ASTM E2848-11
(Test Method)Standard Test Method for Reporting Photovoltaic Non-Concentrator System Performance
Standard Test Method for Reporting Photovoltaic Non-Concentrator System Performance
SIGNIFICANCE AND USE
Because there are a number of choices in this test method that depend on different applications and system configurations, it is the responsibility of the user of this test method to specify the details and protocol of an individual system power measurement prior to the beginning of a measurement.
Unlike device-level measurements that report performance at a fixed device temperature of 25°C, such as Test Methods E1036, this test method uses regression to a reference ambient air temperature.
System power values calculated using this test method are therefore much more indicative of the power a system actually produces compared with reporting performance at a relatively cold device temperature such as 25°C.
Using ambient temperature reduces the complexity of the data acquisition and analysis by avoiding the issues associated with defining and measuring the device temperature of an entire photovoltaic system.
The user of this test method must select the time period over which system data are collected, and the averaging interval for the data collection within the constraints of 8.3.
It is assumed that the system performance does not degrade or change during the data collection time period. This assumption influences the selection of the data collection period because system performance can have seasonal variations.
The irradiance shall be measured in the plane of the modules under test. If multiple planes exist (particularly in the case of rolling terrain), then the plane or planes in which irradiance measurement will occur must be reported with the test results. In the case where this test method is to be used for acceptance testing of a photovoltaic system or reporting of photovoltaic system performance for contractual purposes, the plane or planes in which irradiance measurement will occur must be agreed upon by the parties to the test prior to the start of the test.
Note 1—In general, the irradiance measurement should occur in the plane in which the...
SCOPE
1.1 This test method provides measurement and analysis procedures for determining the capacity of a specific photovoltaic system built in a particular place and in operation under natural sunlight.
1.2 This test method is used for the following purposes:
1.2.1 acceptance testing of newly installed photovoltaic systems,
1.2.2 reporting of dc or ac system performance, and
1.2.3 monitoring of photovoltaic system performance.
1.3 This test method should not be used for:
1.3.1 testing of individual photovoltaic modules for comparison to nameplate power ratings,
1.3.2 testing of individual photovoltaic modules or systems for comparison to other photovoltaic modules or systems,
1.3.3 testing of photovoltaic systems for the purpose of comparing the performance of photovoltaic systems located in different places.
1.4 In this test method, photovoltaic system power is reported with respect to a set of reporting conditions (RC) including: solar irradiance in the plane of the modules, ambient temperature, and wind speed (see Section 6). Measurements under a variety of reporting conditions are allowed to facilitate testing and comparison of results.
1.5 This test method assumes that the solar cell temperature is directly influenced by ambient temperature and wind speed; if not the regression results may be less meaningful.
1.6 This test method is not applicable to concentrator photovoltaic systems; as an alternative, Test Method E2527 should be considered for such systems.
1.7 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Standards Content (Sample)
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Designation: E2848 − 11
StandardTest Method for
Reporting Photovoltaic Non-Concentrator System
Performance
This standard is issued under the fixed designation E2848; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
1.1 This test method provides measurement and analysis
bility of regulatory limitations prior to use.
procedures for determining the capacity of a specific photovol-
taic system built in a particular place and in operation under
2. Referenced Documents
natural sunlight.
2.1 ASTM Standards:
1.2 This test method is used for the following purposes:
D6176 Practice for Measuring Surface Atmospheric Tem-
1.2.1 acceptance testing of newly installed photovoltaic
perature with Electrical Resistance Temperature Sensors
systems,
E772 Terminology of Solar Energy Conversion
1.2.2 reporting of dc or ac system performance, and
E824 Test Method for Transfer of Calibration From Refer-
1.2.3 monitoring of photovoltaic system performance.
ence to Field Radiometers
1.3 This test method should not be used for: E927 Specification for Solar Simulation for Photovoltaic
1.3.1 testing of individual photovoltaic modules for com-
Testing
parison to nameplate power ratings, E948 Test Method for Electrical Performance of Photovol-
1.3.2 testing of individual photovoltaic modules or systems
taic Cells Using Reference Cells Under Simulated Sun-
for comparison to other photovoltaic modules or systems, light
1.3.3 testing of photovoltaic systems for the purpose of
E973 Test Method for Determination of the Spectral Mis-
comparing the performance of photovoltaic systems located in match Parameter Between a Photovoltaic Device and a
different places.
