ASTM E2848-13(2018)

Standard Test Method for Reporting Photovoltaic Non-Concentrator System Performance

SIGNIFICANCE AND USE
5.1 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.  
5.2 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.  
5.2.1 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.  
5.2.2 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.  
5.2.3 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.  
5.2.4 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.  
5.3 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 measurem...
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 The capacity measured according to this test method should not be used to make representations about the energy generation capabilities of the system.  
1.7 This test method is not applicable to concentrator photovoltaic systems; as an alternative, Test Method E2527 should be considered for such systems.  
1.8 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.9 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...

General Information

• Status: Historical
• Publication Date: 30-Apr-2018
• ICS: 27.160 - Solar energy engineering
• Technical Committee: E44 - Solar, Geothermal and Other Alternative Energy Sources
• Drafting Committee: E44.09 - Photovoltaic Electric Power Conversion

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: E2848 − 13 (Reapproved 2018) An American National Standard
Standard Test 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 1.8 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this
1.1 This test method provides measurement and analysis
standard.
procedures for determining the capacity of a specific photovol-
1.9 This standard does not purport to address all of the
taic system built in a particular place and in operation under
safety concerns, if any, associated with its use. It is the
natural sunlight.
responsibility of the user of this standard to establish appro-
1.2 This test method is used for the following purposes:
priate safety, health, and environmental practices and deter-
1.2.1 acceptance testing of newly installed photovoltaic
mine the applicability of regulatory limitations prior to use.
systems,
1.10 This international standard was developed in accor-
1.2.2 reporting of dc or ac system performance, and
dance with internationally recognized principles on standard-
1.2.3 monitoring of photovoltaic system performance.
ization established in the Decision on Principles for the
1.3 This test method should not be used for:
Development of International Standards, Guides and Recom-
1.3.1 testing of individual photovoltaic modules for com-
mendations issued by the World Trade Organization Technical
parison to nameplate power ratings,
Barriers to Trade (TBT) Committee.
1.3.2 testing of individual photovoltaic modules or systems
2. Referenced Documents
for comparison to other photovoltaic modules or systems,
1.3.3 testing of photovoltaic systems for the purpose of
2.1 ASTM Standards:
comparing the performance of photovoltaic systems located in
D6176 Practice for Measuring Surface Atmospheric Tem-
different places.
perature with Electrical Resistance Temperature Sensors
E772 Terminology of Solar Energy Conversion
1.4 In this test method, photovoltaic system power is
E824 Test Method for Transfer of Calibration From Refer-
reported with respect to a set of reporting conditions (RC)
ence to Field Radiometers
including: solar irradiance in the plane of the modules, ambient
E927 Specification for Solar Simulation for Photovoltaic
temperature, and wind speed (see Section 6). Measurements
Testing
under a variety of reporting conditions are allowed to facilitate
E948 Test Method for Electrical Performance of Photovol-
testing and comparison of results.
taic Cells Using Reference Cells Under Simulated Sun-
1.5 This test method assumes that the solar cell temperature
light
is directly influenced by ambient temperature and wind speed;
E973 Test Method for Determination of the Spectral Mis-
if not the regression results may be less meaningful.
match Parameter Between a Photovoltaic Device and a
1.6 The capacity measured according to this test method Photovoltaic Reference Cell
E1036 Test Methods for Electrical Performance of Noncon-
should not be used to make representations about the energy
generation capabilities of the system. centrator Terrestrial Photovoltaic Modules and Arrays
Using Reference Cells
1.7 This test method is not applicable to concentrator
E1040 Specification for Physical Characteristics of Noncon-
photovoltaic systems; as an alternative, Test Method E2527
centrator Terrestrial Photovoltaic Reference Cells
should be considered for such systems.
E1125 Test Method for Calibration of Primary Non-
Concentrator Terrestrial Photovoltaic Reference Cells Us-
ing a Tabular Spectrum
This test method 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. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved May 1, 2018. Published May 2018. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 2011. Last previous edition approved in 2013 as E2848-13. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/E2848-13R18. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2848 − 13 (2018)
E1362 Test Methods for Calibration of Non-Concentrator 3.2.5 sampling interval, n—the elapsed time between scans
Photovoltaic Non-Primary Reference Cells of the sensors used to measure power, irradiance, ambient
E2527 Test Method for Electrical Performance of Concen- temperature and wind speed. Individual data points used for the
trator Terrestrial Photovoltaic Modules and Systems Un- performance test are averages of the values recorded in these
der Natural Sunlight scans. There are multiple sampling intervals in each averaging
G138 Test Method for Calibration of a Spectroradiometer interval.
