Research Article Accelerated Life Test for Photovoltaic ...downloads.hindawi.com/journals/ijp/2016/9825683.pdf · cantly reduce the necessary time for the ageing tests for di erent

Research ArticleAccelerated Life Test for Photovoltaic Cells UsingConcentrated Light

Daniel Tudor Cotfas Petru Adrian Cotfas Dan Ion Floroian and Laura Floroian

Electrical Engineering and Computer Science Faculty Transilvania University of Brasov 500036 Brasov Romania

Correspondence should be addressed to Daniel Tudor Cotfas dtcotfasunitbvro

Received 14 April 2016 Revised 7 June 2016 Accepted 3 July 2016

Academic Editor Prakash Basnyat

Copyright copy 2016 Daniel Tudor Cotfas et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

This paper presents a new method developed to significantly reduce the necessary time for the ageing tests for different types ofphotovoltaic cells Two ageing factors have been applied to the photovoltaic cells the concentrated light and the temperature Themaximum power of the photovoltaic cells was monitored during the ageing process The electrical dc and ac parameters of thephotovoltaic cells were measured and analyzed at 1 sun irradiance before and after the test stress During the test two photovoltaiccells are kept at maximum power point and the other two are kept at open circuit voltage point The method is validated throughthe results obtained for the monocrystalline silicon solar cell

1 Introduction

The reliability and durability are two important factors forthe new photovoltaic cells and panels today perhaps at leastas important for them as the price per watt The lifetime ofnew photovoltaic cells such as but not only themultijunctioncells used in concentrated light whose efficiency is 46 [1]and the very promising perovskite solar cells whose efficiencyincreases very quickly at 201 [2] is not known

Therefore a predictive model for the lifetime and thebehavior of the new photovoltaic cells and panels is veryimportant for producers as well as for customersThe acceler-ated ageing test for the photovoltaic cells and panels is one ofthe main analyses which are the base of the predictive model[3 4]

There are several methods to realize the acceleratedageing test for photovoltaic cells and panels indoors such as

(i) Damp Heat Test (DH) the ageing factors are thetemperature and the relative humidity the values forthese two factors are 85∘C and 85 the time for theageing test is over 2000 hours [5]

(ii) Highly Accelerated Stress Test (HAST) the ageingfactors are the temperature and the relative humiditybut their values grow in comparison to DH so the

temperature can be 110∘C 130∘C or 150∘C and thehumidity can be 85 or 100 the increasing of theageing factors values leads to the decrease of the timefor the ageing test in this case the time for the ageingtest is around 400 hours

(iii) step-stress accelerated ageing tests the ageing factorsare the temperature and the injected current toemulate constant illumination the temperature canbe 130∘C 150∘C or 170∘C and the value of the currentis equal to the value of the short circuit current 119868sc at1 sun multiplied with 700 or 1050 the test being madefor multijunction solar cells [6]

(iv) thermal cycling test this method uses the variationof the temperature between minus40∘C and 85∘C and theinjected current to emulate constant illumination theamount of the cycling varies in function of the upperlimit of the temperature 500 for 110∘C 1000 for 85∘Cor 2000 for 65∘C the injected current in the solar cellis equal to 125 times 119868sc times no of suns [7]

(v) potential induced degradation (PID) the ageing fac-tors for the photovoltaic modules are the external biasvoltage the temperature and the relative humiditytheir values are 1000V 50∘C and 50 [5] or 600V65∘C and 85 [8]

Hindawi Publishing CorporationInternational Journal of PhotoenergyVolume 2016 Article ID 9825683 7 pageshttpdxdoiorg10115520169825683

2 International Journal of Photoenergy

The lifetime for the Si photovoltaic panels now is knownand it is over 25 years [9] The failure criterion is when itsmaximum power decreases with at least 20 from the initialmaximum power [10]

Nunez et al had defined a degradation failure criterionfor the multijunction cells [11] The failure limit is whenthe maximum power decreases with at least 25 from theinitial maximum power Nunez et al considered that a powerloss of up to 20 is generated by the other elements of theconcentrator photovoltaic system

The degradation failure criterion for the silicon pho-tovoltaic cell corresponds to losing 10 of the maximumpower through light-induced power degradation occurrenceofmicrocracks increase in series resistance decrease of shuntresistance and so forth [12ndash14]

