IEC 62862-1-5:2024

IEC 62862-1-5 ®
Edition 1.0 2024-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Solar thermal electric plants –
Part 1-5: Performance test code for solar thermal electric plants

Centrales électriques solaires thermodynamiques –
Partie 1-5: Code d’essai de performance pour centrales électriques solaires
thermodynamiques
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IEC 62862-1-5 ®
Edition 1.0 2024-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Solar thermal electric plants –

Part 1-5: Performance test code for solar thermal electric plants

Centrales électriques solaires thermodynamiques –

Partie 1-5: Code d’essai de performance pour centrales électriques solaires

thermodynamiques
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 27.160 ISBN 978-2-8322-8292-2

– 2 – IEC 62862-1-5:2024 © IEC 2024
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 8
4 Symbols . 8
5 Performance reference . 9
5.1 Requirements . 9
5.2 Simulation model . 9
6 General test guidelines . 10
6.1 General . 10
6.2 Test procedure . 11
6.3 Guidelines for each type of test . 12
6.3.1 General . 12
6.3.2 Short-duration tests . 12
6.3.3 Long-duration tests . 13
6.4 Test boundary . 13
7 Instruments and methods of measurement . 14
7.1 General . 14
7.2 General requirements . 14
7.3 Required measurements . 14
7.3.1 Direct solar irradiance. 14
7.3.2 Heat transfer fluid flow rate . 16
7.3.3 Temperatures . 16
7.3.4 Wind speed . 17
7.3.5 Relative humidity . 17
7.3.6 Atmospheric pressure . 17
7.3.7 Net plant electricity generation: delivered electricity to the grid minus
received electricity from the grid . 17
7.3.8 Electricity consumption at auxiliary transformer . 18
8 Performance calculations . 18
8.1 Available solar radiation energy . 18
8.2 Plant electricity consumption . 19
8.3 Net electricity . 19
8.4 Non-solar energy . 20
8.5 Net plant efficiency . 20
8.6 Recording and processing data . 21
8.7 Results presentation . 21
8.8 Acceptance test procedure . 22
9 Performance test report . 23
9.1 General . 23
9.2 Executive summary . 23
9.3 Introduction . 23
9.4 Instrumentation . 24
9.5 Calculations and results . 24
9.6 Conclusions . 24

9.7 Annexes. 24
Annex A (normative) Uncertainty calculation . 25
A.1 Purpose and assumptions . 25
A.2 Equations for calculating net plant efficiency . 25
A.3 Considerations for calculating uncertainties . 26
A.4 Basic equations for calculating uncertainties . 27
A.5 Calculating uncertainties . 27
A.5.1 General . 27
A.5.2 Type B uncertainty of the direct solar irradiance . 29
A.5.3 Type B uncertainty of the electrical power . 29
A.5.4 Type B uncertainty of the mass flow rate of heat transfer fluid in the
auxiliary heater . 29
A.5.5 Type B uncertainty of the enthalpy difference of heat transfer fluid in the
auxiliary heater . 31
A.6 Alternative method for calculating the uncertainty of net plant efficiency . 31
A.7 Calculation of Type B standard uncertainty when redundant instruments are
used . 32
A.7.1 General . 32
A.7.2 Type B standard uncertainty of temperatures measured with two
redundant sensors . 32
A.7.3 Type B standard uncertainty of direct solar irradiance . 32
Annex B (informative) Example of uncertainty of net efficiency calculated following the
procedure in Clause A.5 . 34
B.1 General . 34
B.2 Technical data of instruments and DAS . 35
B.2.1 Measured electrical power . 35
B.2.2 Temperature . 35
B.2.3 Flow rate . 35
B.2.4 Direct solar irradiance. 35
Annex C (informative) Example of uncertainty of net efficiency calculated following the
alternative procedure described in Clause A.6 . 40
C.1 General . 40
C.2 Step 1: . 40
C.3 Step 2: . 41
C.4 Step 3: . 41
Bibliography . 42

Figure 1 – Energy flows in a solar thermal power plant . 6
Figure 2 – Required simulation model inputs and outputs . 10
Figure 3 – Generic test boundary and energy flows . 14
Figure 4 – Typical electrical connections in a power plant . 18
Figure 5 – Examples of acceptance criteria – Comparison of the measured value (M)
against the reference value (RV) with uncertainty bands . 23

