ASTM E2848-13(2023)

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: E2848 − 13 (Reapproved 2023) 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, and
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 Classification for Solar Simulators for Electrical Per-
temperature, and wind speed (see Section 6). Measurements
formance Testing of Photovoltaic Devices
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
Photovoltaic Reference Cell
1.6 The capacity measured according to this test method
should not be used to make representations about the energy E1036 Test Methods for Electrical Performance of Noncon-
centrator Terrestrial Photovoltaic Modules and Arrays
generation capabilities of the system.
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 Aug. 1, 2023. Published August 2023. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 2011. Last previous edition approved in 2018 as E2848 – 13 (2018). Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/E2848-13R23. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2848 − 13 (2023)
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
trator Terrestrial Photovoltaic Modules and Systems Un- the performance test are averages of the values recorded in
der Natural Sunlight these scans. There are multiple sampling intervals in each
G138 Test Method for Calibration of a Spectroradiometer averaging 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) 2
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
system performance are reported. The reporting conditions 3.3.23 T —ambient temperature, °C
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
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 (2023)
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 data set 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
nonlinear operation at or around the RC. For instance, in larger
modules under test. If multiple planes exist (particularly in the
photovoltaic systems, the ratio of installed DC capacity to AC
case of rolling terrain), then the plane or planes in which
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 irradiance modeling tools
plane or planes in which irradiance measurement will occur
that can be used to develop an hourly year-long data set for POA
must be agreed upon by the parties to the test prior to the start irradiance at a project site based on historical global horizontal irradiance
data or, if available, from data measured directly at the project site.
of the test.
NOTE 3—Historically, a specific case of RC known as “Performance
NOTE 1—In general, the irradiance measurement should occur in the Test Conditions,” or “PTC,” have been used commonly. PTC conditions
plane in which the majority of modules are oriented. Placing the use plane-of-array irradiance equal to 1000 W/m , ambient temperature
measurement device in a plane with a larger tilt than the majority will equal to 20 °C, and wind speed equal to 1 m/s. The PTC parameters were
cause apparent under-performance in the winter and over-performance in based on the Nominal Terrestrial Environment (NTE) conditions that
the summer. define the Nominal Operating Cell Temperature (NOCT) of an individual
E2848 − 13 (2023)
solar cell inside a module (see Annex A1 in Test Methods E1036).
correction, the test report must clearly state that the test result
However, NTE differs from PTC in that it specifies a lower irradiance of
includes uncertainty of an unknown magnitude due to spectral
800 W/m .
mismatch in addition to the reported uncertainty.
7.2.3.2 Reference devices used in this test shall be primary
7. Apparatus
or secondary reference devices as defined in Terminology
7.1 Ambient Air Temperature Measurement Equipment—
E772. If the in-situ calibration procedure outlined in Annex A2
The instrument or instruments used to measure the ambient air
is not employed, the reference device must be calibrated
temperature shall have a resolution of at least 0.1 °C, and shall
according to Test Methods E1362 using the hemispherical
have a total error of less than 61 °C of reading. The sensor
spectral irradiance distribution in Tables G173.
should be mounted in the immediate vicinity of the photovol-
7.2.3.3 Recommended physical characteristics of photovol-
taic system under test, but should not be so close to the
taic reference devices are available in Specification E1040.
modules as to be in the thermal boundary layer of the array.
7.2.3.4 Note that the calibration values of photovoltaic
The sensor shall be mounted with an aspirated radiation shield
reference devices are temperature sensitive and require mea-
as defined in 3.2.3 of Practice D6176. Practice D6176 contains
surement of the reference device’s temperature during the data
additional guidance for ambient air temperature measurements.
collection period. Reference devices that adhere to Specifica-
7.2 Irradiance Measurement Equipment—The irradiance
tion E1040 must have a temperature sensor.
measurement equipment shall be mounted coplanar (to within
7.3 Wind Speed Measurement Equipment—The instrument
1°) with the photovoltaic system under test and shall be
used to measure the wind speed shall have an uncertainty of
connected to a data acquisition system. The equipment should
less than 0.5 m/s, and should be mounted in the immediate
be mounted in a location that minimizes, and ideally
vicinity of the system under test. Because of the many possible
eliminates, shading of and reflections on the instrument.
system configurations, care should be taken to minimize effects
7.2.1 A calibrated hemispherical pyranometer (instruments
on the instrument readings from the system or nearby ob-
with fields of view approaching 180°, see Terminology E772)
stacles. Averaging readings from multiple instruments for large
is the most common choice for measurement of the incident
systems may be required.