2 Method

The main goal of the accelerated life test is to reduce thetesting time under simulated working conditions In DH testthe necessary time is around 2000 h and the target of the newmethods is tens or some hundreds of hours

There are many methods to perform the accelerated lifetest but there is scarce research using light as ageing factorbecause the majority use a climatic chamber and thereforethe concentrated light is difficult to use [11] The researchershad emulated the work conditions in concentrated light byinjection of the forward current equivalent to the photogener-ated current by the photovoltaic cell at the level of the desiredconcentration [11 15] In this case the stress produced on thephotovoltaic cells by the high concentrated light cannot betaken into consideration

The paper presents a new method for the acceleratedlife test using the concentrated light obtained from a solarsimulator with a xenon lamp (calledALTCL) Due toworkingconditions there are two stress factors light and temperature

The experiment set-up to apply the new method consistsof the solar simulator the photovoltaic cells themeasurementsystem and the photovoltaic cells support cooled with waterwhich is provided with a variable flow of water [16]

21 Solar Simulator The experiments were performed atSolar Technology Laboratory of Paul Scherrer Institute (PSI)Villigen Switzerland using the high-flux solar simulator(HFSS) which has ten xenon arc lamps cooled with highpressurewater Figure 1Thehighly concentrated light similarto the solar radiation is obtained in the focal plane using thelamps

The lamp reflector is designed as a truncated ellipsoid[17 18]The accelerated ageing test was performed using onlyone of the ten xenon arc lamps which works at 106 kW Theelectric power of the lamp was maintained quasi-constantusing an automatic system

22 Photovoltaic Cellsrsquo Water Cooled Support The photo-voltaic cellsrsquo water cooling support allows themounting of thefour PV cells in different configurations and the maintaining

of the PV cells temperature quasi-constant during the mea-surements under concentrated light [16] see Figure 2

The facility of the various mounting of the photovoltaiccells is necessary to have the PV cells illuminated with thesame or with the different levels of the concentrated light

The temperature of the photovoltaic cells can be adjustedusing the levels of illumination and also the variable waterflow which can be assured by the automatic pump systemThe distribution of the illumination levels obtained with onexenon lamp at PSI is presented in Figure 3

The photovoltaic cells were positioned so all of them areuniformly illuminated with the same radiative flux 190 sunsThe shutter of the solar simulator was gradually opened untilthe temperature of the photovoltaic cells was 150∘C plusmn 2∘C

23 Measurement System The measurements were per-formed in concentrated light and under illumination at 1 sun

The measurements in concentrated light were performedat PSI using a system based on cRIO from National Instru-ments and a module developed by our team which allowsmeasuring the current voltage characteristics I-V for allfour photovoltaic cells simultaneously and also their tem-perature The photovoltaic cellsrsquo temperature was measuredusing a thermocouple for each of them The maximumpower can be determined by measuring I-V characteristicof the photovoltaic cells For measuring the current andvoltage on the photovoltaic cells the NI 9227 and NI 9215modules were used The first module is used to measure thecurrent through the photovoltaic cells and the second oneis used for measuring their output voltage These modulesallow measuring all four channels at the same time Thedynamic load used for measuring I-V characteristics of thephotovoltaic cell is based on a large capacitor The solar celltemperatures are measured with a NI 9211 module whichallows sampling simultaneously for all four channels TheDIO (Digital Input Output) NI 9401 module is used for start-ing I-V characteristic measurements Betweenmeasurementsof two consecutive I-V characteristics a load can be applied tothe photovoltaic cellsThe applied load is based on aMOSFETwhich is controlled using the four analog outputs of the NI9269 module Some of the studied photovoltaic cells weremaintained in the maximum power point regime while theothers were maintained in the open circuit regime

The measurements under 1-sun illumination were per-formed using the Autolab PGSTAT100 This system allowsmeasuring I-V characteristic under illumination using thepotentiostat mode and also plotting and fitting the Nyquistdiagram using the Fra (Frequency Response Analyzer) mod-ule

24 Photovoltaic Cells The photovoltaic cells chosen forthe experiment are commercial monocrystalline silicon cellsand InGaPInGaAsGemultijunction cells Four photovoltaiccells were tested two of each type In each pair of photovoltaiccells one of them was measured with load and one withoutload

