Evaluation of NO x, SO x and CO 2 Emissions of Taiwan s Thermal Power Plants by Data Envelopment Analysis

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1 Aerosol ad Air Quality Research, 13: , 2013 Copyright Taiwa Associatio for Aerosol Research ISSN: prit / olie doi: /aaqr Evaluatio of NO x, SO x ad CO 2 Emissios of Taiwa s Thermal Power Plats by Data Evelopmet Aalysis Chia Hao Liu 1, Sue J. Li 2*, Charles Lewis 3 1 Istitute of Nuclear Eergy Research, Lugta, Taoyua 32546, Taiwa 2 Sustaiable Evirometal Research Ceter (SERC), Departmet of Evirometal Egieerig, Natioal Cheg Kug Uiversity, Taia 701, Taiwa 3 Departmet of Resources Egieerig, Natioal Cheg Kug Uiversity, Taia 701, Taiwa ABSTRACT A itegrated evirometal ad operatioal evaluatio model is costructed by data evelopmet aalysis (DEA) to examie seve thermal power plats operatig i Taiwa durig Iputs ad desirable outputs alog with udesirable outputs, icludig CO 2, SO x, ad NO x emissios, were simulated. A slack variable aalysis was coducted to idetify possible ways to improve the iefficiet power plats. I additio, three models were compared to idetify the actual magitude of iefficiecy. The results idicate that the itegrated efficiecy ad productio scale of some plats were iefficiet durig Reductios i fuel cosumptio ad CO 2 emissios are idetified as the major strategies to improve efficiecy. Other optios iclude modifyig pre-existig maagemet measures, istallig pollutio prevetio cotrols ad resizig the scale of the power plat. It is aticipated that the fidigs of this study will help policymakers to achieve better evirometal ad operatioal performace with regard to existig thermal power plats. Keywords: Evirometal performace; Utility efficiecy of power geeratio; CO 2 reductio; Exteded DEA model. INTRODUCTION Electricity is the foudatio of a coutry s atioal ecoomic developmet ad a essetial elemet of daily moder life. Due to the rapid growth of Taiwa s ecoomy ad idustrial developmet, the electricity cosumptio has icreased rapidly. It grew from 134,307 GWh i 1996 to 242,244 GWh i 2011, a average aual icrease of 4.01%; while the aual growth rate of domestic eergy cosumptio is oly 3.27% (Bureau of Eergy, 2012a). This shows that the growth rate of electricity cosumptio is higher tha that of total eergy cosumptio. However, electricity from thermal power geeratio at its productio stage requires other eergy iput sources such as coal, oil ad atural gas. Therefore, electricity cosumptio results i large emissios of CO 2, NO x ad SO x, ad causes various evirometal damages such as greehouse effects ad acid rai. I Taiwa, the CO 2 emissio from the electricity sector i 2011 accouted for 65.5% of total CO 2 emissios. Thus, the electricity sector is the most sigificat source of CO 2 emissios i Taiwa. * Correspodig author. Tel.: ; Fax: address: t15197@mail.cku.edu.tw Presetly, Taiwa is ot a member of the UNFCCC, yet the total CO 2 emissio i Taiwa cotributes 0.89% worldwide, ad Taiwa raks 20rd i the world regardig total CO 2 emissio (Iteratioal Eergy Agecy, 2012). I order to respod to the post-kyoto Protocol iteratioal treds ad challeges ad to cope with the icreasig electricity cosumptio as Taiwa moves toward sustaiable developmet, the govermet issued the "Sustaiable Eergy Policy Covetio", ad set up several goals. First, the total emissio of CO 2 by 2025 should be set back to the year 2000 level. Secod, the eergy efficiecy should be raised 2% aually for the ext eight years. Third, the proportio of low carbo fuel of power geeratio system should be o less tha 55% by Yet, despite the growig evirometal cocers ad related policy objectives, few empirical quatitative aalyses regardig the performace evaluatio of power geeratio i Taiwa have bee coducted. The focus of this study is to costruct a itegrated performace evaluatio model by data evelopmet aalysis (DEA) (Chares et al., 1978). This itegrated model is aimed to evaluate both techical ad evirometal efficiecies of Taiwa thermal power plats by cosiderig desirable variables as well as udesirable variables, such as CO 2, SO x ad NO x. Also, a slack variable aalysis is coducted to idetify optios to improve iefficiet power plats. I additio, magitudes of iefficiecy are idetified by model comparisos. We

