertical wind profile for different roughness
lengths z0, assumed “geostrophic wind” of
15 m/s
Wind Regime in India
 Wind climatology in India is influenced by the strong monsoon circulations
 South west monsoon during May to Sept brings the best winds
 Wind speed during November to March is low, except in Southern tip of
Tamil Nadu
 Best Windy Sites are in Kerala, Karnataka, Tamil Nadu, Gujarat, Andhra
Pradesh and Maharashtra
POWER IN THE WIND
From Wind to Electric Power
Power (translation) = Force x Velocity (P=F V) or
Power (rotation) = Torque x rotational speed (P=T x co)
P= KE*m
KE - Kinetic Energy ,=1/2mV 2 m - mass flow rate=pAV
Pwind = Cp 1/2 pV3 A
Cp efficiency (“Betz” max. = 16/27)
1/2 pV2
Dynamic pressure at 1 m2
p
Air density (~1.22 kg/m3)
V
Wind speed
A
Gross rotor area
Wind Resource Assessment
Main objective is to identify potentially windy
areas that also possess other desirable qualities
for wind project development
WIND RESOURCE ASSESSMENT
TECHNIQUES
Prospecting (Large area Screening & Field visits).
 Validation (Wind measurements & Data Analysis)
 Micro Survey & Micrositing.

PROSPECTING
PROSPECTING STEPS
●
●
●
●
●
Preliminary area identification
Ranking of candidate sites
Selection of tower location(s)
Development of a monitoring plan
Quality assurance
Preliminary Area Identification
Objective is to determine or verify whether sufficient
wind resources exist within an area to justify further
site-specific investigation
 Large area screening- wind resource map look up
 use of existing wind data-nearby airport
 topographic indicators
 field surveys
 flagged trees
 accessibility
 land use– obstructions
 available land area
Large area Screening and Existing data
•
large-area screening usually begins
with a review of
– existing wind resource maps, data
and
other meteorological informations
(pressure, temperature etc.)
– analysis of the climatology of the
region along with the topographical
maps (such as terrain form, land
use and land cover, and other
logistics like accessibility, grid
availability etc.).
use of existing wind data-nearby airport
nearby airport measurement wind data
Long term re analysis data (NCEP/NCAR/MERRA)
WPAD MAP AT 50 m
States / UTs
Andaman & Nicobar
Andhra Pradesh
Arunachal Pradesh*
Installable
Potential
(MW) 50 m Level
2
5394
201
Assam*
53
Chhattisgarh*
23
Gujarat
10609
Himachal Pradesh *
20
Jammu & Kashmir *
5311
Karnataka
8591
Kerala
Lakshadweep
Madhya Pradesh
Maharashtra
Manipur*
Meghalaya *
Nagaland *
Orissa
Rajasthan
Sikkim *
Tamil Nadu
790
16
920
5439
7
44
3
910
5005
98
5374
Uttarakhand *
161
Uttar Pradesh *
137
West Bengal*
Total
22
49130
State Name
Andaman
&Nicobar Islands
Andhra Pradesh
Arunachal Pradesh*
Assam*
Bihar
Chhattisgarh*
Dieu Damn
Gujarat
Haryana
Himachal Pradesh *
Jharkhand
Jammu & Kashmir *
Karnataka
Kerala
Lakshadweep
Madhya Pradesh
Maharashtra
Manipur*
Installable
Potential MW
365
14497
236
112
144
314
4
35071
93
64
91
5685
13593
837
16
2931
5961
56
Meghalaya *
82
Nagaland *
Orissa
Pondicherry
Rajasthan
Sikkim *
Tamil Nadu
Uttarakhand *
Uttar Pradesh *
West Bengal*
Total
16
1384
120
5050
98
14152
534
1260
22
102788
TOPOGRAPHIC INDICATORS
Field visits

To look for physical evidence to support the
wind resource estimate developed in the largearea screening.

Another purpose of the site visit is to select a
possible location for a wind monitoring station.
Consistently bent trees and vegetation, for
example, are a sure sign of strong winds.
Ranking of Candidate Sites
Objective is to compare areas to distinguish relative
development potential
 In addition to accessibility, land use, obstructions, and
available land area, siting criteria could include:
 proximity to transmission lines
 potential impact on local aesthetics
 cellular phone service reliability for data transfers
 potential avian interactions
Standard Wind Class
US Wind Class
A site can be classified as one of the Standard seven classes
depending on Wind Power Density/Wind Speed
available at 50 m above ground.
Class
Speed(m/s)
WPD(W/Sq.m)
1
0-5.6
0-200
2
5.6-6.4
200-300
3
6.4-7.0
300-400
4
7.0-7.5
400-500
5
7.5-8.0
500-600
6
8.0-8.8
600-800
7
8.8-11.9
800-2000
Site Selection
The power output of a wind rotor Increases with the cube of the wind
speed. This means that the site for a windmill must be chosen very
carefully to ensure that the location with the highest wind speed in the
area is selected. The site selection is rather easy in flat terrain but much
more complicated in hilly or mountainous terrains.
A number of effects have to be considered :
1.
2.
3.
4.
5.
6.
7.
winds hear; the wind slows down, near the ground, to
an extent determined by the surface roughness.
turbulence; behind building, trees, ridges etc
acceleration; (or retardation) on the top of hills, ridges etc.
Inflow wind
Extreme wind
Gusts
Wake effects
Turbulence and Acceleration of ridge and Obstacle
The flow inclination must not exceed ± 8 degree for any wind direction
Turbulence is variations in wind speed

Close to an obstacle such as a building the wind is strongly
influenced by the presence of the obstacle. The effect
extends vertically to approximately three times the height
of the obstacle, and downstream to 30 to 40 times the
height. If the point of interest is inside this zone, it is
necessary to take the sheltering effects into account,
whereas if the point is outside the zone the building should
be treated as a roughness element.