Table 1 – Symbols and units . 8
Table 2 – Example of a test main results table . 21
Table 3 – Levels of confidence and associated coverage factors (Normal distribution) . 22
Table B.1 – Test values . 34
Table C.1 – Test values . 40

– 4 – IEC 62862-1-5:2024 © IEC 2024
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SOLAR THERMAL ELECTRIC PLANTS –

Part 1-5: Performance test code for solar thermal electric plants

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
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the latest information, which may be obtained from the patent database available at https://patents.iec.ch. IEC
shall not be held responsible for identifying any or all such patent rights.
IEC 62862-1-5 has been prepared by IEC technical committee TC 117: Solar thermal electric
plants. It is an International Standard.
The text of this International Standard is based on the following documents:
Draft Report on voting
117/177/CDV 117/191/RVC
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.

This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
A list of all parts in the IEC 62862 series, published under the general title Solar thermal electric
plants, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn, or
• revised.
– 6 – IEC 62862-1-5:2024 © IEC 2024
INTRODUCTION
Solar thermal power plants are electricity generation plants that use solar radiation to heat a
fluid to a high temperature. This fluid usually transfers its heat to water to produce superheated
steam, which is expanded in a turbine-generator machine to transform thermal energy first into
mechanical energy and finally into electricity. These plants use solar collectors to concentrate
the solar radiation, and they are classified depending on the concentration technology, including
but not limited to parabolic-trough collector (PTC), central receiver collector (CRC) also called
solar tower, and linear Fresnel collector (LFC).
Solar thermal power plants are composed of a solar field interconnected to a power block, but
sometimes they also include a non-solar energy source and a thermal storage system which
enable electricity generation under conditions of reduced or no solar radiation (see Figure 1).
Depending on the concentration technology, the solar field can consist of a set of parabolic-
trough collector rows, linear Fresnel collector rows, or a set of heliostats with a central receiver
located in a tower. All these systems track the sun and collect the energy that it projects in the
form of direct radiation.
The plant performance should be demonstrated, or verified, as part of the commissioning and
acceptance process, for all the configurations agreed by the parties involved.

Figure 1 – Energy flows in a solar thermal power plant
The complexity and duration of performance acceptance tests depend on what these tests are
for. There are several different types of tests:
• Short quasi-stationary tests: Their purpose is to verify the characteristics and features of
the power plant systems (solar field, thermal storage system, power block, and auxiliary
non-solar energy systems).
• Short-duration testing (at least 24 h): The purpose is to verify the performance of the power
plant over a short period of time (usually associated with provisional plant acceptance
testing).
• Long-duration tests (at least 365 days): The purpose is to verify or validate annual plant
production and auxiliary consumptions (electricity and non-solar energy source). (These
tests are usually associated with final plant acceptance.)
• Dispatchability tests: The purpose is to verify the ability of the solar thermal power plant to
respond to grid operator signals regardless of meteorological conditions.
• Durability and integrity testing: The purpose is to verify integrity and validate equipment
durability.
This document focuses on acceptance testing of the complete power plant and defines the
measurement procedures for short-duration and long-duration efficiency testing.

SOLAR THERMAL ELECTRIC PLANTS –

Part 1-5: Performance test code for solar thermal electric plants

1 Scope
The purpose of this document is to provide procedures and guidelines to carry out acceptance
tests for solar thermal power plants, of any concentration technology, with the uncertainty level
given in ISO/IEC Guide 98-3.
This document establishes the measurements, instrumentation and techniques required for
determining the following performance parameters for a given period:
• available solar radiation energy,
• plant electricity consumptions,
• net electricity generation,
• non-solar energy,
• net plant efficiency.
Other parameters that characterize the solar thermal power plant system features are not dealt
with in this document but are the subject of other complementary standards.
This document specifies the characteristics of a calculation tool that serves as a reference for
expected electricity production during the test period and under the real-time solar irradiance
and other meteorological data.
This document is applicable to solar thermal power plants of any size using any concentration
technology, where the sun is the main source of energy, and all elements and systems are
operative. Such power plants can optionally have non-solar energy sources, such as natural
gas or other renewable energies, and a thermal storage system.
This document is applicable to acceptance testing in such power plants, as well as in any other
scenario in which their performance must be known. Acceptance tests serve for the purpose of
verification of a contractual performance measure, and for establishing claims in case of non-
fulfillment of performance. In this document the owner, builder, financier, and any other entity
interested in knowing these features are called "parties involved".
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60044-7, Instrument transformers – Part 7: Electronic voltage transformers
IEC 60044-8, Instrument transformers – Part 8: Electronic current transformers
IEC TS 62862-1-1, Solar thermal electric plants – Part 1-1: Terminology
ISO/IEC Guide 98-3, Uncertainty of measurement – Part 3: Guide to the expression of
uncertainty in measurement (GUM:1995)

