ASTM E2939-13(2018)
(Practice)Standard Practice for Determining Reporting Conditions and Expected Capacity for Photovoltaic Non-Concentrator Systems
Standard Practice for Determining Reporting Conditions and Expected Capacity for Photovoltaic Non-Concentrator Systems
SIGNIFICANCE AND USE
5.1 This practice can be used to determine an expected capacity for an existing or a proposed photovoltaic system in a particular location during a specified period of time (see data collection period in Test Method E2848).
5.2 The expected capacity calculated in accordance with this practice can be compared with the capacity measured according to Test Method E2848 when the RC are the same.
5.3 The comparison of expected capacity and measured capacity can be used as a criterion for plant acceptance.
5.4 The user of this practice must select the performance simulation period over which the reporting conditions and expected capacity will be derived. Seasonal variations will likely cause both of these to change with differing performance simulation periods.
5.5 When this practice is used in conjunction with Test Method E2848, the performance simulation period and the data collection period must agree. If they do not agree, the comparison between expected and measured capacity will not be meaningful.
5.6 Historical or measured5 plane-of-array irradiance, ambient air temperature and wind speed data can be used to select reporting conditions and calculate expected capacity. If historical data are used, the data collection period should match the time period of the measured data in terms of season and length.
5.7 The simulated power output that is used to calculate the expected capacity should be derived from a performance model designed to represent the photovoltaic system which will be reported per Test Method E2848.
SCOPE
1.1 This practice provides procedures for determining the expected capacity of a specific photovoltaic system in a specific geographical location that is in operation under natural sunlight during a specified period of time. The expected capacity is intended for comparison with the measured capacity determined by Test Method E2848.
1.2 This practice is intended for use with Test Method E2848 as a procedure to select appropriate reporting conditions (RC), including solar irradiance in the plane of the modules, ambient temperature, and wind speed, needed for the photovoltaic system capacity measurement.
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
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Designation: E2939 − 13 (Reapproved 2018) An American National Standard
Standard Practice for
Determining Reporting Conditions and Expected Capacity
for Photovoltaic Non-Concentrator Systems
This standard is issued under the fixed designation E2939; 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 2.2 IEEE Standards:
IEEE 1547-2003 Standard for Interconnecting Distributed
1.1 This practice provides procedures for determining the
Resources with Electric Power Systems
expected capacity of a specific photovoltaic system in a
specific geographical location that is in operation under natural
3. Terminology
sunlight during a specified period of time. The expected
3.1 Definitions of terms used in this practice may be found
capacity is intended for comparison with the measured capacity
in Terminology E772, IEEE 1547-2003, and Test Method
determined by Test Method E2848.
E2848.
1.2 This practice is intended for use with Test Method
3.2 Definitions:
E2848 as a procedure to select appropriate reporting conditions
3.2.1 expected capacity, photovoltaic system, n—the pre-
(RC), including solar irradiance in the plane of the modules,
dicted power rating that is derived from meteorological data
ambient temperature, and wind speed, needed for the photo-
and a performance model that describes a specific PV system in
voltaic system capacity measurement.
a specific location and time period.
1.3 The values stated in SI units are to be regarded as
3.2.2 measured capacity, photovolaic system, n—the output
standard. No other units of measurement are included in this
power of a photovoltaic system measured according to Test
standard.
Method E2848.
1.4 This standard does not purport to address all of the
3.2.3 performance model, photovoltaic system, n—a com-
safety concerns, if any, associated with its use. It is the
puter model which, at a minimum, simulates the operation of a
responsibility of the user of this standard to establish appro-
particular photovoltaic system using plane-of-array irradiance,
priate safety, health, and environmental practices and deter-
ambient temperature and wind speed data as inputs to calculate
mine the applicability of regulatory limitations prior to use.
the instantaneous, simulated power output.
1.5 This international standard was developed in accor-
3.2.4 performance simulation period, photovoltaic system,
dance with internationally recognized principles on standard-
n—the period of time over which a single expected capacity
ization established in the Decision on Principles for the
prediction is performed. Compare with data collection period
Development of International Standards, Guides and Recom-
in Test Method E2848.
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
3.2.5 plane-of-array irradiance, POA, n—see solar
irradiance, hemispherical in Terminology E772.
2. Referenced Documents
3.2.6 simulated power output, photovoltaic system,
2.1 ASTM Standards:
n—photovoltaic system power output derived from meteoro-
E772 Terminology of Solar Energy Conversion
logical data and a performance model.
E2848 Test Method for Reporting Photovoltaic Non-
3.2.7 time resolution, meteorological data, n—the time
Concentrator System Performance
interval between individual meteorological data points that has
a maximum averaging interval of 1 h, used to calculate both the
reporting conditions and the expected capacity.
