2-4-2 energy yield assessment

8/12/2019 2-4-2 Energy Yield Assessment

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Workshop on Renewable Energies

November 14-25, 2005

Nadi, Republic of the Fiji Islands

Module 2.4Module 2.4--22

ENERGY YIELD ASSESSMENTENERGY YIELD ASSESSMENTGerhard J. Gerdes

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ContentsContents

power curve of wind turbine and international

regulations for power curve measurements

using power curve and wind data to determine energy

output of a turbine at measurement site and

measurement height

using flow models to calculate wind and energy fordifferent sites and height

extension of results to long term time periods

possible errors


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Power curve overviewPower curve overview

practical power outputcurves follow the power

in the wind curve

up to the rated wind

speed

when rated output

power is reached

power curve generally

dependent of mode of

output control (stall

pitch)

rated wind speed (here 13 m/s)

vrated or vnominal

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Rules for power curve and windRules for power curve and windspeed measurementsspeed measurements

IEC (International Energy Commission) - international

FGW (Frdergesellschaft Wind Energie: Support

Society Wind Energy national German rules (= IEC

with extra conditions)

MEASNET - international (= IEC with extra conditions)

IEA (International Energy Agency) Recommendationfor wind speed measurements (outdated)

generally rules for power measurements (relatively

easy to fulfil) and wind speed measurements (more

difficult)


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0

200

400

600

800

1000

1200

1400

1600

1800

0 5 10 15 20 25

Calculated power curve

Measured power curve

Wind speed at hub height, m/s

Electricalpower,kW

Measured power curve and power curve given by manufacturer

Differences in power curvesDifferences in power curves

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0

100

200

300

400

500

600

700

0 5 10 15 20

Wind Speed [m/s]

Power[kW]

Std.-Conditions

1.1809 kg/m3

1.1356 kg/m3

1.089 kg/m3

Air density effect on power curvesAir density effect on power curves --stallstall


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0

100

200

300

400

500

600

700

0 5 10 15 20

Wind Speed [m/s]

Power[kW]

Std.-Conditions

1.1809 kg/m3

1.1356 kg/m3

1.089 kg/m3

Air density effect on power curvesAir density effect on power curves --

pitchpitch

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Calculation of wind turbine outputCalculation of wind turbine output

two important prerequisites:

thoroughly measured and evaluated wind data for the

site(s) in question, and

an exactly measured power curve, according to

international standards, so that turbines on the world

market can be compared

but still

for both power curve and wind data evaluation error

margins exist, which make an absolute certainty for

output estimation impossible

in addition annual variations of wind resource for a

given region can be substantial (+/- 20 % normal, up to

40 % )


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Power output estimationPower output estimation

needed:

power curve of wind turbine (generally in 1 m/s wind

classes)

wind speed frequency of the site (also in 1 m/s wind

classes)

simple multiplication

in practice, spreadsheet calculation is easy

AEP = Annual Energy ProductionEi = Energy per wind speed class i

fi = Frequency of wind speed class i

Pi = Power WTG in a wind speed class i

iii PfEAEP ==

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Typical power curve 300 kW (table)Typical power curve 300 kW (table)

v [m/s] Power Output (elec.) Power Coefficient

Wind Class [kW] cp [ - ]

1 0 0.00

2 0 0.00

3 4 0.32

4 10 0.36

5 22 0.40

6 38 0.41

7 62 0.42

8 93 0.42

9 133 0.42

10 182 0.42

11 231 0.40

12 269 0.3613 291 0.31

14 300 0.25

15 305 0.21

16 305 0.17

17 305 0.14

18 305 0.12

19 305 0.10

20 305 0.09

21 305 0.08

22 305 0.07

23 305 0.06

24 305 0.05

25 305 0.05

cp,max = 42 %

rated wind speed

vrated = 13.5 m/s

wind class 1

from 0 to 1 m/s;

wind class 2

from 1 to 2 m/s,

etc.

also called bins


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0

200

400

600

800

1000

1200

1 3 5 7 9 11 13 15 17 19 21 23 25

Wind speed [m/s]

