Photovoltaic Module Energy Yield Measurements: Existing Approaches and Best Practice

Photovoltaic Module Energy Yield Measurements:
Existing Approaches and Best Practice
Gabi Friesen, SUPSI-PVLab, Switzerland
Johanna Bonilla, TÜV Rheinland, Germany
Webinar - 12 march 2020

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What is IEA PVPS?
• The International Energy Agency (IEA), founded in 1974, is an autonomous body within the
framework of the Organization for Economic Cooperation and Development (OECD).
• The Technology Collaboration Programme was created with a belief that the future of energy
security and sustainability starts with global collaboration. The programme is made up of
thousands of experts across government, academia, and industry dedicated to advancing
common research and the application of specific energy technologies.
• The IEA Photovoltaic Power Systems Programme (PVPS) is one of
the Technology Collaboration Programme established within the
International Energy Agency in 1993
• 32 members - 27 countries, European Commission, 4 associations
• “To enhance the international collaborative efforts which facilitate the role of photovoltaic solar
energy as a cornerstone in the transition to sustainable energy systems”

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Content
• Introduction (G. Friesen)
• IEA PVPS Task 13 Survey on best practice (G. Friesen)
• Test environment and hardware: Requirements & recommendations (J. Bonilla)
• Field experiences TÜV Rheinland (J. Bonilla)
• Field experiences SUPSI PVLab (G. Friesen)

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Content

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What is it about?
We talk here about:
 medium to long term energy yield
measurements
 single module
 real operating conditions
… and not about:
 system monitoring
 measurements for STC extrapolation
 energy rating

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Energy Rating vs. Energy Yield
Standard Reference Conditions
Short term measurements
Field Conditions
Long term measurements

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Energy Rating for different climates accord. IEC61853
part1: Irradiance and temperature performance measurements and
power rating Pmax,Isc,Voc (G,T, AM1.5, AOI=0)
IEC61853-1:2011
part3: Energy rating of PV modules
IEC61853-3:2018
part4: Standard reference climatic profiles (5 data sets)
IEC61853-4:2018
part2: Spectral response, incidence angle and module operating
temperature measurements Isc(λ), Isc( AOI),Tmod(G,Tamb,wspeed)
IEC61853-2:2016
kWh/Wp

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Why test in different climates?
Different local conditions
• irradiance
• temperature
• spectrum
• soiling
• …
• different module rankings
Validation of IEC 61853 approach!
• and degradation rates
How to perform comparable
measurements!

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Energy Yield Monitoring - Reference documents
DERLAB Technical Guideline (2012)
Long-term PV Module Outdoor Tests
IEC 61724-1 (2017)
PV system performance Part 1: Monitoring
IEA Technical report (2018) on
Photovoltaic Module Energy Yield
Measurements: Existing Approaches
and Best Practice.
MODULE MONITORING
SYSTEM MONITORING
©TÜV Rheinland
ISO 9060 (2018 update)
Pyranometers and Pyrheliometers
©SUPSI

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IEA Survey on Best Practice
Participants
CSIRO – Australia
AIT - Austria
GANTNER – Austria
KU LEUVEN - Belgium
LABORELEC - Belgium
IEE.AC - Cina
University of Cyprus - Cyprus
INES – France
Fraunhofer ISE – Germany
TUV Rheinland - Germany
University of Utrecht - Netherlands
SUPSI - Switzerland
NIST - USA
NREL - USA
SANDIA - USA
5
5
5
new comers
2-4 years
experienced
5-10 years
veterans >10
years, >100
module types
tested
8
2
4
1
none
only electrical
performance
+ module
qualification
+ energy yield
 15 test laboratories
 33 test facilities distributed worldwide
Climates Experience ISO17025 accreditation

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General test requirements
The measurement accuracy depends as much
on the conditions around the measurement
system as on the test equipment itself!
test device
• reference power (kWh/Wp)
• selection of modules
test site
• irradiance uniformity
• temperature uniformity
• soiling
• hardware exposure
test equipment
• hardware definition
• Pm measurement accuracy
• E measurement accuracy
• G, Tmod measurement accuracy
test processing
• data quality
• failure identification
• reporting
Survey questions:
• Background
• Sampling procedures
• Test equipment
• Stand configuration
• Maintenance
• Data processing
• Uncertainties
• Reporting