The reason of the choosing the monocrystalline siliconcells is that the lifetime is knownThemonocrystalline silicon

International Journal of Photoenergy 3

Lamp array(i) 10 Xe-Arc lamps

Experiment in focusReflector array

(i) Ellipsoidal reflector(ii) Protected aluminium

reflective coating

Lambertian target for radiation flux measurements

3-axis traverse

(ii) Travel range

Power and cooling (i) 10 rectifiers(ii) Water and air

cooling

1055 times 800 times 600mm

(i) Maximum load 500kg

(iii) Power rating 15kW (each)(ii) Peak flux gt 10000 kWm2

mm 20kWth(i) Total power through Oslash60

(ii) Power rating 15kW (each)

Figure 1 Schema of the solar simulator

Figure 2The photovoltaic cellsrsquo water cooled support with four PVcells

photovoltaic cells were cut at 05 cm05 cm because thesystem can measure up to 5A and for a good uniformity ofthe illumination The short circuit current measured at 190suns is 165 A and the open circuit voltage is 0668V

InGaPInGaAsGe photovoltaic cells are made to work inconcentrated light Their structure is triple junction and thedimensions are 1 cm1 cmThe short circuit currentmeasuredat 190 suns is 267A and the open circuit voltage is 282V

3 Results and Discussion

The desired temperature for the test 150∘C was obtained andmaintained quasi-constant using only the concentrated lightand the cooling system

Nunez et al [11] proposed two criteria for reliability ofthe photovoltaic cell catastrophic failure instant drop inpower of the photovoltaic cells and degradation failure thepower decreasing with more than 25 for the multijunction

50 suns125 suns190 suns260 suns


PV

Figure 3 The radiative flux map and the positioning of thephotovoltaic cells

photovoltaic cells which work in concentrated light andmorethan 10 for the silicon photovoltaic cells

The photovoltaic cells were subjected to 190-sun concen-trated light and 150∘C for 35 hours and 7 hours per day andin the rest of day they were kept in darkness and at roomtemperature After five days only the second criterion wasobserved

The result of the accelerated ageing test of the monocrys-talline silicon photovoltaic cell without load during theexperiment is presented in Figure 4 The normalized power


Time (h)

350

000

000

000

050

000

100

000

150

000

200

000

250

000

300

000

Fit

081082083084085086087088089

09091092093094095096097098099

1101

PP

o

Pmax

Figure 4 The normalized power of the monocrystalline photo-voltaic cell without load evolution over time

119875119875119900 which is the ratio between the maximum power 119875

determined during the experiment and the initial maximumpower 119875

119900of the photovoltaic cell at 190 suns and 150∘C

is represented over the time The maximum power of thephotovoltaic cell was determined using I-V characteristicwhich was measured every five minutes

The normalized power of the monocrystalline siliconphotovoltaic cell without load decreases exponentially seethe red fitting curve from Figure 4 and the degradationfailure criterion is reached after 10 hours After 20 hours anasymptotic decrease is observed in the normalized powerThe normalized power after 35 hours is 083 which meansa decrease of 17 see Figure 4

The normalized power InGaPInGaAsGe multijunctionphotovoltaic cell without load decreases very slowly and after35 hours it decreases only by 15

The decreasing ratio of the normalized power for thephotovoltaic cells with load during the ageing test after 35hours was lower 6 for the monocrystalline silicon (seeFigure 5) and negligible for the multijunction photovoltaiccell

The photovoltaic cells were analyzed in static regime dcand dynamic regime ac before and after the acceleratedageing test

I-V characteristics and power voltage P-V characteristicsare measured for each photovoltaic cell The measurementswere realized with Autolab under illumination at 1000Wm2irradiance (1 sun) and at this time the temperature of thephotovoltaic cells is maintained constant with thermostat at25∘C plusmn 05∘C

Figure 6 shows I-V and P-V characteristics measured forthe monocrystalline silicon photovoltaic cell without loadbefore and after the accelerated test By analyzing the resultsit is observed that the short circuit current 119868sc decreases with39 plusmn 01 the open circuit voltage decreases with 54 plusmn01 and the maximum power decreases with 182 plusmn 02

102

Time (h)

