IEC 62862-5-2:2022

Solar thermal electric plants - Part 5-2: Systems and components - General requirements and test methods for large-size linear Fresnel collectors

IEC 62862-5-2:2022 specifies the requirements and the test methods for the characterization of a large-size linear Fresnel collector.
This document covers the determination of optical and thermal performance of linear Fresnel collectors, and the tracking accuracy of the collector one-axis tracking system. This test method is for outdoor testing only.
This document applies to linear Fresnel collectors according to Annex A equipped with the manufacturer-supplied sun tracking mechanism.
This document applies to the whole collector field in-situ or as a minimum unit to be tested to an individual collector string (loop) connected to the main piping (flow, return flow) to and from a heat sink, covering the full temperature range of the field.

General Information

• Status: Published
• Publication Date: 09-May-2022
• ICS: 27.160 - Solar energy engineering
• Technical Committee: TC 117 - Solar thermal electric plants
• Drafting Committee: PT 62862-5-2 - TC 117/PT 62862-5-2
• Current Stage: PPUB - Publication issued
• Start Date: 06-Jun-2022
• Completion Date: 10-May-2022

Overview

IEC 62862-5-2:2022 - "Solar thermal electric plants - Part 5-2: Systems and components - General requirements and test methods for large-size linear Fresnel collectors" - specifies requirements and outdoor test methods for characterizing large-size linear Fresnel collectors. The standard covers determination of optical and thermal performance and the tracking accuracy of the collector one‑axis tracking system. It applies to collectors equipped with the manufacturer‑supplied sun tracking mechanism, and to testing a whole collector field in‑situ or, at minimum, an individual collector string connected to the main piping across the field’s full temperature range.

Key topics and technical requirements

• Scope of testing
  • Outdoor performance testing only; in‑situ field or representative string testing.
• Instrumentation and measurements
  • Solar radiation measurement, flow rate, temperature sensors, wind speed, and data acquisition systems.
  • Tracking accuracy measurement provisions.
• Test procedures
  • Collector description and test equipment setup.
  • Cleanliness, boundary test conditions, and measurement protocols.
• Performance characterization
  • Determination of useful power and incidence angle modifier (IAM).
  • Evaluation methods for quasi‑dynamic test (QDT) and dynamic test (DT) procedures.
  • Validation performance testing and optional tracking error tests.
• Data processing and uncertainty
  • Calculation methods, parameter identification (for DT), and uncertainty estimation.
• Reporting and documentation
  • Required reporting format and manufacturer documentation (Annex B).
• Supporting annexes
  • Annex A: Collector description and configurations.
  • Annex C: Test report template.
  • Annex D: Deflectometry mirror testing.
  • Annex E: Tracking error testing.

Applications and who uses this standard

• Manufacturers of linear Fresnel collectors for product development, factory acceptance and performance declaration.
• Independent test laboratories and certification bodies conducting outdoor performance and acceptance tests.
• Project developers, plant operators and EPC contractors validating field performance, commissioning, and acceptance of solar thermal electric plants.
• System designers and modelers who need validated optical/thermal parameters (IAM, efficiency, tracking accuracy) for plant simulation and performance forecasting.
• Investors and regulators seeking consistent, comparable performance evidence for procurement and compliance.

Related standards

• Part of the IEC 62862 series (Solar thermal electric plants) developed by IEC Technical Committee 117. Consult other parts of IEC 62862 for broader system and component requirements and for harmonized test frameworks.

Keywords: IEC 62862-5-2, linear Fresnel collectors, solar thermal electric plants, optical performance, thermal performance, tracking accuracy, outdoor testing, incidence angle modifier, quasi-dynamic test, dynamic test, in‑situ testing.

