yos Un

y cad dth etheWe red watio

southith Unorth aorthe1700 k1 shownomy

inhabitants per square km. The annual population growth rate isabout 6.4%.

Although most of the population has access to electricity, thereare still rural and remote areas that are not electried. As the

highest wind potential in Oman, becomes marginally economicalat a gas price of 6 $/MMBtu. At the opportunity cost of naturalgas price of approximately 3 $/MMBtu and adding a depletionpremium of 3% per annum the cost of wind energy becomescomparable to open cycle gas-turbine (GT) power plants. Thecombined cycle (CCGT) power plants remain cheaper, however.The comparison is made by assuming the economic life of assets(GT, CCGT and 20 MW wind farm) to be 25 years and the realdiscount rate at 7.55%.

* Corresponding author.E-mail addresses: asmalik@squ.edu.om (A. Malik), albadi@squ.edu.om

Contents lists availab

Ener

.e ls

Energy 34 (2009) 15731578(A.H. Al-Badi).oil and gas revenues, which account for about 81% in 2006 of thecountrys export earnings and 48.6% of its gross domestic product(GPD) [2]. The annual crude oil production was nearly 270 millionbarrel in 2006, whereas the annual natural gas production was1,068,888 million cubic feet during the same year [2]. Expandingnatural gas production has become the main focus of Omansstrategy to diversify its economy away from the oil sector. Most ofthe electrical power produced is based on natural gas. The totalland area of Oman is 309,500 km2 with total population of 2.7million people in 2007, thus the population density of around 8.8

area and cathodic protection of pipelines.The wind speed in Oman is relatively high compared with

other gulf countries. Omans southern region appears to havethe highest wind potential. Fig. 2 shows the average wind speedin some of the cities in Oman [4,5]. The highest wind potentialis in Quiroon Hariti and Thumrait. A recent study done onrenewable energy resources for Authority for Electricity Regu-lation of Oman [6] reveals that at the present gas price of1.5 US$/MMBtu wind energy is not economical for grid appli-cation. The wind energy at Quiroon Hariti, (see Fig. 2) the1. Introduction

Oman is located in the extremeArabian Peninsula. It is bordered wthe northwest, Saudi Arabia to the nsouthwest, the Gulf of Oman to the nto the southeast and east. Oman hasthe Land is rocky and sandy [1]. Fig.has a hot and arid climate and its eco0360-5442/$ see front matter 2009 Elsevier Ltd.doi:10.1016/j.energy.2009.07.002eastern corner of theited Arab Emirates tond west, Yemen to theast and the Arabian Seam of coast and most ofs map of Oman. Omanis heavily dependent on

population of Oman is thinly populated and geographically spread,the power systems in Oman are also not interconnected. Moreover,the load in the south is concentrated to small towns/cities andtherefore locally supplied by the diesel generators ranging from1 to 2 MW capacity [3]. To date there has been little fundingprovided for research and development that will provide a roadmap for the growth of the Omani renewable sector. Although theOmans solar potential is excellent, solar energy applications havebeen limited to street lighting, trafc lights, telephone in remoteWind turbineOmanbetween 6.7 and 8.0 years. 2009 Elsevier Ltd. All rights reserved.Diesel-engine as sunk. The simple payback period of the turbine is between 5.1 and 5.4 years and discounted paybackEconomics of Wind turbine as an energfor remote application in oman

A. Malik, A.H. Al-Badi*

Department of Electrical & Computer Engineering, College of Engineering, Sultan Qabo

a r t i c l e i n f o

Article history:Received 6 March 2009Received in revised form28 June 2009Accepted 1 July 2009Available online 3 August 2009

