IEC TS 62862-2-1:2021

Solar thermal electric plants - Part 2-1: Thermal energy storage systems - Characterization of active, sensible systems for direct and indirect configurations

IEC TS 62862-2-1:2021 defines the requirements and the test methods for the characterization of thermal energy storage (TES) systems. This document contains the information necessary for determining the performance and functional characteristics of active direct and indirect thermal energy storage systems based on sensible heat in solar thermal power plants using parabolic-trough collector, Fresnel collector or tower central receiver technology with liquid storage media.
This document includes characterization procedures for testing energy storage system charge and discharge, as well as reporting the results. Test performance requirements are given and the instrumentation necessary for them, as well as data acquisition and processing methods and methods for calculating the results and their uncertainties.

General Information

• Status: Published
• Publication Date: 03-Feb-2021
• ICS: 27.160 - Solar energy engineering
• Technical Committee: TC 117 - Solar thermal electric plants
• Drafting Committee: PT 62862-2-1 - TC 117/PT 62862-2-1
• Current Stage: PPUB - Publication issued
• Start Date: 24-Feb-2021
• Completion Date: 04-Feb-2021

Overview - IEC TS 62862-2-1:2021 (Solar thermal electric plants, TES characterization)

IEC TS 62862-2-1:2021 defines requirements and test methods for the characterization of thermal energy storage (TES) systems used in solar thermal electric plants. The Technical Specification covers active, sensible heat storage systems for direct and indirect configurations using liquid storage media (for example, molten salts) in plants with parabolic‑trough, Fresnel or tower central receiver technologies. It provides the procedures needed to determine storage performance, capacity, losses and related uncertainties.

Key topics and technical requirements

• Scope and classifications

  • Definitions and limits of active sensible TES for direct/indirect configurations.
  • Classification of TES modes and system boundaries.

• Test procedures

  • Standardized tests to measure charge/discharge performance, thermal efficiency, heat capacity, thermal losses and global energy losses.
  • Requirements for test planning, agreed durations and conditions between parties.

• Instrumentation and measurement

  • Minimum instrumentation for accurate results: flow rate, temperature (HTF and wall), level measurements, and meteorological signals (wind, ambient temperature).
  • Data acquisition system requirements and sensor deployment recommendations.

• Data treatment and uncertainty

  • Procedures for data acquisition, processing and calculation of results.
  • Methods for estimating measurement uncertainties, confidence levels and verification procedures.

• Reporting and documentation

  • Test report structure, required data, and documentation to be supplied by manufacturers/suppliers.

Practical applications and users

Who uses IEC TS 62862-2-1:

• TES manufacturers and suppliers - to validate and document storage system performance for procurement and warranty.
• Plant designers and EPC contractors - to size storage, integrate TES with solar fields and power cycles.
• Testing laboratories and certification bodies - to perform standardized charge/discharge tests and evaluate compliance.
• Plant operators and owners/investors - to verify delivered performance, estimate dispatchable energy and predict thermal losses.
• Researchers and consultants - to compare TES technologies (sensible storage, molten salt systems) on a consistent basis.

Practical benefits:

• Enables consistent, comparable performance data for procurement, performance guarantees, modeling and O&M planning.
• Reduces risk by standardizing measurement methods, data processing and uncertainty assessment.

Related standards (context)

• Published by the IEC (International Electrotechnical Commission) and aligned with ISO/IEC directives for standards development. Users should consult other IEC documents on solar thermal electric plants and instrumentation for complementary guidance.

