IEC TS 62446-3:2017

IEC TS 62446-3 ®
Edition 1.0 2017-06
TECHNICAL
SPECIFICATION
colour
inside
Photovoltaic (PV) systems – Requirements for testing, documentation and
maintenance –
Part 3: Photovoltaic modules and plants – Outdoor infrared thermography

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IEC TS 62446-3 ®
Edition 1.0 2017-06
TECHNICAL
SPECIFICATION
colour
inside
Photovoltaic (PV) systems – Requirements for testing, documentation and

maintenance –
Part 3: Photovoltaic modules and plants – Outdoor infrared thermography

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 27.160 ISBN 978-2-8322-4290-2

– 2 – IEC TS 62446-3:2017 © IEC 2017
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 7
4 Requirements of inspection equipment . 9
4.1 General . 9
4.2 Minimum requirements for IR-cameras used for inspecting PV plants . 9
4.3 Requirements for photo cameras for documentation of the findings . 10
4.4 Requirements for equipment to record the ambient conditions . 10
5 Inspection procedure . 11
5.1 General . 11
5.2 Visual inspection . 12
5.3 Environmental conditions . 12
5.4 Imaging procedure . 13
5.4.1 General . 13
5.4.2 Using fast carriers for IR-camera, e.g. aerial drones . 13
5.4.3 Emissivity . 14
6 Software for evaluation . 15
7 Evaluation . 15
7.1 General . 15
7.2 Evaluation of IR images . 16
7.3 Thermal abnormalities . 17
7.3.1 General . 17
7.3.2 Classes of abnormalities (CoA) . 17
7.3.3 Abnormalities of PV modules . 17
7.3.4 Abnormalities of other BOS components . 17
7.4 Projection of temperature differences to nominal irradiance . 18
7.4.1 General . 18
7.4.2 Modules . 20
7.4.3 Other BOS components . 21
8 Inspection report . 21
Annex A (normative) Inspection procedure explanations . 24
A.1 Geometric resolution of the camera . 24
A.2 Angle of view . 24
A.3 Matrix for cell identification . 25
Annex B (normative) Qualification of personnel . 27
Annex C (normative) Matrix for thermal abnormalities of PV modules . 28
Annex D (informative) Polygon measurement as a method of evaluation . 32
Annex E (informative) Beaufort scale . 34
Bibliography . 36

Figure 1 – Impact of camera moving speed . 14
Figure 2 – Dependence of the emissivity of glass on the angle of view [10]. 15
Figure 3 – Examples of influence of wind (left) and cloud movement (right) on
observed temperature pattern . 16

Figure 4 – Example infrared thermograms of a PV string combiner box with cables,
contacts, fuses and switches before (left) and after (right) maintenance on a faulty
contact . 18
Figure 5 – Graphic representation of the correction factor for temperature differences
to nominal irradiance/load conditions as a function of the relative irradiance/load . 19
Figure 6 – Example of image reporting . 23
Figure A.1 – Geometric resolution of the IR camera . 24
Figure A.2 – Angle of view . 25
Figure A.3 – View for the designation of cell position, viewed from the front of a 60-
cell module, with the junction box at the top (rear side) . 26
Figure D.1 – Arithmetic mean value by polygon measurement . 32
Figure D.2 – Arithmetic mean and spot value by polygon measurement . 33

Table 1 – Minimum requirements for IR-cameras . 9
Table 2 – Requirements for equipment to record the ambient conditions . 11
Table 3 – Required inspection conditions . 12
Table 4 – Allocation in classes of abnormalities . 17
Table 5 – Example correction factors for temperature differences to nominal load
conditions based on formula above and Figure 5 . 20
Table E.1 – Beaufort scale taken form World Meteorolgical Organization
(www.wmo.int) and Royal Meteorological Society (www.rmets.org) . 34

– 4 – IEC TS 62446-3:2017 © IEC 2017
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
PHOTOVOLTAIC (PV) SYSTEMS –
REQUIREMENTS FOR TESTING,
DOCUMENTATION AND MAINTENANCE –

Part 3: Photovoltaic modules and plants –
Outdoor infrared thermography
FOREWORD
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Technical specifications are subject to review within three years of publication to decide
whether they can be transformed into International Standards.
IEC TS 62446-3, which is a technical specification, has been prepared by IEC technical
committee 82: Solar photovoltaic energy systems.

