IEC TS 60904-13:2018

Photovoltaic devices - Part 13: Electroluminescence of photovoltaic modules

IEC TS 60904-13:2018(E) specifies methods to:
capture electroluminescence images of photovoltaic modules,
process images to obtain metrics about the images taken in quantitative terms, and
provide guidance to qualitatively interpret the images for features in the image that are observed.  This document is applicable to PV modules measured with a power supply that places the cells in the modules in forward bias.

General Information

• Status: Published
• Publication Date: 28-Aug-2018
• ICS: 01 - GENERALITIES. TERMINOLOGY. STANDARDIZATION. DOCUMENTATION
• ICS: 11.040.50 - Radiographic equipment
• ICS: 11.040.60 - Therapy equipment
• ICS: 27.160 - Solar energy engineering
• Technical Committee: TC 82 - Solar photovoltaic energy systems
• Drafting Committee: WG 2 - TC 82/WG 2
• Current Stage: PPUB - Publication issued
• Start Date: 21-Sep-2018
• Completion Date: 29-Aug-2018

Standards Content (Sample)

IEC TS 60904-13 ®
Edition 1.0 2018-08
TECHNICAL
SPECIFICATION
colour
inside
Photovoltaic devices –
Part 13: Electroluminescence of photovoltaic modules
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IEC TS 60904-13 ®
Edition 1.0 2018-08
TECHNICAL
SPECIFICATION
colour
inside
Photovoltaic devices –
Part 13: Electroluminescence of photovoltaic modules

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 27.160 ISBN 978-2-8322-5991-7

– 2 – IEC TS 60904-13:2018 © IEC 2018
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Imaging . 7
4.1 Apparatus . 7
4.1.1 Electroluminescence imaging camera . 7
4.1.2 Dark room imaging studio or environment . 9
4.1.3 Power supply . 10
4.1.4 Computer interface with camera and power supply for image capture . 11
4.1.5 Image processing and displaying software . 11
4.1.6 Safety and handling . 12
4.2 Procedure . 12
4.2.1 Camera settings and positioning . 12
4.2.2 Camera settings . 13
4.2.3 Sharpness determination and classification . 14
4.2.4 Imaging . 16
4.2.5 Image correction . 17
4.3 Image signal-to-noise ratio . 18
4.3.1 General . 18
4.3.2 Imaging procedure . 18
4.3.3 Analysis . 18
4.3.4 SNR criteria . 19
5 Evaluation of EL images . 20
5.1 Principles of electroluminescence . 20
5.2 Image interpretation . 21
5.2.1 Series resistance . 21
5.2.2 Minority carrier lifetime and diffusion length . 21
5.2.3 Shunt resistance . 21
5.2.4 Assignment of root cause . 21
5.3 Histogram-based analysis of the electroluminescence signal . 21
5.3.1 General . 21
5.3.2 Image information . 22
5.3.3 Bias current effects . 22
5.3.4 Analysis of intensity distributions . 22
5.3.5 Variance . 22
5.3.6 Kurtosis . 22
5.3.7 Skewness . 22
5.3.8 Pixel (or area)-weighted electroluminescence relative to an ideal module . 22
6 Reporting. 22
Annex A (normative) Procedures for image correction. 24
A.1 Dark current and stray light removal. 24
A.2 Vignetting . 24
A.2.1 Vignetting correction . 24
A.2.2 Vignetting as a function of angle from the optical axis . 24
A.2.3 Correction for vignetting . 24

Annex B (informative) Focus . 26
B.1 General . 26
B.2 Application of the Tenengrad function and Sobel operator . 26
Annex C (normative) Quantifying solar cell cracks in photovoltaic modules . 27
C.1 General . 27
C.2 Cell crack modes . 27
C.3 Basis of cell damage quantification . 28
C.4 Procedure . 30
Annex D (informative) . 32
D.1 Qualitative interpretation of electroluminescence images crystalline Si PV
modules . 32
D.2 Qualitative interpretation of electroluminescence images in thin-film PV modules . 36
Bibliography . 39
Figure 1 – Various semiconductor detector materials and their absolute spectral
response [1] . 8
Figure 2 – Electroluminescence emission spectra for (a) Si, (b)

ZnO/CdS/Cu(In,Ga)Se (CIGS) [2], and (c) CdS/CdTe [3] . 8
Figure 3 – Example of frame subtraction given in Figure 3a) to Figure 3c), with images
taken in ideal dark room conditions given in Figure 3d) . 12
Figure 4 – EL image with introduced two edges using aluminum tape . 15
Figure 5 – Edge gradient image 𝑮𝑮𝑮𝑮𝑮𝑮𝑮𝑮𝑮𝑮 from the Figure 4 EL image’s first derivative in
orthogonal direction 𝑮𝑮𝑮𝑮,𝒚𝒚 . 15
Figure 6 – Excerpt of the EL image of Figure 4 and plot of image intensity values
along line L . 15
Figure 7 – Images of regions of multicrystalline silicon solar cells with three SNR
values as labeled . 20
Figure 8 – Emission of light (hν) associated with the electroluminescence process in
solar cells of PV modules . 20
Figure 9 – Scheme for labeling position of cells in a module viewed from the light-
facing side according to coordinates (i,j) in portrait orientation (a) or rotated into
landscape orientation (b), which shall be indicated if applicable . 23
Figure B.1 – EL image of a solar cell (left) and a silicon module (right) . 26
Figure C.1 – Single cell region of a module with 0,1 × I applied showing crack types,
sc
as labeled . 27
Figure C.2 – Example of normalized EL intensity histograms calculated from the EL
images of modules with various levels of cell cracking and resulting power degradation,

indicated by P . 29
max
Figure C.3 – Example of quantifying solar cell cracks in photovoltaic modules: (a) EL
image produced with 0,1· I forward bias current, and (b) image of regions
sc
considered damaged . 31
Table 1 – Detectors and their applicable wavelengths . 7
Table 2 – Sharpness classes, examples of images meeting the criteria of the classes,
and examples of distinguishable features . 16
Table D.1 – Descriptions of observables, features, and known causes, along with
electroluminescence images for crystalline Si modules . 32
Table D.2 – Descriptions of observables, features, and known causes, along with
electroluminescence images for thin-film modules . 36

– 4 – IEC TS 60904-13:2018 © IEC 2018
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
PHOTOVOLTAIC DEVICES –
Part 13: Electroluminescence of photovoltaic modules

FOREWORD
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