Standards Content (Sample)

IEC TS 62862-2-1 ®
Edition 1.0 2021-02
TECHNICAL
SPECIFICATION
colour
inside
Solar thermal electric plants –
Part 2-1: Thermal energy storage systems – Characterization of active, sensible
systems for direct and indirect configurations

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IEC TS 62862-2-1 ®
Edition 1.0 2021-02
TECHNICAL
SPECIFICATION
colour
inside
Solar thermal electric plants –

Part 2-1: Thermal energy storage systems – Characterization of active, sensible

systems for direct and indirect configurations

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 27.160 ISBN 978-2-8322-9320-1

– 2 – IEC TS 62862-2-1:2021 © IEC 2021
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 8
2 Normative references . 8
3 Terms and definitions . 8
4 Symbols and abbreviated terms . 9
5 Thermal energy storage (TES) systems . 10
5.1 Classification of TES systems . 10
5.2 TES systems covered by this document . 10
5.3 TES system limits . 10
5.4 Key components . 10
6 Instrumentation and measurement methods. 11
6.1 General . 11
6.2 Flow rate measurements . 11
6.3 Temperature measurements . 11
6.3.1 Heat transfer fluid temperatures . 11
6.3.2 Wall temperatures . 12
6.4 Level measurements . 12
6.5 Meteorological signal measurements . 12
6.5.1 Wind speed and direction . 12
6.5.2 Ambient temperature . 12
6.6 Data acquisition . 13
7 General requirementson tests . 13
7.1 General . 13
7.2 Test procedure . 13
7.2.1 General . 13
7.2.2 Items to be included in the test procedure . 14
7.2.3 Items to be agreed between the parties . 14
7.3 Definition of the test included in this document . 15
7.3.1 General . 15
7.3.2 Test to determine the thermal efficiency of the storage system . 15
7.3.3 Test to determine the heat capacity of the storage system . 15
7.3.4 Test to determine the thermal losses of the storage system . 16
7.3.5 Test to determine the global losses of the storage system . 16
7.3.6 Test to determine the wall temperature . 16
7.4 Test boundaries . 17
8 Storage system characterization (storage thermal performance and capacity) . 18
8.1 Thermal efficiency and storage capacity (storage thermal performance and
capacity) . 18
8.1.1 Test methodology . 18
8.1.2 Calculation procedure . 19
8.2 Thermal losses of the storage system . 23
8.2.1 Test methodology . 23
8.2.2 Calculation procedure . 23
8.3 Global energy losses of the storage system . 24
8.3.1 General . 24

8.3.2 Test methodology . 24
8.3.3 Calculation procedure . 25
9 Verification procedure . 25
10 Test report (results) . 27
Annex A (informative) Thermal energy storage system types . 28
A.1 Thermal energy storage modes . 28
A.1.1 General . 28
A.1.2 Sensible heat storage . 28
A.1.3 Latent heat storage . 28
A.1.4 Thermochemical energy storage . 29
A.2 TES configuration . 29
A.3 Circulation of the storage medium . 29
Annex B (informative) Description of the main components of the active direct/indirect
TES using molten salts . 31
B.1 Storage media . 31
B.2 Tanks and foundation. 31
B.2.1 Tanks . 31
B.2.2 Foundations . 32
B.2.3 Insulation . 32
B.3 Materials . 32
B.4 Piping . 33
B.5 Pumps . 33
B.6 Heat exchanger . 33
B.7 Safety and control system . 34
B.7.1 General . 34
B.7.2 HTF and MSF leak detection system . 34
B.7.3 Instrumentation . 34
B.7.4 Freeze protection system . 34
B.7.5 Molten salt valves . 36
B.7.6 Blanketing system . 36
B.7.7 Welding control system . 36
B.8 Melting system . 36
Annex C (normative) Data adquisition and treatment . 38
C.1 Flow signal measurement . 38
C.2 Temperature signals measurement . 41
Annex D (informative) Documentation to be provided by the TES
manufacturer/supplier . 44
Annex E (normative) Test report . 46
Bibliography . 48

Figure 1 – Agreed duration between two charges . 16
Figure 2 – General typical diagram of the system and test boundaries for indirect TES
systems . 17
Figure 3 – General typical diagram of the system and test boundaries for direct TES
systems . 18
Figure 4 – Examples of criteria for comparison of the measurement (M) and the
reference value (RV) . 27

