IEC TS 60904-1-2:2019

IEC TS 60904-1-2 ®
Edition 1.0 2019-01
TECHNICAL
SPECIFICATION
colour
inside
Photovoltaic devices –
Part 1-2: Measurement of current-voltage characteristics of bifacial photovoltaic
(PV) devices
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IEC TS 60904-1-2 ®
Edition 1.0 2019-01
TECHNICAL
SPECIFICATION
colour
inside
Photovoltaic devices –
Part 1-2: Measurement of current-voltage characteristics of bifacial photovoltaic

(PV) devices
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 27.160 ISBN 978-2-8322-6409-6

– 2 – IEC TS 60904-1-2:2019 © IEC 2019
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 7
3.1 Bifacial PV device . 7
3.2 Bifaciality . 7
3.3 Rear irradiance driven power gain yield . 7
4 General considerations . 7
5 Apparatus . 8
5.1 General . 8
5.2 Solar simulator with adjustable irradiance levels for single-side illumination . 8
5.3 Solar simulator with adjustable irradiance levels for double-side illumination . 8
5.4 Natural sunlight . 8
5.5 Non-irradiated background and background compensation . 8
6 Additional I-V characterisations for bifacial devices . 9
6.1 General . 9
6.2 Determination of bifacialities . 10
6.3 Determination of the rear irradiance driven power gain yield . 11
6.3.1 General . 11
6.3.2 Outdoor rear irradiance driven power gain yield measurement . 12
6.3.3 Indoor rear irradiance driven power gain yield measurement with single-
side illumination . 13
6.3.4 Indoor rear irradiance driven power gain yield measurement with
double-side illumination . 14
7 I-V characterisation of bifacial PV devices in practice . 15
7.1 General . 15
7.2 I-V measurement of reference bifacial PV devices . 15
7.3 I-V measurement of bifacial PV devices using a reference bifacial device . 16
8 Report . 17
Figure 1 – Scheme of a bifacial PV module and the required non-irradiated
background and aperture . 9
Figure 2 – Front- and rear-side characterization for bifaciality . 10
Figure 3 – Outdoor measurement . 12
Figure 4 – Examples of P as a function of irradiance level on the rear side G (for
max r
outdoor or double-side illumination) or its 1-side equivalent irradiance G for a device
f
of bifaciality ϕ = 80 % . 14
Figure 5 – Transmittances of the device (T ) and its encapsulant (T ) . 15
DUT ENC
Figure 6 – Example of Pmax,BiFi100 and Pmax,BiFi200 derived from the measurement of Pmax
at STC conditions, P and the BiFi coefficient of the reference used in formulae
max,STC
(8) and (9) . 17

Table 1 – Maximum peak power, P , measured at different rear irradiances, G ,
max r
(double-side with Gf = 1 000) or alternatively equivalent front irradiances, GE, and the
rear irradiance driven power gain yield, BiFi, derived from the slope of the linear fit on
Pmax(G ). Also calculated values Pmax,BiFi100 and Pmax,BiFi200. . 14
r
Table 2 – Example of P and P derived from the measurement at STC
max,BiFi100 max,BiFi200
conditions (Gr = 0 and Gf = 1 000) and the rear irradiance driven power gain obtained
from the bifacial reference device, BiFi,ref. . 17

– 4 – IEC TS 60904-1-2:2019 © IEC 2019
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
PHOTOVOLTAIC DEVICES –
Part 1-2: Measurement of current-voltage characteristics of
bifacial photovoltaic (PV) devices

FOREWORD
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
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The main task of IEC technical committees is to prepare International Standards. In
exceptional circumstances, a technical committee may propose the publication of a Technical
Specification when
• the required support cannot be obtained for the publication of an International Standard,
despite repeated efforts, or
• the subject is still under technical development or where, for any other reason, there is the
future but no immediate possibility of an agreement on an International Standard.
Technical Specification are subject to review within three years of publication to decide
whether they can be transformed into International Standards.
IEC TS 60904-1-2, 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:
Draft TS Report on voting
82/1403/DTS 82/1508/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 60904 series, published under the general title Photovoltaic
devices, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
– 6 – IEC TS 60904-1-2:2019 © IEC 2019
PHOTOVOLTAIC DEVICES –
Part 1-2: Measurement of current-voltage characteristics of
bifacial photovoltaic (PV) devices