2 1816 Liu et al., Aerosol ad Air Quality Research, 13: , 2013 hope that the results ca be valuable for policy makig ad for improvig utility efficiecy ad evirometal cocers of coutries with similar thermal power plats. POWER GENERATION IN TAIWAN The aual report from the Bureau of Eergy (2012a, b) idicated that the gross power geeratio i Taiwa grew from 141,963 GWh i 1996 to 252,173 GWh i Taiwa Power Compay (TPC) geerated 170,067 GWh, accoutig for 67.4% of total output, ad 42,287 GWh (16.8%) from idepedet power producers (IPPs) ad 39,760 GWh from cogeeratio (15.8%) i It is worth otig that the percetage of electricity produced from thermal power plats icreased rapidly from 66.4% i 1996 to 78.6% i 2011 (Bureau of Eergy, 2012b). O the other had, due to the atioal goal of a uclear-free homelad policy i Taiwa, the percetage of electricity produced from uclear power plats decreased from 26.6% i 1996 to 16.7% i I additio, the gross electricity geeratio of hydro-power systems reduced from 9,044 GWh (6.4%) i 1996 to 6,902 GWh (2.7%) i Wid power ad other gree eergy supply systems operated o a limited scale ad comprised less tha 1.9% i All of this idicates that thermal power geeratio is curretly the domiat source of electricity i Taiwa. LITERATURE REVIEW Because DEA is the basic approach of this paper, it is importat to review a umber of successful studies related to this method. DEA has bee widely used to study ad compare the efficiecy of eergy idustries, particularly the electricity idustry. Recetly, DEA has also gaied popularity i evirometal performace measuremet due to its empirical applicability. Yaisawarg ad Klei (1994) used DEA to compute a performace aalysis for coalburig plats i the U.S. electric geeratig idustry i the 1980s. Olatubi ad Dismukes (2000) used DEA to evaluate the cost efficiecy of electric utilities i the Uited States. Korhoe ad Luptacik (2004) used the DEA approach to measure the eco-efficiecy of 24 power plats i Europea coutries. Their results idicate DEA ca provide a isight ito the cause of the eco-iefficiecy ad the potetial for improvemet with respect to some particular iput ad outputs. Vecheh et al. (2005) proposed a model for icorporatig udesirable factors i DEA. The proposed model evaluates the efficiecy level of each DMU by cosiderig udesirable iputs ad outputs simultaeously. Zhou et al. (2008) have summarized more tha 100 DEA applicatios for evirometal protectio ad eergy policy. They foud that bechmarkig of electricity utilities accouts for the largest umber of studies, ad the costat returs to scale (CRS) referece techology alog with the radial efficiecy measures are still the most widely used specificatios. Some studies have also bee devoted to modelig udesirable factors i DEA, e.g., Zhag et al. (2008) coducted a eco-efficiecy aalysis for regioal idustrial systems i Chia by takig various udesirable outputs ito accout ad developig DEA-based models. Results idicated that provices with higher level GDP per capita had higher eco-efficiecy relatively with the exceptios of Haia ad Qighai. Sueyoshi ad Sekitai (2009) discussed ie desirable properties to measure the techical efficiecy eed to satisfy from the perspective of productio ecoomics ad optimizatio. Results showed that all the seve DEA models suffer from a problem of multiple projectios ad violate the property o aggregatio of iputs ad outputs. Thus, the seve DEA models do ot satisfy all desirable techical efficiecy properties. Welch ad Barum (2009) estimated the allocatio of coal, gas ad oil iputs that miimize carbo emissios ad costs i fossil-fuel based electricity geeratio. Their results idicated that the gap betwee efficiet cost ad efficiet evirometal productio was wide, ad would require substatial policy itervetio, techological chage ad market adjustmet before it could be arrowed. Yag ad Pollitt (2009) used differet DEA-based efficiecy models to examie the impact of ucotrollable variables together with udesirable outputs based o a research sample of the Chiese coalfired power plats. The results idicated