dd

Rustu Eke , Ali SenturkMugla Stk Kocman University, Clean Energy Research &Mugla Stk Kocman University, Faculty of Sciences, Dep

wereodule

system56 kW0.81 f

xceeding 1700 kW h per square meter. Mugla has a Mediterranean Climate

popularity as more and more architects and constructors begin tounderstand the possibilities available for their clients [2]. Com-pared with PV systems, one of the important advantages of BIPVsystems is that PV modules can replace conventional buildingmaterials. The savings in the purchase and installation of conven-tional materials can lower the net cost of BIPV systems. PV mod-ules provide fully integrated electricity generation while also

ing envelopes. Ifload of buildingcan also bPV moduloling load

tion of building envelopes should also be regarded as partstotal electricity saving when the energy performance of BIPtems is evaluated. In recent years, many theoretical and experi-mental studies have been conducted to maximize the energybenets of BIPV systems, in terms of the power output of PV mod-ules, environmental payback time and thermal analysis with thecooling load reduction of buildings [314].

PV and also BIPV have great potential to contribute to electricityproduction in the urban environment of the south of Turkey. MuglaStk Kocman University has been involved in R&D for photovoltaic

Corresponding author. Tel.: +90 2522111601; fax: +90 2522111472.

Applied Energy 109 (2013) 154162

Contents lists available at

lseE-mail address: erustu@gmail.com (R. Eke).1. Introduction

BIPV is a photovoltaic (PV) application close to being capable ofdelivering electricity at less than the cost of grid electricity to endusers in certain peak demand niche markets [1]. BIPV is growing in

serving as part of the weather protective buildBIPV systems are properly designed, the coolingenvelopes which PV modules are integrated intoinated. Apart from the electricity generation ofcooling energy consumption reduction due to co0306-2619/$ - see front matter Crown Copyright 2013 Published by Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.apenergy.2013.03.087e elim-es, thereduc-of theV sys-Received in revised form 23 March 2013Accepted 25 March 2013Available online 28 April 2013

Keywords:PV systemBIPVAmorphous silicon PV moduleOutdoor performance

which is characterized by long, hot and dry summers with cool and wet winters. Mugla Stk Kocman Uni-versity is the largest PV Park in Turkey consisting of 100 kWp installed Photovoltaic Power Systems(PVPSs) with different PV applications. The 40 kWp building integrated photovoltaic (BIPV) system whichis the rst and largest in Turkey was installed on the faade and the two towers of the Staff Block of theEducation Facultys Building of Mugla Stk Kocman University in February 2008. Triple junction amor-phous silicon photovoltaic modules are used on the faade and single junction amorphous silicon PVmodules are used on the East and West towers of the building. In this paper, the 40 kWp BIPV systemin Mugla, Turkey is presented, and its performance is evaluated. Energy rating (kW h/kWp energy yield),efciencies and performance ratios of both applications are also evaluated for 36 months of operation.Daily, monthly and seasonal variations in performance parameters of the BIPV system in relation to solardata and meteorological parameters and outdoor performance of two reference modules (representingthe modules on faade and towers) in a summer and a winter day are also investigated.

Crown Copyright 2013 Published by Elsevier Ltd. All rights reserved.Article history:Received 13 July 2012

Mugla is located in south wizontal global irradiation eh i g h l i g h t s

The rst and the largest BIPV of Turkey Single and triple junction amorphous m Total generated electricity of the BIPV Annual energy rating is calculated as 8 The PR of the system is found 0.74 and

a r t i c l e i n f oDevelopment Centre, 48120 Kotekli, Mugla, Turkeyartment of Physics, Photovoltaic Material and Device Laboratory, 48120 Kotekli, Mugla, Turkey

installed.performances in BIPV applications are analyzed.is measured as 103,702 kW h for 36 months of operation.h/kWp for a non-optimally oriented plant.or PV systems on towers and facade respectively.

a b s t r a c t

est Turkey at 37130N latitude and 28360E longitude with yearly sum of hor-installationsMonitoring the performance of single ansilicon modules in two building integrate

Applied

journal homepage: www.etriple junction amorphousphotovoltaic (BIPV)