The buildings and rows of trees shelter the met. mast in the
centre of the drawing.
•Back ground turbulence
•Wake turbulence
tops of ridges experience higher wind speeds
due to the effect of wlndshear
The ideal slope angle is said to be 16° (29 m rise
per 100 m horizontal distance) but angles between
6° and 16° are good
VALIDATION
Met Mast
Instruments for Measuring
wind speed and Direction
 cup anemometer
 vane anemometer
 ultrasonic anemometer
 hot-wire anemometer
 other “high-tech” device (SODAR,LIDAR)
Instruments







small vertical axis wind wheel
rotational speed proportional to wind speed
two ways taco generator (analogue signal)
frequency signal (optoelectronic)
most commonly used,
sufficient for most tasks in wind technology
wide range of qualities
Direction of wind is an important factor in the siting of a
wind energy conversion system. If we receive the major
share of energy available in the wind from a certain
direction, it is important to avoid any obstructions to the
wind flow from this side. Wind vanes were used to
identify the wind direction in earlier day’s anemometers

logging of time series (10-minute or 1-hour averages)

channels for 3 or more wind speeds and wind vanes,

air pressure, 2 or more temperatures, humidity

power supply by solar panel and battery

safety system for data storage in case of break down of
power supply

data storage capacity minimum of 2 months
vertica l
REMOTE SENSING INSTRUMENTS
ea st
SODAR
Analysis
•


•
number of manipulations with these data, basically looking at two aspects:
time distribution
frequency distribution
Plotting the monthly averages of each
hour of the day shows the diurnal
fluctuations of the wind speed in that
particular month
Monthly variation
Diurnal variation
Minimum information to be contained in wind data files:
 Mean wind speed measured at two heights. E.g. 30m and 50 m or if
possible hub height. Measurements at two heights are needed in
order to investigate the wind shear.
 Standard deviation over a 10 minutes period in order to determine
turbulence.
 Wind direction. In order to determine main wind directions.
 All the information must be saved in a text file or ASCII file (e.g. *.xls
/*.prn /*.tab*.dat /*.asc /*.txt/).
TECHNIQUES FOR ESTIMATING WIND RESOURCES
• These techniques can be used screen candidate resource areas
for sites with high potential or to estimate wind energy
characteristics at a specific location.
• numerical modeling of flow over terrain
• physical modeling of flow over terrain
• topographical indicators of wind energy potential
• biological indicators of wind energy potential
• geomorphol ogi cal indicators of wind energy potential
• social and cultural indicators of wind energy potential.
• Numerical Modeling

Synoptic scale -is a horizontal length scale of the order of 1000
kilometres (about 620 miles) or more

Meso-about 5 kilometers to several hundred kilometers

Micro-1 km or less, smaller than mesoscale
WIND RESOURCE ASSESSMENT UNIT
Offshore Wind Mapping
•
•
•
•
•
•
Study based on coastal wind monitoring stations.
Study based on data from data buoy deployed by NIOT.
Study based on SAR in association with RISO –DTU
Study based on QUICK SCATT in association with INCOIS
SDI, Scotland has been encaged for preparing feasibility study.
Measurements are being initiated at Dhanushkodi in Ramanathapuram, Tamil Nadu
SAR winds
•
•
•
ENVISAT ASAR WSM images from the
European Space Agency (ESA). The
WSM – Wide Swath Mode – scenes each
cover 400 km x 400 km. As examples two
of the wind maps are shown in Figure.
The figure 1(top) shows an example
from 4 December 2010 characterized
by strong winds whereas the Figure 2
(bottom )shows much weaker winds on
25 September 2010.
A total of 164 WSM scenes are used.
Most of the 164 scenes are from ESA’s
ordering system EOLISA and sent on DVD
to Risø DTU but a few are taken from
ESA’s rolling archive.
There are a total of 164 ocean wind
maps out of which 72 are observed in
the morning and 92 in the evening
Ocean wind map
from ENVISAT
ASAR WSM from 4
December 2010 at
04.30 UTC in
South India.
•
Ocean wind
map from
ENVISAT
ASAR WSM
from 25
September
2010 at
04.43 UTC
in South
India.
OFFSHORE WINDFARM (PROPOSED) AT DHANUSKODI RAMESHWARAM AND
KANYAKUMARI
MICROSURVEY & MICROSITING
MICRO SURVEY
What is micro siting ?
Micro siting is a way to optimize the park layout in
any given site to give the optimum production on site.
- Wind measurements
- Roughness, Obstacles, Orography
- Wind resource estimate
- Turbine layout
- Production estimate, incl. wake losses to other turbines
- Load calculation to ensure a 20 year design lifetime
- Calculate sound emission from the turbines to the
nearest neighbor.
- Create a visualization of the park.
- Calculate shadow flickering
-Recommend another turbine type, turbine layout, hub height,
wind sector management or measurement campaign
All this is something that is done before the park is
erected so you can calculate the feasibility of the
project.
Benefits of siting
• Optimize production
• Analyze and reduce risks
Conclusions

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The wind resource drives project viability.
Wind conditions are site-specific and time/height
variable.
Accuracy is crucial. Wind resource assessment
programs must be designed to maximize accuracy.
Combination of measurement and modeling techniques
gives the most reliable result.
Know the uncertainties and incorporate into decision
making.
Good financing terms depend on it.
Thank you