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Survey results: testing scopes and test requirements
Module benchmarkingDegradation studies Model validations
Example: Thin Film technologiesExample: PV Klima project Example: public NREL data
• relative meas.
accuracy
• comparability of
modules
• long term data
reliability
• comparability of
different sites
• absolute
measurement
accuracy
• synchronization
of data
80%87% 73%
Prototype testing
Example: Coloured modules
67%
©TÜV Rheinland ©SUPSI PVLab ©SUPSI PVLab ©NREL

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Survey results: special test requirements
Special modules Specific losses
Example: BIPV modules Example: PID testing
Special modules
Example: Bifacial modules
• different orientations
and albedo
• additional sensors
• thermal insulation
• additional sensors
• 0-2000 bias voltage
• monitoring of leakage
currents
©SERIS©SUPSI PVLab©SANDIA

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Survey results: electrical performance measurement
MPP tracker (MPPT)IV-tracer (IV)
e.g. micro-inverters or
high precision laboratory
equipment
IV-tracer with MPPT
e.g. programmable
bidirectional power supplies
or capacitive loads
e.g. all-in one solutions
or assembled
instruments.
Example:
Power one
Example:
Kepco
Example:
MPPT3000
0%19%81%
The primary choice for test laboratories is to have the lowest measurement uncertainty and
highest number of information (Isc, Voc, Pmax, Rs, Rsh, …). The low cost solution which would be
sufficient for benchmarking lacks in information on tracking accuracy (static and dynamic).

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Survey results: irradiance measurement
e.g. filtered and
unfiltered cells for
different spectral
response
e.g. fast responding
broadband thermopile
pyranometers
e.g. spectrum radiometer
Reference cellsPyranometers Spectrumradiometer
Example:
Kipp & Zonen CMP21
Example:
ISE reference cell
Example:
EKO MS-711/712
100% 80% 73%
The pyranometer is the primary choice for the calculation of the incoming broadband irradiance
(comparability requirement), whereas the reference cells and the spectral irradiance data are
used for the correction to standard test conditions (STC) or for other data analysis purposes.

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Survey results: temperature measurement
Equivalent cell temperature
calculation accord. IEC
60904-5
e.g. Pt100 RTD or
thermocouples
e.g. contact less
thermometer
Voc methodContact methods Infrared methods
The most used is the contact method (73% RTD versus 27% thermocouples). The majority applies
a single sensor to the module. Only 4 laboratories increase the number of sensors to 2-4 (non-
uniformity or redundancy checks). The infrared method is only used for uniformity checks and the
equivalent cell temperature for the analysis of backsheet-to-cell temperature differences and the
monitoring of BIPV modules.
100%

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Survey results: maintenance measures
daily
-
weekly
daily
-
montly
daily 1-5 times
/week
1-10 min
monthly
ND
>1 month
daily-weekly
ND
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
LOG BOOK VISUAL
INSPECTION
SENSOR
CLEANING
ALERT SYSTEM MODULE
CLEANING
PICTURES
12
11 11
9 9
8 8
7
6
3 3
Data filterMaintenance
The level of quality control measures is generally very high and a large number of data quality
markers are implemented. A case sensitive filtering of erroneous or low-quality data is so easily
possible. E-mail alerts are the most commonly used tool for the notification of problems.
• Optical inspection
• Cleaning procedures
• Maintenance report
• Definition of error markers
• Alert/intervention procedures
• Filter procedures

