ASTM E948-95(2001)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:E948–95 (Reapproved 2001)
Standard Test Method for
Electrical Performance of Photovoltaic Cells Using
Reference Cells Under Simulated Sunlight
This standard is issued under the fixed designation E948; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
TABLE 1 Standard Reporting Conditions
1. Scope
1.1 This test method covers the determination of the elec- NOTE 1—The extraterrestrial solar constant and spectral irradiance
contained in Tables E490 do not represent the latest measurements of
trical performance of a photovoltaic cell under simulated
these quantities. The World Radiation Center recommends a value of
sunlight by means of a calibrated reference cell procedure.
−2
1367Wm for the solar constant along with more reliable measurements
1.2 Electrical performance measurements are reported with
of the extraterrestrial spectral irradiance.
respect to a select set of standard reporting conditions (SRC)
Reference Spectral Irradiance Total Irradiance Temperature
(see Table 1) or to user-specified conditions.
−2
Distribution (Wm ) (°C)
1.2.1 The SRC or user-specified conditions include the cell
Tables E 891 1000 25
temperature, the total irradiance, and the reference spectral
Tables E 892 1000 25
irradiance distribution. Tables E 490 1353 25
1.3 This test method is applicable only to photovoltaic cells
with a linear response over the range of interest.
1.4 The cell parameters determined by this test method
E927 Specification for Solar Simulation for Terrestrial
apply only at the time of test, and imply no past or future
Photovoltaic Testing
performance level.
E973 Test Method for Determination of the Spectral Mis-
1.5 There is no similar or equivalent ISO standard.
match Parameter Between a Photovoltaic Device and a
1.6 This standard does not purport to address all of the
Photovoltaic Reference Cell
safety concerns, if any, associated with its use. It is the
E1021 Test Methods for Measuring Spectral Response of
responsibility of the user of this standard to establish appro-
Photovoltaic Cells
priate safety and health practices and determine the applica-
E 1039 Test Method for Calibration of Silicon Non-
bility of regulatory limitations prior to use.
Concentrator Photovoltaic Primary Reference Cells Under
Global Irradiation
2. Referenced Documents
E1040 Specification for Physical Characteristics of Non-
2.1 ASTM Standards:
concentrator Terrestrial Photovoltaic Reference Cells
E490 Solar Constant and Zero Air Mass Solar Spectral
E1125 Test Method for Calibration of Primary Non-
Irradiance Tables
Concentrator Terrestrial Photovoltaic Reference Cells Us-
E491 Practice for Solar Simulation for Thermal Balance
ing a Tabular Spectrum
Testing of Spacecraft
E1328 Terminology Relating to Photovoltaic Solar Energy
E691 Practice for Conducting an Interlaboratory Study to
Conversion
Determine the Precision of a Test Method
E1362 Test Method for Calibration of Non-Concentrator
E772 Terminology Relating to Solar Energy Conversion
Photovoltaic Secondary Reference Cells
E891 Terrestrial Direct Normal Solar Spectral Irradiance
Tables for Air Mass 1.5
3. Terminology
E892 Tables for Terrestrial Solar Spectral Irradiance atAir
3.1 Definitions—Definitions of terms in this test method
Mass 1.5 for a 37° Tilted Surface
may be found in Terminology E772 and Terminology E1328.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 cell temperature, °C, n—the temperature of the semi-
1 conductor junction of a photovoltaic cell.
This test method is under the jurisdiction of ASTM Committee E44 on Solar,
3.2.2 junction temperature, n—synonym for cell tempera-
Geothermal,andOtherAlternativeEnergySourcesandisthedirectresponsibilityof
Subcommittee E44.09 on Photovoltaic Electric Power Conversion.
ture.
Current edition approved Oct. 10, 1995. Published March 1996.
3.2.3 light source, n—a source of radiant energy used for
Annual Book of ASTM Standards, Vol 15.03.
cellperformancemeasurementsthatsimulatesnaturalsunlight.
Annual Book of ASTM Standards, Vol 14.02.
Annual Book of ASTM Standards, Vol 12.02. 3.3 Symbols:Symbols:
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E948
3.3.1 The following symbols and units are used in this test such as different manufacturers’ products. Repeated measure-
method: ments of the same cell may be used to study changes in device
A—cell area, m performance.
−1
a —temperature coefficient of reference cell,° C 5.3 This test method determines the electrical performance
r
2 −1
C—calibration constant of reference cell, Am W of a cell based upon the output power at a single instant of
−2
E—irradiance, Wm time. It does not provide for integrating the output power over
−2
E —standard reporting irradiance, Wm a given period of time and conditions to predict an energy
o
h—efficiency, % output.
FF—fill factor, % 5.4 Thistestmethodrequiresareferencecellcalibratedwith
I—current, A respect to an appropriate reference spectral irradiance distribu-
I —current with respect to SRC, A tion, such as Tables E490, E891, or E892. It is the respon-
o
I —reference cell short-circuit current, A sibility of the user to determine which reference spectral
r
I —short-circuit current, A irradiance distribution is appropriate for a particular applica-
sc
M—spectral mismatch parameter tion.