Standards Content (Sample)

IEC 62862-5-2 ®
Edition 1.0 2022-05
INTERNATIONAL
STANDARD
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Solar thermal electric plants –
Part 5-2: Systems and components – General requirements and test methods for
large-size linear Fresnel collectors
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IEC 62862-5-2 ®
Edition 1.0 2022-05
INTERNATIONAL
STANDARD
colour
inside
Solar thermal electric plants –

Part 5-2: Systems and components – General requirements and test methods for

large-size linear Fresnel collectors

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 27.160 ISBN 978-2-8322-0096-4

– 2 – IEC 62862-5-2:2022 © IEC 2022
CONTENTS
FOREWORD . 5
1 Scope . 7
2 Normative references . 7
3 Terms, definitions and symbols. 7
3.1 Terms and definitions . 7
3.2 Symbols . 8
4 Testing requirements . 9
5 Instrumentation . 9
5.1 Solar radiation measurement . 9
5.2 Flow rate measurement . 9
5.3 Temperature measurements . 9
5.4 Wind speed measurement . 10
5.5 Data acquisition . 10
5.6 Tracking accuracy measurement . 10
6 Test procedure . 10
6.1 General . 10
6.2 Collector description . 10
6.3 Test equipment . 10
6.3.1 Performance test . 10
6.3.2 Optical characterization for performance testing . 11
6.3.3 Tracking error test . 12
6.4 Measurement procedure . 12
6.4.1 General . 12
6.4.2 Cleanliness . 12
6.4.3 Test conditions . 13
6.5 Calculation and test results evaluation . 13
6.5.1 General . 13
6.5.2 Useful power . 14
6.5.3 Incidence angle modifier (IAM) . 15
6.5.4 Evaluation for the quasi-dynamic test method QDT . 17
6.5.5 Evaluation for the dynamic test method DT . 18
6.5.6 Validation performance test . 19
6.5.7 Tracking error test (optional) . 20
6.5.8 Uncertainty estimation . 21
7 Reporting format . 21
Annex A (informative) Linear Fresnel collector description . 22
A.1 General description . 22
A.1.1 Overview . 22
A.1.2 Collector row structure . 23
A.1.3 Support structure and foundation . 24
A.1.4 Primary reflectors . 24
A.1.5 Mirror support . 24
A.1.6 Mirror drives . 25
A.1.7 Receiver . 25
A.1.8 Receiver tube . 25
A.1.9 Receiver cavity . 26

A.1.10 Receiver support and casing . 27
A.1.11 Tracking system . 27
A.2 Operation modes . 28
Annex B (normative) Documentation to be supplied by the collector manufacturer . 29
B.1 General configuration of the linear Fresnel collector . 29
B.1.1 Model and manufacturer . 29
B.1.2 Axes and movements. 29
B.1.3 Collector grouping . 29
B.2 Geometric characterization of the linear Fresnel collector . 29
B.3 Mechanical characterization of the linear Fresnel collector . 29
B.4 Optical characterization of the linear Fresnel collector . 30
B.5 Description of linear Fresnel collector operating modes . 30
B.5.1 Design operating conditions . 30
B.5.2 Normal operating conditions . 30
B.5.3 Reduced weather/geological operating conditions (features to be
reduced shall be defined (optical, thermal performance) and how much
they are reduced) . 30
B.5.4 Stow conditions . 30
B.5.5 Survival conditions . 30
B.6 Optical and tracking accuracy . 30
B.6.1 Accuracy under normal operating conditions . 30
B.6.2 Accuracy under reduced operating conditions . 30
B.7 Linear Fresnel collector component information . 30
B.7.1 Linear Fresnel collector structure . 30
B.7.2 Receiver tube . 31
B.7.3 Receiver cavity . 31
B.7.4 Primary and secondary reflectors. 31
B.7.5 Drive mechanism . 31
Annex C (normative) Testing report . 32
C.1 General . 32
C.2 Collector characteristics . 32
C.3 Linear Fresnel collector limitations . 33
C.4 Description of the experimental setup . 33
C.5 Results . 33
Annex D (informative) Deflectometry mirror testing . 35
D.1 Mirror shape quality . 35
Annex E (informative) Tracking error testing . 36
Bibliography . 37