Using a Standard Source of Irradiance
3.2.6 utility grid, n—see electric power system in IEEE
G167 Test Method for Calibration of a Pyranometer Using a
1547-2003.
Pyrheliometer
3.3 Symbols: The following symbols and units are used in
G173 Tables for Reference Solar Spectral Irradiances: Direct
this test method:
Normal and Hemispherical on 37° Tilted Surface
−1
3.3.1 α—reference cell I temperature coefficient, °C
G183 Practice for Field Use of Pyranometers, Pyrheliom-
SC
eters and UV Radiometers
3.3.2 a , a , a , a —linear regression coefficients, arbitrary
1 2 3 4
2.2 IEEE Standards:
3.3.3 a, b, c, d—spectral mismatch factor calibration
IEEE 1526-2003 Recommended Practice for Testing the
constants, arbitrary
Performance of Stand-Alone Photovoltaic Systems
2 −1
3.3.4 C—reference cell calibration constant, Am W
IEEE 1547-2003 Standard for Interconnecting Distributed
Resources with Electric Power Systems
3.3.5 C —reference cell calibration constant at SRC,
o
2 −1
Am W
2.3 International Standards Organization Standards:
ISO/IEC Guide 98-1:2009 Uncertainty of measurement—
3.3.6 E—plane-of-array irradiance, W/m
Part 1: Introduction to the expression of uncertainty in
3.3.7 E —irradiance at SRC, plane-of-array, W/m
o
measurement
ISO/IEC Guide 98-3:2008 Uncertainty of measurement— 3.3.8 E (λ)—reference spectral irradiance distribution,
o
−2
−1
Part 3: Guide to the expression of uncertainty in measure- Wm nm
ment (GUM:1995)
3.3.9 E —RC rating irradiance, plane-of-array, W/m
RC
2.4 World Meteorological Organization (WMO) Standard:
−2
3.3.10 E (λ)—spectral irradiance distribution at RC, Wm
RC
WMO-No. 8 Guide to Meteorological Instruments and
−1
nm
Methods of Observation, Seventh Ed., 2008
3.3.11 E (λ)—spectral irradiance distribution, test light
T
−2 −1
source, Wm nm
3. Terminology
3.3.12 F—fractional error in short-circuit current, dimen-
3.1 Definitions—Definitions of terms used in this test
sionless
method may be found in Terminology E772, IEEE 1547-2003,
and ISO/IEC Guide 98-1:2009 and ISO/IEC Guide 98-3:2008.
3.3.13 I —short-circuit current, A
SC
3.2 Definitions of Terms Specific to This Standard:
3.3.14 M—spectral mismatch factor, dimensionless
3.2.1 averaging interval, n—the time interval over which
3.3.15 p—p-value, dimensionless quantity used to deter-
data are averaged to obtain one data point. The performance
mine the significance of an individual regression coefficient to
test uses these averaged data.
the overall rating result
3.2.2 data collection period, n—the period of time defined
3.3.16 P—photovoltaic system power, ac or dc, W
by the user of this test method during which system output
power, irradiance, ambient temperature, and wind speed are
3.3.17 P —photovoltaic system power at RC, ac or dc, W
RC
measured and recorded for the purposes of a single regression
3.3.18 RC—reporting conditions
analysis.
3.3.19 R (λ)—reference cell spectral responsivity, A/W
R
3.2.3 plane-of-array irradiance, POA, n—see solar
irradiance, hemispherical in Tables G173.
3.3.20 R (λ)—test device spectral responsivity, A/W
T
3.2.4 reporting conditions, RC, n—an agreed-upon set of
3.3.21 SRC—standard reporting conditions
conditions including the plane-of-array irradiance, ambient
3.3.22 SE—standard error, W
temperature, and wind speed conditions to which photovoltaic
3.3.23 T —ambient temperature, °C
system performance are reported. The reporting conditions
a
must also state the type of radiometer used to measure the
3.3.24 T —RC rating temperature, °C
RC
plane-of-array irradiance. In the case where this test method is
3.3.25 U —expanded uncertainty with a 95 % coverage
to be used for acceptance testing of a photovoltaic system or 95
probability of photovoltaic system power at RC, W
reporting of photovoltaic system performance for contractual
purposes, RC, or the method that will be used to derive the RC,
3.3.26 λ—wavelength, nm
shall be stated in the contract or agreed upon in writing by the
3.3.27 v—wind speed, m/s
parties to the acceptance testing and reporting prior to the start
of the test. 3.3.28 v —RC rating wind speed, m/s
RC
E2848 − 13 (2018)
4. Summary of Test Method 5.3.1 The linear regression results will be most reliable
when the measured irradiance, ambient temperature, and wind
4.1 Photovoltaic system power, solar irradiance, ambient
speed data during the data collection period are distributed
temperature, and wind speed data are collected over a defined
around the reporting conditions. When this is not the case, the
period of time using a data acquisition system.