that the impact of ucotrollable variables was relatively sigificat. This cofirms the hypothesis that some power plats with relatively low efficiecy scores i the traditioal model achieved theirs i part due to their relatively ufavorable operatig eviromets. Fleishma et al. (2009) examied the effect of air quality regulatios o the efficiecy of US power plats based o both ecoomic ad evirometal outputs. Their results idetified several mixed effects of regulatios o power plat efficiecy whe pollutio abatemet ad electricity geeratio are both icluded as outputs. Liu et al. (2010) surveyed umerous studies, which dealt with the applicatio of DEA to electricity geeratio. Sueyoshi ad Goto (2011) proposed a DEA approach, ad applied it to measure the uified efficiecy of Japaese fossil fuel power geeratio for compariso with other previous DEA approaches. Their results idicated that the implemetatio of the Kyoto Protocol has ot bee effective o the uified efficiecy of Japaese fossil fuel power geeratio durig 2004 to Che et al. (2012) proposed a iteger DEA model with udesirable iputs ad outputs. The proposed model is developed based o the additive DEA model, i which iput ad output slacks are used to compute efficiecy scores. Barros (2013) adopted a distace frotier model to rak the plats accordig to their total productivity for the period The results display strog evidece that the rakigs of techical efficiecy with adjustmets for pollutio differs sigificatly from the rakigs that do ot take pollutio ito accout. I this paper, we exteded the basic DEA model of Liu et al. (2010) to costruct a model to iclude udesirable outputs; therefore, the evirometal ad operatioal efficiecies ca be itegrated ad evaluated. DEA METHODOLOGY The DEA approach is a o-parametric method for determiig a liear efficiecy frotier alog the most

3 Liu et al., Aerosol ad Air Quality Research, 13: , efficiet decisio makig uits (DMUs) so as to measure the efficiecy relative to the rest of DMUs. Efficiecy scores are costructed by measurig how far a utility is from the frotier. DEA also produces detailed iformatio o the efficiecy of each utility, ot oly relative to the efficiecy frotier, but also relative to specific efficiet utilities that ca be idetified as role models or comparators (Hawdo, 2003). I additio, DEA allows for efficiet measuremet of multiple outputs ad multiple iputs without pre-assiged weights ad without specifyig ay fuctioal form o the relatioships betwee variables (Thakur, et al., 2006). Therefore, it is ot oly a o-parametric approach, but also a data-drive frotier aalysis techique that floats a liear surface to rest o empirical observatios (Cooper, et al., 2006). Two DEA models are cosidered i this study to complete the performace aalysis. The first model is the CCR (Chares, Cooper ad Rhodes) model which was coducted by Chares et al. (1978). It is built o the assumptio of costat returs to scale (CRS) of activities. I other words, if variables (x, y) are feasible, the for every positive scalar k, the variables (kx, ky) are also feasible. The secod model, the BCC (Baker, Chares ad Cooper) model, was developed by Baker et al. (1984). It is built o the assumptio of variable returs to scale (VRS) of activities, ad has its productio frotiers spaed by the covex hull of the existig DMUs. The frotiers have piecewise liear ad cocave characteristics, which lead to variable returs to scale characteristics. Details of the basic CCR ad BCC models ca be foud i our previous paper (Liu et al., 2010) i which we evaluated the power-geeratio efficiecy of major thermal power plats i Taiwa by the DEA approach, ad a stability test was coducted to verify the stability of the DEA model. I geeral, the reasos that a DMU is iefficiet may result from iappropriate operatio of the DMU itself or from iadequate scale of the DMU s operatio. The scale efficiecy ca be preseted by the ratio of efficiecy scores of CCR ad BCC models (Sarica ad Or, 2007). I additio, there are two DEA techiques for each of the CCR ad BCC models. The first techique is iputorieted, which aims to miimize iputs while satisfyig at least the give output levels. The other