optimization of energy production system in the dodecanese islands

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Renewable Energy 30 (2005) 195–210

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Optimization of energy production systemin the Dodecanese Islands

C. Koroneos �, N. Zairis, P. Charaklias, N. MoussiopoulosDepartment of Mechanical Engineering, Laboratory of Heat Transfer and Environmental Engineering,

Aristotle University of Thessaloniki, P.O. Box 483, 54124 Thessaloniki, Greece

Received 30 May 2003; accepted 2 May 2004

Abstract

The ongoing depletion of the fossil fuels and the dependency of the economies on themhave made the need for new sources of energy more obvious. Renewable energy sources(RES) can ensure the sustainable development of the communities, and especially of those inwhich RES are in abundance. This study deals with the exploitation of RES in the DodecaneseIslands. Specifically, it is examined the optimum percentage by which the renewable sourcescan participate in the energy production system. Three different scenarios are examined. Thefirst scenario considers that the existent system should be used less than 75% for environ-mental reasons, in the second scenario, a minimization of the electricity production cost issought without any environmental constraints, while in the third scenario, it is consideredthat the RES’ participation in the electricity production would be 30% at most accordingto the current legislation. The environmental impacts from the energy production arequantified and a comparison is made between the impacts resulting from the existingsystem and the system found from the first scenario, because this is the scenario with thehighest penetration of the RES to the energy production system.# 2004 Elsevier Ltd. All rights reserved.

Keywords: Electricity; Energy sources; Renewable energy sources; Optimization; Dodecanese

1. Introduction

The oil crisis that took place in the last years made more obvious the depen-

dency of the world economy on the ‘‘black gold’’. As a consequence, many

countries are making an effort to move towards new energy sources which exist in

C. Koroneos et al. / Renewable Energy 30 (2005) 195–210196

abundance. The aspect of using renewable energy sources (RES) seems to be themost reliable solution, since they are inexhaustible.

Dodecanese Islands, located in the South-East of Greece, could very well use theRES in order to meet their energy needs. The weather of these islands is sunny forthe most part of the year and the high wind speeds make wind energy an attractivesource. Beside solar and wind power, this region can exploit the geothermal fieldwhich exists in the island of Nissyros (Fig. 1 [1]).

This work examines the optimal use of wind power and geothermal energy forelectricity production and the use of solar energy for heating purposes. Threeenergy scenarios are examined, each time taking into account different environmen-tal and economic considerations.

2. The Dodecanese Islands

The cluster of the Dodecanese Islands lies on the far South-Eastern part ofGreece, and it comprises 200 islands, 19 of which are inhabited (Fig. 2). The areaof Dodecanese is 2579 km2 with Rhodes being by far the biggest of all covering54.2% of the total area. The three biggest islands, Rhodes, Kos, Karpathos, coverabout 75% of the total area of Dodecanese. The population of Dodecaneseis 190,071, with Rhodes accounting for the 61.6% and Kos for the 16.3% of thetotal [2].

Because of their geographical position, sun is plentiful for the most part of theyear. Fig. 3 presents the mean monthly air temperature for Dodecanese, whileFig. 4 presents their mean wind speed [3]. It becomes apparent that systems

Fig. 1. Schematic hydrological model of thermal fluid subsurface flow at Nissyros.

197C. Koroneos et al. / Renewable Energy 30 (2005) 195–210

exploiting the RES could be utilized to satisfy the energy requirements or most ofthem in these islands. It should be noted that the wind speed in Karpathos is muchhigher than any other island in the Dodecanese and this could lead to a safehypothesis that wind energy could very easily satisfy all the island’s needs. More-over, the geothermal field which exists in Nissyros could be exploited to produceelectricity and go on the electricity grid of the Dodecanese.

Fig. 2. The Dodecanese Islands.

Fig. 3. Mean monthly air temperature in Dodecanese.


3. Existing energy production system

The electricity production in the Dodecanese Islands is done with autonomous

power stations (APSs), which are installed in several islands, using heavy fuel oil

(HFO) and Diesel. There are three large APSs [4]:

. APS of Rhodes with an installed power of 206,000 kW, which also supplies elec-tricity to Chalki.

. APS of Kos–Kalymnos. Electricity is produced by two stations in Kos andKalymnos. The total installed power is 54,740 and 14,270 kW, respectively.These stations also provide electricity to Leros, Tilos, Lipsi, Telendos, Pserimos,and Nissyros. In Nissyros, there is a backup station with an installed power of310 kW.