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Survey results: module selection and screening
27%
6%
27%
20%
20%
none
STC only
+ VI/EL/IR
+ GD, MATR, SR, TK, …
+ INS/WL
The sampling procedure and STC power used for the normalization of the module energy yield (Ya)
and the module performance ratio (MPR) is different depending on the scope for which the
measurements are performed or the testing capabilities of the laboratories.
Legend:
performance at (STC)
visual inspection (VI)
electroluminescence (EL)
infrared imagining (IR)
irradiance dependency
(GD) temperature
coefficients (TK)
full matrix (MATR)
spectral response (SR),
insulation test (INS)
wet-leakage (WL)
2-3 modules /type
1 reference module 1 or more
spare modules
1 module/type
3-5 modules/type
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
MODULES TESTED IN THE FIELD MODULES STORED IN THE DARK SPARE MODULES
• Test/spare modules
• Reference modules (dark storage)
• Electrical characterisation
• Optical inspection
• Safety testing

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Survey results: reference power
Nominal STC power Pnom as stated by the manufacturer
 commercial approach (sensible to labeling strategies)
Stabilized real STC power Pstab as measured accord. IEC 61215
 most suitable approach for benchmarking, lowest measurement uncertainty, degradation
has to be controlled
Actual STC power Pout as measured during outdoor exposure
 most suitable for the study of meta-stabilities or degradation effects, higher
measurement uncertainty, requires additional measurement of correction parameters,
requires IV-tracer system

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Survey results: typical uncertainty contributions
𝑀𝑀𝑃𝑃𝑃𝑃 =
⁄𝐸𝐸 𝑃𝑃𝑠𝑠𝑠𝑠𝑠𝑠
⁄𝐻𝐻𝐻𝐻 1000
𝑈𝑈𝑀𝑀𝑀𝑀𝑀𝑀 = 2
𝑈𝑈𝑃𝑃𝑠𝑠𝑠𝑠𝑠𝑠
2
2
+
𝑈𝑈𝐸𝐸
2
2
+
𝑈𝑈𝐻𝐻
2
2
+
𝑈𝑈𝑇𝑇
2
2
+
𝑈𝑈𝐴𝐴
2
2
+
𝑈𝑈𝑈𝑈
2
2
Error Source Value k Comment
STC Power: UPstc
module calibration 1.3-3% 2 accredited laboratory accuracy
> 3% 2 STC correction of outdoor data
data sheet value (in alternative
to module calibration)
> 3% 2 manufacturer tolerance (incl. meas. uncertainty)
Irradiance/irradiation: UG, UH
sensor calibration 1.0 – 5% 2 matched reference cell with T corrections
2-8% 2 typical pyranometer calibration
calibration drift (%/year) 0.5 – 1% 2 soiling effects, sensor change
Module performance: UPmax, UE, UYa, UMPR
Power, Umpp
current/voltage measurement 0.05 - 0.1% 2 data acquisition error
1% 2 error due to non-optimal measurement range selection
maximum power 0.1 – 1.5% 2
error in maximum power point tracking, Equipment
temperature error
over expected T range (-10 to
30 °C)
0.0 – 1.0% 2 calibrate at 22 °C but use over much wider range.
resistance losses 0-50% 2 2-vs.4-wire measurement
capacitive effects 0-50% 2 module technology and sweep speed dependent
Time, UT
synchronization 0-1% 2
simultaneous or separate measurement of power and
solar irradiance. Stable or variable sky conditions
Alignment, UA
module/sensors and
module/module
0 - 5% 2
depends on average angle of incidence. 0.5 degree
alignment error on a 60° incidence angle is 1.5%
Uniformity, UU
irradiance 1% 2 single module, large area, albedo, …
temperature 1-4°C 2 single module, large area, wind , mounting, …
Key performance indicator
Module Performance Ratio (MPR)
Uncertainty contributions
Module Performance Ratio (MPR)

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Content

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Test environment and hardware: Requirements & recommendations
1. Mounting structure &
surroundings
• Rack layout
• PV module installation
• Shading
• Albedo
• Sensor positioning
2. Current- voltage
measurements
• Hardware solutions &
configuration
3. Measurement of
enviromental parameters
• In-plane irradiance
• Module temperature
• Meteorological data
• Spectral irradiance
©TÜV Rheinland©TÜV Rheinland
©TÜV Rheinland