Figure 1 – Test equipment installation. 11
Figure 2 – Sketch of one module of linear Fresnel collector as seen from above . 15
Figure 3 – Incidence angles for a linear Fresnel collector . 16
Figure 4 – Sketch of parameter identification procedure used for the DT method [3] . 18
Figure A.1 – General view of a north-south axis Fresnel collector . 22
Figure A.2 – General view of an asymmetric east-west axis Fresnel collector . 23
Figure A.3 – Schematic drawing of individual drive a), group drive b) and field drive c)
options . 25

– 4 – IEC 62862-5-2:2022 © IEC 2022
Figure A.4 – Typical receiver cavity with secondary reflector and glass cover . 26
Figure A.5 – Typical receiver cavity with secondary reflector and without glass cover . 27
Figure A.6 – Typical receiver cavity with multiple parallel tubes . 27

Table C.1 – Alternate tracking accuracy reporting template . 33

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SOLAR THERMAL ELECTRIC PLANTS –

Part 5-2: Systems and components – General requirements
and test methods for large-size linear Fresnel collectors

FOREWORD
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IEC 62862-5-2 has been prepared by IEC technical committee 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
117/148/CDV 117/160/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.

– 6 – IEC 62862-5-2:2022 © IEC 2022
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
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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
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SOLAR THERMAL ELECTRIC PLANTS –

Part 5-2: Systems and components – General requirements
and test methods for large-size linear Fresnel collectors

1 Scope
This part of IEC 62862 specifies the requirements and the test methods for the characterization
of a large-size linear Fresnel collector.
This document covers the determination of optical and thermal performance of linear Fresnel
collectors, and the tracking accuracy of the collector one-axis tracking system. This test method
is for outdoor testing only.
This document applies to linear Fresnel collectors according to Annex A equipped with the
manufacturer-supplied sun tracking mechanism.
The testing method in this document does not apply to any collector under operating conditions
where phase-change of the fluid occurs. Although the principles of this document can be applied
also to collectors with phases-change, however, the sensors (enthalpy, flow, temperatures)
required for that are not described in this document.
This document applies to the whole collector field in-situ or as a minimum unit to be tested to
an individual collector string (loop) connected to the main piping (flow, return flow) to and from
a heat sink, covering the full temperature range of the field.
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, 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)
ISO 9488, Solar energy – Vocabulary
ISO 9806:2017, Solar energy – Solar thermal collectors – Test methods
3 Terms, definitions and symbols
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 9488, ISO 9806:2017,
IEC TS 62862-1-1, and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
– 8 – IEC 62862-5-2:2022 © IEC 2022
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.2 Symbols
Gross collector aperture area (projected mirror area on the ground
A
including the small gaps between facets and positioning of the mirrors
m
G
for the sun in the zenith)
Geometric concentration ratio: gross collector aperture area A
G
C
-
R
divided by the surface area of the receiver Α
R
E
Long-wave infrared sky radiation
W/m
L
Ratio between the optical efficiency of the collector for normal
F
-
c
incidence in a soiled state and a clean state.
Function describing the optical end loss of a collector with finite length
f
-
end
when the sun is in the longitudinal collector plane
G Solar irradiance W/m
H
Height of receiver above mirror plane m
rec
K
Incidence angle modifier for direct beam irradiation -
b
K
Incidence angle modifier for diffuse irradiation -
d
Incidence angle modifier for direct beam irradiation in the transversal
K
-
T
plane
Incidence angle modifier for direct beam irradiation in the longitudinal
K
-
L
plane
L
Length of primary mirror row in one collector module m
m
L
Length of receiver in one collector module m
rec
Q̇ Thermal power net output of the collector W
T
Mean fluid temperature K
m
T
Ambient temperature K
a
u Wind speed m/s
W
Project width of mirror row i on the horizontal m
i
Collector width (Width of mirror field perpendicular to row orientation in
W
m
c
one collector module)
ρ
specular reflectance of the soiled primary mirrors -
test
ρ
specular reflectance of the clean primary mirrors -
nom
θ
Longitudinal solar incidence angle °
LS
θ
Transversal incidence angle °
T
χ
Ratio of specular reflectance of soiled and clean mirror material -
reflector
Collector optical efficiency for direct beam radiation at normal
η
-
0b
incidence
Indices
a ambient
b beam
dif diffuse
L longitudinal
n normal
T transversal
Tilt tilted
4 Testing requirements
The linear Fresnel collector shall be equipped with all the components supplied by the
manufacturer (such as support structure, primary reflectors, receiver casing and support,
receiver tubes, actuator system and control) and mounted according to the manufacturer
instructions.
The different component/elements (such as the receiver parts, reflectors, mirror drives,
structure) should be previously tested separately by current testing methods or standards when
available. The documentation to be fulfilled by the manufacturer shall be according to Annex B.
5 Instrumentation
5.1 Solar radiation measurement
Solar radiation measurement shall be performed using a pyrheliometer for direct irradiance
according to 21.1 of ISO 9806:2017.
Incidence angles will be determined by calculation or with sun position sensors with accuracy
equal or better than ± 0,1° with a resolution of 0,01°.
5.2 Flow rate measurement
Flow rate measurement shall be performed according to 21.4.1 of ISO 9806:2017.
5.3 Temperature measurements
Temperature measurements (inlet, outlet and ambient temperature) shall be performed
according to ISO 9806:2017 with an accuracy better than 1 % of the temperature rise over the
collector
The collector inlet and outlet positions shall be defined by the manufacturer and pairwise
calibrated temperature sensors shall be installed at no more than 200 mm from this point. If due
to constructional constraints it becomes necessary to position the sensor more than 200 mm
away from the collector, then a test shall be made to verify that the measurement of fluid
temperature is not affected.
The problems caused by the concentrated light on the sensors if the sensors are mounted in
the focus zone shall be taken into consideration.
For piping diameters larger than 254 mm, 2 to 3 temperature sensors should be considered for
each position to have a more representative average.