. APS of Karpathos. The total installed power is 10,080 kW. Kassos is also con-nected to this grid.

There are also APSs in Patmos (6880 kW), Simi (5164 kW), Astypalea (1550 kW),

Megisti (452 kW) and Agathonisi (241 kW). It is also of importance to

mention that in order to meet the energy demand in small insular islands, there are

low capacity (0.7 kW) photovoltaic stations installed. Finally, in Karpathos, there

is a wind farm of total installed power of 450 kW.The energy consumption is the highest at the grids of Rhodes and Kos–Kalymnos

as it can be seen from Fig. 5 [4].The energy consumption in Dodecanese has increased over the years 1994–1999

(Fig. 6) by 31% [4]. The grid of Rhodes–Chalki accounts for 65% of the total con-

sumption, while the grid Kos–Kalymnos accounts for 25% of the total.

Fig. 4. Mean monthly wind speed in Dodecanese at ground level.


4. Optimal use of renewable energy sources

4.1. Optimal energy multiple criteria model

In single criterion problems, there is only one criterion examined which depends

on the objective of the problem (e.g. financial output). In multiple criteria pro-

blems, there is not just one solution which can optimize all the criterions together.

. 5. Electricity consumption in every grid of Dodecanese for the year 199
Fig 9.
ig. 6. Consumption of electricity in Dodecanese Islands between 1994 and 1999
F .


In Fig. 7, the multiple criteria model is presented. There are different sources of

energy, which can be used for different final uses. Those sources are: wind power,

solar energy, geothermal energy, the existing electricity production system and the

conventional fuels with direct use. The main categories of final uses are: transpor-

tation, space heating, water heating and electricity for other uses. This model can

include different energy sources and final uses [5].Solar energy can be used in two ways (Fig. 7): first, it can be used by photo-

voltaic elements to produce electricity. In this case, it can be used for all final

uses except transportation. Secondly, it can be used by solar collectors for water

heating. Wind energy is converted into electricity and so it can be used for all final

uses except transportation. Geothermal energy can be used through the installation

of geothermal unit for electricity production, or through the direct use of the geo-

thermal fluid for space and water heating. Finally, conventional fuels are used

either for electricity production (APS), or through direct use for space heating or

transportation.

Fig. 7. Energy sources their final uses.


The objective is to minimize the cost function [5]:

minX4m¼1

Xk

l¼1

KlmXlm ð1Þ

where K is the unit cost of the system and X is the energy amount of each system.The subscripts l and m refer to the energy system and the final use, respectively,and k is the number of systems which correspond to each final use (k ¼ 7 for waterheating, k ¼ 6 for space heating, k ¼ 4 for electricity and other applications andk ¼ 1 for transportation). It should be noted that in this study, the subscript l ¼1; 2; 3; 4 refers to the existing system, the wind power, the solar energy and thegeothermal energy, respectively.

The minimization of the objective function (1) is subject to the followingconstraints:

Social acceptance:

X4

m¼1

Xk

l¼1

ðXlmRlmÞ"

� Zm ð2Þ

Demand:

X4

m¼1

Xk

l¼1

ðXlmÞ"

� Zm ð3Þ

Capacity:

X4

k¼1

Xq

l¼1

ðXljÞ"

� Dk ð4Þ

Reliability:

X4

k¼1

ð1=PRjÞXq

l¼1

ðXljÞ"

� Dk ð5Þ

Pollution:

X4

m¼1

Xk

l¼1

XlmPlm � M ð6Þ

where Rlm is the social acceptance level, Z is the energy need, D is the energy poten-tial, R is the reliability factor, P is the produced amount of CO2 per energyproduction unit and M is the maximum allowable amount of CO2. The subscript jrefers to the energy source, while q is the amount of final uses which correspond toeach source (q ¼ 4 for solar energy, q ¼ 3 for wind power, q ¼ 5 for geothermalenergy and q ¼ 6 for fossil fuels).

Social acceptance factor varies between 0 and 1 (100%) and expresses the socie-ty’s agreement to the use of a specific energy system for a specified final use. In


order to determine the social acceptance factor, a leaflet and questionnaires arenecessary. In the present analysis, the social acceptance factor is considered to be100%, which means that the whole population is in favor of every energy system.

Reliability factor varies between 0 and 1 (100%) and is used to express theproblems of technical feasibility for the production and transfer of energy, and alsothe fact that RES do not constitute a continuous and stable source of energy. Thepresent analysis has been executed on a monthly basis so as to achieve morerepresentative results.