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• Most used: fixed open rack tilted and
oriented optimized depending on the
latitude:
latitude < 25°
•latitude *0.87
•Minimum 10°,
self-cleaning
by rainfall
25°<latitude <
50°
•latitude *0.87
+ 3.1°
latitude > 50°
•Fixed tilt
angle 45°
From: www.solarpaneltilt.com
• Coplanar installation of test modules and
irradiance sensors
1. Mounting structure & surroundings: Mounting Layout
IEC 60904-1

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1. Mounting structure & surroundings: PV module installation
• Temperature gradient from
bottom to top is typically
observed.
• Infrared image of the entire
test sample at irradiance
>800 W/m² .
©TÜV Rheinland
Source: Soltec,, Bifacial gain and production analysis at Bifacial
Tracker Evaluation Center (BiTEC
• Installation at ≥1 m from
ground and at least 10 cm
away from any other object.
• In a row, outer test samples
(left & right) tend to operate
at a lower temperature.
• Additional dummy modules
shall be installed in these
locations to reduce the
environmental variability.
Lower Temp
Devices under
test
Dummy
module
Dummy
module
©TÜVRheinland

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1. Mounting structure & surroundings: PV module shading
• Sources: buildings, trees, fence,
elevation profiles of landscape,
mounting clamps (at high AoI).
• Available commercial analysis tools
superimpose the sun path over the
course of a year on a panoramic 360°
AoI: Angle of incidence
• For bifacial: cables, structure, frame of
module (if appl.), junction box(es), torque
tube (tracking), etc.
• Shading can also
be modeled with
a computer
aided design
(CAD) software
©TÜV Rheinland
©TÜV Rheinland ©TÜV Rheinland

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1. Mounting structure & surroundings: PV module shading
Calculation of the shading limit
angle for parallel arrangement
of mounting racks. The shading
limit coordinates are (SAC, SHC).
L: 2 m
Θ:35°
Row length (DM): 15 m
Row spacing (DR): 4 m
SAC=75.1°
SHC=4.2°
𝑯𝑯𝟐𝟐 = 𝑯𝑯𝟏𝟏 + 𝑳𝑳 ∗ 𝐬𝐬𝐬𝐬 𝐬𝐬 𝜽𝜽
𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫 = 𝑫𝑫𝑹𝑹
𝟐𝟐
+ 𝑫𝑫 𝑴𝑴
𝟐𝟐
𝑺𝑺𝑺𝑺𝒄𝒄 = 𝟗𝟗𝟗𝟗𝟗 − 𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂
𝑫𝑫𝑹𝑹
𝑫𝑫 𝑴𝑴
𝑺𝑺𝑺𝑺𝒄𝒄 = 𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂
𝑳𝑳 ∗ 𝒔𝒔𝒔𝒔 𝒔𝒔 𝜽𝜽
𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫

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1. Mounting structure & surroundings: Albedo (ground reflectance)
• Monofacial PV modules: The
steeper the modules are, the more
reflected radiation they receive.
• Bifacial PV modules: One of the
main influencing factor for
performance
Uniform as possible (relevant
surroundings taken into account)
Boost ground shall consider
seasonalities and mantainance
practices.
Height (>1m)
©TÜV Rheinland

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2. Current- voltage measurements: Hardware solutions
(1) MPPT (2) IV-tracer (3) IV-tracer with MPPT
Description
Maintains the PV Module at its
maximum power point (Pmax).
Measures the current from open
circuit to short-circuit (or vice
versa)
Combination of (1) for MPPT and (2)
for IV-tracing.
Pros
• In accordance to operation in
PV array.
• Power production integration
for accurate energy yield
measurement.
• Lower cost
From the IV scan :
• Non-uniformity effects (ISC
spread)
• I-V correction parameters
• Low irradiance behavior thermal
coefficients
• Power measurement during most
of the operation + full benefit of
IV curve measurements.
• User can see impact of different
MPP tracking methods and
validate impact between MPP
tracking, VOC or ISC conditions.
Cons
• No other parts of the IV curve
are measured (e.g. Isc , Voc).
• Isc operation shall be avoided:
reverse biasing of cells (heating)
• Higher cost.