Keywords:Fuel saver

a b s t r a c t

This paper presents a studsaver. The load and the winthe station is provided wiminimum load recorded atthe site is 5.7 m/s. A 50-kturbine as a fuel saver. Thspecic cost of the selectecomparing to diesel gener

journal homepage: wwwAll rights reserved.fuel saver A case study

iversity, P.O. 33, Al-Khod, Muscat-123, Sultanate of Oman

rried out to investigate the economics of wind turbine as an energy fuelata is taken from a remote agricultural research station in Oman. Presently,lectricity from diesel-engine generating units. The annual peak load andsite is 130 kW and 28 kW respectively. The annual average wind speed at

wind turbine is selected to demonstrate the economic feasibility of thesults show that wind energy utilization is an attractive option with totalind turbine ranges between 7.4 and 8.45 /kWh at 7.55% discount rate

n operating cost of 14.3 /kWh, considering the capital cost of diesel units

le at ScienceDirect

gy

evier .com/locate/energy

Fig. 2. Annual average wind speeds of some sites in Oman (m/s).

nergy 34 (2009) 15731578A. Malik, A.H. Al-Badi / E1574This paper presents a case study to demonstrate the economicfeasibility of wind energy utilization at a remote agriculturalstation. Sections 2 and 3 describe the location of the site and theannual energy consumption at the site respectively. Section 4calculates theWeibull parameters at the site and the power densityat the site. Wind turbine selection and performance is discussed inSection 5. Section 6 shows the economic analysis and discusses theresults. Section 7 concludes the paper.

2. Site selection

From Fig. 2 it is clear that Thumrait site has the second highestaverage annual wind speed compared to other cities. An agricultureresearch station in Najd, 80 km north of Thumrait on the mainhighway connecting Muscat with Salalah, is selected to demon-strate the economic feasibility of the wind power application. Thesite has been selected because of the following reasons:

In December 1996, Ministry of Water resources of Oman(Currently Ministry of Regional Municipality and Waterresources) installed an experimental 10 kW BWC Excel windturbine at Heelat ar Rakah camp around 5 km away from Najdand a design speed of 5.7 m/s was adopted based on Thumraitsite data [7]. Moreover, to insure that the wind speed distri-bution is not different from Thumrait site a newmeteorologicalstation was established at Heelat ar Rakah camp and threemonths of wind-speed data collected and compared with thedata available from Thumrait meteorological station [8]. Smalldifference in the data sets was found as a result the same windspeed is chosen for the selected site at Najd. This system was

The station used to have three sets of generators, each one ratedat 320 kVA, 420 V and 250 kWat 0.8 power factor. The annual peak

Fig. 1. Map of Oman.load and minimum load recorded at the site is 130 kW and 28 kWrespectively. The farm average daily requirement of water is220 m3/day.

Fig. 3 shows a typical daily load curve for the site. It can be seenthat the load is almost constant for most of the time except whenthe water is pumped for few hours. The load factor, which is theratio of average load to peak load, for the daily load curve shown inFig. 3, is 32%. The annual energy is calculated by assuming theannual load factor of 32%, same as that of typical daily load curveshown in Fig. 3, and the peak load recorded at the station.installed for research activity to assess the use of brackishgroundwater for crop irrigation by harnessing wind energy inthe region. By the use of this system, it has been establishedthat Wind energy or wind/solar (hybrid) energy can be usedsuccessfully for the abstraction of groundwater in remotelocations and can be used for irrigation and communitydevelopment purposes [9].

The load data of Najd agriculture research station was readilyavailable.

3. Load curve and annual energy consumption at the site

The size of agricultural research station is about 1 km2 andprovides facility to do experiments on lemon, dates, wheat, cornetc. The station also serves as a rest house (lodge) for theMinistry ofAgriculture staff traveling between Salalah and Muscat.0.0

30.0

60.0

90.0

120.0

7:00AM

9:00AM

11:00AM

1:00PM

3:00PM

5:00PM

7:00PM

9:00PM

11:00PM

1:00AM

3:00AM

5:00AM

Time

Lo

ad

(kW

)

Fig. 3. Typical daily load curve at the at Heelat ar Rakah site.

