ASTM E948-95

NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: E 948 – 95 An American National Standard
Standard Test Method for
Electrical Performance of Photovoltaic Cells Using
Reference Cells Under Simulated Sunlight
This standard is issued under the fixed designation E 948; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number 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 E 490 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
1367 Wm 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
E 973 Test Method for Determination of the Spectral Mis-
apply only at the time of test, and imply no past or future
match Parameter Between a Photovoltaic Device and a
performance level. 4
Photovoltaic Reference Cell
1.5 There is no similar or equivalent ISO standard.
E 1021 Test Methods for Measuring the Spectral Response
1.6 This standard does not purport to address all of the 4
of Photovoltaic Cells
safety concerns, if any, associated with its use. It is the
E 1039 Test Method for Calibration of Silicon Non-
responsibility of the user of this standard to establish appro-
Concentrator Photovoltaic Primary Reference Cells Under
priate safety and health practices and determine the applica-
Global Irradiation
bility of regulatory limitations prior to use.
E 1040 Specification for Physical Characteristics of Non-
Concentrator Terrestrial Photovoltaic Reference Cells
2. Referenced Documents
E 1125 Test Method for Calibration of Primary Non-
2.1 ASTM Standards:
Concentrator Terrestrial Photovoltaic Reference Cells Us-
E 490 Solar Constant and Air Mass Zero Solar Spectral
ing a Tabular Spectrum
Irradiance Tables
E 1328 Terminology Relating to Photovoltaic Solar Energy
E 491 Practice for Solar Simulation for Thermal Balance
Conversion
Testing of Spacecraft
E 1362 Test Method for Calibration of Non-Concentrator
E 691 Practice for Conducting an Interlaboratory Study to
Photovoltaic Secondary Reference Cells
Determine the Precision of a Test Method
E 772 Terminology Relating to Solar Energy Conversion
3. Terminology
E 891 Terrestrial Direct Normal Solar Spectral Irradiance
3.1 Definitions—Definitions of terms in this test method
Tables for Air Mass 1.5
may be found in Terminology E 772 and Terminology E 1328.
E 892 Terrestrial Solar Spectral Irradiance Tables at Air
3.2 Definitions of Terms Specific to This Standard:
Mass 1.5 for a 37° Tilted Surface
3.2.1 cell temperature, °C, n—the temperature of the semi-
E 927 Specification for Solar Simulation for Terrestrial
conductor junction of a photovoltaic cell.
Photovoltaic Testing
3.2.2 junction temperature, n—synonym for cell tempera-
ture.
3.2.3 light source, n—a source of radiant energy used for
This test method is under the jurisdiction of ASTM Committee E-44 on Solar,
cell performance measurements that simulates natural sunlight.
Geothermal, and Other Alternative Energy Sources and is the direct responsibility of
Subcommittee E44.09 on Photovoltaic Electric Power Conversion.
3.3 Symbols:Symbols:
Current edition approved Oct. 10, 1995. Published March 1996.
3.3.1 The following symbols and units are used in this test
Annual Book of ASTM Standards, Vol 15.03.
method:
Annual Book of ASTM Standards, Vol 14.02.
Annual Book of ASTM Standards, Vol 12.02. A—cell area, m
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
E 948
−1
a —temperature coefficient of reference cell,° C time. It does not provide for integrating the output power over
r
2 −1
C—calibration constant of reference cell, Am W a given period of time and conditions to predict an energy
−2
E—irradiance, Wm output.
−2
E —standard reporting irradiance, Wm 5.4 This test method requires a reference cell calibrated with
o
h—efficiency, % respect to an appropriate reference spectral irradiance distribu-
FF—fill factor, % tion, such as Tables E 490, E 891, or E 892. It is the respon-
I—current, A sibility of the user to determine which reference spectral
I —current with respect to SRC, A irradiance distribution is appropriate for a particular applica-
o
I —reference cell short-circuit current, A tion.
r
I —short-circuit current, A
sc
6. Apparatus
M—spectral mismatch parameter
6.1 Photovoltaic Reference Cell—A calibrated reference
P —maximum power, W
m
cell is used to determine the total irradiance during the
R —series resistance, V
s
electrical performance measurement.