– 4 – IEC TS 62862-2-1:2021 © IEC 2021
Table 1 – List of symbols and units . 9
Table 2 – List of subscripts, superscripts and abbreviated terms . 9
Table 3 – Levels of confidence and associated coverage factors (Gaussian
distribution) . 26
Table C.1 – Critical range factor, f(n ), depending on the number of sensors, n ,
q q
available . 39
Table C.2 – Outline of the steps to be followed to calculate the representative flow rate
(volumetric) for each time interval recorded . 40
Table C.3 – Outline of steps to be followed to calculate the representative inlet heat
transfer fluid temperature for each time interval recorded . 43

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SOLAR THERMAL ELECTRIC PLANTS –

Part 2-1: Thermal energy storage systems –
Characterization of active, sensible systems for
direct and indirect configurations

FOREWORD
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rights. IEC shall not be held responsible for identifying any or all such patent rights.
IEC TS 62862-2-1 has been prepared by IEC technical committee 117: Solar thermal electric
plants. It is a Technical Specification.
The text of this Technical Specification is based on the following documents:
Draft TS Report on voting
117/119/DTS 117/127/RVDTS
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 Technical Specification is English.

– 6 – IEC TS 62862-2-1:2021 © IEC 2021
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/standardsdev/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 "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates that it
contains colours which are considered to be useful for the correct understanding of its
contents. Users should therefore print this document using a colour printer.

INTRODUCTION
IEC TC 117 prepares International Standards (and other types of documents) for systems of
solar thermal electric (STE) plants for the conversion of solar thermal energy into electrical
energy and for all the elements (including all sub-systems and components) in the entire STE
energy system. These documents would cover all current different types of systems in the STE
field, as follows:
• Parabolic trough
• Solar tower
• Linear fresnel collectors
• Parabolic dish
• Any other type of system using thermal storage that is not connected to the grid.
The documents define terminology, design and installation requirements, performance
measurement techniques and test methods, safety requirements, and "power quality" issues for
each of the above systems.
In addition to those systems, there are several major components that require standardization,
such as the storage media (oil, molten salt, ceramic, concrete, etc.).

– 8 – IEC TS 62862-2-1:2021 © IEC 2021
SOLAR THERMAL ELECTRIC PLANTS –

Part 2-1: Thermal energy storage systems –
Characterization of active, sensible systems for
direct and indirect configurations

1 Scope
This document defines the requirements and the test methods for the characterization of
thermal energy storage (TES) systems.
This document contains the information necessary for determining the performance and
functional characteristics of active direct and indirect thermal energy storage systems based on
sensible heat in solar thermal power plants using parabolic-trough collector, Fresnel collector
or tower central receiver technology with liquid storage media.
This document includes characterization procedures for testing energy storage system charge
and discharge, as well as reporting the results. Test performance requirements are given and
the instrumentation necessary for them, as well as data acquisition and processing methods
and methods for calculating the results and their uncertainties.
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 TS 62862-1-1:2018, Solar thermal electric plants – Part 1-1: Terminology
IEC 60584-1:2013, Thermocouples – Part 1: EMF specifications and tolerances
IEC 60751:2008, Industrial platinum resistance thermometers and platinum temperature
sensors
ISO 5725-3, Accuracy (trueness and precision) of measurement methods and results – Part 3:
Intermediate measures of the precision of a standard measurement method
ISO 5725-6, Accuracy (trueness and precision) of measurement methods and results – Part 6:
Use in practice of accuracy values
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 terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp

4 Symbols and abbreviated terms
The symbols, units, subscripts, superscripts, and abbreviated terms shown in Table 1 and Table
2 are used in this document.
Table 1 – List of symbols and units
Name Symbol Units Observations
Confidence level  %
Coverage factor FC - dimensionless
Critical range factor f(n) - dimensionless
Energy E J or Wh
Mass flow rate ṁ kg/s
Performance Ƞ %
Power P W
Storage capacity ϕ J or Wh
Storage level  %
Temperature T °C or K
Time t s
The units are those of the variable to which the
Uncertainty s
uncertainty refers
Velocity v m/s
Volumetric flow rate V̇ or Q m /s