This practice is under the jurisdiction of ASTM Committee E44 on Solar,
Geothermal and Other Alternative Energy Sources and is the direct responsibility of
Subcommittee E44.09 on Photovoltaic Electric Power Conversion. 4. Summary of Practice
Current edition approved May 1, 2018. Published September 2013. Originally
4.1 Test Method E2848 provides a procedure to measure the
approved in 2013. Last previous edition approved in 2013 as E2939-13. DOI:
10.1520/E2939-13R18 capacity of a photovoltaic system. The procedure involves a
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on Available from Institute of Electrical and Electronics Engineers, Inc. (IEEE),
the ASTM website. 445 Hoes Ln., Piscataway, NJ 08854, http://www.ieee.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2939 − 13 (2018)
multiple linear regression of output power as a function of 5.4 The user of this practice must select the performance
plane-of-array irradiance, ambient air temperature, and wind simulation period over which the reporting conditions and
speed data collected during the data collection period, which is expected capacity will be derived. Seasonal variations will
a relatively short time period, typically between 3 and 30 days. likely cause both of these to change with differing performance
Using the regression results, the expected capacity (in watts) is simulation periods.
then calculated by substitution of a set of reporting conditions
5.5 When this practice is used in conjunction with Test
consisting of plane-of-array irradiance, ambient air
Method E2848, the performance simulation period and the data
temperature, and wind speed appropriate for the system under
collection period must agree. If they do not agree, the com-
test into the regression equation.
parison between expected and measured capacity will not be
4.2 Although Test Method E2848 states that its procedure is meaningful.
suitable for acceptance testing of newly installed photovoltaic
5.6 Historical or measured plane-of-array irradiance, am-
systems (i.e. acceptance testing), it provides only general
bient air temperature and wind speed data can be used to select
guidance for the selection of the reporting conditions and no
reporting conditions and calculate expected capacity. If histori-
guidance for predicting expected capacity prior to test. Both
cal data are used, the data collection period should match the
the reporting conditions and the expected capacity are neces-
time period of the measured data in terms of season and length.
sary for acceptance testing.
5.7 The simulated power output that is used to calculate the
4.3 This practice provides guidance for selecting the report-
expected capacity should be derived from a performance model
ing conditions needed for Test Method E2848. This practice
designed to represent the photovoltaic system which will be
also provides a procedure for determining the expected capac-
reported per Test Method E2848.
ity of a photovoltaic system.
6. Meteorological Data Procurement
4.4 The procedure for determining expected capacity con-
6.1 Select a meteorological data set that includes at a
sists of the following steps:
minimum, plane-of-array irradiance, ambient temperature and
4.4.1 Procure meteorological data that will be representa-
wind speed for a minimum of 5 contiguous days. This dataset
tive of the POA irradiance, ambient air temperature, and wind
will be used to calculate reporting conditions and expected
speed conditions during the data collection period.
capacity. Another disadvantage is that historical data is rarely
4.4.1.1 This is best accomplished by using meteorological
measured in the plan-of-array. Therefore, the data will have to
data that is of the same time of year and same weather
be transposed into the plane-of-array which will have errors
conditions seen or expected to be seen during E2848.
when compared to actual measurements. Historical or mea-
4.4.2 Procure or develop a performance model representa-
sured meteorological data may be used to calculate reporting
tive of the photovoltaic system,
conditions and expected capacity. Both have advantages and
4.4.3 Substitute the meteorological data into the perfor-
disadvantages.
mance model to calculate the instantaneous, simulated power
output of the photovoltaic system, and
6.2 The advantage of using historical data to calculate
4.4.4 Use the data set to calculate the expected capacity
reporting conditions is that the reporting con
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E2939 − 13 E2939 − 13 (Reapproved 2018)
Standard Practice for
Determining Reporting Conditions and Expected Capacity
for Photovoltaic Non-Concentrator Systems
This standard is issued under the fixed designation E2939; 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
1.1 This practice provides procedures for determining the expected capacity of a specific photovoltaic system in a specific
geographical location that is in operation under natural sunlight during a specified period of time. The expected capacity is intended
for comparison with the measured capacity determined by Test Method E2848.
1.2 This practice is intended for use with Test Method E2848 as a procedure to select appropriate reporting conditions (RC),
including solar irradiance in the plane of the modules, ambient temperature, and wind speed, needed for the photovoltaic system
capacity measurement.
