Tesla Symp Djurisic

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SIXTH INTERNATIONAL SYMPOSIUM NIKOLA TESLA

October 18 – 20, 2006, Belgrade, SASA, Serbia

Prediction of Annual Electricity Production ofPerspective Small Wind-Plant in the Region of

Deliblatska Peščara Nikola Rajaković1, Željko Đurišić1, Momčilo Bubnjević2, Dušan Mikičić1

Abstract – In this paper the annual electricity production of

perspective small wind-plant of installed power 3 0.85MW at

site Čibuk at the periphery of Deliblatska Peščarahas beenestimated. Standard three-hour meteorological measurements ofwind speed at meteorological stations Vršac and Banatski

Karlovac have been used, as well as measurements at custom40m anemometer mast that was installed at site Dolovo. For theprediction of the installed power annual usage factor for a wind-

plant at site Čibuk, available data have been processed insoftware package WAsP. The vectorial topographic map of the

wider target region has been formed, with the detailed analysis oforography, obstacles and terrain roughness. Through

comparative analysis, the paper shows to which extent standardmeteorological data can be used for the prediction of some wind-

plant’s electricity production, as the most relevant factor for theproject cost-effectiveness.

Keywords – Wind-plant, Elctricity production, Capacityfactor, Deliblatska Peščara

I. I NTRODUCTION

Northeastern part of Serbia is characterized by a strongsoutheastern wind. This wind with descending component isstronger than ascending wind that arises simultaneously. Thearea affected by this local wind (Košava) is surrounded bymountains from the south and east, and open towards northand west. Košava mostly occurs during the colder period ofthe year.

Available measured data have shown that Vojvodinarepresents the region of special interest for wind applications.Custom wind measurements in this region are of particularimportance because lowland terrain provides very reliablespace extrapolation of measurements in a wide radius aroundthe measurement mast (20 to 30km).

-----------1 Nikola Rajaković, Željko Đurišić, Dušan Mikičić are with the

Faculty of Electrical Engineering, Bulevar kralja Aleksandra 73,11000 Belgrade, Serbia, E-mail: [email protected];[email protected]; [email protected]

2Momcilo Bubnjevic is with the ACIES Engineering, Belgrade,Serbia, E-mail: [email protected]

Lowland terrain and relatively well developed distributionnetwork in Vojvodina are a precondition for low costs of

connecting perspective wind-plants to electric system. RiverDanube and road infrastructure allow cheap transport of wind-generators from countries of European Union and lowerection costs, which have significant impact on the economyof wind-generators [1], [2]. Vojvodina also has relatively lowkeraunic level, which is also a relevant factor in selectinglocation for a wind-plant. These are the essential reasons forfavouring Vojvodina as a perspective region for wind-plantconstruction.

Based on available custom measurements conducted onanemometer mast of 40m height and using WAsP, a relativelygood wind potential has been determined at a higher numberof micro locations in wider target region Deliblatska Peščara.

Wind is characterized by relatively stable streaming withoccasional occurrence of squalls that rarely exceed 25m/s.

As a specific example, annual capacity factor of perspectivewind-plant at site Čibuk will be analysed. Figure 1 presentssatellite snapshot of wider region around target location.

Fig. 1. Satellite snapshot of wider region aroundtarget site Čibuk

The objective of the analysis was the construction ofwind-plants with three turbines Vestas V-52, each of 850 kWnominal power, so wind-plant installed power would be 2550

kW. Wind turbines would be put on masts at 55m altitudes.