1 Scope
This part of IEC 60904 describes procedures for the measurement of the current-voltage (I-V)
characteristics of bifacial photovoltaic devices in natural or simulated sunlight. It is applicable
to single PV cells, sub-assemblies of such cells or entire PV modules.
The requirements for measurement of I-V characteristics of standard (monofacial) PV devices
are covered by IEC 60904-1, whereas this document describes the additional requirements for
the measurement of I-V characteristics of bifacial PV devices.
This document may be applicable to PV devices designed for use under concentrated
irradiation if they are measured without the optics for concentration, and irradiated using
direct normal irradiance and a mismatch correction with respect to a direct normal reference
spectrum is performed.
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 60891, Photovoltaic devices – Procedures for temperature and irradiance corrections to
measured I-V characteristics
IEC 60904-1, Photovoltaic devices – Part 1: Measurement of photovoltaic current-voltage
characteristics
IEC 60904-2, Photovoltaic devices – Part 2: Requirements for reference devices
IEC 60904-3, Photovoltaic devices – Part 3: Measurement principles for terrestrial
photovoltaic (PV) solar devices with reference spectral irradiance data
IEC 60904-4, Photovoltaic devices – Part 4: Reference solar devices – Procedures for
establishing calibration traceability
IEC 60904-5, Photovoltaic devices – Part 5: Determination of the equivalent cell temperature
(ECT) of photovoltaic (PV) devices by the open-circuit voltage method
IEC 60904-7, Photovoltaic devices – Part 7: Computation of the spectral mismatch correction
for measurements of photovoltaic devices
IEC 60904-8, Photovoltaic devices – Part 8: Measurement of spectral responsivity of a
photovoltaic (PV) device
IEC 60904-9, Photovoltaic devices – Part 9: Solar simulator performance requirements

IEC TS 61836, Solar photovoltaic energy systems – Terms, definitions and symbols
IEC TS 62446-3, Photovoltaic (PV) systems - Requirements for testing, documentation and
maintenance - Part 3: Photovoltaic modules and plants - Outdoor infrared thermography
IEC 62788-1-4, Measurement procedures for materials used in photovoltaic modules –
Part 1-4: Encapsulants – Measurement of optical transmittance and calculation of the
solar-weighted photon transmittance, yellowness index, and UV cut-off wavelength
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC TS 61836 and the
following apply.
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 bifacial PV device
PV device, both surfaces of which (front and rear sides) are used for power generation
3.2 bifaciality
property expressing the ratio between the main characteristics of the rear side and the front
side of a bifacial PV device quantified by specific bifaciality coefficients
Note 1 to entry: Unless otherwise specified, the bifacialities are typically referred to Standard Test Conditions
STC. The main bifacialities are:
Short-circuit current bifaciality: ϕ
–
ISC
– Open-circuit voltage bifaciality: ϕ
VOC
Maximum power bifaciality: ϕ
–
Pmax.
3.3 rear irradiance driven power gain yield
BiFi
quantity which indicates the power gain, in addition to that obtained at STC conditions, per
unit of rear irradiance
-2
Note 1 to entry: It is expressed in W/(Wm ).
4 General considerations
The final performance of bifacial PV devices in a power plant depends not only on the spatial
distribution of the irradiance incident onto the front surface, but additionally on that incident
onto rear surface of the device, which is strongly affected by site-specific conditions, such as
albedo, reflective surface size, the racking system, the device’s elevation and its tilt angle.
Due to these dependences and in order to obtain comparable measurement results, I-V
characterisation is extended to quantify the bifaciality of the device and the rear irradiance
driven power gain yield it can yield. Bifaciality is an intrinsic property of the device, unlike the
site-specific conditions such as albedo. The measurement conditions for bifacial devices
should strive to generate extra photocurrent proportional to their bifaciality. In general, this
can be achieved with a test spectrum close to the reference spectrum such as provided by
natural sunlight under suitable conditions or with a solar simulator whose irradiance level is

– 8 – IEC TS 60904-1-2:2019 © IEC 2019
adjustable. However, measurement conditions will never be perfect and will deviate from the
reference conditions. This document sets limits on the permissible deviations for obtaining
valid measurements. Smaller deviations are preferable, but may not be achievable in all
cases. In any case, the deviations of the measurement conditions from the reference
conditions shall be accounted for in the analysis of measurement uncertainty.
5 Apparatus
5.1 General
In addition to the apparatus requirements described in IEC 60904-1, one of the equipment
sets described in 5.2, 5.3 and 5.4 and that described in 5.5 is necessary for the
characterisation of bifacial devices.
5.2 Solar simulator with adjustable irradiance levels for single-side illumination
A solar simulator, as defined in IEC 60904-9, with adjustable irradiance level shall be used for
the I-V characterisation of bifacial devices. Simulators shall be able to provide irradiance
-2 -2
levels above 1 000 Wm (typically up to 1 200 Wm ). The simulator’s non-uniformity of
irradiance shall be below 5 % and shall remain below this value at irradiance levels used for
the characterisation of bifacial devices. The non-uniformity of irradiance, the spectral
distribution and the temporal instabilities of irradiance shall be measured at the irradiance
levels used for the characterisation of bifacial devices and those values used for corrections
(such as spectral mismatch correction) and uncertainty evaluation.
-2
For irradiances used above STC (>1 000 Wm ), the spatial uniformity, spectral distribution
-2 -2
and temporal instability at 1 100 Wm and 1 200 Wm shall be measured.
5.3 Solar simulator with adjus
...