spectral analysis of various thin film modules using high precision

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1,55 1,57 1,59 1,61 1,63 1,65 1,67 1,69 1,71 1,73 1,75

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This poster contains results of high-precision indoor and outdoor measurements of different PV module technologies performed at the headquarters of TVRheinland, Cologne, from May 2010 to September 2012. Modules based on CdTe, CI(G)S, a-Si, a-Si/-Si, a-Si/a-Si and c-Si (mono and poly)semiconductors were analyzed nondestructively according to their spectral response with a new test equipment and technology specific differences arepointed out. After the indoor characterization the modules were exposed outdoor for one year, steadily measuring the maximum power point PMPP and the I/V-curves with the corresponding solar spectrum. With this extensive data volume it is possible to describe the spectral conditions at the test-site in Cologneusing the APE-Method. In a next step the influence on the module performance and the energy yield of the different technologies are analyzed. The photocurrent is calculated theoretically by the integral of spectral response data and spectral measurements and compared to temperature and irradiancecorrected real outdoor measurements.

Depending on the position of the sun related to the module and theatmosphere the spectral distribution of solar irradiation can be shifted intoblue or red wavelength areas. Some technologies can benefit while othersmay be disadvantaged depending on their spectral response. In what wayand why these spectral shifts happen in the course of a day and theseason and what influence they have on the energy yield of a certaintechnology are described in the following.

Markus Schweiger, Ulrike Jahn, Dr. Werner Herrmann TV Rheinland Energie und Umwelt GmbH, Am Grauen Stein, 51105 Kln, Germany

Tel.: +49 221 806-2232, Fax: +49 221 806-1350, E-Mail: Markus.Schweiger@de.tuv.com, Ulrike.Jahn@de.tuv.com

RESULTS

This work has been supported by the GermanFederal Ministry for the Environment, NatureConservation and Nuclear Safety (BMU)within contract No. 0325070A.

CONCLUSIONS

SPECTRAL ANALYSIS OF VARIOUS THIN FILM MODULES USING HIGH PRECISION SPECTRAL RESPONSE DATA AND

SOLAR SPECTRAL IRRADIANCE DATA

Figure 1 Non-destructive measurement of the spectral response (SR) of a triple-junction module with a new test equipmentat TV Rheinland, Cologne

Spectral response of different PV module technologies

Characterizing solar spectrum with the average photon energy (APE)

Influence of spectrum on performance and yield

In 2013 TV Rheinland will start extensive energy yieldmeasurements at five different locations all over the world.Participation requests can be sent to the authors.

Significant differences in SR-Signal of CI(G)S and a-Si specimens

APE-Method appropriate method to describe solar spectrum

Automatable procedure to correct T, G and MM developed

Sinus-shaped performance fluctuation of a-Si because of spectrum

Spectrum not significant for energy yield of c-Si and most CI(G)S

Annual gains of +3% (some a-Si) and +1% (CdTe) calculated in 11/12

INTRODUCTION

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Norm AM1.5 a-Si CIS CdTe CIGS poly c-Si mono c-Si CIGS

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Top-Layer Bottom-Layer

The new SR-equipment issuitable for all commonmodule designs (Fig. 1)

Step-size 1nm for single-,double- and triple-junctionspecimens

Large spread of the spectralresponse for different moduletechnologies (Fig. 2)

Also large technology internalspreads for a-Si and CI(G)S(Fig. 3 + 4)

The spectral mismatch (MM)and the theoretical photocurrent can be calculated toimprove PMax determinationand outdoor monitoring

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Spectrum < 1.65 eV red

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Winter red spectrum (Fig. 5 + 8)

Calculated Measured

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AM1,5g Summer (21.08.2010) Fall (10.10.2010) Winter (29.01.2011) Spring (19.04.2011)

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Figure 5 Solar spectral irradiance drift for cloudless days insummer (blue), spring (green), fall (yellow) and winter (red)for modules mounted facing south and 35 tilted in Cologne

Figure 9 Correcting spectral effects of an a-Si specimenFigure 8 Seasonal variations of APE-values and averageAPE-value per month

Figure 6 Dependency of ISC on spectral changes,calculated with formula, normalized to ISC,STC at 1.65 eV

Figure 7 Dependency of ISC on spectral changes, measured(T, G corrected), normalized to ISC,STC at 1.65 eV

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Figure 2 Rel. spectral response signal of different PV-module technologies in comparison with IEC 60904-3spectrum

Figure 3 + 4 Rel. spectral response signal of differentCI(G)S and a-Si modules, illustrating significant differenceswithin the same thin-film technology

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Results of calculated and measured ISC (APE) almost similar (Fig. 6+7)

Dependency of a-Si/-Si on spectrum screened out as combination ofa-Si behavior for APE < 1.65eV and -Si behavior for APE > 1.65eVsignificant losses because of current mismatch expected

Almost no dependency of c-Si and most CI(G)S on spectrum

Strong dependency of a-Si and small dependency of CdTe on spectrum

The seasonal average spectrum was calculated to 1.68 eV in 2011/12. Small gains of max. +3% (some a-Si) and +1% (CdTe) possible.