Table 2 – List of subscripts, superscripts and abbreviated terms
Script Meaning
* Instantaneous value
AMB Ambient
C Charge
D Discharge
DCS Distributed control system
E Electrical
HTF Heat transfer fluid
i, j, k Numbering value
IN Inlet
OUT Outlet
M, N Number of data recorded or representative
MSF Molten salt fluid
Q Flow meter number
RTD Resistance temperature detector
T Thermal
TES Thermal energy storage
– 10 – IEC TS 62862-2-1:2021 © IEC 2021
5 Thermal energy storage (TES) systems
5.1 Classification of TES systems
Thermal storage can be classified according to several different criteria:
• Thermal energy storage mode: thermal energy supplied by the solar field may be stored as
sensible heat, latent heat, reaction heat or a combination of them.
• Circulation of the storage medium: TES systems can be classified as active or passive.
• System configuration: thermal energy storage systems may be direct or indirect.
For more details regarding the types of TES systems, refer to Annex A.
5.2 TES systems covered by this document
This document covers active sensible two-tank direct and indirect thermal storage systems
using "molten salt" as the storage media. The term "molten salt" shall be considered
synonymous with "solar salt" in any part of this document. Furthermore, in the case of direct
storage, molten salts are also used as the HTF.
5.3 TES system limits
The boundary limits of the different TES systems covered in this document are described below.
In the case of indirect systems:
a) the limit is the inlet at the HTF side of the heat exchanger between the HTF and molten salt.
b) the limit is the outlet at the HTF side of the heat exchanger between the HTF and molten
salt.
In the case of direct systems:
c) the limit is the inlet side of the TES: the inlet at the cold tank and the inlet at the hot tank.
d) the limit is the outlet side of the TES: the outlet at the cold tank and the outlet at the hot
tank, when discharging the TES.
Refer to 7.4 for the system boundaries diagrams.
5.4 Key components
All the following types of equipment, at a minimum, are considered as key components of the
thermal energy storage system:
• storage medium,
• storage tanks,
• piping,
• heat exchangers (in the case of indirect storage systems),
• electrical system,
• control systems,
• safety systems,
• pumps and valves,
• instrumentation: pressure gauges, thermocouples, flow meters, level gauges.
___________
The description of "molten salt" is provided in Annex B.

For more details regarding the components of a TES system, refer to Annex B.
The documentation that should be provided by the TES manufacturer/supplier is given in
Annex D.
6 Instrumentation and measurement methods
6.1 General
The following measurements in this Clause 6 shall be taken and recorded during testing.
6.2 Flow rate measurements
The flow meter to be used for the flow rate measurement should provide Type B uncertainty
below 1 % in flow rate measurements within the heat transfer fluid working temperature range.
During instrument installation, special attention should be given to all the requirements for
ensuring proper equipment functioning (e.g., respecting the length of straight sections upstream
and downstream from the flow meter, what direction the sensor should be facing, etc.), which
shall be defined by the supplier.
When the flow meter measures the volumetric flow rate in m /s, the density of the heat transfer
fluid, which is a function of temperature, shall be calculated. For this, a temperature sensor is
installed as close as possible to the flow meter, but without preventing it from working properly.
*
The instantaneous volumetric flow rate of the heat transfer fluid V̇ or Q which feeds the storage
system in time t is measured in m /s.
For reliable measurement, at least two independent flow meters are required, located at the
inlet and outlet of the storage system. Furthermore, the minimal installation conditions required
by the manufacturer should be respected.
Flow rate measurement treatment shall be performed according to Clause C.1.
6.3 Temperature measurements
6.3.1 Heat transfer fluid temperatures
The instantaneous temperatures of the heat transfer fluid are measured at time t, at a maximum
distance of 5 m from the inlet or outlet of the test boundary. If this is not possible, they are
measured at the closest point to the inlet or outlet of the test boundary. These temperatures
may be given by any temperature measurement device, thermocouple or RTD, as long as the
sensor part of the device is well within the fluid and is resistant to its contact, or, alternatively,
the sensor is within the thermowell, and is also well within the fluid and is in contact with the
inner wall which enables it to be read correctly. For long connection lengths to the measurement
point, an analogical-digital conversion protocol is recommended.
Instantaneous data shall be recorded by the data acquisition system for a period of less than
1 min. At least three independent sensors are required at the inlet and as many at the outlet,
so there are at least the required number of instantaneous data series detailed in Clause C.2.
The uncertainties considered in the measurement are those of the measurement sensor,
extension and compensating cables, and the data acquisition system device. In the case of
thermocouples, the uncertainties shall be of Class 1 in accordance with IEC 60584-1 and
Class A in accordance with IEC 60751 for RTDs.