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2. Current- voltage measurements: Hardware characteristics and configuration
DC Load:
Dedicate current and
voltage sensing lead
(4-wire connections)
Loads at controlled-
temperature
environment
Requirements & accuracy of the equipment have to comply with IEC 60904-1 and IEC
61829-Voltages and currents instrumentation accuracy of at least ±0,2 %.
I-V Scan
Sweep time<1-2 sec. (scatter variable clouds)
≥50 measurement points, optimized at
relevant parameters (ISC, VOC, PMAX)
≥10 Sample points per meas. point
©TÜV Rheinland

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3. Measurement of enviromental parameters: Irradiance measurement
©TÜV Rheinland
In-plane irradiance
Tilted
Pyranometer
(ISO-9060)
Direct normal irradiance
Tracking
First class pyrheliometer
Diffuse horizontal
irradiance
Horizontal
Pyranometerwith a
with shading ball
Global
horizontal
irradiance
Horizontal
Pyranometer©TÜV Rheinland ©TÜV Rheinland
In-plane diffuse irradiance
Tilted
Pyranometer with a with shading ball
Spectrally sensitive ‘effective’ irradiance
Tilted
Reference cell(s) spectrally /angular selective
 Tilted sensors and
modules coplanar
installation at module
close proximity and
height.
 Regulary cleaning
and inspection.
 Regulary calibration
at least every two
years and track the
drift and bias on a
quarterly basis

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3. Measurement of enviromental parameters: Meteorological data & spectrum
Ambient temperature (Tamb)±
Win speed & direction
Air pressure Precipitation
Real humidity
Soiling ratio/snow
coverage
Environmental sensors:
IEC 61724-1 requirements
Spectral irradiance
• Measured spectrum- Spectroradiometer :
• Simulated spectrum:
Radiative Transfer Models (RTM), given a set of
atmospheric parameters and geographic
coordinates
RTM has three categories: Sophisticated rigorous,
parametric and statistical models
Wavelength range
depending on type:
From 220-350 nm to
1100,1700 or 2500 nm
©TÜV Rheinland
©TÜV Rheinland

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Summary of best practices recommendations
General requirements
Measurement
requirements &
accuracy of the
equipment
IEC 60904-1
IEC 61829
Data acquisition
requirements
IEC 61724-1 (systems)
• V-I instrumentation accuracy of at least ±0,2 %.
• Irradiance: Calibrated reference device or a
pyranometer, spectrally matched or correction.
• Temperature accuracy ± 1°C with repeatability
0.5°C.
• Coplanar installation of module and irradiance
sensors ±2°. Less than 0.5° is recommended
• Tamb accuracy better than 1K
• Sampling interval: irradiance-depended
parameters ≤1min, others 1-10 min
• Measurement uncertainty of ±2.0% at the
inverter level for a class A measurement
(highest accuracy). For single modules, a better
accuracy is aspired
• Synchronization needed when comparing different devices
• Number and positioning of sensors should be adapted to the
scope and type of device under test.
• All system maintenance, including cleaning of sensors and
modules, or soiling state of modules, shall be documented
• Data availability = recommended > 90%

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Content

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Field experiences TÜV Rheinland
• MPP tracking (30 sec)
• I-V curve (10 min)
• Temperature of the back of
the module, TBoM (30 sec)
• In plane spectral irradiance
(1min)
• Meteorological data (30 sec)
• Grear pyranometers (30 sec)
Four unique outdoor testing locations with identical setups

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Cologne, Germany: August 2017 to July 2018
16 PV modules: monofacial vs. bifacial
Mounting conditions 2 racks, fixed, pitch 11m
Height above ground 1.5 m
Tilt angle 35° South
Ground gravel (albedo 30%)
Annual in-plane solar
irradiation HPOA, Annual
1231.1 kWh/m²
Annual in-plane rear
irradiation Hrear, Annual
169.4 kWh/m²
HPoA_rear/HPoA_front [%] 13.8%
1st Rack
2nd Rack
Monofacial c-Si Bifacial c-Si thin-film