techique is outputorieted, which attempts to maximize the output without requirig more of ay of the observed iput values (Cooper et al., 2000). I this study, we use the iput-orieted rather tha output-orieted DEA techique to evaluate the performace of Taiwa s power plats because these plats do ot take competitive positios i the electric market. The amout of overall electricity geerated is mostly based o policies ad distributio regulatios from the relevat authorities. I this study, we treat the udesirable outputs as iputs i our exteded DEA model for evirometal efficiecy aalysis. Treatig the udesirable outputs like classic iputs to be miimized i the DEA model was already valued as a quite ituitive approach (Dyckhoof ad Alle, 2001). Assume there are DMUs, each cosumig m iputs ad producig s outputs. The outputs correspodig to idices 1, 2,, t are desirable ad the outputs correspodig to idices t + 1, t + 2,, s are udesirable outputs. We would like to produce as may desirable outputs as possible ad ot produce m udesirable outputs. Let x R s ad Y R be the matrices with o-egative elemets, ad cotai the observed iput ad output for the DMUs. We decompose matrix Y ito two parts: Y Y Y g b where a t matrix Y g represets desirable ( good ) outputs ad a (s t) matrix Y b represets udesirable ( bad ) outputs (Dyckhoof, 1994). I additio, we deote X ij the quatity of iput i cosumed by DMU j, ad Y rj the quatity of output r geerated from DMU j. We decompose the vector Y rj ito two parts: Y rj Y Y g rj b rj where the vectors Y rj g ad Y rj b stad for the desirable ad udesirable output-values of uit j. We will perform the calculatios with a CCR model but the results ca be geeralized to other DEA models as well. Treatig the udesirable outputs as iputs, the ratio form of the CCR model is give as follows: max m h r rk r 1 k m s Subject to t r 1 vx t i ij r rj i1 rt1 r uy u y i ik r rk i1 rt1 s rj 1 ; j 1,..., u, v 0, r 1,..., s i 1,..., m r vx i uy u y The above model is difficult to solve because of its fractioal objective fuctio. I order to make the liear problem easier to solve ad reduce the umber of costraits, a stadard techique (Chares et al., 1978; Chares et al., 1979) to trasform the above fractioal model ito a liear mode is used, ad the dual of CCR model is obtaied. It ca be preseted as follows: mi m t s g b k sik srk s rk i1 r1 rt1 Subject to (1) (2) (3) (4) (5)

4 1818 Liu et al., Aerosol ad Air Quality Research, 13: , 2013 k ik j ij ik j1 g g g rk j rj rk j1 b b b k rk j rj rk j1 g b j ik rk rk X X s 0 ; i 1,..., m Y Y s 0 ; r 1,..., t Y Y s 0 ; r t1,..., s, s, s, s 0 ; j 1,..., The correspodig BCC model is listed below: mi m t s g b k sik srk s rk i1 r1 rt1 Subject to k ik j ij ik j1 g g g rk j rj rk j1 b b b k rk j rj rk j1 j1 (6) (7) X X s 0 ; i 1,..., m Y Y s 0 ; r 1,..., t Y Y s 0 ; r t1,..., s 1 j g b, s, s, s 0 ; j 1,..., j ik rk rk The above model itegrates the udesirable outputs ito cosideratio, ad the DMU ca reduce simultaeously the iputs ad udesirable outputs to icrease evirometal efficiecy (Dyckhoof ad Alle, 2001). DATA CONSOLIDATION I Taiwa, there are more tha 20 state-ru ad a few private thermal power plats. Amog these plats, the utilities belogig to Taiwa Power Compay (TPC) with complete operatioal statistics were selected for evaluatio so as to maitai high level data quality. After screeig, (8) oly 7 thermal power plats were icluded i this study. The basic parameters (year of operatio, fuel type) of thermal power plats are preseted i Table 1. The ifluece of fuel type is ot cosidered i this study due to the structure settig of the performace evaluatio. The mai operatioal data for years were obtaied from the Aual Operatio Statistics ( ) (Taiwa Power Compay, 2009). The data used i the DEA estimatio comprised iformatio for 7 DMUs durig 8 years for a total of 56 observatios. I estimatig efficiecy measures of the thermal power plats i Taiwa, our study adopts six variables as iputs ad outputs. Iputs iclude istalled capacity ad heatig value of total fuels, while the outputs cotai oe desirable output (et electricity produced) ad three udesirable outputs (CO 2, NO x, SO x ). The data