350

000

000

000

050

000

100

000

150

000

200

000

250

000

300

000

09091092093094095096097098099

1101

PP

o

FitPmax

Figure 5 The normalized power of the monocrystalline photo-voltaic cell with load evolution over time

The shape of I-V characteristic around the knee (themaximum power point) for the aged photovoltaic cell showsan important modification This can be explained by theincreasing of the series resistance 119877

119904 and the decreasing of

the shunt resistance 119877shI-V and P-V characteristics measured for the InGaP

InGaAsGe multijunction photovoltaic cell without loadbefore and after the accelerated test are presented in Figure 7The maximum power decreases with 15 plusmn 01 whereas119868sc and 119881oc remain quasi-constant after the ageing processThe shape of I-V characteristic measured after the ageingprocess remains almost unchanged only the effect of theslight increase in the series resistance being observed

The impedance spectroscopy [19 20] with the frequencydomain technique is used to analyze the parameters of thephotovoltaic cells in dynamic regime before and after theageing process An ac pure sinusoidal signal with amplitudesmaller than the thermal voltage (119896119879119890) is superposed onthe dc bias signal The measurements were performed atbias voltage equal to 119881max the voltage corresponding tothe maximum power point The photovoltaic cells weremaintained at 25∘C plusmn 05∘C and were illuminated at 1 sun

The Nyquist diagrams before and after the ageing pro-cess for themonocrystalline silicon photovoltaic cell withoutload are presented in Figure 8 and those for the InGaPInGaAsGe multijunction photovoltaic cell without load arepresented in Figure 9 The important ac parameters of thephotovoltaic cells are obtained using the fitting procedurewith the equivalent ac circuit and they are presented inTable 1

The results obtained for the ac parameters of the photo-voltaic cells confirm analysis for the behavior of the photo-voltaic cells in static regime The series resistance stronglyincreases for the monocrystalline silicon photovoltaic cell


Before ageingAfter ageing

0000

0002

0004

0006

0008

0010

I (A

)

01 02 03 04 05 0600V (V)

(a)


0000

0001

0002

0003

0004

P (W

)

01 02 03 04 05 0600V (V)

(b)

Figure 6 The monocrystalline silicon photovoltaic cell without load before and after ageing process (a) I-V characteristics (b) P-Vcharacteristics

00 05 10 15 20 25 300000

0002

0004

0006

0008

0010

0012

0014


I (A

)

V (V)

(a)

00 05 10 15 20 25 300000

0005

0010

0015

0020

0025

0030


P (W

)

V (V)

(b)

Figure 7The InGaPInGaAsGe multijunction photovoltaic cell without load before and after ageing process (a) I-V characteristics (b) P-Vcharacteristics

Table 1 The ac parameters of the photovoltaic cells at 1000Wm2 and 25∘C

Type of photovoltaic cell Ageing test 119877119904

[Ω] 119877119901

[Ω] 119862 [nF]

Monocrystalline silicon without load Before 023 plusmn 001 4967 plusmn 02 6443 plusmn 35After 076 plusmn 001 2423 plusmn 016 4324 plusmn 25

Monocrystalline silicon with load Before 022 plusmn 001 4971 plusmn 02 6423 plusmn 35After 045 plusmn 001 3823 plusmn 016 5524 plusmn 25

InGaPInGaAsGe without load Before 087 plusmn 0012 1842 plusmn 012 (1943 plusmn 01) lowast 103

After 0881 plusmn 0012 1839 plusmn 012 (1942 plusmn 01) lowast 103


0 10 20 30 40 500

5

10

15

20


Z998400 (Ω)

minusZ

998400998400(Ω

)

Figure 8 Nyquist plot of the monocrystalline silicon photovoltaiccell without load before and after ageing process


2 4 6 8 10 12 14 16 18 200Z

998400 (Ω)

0

2

4

6

8

10

minusZ

998400998400(Ω

)

Figure 9 Nyquist plot of the InGaPInGaAsGe multijunctionphotovoltaic cell without load before and after ageing process

whereas for the multijunction photovoltaic cell it slightlyincreases The same behavior is determined for the decreaseof the shunt resistance and for the capacitance

4 Conclusions

A newmethod for the accelerated life test of the photovoltaiccells was developed and verifiedThe novelty of themethod isthe use of only concentrated light and the cooling system soas to have two ageing factors the light and the temperature