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Cologne, Germany: 1st Rack
[%]
1000/
/
2
,
−












=
∑
∑
WmG
PP
MPR
months
PoA
STCMPP
months
MPP
 MPR=1 The mean PV module efficiency
corresponds to its STC efficiency
 MPR≠1 Performance gain/losses due to
module temperature, low
irradiance behavior, spectral or
angular effects, degradation or
meta-stability
More @ Bonilla J. et al (2018): Energy Yield Comparison between Bifacial and
Monofacial PV Modules: Real World Measurements and Validation with Bifacial
Simulations, EUPVSEC 2018.
+11.6%
+6.6%

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Tempe, USA: Sep 2018 to August 2019
Tilt angle 33.5° South
Ground
Dark gravel + sand
(albedo 13.4%)
In-plane (front) solar irradiation
HPoA_ front
2237.3 kWh/m²
In-plane rear irradiation HPoA_rear, 229.2 kWh/m²
1st Rack
©TÜV Rheinland
More @ Saal J. et al (2019): Energy Yield Comparison between Bifacial and
Monofacial PV Modules: Real World Measurements in Desert climate (BWh),
EUPVSEC 2019.
+8.2%

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Thuwal, Saudi Arabia: Oct 18 to Sep 2019
Ground
Sand with gravel
(albedo: 30.1%)
HPoA_ front
2029.2 kWh/m²
1st Rack
©TÜV Rheinland
+12.7%

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Chennai, India: Sep 18 to Aug 2019
Ground
White stones
(Albedo 49.9%)
HPoA_ front
1857.1 kWh/m²
1st Rack
@TÜV Rheinland
+22.4%

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Summary field experiences TÜV Rheinland
Cologne
(Germany)
Tempe
(Arizona)
Chennai
(India)
Thuwal
(Saudi-Arabia)
Installation height above
ground
1.5 m 1.3 m 1.3 m 1.3 m
PV module Inclination and
orientation
35° South 32.5 South 15° South 25° South
Ground surface Colored gravel
Dark gravel with
sand
White gravel Sand with gravel
Ground albedo factor 0.3 0.14 0.5 0.3
Monofacial PV modules 12 modules 8 modules 4 modules 4 modules
Bifacial PV modules
4 modules
BF = 0.85 - 0.89
3 modules
BF = 0.75 - 0.85
4 modules
BF = 0.74 - 0.91
4 modules
BF = 0.74 - 0.90
Monitoring period AUG 17 – JUL 18 SEP 18 – AUG 19 SEP 18 – AUG 19 OCT 18 – SEP 19
Ratio Rear/Front irradiance 13.8% 10.2% 25.5% 15.1%
Average bifacial gain +11.6% +8.2% +22.4% +12.7%

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Content

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History of Outdoor testing at SUPSI
1991 set-up of R&D outdoor test facility
1993 1º test cycle
1994 2º test cycle
2006 new MPPT3000
2007 1º BIPV test stand
2008 11º test cycle
2009 industry oriented services
2010 remote testing for industry
2011 12º test cycle (4 years) on thin film modules
2-6º BIPV test stand
2018 13º test cycle colored and bifacial modules
2020 14º test cycle innovative modules (summer 2020)
1989-1996
MPPT 1º
generation
2006-today
MPPT3000
aprox. 70 units
2020
Gantner OTF
36 units
·····
3-10º test cycle
meas. accuracy
module
technologies
quality control
meas. parameters
building simulations
extra stress factors
1991
outdoor
testing
2001
indoor
testing
2010
reliability
testing
Swiss Solar Price 2001
More then 190 different PV module types tested!
1996-2006
MPPT 2º
generation
···

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Examples of outdoor testing facilities at SUPSI
• Standard open-rack’s
• Façade elements
• Solar windows
• Roof tiles
• Bifacial modules
• Antisoiling coatings
• Colored modules
• …
Façade mock-up1° test cicle
(1990-1993)
13° test cicle – bifacial modules Semi-transparent modules
Roof mock-up
12° test cicle