Deliblatska

Peščara

Target site



In order to evaluate cost-effectiveness of perspectivewind-plant, it is necessary to determine, as reliably as

possible, it’s installed power usage factor that dominantlyaffects the price of electric energy produced by wind-plant.This factor is very sensitive to errors in wind speedestimation, as wind power depends on the third power of windspeed [3]. Due to this fact, it is necessary to dispose ofaverage ten-minute measurements in order to give the best

possible estimation of wind speed integration over time, i.e.specific annual available wind energy. Considering that thesemeasurements are performed during a relatively short time

period, mostly a year, it is necessary to perform climatologiccorrection of measurements in order to determine the “averageyear”. In this respect, it is also necessary to includemeteorological measurements in the analysis. The space andwind speed height profile extrapolation require usage ofcomplex terrain models that involve orography, roughness,obstacles and river paths. This analysis uses WAsP, as

professional software for this kind of applications. Theanalysis has been conducted based on real wind speed

measurements and real terrain conditions for a perspectivesmall plant with real wind-generator characteristics.

II. PREDICTION OF WIND-PLANT CAPACITY FACTOR

USING STANDARD METEOROLOGICAL DATA

The meteorological network in Serbia provides continuouswind recording. Wind speed measurements are conducted atstandard height of 10m. Anemometers are generally of oldertypes with tape recording (anemographs), thereby makinghourly average wind speed data mostly unavailable. In lasttwo years, modern digital equipment with remote

measurement readings of wind parameters has been installedat several measurement stations in Serbia. Data on three-hourmeasurements of wind speed and direction are available indigital form. Determining the extent to which this data can beused in wind-plant planning is of particular interest.

For the analysis of perspective wind-plant at site Čibuk,data of wind measurements in hydrometeorology stationsBanatski Karlovac and Vršac have been used in this paper.Standard data on three-hour wind speeds for the period from1999 to 2006 were collected. Data were processed and

prepared for usage in software package WAsP. Also,measurement stations were visited and their exact locationswere determined with GPS receiver, as well as position and

character of obstacles in their wider surroundings. A uniquevectorial topographic map of wider region has been formed,with precisely entered terrain roughness data and river paths.Figure 2 depicts the used vectorial map with the followinglocations indicated on it: hydrometeorologic station Vršac (1),hydrometeorologic station Banatski Karlovac (2), 40m windmast (3) and turbine sites (wind turbine symbol). In Table Ithe results of WAsP estimation of overall and individualexpected annual electric energy production (AEP) for theanalysed wind-plant, as well as wind parameters calculated forselected location, have been showed. Calculations were madeusing seven-year data on wind speed and directionmeasurements at measurement station Vršac.

Fig. 2 Vectorial topographic map of the analysed region

TABLE IESTIMATED WIND PARAMETERS AND ANNUL PRODUCTION OF WIND

PLANT AT SITEČIBUK , OBTAINED FROM SEVEN-YEAR CLIMATOLOGIC

WIND MEASUREMENTS AT MEASUEMENT STATION VRŠAC

Ia) Summary results

Ib) Site results

Ic) Site wind characteristics

TABLE IIESTIMATED WIND PARAMETERS AND ANNUL PRODUCTION OF WIND

PLANT AT SITE ČIBUK , OBTAINED FROM SEVEN-YEAR CLIMATOLOGIC

WIND MEASUREMENTS AT MEASUEMENT STATION BANATSKI

K ARLOVAC

IIa) Summary results

IIb) Site results

IIc) Site wind characteristics

1

2

3



Quantities in Table Ic have the following meaning: U –estimated average annual wind speed, E - average specificwind power, A and k – corresponding parameters of Weibull’sdistribution density of wind speed probabilities. All

parameters relate to the height at which wind-turbine isinstalled (55m).

Table II shows the results of calculation using data on three-hour wind speed measurements, for the same time period as in

previous analysis, obtained at station Banatski Karlovac.Analysing acquired results, a conclusion can be made that

there is a big difference in calculated expected annual production of analysed wind-plant when measurements fromVršac and measurements from Banatski Karlovac are used.According to data from hydrometeorologic station Vršac,expected power usage factor of the wind-plant at annual levelis:

%75,2910085,038760

6643100

87601

1 =⋅⋅⋅

=⋅

=

nP

AEP Net τ

According to data from hydrometeorologic station at

Banatski Karlovac, expected capacity usage factor is:

%33,1810085,038760

4093100

87602

2 =⋅⋅⋅

=⋅

=

nP

AEP Net τ

According to data of wind parameters measurements athydrometeorologic station Vršac, Čibuk site is very

promising, but considering data from Banatski Karlovac, thesite is below average. This yields a conclusion that the

prediction of electricity production based on standard three-hour meteorological data on wind speed measurements is veryunreliable and can not be used even for general estimates.Large deviations are present because standard three-hour windspeed measurements represent “samples” that are not dense

enough to yield an estimation of integral energy produced bywind-generator.