Frequency[h/year] Total Hours per Year 8760h/a

Wind speed frequency distributionWind speed frequency distribution

Weibull parameters:

k = 2, A = 6.7 m/s

equals vavg = 6.0 m/s

vavg = average wind speed

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Typical power curve 300 kWTypical power curve 300 kW

0

50

100

150

200

250

300

350

0 5 10 15 20

Wind Speed [m/s]

Power

[kW]


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Energy production per wind speedEnergy production per wind speed

binbin

0

10'000

20'000

30'000

40'000

50'000

60'000

70'000

80'000

90'000

1 3 5 7 9 11 13 15 17 19 21 23 25

Wind speed [m/s]

Energy[kWh]

Annual Energy Yield578355kWh/a

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Calculation of annual energy yieldCalculation of annual energy yieldbased on measurementbased on measurement

0

50

100

150

200

250

300

350

0 5 10 15 20

Wind Speed [m/s]

Power[kW]

0

200

400

600

800

1000

1200

1 3 5 7 9 11 13 15 17 19 21 23 25

Wind speed [m/s]

Frequency[h/year]

0

10'000

20'000

30'000

40'000

50'000

60'000

70'000

80'000

90'000

1 3 5 7 9 11 13 15 17 19 21 23 25

Wind speed [m/s]

Energy[kWh]

Wind Wind Power frequency Energy

[m/s] [mph] [kW] [h/year] [kWh/year]

1 2,2 0,0 372,0 0,0

2 4,5 0,0 702,0 0,0

3 6,7 3,7 941,0 3481,7

4 8,9 10,0 1077,0 10770,0

5 11,2 21,6 1107,0 23911,2

6 13,4 38,3 1046,0 40061,8

7 15,7 62,4 920,5 57439,2

8 17,9 93,1 759,5 70709,5

9 20,1 132,6 592,0 78499,2

10 22,4 181,8 435,0 79083,0

11 24,6 230,5 303,5 69956,8

12 26,8 269,3 201,5 54264,0

13 29,1 290,5 127,5 37038,8

14 31,3 300,0 77,5 23250,0

15 33,6 305,0 45,0 13725,0

16 35,8 305,0 25,0 7625,0

17 38,0 305,0 15,0 4575,0

18 40,3 305,0 7,0 2135,0

19 42,5 305,0 3,0 915,0

20 44,7 305,0 1,8 549,0

21 47,0 305,0 0,8 244,0

22 49,2 305,0 0,3 91,5

23 51,4 305,0 0,1 30,5

24 53,7 305,0 0,0 0,0

25 55,9 305,0 0,0 0,0

Total 8760 h 578355 kWh


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Further calculations are neededFurther calculations are needed

From measurement height to turbine hub height From measurement site to different wind turbine sites

for a planned wind farm

From one year measurement period to long-term

estimation

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Measurement and longMeasurement and long--termtermbehaviour of wind speedbehaviour of wind speed

Wind speed is typically measured on potential wind

turbine sites for a limited period of time short-term

measurement (e.g. 1 year)

For the purpose of energy yield assessment this

has to be done with high accuracy.

To estimate energy production not only for the time ofthe measurement but for a longer time, information on

the long-term behaviour of the wind must be used:

Long-term correction has to be performed

The quality of this long-term data can be lower than

for the short-term measurement

The quality of the long-term measurement should

be stable in time


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Measurement concept includingMeasurement concept including

long term comparisonlong term comparison

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Long term variation of the annualLong term variation of the annualaverage wind speedaverage wind speed

45 years of data

40%

60%

80%

100%

120%

140%

160%

180%

1959 1964 1969 1974 1979 1984 1989 1994 1999

0 m/s

2 m/s

4 m/s

6 m/s

8 m/s

10 m/s

12 m/s

14 m/s

Normalised Average Production

vwind_hub-height

10 years sliding average (production)


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MeasureReference-Site:

Available long term data +

short term data (time series)

Reference-Site:

Available long term data +

short term data (time series)

Prognosis-Site:

Average time compatibel to

referenz-site

Prognosis-Site:

Average time compatibel to

referenz-site

Correlation

(Regression) of twelve

sectors each 30 degree

Correlation

(Regression) of twelve

sectors each 30 degreeCorrelate

Prediction of long term

windspeed distribution at

prognosis-site

Prediction of long term

windspeed distribution at

prognosis-sitePredict

Long Term Correlation withLong Term Correlation with

MeasurementMeasurement -- CorrelationCorrelation --

Prediction (MCP)Prediction (MCP) -- MethodMethod

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Extended energy yield assessmentExtended energy yield assessmentfor wind farmsfor wind farms

The evaluation of a wind speed measurement results in

an energy yield, which is valid for the measurement

period and the measurement height only

To transfer the measurement to other sites in a wind

farm area and to different heights, a micrositing model

is required To extend the wind speed evaluation results to a longer

time period than the measurement period, a long term

correlation method is required


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Transfer to different sites and heightTransfer to different sites and height

transfer to different height (h1 to h2)

transfer to different locations

h1

h2

measurement site

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Methods of energy yield assessmentMethods of energy yield assessment

in situ wind

measurements

in situ wind

measurements

energy yield predictionenergy yield prediction

meteorological

long term data

meteorological

long term data

long term correlationlong term correlation

micro - siting - modelmicro - siting - model


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Wind atlas methodWind atlas method resulting inresulting in

energy yieldenergy yield

Roughness descriptionRoughness description

Obstacle descriptionObstacle description

Orography descriptionOrography description

Meteorological dataMeteorological data

Power curve

Power curve

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100

200

300

400

500

600

700

0 5 10 15 20

Wind Speed [m/s]

Po

wer[kW]

Annual Energy Production

AEP

Annual Energy Production

AEP

calculation of expected

annual energy yield

calculation of expected

annual energy yield

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Influence of wind speed deviationsInfluence of wind speed deviationson energy productionon energy production

A small deviation of the average wind speed

around 5 m/s results in large deviation of

annual energy production (AEP):

wind speed deviation AEP deviation

vavg = 5 m/s

10 % 20 %

20 % 45 %

vavg = average wind speed


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Sources of possible uncertaintiesSources of possible uncertainties

Meteorological input data: Gaps in the recorded data

Poor or not calibrated anemometer

Damaged or malfunctioning sensors

Change of obstacles in the vicinity of the met mast

(trees, buildings, etc.)

Calculation methods:

Not suitable for complex terrain

Input of roughness, obstacles and orography

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Sources of possible uncertaintiesSources of possible uncertainties

Power curve:

Theoretical curve

Inaccuracy of the measurements

Losses:

Wind farm efficiency Availability of the turbines

Electrical losses / efficiencies


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How to perform an energy yieldHow to perform an energy yield

assessment 1assessment 1

select site for WT(s) installation access (roads, bridges, narrow through roads

grid (distance, voltage, capacity)

general infrastructure (lorries and cranes)

perform a wind speed measurement evaluate data in generating wind speed distribution

get a measured, certified WT power curve

calculate energy yield from the distribution, if met-mastis located at the proposed turbine site

otherwise a wind turbine siting model has to be used

retrieve long-term wind data from a nearby met-station best is hourly data over 10 years or more

otherwise: two wind rose tables (e.g. wind frequency in25 wind speed classes versus 12 wind direction sectors) first table for short-term measurement duration

second table for long-term measurement duration

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How to perform an energy yieldHow to perform an energy yieldassessment 2assessment 2

inspect long-term measurement-station

take with you detailed map, compass, camera and GPS,

if available

determine exact location by means of GPS or detailed

map

make picture from met-mast

make picture 360 around the met-mast (for landscape

description), clearly identify North direction ask for height of tower or estimate

make a sketch of all obstacles in the neighbourhood

(estimate distance, angle and height) indicate kind

(bush, tree, building)

perform long term correction to gain long-term energy

yield

GPS = geographical positioning system


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Wind speed data evaluation software: www.ammonit.de

www.nrgsystems.com

General information on wind energy:

www.windpower.dk

2-4-2 energy yield assessment

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