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Example 1: colored modules
Questions:
• How much energy is lost by increasing the aesthetics of PV?
• Can this loss be predicted by applying the measurement techniques proposed by the
IEC 61853 Energy Rating standard part 1 and part 2?
Project funded by the Swiss Federal Office of Energy (SFOE) under the project ENHANCE.
13° test cicle – colored modules (prototypes delivered by manufacturers or from pilot projects)

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Example 1: colored modules
Answers:
• Depending on the color technology, yield differences respect to the reference modules
of 16-45% have been observed.
• Light absorption, thermal, Isc (AOI + Spec), bifacial and low irradiance losses/gains
were calculated. Thermal and bifacial gains partially compensates absorption losses.
Project funded by the Swiss Federal Office of Energy (SFOE) under the project ENHANCE.
9.5%
4.8%
-0.1%
-3.9% -4.4% -5.3%
-5.5%
-23.8%
-44.5%
-28.3%
-34.4%
-16.0%
-45.1%
-38.8%
ΔWh/W (Pmeas) ΔWh/m² (active area)
For details see http://www.supsi.ch/isaac_en/eventi-comunicazioni/eventi/2019/2019-11-08.html

PVPS
47
Example 1: colored modules (white module)
The white module reaches up to 10ºC lower
temperatures respect to its reference module and a
thermal gain of 3.3%.
0
10
20
30
40
50
60
70
08:38 10:19 12:00 13:40 15:21 17:02 18:43
Backofmoduletemperature(°C)
transparent REF white light grey white flag terracotta red facade
©SUPSI

PVPS
48
Example 2: Degradation study on insulated modules
Questions:
• Does insulated BIPV modules are more affected by degradation than ventilated
modules due to the higher temperatures?
• Are the c-Si Glass/PVB/Glass modules less affected by degradation than the
Glass/EVA/Tedlar modules?
Tmax,vent = 67°C
Tmax,ins= 92°C
©SUPSI

PVPS
49
Example 2: Degradation study on insulated modules
Answers (ongoing activity done within PEARL PV COST action):
• Different degradation rates was observed for the insulated respect to the ventilated
modules. An increase in visual defects is observed for the insulted modules, but
degradation rates are below 0.5%/year.
Gok, A., et al. The influence of operating temperature and thermal insulation on the performances of different BIPV modules. Submitted to IEEE Journal of Photovoltaics
After 5 years the
insulated modules
shows significantly
more
• micro cracks
• grid finger
interruptions
G/EVA/BS G/PVB/G

iea-pvs.org
Thank you
Gabi Friesen, Johanna Bonilla – IEA PVPS Task13
Gabi.Friesen@supsi.ch Johanna.Bonilla@de.tuv.com
http://www.iea-pvps.org/index.php?id=493
The technical Report is available for download under:

PVPS
51
3. Measurement of enviromental parameters: Module temperature
Contact method
•Pt100 RTD (Resistance
Temperature Detectors) and
thermocouples
•uncertainty: 0.1-0.25 °C (k=1)
PT100s: lowest , but higher cost
•Backsheet-to-cell temperature
correction:
Open-circuit voltage (Voc) method
•IEC 60904-5: One-diode model to
convert the voltage into a
temperature
•Calibration of the model : contact
temperature measurements at
different irradiances
•0.1-0.6 °C, if well calibrated on
module
IR method
•Most important role: operator
training.
•Best results are obtained at higher
irradiances
•Rapidly deployable in the field,
and allow temperature differences
to be easily observed (hot spot).
•0.1-1.0 °C, depending on quality
(and cost)
©TÜV Rheinland
©indiamart.com