The text of this technical specification is based on the following documents:
Enquiry draft Report on voting
82/1188/DTS 82/1242A/RVDTS
Full information on the voting for the approval of this technical specification can be found in
the report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 62446 series, published under the general title Photovoltaic (PV)
systems – Requirements for testing, documentation and maintenance, can be found on the
IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC website under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• transformed into an International standard,
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

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– 6 – IEC TS 62446-3:2017 © IEC 2017
PHOTOVOLTAIC (PV) SYSTEMS –
REQUIREMENTS FOR TESTING,
DOCUMENTATION AND MAINTENANCE –

Part 3: Photovoltaic modules and plants –
Outdoor infrared thermography
1 Scope
This part of IEC 62446 defines outdoor thermographic (infrared) inspection of PV modules
and plants in operation. The inspection can include cables, contacts, fuses, switches,
inverters, and batteries. This inspection supports the preventive maintenance for fire
protection, the availability of the system for power production, and the inspection of the
quality of the PV modules. Included in this document are the requirements for the
measurement equipment, ambient conditions, inspection procedure, inspection report,
personnel qualification and a matrix for thermal abnormalities as a guideline for the
inspection.
This document defines outdoor thermography on photovoltaic (PV) modules and Balance-of-
system (BOS) components of PV power plants in operation, using passive techniques
(standard system operating conditions under natural sunlight, without any external power or
irradiation sources). IEC 60904-12-1 covers general methods for laboratory or production-line
PV module thermographic imaging but not the specific details that are most relevant to
outdoor imaging of operational power plants including BOS components.
Two different levels of inspections are currently used:
a) A simplified thermographic inspection. This is a limited inspection to verify that the PV
modules and BOS components are functioning, with reduced requirements for the
qualification of personnel. For example, during a basic commissioning of a PV plant.
Authoritative conclusions regarding module quality are not possible with this inspection,
and examples of abnormalities are provided to aid the inspector.
b) A detailed thermographic inspection and analysis. This may include thermal signatures
which differ from the examples provided, and therefore requires a deeper understanding of
the thermal abnormalities. For example, it may be used for periodic inspections according
to the IEC 62446 series and for trouble-shooting the cause of underperforming systems.
Absolute temperature measurements may be made. An authorized expert in PV plants,
together with thermography experts can perform the inspection.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements of this document. For dated references, only the edition
cited applies. For undated references, the latest edition of the referenced document (including
any amendments) applies.
IEC 60050-131, International Electrotechnical Vocabulary – Part 131: Circuit theory
IEC 60216-2, Electrical insulating materials – Thermal endurance properties – Part 2:
Determination of thermal endurance properties of electrical insulating materials – Choice of
test criteria
IEC 60216-5, Electrical insulating materials – Thermal endurance properties – Part 5:
Determination of relative thermal endurance index (RTE) of an insulating material