– 10 – IEC 62862-5-2:2022 © IEC 2022
5.4 Wind speed measurement
The mean wind speed in the horizontal plane shall be determined with a standard uncertainty
< 0,5 m/s. The sensor shall be installed at (10 ± 0,1) m height from the ground. The sensor
shall be installed within the collector field / solar plant. If there is no wind speed sensor close
enough to the meteorological station of the plant, one temporary sensor should be added at a
distance from the collector extremity (end support as shown in Figure A.1) not larger than 100 m
away.
5.5 Data acquisition
Data acquisition shall be according to 23.5.3 of ISO 9806:2017.
5.6 Tracking accuracy measurement
Experimental tracking accuracy measurements can be obtained using inclinometers. Resolution
of the inclinometers shall be at least 0,01° and accuracy shall be better than 0,1° over the whole
range of tracking angles. Combination of two or more inclinometers often solves this
requirement.
The true tracking angle is measured at two locations of the collector, one near the centre (where
the drive system is usually located) another one at one collector end.
A more detailed tracking error testing is optional (see 6.3.3).
6 Test procedure
6.1 General
Performance testing includes at least the assessment of the heat power delivered by the
collector under various operating and environmental conditions and the measurement of the
dependence of the thermal performance on the incidence angle of the irradiation onto the
collector. These two sets of parameters are required for the calculation of the collector heat
output. If possible, an effective thermal capacity according to ISO 9806:2017 should be also
determined. A minimum collector unit (Figure 1) as already stated in the scope may be a
complete collector row, a loop or even a subfield, covering the whole temperature range of
operation.
6.2 Collector description
The description of collector(s) should be supplied by the manufacturer according to Annex B.
All the components of the tested collector (reflectors, receiver, structure, etc.) shall be
representative of the product. The components shall have been selected randomly from the
production during the erection of the collector.
All the serial numbers and identification of those components should be reported in the testing
report.
6.3 Test equipment
6.3.1 Performance test
The sensors shall be mounted according to ISO 9806:2017. A scheme of principle for the test
installation is presented in Figure 1.

