ASTM E2939-13(2023)

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.

General Information

• Status: Published
• Publication Date: 31-Jul-2023
• ICS: 27.160 - Solar energy engineering
• Technical Committee: E44 - Solar, Geothermal and Other Alternative Energy Sources
• Drafting Committee: E44.09 - Photovoltaic Electric Power Conversion

Relations

• Refers: ASTM E772-13 - Standard Terminology of Solar Energy Conversion
• Effective Date: 01-Sep-2013
• Refers: ASTM E2848-13 - Standard Test Method for Reporting Photovoltaic Non-Concentrator System Performance
• Effective Date: 01-Sep-2013
• Refers: ASTM E2848-11e1 - Standard Test Method for Reporting Photovoltaic Non-Concentrator System Performance
• Effective Date: 01-Nov-2011
• Refers: ASTM E2848-11 - Standard Test Method for Reporting Photovoltaic Non-Concentrator System Performance
• Effective Date: 01-Nov-2011
• Refers: ASTM E772-11 - Standard Terminology of Solar Energy Conversion
• Effective Date: 01-Sep-2011
• Refers: ASTM E772-05 - Standard Terminology Relating to Solar Energy Conversion
• Effective Date: 01-Apr-2005
• Refers: ASTM E772-87(1993)e1 - Standard Terminology Relating to Solar Energy Conversion
• Effective Date: 27-Feb-1987
• Refers: ASTM E772-87(2001) - Standard Terminology Relating to Solar Energy Conversion
• Effective Date: 27-Feb-1987

Overview

ASTM E2939-13(2023), "Standard Practice for Determining Reporting Conditions and Expected Capacity for Photovoltaic Non-Concentrator Systems," provides standardized procedures for calculating and reporting the expected capacity of photovoltaic (PV) systems operating under natural sunlight in specific geographical locations and periods. This standard is essential for organizations and professionals involved in the performance assessment, commissioning, and acceptance testing of PV installations. It supports consistent comparisons between predicted and measured system capacities, ensuring reliable performance evaluation and system verification.

Key Topics

• Expected Capacity Determination
  The standard outlines how to derive the expected power rating of a specific PV system by applying meteorological data (such as plane-of-array irradiance, ambient temperature, and wind speed) and system-specific performance models. This data helps predict operational output for given periods.

• Selection of Reporting Conditions
  Reporting conditions, including solar irradiance, temperature, and wind speed, are critical for consistent system capacity measurement. The standard provides guidance on selecting these conditions based on historical or measured meteorological data, aligned with the duration of the performance simulation period.

• Performance Simulation and Data Alignment
  It is essential for the simulation period and data collection period (referenced in ASTM E2848) to match. Misalignment can render capacity comparisons invalid.

• Comparison for Acceptance Testing
  By comparing the expected capacity (predictive) against the measured capacity (actual, as per ASTM E2848), stakeholders can determine if a new or existing PV plant meets acceptance criteria.

• Documentation and Reporting
  The standard also specifies minimal reporting requirements, including descriptions of the modeling approach, resource data sources, meteorological parameters used, and the statistical quality of regressions applied.

Applications

This standard has significant practical value for:

• PV System Commissioning & Acceptance
  Ensures that newly installed systems are tested against robust, location-specific capacity expectations, supporting fair acceptance testing and contract fulfillment.

• Performance Benchmarking
  Enables consistent benchmarking and comparison between expected and measured outputs, contributing to operational transparency and system optimization.

• Quality Assurance
  Facilitates quality control in ongoing operations by verifying that existing PV systems perform within expectations tied to historical meteorological conditions.

• Reporting Transparency
  Provides a clear methodology for documenting and communicating expected versus actual performance to stakeholders, investors, or regulatory bodies.

• Design and Planning
  Useful in project planning for predicting performance, aiding in feasibility studies and investment decisions using robust, data-driven metrics.

Related Standards

• ASTM E2848 - Test Method for Reporting Photovoltaic Non-Concentrator System Performance. This is a companion document detailing the measurement of PV system output, which should be used in conjunction with ASTM E2939.
• ASTM E772 - Terminology of Solar Energy Conversion. Reference for definitions relevant to PV systems and meteorological factors.
• IEEE 1547 - Standard for Interconnecting Distributed Resources with Electric Power Systems. Provides requirements for the safe interconnection of PV systems.
• International Standards Principles - Developed following internationally recognized guidelines per the World Trade Organization TBT Committee.

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Keywords: photovoltaic capacity reporting, ASTM E2939, PV system expected capacity, acceptance testing, performance modeling, reporting conditions, non-concentrator photovoltaic systems, meteorological data analysis, ASTM PV standards.

Standards Content (Sample)

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.
Designation: E2939 − 13 (Reapproved 2023) 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 photovol-
and a performance model that describes a specific PV system in
taic 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 calcu-
mine the applicability of regulatory limitations prior to use.
late 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
This practice is under the jurisdiction of ASTM Committee E44 on Solar, reporting conditions and the expected capacity.
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 Aug. 1, 2023. Published August 2023. Originally
4.1 Test Method E2848 provides a procedure to measure the
approved in 2013. Last previous edition approved in 2018 as E2939 – 13 (2018).
DOI: 10.1520/E2939-13R23.
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 [e-mail]. 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 (2023)
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 three and 30 likely cause both of these to change with differing performance
days. Using the regression results, the expected capacity (in simulation periods.
watts) is then calculated by substitution of a set of reporting
5.5 When this practice is used in conjunction with Test
conditions 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
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 five contiguous days. This data
tive of the POA irradiance, ambient air temperature, and wind
set 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 plane-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 Test Method
when compared to actual measurements. Historical or mea-
E2848.
sured meteorological data may be used to calculate reporting
4.4.2 Procure or develop a performance model representa-
conditions and expected capacity. Both have advantages and
tive of the photovoltaic system,
disadvantages.
4.4.3 Substitute the meteorological data into the perfor-
mance model to calculate the instantaneous, simulated power
6.2 The advantage of using historical data to calculate
output of the photovoltaic system, and
reporting co
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