IEC 60269-1, Low-voltage fuses – Part 1: General requirements
IEC 61095, Electromechanical contactors for household and similar purposes
IEC 61215-1, Terrestrial photovoltaic (PV) modules – Design qualification and type approval –
Part 1: Test requirements
IEC 61439-1, Low-voltage switchgear and controlgear assemblies – Part 1: General rules
IEC 61724-1, Photovoltaic system performance – Part 1: Monitoring
IEC 61730-1, Photovoltaic (PV) module safety qualification –Part 1: Requirements for
construction
IEC 61730-2, Photovoltaic (PV) module safety qualification –Part 1: Requirements for testing
IEC TS 61836, Solar photovoltaic energy systems – Terms, definitions and symbols
IEC 62109-1, Safety of power converters for use in photovoltaic power systems – Part 1:
General requirements
IEC 62446-1, Photovoltaic (PV) systems – Requirements for testing, documentation and
maintenance – Part 1: Grid connected systems – Documentation, commissioning tests and
inspection
IEC 62446-2:–, Photovoltaic (PV) systems – Requirements for testing, documentation and
maintenance – Part 2: Grid connected photovoltaic (PV) systems – Maintenance of PV
systems
IEC 62930:–, Electric cables for photovoltaic systems with a voltage rating of 1,5 kV d.c.
ISO 9488, Solar energy – Vocabulary
ISO 9712, Non-destructive testing — Qualification and certification of NDT Personnel
VATh- Directive, Electrical Infrared Inspections – Low Voltage. Planning, execution and
documentation of infrared surveys on electrical systems and components ≤1kV
(http://www.vath.de/docs/richtlinien/VATh-Richtlinie_Elektro_NS+PV_engl_web.pdf)
EN 16714-3, Non-destructive testing – Thermographic testing of electric installations
EN 50110-1, Operation of electrical installations – Part 1: General requirements
DGUV BGV/GUV-V A3 E, Accident prevention regulations, Electrical installations and
equipment
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC TS 61836,
ISO 9488, IEC 60050-131 and the following apply.
___________
To be published.
– 8 – IEC TS 62446-3:2017 © IEC 2017
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
abnormal thermal behavior
thermal signature of an element that cannot be explained by its operating condition or its
technical design, e.g. position of load resistors
[SOURCE:IEC 60050-903:2013, Amendment 1:2014, 903-01-22; modified: adapted to thermal
behavior]
3.2
reflected temperature
T
refl
mean apparent temperature of the ambient that is reflected by the object towards the IR-
camera
Note 1 to entry: Measured in Celsius (°C).
Note 2 to entry: Some manufactures of IR cameras use the term: ambient temperature.
3.3
atmospheric air temperature
defined in Celsius (°C) for the geographic installation location as measured and documented
by meteorological services for this geographic location
3.4
Beaufort (scale)
Bft
quantifies wind speed by phenomenological criteria, e.g. movement of branches and trees
SEE: Annex E.
3.5
cloud coverage
for the inspection two types of clouds are to differ: Cumulus and Cirrus. The cloud coverage
should be given in okta (part of eight of cloud coverage)
SEE: ISO 15469:2004[18] .
3.6
emissivity of the object
ε
ratio of the thermal radiation that is emitted by the surface of an object compared to a black
body radiator both at the same temperature
3.7
Instantaneous Field of View
IFOV
field of view of one pixel of an IR-camera-lens combination
Note 1 to entry: Measured in milliradian (mrad).
___________
Numbers in square brackets refer to the Bibliography.