SciVerse ScienceDirect

Energy

vier .com/ locate/apenergy

Nomenclature

PV photovoltaicBIPV building integrated photovoltaicPVPS photovoltaic power systemSTC standard test conditionsPVSYST photovoltaic systems simulation softwarePR performance RatioPOA Plane of arraympp maximum power pointIsc short circuit current (A)Voc open circuit voltage (V)

Vin inverter DC input voltage (V)Iin inverter DC input current (A)Iout inverter AC output current (A)Vout inverter AC output voltage (V)Po nominal power at STC (W)Yf nal yield (kW h/kWp)Ht plane of array irradiation (kW h/m2)Yr reference yield ((kW h/m2)/(kW/m2))gA,mean array efciency (%)gPV,STC PV module efciency at STC (%)

R. Eke, A. Senturk / Applied Energy 109 (2013) 154162 155materials, devices and systems since 1996. Currently Mugla StkKocman University Clean Energy R&D Centre is one of the leadingestablishments in the eld having the largest PV park with manydifferent demonstration photovoltaic power systems (PVPSs) inthe main campus. With the installed PVPS, Mugla Stk KocmanUniversity covers approximately 4% of the electricity demand ofthe main Campus. The rst and largest BIPV application of Turkeywas installed on the faade and the two towers of the Staff Blockof Education Facultys Buildings which is formerly an administra-tion building of Mugla Stk Kocman University (Fig. 1) [15].

In this study, single junction and triple junction amorphous sil-icon PV modules are installed on a building and chosen in differentapplications to compare the energy rating results in a Mediterra-nean climate but in a high altitude province.

The single junction cell has the limitation that it cannot absorblow energy photons and as such has relatively low efciency. Toovercome this limitation, multi junction solar cells, such as doubleand triple junction solar cells, based on the spectral splitting prin-ciple have been devised. In addition to better efciency, thestacked solar cell also shows better stability as the problem ofphoto degradation associated with amorphous silicon solar cellsis less manifested in it than its single junction counterpart [16].

Pmpp nominal power, power at mpp (Wp)Impp current at mpp (A)Vmpp voltage at mpp (V)A PV area (m2)Pout inverter output power (W)Each cell is composed of three semiconductor junctions stackedon top of each other. The bottom cell absorbs the red light, the mid-dle cell the green/yellow light and the top cell absorbs the bluelight and this spectrum splitting capability is one of the keys tohigher efciencies and higher energy output, especially at lowerirradiation levels and under diffuse light [17]. Seasonal effects onthe outdoor performance of amorphous modules are also reportedfor various locations in previous studies [18-22].

Fig. 1. Mugla Stk Kocman University BIPV System (single and tripleSingle and triple junction amorphous silicon PV modules areused in this 40 kWp BIPV demonstration project. Daily, monthlyand seasonal variations in performance parameters of the systemin relation to solar data and meteorological parameters are moni-tored and results are available internally at the University website.

2. Description of the 40 kWp BIPV system

TWIN 140 and TWIN75 triple junction amorphous silicon mod-ules were used on the faade of the ve oors. Totally 405 m2 ofthe faade is covered. Totally 210 TWIN140 and 10 TWIN75 mod-ules are installed on 54 m length and 21 m height with 30 south-east facing of the building. The modules were installed usingspecially designed mounting units with 60 tilt angles and 25 cmapart from the building for the ventilation. The PV array is com-prised of 10 parallel strings where each string has 21 TWIN 140and one TWIN 75 module (Fig. 2). The 30.15 kWp PVPS on the fa-ade was connected to the campus grid with four 6 kW three phaseinverters.

SUNone 64 single junction amorphous silicon modules were in-stalled vertically and 10 cm apart from the walls of the east andwest towers of the building (Fig. 3). The 10.24 kWp PVPS cover

gave overall system efciency (%)Tm module operating temperature (K)Euse or Eout useful energy (kW h)136 m2 surface areas on the two towers and the systems are con-nected to the campus grid with two 5 kW single phase inverters.The effective photovoltaic area is about 112 m2 and 324 m2 forthe PV modules on both towers and faade respectively.