III. PREDICTION OF WIND-PLANT CAPACITY

FACTOR BASED ON MEASUREMENTS OF WIND

PARAMETERS AT CUSTOM MEASUREMENTS MAST The summary of previous analysis is that for planning a

wind-plant construction it is necessary to conduct customwind speed measurements at selected site and, if possible, atan altitude that corresponds to the wind-turbine axle. In thegiven case, wind speed measurements used are from 40m

anemometer mast installed at site Dolovo, that is located at3.5km distance from analysed site Čibuk.

Table III shows the results of WAsP calculation of theexpected annual production for analysed wind-plant, based onmeasurements at 40m anemometer mast. The calculation usesaverage ten-minute measurements of wind speed anddirection, at 40m altitude, during one year period. Spaceextrapolation has been performed using the same vectorialtopographic map as in previous analyses.

Based on custom speed measurements on 40m anemometermast, the estimated net annual production of wind-plant is

Net AEP3=4711MWh. The capacity usage factor that

corresponds to this production is:

%09,2110085,038760

4711100

87603

3 =⋅⋅⋅

=⋅

=

nP

AEP Net τ

TABLE IIIESTIMATED WIND PARAMETERS AND ANNUL PRODUCTION OF WIND

PLANT AT SITE ČIBUK , OBTAINED FROM MEASUREMENTS OF WIND

PARAMETERS ON 40M ANEMOMETER MAST AT SITE DOLOVO

IIIa) Summary results

IIIb) Site results

IIIc) Site wind characteristics

The obtained capacity usage factor, regarding selectedwind-generators of relatively small power and high cut-inwind speed of 4 m/s, shows that there is a significanttechnically usable wind potential at selected location thatallows construction of even small wind-plants which could beconnected to the existing medium-voltage 20kV network. Ifmore powerful generators would be installed at selected site,capacity factor would be considerably higher. For instance,this factor would be about 30% for wind-generators E-82 of 2MW, [4]. The explanation comes from the fact that biggerwind-generators are placed on higher masts, and additionally,cut-in wind speed for E-82 wind-generator is 2.5 m/s, so theytake advantage of even very weak winds.

A. Climatologic Correction Analysis of wind-plant productivity based on custom

measurements can be taken as very reliable. However, it is

based only on one-year measurements and such a year can bemore or less windy than the average year for the designedlifetime of wind-plant (20-25 years). Regarding producedelectric energy, annual variations can reach 30%, so it isnecessary to put weighting factors on available measurementsin order to have the average results. To obtain average annual

production, the cost-benefit analysis for some wind-plantshould be performed. It is necessary to have themeasurements for several years period (like in determining theflow for hydro-plants design). Such custom windmeasurements (unlike hydrologic flow measurements) usuallydo not exist, so the only available are standardhydrometeorologic measurements.



In this paper a climatologic correction for estimated production of the analysed wind-plant will be performed usingseven-year data on wind speed measurements at measurementstations Vršac and Banatski Karlovac. Figure 3 showscomparative time diagrams of wind speed variations duringDecember 2005, obtained according to three-hour data fromhydrometeorologic stations and average three-hour windspeed measurements at measurement mast, at 20m altitude.

