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
• Current Stage: PPUB - Publication issued
• Completion Date: 04-Feb-2021

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
IEC TS 62862-2-1:2021-02(en)
---------------------- Page: 1 ----------------------
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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

Warning! Make sure that you obtained this publication from an authorized distributor.

® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 3 ----------------------
– 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

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IEC TS 62862-2-1:2021 © IEC 2021 – 3 –

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

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– 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

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IEC TS 62862-2-1:2021 © IEC 2021 – 5 –
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.

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– 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.
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IEC TS 62862-2-1:2021 © IEC 2021 – 7 –
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.).
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– 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
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IEC TS 62862-2-1:2021 © IEC 2021 – 9 –
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
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– 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.
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IEC TS 62862-2-1:2021 © IEC 2021 – 11 –
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

...