3.8
Noise Equivalent Temperature Difference
NETD
smallest temperature difference detectable by an IR-camera
Note 1 to entry: Measured in millikelvin (mK).
3.9
thermal steady state conditions
usable measurement conditions, which show stable temperatures and temperature differences
4 Requirements of inspection equipment
4.1 General
This clause states the minimum requirements for equipment used for thermographic (infrared)
inspection within the scope of this document. It includes requirements for the infrared (IR)
camera, the photo camera and equipment to record ambient conditions.
All equipment shall be date and time synchronized prior to use, to easily match images to
system conditions, for example the in plane irradiation, and DC-load of the plant.
4.2 Minimum requirements for IR-cameras used for inspecting PV plants
The specifications of the infrared camera shall fulfil the minimum requirements according to
Table 1.
Table 1 – Minimum requirements for IR-cameras
Features Minimum requirements
a Spectral response 2 µm to 5 µm (mid wavelength) or 8 µm to 14 µm (long
wavelength)
b Temperature-sensitivity and calibration –20 °C to +120 °C
range (object temperature range)
c Operating ambient air temperature –10 °C to +40 °C
range
d Thermal sensitivity NETD ≤ 0,1 K at 30 °C
e Geometric resolution 1) PV module: max. 3 cm of the module edge per pixel
2) Electrical connections: The geometrical resolution (Real
measurement spot ) has to match the smallest object area to
be verified.
Futher details can be found in Clauses A.1 and A.2.
f Absolute error of measurement
< ± 2 K
g Adjustable parameters Emissivity (ε), reflected temperature (T )
refl
h Adjustable functions Focus, temperature level and span
i Measurement functions Measuring spot, measuring area with average and maximum
temperature
– 10 – IEC TS 62446-3:2017 © IEC 2017
Features Minimum requirements
j Calibration The measuring system (camera, lens, aperture and filter): The
thermographic camera shall be traceably calibrated at least every
two years. The calibration has to be documented. If the camera is
not compliant (absolute temperature and/or temperature
differences), it may be readjusted by the manufacturer.
k Documentation Storing of the infrared picture with all radiometric information to be
able to determine absolute temperatures. Non-radiometric pictures
can only provide pattern and eventually temperature differences.
1 Cameras operating in wavelength range of 2 µm to 5 µm shall only be used for thermography of electrical
BOS components, e.g. fuses. Due to the transparency of glass in the range of 3 µm the use of that range on
PV modules can lead to measurement errors.
2 3 cm length of edge per pixel equals 5 x 5 pixel on a 6“ PV cell.
3 The real measuring spot mostly is defined as 3 x 3 pixel, for high-quality optics.

Use of an IR camera with resolution ≥ 320 x 240 pixels and a separate photo camera are
recommended, with monitor and remote control or a swivelling display.
4.3 Requirements for photo cameras for documentation of the findings
Visual photos documenting the state of the module/plant are recommended, however visual
photos of any thermal abnormality are required. One photo of every safety relevant
abnormality (see Table 4) shall be taken.
The resolution of the visual photo shall be significantly higher than the IR image and shall
have a similar field of view to sufficiently capture all details of the object (e.g., busbars,
ribbons of a solar cell, broken front glass, fuse and fuse holder). It shall be ensured that IR
and visual photo capture the same area of interest while fulfilling the resolution requirement.
A separate photo camera and IR camera are recommended, in order to ensure sufficient
resolution of visual photo (typically at least 30 times higher).
NOTE In many cases, the basic photo camera which is integrated into the infrared camera is not able to provide
the requested resolution. For an IR camera of 640 x 480 pixel a separate photo camera with at least 9 Mpix is
suitable.
4.4 Requirements for equipment to record the ambient conditions
To detect thermographic abnormalities correctly, certain ambient conditions have to be met.
Equipment to measure these conditions should be compliant to the minimum requirements in
Table 2.
Table 2 – Requirements for equipment to record
the ambient conditions
Parameter Equipment Accuracy
a Irradiance Irradiance sensor (crystalline
Calibration: ± 5 %
silicon cell or pyranometer)
b Ambient (air) temperature Temperature sensor (shielded
Calibration: ±2 K
from direct light and wind)
c Wind speed Bft scale (visual) or anemometer Estimation
d Cloud coverage Photo camera Estimation
e Degree of soiling Photo camera Estimation
Estimation can be done using
procedure according to
IEC 61724-1
f Module or string current DC (clamp) ampere meter (or Calibration: ± 2 %
inverter reading
Note that the inverter reading may not give accurate results or be calibrated. Though it may be useful for
some BOS components, it may also not have resolution for PV string-level current measurement.