P —maximum power, W
m
R —series resistance, V
6. Apparatus
s
T—temperature,° C
6.1 Photovoltaic Reference Cell—A calibrated reference
T —standard reporting temperature,° C
o
cell is used to determine the total irradiance during the
T —temperature of reference cell,° C
r
electrical performance measurement.
V—voltage, V
6.1.1 Reference cells may be calibrated in accordance with
V —voltage with respect to SRC, V
o
Test Methods E1039, E1125, or E1362, as is appropriate for
V —open-circuit voltage, V
oc
a particular application.
NOTE 1—No reference cell calibration standards presently exist for
4. Summary of Test Method
space applications, although procedures such as high-altitude balloon and
4.1 The performance test of a photovoltaic cell consists of
low-earth orbit flights are being used to calibrate such reference cells.
measuring the electrical current versus voltage (I-V) charac-
6.1.2 A current measurement instrument (see 6.3) shall be
teristic of the cell while illuminated by a suitable light source.
used to determine the I of the reference cell under the light
sc
4.2 Acalibratedphotovoltaicreferencecell(see6.1)isused
source.
to determine the total irradiance during the test and to account
6.2 Test Fixture— Both the cell to be tested and the
for the spectral distribution of the light source.
referencecellaremountedinafixturethatmeetsthefollowing
4.3 Simulated sunlight is used as the light source for the
requirements.
electrical performance measurement, and solar simulation
6.2.1 Thetestfixtureshallensureauniformlateraltempera-
requirements are defined in Specification E927 (terrestrial
ture distribution to within 60.5°C during the performance
applications) and Practice E491 (space applications).
measurement.
4.4 The data from the measurements are corrected to stan-
6.2.2 The test fixture shall include a provision for maintain-
dard reporting conditions, or to optional user-specified report-
ing a constant cell temperature for both the reference cell and
ingconditions.Thestandardreportingconditionsaredefinedin
the cell to be tested (see 7.6.1).
Table 1.
4.4.1 Measurement error caused by deviations of the irradi- NOTE 2—When using pulsed or shuttered light sources, it is possible
thatthecelltemperaturewillincreaseuponinitialillumination,evenwhen
ance conditions from the SRC is corrected using the total
the cell temperature is controlled.
irradiance measured with the reference cell and the spectral
mismatch parameter, M, which is determined in accordance
6.2.3 Thetestfixture,whenplacedinthesimulatedsunlight,
with Test Method E973.
shallensurethatthefield-of-viewofboththereferencecelland
4.4.2 Measurement error caused by deviation of the cell
the cell to be tested are identical.
temperaturefromtheSRCisminimizedbymaintainingthecell
NOTE 3—Some solar simulators may have significant amounts of
temperature close to the required value (see 7.6.1).
irradiation from oblique or non-perpendicular angles to the test plane. In
these cases, it is important that the cell to be tested and the reference cell
5. Significance and Use
have similar reflectance and cosine-response characteristics.
5.1 It is the intent of this test method to provide a recog-
6.2.4 A four-terminal connection (also known as a Kelvin
nized method for testing and reporting the electrical perfor-
connection, see Fig. 1) from the cell to be tested to the I-V
mance of photovoltaic cells.
measurement instrumentation (see 6.3-6.5) shall be used.
5.2 The test results may be used for comparison of cells
6.3 Current Measurement Equipment— The instrument or
among a group of similar cells or to compare diverse designs,
instruments used to measure the cell current and the I of the
sc
reference cell shall have a resolution of at least 0.02% of the
maximum current encountered, and shall have a total error of
less than 0.1% of the maximum current encountered.
Wehrli, C., Extraterrestrial Solar Spectrum, Publ. No. 615, Physikalisch-
6.4 Voltage Measurement Equipment—The instrument or
Meteorologisches Observatorium and World Radiation Center, Davos Switzerland,
1985. instruments used to measure the cell voltage shall have a
E948
7.1.1 If the total irradiance during the performance mea-
surement as measured by the reference cell is within 62%of
the standard reporting total irradiance, the series resistance is
not needed.
7.2 Measure the cell area, A, using the definition in Termi-
nology E1328.
7.3 Determine the spectral mismatch parameter, M, using
Test Method E973.
7.4 Mount the cell to be tested and the reference cell in the
test fixture.
NOTE 5—Any nonuniformity of irradiance (see Specification E927)
between the locations of the reference cell and the cell to be tested will
introduce a bias error in the measured cell performance.
7.4.1 Ifapulsedorshutteredlightsourceisused,exposethe
test fixture to the source illumination.
FIG. 1 I-V Measurement Schematic
7.5 Measure the temperature of the reference cell, T .
r
7.5.1 If the temporal instability of the light source (as
defined in Specification E927) is less than 0.1%, the total
resolution of at least 0.02% of the maximum voltage encoun-
irradiance may be determined with the reference cell prior to
tered, and shall have a tota
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