Photovoltaic Reference Cell
E1036 Test Methods for Electrical Performance of Noncon-
1.4 In this test method, photovoltaic system power is
centrator Terrestrial Photovoltaic Modules and Arrays
reported with respect to a set of reporting conditions (RC)
Using Reference Cells
including:solarirradianceintheplaneofthemodules,ambient
E1040 Specification for Physical Characteristics of Noncon-
temperature, and wind speed (see Section 6). Measurements
centrator Terrestrial Photovoltaic Reference Cells
under a variety of reporting conditions are allowed to facilitate
E1125 Test Method for Calibration of Primary Non-
testing and comparison of results.
Concentrator Terrestrial Photovoltaic Reference Cells Us-
1.5 This test method assumes that the solar cell temperature
ing a Tabular Spectrum
is directly influenced by ambient temperature and wind speed;
E1362 Test Method for Calibration of Non-Concentrator
if not the regression results may be less meaningful.
Photovoltaic Secondary Reference Cells
1.6 This test method is not applicable to concentrator E2527 Test Method for Electrical Performance of Concen-
photovoltaic systems; as an alternative, Test Method E2527 trator Terrestrial Photovoltaic Modules and Systems Un-
should be considered for such systems. der Natural Sunlight
G138 Test Method for Calibration of a Spectroradiometer
1.7 The values stated in SI units are to be regarded as
Using a Standard Source of Irradiance
standard. No other units of measurement are included in this
G167 Test Method for Calibration of a Pyranometer Using a
standard.
Pyrheliometer
1.8 This standard does not purport to address all of the
G173 TablesforReferenceSolarSpectralIrradiances:Direct
safety concerns, if any, associated with its use. It is the
Normal and Hemispherical on 37° Tilted Surface
This test method is under the jurisdiction of ASTM Committee E44 on Solar,
GeothermalandOtherAlternativeEnergySources,andisthedirectresponsibilityof For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Subcommittee E44.09 on Photovoltaic Electric Power Conversion. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Current edition approved Nov. 1, 2011. Published December 2011. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/E2848-11. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2848 − 11
G183 Practice for Field Use of Pyranometers, Pyrheliom- 3.3.3 P—photovoltaic system power, ac or dc, W
eters and UV Radiometers
3.3.4 P —photovoltaic system power at RC, ac or dc, W
o
2.2 IEEE Standards:
3.3.5 T —ambient temperature, °C
a
IEEE 1526-2003 Recommended Practice for Testing the
3.3.6 T —RC rating temperature, °C
o
Performance of Stand-Alone Photovoltaic Systems
3.3.7 v—wind speed, m/s
IEEE 1547-2003 Standard for Interconnecting Distributed
Resources with Electric Power Systems
3.3.8 v —RC rating wind speed, m/s
o
2.3 International Standards Organization Standards:
3.3.9 p—p-value, a dimensionless quantity used to deter-
ISO/IEC Guide 98-1:2009 Uncertainty of measurement—
mine the significance of an individual regression coefficient to
Part 1: Introduction to the expression of uncertainty in
the overall rating result
measurement
3.3.10 SE—standard error, W
ISO/IEC Guide 98-3:2008 Uncertainty of measurement—
3.3.11 U —expanded uncertainty with a 95 % coverage
Part 3: Guide to the expression of uncertainty in measure- 95
probability of photovoltaic system power at RC, W
ment (GUM:1995)
2.4 World Meteorological Organization (WMO) Standard:
4. Summary of Test Method
WMO-No. 8 Guide to Meteorological Instruments and
Methods of Observation, Seventh Ed., 2008
4.1 Photovoltaic system power, solar irradiance, ambient
temperature, and wind speed data are collected over a defined
3. Terminology
period of time using a data acquisition system.