reported power will be an extrapolation to the reporting
4.2 Multiple linear regression is then used to fit the collected
conditions.
data to the performance equation (Eq 1) and thereby calculate
5.4 Accumulation of dirt (soiling) on the photovoltaic mod-
the regression coefficients a , a , a , and a .
1 2 3 4
ules can have a significant impact on the system rating. The
P 5 E~a 1a · E1a · T 1a · v! (1)
1 2 3 a 4
user of this test may want to eliminate or quantify the level of
4.3 Substitution of the RC values E , T , and v into Eq 1 soiling on the modules prior to conducting the test.
o o o
then gives the ac or dc power at the reporting conditions.
5.5 Repeated regression calculations on the same system to
P 5 E ~a 1a · E 1a · T 1a · v ! (2) the same RC and using the same type of irradiance measure-
RC RC 1 2 RC 3 RC 4 RC
ment device over successive data collection periods can be
4.4 The collected input data and the performance at the
used to monitor performance changes as a function of time.
reporting conditions are then reported.
5.6 Capacity determinations are power measurements and
5. Significance and Use
are adequate to demonstrate system completeness. However, a
single capacity measurement does not provide sufficient infor-
5.1 Because there are a number of choices in this test
mation to project the energy generation potential of the system
method that depend on different applications and system
over time. Factors that may affect energy generation over time
configurations, it is the responsibility of the user of this test
include: module power degradation, inverter clipping and
method to specify the details and protocol of an individual
overloading, shading, backtracking, extreme orientations, and
system power measurement prior to the beginning of a mea-
filtering criteria.
surement.
5.2 Unlike device-level measurements that report perfor-
6. Reporting Conditions
mance at a fixed device temperature of 25°C, such as Test
6.1 The user of this test method shall select appropriate RC.
Methods E1036, this test method uses regression to a reference
In the case where this test method is to be used for acceptance
ambient air temperature.
testing of a photovoltaic system or reporting of photovoltaic
5.2.1 System power values calculated using this test method
system performance for contractual purposes, the RC, or the
are therefore much more indicative of the power a system
method that will be used to derive the RC, must be agreed upon
actually produces compared with reporting performance at a
by the parties to the test.
relatively cold device temperature such as 25°C.
6.1.1 Reporting conditions may be selected either on the
5.2.2 Using ambient temperature reduces the complexity of
basis of expected conditions or actual conditions during the
the data acquisition and analysis by avoiding the issues
data collection period. Choose RC irradiance and ambient air
associated with defining and measuring the device temperature
temperature values that are representative of the POA irradi-
of an entire photovoltaic system.
ance and ambient air temperature for the system location for a
5.2.3 The user of this test method must select the time
clear day in the data collection period. When the selection is
period over which system data are collected, and the averaging
based on expected conditions, irradiance can be evaluated from
interval for the data collection within the constraints of 8.3.
a year-long hourly dataset of projected POA values calculated
5.2.4 It is assumed that the system performance does not
from historical data measured directly on the system site or at
degrade or change during the data collection time period. This
a nearby site. Ambient temperatures can be evaluated by a
assumption influences the selection of the data collection
review of historical data from the site or a nearby location.
period because system performance can have seasonal varia-
Reporting conditions should be chosen such that the system is
tions.
not subject to frequent shading, inverter clipping or other
5.3 The irradiance shall be measured in the plane of the
non-linear operation at or around the RC. For instance, in
modules under test. If multiple planes exist (particularly in the
larger photovoltaic systems, the ratio of installed DC capacity
case of rolling terrain), then the plane or planes in which
to AC inverter capacity may be such that the inverter limits the
irradiance measurement will occur must be reported with the
production of the modules under certain conditions. If this is
test results. In the case where this test method is to be used for
the case, care should be taken to choose a reference within the
acceptance testing of a photovoltaic system or reporting of
normal operating range of the inverters.
photovoltaic system performance for contractual purposes, the
NOTE 2—There are many publicly-available irradia
...