– 12 – IEC TS 62862-2-1:2021 © IEC 2021
6.3.2 Wall temperatures
Temperature measurements of the external wall of insulation of the hot and cold tank shall be
performed to monitor that the external surface temperature does not exceed 55 °C.
The instantaneous temperatures of the external wall are measured continuously at four
equidistant points around the tank circumference at least at two different elevations.
The lower elevation shall be at 1,5 m above the platform where the tank is erected. The higher
elevation corresponds to the centre of the band that comprises the ¾ portion of the tank height.
These temperatures may be given by any temperature measurement device, thermocouple or
RTD.
Instantaneous data shall be recorded by the data acquisition system for a period of less than
1 h.
The uncertainties considered in the measurement are those of the measurement sensor,
extension and compensating cables, and the data acquisition system device, that is, Type B
uncertainties. The maximum Type B uncertainty allowed in transfer flow temperature is ±1,5 °C.
6.4 Level measurements
The instantaneous level of the heat storage fluid in the hot tank shall be measured continuously.
These levels may be given by any continuous level sensors, as long as the sensor part of the
device is suitable as regards the fluid and the physical characteristics of the fluid.
Any maximum deviation with respect to nominal values shall be agreed upon by the parties and
included in the test procedure. Instantaneous data shall be recorded by the data acquisition
system for a period of less than 1 min. At least two independent sensors are required in the hot
tank.
The uncertainties considered in the measurement are those of the measurement sensor and
the device, that is, Type B uncertainties. The maximum Type B uncertainty allowed in level
measurement is ±0,1 m.
6.5 Meteorological signal measurements
6.5.1 Wind speed and direction
Since wind speed and direction affect storage system thermal losses, they shall be measured
during testing to determine storage system overall energy and thermal losses. Wind speed is
measured by anemometers located at a height no lower than 10 m from the ground, and outside
of the range of disturbances caused by adjacent elements. These sensors shall have an
uncertainty of ±0,5 m/s or less. If there are several anemometers, the measurement nearest the
storage system shall be taken as valid for each record.
For each anemometer, 1 s records shall be used to calculate the mean wind speed during a
recording interval of no longer than 10 min.
These measured data records shall be included in the test report and shall be processed as
defined in the test procedure.
6.5.2 Ambient temperature
This measurement is only necessary in tests for calculating storage system overall energy and
thermal losses.
Maximum Type B uncertainty associated with ambient temperature data recorded by the data
acquisition system shall be ±1 °C.
Ambient temperature shall be measured at a position near the storage system, with the sensor
protected from nearby heat sources, such as direct solar radiation. It should be especially
verified that the sensor position is not within the field of hot air currents caused by gas or vapour
emitted by nearby equipment.
The measured data recorded shall be included in the test report and shall be processed as
defined in the test procedure.
6.6 Data acquisition
All measured signals shall be (i) recorded by a computer controlled data acquisition system that
shall be connected to the DCS of the power plant and (ii) verified with visual readings.
In some extreme conditions where it is not possible to install a temporary computer controlled
data acquisition system, data may be recorded manually in suitable form sheets with date and
time.
During the test period and when not specified otherwise:
1) the measurements automatically recorded on a computer shall be taken instantaneously,
meaning at least every 30 s, and
2) any data collected in writing shall be recorded on data sheets not less than six (6) times per
hour, except for flow measurements, which shall be carried out and recorded not less than
twelve (12) times per hour. Ambient and wall temperatures should be measured once every
hour.
The data collection system shall be designed to:
a) comprise multiple instrument outputs,
e) gather all the necessary data simultaneously, meaning within a maximum interval of 5 s,
f) run any necessary calculations with data collected at the same time, and
g) store data and simulation results.
At all representative operating conditions during each test run, all the DCS screens (showing
pressures, temperatures, flows, power, operating status, etc.) shall be printed for inclusion in
the test report appendices.
Data collected by temporary test instruments shall be recorded in a dedicated collection system.
All test data (raw and processed data) shall be available.
7 General requirements on tests
7.1 General
Some general requirements for thermal energy storage system characterization testing are
defined.
7.2 Test procedure
7.2.1 General
A detailed document about the test plan called the test procedure shall be prepared and
approved by the parties involved before testing. This basic document shall include all the details