The PV modules were secured on aluminum rods forming a sup-port framework. The specications of used PV modules and invert-ers in PV systems are given in Table 1 [23] and Table 2 [24]respectively.

junction amorphous silicon PV modules on 2 towers and faade).

Ene156 R. Eke, A. Senturk / AppliedThe operation of the monitoring system started on July 2008,and since then, it has been in continuous operation.

The data acquisition system consists of a Sun-log data logger,two PT100 temperature sensors and two irradiation sensors whichare silicon photodiodes and used only to show the irradiation val-ues on the display for both tilted surfaces and they are installed onthe east side of the building. The electrical parameters; DC inputvoltage and current, AC output voltage, current, power and dailyelectricity output of each inverter are collected from 6 invertersfor 15 min period. A large display is also installed with the system

Fig. 2. Installation of ventilated faade BIPV installation (with 30 south-facingtriple junction amorphous silicon PV modules).

Fig. 3. Installation of 30 south-facing single junction amorphous silicon PVmodules on two towers.Table 1PV module specications under STC (sunset-a 2011).

PV module type

On towers (verticallyinstalled)

On faade (60tilted)

Single junctionamorphous Silicon

Triple junctionamorphous silicon

SUNone 64 TWIN75 TWIN140

Nominal power (Wp) 64 75 140Impp (A) 0.96 4.40 4.25Vmpp (V) 66.50 17.00 32.80Isc (A) 1.20 5.20 5.20Voc (V) 86.00 21.00 47.10Area (m2) 0.95 0.99 1.95PV cell area (m2) 0.76 0.95 1.87Temperature coefcient,

lP,mpp [%/K]0.25 0.21 0.21

Table 2Inverter specications (sunset-b 2011).

Inverter type

Sun3Grid 5000single phase

Sun3Grid 60003 phase

Pout (W) 5000 6000Min. Vin (V) 340 340Max. Vin (V) 600 600Max Iin (A) 14.5 18.0Max Iout (A) 20.9 26.0Vout (V) 195254 195254

rgy 109 (2013) 154162to show some electrical outputs of the BIPV system to public. Thedisplay allows seeing the following parameters:

Actual power and electricity output of the BIPV systems fromstart-up faade and towers (individually).

Measured vertical irradiation.

Measured backside temperature of a PV module on the towers. Measured ambient temperature.The operating temperature of a single junction amorphous sili-

con module on towers is measured (Fig. 4a) on west tower and pre-sented in Fig. 4b for two representative days of summer andwinter. It can be easily seen that module operating temperaturereaches only 45 C for both representative days because of the inci-dent angle of sunlight during the day. Measured POA irradiation onvertical surfaces reaches up to 980 W/m2 in 17th of January wheremaximum POA irradiation on vertical surfaces is only measured as680W/m2 in 17th of June.

2.1. Performance indicators

The most appropriate performance indicators of grid-connectedPV systems are given in Table 3 [2527]. Yf is the nal PV systemyield and dened as the ratio of Eout or Euse (the PV system output)to PV array nominal power:

Yf EoutPokWhkWp

1

where Po is the installed PV power at STC. The reference yield Yr isthe ratio of total plane of array (POA) irradiation Ht (kW h/m2) to ar-ray reference irradiation (1 kW/m2),

EneR. Eke, A. Senturk / AppliedYr Ht1kWh=m2

kW=m2

2

The other important parameter is the overall system efciency,gave, which denes the real conversion efciency of the solar en-ergy to useful energy collected from the PV covered area A (m2),

gave Eout

Ht A % 3

The performance ratio (PR) indicates the overall effects of losseson a PV arrays normal power output depending on array temper-ature and incomplete utilization of incident solar radiation andsystem component inefciencies (primarily inverter efciencyand line losses) or failures. PR is the ratio of PV energy actually pro-duced with the energy which would be delivered if the PV plantwere operating at STC conditions and expressed as:

in this case due to the full integration of the PV system.