Key
1 pump 6 temperature sensor (T )
out
2 flow meter 7 ambient temperature sensor (T )
a
3 temperature sensor 8 direct solar irradiance sensor
4 temperature sensor (T ) 9 anemometer
in
5 linear Fresnel collector unit

Figure 1 – Test equipment installation
During the tests of a linear Fresnel collector it will be necessary to guarantee that the reflectors
and glass envelopes of the receivers are kept clean. For testing purposes, the cleanliness factor
is defined as the ratio between the average optical efficiency during the test and the optical
efficiency with ideal clean surfaces. Depending on the receiver construction, not only the
cleanliness of the primary mirrors, but to a lesser degree also soiling of the tubular or plane
glass cover, and the secondary reflector may impact the collector cleanliness. The target is to
keep the collector’s cleanliness factor F within the range 0,95 < F < 1,0.
c c
6.3.2 Optical characterization for performance testing
6.3.2.1 Cleanliness
If possible, the collector components primary mirrors, secondary mirrors and cover glasses
should be cleaned before the testing. However, in outdoor testing soiling may occur
continuously. Therefore, it is important to determine the average cleanliness of a collector
before and after a performance test in order to be able to relate the results to a maximum
performance with clean mirrors.
The reflectance of the primary mirrors ρ (clean state) and ρ (soiled) will be measured with
nom test
a portable reflectometer. ρ and ρ shall be measured with the same equipment.
nom test
So far there is no field instrumentation available to determine the degree of dirt in the receiver
cover and on a secondary reflector once installed in the collector; as the receiver faces the
ground it is assumed a good approach to neglect the much smaller percentage of reduction in
optical efficiency due to soiling during the test period of the cleaned glass cover and secondary
mirror compared to fast soiling of primary mirrors.

– 12 – IEC 62862-5-2:2022 © IEC 2022
The determination of cleanliness on the primary mirrors during the test period is mandatory. If
the average global cleanliness factor F falls below 0,95, the collector (both reflectors and
c
transparent covers) should be cleaned as a consequence for the next measurement period.
6.3.2.2 Mirror shape quality
Optionally the quality of the mirror shape may be tested in the laboratory by an appropriate
means, if the measured thermal performance and the theoretical or simulated performance
show huge difference. For example deflectometry, fringe reflection techniques or a similar
technique may be used to check the quality for individual mirror shapes. See Annex D.
6.3.3 Tracking error test
The solar tracking systems should be installed and calibrated according to the manufacturer’s
recommendations.
Optionally the tracking accuracy of individual mirror rows may be tested, if the measured
thermal performance and the theoretical or simulated performance show huge difference. See
Annex E.
6.4 Measurement procedure
6.4.1 General
The thermal performance test to determine optical efficiency at normal incidence , heat losses
and incidence angle modifier shall be performed according to ISO 9806:2017 using the quasi-
dynamic test method (QDT) or the dynamic test method (DT) specified by the SolarPACES
DISPAT Guideline [4] (see also [3]). The wind speed shall be less than 5,5 m/s during the
testing period. The testing shall be performed outside under real weather conditions. In order
to identify measurement periods for QDT with suitable environmental conditions, the
specifications of ISO 9806:2017 apply. For DT the specifications shall be similar for the test
period, however the requirements on the stability of irradiance or temperature conditions do not
apply.
6.4.2 Cleanliness
The assessment of cleanliness shall be based on primary mirror reflectance measurements
using the SolarPACES Guideline on mirror reflectance [1]. There should be a measurement of
at least 3 clean samples to assess the “clean” reflectance ρ of a mirror as the average value.
nom
The determination of cleanliness from reflectance-measurements should be done for each test
day. Cleanliness of the collector to be tested shall be measured after performing a cleaning
procedure and at the end of the measurement day. It should be measured at least on 10 different
positions (select random primary mirror rows at each position).
The reflectors cleanliness factor χ is determined for each sequence of the test at least in
reflector
10 positions of the collector considered. If the values of reflectance differ by more than ±5 %
points, the average of 20 different positions should be taken. The number and position of points
measured should be reported in the test report.
The global collector cleanliness is approximately estimated by Formula (1), only taking into
account the effect of primary mirror soiling:

Numbers in square brackets refer to the Bibliography.