PVPS
52
MPP tracking
•Avoid operation at local maximum
instead of at the MPP. Fast and
accurate algorithms are needed.
•Know the tracking efficiency (static
and dynamic)
•Optimize algorithms of MPPT for all
technologies independently of the fill
factor (FF) to allow a fair comparison
of the results.
•Systematic cross-checking of the
MPPT data with IV-data (different
conditions and technologies)
Data sampling and synchronization
•Eliminate or use only high quality
multiplexers
•Synchronize the IV scans of all PV
modules.
•Recommended interval for IV scans is
1 min.
•The data acquisition rate for
environmental parameters should be
in the range of 1-10 Hz, with
averaging to a target sampling
frequency of 1-5min.
Shunts
•Typical range is 1 mΩ to 10 mΩ.
•calibration certificates
• low thermal drift characteristics
•Calibrated shunt resistance
uncertainty ≤0.01%
• The temperature coefficient should
be below ±5 ppm/K (20 to 60°C).

PVPS
53
Cables
•Four-wire connections :
Two for the module
power and a current
•two wires for a zero-
current voltage
measurement
•Wires cross sectional
area: >20 m distance: ≥6
mm2 . <20 m: 4 mm2
•If a four-wire connection
is not made, cabling
lengths should be
minimized and the
voltage drop should be
characterized.
Connectors
•Standard PV module
connectors (e.g., MC4)
•Y-connectors for splitting
the PV module
connectors into a 4-wire
configuration
•Periodically check the
connection resistance
Fuses and overvoltage
protection
•Do not use protection
devices or design them
so that there is minimal
impact on the signals
(uncertainty)
Checks and validation
•Quantify the voltage
drop at the short-circuit
condition and calculate
the difference between
the measured and true
module Isc
•Quantify any current flow
at the open-circuit
condition and calculate
the difference between
the measured and true
module Voc
Calibration
•Calibrate the
measurement equipment
according to
manufacturer
specifications
•Calibrate at least every
two years and track the
drift and bias on a
quarterly basis

PVPS
54
Recommendations on sampling procedures
Benchmarking
 clear and same procedure for all modules for a fair rating
 consideration of manufacturer distribution and binning
 selection from flasher list values
 characterization and stabilization in accordance with IEC 61215
Long-term measurements
 min 2 modules/type for cross verification
 dark reference module for control measurements with solar simulator
 Sorting of damaged/not representative modules (VI, EL)

PVPS
55
Recommendations for uncertainty declarations
 measurement accord. best practice guidelines (minimize uncertainties).
 calculation accord. standards e.g. ISO/IEC Guide 98-1 and ISO/IEC Guide 98-3.
 there exist no unique reference conditions for the module energy measurements
→ calculation of uncertainties specific to time, location and test facility.
 reporting of integration time (year, month, day, hour or minute).
Ref: A. Driesse; PVSENSOR project, Daily and annual profile of the measurement error (minute
and weekly resolution) caused by angle-of-incidence, spectrum and temperature for a reference
cell located in Golden Colorado, tilted 40° South.

PVPS
56
Further analysis : Linear performance loss analysis (LPLA)
Quantification of Energy Losses/Gain:
∆𝑀𝑀𝑀𝑀𝑀𝑀𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏 =
𝜑𝜑𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏 ∗ 𝐻𝐻𝑟𝑟𝑒𝑒𝑒𝑒𝑒𝑒 [𝑘𝑘𝑘𝑘𝑘/𝑚𝑚𝑚]
𝐻𝐻𝐻𝐻𝐻𝐻𝐻𝐻 + 𝐻𝐻𝐻𝐻𝐻𝐻𝐻𝐻𝐻𝐻 [𝑘𝑘𝑘𝑘𝑘/𝑚𝑚𝑚]
More @ Schweiger, M. et al. (2017), “Performance stability of
photovoltaic modules in different climates, Progress in Photovoltaics:
Res. Appl. [DOI: 10.1002/pip.2904].
bifiAOISMMSOIL
LIRRTEMPCAL
MPRMPRMPRMPR
MPRMPRMPR
∆+∆−∆±∆−
∆±∆−= %100
For all PV modules ΔMPRSOIL= -0.5% was considered, based on the measurements of two
reference cells, one soiled and one regularly cleaned.

Photovoltaic Module Energy Yield Measurements: Existing Approaches and Best Practice

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