3.1 Definitions—Definitions of terms used in this test
4.2 Multiplelinearregressionisthenusedtofitthecollected
method may be found in Terminology E772, IEEE 1547-2003,
data to the performance equation (Eq 1) and thereby calculate
and ISO/IEC Guide 98-1:2009 and ISO/IEC Guide 98-3:2008.
the regression coefficients a , a , a , and a .
1 2 3 4
3.2 Definitions of Terms Specific to This Standard:
P 5 E a 1a ·E1a ·T 1a ·v (1)
~ !
1 2 3 a 4
3.2.1 averaging interval, n—the time interval over which
4.3 Substitution of the RC values E , T , and v into Eq 1
o o o
data is averaged to obtain one data point. The performance test
then gives the ac or dc power at the Reporting Conditions.
is performed using these averaged data.
P 5 E ~a 1a ·E 1a ·T 1a ·v ! (2)
o o 1 2 o 3 o 4 o
3.2.2 data collection period, n—the period of time defined
4.4 The collected input data and the performance at the
by the user of this test method during which system output
reporting conditions are then reported.
power, irradiance, ambient temperature, and wind speed are
measured and recorded for the purposes of a single regression
analysis. 5. Significance and Use
3.2.3 plane-of-array irradiance, POA, n—see solar 5.1 Because there are a number of choices in this test
irradiance, hemispherical in Tables G173.
method that depend on different applications and system
configurations, it is the responsibility of the user of this test
3.2.4 reporting conditions, RC, n—an agreed-upon set of
method to specify the details and protocol of an individual
conditions including the plane-of-array irradiance, ambient
system power measurement prior to the beginning of a mea-
temperature, and wind speed conditions to which photovoltaic
surement.
system performance are reported. The reporting conditions
must also state the type of radiometer used to measure the
5.2 Unlike device-level measurements that report perfor-
plane-of-array irradiance. In the case where this test method is
mance at a fixed device temperature of 25°C, such as Test
to be used for acceptance testing of a photovoltaic system or
Methods E1036, this test method uses regression to a reference
reporting of photovoltaic system performance for contractual
ambient air temperature.
purposes, RC shall be stated in the contract or agreed upon in
5.2.1 System power values calculated using this test method
writing by the parties to the acceptance testing and reporting
are therefore much more indicative of the power a system
prior to the start of the test.
actually produces compared with reporting performance at a
relatively cold device temperature such as 25°C.
3.2.5 sampling interval, n—the elapsed time between scans
5.2.2 Using ambient temperature reduces the complexity of
of the sensors used to measure power, irradiance, ambient
the data acquisition and analysis by avoiding the issues
temperatureandwindspeed.Individualdatapointsusedforthe
associated with defining and measuring the device temperature
performance test are averages of the values recorded in these
of an entire photovoltaic system.
scans. There are multiple sampling intervals in each averaging
5.2.3 The user of this test method must select the time
interval.
period over which system data are collected, and the averaging
3.2.6 utility grid, n—see electric power system in IEEE
interval for the data collection within the constraints of 8.3.
1547-2003.
5.2.4 It is assumed that the system performance does not
3.3 Symbols: The following symbols and units are used in
degrade or change during the data collection time period. This
this test method:
assumption influences the selection of the data collection
3.3.1 E—plane-of-array irradiance, W/m
period because system performance can have seasonal varia-
3.3.2 E —RC rating irradiance (plane-of-array), W/m tions.
o
E2848 − 11
NOTE 3—Historically, a specific case of RC known as “Performance
5.3 The irradiance shall be measured in the plane of the
Test Conditions”, or “PTC”, have been used commonly. PTC conditions
modules under test. If multiple planes exist (particularly in the
use plane-of-array irradiance equal to 1000 W/m , ambient temperature
case of rolling terrain), then the plane or planes in which
equal to 20°C, and wind speed equal to 1 m/s. The PTC parameters were
irradiance measurement will occur must be reported with the
based on the Nominal Terrestrial Environment (NTE) conditions that
test results. In the case where this test method is to be used for
define the Nominal Operating Cell Temperature (NOCT) of an individual
solar cell inside a module (see Annex A1 in Test Methods E1036).