𝜌𝜌̄test
𝐹𝐹 ≅𝜒𝜒 = (1)
C reflector
𝜌𝜌
nom
Where
ρ  is the arithmetic average of measurements of ρ before and after each test sequence,
test test
ρ is the specular reflectance measured of the primary reflectors of the collector, and
test
ρ is the reference value of the specular reflectance of the primary reflector material
nom
installed in the collector.
The secondary mirror may be also qualified if accessible to measurements (uncovered receiver
cavity).
If the receiver tube is covered by a cover glass (cylindrical, plane) the cleanliness should be
also evaluated after cleaning using the portable reflectometer, if that is feasible. A temporary
black background behind the sheet of glass at the measurement position is recommended. In
this case Formula (1) may be modified accordingly.
6.4.3 Test conditions
6.4.3.1 Quasi-dynamic testing
The test conditions as specified in ISO 9806:2017, Clause 23 shall be applied as far as possible.
In real installations however the variation of collector input temperature might be limited and it
could be impossible to fully cover the whole allowed temperature range of operation.
6.4.3.2 Dynamic testing
With the DT method the conditions to be fulfilled are not restricted to steady-state. Neither the
inlet temperature nor the mass flow rate has to be kept constant, in addition to accepting any
variation of the direct irradiance. In real installations however the variation of collector input
temperature might be limited and it could be impossible to fully cover the whole allowed
temperature range of operation.
All test day types as described in ISO 9806:2017, 23.6.2 for QDT shall be included in the test
period used for DT.
6.5 Calculation and test results evaluation
6.5.1 General
Calculation of the test results shall be performed according to Clause 24 of ISO 9806:2017 for
the quasi-dynamic test method QDT and using similar modelling formulas for the dynamic test
method DT specified by the SolarPaces DISPAT Guideline [3],[4].
The increase of specific enthalpy of the fluid within the collector Δh is equal to Δh = h − h .
out in
Polynomial approximations or interpolation of tabulated values can be used for the specific
enthalpy h(T) of the heat transfer fluid.
The fluid data table of the specific enthalpy (or specific heat capacity) depending on the
temperature shall be measured in the entire working range by a laboratory, any other
independent body or obtained from a referenced literature data. This data shall be documented
and referenced.
– 14 – IEC 62862-5-2:2022 © IEC 2022
The experimental useful power output therefore has to be determined for each time-step as

Qm=×=Δh m× h −h .
( )
out in
6.5.2 Useful power
The general single node model of the collector according to ISO 9806:2017 is written as
Formula (2) using a parametrization of optical characteristics and thermal losses.
 
η K (θ ,θ )G +K G −a (TT−−) a (TT− ) −au (TT−−)
( )
0 b LS T bT d dif 1 ma 2 ma 3 ma
 

QA= (2)
G
dT
 
 4
44m
a E −σT −a −auG −au E −σT −a (T −T )
( ) ( )
4 La 5  6 hem 7 La 8m a
 
dt
  
Simplifications are set for collectors depending on the receiver type and concentration. For
collectors where
• The sky is shielded from the receiver tubes by a cover or cavity: a = a =0.
4 7
• Receiver tubes are protected from wind by a transparent cover (cover may be flat or tubular
glass): a =a =0.
3 6
• The geometric concentration ratio is higher than 20, K =a =a =a =0.
d 4 6 7
In this case the collector model would be given by Formula (3) assuming that with a good
tracking:
 24dT 

m

Q A η K θθ, G− a TT−− a TT−− a− a TT− (3)
( ) ( ) ( ) ( )
G 0,b b LS T bT 1 m a 2 m a 5  8 m a
 