– 8 – IEC 62862-1-5:2024 © IEC 2024
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC TS 62862-1-1 apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
4 Symbols
The symbols and units used in this document are displayed in Table 1.
Table 1 – Symbols and units
Symbol Description Units
A
Net collection area
m
net
C Specific heat capacity J/(kg·K)
p
E Direct normal solar irradiance
W/m
b
E Net electricity generated and delivered to the grid kWh
el,net
E
Thermal energy supplied by fossil fuels and/or other non-solar kWh
ns
energies
h Specific enthalpy J/kg
Mass flow rate kg/s

m
N Number of single elements in operation in the solar field: -
col
parabolic-trough collectors, Fresnel reflectors or heliostats
P Power kW
p
Atmospheric pressure Pa
atm
RH Relative humidity %
t Time h
T Temperature ºC
U Type B uncertainty
B
v
Wind speed m/s
Volumetric flow
 m /s
V
Greek symbols
Difference or variation -
∆
Net plant efficiency %
η
plant,net
ρ Density
kg/m
τ Test time s
Subscripts
accum cumulative value
atm atmospheric
aux at auxiliary transformer high voltage side

Symbol Description Units
avail available in the aperture area of the plant solar field
con consumption
el electricity
gross at generator terminals
HTF heat transfer fluid
i, j time interval, index
in, out inlet, outlet
net net value
ns non solar
plant related to the power plant
solar solar radiation
startup at startup transformer high voltage side
tr transformer
trloss transformer losses
util useful
0, end initial and final time
5 Performance reference
5.1 Requirements
According to this document, the verification of performance for a solar thermal power plant
requires:
a) The use of a power plant simulation model, hereinafter "simulation model", to generate
reference values from the input and boundary conditions existing during a test.
b) To define the verification procedure, that is, the way measurements are to be compared with
the reference considering uncertainties.
Subclause 5.2 defines the simulation model, while the verification procedure is defined in 8.8.
5.2 Simulation model
This document establishes that the simulation model of the tested solar power plant and its
systems is an essential element in the acceptance process. The simulation model to be used
shall be agreed by the parties involved, and its validation shall be documented. It is
recommended that the simulation model meet at least the requirements listed in Clause 5.
Owing to the importance of inertial and transient phenomena during performance tests, the
simulation model shall be dynamic, or at least consider solar field inertia phenomena, to be able
to calculate the reference performance indicators, like electrical power or plant efficiency, for
the test boundary conditions.
For short-duration and long-duration efficiency tests, the simulation model will commonly
include the following inputs and outputs (see Figure 2):
• Input specifications:
– power plant location (geographic latitude and longitude);
– test start and end dates and times;

– 10 – IEC 62862-1-5:2024 © IEC 2024
– date and time, direct solar irradiance, and other meteorological conditions during testing
(temperature, wind speed, atmospheric pressure, relative humidity, and, if needed by
the simulation model, wind direction), recorded in time intervals no longer than 10 min
and averaged as specified in 8.6;
– plant operating modes during testing;
– solar field and power plant availability during testing;
– reflectance of mirrors in the solar field over time;
– starting conditions of the thermal storage system;
– starting conditions of the power plant when testing begins (type of startup);
– non-solar energy consumption during testing.
• Output specifications:
– available solar radiation energy;
– net electricity production (at test boundaries);
– auxiliary electricity consumption;
– consumption of electricity imported from the grid.

Figure 2 – Required simulation model inputs and outputs
The simulation model used in the acceptance process shall be previously validated and agreed
upon by the parties involved. It is recommended that the simulation model validation include
the following:
• Verification that the simulation model reproduces nominal performance values at reference
conditions (i.e., design point conditions).
• Consistency in predicting performance values at conditions other than those of reference,
showing that when input parameters are varied, output trends are congruent with these
variations.
6 General test guidelines
6.1 General
Clause 6 provides the general instructions to carry out performance tests for solar thermal
power plants, with the steps required to plan, prepare, and perform them.