5 Inspection procedure
5.1 General
An inspection of the PV plant should be done during the commissioning and operation of the
power plant, in accordance with applicable health and safety regulations. The recommended
interval for periodic thermography inspections is four years but the applied intervals for a
specific installation shall be agreed upon with the owner / operator, or they might be defined
by national electric codes and safety regulations for electrical installations.
The owner, operator or an authorized person shall give the inspector(s) an introduction into
the safety specific regulations of the PV plant to be inspected, including details of the plant
and electrical layout. A second person should be present during inspection, and may be
required by local safety regulations. At least one of the persons performing the inspection
shall have technical knowledge of the specific system, and of PV plants in general.
Inspections shall be done following applicable safety regulations, for example in accordance
to EN 50110-1 or DGUV BGV/GUV-V A3 E.
The detailed inspection scope shall be defined prior to the inspection and agreed in writing
between the involved parties.
The plant shall be under operating conditions. The part of the system under evaluation shall
be in thermal steady state condition and free of partial shading (if possible). Soiling should be
low (less than 10 % operating current Impp loss) and homogeneous, without causing partial
shading (e.g., by bird droppings, leaves, vegetation) to avoid thermal effects. If strong soiling
or partial shading due to, for example bird droppings, is observed on the PV modules, it is
recommended to clean the entire system prior to inspection. Note that the performance of the
system may change as a result of the cleaning. Ensure modules are at thermal steady state
after cleaning prior to performing infrared imaging inspection.
For quantification of soiling, it is recommended to conduct measurements according to
IEC 61724-1. This might be helpful to compare measurements from periodic inspections.
Collecting IR images can be done in different ways, e.g., using tripods, by hand or drones.
Care shall be taken that the method selected still meets the resolution requirements, and to
ensure understanding of the method used (e.g., reflections). Any known deviations or
limitations shall be noted in the inspection report.

– 12 – IEC TS 62446-3:2017 © IEC 2017
National regulations and laws may apply to using IR cameras and other equipment like
drones.
The inspection results verify the status at the time of inspection. Issues of intermittent or
changing nature may or may not be captured at the time of inspection.
5.2 Visual inspection
Prior to the thermographic inspection of the PV plant, it is recommend to do a visual
inspection to determine whether the requirements of 5.1 are met. Observations such as bird
droppings, strong soiling, burn spots on modules or other Balance of System (BOS)
components shall be documented by photos and location prior to the thermographic
inspection. If possible, those findings should be resolved (e.g. by cleaning) prior to the
thermographic inspection especially during comissioning. Photos post-cleaning (pre-imaging)
should be documented. However, it may be desireable to conduct the thermography
inspection without cleaning, e.g. for a root-cause analysis for a poor performing PV power
plant.
Upon observation of thermal anomalies, it is desireable to visually inspect the component and
visually observe any abnormal conditions in the area. The PV module visual inspection
procedures in IEC 61215-1 and IEC 61730-2 may be useful references. A visual photo shall
be captured for every thermal abnormality type.
5.3 Environmental conditions
The inspection should be performed under the conditions specified in Table 3.
Table 3 – Required inspection conditions
Parameter Limits
• Minimum 600 W/m in the plane of the PV module for PV module inspection
a Irradiance
• Measured operating current shall be a minimum of 30 % of rated system current
within the inspected current path (typically > 30 % of PV module name plate Isc at
STC (equals typically > 300W/m in the plane of the PV modules) for inspection of
other electrical components (e.g. cables, connectors, connections). Recommended
for inspection are > 600 W/m .
NOTE Example for single string with no parallel connection: 30 % of STC Isc current.
Isc to be taken from PV module name plate and not to be measured on PV plants.
b Wind speed Maximum 4 Bft or 28 km/h (see Annex E)
c Cloud coverage Maximum 2 okta of sky covered by cumulus clouds
d Soiling No or low. Cleaning recommend, e.g. if bird droppings exist.

NOTE For cloud coverage, find further information in ISO 15469:2004.
After change in operating conditions, for example load or irradiance (due to e.g. cirrus clouds)
of >10 % per minute, a waiting time of 15 min is recommended to regain the steady state
measurement conditions.
The cloud coverage should not consist of more than 2 okta of cumulus clouds, because of
misleading reflections on the modules.