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
E772 Terminology of Solar Energy Conversion
E2848 Test Method for Reporting Photovoltaic Non-Concentrator System Performance
2.2 IEEE Standards:
IEEE 1547-2003 Standard for Interconnecting Distributed Resources with Electric Power Systems
3. Terminology
3.1 Definitions of terms used in this practice may be found in Terminology E772, IEEE 1547-2003, and Test Method E2848.
3.2 Definitions:
3.2.1 expected capacity, photovoltaic system, n—the predicted power rating that is derived from meteorological data and a
performance model that describes a specific PV system in a specific location and time period.
3.2.2 measured capacity, photovolaic system, n—the output power of a photovoltaic system measured according to Test Method
E2848.
3.2.3 performance model, photovoltaic system, n—a computer model which, at a minimum, simulates the operation of a
particular photovoltaic system using plane-of-array irradiance, ambient temperature and wind speed data as inputs to calculate the
instantaneous, simulated power output.
3.2.4 performance simulation period, photovoltaic system, n—the period of time over which a single expected capacity
prediction is performed. Compare with data collection period in Test Method E2848.
This practice is under the jurisdiction of ASTM Committee E44 on Solar, Geothermal and Other Alternative Energy Sources and is the direct responsibility of
Subcommittee E44.09 on Photovoltaic Electric Power Conversion.
Current edition approved Sept. 1, 2013May 1, 2018. Published September 2013. DOI: 10.1520/E2939-13Originally approved in 2013. Last previous edition approved in
2013 as E2939-13. DOI: 10.1520/E2939-13R18
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Available from Institute of Electrical and Electronics Engineers, Inc. (IEEE), 445 Hoes Ln., Piscataway, NJ 08854, http://www.ieee.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2939 − 13 (2018)
3.2.5 plane-of-array irradiance, POA, n—see solar irradiance, hemispherical in Terminology E772.
3.2.6 simulated power output, photovoltaic system, n—photovoltaic system power output derived from meteorological data and
a performance model.
3.2.7 time resolution, meteorological data, n—the time interval between individual meteorological data points that has a
maximum averaging interval of 1 h, used to calculate both the reporting conditions and the expected capacity.
4. Summary of Practice
4.1 Test Method E2848 provides a procedure to measure the capacity of a photovoltaic system. The procedure involves a
multiple linear regression of output power as a function of plane-of-array irradiance, ambient air temperature, and wind speed data
collected during the data collection period, which is a relatively short time period, typically between 3 and 30 days. Using the
regression results, the expected capacity (in watts) is then calculated by substitution of a set of reporting conditions consisting of
plane-of-array irradiance, ambient air temperature, and wind speed appropriate for the system under test into the regression
equation.
4.2 Although Test Method E2848 states that its procedure is suitable for acceptance testing of newly installed photovoltaic
systems (i.e. acceptance testing), it provides only general guidance for the selection of the reporting conditions and no guidance
for predicting expected capacity prior to test. Both the reporting conditions and the expected capacity are necessary for acceptance
testing.
4.3 This practice provides guidance for selecting the reporting conditions needed for Test Method E2848. This practice also
provides a procedure for determining the expected capacity of a photovoltaic system.
4.4 The procedure for determining expected capacity consists of the following steps:
4.4.1 Procure meteorological data that will be representative of the POA irradiance, ambient air temperature, and wind speed
conditions during the data collection period.
4.4.1.1 This is best accomplished by using meteorological data that is of the same time of year and same weather conditions
seen or expected to be seen during E2848.
4.4.2 Procure or develop a performance model representative of the photovoltaic system,
4.4.3 Substitute the meteorological data into the performance model to calculate the instantaneous, simulated power output of
the photovoltaic system, and
4.4.4 Use the data set to calculate the expected capacity according to Section 9 of Test Method E2848.
4.5 The expected capacity can then be compared with the capacity measured during an acceptance test of a photovoltaic system,
if both capacities are determined from the same reporting conditions.
5. Significance and Use
5.1 This practice can be used to determine an expected capacity for an existing or a proposed photovoltaic system in a particular
location during a specified period of time (see data collection period in Test Method E2848).
5.2 The expected capacity calculated in accordance with this practice can be compared with the capacity measured according
to Test Method E2848 when the RC are the same.
5.3 The comparison of expected capacity and measured capacity can be used as a criterion for plant acceptance.
5.4 The user of this practice must select the performance simulation period over which the reporting conditions and expected
capacity will be derived. Seasonal variations will likely cause both of these to change with differing performance simulation
periods.
5.5 When this practice is used in conjunction with Test Method E2848, the performance simulation period and the data
collection period must agree. If they do not agree, the comparison between expected and measured capacity will not be meaningful.
5.6 Historical or measured plane-of-array irradiance, ambient air temperature and wind speed data can be used to select
reporting conditions and calculate expected capacity. If historical data are used, the data collection period should match the time
period of the measured data in terms of season and length.
5.7 The simulated power output that is used to calc
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