Fu 1 expuc

k(7)

and the probability density function by

f u dFdu

kc

uc

k1exp

uc

k; k > 0;u > 0; c > 1

(8)

The parameters c and k are calculated from the wind data of oneyear obtained from Thumrait station. The value of shape parameterwith 95% condence interval ranges from 2.79 to 3.10 with mean of2.94 and a standard error of 0.078. The value of scale parameterwith 95% condence interval ranges from 6.00 to 6.48 with a meanof 6.24 and a standard error of 0.122.

approximately 10 m and z2 is the height at which a wind speedestimate is desired. The parameter a, dened as wind shear expo-

nergy 34 (2009) 15731578 1575Therefore,

Annual Energy kWh Peak load kWTotal number of annual hours hrsLoad factor (1)

Hence,

Annual Energy kWh 130 kW 8760 h 0:32 364416 kWh (2)

As the minimum load at the site is 28 kW the base-load energyis:

Base-load Energy kWh 28 kW 8760 h 245;280 kWh (3)

4. Power density and Weibull parameters at the site

Power density is a term frequently used in wind energy litera-ture because it is convenient shorthand for how energetic thewinds are during a period of time. Power density is dened as

PA 1

2ru3

W=m2

(4)

where P, power available in wind (W); r, air density (kg/m3);u, velocity of the wind (m/s); A, an area through which the windpasses normally (m2).

Although the power equation above gives us the power in thewind, the actual power that we can extract from the wind issignicantly less than this gure suggests. It can be shown theo-retically that any wind turbine can only possibly extracta maximum of 59.3% of the power from the wind, which is knownas Betz limit. The actual extracted power will depend on manyfactors, such as the type of machine and rotor, the blade design, andthe friction losses. Therefore, the power produced by the windmachine is given as:

PA 1

2Cpru3

W=m2

(5)

where, Cp is the coefcient of performance of the wind machine.Wind turbine manufacturers assume that air density is 1.225

kg/m3, representing air pressure at sea level and a temperature of15 C. The site with an average temperature of 26 C and anelevation of 400 m above sea level has an air density of about1.13 kg/m3. Substituting the air density value at the site, Eq. (4)becomes:

PA 0:565u3

W=m2

(6)

Since the cubes average is greater than the cube of the average,power density is calculated by summing a series of powerdensity calculations for each wind speed and its frequency ofoccurrence. There are several density functions, which can beused to describe the wind speed frequency curve. However,much attention has been given to the Weibull function, since itis a good match with the experimental data [10]. In some casesthe Rayleigh distribution, a special case of the former, ispreferred.

The Weibull distribution is characterized by two parameters;the shape parameter k (dimensionless) and the scale parameterc (m/s). The cumulative distribution function for wind velocity u is

A. Malik, A.H. Al-Badi / Egiven by:nent, is determined empirically and is site-specic. The averagevalue of a has been determined bymanymeasurements around theworld to be about one-seventh (1/7). The meanwind speed at 36 mtower height is then 6.85 m/s. Using the average value of a, and theannual mean wind speed at 36 m above the exposed area theannual mean wind power density for the site is 242W/m2.

5. Wind turbine selection

A single 50-kWwind turbine of TeKVal Intl Inc [11], the TekVal-50 kWmodel, is selected to demonstrate the economical utilizationof wind energy at the site. The reason for choosing this model isthat the size is reasonable to match the base-load, and the quotedprice of the unit with tower height of 36 m was readily availablefrom the manufacturer including the wind turbine specications.The TekVal-50 kW is rated at 50 kW at a wind speed of 13 m/s(29 mph).

Table 1 shows the inputs necessary to calculate the Weibullperformance calculation for the selected wind turbine. An averageUsing the value of k as 2.94 and c as 6.24 in Eq. (8) the windprobability density is found at different weed speed and plotted inFig. 4. Based on theWeibull density function the annual meanwindpower density for the site at 10 m above exposed area is 138 W/m2.Usingk 3.1and c 6.0 the lowervalueofpowerdensity is120W/m2and with k 2.79 and c 6.48 the upper value of power density is159W/m2. The annual meanwind power density can be estimated atother tower heights by the following formula:

uz2uz1

z2z1

a(9)