The duration of the life test is reduced considerablyfor example 10ndash20 hours for the monocrystalline silicon

photovoltaic cells without load at 190 suns For monocrys-talline silicon cell with load the degradation after 35 hat the same illumination is 6 The maximum power ofInGaPInGaAsGemultijunction cell without load at 190 sunsafter 35 hours decreases with 15 which means it does notreach the limit of the degradation failure

The maximum power of the photovoltaic cells withload decreases slighter than the maximum power of thephotovoltaic cells without load which proves that lifetime ofthe photovoltaic panels increases if they work in load

The parameters of the photovoltaic cells were analyzed instatic and dynamic regime at 1 sun and 25∘C using I-V andP-V characteristics and the Nyquist diagrams The behaviorof the short circuit current open circuit voltage maximumpower series and parallel resistance and capacitance beforeand after the ageing process was studied

The future research will consist of increasing the durationof the life test for themultijunction photovoltaic cells until thelimit of the degradation failure criterion is reached and alsowe will apply the method validated by present work to testother type of photovoltaic cells

Competing Interests

The authors declare that they have no competing interests

Acknowledgments

Financial support by the Access to Research Infrastructuresactivity in the 7th Framework Programme of the EU (SFERA2 Grant Agreement no 312643) is gratefully acknowledgedThe authors are thankful to Y Baeuerle DWuillemin and CWieckert aswell as further coworkers from the Solar Technol-ogy Laboratory of Paul Scherrer Institute Villigen Switzer-land where all the measurements in concentrated light wereperformed They hereby acknowledge the structural fundsproject PRO-DD (POS-CCE O221 ID 123 SMIS 2637 no112009) for providing a part of the infrastructure used in thiswork

References

[1] M A Green K Emery Y Hishikawa W Warta and E DDunlop ldquoSolar cell efficiency tables (version 44)rdquo Progress inPhotovoltaics Research and Applications vol 23 pp 1ndash9 2015

[2] M I Ahmed A Habib and S S Javaid ldquoPerovskite solar cellspotentials challenges and opportunitiesrdquo International Journalof Photoenergy vol 2015 Article ID 592308 13 pages 2015

[3] US Department of Energy Sandia and NREL ldquoAcceleratedaging testing and reliability in photovoltaics Solar energytechnology programrdquo 2008

[4] D C Jordan and S R Kurtz ldquoPhotovoltaic degradation ratesmdashan analytical reviewrdquo Progress in Photovoltaics Research andApplications vol 21 no 1 pp 12ndash29 2013

[5] A Phinikarides N Kindyni GMakrides andG E GeorghiouldquoReview of photovoltaic degradation rate methodologiesrdquoRenewable and Sustainable Energy Reviews vol 40 pp 143ndash1522014


[6] J R Gonzalez M Vazquez N Nunez C Algora I Rey-Stolleand B Galiana ldquoReliability analysis of temperature step-stresstests on IIIndashV high concentrator solar cellsrdquo MicroelectronicsReliability vol 49 no 7 pp 673ndash680 2009

[7] G J Lin L J Wang J Q Liu W P Xiong M H Song andZ H Wu ldquoAccelerated aging tests of high concentration multi-junction solar cellsrdquo Procedia Environmental Sciences vol 11 pp1147ndash1152 2011

[8] C R Osterwald T J McMahon and J A del Cueto ldquoElec-trochemical corrosion of SnO

2

F transparent conducting layersin thin-film photovoltaic modulesrdquo Solar Energy Materials andSolar Cells vol 79 no 1 pp 21ndash33 2003

[9] E Kaplani ldquoDetection of degradation effects in field-agedc-Si solar cells through IR thermography and digital imageprocessingrdquo International Journal of Photoenergy vol 2012Article ID 396792 11 pages 2012

[10] M Vazquez and I Rey-Stolle ldquoPhotovoltaic module reliabilitymodel based on field degradation studiesrdquo Progress in Photo-voltaics Research and Applications vol 16 no 5 pp 419ndash4332008

[11] NNunez J R GonzalezMVazquez C Algora and P EspinetldquoEvaluation of the reliability of high concentrator GaAs solarcells by means of temperature accelerated aging testsrdquo Progressin Photovoltaics Research and Applications vol 21 no 5 pp1104ndash1113 2013