5.4 Imaging procedure
5.4.1 General
The distance between the inspected object and the IR-camera shall fulfil the geometrical
resolution, specified in 4.2, while required safety distances according to safety regulations are
met. (See Clauses A.1 and A.2)
The IR-camera image shall be taken as perpendicular to the PV module surface as possible.
At the same time, self-reflection of measuring personnel and IR-camera apparatus, and
reflection of heated objects like sun, near-by buildings and trees shall be avoided. In cases
where the image cannot be taken perpendicular to the PV module surface, e.g. a small
installation with limited ability to raise the camera, the angle between the camera and the PV
module plane should still be greater than 30° (see Clause A.2).
Adjust the camera emissivity based on surface conditions of the object under investigation
(e.g. soiling of module front glass or dust on shiny parts of e.g. fuse holders).
The DC-load of the plant shall be monitored and recorded to avoid measurements under
undefined load conditions due to grid events (e.g. strings are open circuit or short circuit).
Together with the thermographic image, a photo of the same area shall be taken for each type
of thermal finding. The exact position of all the findings in the inspected system shall be
documented, as well as the operating conditions including local DC load and environmental
conditions.
Two different levels of quality of examinations are currently used:
a) Simplified inspection:
The simplified thermographic inspection with reduced requirements for the qualification of
personnel (see Annex B). This is for a limited inspection to test the basic functioning of the
PV modules. For example, during the commissioning of systems. Authoritative conclusions
regarding module quality are not possible. No absolute temperatures are determined,
therefore thermal patterns are used to evaluate the abnormalities. Refer to the examples
in Annex C.
b) Detailed inspection:
The detailed thermographic inspection and analysis, which may include thermal patterns
which differ from the examples in the Annexes. This may be useful for trouble-shooting
and for periodic inspections according to IEC 62446-1 and future IEC 62446-2. Absolute
temperature measurements are determined during this detailed inspection. An authorized
expert for PV plants, together with thermographic experts, shall have advanced
qualifications as per Annex B.
5.4.2 Using fast carriers for IR-camera, e.g. aerial drones
Aerial drones are increasingly being used as part of the tool kit for fault detection and
localization in PV plants. It should be noted that while drones help scale, automate and
accelerate detection of faulty areas within a large power plant, such techniques can lack the
resolution to detect fine component artifacts or identify specific failure modes. Such an
inspection by drones is classified as simplified inspection procedure of the whole PV array in
order to find PV sub arrays/strings/modules with obvious noticeable problems.
In the case where imaging is performed using a fast carrier, the moving speed of the camera
should always be chosen with respect to the time constant of the camera’s IR-detector to
avoid smearing effects (compare the following pictures in Figure 1). Smearing influences
visual pattern and absolute and relative temperatures. Relevant smearing effects on common
IR camera bolometer detectors, when used for PV-modules and systems, may already appear
at a moving speed of 3 m/s.
– 14 – IEC TS 62446-3:2017 © IEC 2017
For large-area imaging such as through use of drones, consider irradiance and system
stability, especially if images will be stitched together and not individually mapped to system
performance (instantaneous DC string current).
Ensure the geometric resolution requirements are met, especially if the distance between the
IR camera and PV module is large. If the requirements are not met, it is a deviation to the
procedure.
NOTE A typical approach is to do this simplified inspection at the whole PV array to find PV modules or strings
with noticeable problems. Afterwards a detailed inspection is done at these PV modules. This partial or detailed
inspection can be agreed in a contract, along with the thresholds for deciding what sort of issue in the simplified
procedure would warrant the detailed approach described in this document.