Fig. 4. (a) Temperature sensor location and (b) temperature prole of a singlejunction amorphous silicon PV module on towers.Initial predictions using the PVSYST simulation program indi-cated that the PV systems would deliver about 40,000 kW h peryear [15]. Despite this, the PV systems are not performing as ex-pected because of some severe shading effects. But the total gener-ated electricity is measured as 103,702 kW h for 36 months ofoperation between July 2008 and June 2011. Daily and cumulativeelectricity outputs of both PV systems on faade, towers and theirtotal are depicted in Fig. 5. Cumulative output of the PV systemson the faade and towers are measured as 79,914 kW h andPR YfYr

4

PR is an index that gure out the relationship between the ac-tual and theoretical energy outputs of the PV system. Using thePR, one can compare the energy output of the PV system with thatof other PV systems with different geographically location or ratedpower or monitor the status of the PV power plant over a long per-iod [2831], PR is a measure of the quality of a PV power plant thatis often described as a quality factor [3234].

3. Results

The PV system at the Staffs block of Education Faculty Buildingof Mugla Stk Kocman University was installed and began opera-tion in 17th February 2008. The performance of the PV systemhas been monitored continuously since July 2008. Single and triplejunction amorphous silicon based PV modules are used in PV sys-tems. There are several phenomena mainly inuence the behaviorof an amorphous silicon PV plant [35].

These are:

optical losses due to the 90 and 60 tilt of the 2 BIPV systems; degradation and regeneration cycles due to the typical a-SiStaeblerWronski effect [36];

spectral effects due to the narrow spectral response of a-Si [21]; intrinsic loss of power due to higher operating temperature(negative temperature coefcients), particularly pronounced

Table 3Performance indicators.

Derived parameter Symbol

Useful energy Euse or EoutNominal power (W) PoFinal yield (kW h/kWp) YfReference yield ((kW h/m2)/(kW/m2)) YrPerformance ratio PRArray efciency gA,meanOverall system efciency gavePV module efciency at STC gPV,STCModule temperature Tm

rgy 109 (2013) 154162 15723,788 kW h respectively. Monthly total electricity output of eachPV systems in the BIPV application is given in Table 4. Annual en-ergy rating for triple junction amorphousmodules based PV systemon the faade is 884 kW h/kWp and single junction amorphousmodules based PV systems on the towers is calculated as774 kW h/kWp. Triple junction PV modules which are installed onthe faade produces 77% of the total electricity where these mod-ules form 75% of the installed power. Normalized monthly electric-ity output of the PV systems are also calculated for the monitoringperiod and given in Fig. 6. It is known that the triple junction PVmodules always perform better than single junction PV modulesbecause of its large spectral response. But it is clear that in winterper installed power performances are closer because of the installa-tion tilt. Only in December 2010 and in January 2011, monthly per-formances of single junction modules are more than triple junction

Ene158 R. Eke, A. Senturk / Appliedmodules. In fact it is not true to compare the different types ofinstallations of different types of modules. Thus, two referencemodules, (one single junction, SUNone64) representing the PV sys-tems on the towers and one triple junction (TWIN140) representingthe PV systems on faade are tested in Mugla Stk Kocman Univer-sity Outdoor Test site which is located on the top of the Mentese Li-brary. Both modules are oriented directly south with 15 and 35 ofinclination during the tests in summer and winter respectively. Thecurrentvoltage curves of the reference PV modules are taken in a2 min period from sunrise to sunset for 12 months from March2008 to April 2009. Two representative days are selected for sum-mer and winter seasons. These are 17th of June 2008 and 17th ofJanuary 2009. January is in themiddle of thewinter season and Juneis in the beginning of the summer season where the selected daysare both representing the days for chosen months with clear sky.Test results and energy rating calculations of PV modules and sys-tems are summarized in Table 5. Calculated normalized daily elec-tricity from the currentvoltage curves of the tested modules aregiven in Fig. 7. Both tested modules start generating current at7.15 am and stop after 10 h of operation in 17th of January and theyoperate more than 14 h in 17th of June between 6.27 am and

Fig. 5. Daily and cumulative electricity output o

Table 4Monthly total electricity outputs of PV systems from July 2008 to June 2011.