solar irradiance. Pyranometers used in this test shall be
7.3.1 Ultrasonic wind speed instruments are preferred be-
calibrated using Test Method E824 or Test Method G167. Test
cause they do not have the dead band between 0 and 0.5 m/s in
Method E824 is a transfer calibration from a reference to a field
which mechanical cup-based wind speed instruments are
pyranometer, while Test Method G167 involves calibration
unable to rotate.
against either of two types of narrow field-of-view pyrheliom-
7.4 Power Measurement Equipment, ac—System ac power
eters. The uncertainty of the pyranometer calibration is a
is typically measured at the point of interconnection, however,
function of the calibration method, with the Type I calibration
the measurement point can be any point specified by the users
in Test Method G167 giving the lowest uncertainty.
of this test. The measurement point shall be specified and
7.2.2 Pyranometers are sensitive to both temperature and
agreed to prior to the start of the test. AC power shall be
the angle of incidence of irradiance, so may require measure-
measured with a total uncertainty of 61.5 % or less of the
ment of device temperature and angle of incidence during the
expected power value at RC.
data collection period. It is recommended that pyranometer
responsivity be characterized to the extent practicable. Sections
7.5 Power Measurement Equipment, dc—System dc power
5.5, 5.5.1, 5.5.2, and 5.5.3 in Practice G183 describe pyranom-
is typically measured at the input of the inverter or other power
eter characteristics which influence the level of uncertainty in
conditioning units using calibrated shunt resistors and voltage
solar radiation data and should be considered.
dividers. IEEE 1526-2003 and Test Methods E1036 shall be
7.2.3 Optional—A calibrated photovoltaic reference device
used to specify dc current and voltage measurements on
may be used in place of a pyranometer if it is mutually agreed
photovoltaic systems.
by the parties to the test prior to the start of the test.
8. Procedure
7.2.3.1 Annex A1 and Annex A2 present information and
procedures related to the use of photovoltaic reference devices
8.1 Connect the required instrumentation for the photovol-
as radiometers. It is strongly recommended that these proce-
taic system under test to the data acquisition system.
dures be used if a photovoltaic reference device is chosen. Use
8.2 For each averaging interval, measure and record the
of photovoltaic reference devices can significantly reduce
average system power, solar irradiance, ambient temperature,
uncertainty in the overall test result when they are calibrated
and wind speed over the interval.
with respect to the RC. This type of calibration introduces
complexity (and therefore cost) to the test. The additional 8.3 Continue data acquisition until the end of the data
complexity and cost is justified for large-scale commercial and collection period. This will constitute one complete data set.
utility-scale photovoltaic plants, but will not be economically The data collection period shall be at least three (3) days and
feasible for small commercial or residential installations. at most four (4) weeks. The default data averaging interval is
While the test may be carried out with a photovoltaic reference 15 min. Data is collected until a minimum of 50 data points
device without executing the corrections described in Annex (averaging intervals, post filtering) are available for the regres-
A1 and Annex A2, it is critical that the user understand the sion. The data set shall include data from at least three separate
information presented in them. If a photovoltaic reference days. If sufficient data is not collected in four weeks, then begin
device is used without applying the procedures for spectral using a four-week “moving window.” For example, if the
E2848 − 13 (2023)
original test start date is January 1 and data collection begins exceeds two standard deviations of the mean residual should be
on January 1, and by January 28 there are not 50 data points investigated and may be excluded if they do not meet the filter
available for the regression, then adjust the start of the data criteria.
collection period to January 2 and continue collecting data 9.1.4 Missing Data—If any of the four regression param-
through January 29, and so on. eters (power, plane-of-array irradiance, ambient temperature,
or wind speed) are missing for an averaging interval, all data
NOTE 4—50 data points using 15-min averaging intervals represents
for this averaging interval shall be excluded.
approximately 12.5 h of system operating time. If smaller averaging
9.1.5 DAS Equipment Malfunction—If any of the four
intervals are used, the minimum data point requirement may be increased.
regression parameters (power, plane-of-array irradiance, ambi-
For example, if 5-min averaging intervals are used, then 150 data points
would be needed to represent the same number of system operating hours.
ent temperature, or wind speed) is affected by a DAS recording
error or sensor equipment malfunction, all data for this
8.3.1 The data collection period shall be chosen to ensure
averaging interval shall be excluded. If more than a few
that all criteria described in 8.3 are met after excluding data per
averaging intervals in a data collection period are affected by
the data selection guidelines outlined in 9.1.
DAS errors or equipment malfunctions, it is recommended that
the sensing apparatus be investigated prior to proceeding with
9. Calculation of Results
the test.