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: E2848 − 13 E2848 − 13 (Reapproved 2018)
Standard Test 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
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 The capacity measured according to this test method should not be used to make representations about the energy generation
capabilities of the system.
1.7 This test method is not applicable to concentrator photovoltaic systems; as an alternative, Test Method E2527 should be
considered for such systems.
1.8 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.9 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.
1.10 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:
D6176 Practice for Measuring Surface Atmospheric Temperature with Electrical Resistance Temperature Sensors
E772 Terminology of Solar Energy Conversion
E824 Test Method for Transfer of Calibration From Reference to Field Radiometers
This test method 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 2013May 2018. Originally approved in 2011. Last previous edition approved in 20112013 as
ε1
E2848-11-13. . DOI: 10.1520/E2848-13.10.1520/E2848-13R18.
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 the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2848 − 13 (2018)
E927 Specification for Solar Simulation for Photovoltaic Testing
E948 Test Method for Electrical Performance of Photovoltaic Cells Using Reference Cells Under Simulated Sunlight
E973 Test Method for Determination of the Spectral Mismatch Parameter Between a Photovoltaic Device and a Photovoltaic
Reference Cell
E1036 Test Methods for Electrical Performance of Nonconcentrator Terrestrial Photovoltaic Modules and Arrays Using
Reference Cells
E1040 Specification for Physical Characteristics of Nonconcentrator Terrestrial Photovoltaic Reference Cells
E1125 Test Method for Calibration of Primary Non-Concentrator Terrestrial Photovoltaic Reference Cells Using a Tabular
Spectrum
E1362 Test Methods for Calibration of Non-Concentrator Photovoltaic Non-Primary Reference Cells
E2527 Test Method for Electrical Performance of Concentrator Terrestrial Photovoltaic Modules and Systems Under Natural
Sunlight
G138 Test Method for Calibration of a Spectroradiometer Using a Standard Source of Irradiance
G167 Test Method for Calibration of a Pyranometer Using a Pyrheliometer
G173 Tables for Reference Solar Spectral Irradiances: Direct Normal and Hemispherical on 37° Tilted Surface
G183 Practice for Field Use of Pyranometers, Pyrheliometers and UV Radiometers
2.2 IEEE Standards:
IEEE 1526-2003 Recommended Practice for Testing the Performance of Stand-Alone Photovoltaic Systems
IEEE 1547-2003 Standard for Interconnecting Distributed Resources with Electric Power Systems
2.3 International Standards Organization Standards:
ISO/IEC Guide 98-1:2009 Uncertainty of measurement—Part 1: Introduction to the expression of uncertainty in measurement
ISO/IEC Guide 98-3:2008 Uncertainty of measurement—Part 3: Guide to the expression of uncertainty in measurement
(GUM:1995)
2.4 World Meteorological Organization (WMO) Standard:
WMO-No. 8 Guide to Meteorological Instruments and Methods of Observation, Seventh Ed., 2008
3. Terminology
3.1 Definitions—Definitions of terms used in this test method may be found in Terminology E772, IEEE 1547-2003, and
ISO/IEC Guide 98-1:2009 and ISO/IEC Guide 98-3:2008.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 averaging interval, n—the time interval over which data are averaged to obtain one data point. The performance test uses
these averaged data.
3.2.2 data collection period, n—the period of time defined by the user of this test method during which system output power,
irradiance, ambient temperature, and wind speed are measured and recorded for the purposes of a single regression analysis.
3.2.3 plane-of-array irradiance, POA, n—see solar irradiance, hemispherical in Tables G173.
3.2.4 reporting conditions, RC, n—an agreed-upon set of conditions including the plane-of-array irradiance, ambient
temperature, and wind speed conditions to which photovoltaic system performance are reported. The reporting conditions must
also state the type of radiometer used to measure the plane-of-array irradiance. 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, RC, or
the method that will be used to derive the RC, shall be stated in the contract or agreed upon in writing by the parties to the
acceptance testing and reporting prior to the start of the test.
3.2.5 sampling interval, n—the elapsed time between scans of the sensors used to measure power, irradiance, ambient
temperature and wind speed. Individual data points used for the performance test are averages of the values recorded in these scans.
There are multiple sampling intervals in each averaging interval.
3.2.6 utility grid, n—see electric power system in IEEE 1547-2003.