IEC IEC
a) Picture captured with slow camera moving b) Picture captured at high camera moving speed
speed without noticeable smearing with unacceptable smearing
Figure 1 – Impact of camera moving speed
5.4.3 Emissivity
Estimating the emissivity of the examined surface is the responsibility of the qualified
thermographer, particularly in the case of detailed inspection. The emissivity of a surface
depends on many factors. Many of them are less relevant for the given task (such as the
exact spectral range of the (LW)-IR-camera, surface and ambient temperature, surface
geometry, etc.).
For the simplified inspection, the most important dependencies and some common values are
given for common surface and ambient temperatures, surfaces without holes and (LW)-IR-
cameras (note that less common MW-IR-cameras differ significantly):
For the practice of thermography on PV modules and BOS components, it is important to
understand the following three dependencies: first material, second surface (includes soiling)
and third angle of view. Dependencies and values are given by examples.
a) Materials such as unoxidised metal (parts made out of stainless steel), polished
aluminium parts and some BOS components have very low emissivities around ε = 0,1 to
ε = 0,3, therefore an accurate temperature determination is not possible.
b) Most insulation synthetics and ceramics have emissivity around ε = 0,9.
c) Rough oxidated aluminium of module frames and mounting clamps and some BOS
components typically show values above unoxidised metal, but below glass, typically
about ε = 0,4 to ε = 0,7.
d) Materials like glass have higher emissivities around ε = 0,85. Glass with a rough surface,
such as textured glass or glass with high degree of soiling may have an emissivity up to
ε = 0,9.
e) On non-ferrous glass the emissivity decreases with the angle of view, so at around 45° the
emissivity will be around ε = 0,8 and at 30° it can be around ε = 0,75 or lower.
(See Figure 2 and also Clause A.2.)
Angle of view on module
at T = –50 °C
refl
at T = 250 °C
refl
IEC
Figure 2 – Dependence of the emissivity of
glass on the angle of view [10]
6 Software for evaluation
Using software, it is possible to transfer the radiation density values measured by the IR-
camera into absolute temperature values. The calculations may be done directly using the IR-
camera software, which updates the temperature labels on the display screen and in the
saved file. Care shall be taken when interpreting any temperature values, as they may not be
absolute temperatures if the correct parameters were not set. To obtain temperature values, it
is necessary to set specific parameters, in particular:
a) emissivity, ε,
b) reflected temperature, T
refl,
c) temperature level and span,
d) different measuring tools (e.g. spot measurement, polygons) under specification of
minimum, maximum and arithmetic mean value for the temperature data.
7 Evaluation
7.1 General
The following measurements and observations are important for evaluation or validation:
a) maximum temperatures,
b) temperature differences,
c) temperature profiles,
d) cloud, cloud movement, cloudiness (see example in Figure 3 right),
Emissivity
– 16 – IEC TS 62446-3:2017 © IEC 2017
e) wind speed and direction (see example in Figure 3 left),
f) previous mechanical stress from installation history logfile,
g) soiling,
h) visual inspection,
i) irradiance and/or DC load of system.
Results and recommendations of previous inspections should also be taken into
consideration.
During a simplified thermographic inspection of a PV plant no exact temperatures are
determined. Here the main focus is only on evaluating certain thermographic patterns as
shown in Annex C. To evaluate absolute temperature and temperature differences, a detailed
inspection shall be done with appropriate qualified personel (see Annex B). General guidance
can be found in EN 16714-3 and VATh-Directive.

IEC IEC
Figure 3 – Examples of influence of wind (left) and cloud movement (right)
on observed temperature pattern
7.2 Evaluation of IR images
This subclause introduces several techniques to evaluate IR images. Other procedures exist
and can be applied also.
a) Patterns (Simplified inspection, see Annex C)
The abnormaity is classified and evaluated by a known thermal pattern. Measurement of
absolute and relative temperature values are not neccesary but can supplement thermal
patterns as plausibility check.
b) Temperatures of point abnormalities (Detailed inspection, see Annex D)
Use an algorithm to determine highest temperature in the image. This can be done using
different types of tools such as “freehand spot” or “maximum spot within an area” in the
camera and image processing software.
c) Extended areas (Detailed inspection, see Annex D)
Use different types of tools such as “rectangle”, “circle” or “polygon areas” to calculate the
mean temperatures of the areas, using the camera and image processing software.
d) Relative temperatures (Detailed inspection, see Annex D)
Can be calculated between point abnormalities and/or the mean values of extended areas,
with consideration of the uncertainty of measurement.
e) Absolute temperatures (Detailed inspection, see Annex D)
...