Faade (kW h) Towers (kW h)

2008 2009 2010 2011 2008 20

January 1602 1569 1725 50February 1448 1636 1704 43March 2396 2646 2197 69April 1860 2598 1901 53May 1946 2369 1865 45June 2163 2077 1923 60July 2411 2354 2447 746 70August 2721 2823 2693 881 85September 2892 2890 2826 932 92October 3088 2693 2249 972 63November 2224 2661 2169 733 76December 1927 1532 1513 619 47rgy 109 (2013) 1541627.52 pm. Test results show that the single junction PV module gen-erates 8.8% more electricity than the triple junction PV module in asummer day. Beside this; the triple junction module generates 2.2%more electricity than single junction module on a clear sky winterday in Mugla climatic conditions. This would be attributed to thehigh ambient temperature in summer (and the encapsulation dif-ference between the modules) where 25 C temperature differenceis measured between the maximum ambient temperatures in sum-mer and winter for the selected days.

Operating temperature reaches its highest value at noon timeand it is measured about 45 C for PVmodules on towers (verticallyinstalled) both in summer andwinter but for 15 tilted testmodulesthe operating temperature in summer is measured about 70 C atnoon. Daily power curves of the PV systems on the building are alsomeasured and given in Fig. 8 for the same days in summer and win-ter. In wintermonths (with low operating temperature and low rowshading effect between oors) powers are measured higher than insummer months. Because of the facing of the building (30 eastfrom south) and different daylight saving time there is an obviousshift between the maximum operating power values of the PV sys-tems in Fig. 8. For faade, the shift between maximum values is

f PV systems (on faade, towers and total).

Total, Faade + Towers (kW h)

09 2010 2011 2008 2009 2010 2011

3 482 593 2106 2051 23180 488 499 1878 2123 22033 786 335 3089 3432 25326 756 617 2396 3354 25188 688 590 2403 3056 24561 571 610 2764 2648 25330 674 3157 3054 31226 807 3602 3680 35006 906 3824 3816 37332 696 4061 3325 29452 704 2957 3422 28749 470 2546 2011 1983

Fig. 6. Normalized monthly electricity output of the PV systems (on faade and towers).

Table 5PV system output and test results of reference single and triple junction amorphous silicon PV modules.

Single junction amorphous module (SUNone 64) Triple junction amorphous module (TWIN140)

17th of January 2009 17th of June 2008 17th of January 2009 17th of June 2008

Towers Test module Towers Test module Facade Test module Facade Test module

Operation hours (h) 09.18 10.15 13.24 14.30 09.17 10.00 13.25 14.15Effective solar radiation (kW h/m2) 4.93 5.55 4.34 9.57 4.65 5.64 5.45 9.57Average inverter efciency (%) 88.00 88.00 92.00 92.00 Average PV efciency (%) 6.33 5.45 5.32 6.12 6.92 4.87 4.78 4.96Daily energy rating (kW h/kWp day) 3.41 (AC) 3.59 (DC) 2.53 (AC) 6.95 (DC) 3.46 (AC) 3.67 (DC) 2.80 (AC) 6.34 (DC)

Fig. 7. Normalized daily electricity output of the reference modules for selecteddays representing summer and winter.

Fig. 8. Power output of the PV systems (on faade and towers) for selected daysrepresenting summer and winter.

R. Eke, A. Senturk / Applied Energy 109 (2013) 154162 159

Ene160 R. Eke, A. Senturk / Appliedabout 45 min but for towers the shift is less than 30 min. Also thetemperature coefcients lPmpp [%/K] of the used PV modules aregiven constant and given at STC as 0.21 and 0.25 for single andtriple junction, respectively (Table 1). In the previous works it isfound out that the power-temperature behavior of amorphous sili-con PV modules is nonlinear because of the different cell physics of

Fig. 9. Measured daily horizontal irradiatio

Fig. 10. Average PV system (on faade and towers)rgy 109 (2013) 154162amorphous silicon solar cells [3739]. Single junction PV modulespower decreases severely than triple junction PV modules fewerthan 70 C of operating temperature in summer. And this also ex-plains the better performance of single junction modules in winter.PV systems reach maximum power about 11.00 am in winter be-cause of the east facing (Azimuth 30) of the building. After

n for 36 months test period in Mugla.