4.2. Application of multiple criteria model in the Dodecanese Islands

The energy model as applied to the Dodecanese Islands takes into considerationcertain peculiarities unique to the islands. Specifically, transportation and spaceheating are not examined because it was not possible to determine the exact energyneeds for these uses. Furthermore, only conventional fuels (direct use) are used fortransportation (Fig. 7). As a result, transportation does not affect the problem’soptimal solution. Also, it was not possible to estimate the cost of direct use of con-ventional fuels. The same problem stands for the geothermal energy as well. As faras solar energy is concerned, it is suggested only the use of solar collectors, whilethe installation of photovoltaics for electricity production is not examined, due totheir high cost and the low output they have.

Under these assumptions, the objective function which needs to be minimized is:

X4

m¼1

Km ð10Þ

where the cost of each source, Km, may consist of a fixed cost, Kf , and a cost whichvaries with the energy amount produced by the source, Kvar, i.e.:

Km ¼ Kf þKvar Xm ð7Þ

The problem is examined for each grid of the existing system separately. The useof solar energy and wind power is examined for all grids, while the installation ofgeothermal unit is examined only for Kos–Kalymnos grid, as this one includesNissyros, the only island in which geothermal energy is available.

The cost function is the sum of the costs of each energy source. The cost of theexisting electricity production system, K1, is:

K1 ¼ K11 þK12 X1 ð8Þ

where K11 is the fixed production cost and K12 is the fuel cost per kWh consumed.Table 1 presents the fixed and the fuel cost for each APS [4].

The cost for the wind power stations depends on the type of the wind turbineschosen. For a wind turbine with nominal power 600 kW, the cost, K2 in 4/year,which consists of the fixed cost of purchase, transfer, installation and of theoperation cost, is given by [6]:

K2 ¼ 23; 777þ 46; 821 X2 ð9Þ


Considering that the life span of a solar collector is 15 years, the cost of instal-lation and operation of solar collectors, K3, in 4/year is given by [7]:

K3 ¼ 9250 X3 ð10ÞFinally, the cost of installation and operation of the geothermal field, K4,

depends on the nominal power of the plant. For a plant with nominal power 10 MW,the cost in 4/year—including the cost of installation and operation of the unit—isgiven by [8]:

K4 ¼ 1; 526; 045þ 0:035 X4 ð11ÞThe energy needs are the sum of the electricity consumption and the consump-

tion of energy for hot water. The energy potential of the Dodecanese Islands inRES, and especially in solar energy, wind power and geothermal energy, ispresented in Table 2. For the solar energy, it is assumed that the collectors cancover an area of 3% for the big islands and 5% for the smaller islands. Forthe wind power potential, it is assumed that 300 wind turbines can be installedaltogether based on the morphology of the islands.

The efficiency of the solar collectors is taken to be 15%, while for the wind tur-bines it is considered that 15% of the power produced is lost. Also, the geothermalplant is considered to have an availability of 90%.

The emitted CO2 from the existing system is 0.88 kg/kWh. The RES produce zeroor low emissions of CO2. Specifically, for the solar collectors and the wind turbines,CO2 is emitted only during their production stage, while the CO2 emitted from ahigh enthalpy geothermal field, in the island of Nissyros, is 0.02595 kg/kWh [10].

Three scenarios are examined. The objective in each scenario is the minimizationof the energy production cost. The first scenario examines the minimization of the

Table 1

Fixed and fuel costs for each APS for the year 1999

APS
Fixed cost (4/year) F uel cost (4/kWh consumed)
Rhodes
25,433,987 0 .037
Kos–Kalymnos
14,392,766 0 .044
Karpathos
2,784,367 0 .133
Astypalea
973,068 0 .168
Megisti
661,599 0 .146
Simi
1,135,818 0 .131
Patmos
1,526,668 0 .137
Agathonisi
168,836 0 .211
Table 2

Potential of renewable energy in Dodecanese [1,9]

Renewable source
Potential
Solar energy
1:6 1011 kWh=year
Wind power
52 MW
Geothermal energy
10 MW


energy production cost, taking into account that the participation of the existentenergy production system should be reduced by, at least, 25% in order to reducethe environmental impacts. The second scenario presents the optimal participationof each energy source, without any environmental constraints. The third scenariopresents the optimal participation of each energy source, taking into account thatat most 30% of the electricity, according to the current legislation, should comefrom RES, and specifically in this analysis from wind turbines.