9.1 Selection of Data:
9.1.6 Irradiance Outside of Range—Select a range of irra-
diance values over which the regression will be performed, and
9.1.1 The following filter criteria (described further in 9.1.2
– 9.1.10) should be applied to the data set in the following exclude data outside of this range. Ranges of E 6 20 % have
RC
been shown to give reliable results. Larger ranges may be
order:
selected if the test is performed during a season in which the
9.1.1.1 Visual examination (9.1.2).
range E 6 20 % will yield an insufficient number of data
RC
9.1.1.2 Preliminary regression (9.1.3).
points or will eliminate too many days from the data set. In
9.1.1.3 Missing data (9.1.4).
general, a range that allows for a data set with 100 or more data
9.1.1.4 DAS equipment malfunction (see 9.1.5).
points is preferred. Larger ranges (up to E 6 50 %) may also
RC
9.1.1.5 Irradiance outside of range (9.1.6).
be selected if data are limited to periods with stable sky
9.1.1.6 Unstable conditions (optional, see 9.1.7). conditions (see 9.1.7).
9.1.7 Unstable Conditions (optional)—When climate and
9.1.1.7 Inverter not peak power point tracking (see 9.1.8).
season allow, limiting the selection of data to periods of clear,
9.1.1.8 Obscuration of the system or radiometer by shading
stable sky conditions is recommended. Selecting data exclu-
(see 9.1.9).
sively from clear-sky periods will reduce the scatter in the
9.1.1.9 Radiometer not coplanar with system under test (see
regression significantly, reducing the statistical uncertainty in
9.1.10).
the regression result. As with selection of an irradiance range,
9.1.2 Visual Examination—Most data that will be filtered
excluding data during unstable conditions can reduce the data
out based on the filter criteria above can be quickly recognized
set to too few data points or too few days. Stability criteria may
using a simple visualization. Make a graphical plot of the
be relaxed if they prove too stringent for the data collection
output power versus irradiance for the entire data set. For
period or climate. Limiting data to clear, stable sky conditions
systems that have power conditioning units that perform
can be accomplished using one of the following techniques:
maximum power point tracking, such as inverters, this plot
9.1.7.1 Statistical Technique—Calculate the mean and stan-
should have a linear relation between power and irradiance.
dard deviation of sampling intervals for each averaging interval
Points that appear as outliers on this plot should be investigated
(data point) in the data collection period. Next, compute the
and excluded if they are found to not meet the filter criteria.
standard deviation as a percentage of the mean. For instance, if
Additionally, nonlinear power-irradiance characteristics should
the data sampling interval is 5 s and the averaging interval is
be investigated; a common cause is an inverter that begins to
5 min, compute the standard deviation of each of the 60
malfunction at some time during the data collection period.
sampled points and compare it to the mean of those 60 points.
Plots with two or more distinct lines can be the result of power
This percent standard deviation for each period can then be
losses. Irradiance measurement instruments that are not
used to assess operating stability and formulate data exclusion
mounted coplanar with the system under test will split the
criteria. Typical maximum allowable values are on the order of
power-irradiance relationship into double concave and convex
2 to 4 %.
curves between morning and afternoon data. Suspect data shall
9.1.7.2 Visual Technique—Alternately, make a graphical
be investigated to find the root cause, and shall be excluded if
plot of the output power and irradiance versus time for the
they do not meet the filter criteria.
entire data set. Visually inspect the plot to identify days with
9.1.3 Preliminary Regression—Another method to quickly
little to no cloud cover where irradiance changes relatively
identify data that may be excluded is to perform a preliminary
slowly throughout the day. Fig. 1 shows an example of a
regression and search for statistical outliers. After computing
the regression coefficients per 9.2, evaluate Eq 1 for each
averaging interval and calculate the residual between the
Kimber, et al., “Improved Test Method to Verify the Power Rating of a
measured power and the power computed using the regression
Phtovoltaic (photovoltaic) Project,” Proceedings of the 34th IEEE Photovoltaic
coefficients in Eq 1. Averaging intervals for which the residual Specialists Conference, Philadelphia, PA, USA, June 7–12, 2009.
E2848 − 13 (2023)
FIG. 1 Example Plot of Irradiance and System Power as a Function of Time, with Preferable Days Circled
ten-day period in which the clear days are indicated by circles A evaluation of uncertainty should use the standard error of
around the data. Exclude data from periods in which irradiance estimate, SE, and the Type B evaluation of uncertainty should
changes too quickly. include the expanded uncertainties of th
...