of iputs ad desirable output are obtaied from publicly available iformatio of TPC. I additio, the data of udesirable output is gathered through TPC aual sustaiability reportig (Taiwa Power Compay, 2010) ad questioaires from power plats. The variables are described i Table 2. The combiatio of the measured idicators esures adherece to the DEA covetio that the miimum umber of DMU observatios should be greater tha or equal to three times the umber of iputs plus outputs (Raab ad Lichty, 2002). I our study, 56 observatios are greater tha three times the sum of iput ad output variables [56 3(2 + 4)]. Moreover, by calculatig the correlatio coefficiets betwee iputs ad outputs, a sigificat correlatio was foud. The isotoicity that the DEA model required is fulfilled ad thus the iput ad output variables ca be used for this research to measure the combied operatioal ad evirometal efficiecies (Liu et al., 2010). Table 1. Basic parameters of seve thermal power plats i Taiwa. Power plat Year of operatio Fuel type Hsiehho 1977 oil Likou 1968 coal Taichug 1991 coal Tali 1969 coal/oil/ atural gas Hsita 1982 atural gas Tughsiao 1980 atural gas Napu 1993 atural gas Table 2. Iput/output variables. Variable Uit Descriptio Heatig value of total fuels 10 9 Sum of the heat value of fossil fuels that used by power calories Iput plat s operatio Istalled capacity MW Maximum desig load of geerated electricity per moth Desirable output Net electricity produced MWh Sum of geerated electricity without electric eergy cosumed by power plat CO 2 toes Carbo dioxide emissios from power plat s operatio Nitroge oxides icludig various itroge compouds such Udesirable NO x toes as NO ad NO output 2 emissios from power plat s operatio Sulfur oxides such as SO SO x toes 2 emissios from power plat s operatio

5 Liu et al., Aerosol ad Air Quality Research, 13: , RESULTS AND DISCUSSION I this study, two iputs with oe desirable output ad three udesirable outputs are used to estimate the efficiecy of thermal power plats i Taiwa. The estimated efficiecy cosiders ot oly the techical performace but also the air pollutio cotrol. Results of the average efficiecy scores i are listed i Table 3. The rage of CCR efficiecy scores amog all thermal power plats are from to 0.990, ad the rage of BBC efficiecy scores are from to It is oticed that Napu power plat has the best performace relative to other utilities, ad Tali power plat is the worst utility i both CCR ad BCC efficiecy evaluatio. O the other had, scale efficiecy scores rage from (Likou) to (Hsiehho) (Table 3). This idicates that Hsiehho power plat is operatig o the best productio scale for utilities; while the Likou power plat could be replaced or add geerators with larger capacity to icrease electricity supply ad expad its scale. I fact, the expasio pla of Likou power plat has bee supported by the Executive Yua i 2005 ad passed the evirometal impact assessmet by Evirometal Protectio Admiistratio (EPA) i By replacig the 30 year-old thermal geerators with three 800 MW ew supercritical coal-fired geerators, the performace of Likou power plat is expected to improve sigificatly by The results i Table 3 show that the average CCR, BCC ad scale efficiecy scores are 0.887, ad 0.958, respectively. It meas that, cosiderig the uified efficiecy ad the productio scale, some plats such as Hsiehho, Likou ad Tali are iefficiet i Power plats i this study ca be divided ito four groups accordig to type of power geerator. First, the Napu ad Tughsiao power plats are gas-fired combied-cycle power plats, ad their et heat efficiecy was 39 43% durig 2001 to Secod, Hsiehho ad Tali power plats are coal-fired steam turbie power plats, ad their et heat efficiecy was 33 35% i Third, Likou ad Taichug power plats have ot oly steam turbie geerators but also gas turbie geerators. Both of them are coal-fired power plats; the et heat efficiecy of steam turbie geerators was 31 36%, ad the et heat efficiecy of gas turbie geerators was 26 28%. Fially, Hsita power plat has coal-fired steam turbie geerators ad gas-fired combied-cycle geerators, ad the rage of its et heat efficiecy is 35 44%. Table 3 shows that