In this equation z1 is usually taken as the height of measurement,Fig. 4. Weibull density function for the site.

value of wind shear exponent is used to calculate the wind speed atthe hub of the tower. Air density factor is a derating factor used topredict the performance of turbine at the site conditions. The airdensity factor is worked out from the ratio of air density at the site(1.13 kg/m3) to the air density that wind turbine manufacturersassume (1.225 kg/m3). Turbulence Factor is another derating factorfor turbulence, product variability, and other performance inu-encing factors. Setting this factor to 0% will over-predict perfor-mance for most situations; here 10% is used for derating the turbine

104,300120,100 kWh.The following assumptions are used in economic analysis:

Table 1Input for the Weibull performance calculations.

Ave. wind (m/s) 5.7Weibull k 2.94Weibull c 6.24Site altitude (m) 400Site average temperature 26 CAir density factor 7.8%Turbulence factor 10.0%Anemometer height (m) 10Tower height (m) 36Wind shear exp. a 0.143Hub average wind speed (m/s) 6.85

A. Malik, A.H. Al-Badi / Energ1576power. So the combined derating is around 17%.Table 2 shows the Weibull performance calculations for the

selected wind turbine. Wind speed probability is calculated asa Weibull curve dened by the average wind speed and a shapefactor, k, at the tower height. To facilitate piece-wise integration,the wind speed range is broken down into bins of 1 m/s in width(Column 1). For each wind speed bin, instantaneous wind turbinepower (Column 2) is taken from the manufacturer curve. Thispower is derated (Column 3) by two derating factors mentionedearlier. The derated power is then multiplied by the Weibull windspeed probability (Column 4) and the total annual hours to get thenet average turbine energy output (Column 5) contributed by windspeeds in that bin. The sum of these contributions is the annualenergy output of the turbine. Column 6 of the table is the modiedturbine energy discussed in the next section.

Figure 5 shows the wind turbine power performance both atideal conditions and at the site conditions.

Table 2Weibull performance calculations for the selected wind turbine.

Wind speedBin (m/s)

Power(kW)

Deratedpower (kW)

Windprobability (f)

Annualenergy (kWh)

Modiedannualenergy (kWh)

1 0.00 0.00 0.78% 0.00 0.002 0.00 0.00 2.93% 0.00 0.003 1.02 0.85 6.14% 455.37 455.37

4 2.55 2.12 9.82% 1819.63 1819.635 5.10 4.23 13.09% 4854.60 4854.606 8.74 7.25 15.07% 9572.66 9572.667 15.23 12.64 15.13% 16751.13 16751.138 23.31 19.34 13.29% 22513.24 22513.249 32.89 27.29 10.17% 24314.92 24314.9210 44.52 36.94 6.74% 21827.88 16544.0111 53.45 44.35 3.85% 14941.38 9432.5212 55.00 45.64 1.87% 7468.73 4582.1413 53.00 43.98 0.77% 2950.15 1878.2514 50.00 41.49 0.26% 952.86 643.0515 46.00 38.17 0.07% 248.04 181.9516 41.00 34.02 0.02% 51.14 42.0917 35.00 29.04 0.00% 8.17 7.8718 28.00 23.23 0.00% 0.98 0.9819 24.00 19.92 0.00% 0.10 0.1020 22.00 18.26 0.00% 0.01 0.01