T—temperature,° C
6.1.1 Reference cells may be calibrated in accordance with
T —standard reporting temperature,° C
o
Test Methods E 1039, E 1125, or E 1362, as is appropriate for
T —temperature of reference cell,° C
r
a particular application.
V—voltage, V
V —voltage with respect to SRC, V NOTE 1—No reference cell calibration standards presently exist for
o
space applications, although procedures such as high-altitude balloon and
V —open-circuit voltage, V
oc
low-earth orbit flights are being used to calibrate such reference cells.
4. Summary of Test Method
6.1.2 A current measurement instrument (see 6.3) shall be
4.1 The performance test of a photovoltaic cell consists of
used to determine the I of the reference cell under the light
sc
measuring the electrical current versus voltage (I-V) charac-
source.
teristic of the cell while illuminated by a suitable light source.
6.2 Test Fixture— Both the cell to be tested and the
4.2 A calibrated photovoltaic reference cell (see 6.1) is used
reference cell are mounted in a fixture that meets the following
to determine the total irradiance during the test and to account
requirements.
for the spectral distribution of the light source.
6.2.1 The test fixture shall ensure a uniform lateral tempera-
4.3 Simulated sunlight is used as the light source for the
ture distribution to within 60.5°C during the performance
electrical performance measurement, and solar simulation
measurement.
requirements are defined in Specification E 927 (terrestrial
6.2.2 The test fixture shall include a provision for maintain-
applications) and Practice E 491 (space applications).
ing a constant cell temperature for both the reference cell and
4.4 The data from the measurements are corrected to stan-
the cell to be tested (see 7.6.1).
dard reporting conditions, or to optional user-specified report-
NOTE 2—When using pulsed or shuttered light sources, it is possible
ing conditions. The standard reporting conditions are defined in
that the cell temperature will increase upon initial illumination, even when
Table 1.
the cell temperature is controlled.
4.4.1 Measurement error caused by deviations of the irradi-
6.2.3 The test fixture, when placed in the simulated sunlight,
ance conditions from the SRC is corrected using the total
shall ensure that the field-of-view of both the reference cell and
irradiance measured with the reference cell and the spectral
the cell to be tested are identical.
mismatch parameter, M, which is determined in accordance
with Test Method E 973.
NOTE 3—Some solar simulators may have significant amounts of
4.4.2 Measurement error caused by deviation of the cell 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
temperature from the SRC is minimized by maintaining the cell
have similar reflectance and cosine-response characteristics.
temperature close to the required value (see 7.6.1).
6.2.4 A four-terminal connection (also known as a Kelvin
5. Significance and Use
connection, see Fig. 1) from the cell to be tested to the I-V
5.1 It is the intent of this test method to provide a recog-
measurement instrumentation (see 6.3-6.5) shall be used.
nized method for testing and reporting the electrical perfor-
6.3 Current Measurement Equipment— The instrument or
mance of photovoltaic cells.
instruments used to measure the cell current and the I of the
sc
5.2 The test results may be used for comparison of cells
reference cell shall have a resolution of at least 0.02 % of the
among a group of similar cells or to compare diverse designs,
maximum current encountered, and shall have a total error of
such as different manufacturers’ products. Repeated measure-
less than 0.1 % of the maximum current encountered.
ments of the same cell may be used to study changes in device
6.4 Voltage Measurement Equipment—The instrument or
performance.
instruments used to measure the cell voltage shall have a
5.3 This test method determines the electrical performance
resolution of at least 0.02 % of the maximum voltage encoun-
of a cell based upon the output power at a single instant of
tered, and shall have a total error of less than 0.1 % of the
maximum voltage encountered.
6.5 Variable Load— An electronic load, such as a variable
Wehrli, C., Extraterrestrial Solar Spectrum, Publ. No. 615, Physikalisch-
resistor or a programmable power supply, used to operate the
Meteorologisches Observatorium and World Radiation Center, Davos Switzerland,
1985. cell to be tested at different points along its I-V characteristic.
E 948
7.4 Mount the cell to be tested and the reference cell in the
test fixture.
NOTE 5—Any nonuniformity of irradiance (see Specification E 927)
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 If a pulsed or shuttered light source is used, expose the
test fixture to the source illumination.
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 E 927) is less than 0.1 %, the total
irradiance may be determined with the reference cell prior to
the performance measurement. In this case, use the following
steps to measure the total irradia
...