[12] M Paggi I Berardone A Infuso and M Corrado ldquoFatiguedegradation and electric recovery in Silicon solar cells embed-ded in photovoltaic modulesrdquo Scientific Reports vol 4 article4506 pp 1ndash7 2014

[13] D DeGraaff R Lacerda and Z Campeau ldquoDegradationmech-anisms in Si module technologies observed in the field theiranalysis and statisticsrdquo in Proceedings of the NREL PhotovoltaicModule Reliability Workshop Golden Colo USA February2011

[14] P Basnyat B Sopori S Devayajanam et al ldquoExperimentalstudy to separate surface and bulk contributions of light-induced degradation in crystalline silicon solar cellsrdquo EmergingMaterials Research vol 4 no 2 pp 239ndash246 2015

[15] C Algora ldquoReliability of IIIndashV concentrator solar cellsrdquoMicro-electronics Reliability vol 50 no 9ndash11 pp 1193ndash1198 2010

[16] D T Cotfas P A Cotfas D Floroian L Floroian and MCernat ldquoAgeing of photovoltaic cells under concentrated lightrdquoin Proceedings of the 2015 Intl Aegean Conference on ElectricalMachines amp Power Electronics (ACEMP rsquo15) and Intl Conferenceon Optimization of Electrical amp Electronic Equipment (OPTIM)amp 2015 Intl Symposium on Advanced Electromechanical MotionSystems (ELECTROMOTION rsquo15) Side Turkey September2015

[17] J Petrasch P Coray A Meier et al ldquoA novel 50 kW 11000 sunshigh-flux solar simulator based on an array of xenon arc lampsrdquoASME Journal of Solar Energy Engineering vol 129 no 4 pp405ndash411 2007

[18] I Alxneit and H Schmit ldquoSpectral characterization of PSIrsquoshigh-flux solar simulatorrdquo Journal of Solar Energy Engineeringvol 134 no 1 Article ID 011013 2012

[19] M Toivola J Halme L Peltokorpi and P Lund ldquoInvestiga-tion of temperature and aging effects in nanostructured dyesolar cells studied by electrochemical impedance spectroscopyrdquoInternational Journal of Photoenergy vol 2009 Article ID786429 15 pages 2009

[20] D T Cotfas P A Cotfas and S Kaplanis ldquoMethods andtechniques to determine the dynamic parameters of solar cells

reviewrdquo Renewable and Sustainable Energy Reviews vol 61 pp213ndash221 2016

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

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Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

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Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of


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Applied ChemistryJournal of



Theoretical ChemistryJournal of


Journal of

Spectroscopy

Analytical ChemistryInternational Journal of


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Quantum Chemistry


Organic Chemistry International

ElectrochemistryInternational Journal of



CatalystsJournal of


The lifetime for the Si photovoltaic panels now is knownand it is over 25 years [9] The failure criterion is when itsmaximum power decreases with at least 20 from the initialmaximum power [10]

Nunez et al had defined a degradation failure criterionfor the multijunction cells [11] The failure limit is whenthe maximum power decreases with at least 25 from theinitial maximum power Nunez et al considered that a powerloss of up to 20 is generated by the other elements of theconcentrator photovoltaic system

The degradation failure criterion for the silicon pho-tovoltaic cell corresponds to losing 10 of the maximumpower through light-induced power degradation occurrenceofmicrocracks increase in series resistance decrease of shuntresistance and so forth [12ndash14]

2 Method

The main goal of the accelerated life test is to reduce thetesting time under simulated working conditions In DH testthe necessary time is around 2000 h and the target of the newmethods is tens or some hundreds of hours

There are many methods to perform the accelerated lifetest but there is scarce research using light as ageing factorbecause the majority use a climatic chamber and thereforethe concentrated light is difficult to use [11] The researchershad emulated the work conditions in concentrated light byinjection of the forward current equivalent to the photogener-ated current by the photovoltaic cell at the level of the desiredconcentration [11 15] In this case the stress produced on thephotovoltaic cells by the high concentrated light cannot betaken into consideration

The paper presents a new method for the acceleratedlife test using the concentrated light obtained from a solarsimulator with a xenon lamp (calledALTCL) Due toworkingconditions there are two stress factors light and temperature