combied cycle power plats (Napu ad Tughsiao) are clearly more efficiet tha steam turbie power plats (Hsiehho ad Tali). Based o the BCC efficiecy scores i Table 3, the Tali power plat is the most techically iefficiet utility durig This may result from more tha 30 years of old geerators ad the absece of available space to set up the flue gas desulfurizatio (FGD) ad selective catalytic reductio (SCR) uits to further reduce the cocetratio of SO x ad NO x emissios. If we compare the Likou ad Taichug power plats, the CCR efficiecy of the former (0.755) is foud to be more iefficiet tha the latter (0.977), eve though they have similar kids of geeratio facilities but the operatio period of the Likou power plat is 20 years loger tha that of the Taichug power plat. Also, aother reaso for the differece i performace ca be related to differet productio scales. The scale efficiecy of the Likou power plat is oly 0.807, while the Taichug power plat s scale efficiecy score is up to The uified performace of evaluated power plats ca be divided ito three groups. First, the CCR, BCC ad scale efficiecy scores of the Tughsiao ad Napu power plats have progressed year by year. I , their efficiecy scores all reached 1.0. It meas that they are at the optimal productio level ad have steady performace. This is because that they have ovel equipmet with high operatioal quality, ad they use atural gas which is more evirometal friedly tha coal ad oil as the fuel. Secodly, the Hsiehho ad Tali power plats have lower BCC efficiecy while their scale efficiecy scores are close to 1.0. This idicates that they are techically iefficiet, although they are already o the optimal productio scale. The over use of electricity ad excess pollutat emissios are the mai reasos causig the low BCC efficiecy of the Tali power plat. Thirdly, the Likou ad Hsita power plats have higher BCC efficiecy tha their scale efficiecy durig , idicatig that their operatioal processes ad evirometal maagemet are quite appropriate. The scale efficiecy of the Hsita plat has bee improved over the period, resultig i a more competitive coditio of the plat. O the cotrary, the Likou power plat curretly eeds more improvemet directed toward icreasig the productio scale. I additio, a slack variable aalysis is coducted to idetify optios to improve the performace of iefficiet Table 3. Efficiecies of thermal power plats i Power plat CCR efficiecy a BCC efficiecy b Scale efficiecy Hsiehho Likou Taichug Tali Hsita Tughsiao Napu Average a CCR efficiecy stads for overall efficiecy. By (1), CCR efficiecy = BCC efficiecy Scale efficiecy. b BCC efficiecy represets pure techical efficiecy.

6 1820 Liu et al., Aerosol ad Air Quality Research, 13: , 2013 utilities. Cosiderig two iput variables (Table 4), the results show that 3 DMUs have iappropriate istalled capacity ad 8 DMUs use too much fossil fuel. I brief, reductio i fuel cosumptio is the most effective improvemet for major iefficiet utilities. Cosiderig three udesirable output variables, we fid that more tha 40 DMUs have excess NO x, SO x ad CO 2 emissios. Amog them, although the umber of DMUs with excess SO x is higher tha that with the other two emissios, it is worth otig that the excess CO 2 emissio sigificatly domiates that of NO x ad SO x. For this reaso, CO 2 emissio reductio should be the first priority to lower the evirometal impacts to maitai sustaiable developmet for overall better performace of thermal power plats i Taiwa. Results i Table 4 show that most power plats have o excess istalled capacity ad heatig value of total fuels i It idicates that the desig capacity ca meet the electricity demad requiremet, ad the fuel cosumptio ad allocatio is uder suitable cotrol. I additio, most power plats except for the Tughsiao ad Napu plats have excess air emissios, especially large amout of CO 2 emissios. This situatio could be improved by the adjustmet of fuel structure, promotio of geerator heat rate ad adoptio of low sulfur fuels i the future. The efficiecy scores from the DEA calculatios ca be chaged by the umber of DMU ad iput/output variables. Due to the ature of the DEA approach, addig more variables ot