5. Results of the three scenarios

The mathematical solution of the first scenario shows that in the Dodecanese,there should be installed 90 wind turbines (W/T) with a nominal power of 600 kWand 47 turbines with a nominal power of 1500 kW. Furthermore, it is suggestedthat there should be installed 4484 m2 of new solar collectors. The total financialcost appears to be reduced by 7.6%. The optimal participation of each energysource in the first scenario is presented in Fig. 8.

The mathematical solution of the second scenario shows there should beinstalled 90 W/T with a nominal power of 600 kW and four turbines with a nom-inal power of 1500 kW. In this case, it is suggested that there should be installed2240 m2 of new solar collectors. The annual cost of the electricity production isreduced by 7.9%, however, the participation of RES is limited to 28% (Fig. 9).

The third scenario shows that there should be installed 90 W/T with a nominalpower of 600 kW and 21 turbines with a nominal power of 1500 kW. It is also sug-gested that there should be installed 2240 m2 of new solar collectors. The annualcost of electricity production is reduced by 7.8%. The participation of each energysource is shown in Fig. 10.

Table 3 shows the results of the optimal use of each energy source for the threescenarios.

Fig. 8. Optimal participation of each energy source in the first scenario.


As it can be seen from Figs. 8–10, the geothermal energy is not used. This is dueto the fact that the construction of the geothermal plant is not profitable, as theother RES, i.e. the wind power and the solar energy, are cheaper.

6. Life cycle analysis

Life cycle assessment (LCA) is a tool used to identify and quantify the environ-mental performance of a process or a product from ‘‘cradle to grave’’. LCA meth-odology provides a quantitative basis for assessing potential improvements inenvironmental performance of a system throughout the life cycle. It consists offour phase-stages: (a) goal definition and scoping, (b) inventory analysis, (c) impactassessment, and (d) interpretation [11].

Fig. 10. Optimal participation of each energy source in the third scenario.

Fig. 9. Optimal participation of each energy source in the second scenario.


Goal definition and scoping is the phase of the LCA process that defines thepurpose and method of including life cycle environmental impacts into thedecision-making process. Life cycle inventory (LCI) is a process of quantifyingenergy and raw material requirements, atmospheric emissions, waterborne emis-sions, solid wastes, and other releases for the entire life cycle of a product, process,or activity. The life cycle impact assessment (LCIA) phase is the evaluation ofpotential human health and environmental impacts of the environmental resourcesand releases identified during the LCI. Impact assessment addresses ecological andhuman health effects; it can also address resource depletion. An LCIA attempts toestablish a linkage between the product or process and its potential environmentalimpacts. The impact assessment phase can be further divided into the followingsteps: (i) selection and definition of impact categories, (ii) classification in whichassigning LCI results are assigned to the impact categories, (iii) characterization,(iv) normalization, (v) grouping, (vi) weighting, and (vii) evaluating and reportingLCIA results. The interpretation phase is a systematic technique to identify, quan-tify, check, and evaluate information from the results of the LCI and the LCIA,and communicate them effectively [11].

The objective here is to examine the environmental impacts of the energy pro-duction in Dodecanese, from the existing system and from the system resulting

Table 3

Optimal participation of each source to the energy production system for the three scenarios

Energy source P
ower
produced (kWh)

Number of W/T or

m2 of solar collectors

Percentage of

participation

First scenario

Wind power 2
86,912,150 90 W/T of 600 kW, 47 W/T
of 1500 kW

40

Solar energy
36,347,145 58,209 m2 (4484 m2 new) 5
Present system 4
02,668,960 – 55
Total 7
25,928,255 90 W/T of 600 kW, 47 W/T of
1500 kW, 58,209 m2 (4484 m2 new)

100

Second scenario

Wind power 1
70,950,998 90 W/T of 600 kW, 4 W/T
of 1500 kW

23

Solar energy
35,037,188 55,965 m2 (2240 m2 new) 5
Present system 5
18,497,059 – 72
Total 7
25,928,255 90 W/T of 600 kW, 4 W/T of
1500 kW, 55,965 m2 (2240 m2 new)

100

Third scenario

Wind power 2
06,009,020 90 W/T of 600 kW, 21 W/T
of 1500 kW

28

Solar energy
35,037,188 55,965 m2 (2240 m2 new) 5
Present system 4
84,882,047 – 67
Total 7
25,928,255 90 W/T of 600 kW, 4 W/T of
1500 kW, 55,965 m2 (2240 m2 new)

100


from the first scenario, because this is the scenario with the highest participation ofthe RES to the energy production system. The impact assessment stage of the LCAstudy includes the determination of impact categories, the categorization, the char-acterization, the normalization and the evaluation.

