Photovoltaic devices - Part 1-2: Measurement of current-voltage characteristics of bifacial photovoltaic (PV) devices

IEC TS 60904-1-2:2019 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.
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. This document describes the additional requirements for the measurement of I-V characteristics of bifacial PV devices.

General Information

Status
Published
Publication Date
28-Jan-2019
Current Stage
PPUB - Publication issued
Completion Date
29-Jan-2019
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IEC TS 60904-1-2:2019 - 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
IEC TS 60904-1-2:2019-01(en)
---------------------- Page: 1 ----------------------
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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

Warning! Make sure that you obtained this publication from an authorized distributor.

® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 3 ----------------------
– 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

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

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IEC TS 60904-1-2:2019 © IEC 2019 – 3 –
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

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

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– 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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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.
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IEC TS 60904-1-2:2019 © IEC 2019 – 5 –
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.

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– 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

---------------------- Page: 8 ----------------------
IEC TS 60904-1-2:2019 © IEC 2019 – 7 –
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
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

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– 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.

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
...

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