6.2 Test procedure
The test procedure is a detailed document on the test plan, which shall be prepared and
approved beforehand by the parties involved. This basic document shall include all the details
for preparing and conducting a test, as well as how to make calculations and report the results.
It is recommended that it includes at least the following:
1) Purpose of the test, indicating foreseen duration.
2) Features to be verified, along with their guaranteed values and uncertainty margins, if
applicable.
3) Test boundaries, identifying the input and output flows and measurement points.
4) Basic test plan.
5) Description of the activities to be performed during test preparation, such as calibration and
verification of measurement equipment, training of personnel who take part in the test,
inspection and cleaning of equipment, and carrying out a pretest if so agreed. The
instrumentation that is to be used during the tests shall meet the specifications defined in
Clause 7. All measuring equipment, both permanent and temporary instruments, necessary
for the test, shall be checked, inspected, and tuned before starting the test.
6) Description of activities to be carried out during the test, such as checking the conditions
necessary to start, interrupt, suspend or end the test, operating conditions, adjustments
permitted before and during the test, and details about data recording. The test conditions
shall not at any time surpass the maximum limits of the equipment involved, as set by their
suppliers, nor those of the normal plant operating procedures.
7) Description of plant operating conditions, including both major and auxiliary equipment that
affect test results.
8) Procedure for determining the solar field cleanliness factor.
9) List of plant instruments and measuring equipment, including tag, description, calibration,
location, number, type, uncertainty (accuracy) and main technical data.
10) Calibration certificates of listed instruments.
11) Prior uncertainty analysis, establishing the uncertainties estimated by non-statistical
procedures.
12) Methodology for determining the meteorological variables, such as direct normal radiation,
wind speed, atmospheric pressure, ambient temperature and relative humidity.
13) Sampling methods for the heat transfer fluid, the storage medium or the non-solar energy
sources, if any. Indication of preparation, sampling frequency, parameters to be determined,
and analysis methods.
14) Identification of the laboratory that will analyze the heat transfer fluid and storage medium
or non-solar energy source, if any.
15) Thermo-physical property tables for heat transfer fluid and storage medium or non-solar
energy source, if any.
16) Format in which data and results will be recorded and supplied.
17) Data averaging and validation procedures for redundant measurements.
18) Data verification and rejection criteria. Procedure to solve data acquisition system (DAS)
failures, generating gaps in the records, with criteria to complete or discard such periods.
19) Data distribution procedure. The measured data shall be stored in electronic data files that
shall be available to the parties involved. Processed values and calculations derived from
these data shall be done in different files from the original files. Final reports on results shall
include the original data files.
20) Specific reference and description of the simulation model used to obtain acceptance
criteria. It shall include acceptable deviation limits between measured and calculated values
using the simulation model, considering uncertainties.
21) Procedure for determining the effect of degradation of plant components, if applicable.

– 12 – IEC 62862-1-5:2024 © IEC 2024
22) Procedure for verifying plant performance.
If the parties involved consider it advisable, any of the above can be excluded.
6.3 Guidelines for each type of test
6.3.1 General
Within the scope of this document, guidelines for two types of performance tests are given:
short-duration (at least 24 h), and long-duration (at least 365 days). The specific duration,
agreed by the parties, shall be indicated in the test procedure.
For short-duration tests, it is recommended to keep the thermal storage inactive. But in cases
where the use of the thermal storage system, if any, was necessary, a procedure shall be
considered to check the complete charge/discharge of the system during the test period; for
example, recording initial and final temperatures and levels.
For long-duration tests, the influence on the calculated efficiency of the difference between
initial and final thermal storage conditions is negligible.
6.3.2 Short-duration tests
The purpose of short-duration tests is to verify plant performance for at least 24 h. The operating
parameters required for acceptance of the complete solar thermal power plant during these
tests are available solar radiation energy, net electricity generation, electricity consumption,
non-solar energy consumption and net efficiency.
It is recommended that a short pretest be done, for example during a couple of hours before
beginning the short-duration test, to check that the plant meets the conditions to start the test
and that the measurement equipment and DAS are working properly. The pretest is also used
to analyze whether system adjustments are necessary before starting the plant performance
acceptance test. Specifications for the pretest shall be stipulated in the test procedure.
Short-duration tests shall last at least 24 h to enable evaluation of the plant, taking into account
all subsystems and operating modes in which plant performance is to be verified. If the solar
thermal power plant has a thermal storage system, the test to verify overall plant efficiency shall
be long enough to include the complete charge/discharge process from beginning to end of
testing.
For short-duration performance tests, the parties involved shall agree on the conditions under
which the tests are to be performed and define them in the test procedure. It is suggested that
the test be repeated at least three times to reduce uncertainties.
All instruments used shall be checked before the test. After the test, instruments suspected of
abnormalities should be rechecked. The result of these checks shall be collected in a report
that also includes the calibration certificates. These reports shall be distributed among the
parties.
It is recommended that the heat transfer fluid temperature be homogenized in the solar thermal
power plant before beginning the test.
The short-duration tests shall be done on clear days and with a maximum direct solar irradiance
of no less than 700 W/m for at least 4 h. A clear day is understood to be one on which possible
solar radiation transients do not surpass 5 % of sunlight hours. A solar radiation transient means
a time interval of no longer than 30 min, in which the solar radiation is significantly lowered due
to clouds, recording a clarity index below 0,5 for the period in consideration. The clarity index
is defined as the quotient of global horizontal irradiance and the product of extraterrestrial solar
irradiance by the cosine of the solar zenith angle (according to ISO 9488). In those cases, in