– 14 – IEC TS 62862-2-1:2021 © IEC 2021
for preparing and performing the tests, as well as calculating and presenting the results. The
document shall include two groups of points agreed by the parties: those points which are
required and those which are optional.
7.2.2 Items to be included in the test procedure
The test procedure shall include at least the following:
1) Description of the thermal energy storage system, operating modes, nominal heat transfer
fluid conditions during storage tank charge and discharge, nominal storage capacity,
nominal cold tank temperature, nominal hot tank temperature, storage hours, thermal
performance and full charge and discharge times.
2) Definition of the 0 % and 100 % storage level indicating the hot tank and cold tank levels
and temperatures.
3) Thermal energy storage system boundary, identifying measurement points.
4) Exhaustive list of measurement instruments and equipment, describing coding, calibration,
location, amount, type, uncertainty and main technical data. The instrumentation to be used
for testing shall comply with specifications in Clause 6. All the measurement equipment
necessary, both permanent instruments installed in the plant and any temporary instruments
shall be checked, inspected and adjusted before beginning testing.
5) Calibration certificates for the instruments listed.
6) Heat transfer fluid and storage medium properties as a function of the working temperature.
7) Purpose of testing, indicating how long tests are supposed to take.
8) Definition of the reference test conditions for the site shall include ambient temperature,
relative humidity, wind speed, elevation, atmospheric pressure, etc. The values of these
reference test conditions shall be the same as the design conditions which may be corrected
with the adequate provided correction curves.
9) Basic test plans: the test conditions shall at no time exceed the maximum limitations of
equipment involved as stated by the supplier, or normal plant operating procedures.
10) Definition of any acceptable maximum deviations from values given in the test plan.
11) Data recording and processing shall be in accordance with specifications in Clause 6. The
procedure to be followed in case of discrepancies in data recorded for a same physical
quantity.
12) Confidence level, and therefore, coverage factor, for calculating expanded uncertainty of
different characteristic parameters.
13) Wind speed and direction and ambient temperature data processing.
14) Test result evaluation method. Parameters to be verified, along with their guaranteed values
and/or system reference, and criteria for comparison, if applicable.
15) Definition of correction factors applicable to the results when there are deviations between
nominal values and those measured during testing.
7.2.3 Items to be agreed between the parties
If the parties involved deem it so advisable, they may exclude some of the following
recommendations from the test procedure:
1) Reference to plant operating methods, including primary and auxiliary equipment which
could affect the test results.
2) Sampling, preparation and analysis methods for heat transfer fluid and storage medium
and/or substances related to the non-solar energy supply, if any, indicating how and with
what frequency their properties are measured or calculated.
3) Identification of the laboratory that analyses the heat transfer fluid and storage medium
and/or substances related to the non-solar energy supply, if any.