oly elarges DEA efficiecy scores, but it also potetially hides the actual magitude of iefficiecy. For this reaso, we costructed the origial model (Model 1), ad two other models (Models 2 ad 3) to fid the sesitivity of the efficiecy magitude by alterig some iputs. Both Models 2 ad 3 are developed with oe iput, oe desirable output ad three udesirable outputs (Table 5), ad the results from the model compariso are show i Table 6. I additio, the Spearma rak correlatio test was also used, ad the correlatio coefficiets betwee Model 1 ad the other two models are ad These correlatio coefficiets sigify that the results are positively related ad stable across model specificatios. Based o Model 1 ad Model 2, the most efficiet plat is the Napu plat; however, the least efficiet plat from Model 1 is the Taili plat ad the Likou plat i Model 2. The average score reduces from i Model 1 to i Model 2. For most power plats, the variatios of efficiecy scores betwee Model 1 ad Model 2 are less tha 0.2, with the exceptio of the Taichug plat. The Taichug plat appears to be more efficiet tha most plats i Model 1, because it has the largest istalled capacity i Taiwa, therefore it ca produce more electricity tha other plats. I Model 2, the relative efficiecy of the Taichug plat is smaller, because this model was coducted without iput of the istalled capacity, ad oly cosidered heatig value of total fuels. The Hsita plat, which has the secod largest istalled capacity, also has similar chage i results betwee Model 1 ad Model 2. Improvemets to the Taichug ad Hsita plats should be orieted to better choice of fuel use, ehacemet of pollutio cotrol ad operatio stadards to improve the efficiecy of electricity geeratio. Comparig results of Model 1 ad Model 3, the most efficiet plat is the Napu plat, ad the least efficiet plat is the Taili plat. The average score reduces lightly from i Model 1 to i Model 3 due to Model 3 lackig oe iput. The differece of efficiecy scores of all power plats betwee Model 1 ad Model 3 are less tha 0.1. It shows that the gap betwee Model 1 ad Model 3 is smaller tha that betwee Model 1 ad Model 2, ad the results of Model 3 is more cosistet with Model 1. Cosiderig the results of Model 2 ad Model 3, the most efficiet plat is the Napu plat, ad the least efficiet plat i Model 2 is the Likou plat, yet i Model 3 it is the Taili plat. The Taichug ad Hsita plats have some differeces i efficiecy scores i Model 2 ad Model 3. I summary, the above results idicate that Model 1 ad Model 3 are more cosistet i results due to the domiatio by the iput istalled capacity. CONCLUSIONS I this study, three udesirable outputs are itegrated with oe desirable output ad two iputs to evaluate the uified efficiecy of Taiwa s thermal power plats by the DEA method. The precedig aalysis shows that some power plats such as Hsiehho, Likou ad Tali were iefficiet i This situatio could be improved by the adjustmet of fuel structure, promotio of geerator heat rate ad adoptio of low sulfur fuels i the future. I additio, by replacig the 30 year-old thermal geerators with three 800 MW ew supercritical coal-fired geerators, the performace of Likou power plat is expected to improve sigificatly by The results of this study demostrate that combied cycle power plats are more efficiet tha steam turbie power plats. I additio, combied cycle power plats (Tughsiao ad Napu) made cotiual progress i overall performace durig It is suggested whe a ew power plat is proposed, a itegrated gasificatio combied cycle (IGCC) ad combied heat ad power (CHP) power plat with the best available techologies (BAT) should be cosidered for the future. Results from comparig three models idicate that the origial model (Model 1 with two iputs, oe desirable output, ad three udesirable outputs) ca hide the actual magitude of iefficiecy of the Taichug power plat, because of its large istalled capacity, ad operators of the Taichug plat have the advatage of measurig the margial cost ad the margial pollutat emissios from electricity geeratio to evaluate efficiecy scores. Also, results of Model 1 ad Model 3 are more cosistet due to the domiatio of the iput parameter istalled capacity. Accordig to the slack variable aalysis, reductio i fuel cosumptio ad CO 2 emissios are the most effective methods to improve the efficiecy of thermal power plats. Fidigs of this study ca be beeficial for ehacig the evirometal performace ad power geeratig efficiecy policies of thermal power plats. Also, the method used i