Total 100.00% 128,730.99 113,594.526. Results and discussions

The annual energy the turbine capable to produce is between114,300140,000 kWh with k 3.1 and c 6.0 for the lower valueof energy and with k 2.79 and c 6.48 the upper value of energy.With mean value of k 2.94 and c 6.24 the annual energy is128,700 kWh (see Table 2). However, all the energy producedcannot be assumed to be utilized because there may be intervalswhen the turbine can produce more power but the load demand atthat particular hour is not there. The most pessimistic case is takento demonstrate the economic feasibility. The most pessimistic caseis that the power produced over and above the base-load isassumed unutilized. However, one can do analysis in which theturbine power that exceeds the base-load can be shown to eithermeet some of the demand above the base-load by nding some sortof coincidence factor between the load and the wind energy orassumed to be utilized in storing water in a water tank which couldbe used later for agricultural purposes when the wind is not there.But that will complicate our analysis. In the former case a detailedstudy is required to nd the coincidence factor between the loadand the wind energy and in the latter case a storage tank has to besized and the cost of the storage tank should be included So forsimplicity purposes wewill assume here that any power and henceenergy produced over and above the base-load is non-utilizable.The column 6 of Table 2, therefore, is the modied energy output inwhich for those hours or percentage probability when the turbinepower exceeds base-load (28 kW) the energy is recalculated withxing the turbine output to 28 kW. The energy produced with thepessimistic case is 113,600 kWh. The range of energy producedwith the pessimistic scenario for the two sets of values of k and c is

0.00

10.00

20.00

30.00

40.00

50.00

60.00

1 3 5 7 9 11 13 15 17 19Wind Speed (m/sec)

Po

we

r (k

W)

Ideal PowerDerated Power

Fig. 5. Wind turbine performance at the site.

y 34 (2009) 15731578 Discount rate: 7.55% (Omani Government has recently usedthis rate [6]).

Base load to be served will not decrease over the lifetime of theproject.

Diesel fuel prices will not decrease over the period; anyincrease in fuel prices will not invalidate the conclusions ratherreinforce them. A constant fuel prices for the analysis is used.The economic cost of diesel plus transportation, storage andhandling cost is considered equal to the market price of diesel(nancial cost in Oman).

Capital cost of diesel-engine generators considered sunk. The TekVal-50 kW standard system quoted prices is US$65,900. Assuming about 20% installation cost the expectedprice after installation will be w$80,000.

Wind turbine life is 20 years (Manufacturers claim).

Table 3Diesel Cost Analysis.

Items Symbols/formul

No. of barrels in one ton of gas-diesel oil [12] D1No. of imperial gallons in one barrel D2No. of liters in one imperial gallon D3No of liters per ton of oil (calc.) D4D1D2Energy in Joules in each ton D5Energy in Joules per liter (calc.) D6D5/D4No. of Joules per BTU D7Energy in Btu per liter (calc.) D8D6/D7No. of liters in one MBtu D9 106/D8Cost of diesel oil transportation and handling D10Average heat rate for the diesel (assumed) D11The cost of fuel in $/kWh D12D9D10Assuming O&M cost 10% of fuel cost D13Total fuelO&M cost D14D12D1Total cost of electricity (assuming 5% losses) D15D14/(1

A. Malik, A.H. Al-Badi / EnergTable 4Wind turbine cost analysis.

Items Symbols/formula Quantity Units

Capital cost of turbine (approx.) W1 80,000 $Life of turbine W2 20 YrsDiscount Rate W3 7.55 %Capital recovery factor (CRF)(calc.) W4 W31W3W21W3W21 0.09847 %Annutized cost of turbine (calc.) W5W4W1 7877 $Energy generated by the turbine

(found in Table 2)W6 113,600 kWh6.1. Diesel cost analysis

Table 3 provides the stepwise procedure adopted to calculatethe cost of electricity by diesel generating units. The cost of elec-tricity generated by diesel generating units is about 14.3 /kWh.

6.2. Wind turbine cost analysis

Table 4 provides the stepwise procedure adopted to calculatethe cost of electricity by wind turbine unit. The cost of electricitygenerated by wind turbine unit is about 7.8 /kWh at 113,600 kWh

Table 5Economic analysis.

