WIND RESOURCE ASSESSMENT TECHNIQUES

K.BoopathiScientist & Wind Resource Assessment Unit Chief,WRAWind Resource Assessment Centre for Wind Energy TechnologyChennai

boopathi@cwet.res.in

Dr.S.GomathinayagamExecutive DirectorCentre for Wind Energy TechnologyChennaied@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

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.

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

Wind speed characteristics

Horizontal and Inter annual Variability

Vertical Wind VariabilityTemporal 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 PowerPower (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

Main objective is to identify potentially windy areas that also possess other desirable qualities for wind project development

Wind Resource Assessment

Prospecting (Large area Screening & Field visits).

Validation (Wind measurements & Data Analysis)

Micro Survey & Micrositing.

WIND RESOURCE ASSESSMENT TECHNIQUES

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 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.).

Large area Screening and Existing data

use of existing wind data-nearby airport

nearby airport measurement wind dataLong term re analysis data (NCEP/NCAR/MERRA)

WPAD MAP AT 50 m

States / UTs Installable Potential(MW) 50 m Level

 

 

Andaman & Nicobar 2  

Andhra Pradesh 5394  

Arunachal Pradesh* 201  

Assam* 53  

Chhattisgarh* 23  

Gujarat 10609  

Himachal Pradesh * 20  

Jammu & Kashmir * 5311  

Karnataka 8591  

Kerala 790  

Lakshadweep 16  

Madhya Pradesh 920  

Maharashtra 5439  

Manipur* 7  

Meghalaya * 44  

Nagaland * 3  

Orissa 910  

Rajasthan 5005  

Sikkim * 98  

Tamil Nadu 5374  

Uttarakhand * 161  

Uttar Pradesh * 137  

West Bengal* 22  

Total 49130  

State NameInstallable Potential MW

Andaman&Nicobar Islands 365 Andhra Pradesh 14497 Arunachal Pradesh* 236 Assam* 112 Bihar 144 Chhattisgarh* 314 Dieu Damn 4 Gujarat 35071 Haryana 93 Himachal Pradesh * 64 Jharkhand 91 Jammu & Kashmir * 5685 Karnataka 13593 Kerala 837 Lakshadweep 16 Madhya Pradesh 2931 Maharashtra 5961 Manipur* 56

Meghalaya * 82

Nagaland * 16 Orissa 1384 Pondicherry 120 Rajasthan 5050 Sikkim * 98 Tamil Nadu 14152 Uttarakhand * 534 Uttar Pradesh * 1260 West Bengal* 22   Total 102788

TOPOGRAPHIC INDICATORS

To look for physical evidence to support the wind resource estimate developed in the large-area 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.

Field visits

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

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

Standard Wind Class

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. winds hear; the wind slows down, near the ground, to an extent determined by the surface roughness.2. turbulence; behind building, trees, ridges etc3. acceleration; (or retardation) on the top of hills,

ridges etc.4. Inflow wind5. Extreme wind6. Gusts7. Wake effects

Turbulence and Acceleration of ridge and Obstacle

Turbulence is variations in wind speed

•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

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.

The flow inclination must not exceed ± 8 degree for any wind direction

VALIDATION

Met Mast

Instruments for Measuring wind speed and Direction

cup anemometer vane anemometer ultrasonic anemometer hot-wire anemometerother “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

REMOTE SENSING INSTRUMENTS

ea st

verti

cal

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

Diurnal variation

Monthly 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

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

WIND RESOURCE ASSESSMENT UNIT

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.

- Production estimate, incl. wake losses to other turbines

- Calculate sound emission from the turbines to the nearest neighbor.

- Create a visualization of the park.

All this is something that is done before the park is erected so you can calculate the feasibility of the project.

- Load calculation to ensure a 20 year design lifetime

- Calculate shadow flickering

- Wind measurements

-Recommend another turbine type, turbine layout, hub height, wind sector management or measurement campaign

- Wind resource estimate- Turbine layout

- Roughness, Obstacles, Orography

Benefits of siting

• Optimize production • Analyze and reduce risks

Conclusions

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