The emissions of the system have been grouped into impacts (characterizationstep) based on the Sima-Pro method [12]. Eight impact categories were considered:greenhouse effect, ozone depletion, acidification, eutrophication, heavy metals,carcinogenesis, winter smog and summer smog formation. Table 4 and Fig. 11summarize the results from the categorization of the impacts, for the functionalunit chosen, for the existing system and the system resulting from the first scenario.

Normalization reveals which effects are large, and which effects are small, inrelative terms. It says nothing of the relative importance of these effects. Valuation

Table 4

Categorized values for each impact category for the existing system and for the system resulting from

the first scenario, per kWh produced

Impact category E
quivalent mass Existing system S ystem from first scenario
Greenhouse effect g
CO2-eq 8:9766 102 4 :9244 102
Ozone depletion g
CFC 11-eq 1:0512 10�3 5 :7667 10�4
Acidification g
SO2-eq 1:1271 101 6 .1834
Eutrophication g
PO4-eq 2:6551 10�1 1 :4565 10�1
Heavy metals g
Pb-eq 3:1313 10�2 1 :7178 10�2
Carcinogenesis g
B(a)P-eq 3:9273 10�5 2 :1545 10�5
Winter smog g
SPM-eq 1.9625 1 .0766
Summer smog g
C2H4-eq 9:1982 10�1 5 :0460 10�1
Fig. 11. Categorized results.


factors are used for this purpose. The evaluation of the environmental score of

each effect is calculated based on the simple formula:

Environmental score ¼ characterised value normalisation

weighting factor ð12Þ

Due to lack of such factors for Greece, Holland and European factors have been

used for the evaluation process. These factors are shown in Table 5 [12].Figs. 12 and 13 show the normalized and evaluation scores for the existing sys-

tem and the system resulting from the first scenario, respectively, while Fig. 14 pre-

sents the indicator graph for the two systems. It is shown that the environmental

impacts from the existing system are higher than those from the system resulting

from the first scenario where 48% of the energy is produced using RES. Also, it

can be seen from Fig. 13 that the categories most affected by the energy production

are the heavy metals and the acidification.

Table 5

Normalization and weighting factors

Impact category N
ormalization factor W eighting factor
Greenhouse effect 0
.0000742 2.5
Acidification 0
.00888 1 0
Eutrophication 0
.0262 5
Winter smog 0
.0106 5
Summer smog 0
.0507 2.5
Solid waste 0
0
Fig. 12. Normalization results.


7. Conclusions

The optimization of the energy production system of Dodecanese Islands, withobjectives the minimization of the energy production cost and the emissions (firstscenario) is achieved by: (a) installation of 90 W/T with a nominal power of 600 kW,(b) installation of 47 W/T with a nominal power of 1500 kW, (c) installation of

Fig. 13. Valuation results.

Fig. 14. Indicator graph.


4483 m2 of new solar collectors. The solar collectors participate in the total sup-plied energy by 5%, wind turbines participate by 40% and APSs participate by55%. The annual energy production cost, in this scenario, is reduced by 7.6% inrelation to the existent system.

When the energy production cost is minimized without taking into considerationany environmental constraints (second scenario) it is suggested: (a) installation of90 W/T with a nominal power of 600 kW, (b) installation of 4 W/T with a nom-inal power of 1500 kW, (c) installation of 2240 m2 of new solar collectors. Thesolar collectors participate in the total supplied energy by 5%, wind turbines par-ticipate by 23% and APSs participate by 72%. The annual energy productioncost, in this scenario, is reduced by 7.9% in relation to the existent system.

A third scenario considers that the RES participate in the electricity productionsystem at most by 30%. The results suggest: (a) installation of 90 W/T with a nom-inal power of 600 kW, (b) installation of 21 W/T with a nominal power of 1500 kW,(c) installation of 2240 m2 of new solar collectors. The solar collectors participatein the total supplied energy by 5%, wind turbines participate by 28% and APSsparticipate by 67%. The annual energy production cost, in this scenario, is reducedby 7.8% in relation to the existent system.

From the LCA conducted, it is obvious that the heavy metals and the acidifi-cation are the categories in which the two systems under examination contributemost, while carcinogenesis and eutrophication are the categories that are less affec-ted by the energy production from both systems.

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