Items Symbols/formula Quantity Units

Total annual load energy E1 364,416 kWhEnergy replaced by wind annually E2W8 107,920 kWhCost of supplying wind energy (calc.) E3 E2W10 540 $Cost of supplying replaced energy

with diesel (calc.)E4 E2D15 15,419 $

Savings by the wind E5 E4 E3 14,880 $Net savings including

depreciation (calc.)E6 E5W5 7002 $

Net present value (calc.) E7 E6/W4 71,116 $Simple payback period E8W1/E5 5.4 yrsDiscounted payback period E9 is calculated

indirectly usingthe followingformula:E5 W1W31W3

E9

1W3E91

7.2 yrs

Loss of energy 5% assumed (calc.) W7 0.05W6 5,680 kWhNet useful energy (calc.) W8W6W7 107,920 kWhCapital cost/kWh (calc.) W9W5/W8 0.073 $/kWhO&M cost (assumed, claimed to be

maintenance free)W10 0.0050 $/kWh

Total specic cost W11W9W10 0.0780 $/kWhTable 6Results of economic analysis for two different sets of values of k and c.

Items k 3.1 and c 6.0 k 2.79 and c 6.48Total annual load energy (kWh) 114,300 kWh 140,000 kWhUtilizable energy (pessimistic case) 104,300 kWh 120,100 kWhNet useful energy after 5% losses 99085 kWh 114,095 kWhTotal specic cost 8.45 /kWh 7.40 /kWhSavings by the wind $ 13,622 $ 15,731Net present value (calc.) $58,745 $79,763Simple payback period 5.9 yrs 5.1 yrsDiscounted payback period 8.0 yrs 6.7 yrs

a Quantity Units

7.23 barrels/ton35 gal/barrel4.54609 ltires/gal

D3 1,150.39 litres/ton4.25E10 J/ton36935362 J/litre1,055 J/Btu35,009.82 Btu/ltr28.56 litres/Mbtu0.36 $/litre12,000 Btu/kWh

D11/D106 0.1234 $/kWh0.0123 $/kWh

3 0.1357 $/kWh0.05) 0.1429 $/kWh

y 34 (2009) 15731578 1577with a range from 7.4 to 8.45 /kWh for 120,100104,300 kWh,respectively.

6.3. Economic analysis

Table 5 provides the stepwise procedure adopted to do economicanalysis. The annual wind energy savings by replacing the energygeneratedbydiesel units is $14,880. Thenet present value is $70,000with simple payback of 5.4 years and the discounted payback of7.2 years. The analysis can easily be repeated for different discountrates or assumptions using the same stepwise procedure. Table 6provides the results of Economic Analysis for two different sets ofvalues of k and c.

7. Conclusion

In this article a case study of wind turbine as energy-fuel saverwas investigated. A site was selected to demonstrate the economicsof wind-diesel hybrid system. At the selected site typical daily loadcurveanda co-relatedwind speeddata atnearbystationwasknown.From thewind speed dataWeibull shape and scale parameterswereworked out. A 50-kW turbine performance, at differentwind speedsis taken from the manufacturer curve (WindCad model). The idealperformance of turbine is then derated for the site conditions andthe annual energy that the turbine can produce is worked out byassuming Weibull distribution of wind speed. The annual energygenerated by wind is then modied to account for any mismatchbetween the load above base-load and the turbine output abovebase-load (a complete mismatch is assumed taking a very pessi-mistic case). The specic or life cycle cost of the turbine is thenworked out. The specic cost ranges between 7.4 and8.45 /kWh. Tojustify the wind turbine integration into the existing diesel gener-ation the diesel generation operating cost is worked out. It is found

that the operating cost of diesel generation is 14.3 /kWh which isroughly 1.71.8 times the specic cost of wind turbine. This showsthat the turbine can be economically embedded into the existingsystem. The simple payback period of the turbine ranges between5.1 snd5.9 years and discounted payback is between 6.7 and 8.0years at 7.55% discount rate.

Acknowledgements

The authors acknowledge the nancial support provided bySultan Qaboos University internal research grant.

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A. Malik, A.H. Al-Badi / Energy 34 (2009) 157315781578

Economics of Wind turbine as an energy fuel saver - A case study for remote application in omanIntroductionSite selectionLoad curve and annual energy consumption at the sitePower density and Weibull parameters at the siteWind turbine selectionResults and discussionsDiesel cost analysisWind turbine cost analysisEconomic analysis

ConclusionAcknowledgementsReferences