The experiment set-up to apply the new method consistsof the solar simulator the photovoltaic cells themeasurementsystem and the photovoltaic cells support cooled with waterwhich is provided with a variable flow of water [16]

21 Solar Simulator The experiments were performed atSolar Technology Laboratory of Paul Scherrer Institute (PSI)Villigen Switzerland using the high-flux solar simulator(HFSS) which has ten xenon arc lamps cooled with highpressurewater Figure 1Thehighly concentrated light similarto the solar radiation is obtained in the focal plane using thelamps

The lamp reflector is designed as a truncated ellipsoid[17 18]The accelerated ageing test was performed using onlyone of the ten xenon arc lamps which works at 106 kW Theelectric power of the lamp was maintained quasi-constantusing an automatic system

22 Photovoltaic Cellsrsquo Water Cooled Support The photo-voltaic cellsrsquo water cooling support allows themounting of thefour PV cells in different configurations and the maintaining

of the PV cells temperature quasi-constant during the mea-surements under concentrated light [16] see Figure 2

The facility of the various mounting of the photovoltaiccells is necessary to have the PV cells illuminated with thesame or with the different levels of the concentrated light

The temperature of the photovoltaic cells can be adjustedusing the levels of illumination and also the variable waterflow which can be assured by the automatic pump systemThe distribution of the illumination levels obtained with onexenon lamp at PSI is presented in Figure 3

The photovoltaic cells were positioned so all of them areuniformly illuminated with the same radiative flux 190 sunsThe shutter of the solar simulator was gradually opened untilthe temperature of the photovoltaic cells was 150∘C plusmn 2∘C

23 Measurement System The measurements were per-formed in concentrated light and under illumination at 1 sun

The measurements in concentrated light were performedat PSI using a system based on cRIO from National Instru-ments and a module developed by our team which allowsmeasuring the current voltage characteristics I-V for allfour photovoltaic cells simultaneously and also their tem-perature The photovoltaic cellsrsquo temperature was measuredusing a thermocouple for each of them The maximumpower can be determined by measuring I-V characteristicof the photovoltaic cells For measuring the current andvoltage on the photovoltaic cells the NI 9227 and NI 9215modules were used The first module is used to measure thecurrent through the photovoltaic cells and the second oneis used for measuring their output voltage These modulesallow measuring all four channels at the same time Thedynamic load used for measuring I-V characteristics of thephotovoltaic cell is based on a large capacitor The solar celltemperatures are measured with a NI 9211 module whichallows sampling simultaneously for all four channels TheDIO (Digital Input Output) NI 9401 module is used for start-ing I-V characteristic measurements Betweenmeasurementsof two consecutive I-V characteristics a load can be applied tothe photovoltaic cellsThe applied load is based on aMOSFETwhich is controlled using the four analog outputs of the NI9269 module Some of the studied photovoltaic cells weremaintained in the maximum power point regime while theothers were maintained in the open circuit regime

The measurements under 1-sun illumination were per-formed using the Autolab PGSTAT100 This system allowsmeasuring I-V characteristic under illumination using thepotentiostat mode and also plotting and fitting the Nyquistdiagram using the Fra (Frequency Response Analyzer) mod-ule

24 Photovoltaic Cells The photovoltaic cells chosen forthe experiment are commercial monocrystalline silicon cellsand InGaPInGaAsGemultijunction cells Four photovoltaiccells were tested two of each type In each pair of photovoltaiccells one of them was measured with load and one withoutload

The reason of the choosing the monocrystalline siliconcells is that the lifetime is knownThemonocrystalline silicon





reflective coating


3-axis traverse

(ii) Travel range


cooling















PV






Time (h)

350

000

000

000

050

000

100

000

150

000

200

000

250

000

300

000

Fit

081082083084085086087088089

09091092093094095096097098099

1101

PP

o

Pmax












102

Time (h)

350

000

000

000

050

000

100

000

150

000

200

000

250

000

300

000

09091092093094095096097098099

1101

PP

o

FitPmax











0000

0002

0004

0006

0008

0010

I (A

)

01 02 03 04 05 0600V (V)

(a)


0000

0001

0002

0003

0004

P (W

)

01 02 03 04 05 0600V (V)

(b)


00 05 10 15 20 25 300000

0002

0004

0006

0008

0010

0012

0014


I (A

)

V (V)

(a)