acceptance testing of a photovoltaic system or reporting of
However, NTE differs from PTC in that it specifies a lower irradiance of
photovoltaic system performance for contractual purposes, the
800 W/m .
plane or planes in which irradiance measurement will occur
must be agreed upon by the parties to the test prior to the start
7. Apparatus
of the test.
7.1 Ambient Air Temperature Measurement Equipment—
NOTE 1—In general, the irradiance measurement should occur in the The instrument or instruments used to measure the ambient air
plane in which the majority of modules are oriented. Placing the
temperature shall have a resolution of at least 0.1°C, and shall
measurement device in a plane with a larger tilt than the majority will
have a total error of less than 61°C of reading. The sensor
cause apparent under-performance in the winter and over-performance in
should be mounted in the immediate vicinity of the photovol-
the summer.
taic system under test, but should not be so close to the
5.3.1 The linear regression results will be most reliable
modules as to be in the thermal boundary layer of the array.
when the measured irradiance, ambient temperature, and wind
The sensor shall be mounted with an aspirated radiation shield
speed data during the data collection period are distributed
as defined in 3.2.3 of Practice D6176. Practice D6176 contains
around the reporting conditions. When this is not the case, the
additionalguidanceforambientairtemperaturemeasurements.
reported power will be an extrapolation to the reporting
7.2 Irradiance Measurement Equipment—The irradiance
conditions.
measurement equipment shall be mounted coplanar (to within
5.4 Accumulation of dirt (soiling) on the photovoltaic mod-
1 degree) with the photovoltaic system under test and shall be
ules can have a significant impact on the system rating. The
connected to a data acquisition system. The equipment should
user of this test may want to eliminate or quantify the level of
be mounted in a location that minimizes, and ideally
soiling on the modules prior to conducting the test.
eliminates, shading of and reflections on the instrument.
7.2.1 A calibrated hemispherical pyranometer (instruments
5.5 Repeated regression calculations on the same system to
with fields-of-view approaching 180°, see Terminology E772)
the same RC and using the same type of irradiance measure-
is the most common choice for measurement of the incident
ment device over successive data collection periods can be
solar irradiance. Pyranometers used in this test shall be
used to monitor performance changes as a function of time.
calibrated using Test Method E824 or Test Method G167. Test
Method E E824 is a transfer calibration from a reference to a
6. Reporting Conditions
field pyranometer, while Test Method G167 involves calibra-
6.1 The user of this test method shall select an appropriate
tion against either of two types of narrow field-of-view
RC prior to the start of the test. In the case where this test
pyrheliometers.The uncertainty of the pyranometer calibration
method is to be used for acceptance testing of a photovoltaic
is a function of the calibration method, with the Type I
system or reporting of photovoltaic system performance for
calibration in Test Method G167 giving the lowest uncertainty.
contractual purposes, the RC must be agreed upon by the
7.2.2 Pyranometers are sensitive to both temperature and
parties to the test prior to the start of the test.
the angle of incidence of irradiance, so may require measure-
6.1.1 Choose RC irradiance and ambient air temperature
ment of device temperature and angle of incidence during the
values that are representative of the in-plane irradiance and
data collection period. It is recommended that pyranometer
ambient air temperature expected for the system location for a
responsivitybecharacterizedtotheextentpracticable.Sections
clear day in the data collection period. Irradiance conditions
5.5, 5.5.1, 5.5.2, and 5.5.3 in Practice G183, describes pyra-
can be evaluated based on a year-long hourly dataset of
nometercharacteristicswhichinfluencethelevelofuncertainty
projected POAvalues calculated from histori
...
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