7 Liu et al., Aerosol ad Air Quality Research, 13: , Power Plat Hsiehho Likou Taichug Tali Hsita Tughsiao Napu Table 4. Slack variable aalysis of thermal power plats i Taiwa ( ). Year Excess istalled Capacity (MW) Excess heatig value of total fuels (109 cal) Excess NO x (toes) Excess SO x (toes) Excess CO 2 (toes) , , , , , , ,120 7,106 1,116, ,311 6,140 1,038, , , , , ,978 1,091, ,567 1, , , , , , , , , , , ,054 2,261 1,520, ,801 2,708 1,545, ,865 1, , ,156 1, , , ,041, , ,657, ,017, ,805 1,236, ,562 1,438, ,041 7,122 1,565, , ,073 6,833 1,408, ,408 1,744, ,318 7,129 1,516, ,479 7,067 1,660, ,154 6,774 1,481, ,173 11,695 1,381, ,741 1,588, ,096 2,355 1,489, ,064 1, , , , , , , , , , ,689 12, , ,294 4, , ,424 2,211 3, ,988 3, , , , , ,600 1, , , , , ,

8 1822 Power Plat Year Liu et al., Aerosol ad Air Quality Research, 13: , 2013 Excess istalled Capacity (MW) Table 4. (cotiued). Excess heatig value of total fuels (109 cal) Excess NO x (toes) Excess SO x (toes) Excess CO 2 (toes) Table 5. Iput/Output used i three models Variable Model 1 Model 2 Model 3 Iput Istalled capacity Heatig value of total fuels Istalled capacity Heatig value of total fuels Desirable Output Net electricity produced Net electricity produced Net electricity produced Udesirable Output CO 2 CO 2 CO 2 SO x SO x SO x NO x NO x NO x Table 6. Average efficiecy scores of the differet models. Power plats Model 1 Model 2 Model 3 Hsiehho Likou Taichug Tali Hsita Tughsiao Napu Average this research ca be applied to coutries with similar power plat structures for evaluatio of evirometal ad operatioal efficiecies ad meas for improvemet. Future research could be exteded to iclude thermal power plats with differet categories accordig to fuel type for further assessmet of the relative efficiecies by DEA. ACKNOWLEDGEMENTS We wish to thak Taiwa s Natioal Sciece Coucil (Project NSC E MY3) for fiacial support. Also, we appreciate the valuable commets ad suggestios from the reviewers ad the editors of our mauscript. REFERENCES Baker, R.D., Chares, A. ad Cooper, W.W. (1984). Some Models for Estimatig Techical ad Scale Iefficiecies i Data Evelopmet Aalysis. Maage. Sci. 30: Barros, J. (2013). Performace Measuremet of Thermoelectric Geeratig Plats with Udesirable Outputs ad Radom Parameters. It. J. Electr. Power Eergy Syst. 46: Bureau of Eergy (2012a). Eergy Balace Sheet, Bureau of Eergy, Miistry of Ecoomic Affairs, Taipei, Taiwa. Bureau of Eergy (2012b). Eergy Statistical Aual Reports, Bureau of Eergy, Miistry of Ecoomic Affairs, Taipei, Taiwa. Chares, A., Cooper, W.W. ad Rhodes, E. (1978). Measurig the Efficiecy of Decisio Makig Uits. Eur. J. Oper. Res. 2: Chares, A., Cooper, W.W. ad Rhodes, E. (1979). Short Commuicatio: Measurig Efficiecy of Decisio Makig Uits. Eur. J. Oper. Res. 3: 339. Che, C.M., Du, J., Huo, J. ad Zhu, J. (2012). Udesirable Factors i Iteger-valued DEA: Evaluatig the Operatioal Efficiecies of City Bus Systems Cosiderig Safety Records. Decis. Support Syst. 54: Cooper, W.W., Seiford, L.M. ad Toe, K. (2000). Data Evelopmet Aalysis: A Comprehesive Text with Models, Applicatios, Refereces, ad DEA-Solver Software, Kluwer Academic Publishers, Norwell, Massachusetts, USA. Cooper, W.W., Seiford, L.M. ad Toe, K. (2006). Itroductio to Data Evelopmet Aalysis ad Its Uses: with DEA-Solver Software ad Refereces, Spriger, New York, USA. Dyckhoff, H. (1994). Betriebliche Produktio, Spriger Verlag, Berli, Germay (i Germa). Dyckhoff, H. ad Alle, K. (2001). Measurig Ecological Efficiecy with Data Evelopmet Aalysis (DEA). Eur. J. Oper. Res. 132: Fleishma, R., Alexader, R., Bretscheider, S. ad Popp, D. (2009). Does Regulatio Stimulate Productivity? The Effect of Air Quality Policies o the Efficiecy of US Power Plats. Eergy Policy 37:

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