2014 PV Performance Modeling Workshop: Irradiance- and Temperature-dependent PV Module Performance Measurement: Rajeev Singh, PV Evolution Labs

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Irradiance- and
Temperature-dependent
PV Module Performance
Measurement Rajeev Singh, John Watts
2014 PV Module Performance
Modeling Workshop
May 5, 2014

Review of IEC standards specifying temperature-dependent PV
module performance measurement
Issues with outdoor measurement of temperature coefficients
Indoor vs. outdoor measurements
Variables of irradiance- and temperature-dependent PV module
performance measurements
PVEL’s indoor measurement approaches
WHY IS THERE VARIABILITY?Outline

Standards specify linear reference devices to
set/determine irradiance
Spectral control or correction is required
WHY IS THERE VARIABILITY?IEC Standards: Irradiance
Standard Stated Purpose
Indoor /
Outdoor
Simulator
Class
Irradiance
Reference
Spectral
Correction
IEC 60904-1 2006 I-V Measurement
Both BBB
Linear Yes
IEC 60891 2009 G & T Corrections to I-V Linear Yes
IEC 61853-1 2010 PMAX(G,T) Linear Yes
IEC 61215/61646 2005 Module Qualification Linear Do not alter

Standards insufficiently specify temperature control methods and
their caveats
Poor harmony regarding temperature measurement approach
Cell temperature measurement methods are not discussed
In-plane temperature uniformity is specified in only one instance
WHY IS THERE VARIABILITY?IEC Standards: Temperature
Standard Year Stated Purpose
Indoor /
Outdoor
Simulator
Class
Temperature
Control
Guidance
Measurement
Method
Number of
Sensors
Sensor
Location
(Backsheet
or Cell)
Temperature
Uniformity
Requirement
IEC 60904-5 2011 Equivalent Cell Temperature (ECT)
Both BBB None
VOC and β N/A N/A No
IEC 60904-1 2006 I-V Measurement Sensor or ECT ? ? No
IEC 60891 2009 G & T Corrections to I-V Sensor 4 (Averaged) ? ± 2 °C
IEC 61853-1 2010 PMAX(G,T) Sensor or ECT 3 (Averaged) ? No
IEC 61215/61646 2005 Module Qualification Sensor ? ? No

WHY IS THERE VARIABILITY?
Outdoor Backsheet-referenced
Temperature Coefficients Measurement
RBS: Thermal resistance of back-side
EVA, backsheet
∆𝑇 = 𝑄𝑅𝑡ℎ
20
30
40
50
60
0 5 10 15 20 25 30 35 40
Backsheet Temperature (°C)
Cell Temperature (°C)
Temperature(°C) Measurement Time (arb.)
Results in overestimation
of temperature coefficient
magnitudes

WHY IS THERE VARIABILITY?
Outdoor Measurement of
VOC(T) – Beta (β)
-0.9
-0.8
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
1NoBox
2NoBox
3NoBox
4NoBox
1ThermalBox
2ThermalBox
3ThermalBox
4ThermalBox
Outdoor Measurement Results
Cell Probe
BS Probe 2
BS Probe 3
BS Probe 4
BS Probe 5
Measured(%/°C)
Trial
Backsheet view of test module temperature
probe locations
Cell probe (CP) is a hypodermic
thermocouple needle inserted underneath
backsheet and contacting cell busbar
Backsheet (BSx) probes are standard
thermocouples adhered to backsheet using
Kapton (polyimide) tape
CP
2
3
54
J-BOX
In-plane temperature uniformity
is poor
𝑑𝑇
𝑑𝑡
𝑥, 𝑦 varies with position
VOC(T) is often nonlinear

Indoor Flash Test
Good in-plane temperature
uniformity
Steady-state
Stable irradiance
Uncollimated light
Non-uniform irradiance
Class A+: ≤ 1 %
Not AM1.5
Class A+: ± 12.5 %)
WHY IS THERE VARIABILITY?Indoor Flash Testing vs. Outdoor
Outdoor
Poor in-plane temperature
uniformity
Not steady-state
Possibly stable irradiance
2-axis tracker
Collimated light
Uniform irradiance
Possibly AM1.5

Irradiance-dependent
Constant spectrum
throughout range
Neutral density filters
Constant bulb power
Power accuracy
Linear feedback
WHY IS THERE VARIABILITY?Specific Lab. Measurement Variables
Temperature-dependent
In-plane uniformity
Controlled environment,
flash tester
Steady-state
Controlled environment,
flash tester
Measurement location
Cell temperature probe or
isothermal conditions

WHY IS THERE VARIABILITY?Indoor Measurement Techniques
Cell temperature probes
Exposed optical surface
In-plane uniformity: ± 2 °C
Back-side Heating Uniform Heating
Backsheet temperature probes
Glass window
In-plane uniformity: ± 0.5 °C

WHY IS THERE VARIABILITY?Irradiance Control
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
0 200 400 600 800 1000 1200
Residual(%)
Irradiance (W/m
2
)
IEC 61853-1 ISC Residuals
Irradiance sensor (feedback)
calibrated at 1000 W/m2
IEC 60904-10: < 2 % non-linearity
PVEL: < 1 % non-linearity at all
temperatures and throughout
irradiance range

WHY IS THERE VARIABILITY?Temperature Control
8.05
8.1
8.15
8.2
8.25
8.3
20 25 30 35 40 45 50 55
PVEL Measurement of Scheuten Multisol P6-54c
Isc(T)
y = 7.9475 + 0.0055727x R= 0.99953
Isc(A)
Temperature (°C)
20
30
40
50
60
0 50 100 150
BS #1
BS #2
BS #3
BS #4
BS #5
C
Temperature(°C)
Time (minute)

IEC measurement standards acceptably address irradiance-
dependent measurements but do not provide adequate
treatment of temperature-dependent measurement
consideration
Outdoor measurement accuracy is difficult to achieve
PVEL has developed in-house methods to improve
temperature-dependent measurement accuracies
PVEL’s temperature coefficients measurements indicate that
datasheet coefficients are overestimated in magnitude
PVEL’s state-of-the-art measurement system will be online in
May 2014
Compare back-side heating method to isothermal chamber system
Conclusions

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Rajeev@PVEL.com
John@PVEL.com
Thank You

2014 PV Performance Modeling Workshop: Irradiance- and Temperature-dependent PV Module Performance Measurement: Rajeev Singh, PV Evolution Labs

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2014 PV Performance Modeling Workshop: Irradiance- and Temperature-dependent PV Module Performance Measurement: Rajeev Singh, PV Evolution Labs