Fig. 3. Comparative diagrams of wind speed variations

measured at meteorological stations and at anemometer mast

In comparative analysis in Figure 3, a relatively goodmatching of measurements can be noticed, even though the“samples” of three-hour measurements in hydrometeorologicstations are compared to average three-hour wind speedsmeasured at custom measurement mast. Analysis in Figure 7shows that measurements pertain to the same climatologicregion. The interesting point is that in the same time interval(December 12th/13th) measuring instruments froze at all threemeasurement sites.

Table IV shows estimated electricity production in theanalysed wind-plant, based on available data on wind-speed

measurements at measurement stations, that correspond to 1year measurement period at site Dolovo, and based on data forseven years period (1999-2006). The objective of thiscomparative analysis is to evaluate how much wind potentialin the year during which custom measurement had beenconducted deviates from seven-year average.

Analysis in Table IV shows that wind potential in one year period during which measurements had been performed at siteDolovo was below seven years average, and this is indicated

by measurement data from both analysed measurementstations.

The interesting point is that both measurement stationsindicate the same difference in expected annual electric

energy production when seven-year and one-yearmeasurements are used, and this difference is about∆ AEP=500MWh/year. If this correction is accepted in itsabsolute value, the expected annual production of analysedwind-plant would be about 5.200GWh, so the correspondingaverage annual capacity usage factor would be:

%33,2310085,038760

5004711100

87603

3 =⋅⋅⋅

+=

⋅

∆+=

n

avr P

AEP AEP Net τ

The obtained capacity usage factor indicates the significantusable wind potential in the region Južni Banat, where evenconsiderably better micro locations for perspectiveconstruction of wind-plants can be identified, by detailed

analysis based on available measurements.

TABLE IVESTIMATED ANNUAL ELECTRICITY PRODUCTION IN A WIND-PLANT AT

SITEČIBUK , BASED ON ONE-YEAR AND SEVEN-YEAR MEASUREMENTS OF

WIND SPEED AT MEASUREMENT STATIONS AND USING MEASUREMENT MAST

IV. CONCLUSION

In this paper the annual capacity usage factor for a perspective wind-plant of installed power 3×850 kWh at siteČibuk at the periphery of Deliblatska Peščara has beenestimated. Using professional software package WAsP,comparative analysis of perspective wind-plant expected

production has been performed, based on long-time windspeed measurements at measurement stations Vršac andBanatski Karlovac, as well as on specific measurements at40m measurement mast at site Dolovo. Obtained resultsindicate that wind-plant planning can not be done just basedon meteorological measurements and that it is necessary toconduct specific measurements.

Based on specific one-year measurements at 40manemometer mast with climatologic correction and seven-yeardata from measurement stations Vršac and Banatski Karlovac,average annual capacity usage factor of the analysed wind-

plant has been evaluated to the value of 23.33%. Estimated capacity usage factors indicate significant usablewind potential in the region Južni Banat, where according to

available measurements even significantly better microlocations can be identified for perspective construction ofwind-plants in Serbia. In addition to wind potential for theanalysed region, low costs of transport, connection to networkand maintenance should be expected, due to an accessibleterrain with built-up road infrastructure and electric network.

ACKNOWLEDGEMENT

This work was supported by European Commission,Directorate General on Research and TechnologyDevelopment and International Co-operation Activities(INCO) under contract no FP6-509161 (RISE Project )

R EFERENCES

[1] Ž. Đurišić, M. Đurić, D. Mikičić, Đ. Diligenski, Economics ofwind farms, ELECTRA III, Conference Proceedings, pp 124-130. Herceg Novi, June 2004.

[2] J. Beurskens, P. H. Jensen, Economics of wind energy, Renewable Energy World , Vol. 4, No 4, 2001.

[3] M. Đurić, A. Čukarić, Ž. Đurišić, Power plants, Belgrade, 2004.

[4] Ž. Đurišić, N. Rajaković, D. Mikičić, M. Bubnjević, FeasibilityAnalysis of Wind-plant in the Region of Deliblatska Peščara(Serbia), Proc. of 6th Balcan Power Conference, Ohrid,Macedonia, June 2006.

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Tesla Symp Djurisic