which weather conditions at the site make it very difficult to achieve these conditions, the parties
involved can agree on other criteria which shall be defined in the test procedure.
It is recommended to carry out the test when it is not necessary to use antifreeze systems for
the heat transfer fluid or the storage fluid.
Required simulation model inputs and outputs are defined in 5.2.
6.3.3 Long-duration tests
Long-duration tests, lasting at least 365 days, evaluate plant performance under normal
operation subjected to seasonally varying technical, weather and electricity supply conditions.
This test will show a faithful image of real plant performance. Although the usual period of that
test is a full one year, the test procedure shall specify if it is continuous or if it can be temporarily
suspended. Abnormal operating conditions or unusual maintenance activities shall be identified,
evaluated, and documented.
The operating parameters required for acceptance or verification of the solar thermal power
plant performance during these tests are available solar radiation energy, net electricity
generation, electricity consumption, non-solar energy consumption, and net efficiency.
All instruments used shall be checked before starting the test and regularly during the test,
especially those suspected of abnormal behaviour. The result of these checks shall be collected
in a report that also includes the calibration certificates. These reports shall be distributed
among the parties.
The thermal storage system shall be considered an intermediate heat transfer subsystem, and
therefore it is not necessary to measure specific variables of this subsystem during the tests.
Required simulation model inputs and outputs are defined in 5.2.
6.4 Test boundary
The test boundary is defined as the limits enclosing the solar power plant where the inlet and
outlet energy flows shall be measured to calculate the plant performance. It is not necessary to
determine the energy flows inside the boundary unless they serve to verify the operating
conditions or to evaluate subsystem performance.
The test boundary is specific to each plant and shall be defined in the test procedure. Figure 3
shows a generic diagram of the test boundary for a solar thermal power plant, with fossil fuel
as the non-solar energy source and a thermal storage system. Clause 7 provides more detailed
information on what measurements to take and how.

– 14 – IEC 62862-1-5:2024 © IEC 2024

Figure 3 – Generic test boundary and energy flows
Energy received by solar thermal power plants comes mainly from the sun (primary energy
source), but also from fossil fuel or other renewable energies (non-solar energy). Net electricity
generation is the plant output variable. Thermal storage systems are inside the test boundary,
so they are not considered inlet/outlet energy sources. Both the verification of solar field
efficiency and thermal storage system characteristics are out of the scope of this document.
7 Instruments and methods of measurement
7.1 General
Clause 7 describes the instruments and test procedures necessary to obtain the required
accuracy level for the solar power plant performance evaluation, including the type of
measurements to be made, how to make them, and the instrument specification.
7.2 General requirements
The plant shall have an automatic data acquisition system (DAS) to record and store
simultaneous measurements.
Process instrumentation, portable instruments, and alternative sensors can be used in the test,
if they comply with the specifications agreed by the parties.
All instruments used in the test shall have a calibration certificate not older than one year when
starting the test. During long-duration tests, instrumentation shall be checked regularly,
recalibrating those suspected of malfunctioning.
The contribution of individual instruments uncertainties to the result uncertainty is
...