efciency variation for 36 months test period.

of

Ene11.00 am the shading effect starts from the east parts and the powerof the system drops notably. In summer this point shifts towardsnoon but again the power drops because of the shading effect. Max-

Fig. 11. Average performance ratioR. Eke, A. Senturk / Appliedimum total power of the systems is measured as 29.32 kW on 24thof October 2010 at 11.45 am. Besides this, maximum power is mea-sured as 22.27 kW and 8.8 kW for the PV systems on faade andtowers, respectively about 11.00 am and the maximum daily elec-tricity fed to grid is measured as 164 kW h.

The building is facing to an open area, so there is no shadingobstacle except strings shading and a small tree as it can be seenfrom Fig. 1. When the sun is high, PV arrays in front of the windowsof each oor represent a source of shading during summer at noonperiods.

Daily horizontal irradiation is measured with a Kipp&ZonnenCM11 type high precision pyranometer on the top of Mentese Li-brary which is close to the BIPV system. The results are used toanalyze the irradiation distribution in the province for the moni-toring period and given in Fig. 9. In contrast with the increasingirradiation in summer system efciency (Fig. 10) and calculatedPR (Fig. 11) decreases in hot summer months and both increasein cold winter months as reported in previous works [17,40,41].The overall system efciency and the performance ratio of the tri-ple junction amorphous silicon PV systems on the faade are calcu-lated higher than the single junction amorphous silicon moduleson the towers for 36 months of operation. The degradation in theefciencies of PV modules are not analyzed in the present work.

4. Conclusion

The installation and performance results of the largest grid-con-nected BIPV system in Turkey after 36 months of operation havebeen reported. The Single junction (with 10.24 kWp nominalpower and vertically oriented on two towers) and triple junction(with 30.15 kWp nominal power and 60 x tilt on faade)amorphous silicon PV modules are used in this 40 kWp BIPVdemonstration project. Total generated electricity of the BIPV sys-tem is measured as 103,702 kW h for 36 months of operation be-tween July 2008 and June 2011. The average efciency for the

PV systems on faade and towers.rgy 109 (2013) 154162 161single junction amorphous silicon PV modules on the towers isfound as 5.58% during the monitoring period while the conversionefciency increases up to 6.5% in cold but clear sky winter days.Average efciency of the triple junction amorphous silicon PVmodules on the facade is found as 5.99%. The PR of the system isalso calculated for both PV systems and it is found as 0.74 and0.81 for the PV systems on the towers and facade respectively. Sin-gle junction PV modules power decreases severely than triple junc-tion PV modules fewer than 70 C of operating temperature insummer. And this also explains the better performance of singlejunction modules in winter. It is shown that triple junction amor-phous silicon PV systems perform better than single junctionamorphous in a long period. According to the results obtained fromthe tested PV modules deployed Mugla Stk Kocman UniversityOutdoor Test site, single junction amorphous silicon SUNone64modules daily energy rating is calculated between 3.59 and6.95 kW h/kWp and for triple junction TWIN140 module daily en-ergy rating is calculated between 3.67 and 6.34 kW h/kWp wherethe overall BIPV systems annual energy rating is calculated as856 kW h/kWp after 36 months of operation.

The cooling load in summer is not analyzed in detail but directsun light is shaded with the PV modules installed between theoors and the staffs using the front side of the building are pleasedfrom the decreased temperature of their rooms. It is shown thatthin lm amorphous silicon photovoltaic modules are a goodchoice for covering the buildings and decreasing the cooling loadof building envelopes if the system is designed well.

Acknowledgements

This work was supported by Mugla Stk Kocman University Sci-entic Research Projects (BAP) with the code 08/10 and implanted

by SUNSET Energietechnik GmbH. Some part of this study is pre-sented as a visual presentation in 24th EUPVSEC in 2009.

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Monitoring the performance of single and triple junction amorphous silicon modules in two building integrated photovoltaic (BIPV) installations1 Introduction2 Description of the 40kWp BIPV system2.1 Performance indicators

3 Results4 ConclusionAcknowledgementsReferences