3.3 Symbols: The following symbols and units are used in this test method:
−1
3.3.1 α—reference cell I temperature coefficient, °C
SC
3.3.2 a , a , a , a —linear regression coefficients, arbitrary
1 2 3 4
3.3.3 a, b, c, d—spectral mismatch factor calibration constants, arbitrary
2 −1
3.3.4 C—reference cell calibration constant, Am W
2 −1
3.3.5 C —reference cell calibration constant at SRC, Am W
o
3.3.6 E—plane-of-array irradiance, W/m
3.3.7 E —irradiance at SRC, plane-of-array, W/m
o
−2 −1
3.3.8 E (λ)—reference spectral irradiance distribution, Wm nm
o
E2848 − 13 (2018)
3.3.9 E —RC rating irradiance, plane-of-array, W/m
RC
−2 −1
3.3.10 E (λ)—spectral irradiance distribution at RC, Wm nm
RC
−2 −1
3.3.11 E (λ)—spectral irradiance distribution, test light source, Wm nm
T
3.3.12 F—fractional error in short-circuit current, dimensionless
3.3.13 I —short-circuit current, A
SC
3.3.14 M—spectral mismatch factor, dimensionless
3.3.15 p—p-value, dimensionless quantity used to determine the significance of an individual regression coefficient to the
overall rating result
3.3.16 P—photovoltaic system power, ac or dc, W
3.3.17 P —photovoltaic system power at RC, ac or dc, W
RC
3.3.18 RC—reporting conditions
3.3.19 R (λ)—reference cell spectral responsivity, A/W
R
3.3.20 R (λ)—test device spectral responsivity, A/W
T
3.3.21 SRC—standard reporting conditions
3.3.22 SE—standard error, W
3.3.23 T —ambient temperature, °C
a
3.3.24 T —RC rating temperature, °C
RC
3.3.25 U —expanded uncertainty with a 95 % coverage probability of photovoltaic system power at RC, W
3.3.26 λ—wavelength, nm
3.3.27 v—wind speed, m/s
3.3.28 v —RC rating wind speed, m/s
RC
4. Summary of Test Method
4.1 Photovoltaic system power, solar irradiance, ambient temperature, and wind speed data are collected over a defined period
of time using a data acquisition system.
4.2 Multiple linear regression is then used to fit the collected data to the performance equation (Eq 1) and thereby calculate the
regression coefficients a ,a ,a , and a .
1 2 3 4
P 5 E a 1a · E1a · T 1a · v (1)
~ !
1 2 3 a 4
4.3 Substitution of the RC values E ,T , and v into Eq 1 then gives the ac or dc power at the reporting conditions.
o o o
P 5 E a 1a · E 1a · T 1a · v (2)
~ !
RC RC 1 2 RC 3 RC 4 RC
4.4 The collected input data and the performance at the reporting conditions are then reported.
5. Significance and Use
5.1 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.
5.2 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.
5.2.1 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.
5.2.2 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.
5.2.3 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.
5.2.4 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.
5.3 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.
E2848 − 13 (2018)
NOTE 1—In general, the irradiance measurement should occur in the plane in which the majority of modules are oriented. Placing the measurement
device in a plane with a larger tilt than the majority will cause apparent under-performance in the winter and over-performance in the summer.
5.3.1 The linear regression results will be most reliable when the measured irradiance, ambient temperature, and wind speed
data during the data collection period are distributed around the reporting conditions. When this is not the case, the reported power
will be an extrapolation to the reporting conditions.
5.4 Accumulation of dirt (soiling) on the photovoltaic modules can have a significant impact on the system rating. The user of
this test may want to eliminate or quantify the level of soiling on the modules prior to conducting the test.
5.5 Repeated regression calculations on the same system to the same RC and using the same type of irradiance measurement
device over successive data collection periods can be used to monitor performance changes as a function of time.
5.6 Capacity determinations are power measurements and are adequate to demonstrate system completeness. However, a single
capacity measurement does not provide sufficient information to project the energy generation potential of the system over time.
Factors that may affect energy generation over time include: module power degradation, inverter clipping and overloading,
shading, backtracking, extreme orientations, and filtering criteria.
6. Reporting Conditions
6.1 The user of this test method shall select appropriate RC. 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 RC, or the method
that will be used to derive the RC, must be agreed upon by the parties to the test.
6.1.1 Reporting conditions may be selected either on the basis of expected conditions or actual conditions during the data
collection period. Choose RC irradiance and ambient air temperature values that are representative of the POA irradiance and
ambient air temperature for the system location for a clear day in the data collection period. When the selection is based on
expected conditions, irradiance can be evaluated from a year-long hourly d
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