4) Description of activities to be performed during preparation of the test, such as verification
of measurement equipment, training of personnel taking part in the test or any preliminary
testing.
5) Detailed description of activities to be performed during testing, such as checking conditions
for starting and ending the test, operating method, adjustments permitted before and after
the test and data acquisition.
6) Data acceptance and rejection criteria. If the data acquisition system should fail and there
are gaps in the data, it shall be agreed how to complete the data or what time interval without
data is considered not to affect the final result.
7) Procedure for data distribution. The measured data shall be stored in files that shall be
made available to the interested parties. Processing and calculations derived from these
data shall be performed in different files from the original measurements, and a final report
on results shall be written giving the explicit results of the tests.
8) Specific reference to the simulation model used to find the guarantee values and its
description.
9) Procedure for determining the effect of thermal energy storage system component
degradation.
10) Test to determine overall thermal energy storage system losses.
11) Other tests not described in this document.
7.3 Definition of the test included in this document
7.3.1 General
A preliminary test should be performed to check that the plant is in condition to start testing,
that the measurement equipment and data acquisition systems are working properly, that the
expected uncertainty in the result is acceptable, and that the worksheet and model show the
algorithms described in the procedure. It should be a short test, for example two hours long,
before starting storage system testing.
Calibration reports and working conditions of all the instrumentation used shall be adequate.
After testing, only of those instruments suspected of malfunctioning should be verified for
adequate working condition and calibration reports.
Besides the following types of tests that shall be performed, the wall temperature as well as the
status of storage for the TES system shall be monitored.
7.3.2 Test to determine the thermal efficiency of the storage system
This test consists of charging the thermal energy storage system from a 0 % initial state to
100 % and discharging it immediately afterwards to 0 %, recording the variables given in
Clause 6 for determining thermal performance of the thermal energy storage system. During
both charging and discharging, the measurements shall be very near nominal conditions. Any
maximum deviation with respect to nominal values shall be agreed upon by the parties in the
test procedure. The entire test shall be performed without any external energy supply, except
for what is necessary to ensure safe functioning of the storage system.
7.3.3 Test to determine the heat capacity of the storage system
The variables recorded and described in Clause 6 may be used to determine the storage system
capacity, or a similar test may be done, that is, starting out with the storage system fully charged
(100 %) it is fully discharged immediately afterwards, recording the variables given in Clause 6.
During discharging, the measurements shall be very near nominal conditions. Any maximum
deviation with respect to nominal values shall be agreed upon by the parties in the test
procedure. The entire test shall be performed without any external energy supply, except for
what is necessary to ensure safe functioning of the storage system.

– 16 – IEC TS 62862-2-1:2021 © IEC 2021
7.3.4 Test to determine the thermal losses of the storage system
Storage system thermal losses shall be determined by the difference between the energy
discharged by the storage system immediately after having reached full charge of 100 % and
the energy discharged by it after the agreed test duration between charge and discharge defined
in the test procedure. In this test, two scenarios related to the same operating mode, the storage
system discharge mode, are compared.
The agreed duration between the two charges should not exceed 25 h and the entire test shall
be done without any external energy supply, except for what is necessary to ensure safe
functioning of the storage system. See Figure 1 for the agreed duration between two charges.

Figure 1 – Agreed duration between two charges
7.3.5 Test to determine the global losses of the storage system
The overall energy loss from the storage system shall be determined by the difference between
the energy transferred to the system during full charge (100 %) and the total energy it delivers,
when the duration defined in the test procedure has passed. In this test, two scenarios related
to different storage system operating modes, the charge and discharge modes, are compared.
These scenarios may be the scenarios described in 7.2.3 or any other scenarios agreed
be
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