00 05 10 15 20 25 300000

0005

0010

0015

0020

0025

0030


P (W

)

V (V)

(b)




[Ω] 119877119901

[Ω] 119862 [nF]






0 10 20 30 40 500

5

10

15

20


Z998400 (Ω)

minusZ

998400998400(Ω

)



2 4 6 8 10 12 14 16 18 200Z

998400 (Ω)

0

2

4

6

8

10

minusZ

998400998400(Ω

)



4 Conclusions







Competing Interests


Acknowledgments


References










2
























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of





reflective coating


3-axis traverse

(ii) Travel range


cooling















PV






Time (h)

350

000

000

000

050

000

100

000

150

000

200

000

250

000

300

000

Fit

081082083084085086087088089

09091092093094095096097098099

1101

PP

o

Pmax












102

Time (h)

350

000

000

000

050

000

100

000

150

000

200

000

250

000

300

000

09091092093094095096097098099

1101

PP

o

FitPmax











0000

0002

0004

0006

0008

0010

I (A

)

01 02 03 04 05 0600V (V)

(a)


0000

0001

0002

0003

0004

P (W

)

01 02 03 04 05 0600V (V)

(b)


00 05 10 15 20 25 300000

0002

0004

0006

0008

0010

0012

0014


I (A

)

V (V)

(a)

00 05 10 15 20 25 300000

0005

0010

0015

0020

0025

0030


P (W

)

V (V)

(b)




[Ω] 119877119901

[Ω] 119862 [nF]






0 10 20 30 40 500

5

10

15

20


Z998400 (Ω)

minusZ

998400998400(Ω

)



2 4 6 8 10 12 14 16 18 200Z

998400 (Ω)

0

2

4

6

8

10

minusZ

998400998400(Ω

)



4 Conclusions







Competing Interests


Acknowledgments


References










2
























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


Time (h)

350

000

000

000

050

000

100

000

150

000

200

000

250

000

300

000

Fit

081082083084085086087088089

09091092093094095096097098099

1101

PP

o

Pmax












102

Time (h)

350

000

000

000

050

000

100

000

150

000

200

000

250

000

300

000

09091092093094095096097098099

1101

PP

o

FitPmax











0000

0002

0004

0006

0008

0010

I (A

)

01 02 03 04 05 0600V (V)

(a)


0000

0001

0002

0003

0004

P (W

)

01 02 03 04 05 0600V (V)

(b)


00 05 10 15 20 25 300000

0002

0004

0006

0008

0010

0012

0014


I (A

)

V (V)

(a)

00 05 10 15 20 25 300000

0005

0010

0015

0020

0025

0030


P (W

)

V (V)

(b)




[Ω] 119877119901

[Ω] 119862 [nF]






0 10 20 30 40 500

5

10

15

20


Z998400 (Ω)

minusZ

998400998400(Ω

)



2 4 6 8 10 12 14 16 18 200Z

998400 (Ω)

0

2

4

6

8

10

minusZ

998400998400(Ω

)



4 Conclusions







Competing Interests


Acknowledgments


References










2
























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



0000

0002

0004

0006

0008

0010

I (A

)

01 02 03 04 05 0600V (V)

(a)


0000

0001

0002

0003

0004

P (W

)

01 02 03 04 05 0600V (V)

(b)


00 05 10 15 20 25 300000

0002

0004

0006

0008

0010

0012

0014


I (A

)

V (V)

(a)

00 05 10 15 20 25 300000

0005

0010

0015

0020

0025

0030


P (W

)

V (V)

(b)




[Ω] 119877119901

[Ω] 119862 [nF]






0 10 20 30 40 500

5

10

15

20


Z998400 (Ω)

minusZ

998400998400(Ω

)



2 4 6 8 10 12 14 16 18 200Z

998400 (Ω)

0

2

4

6

8

10

minusZ

998400998400(Ω

)



4 Conclusions







Competing Interests


Acknowledgments


References










2
























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


0 10 20 30 40 500

5

10

15

20


Z998400 (Ω)

minusZ

998400998400(Ω

)



2 4 6 8 10 12 14 16 18 200Z

998400 (Ω)

0

2

4

6

8

10

minusZ

998400998400(Ω

)



4 Conclusions







Competing Interests


Acknowledgments


References










2
























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of





2
























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of










Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

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