dt

 
Alternatively to G also the direct normal irradiation G (DNI) may be used, with the incidence
bT bn
angle modifiers K’ including the cosine effect on the aperture: K’ =K cos(θ).
b b
In case the receiver tubes are evacuated tubes the infrared radiation transport is dominating
and convection-conduction inside the tubes is negligible, therefore in this case a should be set
to zero (Formula 4a). In all other cases the convection is not negligible and instead a =0
(Formula 4b) should be used:
dT 4

m

Q A η K θθ, G− a TT−− a− a TT−
( ) ( ) ( ) (4a)
G 0,b b LS T bT 1 m a 5 8 m a

dt


2 dT

m

Q A η K θθ, G− a TT−− a TT−− a (4b)
( ) ( ) ( )
G 0,b b LS T bT 1 m a 2 m a 5 
dt


A is the solar collector gross aperture area (see definition in IEC TS 62862-1-1), as shown in
G
Figure 2, L and W the gross length and projected width of a reflector module, and N the number
i
of reflectors, respectively.
=
=
=
A NL× × W
(5)
G m ∑ i
all mirror rows i
The solar collector gross aperture includes the small gaps between mirrors in a line, however
it excludes the large gaps between mirror rows or between collector modules connected in
series. The projected width of mirrors below the receiver is included even when parts are
shaded in the position where the sun is in the zenith.

Key
L mirror length
m
W collector width
c
Gross aperture area definition: N primary mirrors should be oriented for the sun in the zenith position.
Figure 2 – Sketch of one module of linear Fresnel collector as seen from above
Formula 4a will be preferred, with a parameter for heat losses. If the sum of residuals of the
modelled and measured values is smaller with Formula 4b, and the t-ratio (parameter
value/standard deviation of parameter) of the a parameter is less than 3, then Formula 4b will
be used, with a parameter for heat losses.
6.5.3 Incidence angle modifier (IAM)
When the incidence angles are different from 0° (θ ≠ 0° or/and θ ≠ 0°), the value of the
LS T
incidence angle modifier, K(θ ; θ ), is obtained from Formula (6). The set of values K (θ ) and
LS T L LS
K (θ )obtained as function of the solar incidence angles θ and θ (see Figure 3) shall be
T T LS T
determined as a list of values in tabular form representative for discrete values in intervals of
maximum 10° in the range of 0° to 60° and maximum 15° between 60° and 90”. The values for
90° incidence are set to zero. The functions K (θ ) and K (θ ) for specific angles shall be
L LS T T
interpolated linearly between two angles:
K θ ; θ ≅×Kθ K θ
( ) ( ) ( ) (6)
LS T L LS T T
=
– 16 – IEC 62862-5-2:2022 © IEC 2022
If the Fresnel collector is non-symmetric, positive and negative angles are required for both
angles. The signed convention angles shall be defined in the testing report. It should be recalled
that the end-losses f (see Formula (10)) have to be included in the useful power Formula
end
(4), because the function K defined in Formula (5) is valid for an infinitely long collector [4].
Both QDT and DT methods allow a direct assessment of the biaxial (two-dimensional) IAM-
matrix values of a LFR. The values of the IAM along the transversal and longitudinal axis can
be read in and be optimized automatically according to the measured data.
The longitudinal incidence angle modifier function K (θ ) shall not include the end-effect of a
L LS
finite collector [2].
It is recommended to use a tabulated incidence angle modifier with linear interpolation between
the sampling points.
Key
θ longitudinal solar incidence angle
LS
θ transversal incidence angle
T
Figure 3 – Incidence angles for a linear Fresnel collector
From Figure 3 the calculation of the different incidence angles can be derived:

-1
θ = tan | sinγθ| × tan (7)
( )
Tz
−1
θ tan cosγθ× tan (8)
( )
Lz
−1
θ sin (cosγθ× sin ) (9)
LS z
The effect of finite length of mirror rows and receiver for longitudinal solar angles larger than
0° is approximately described in the following formula (for equal length of receiver and mirror
rows with no offset of the two components).
H
eff
f θθ1− tan
( ) ( ) (10)
end LS LS
L
rec
W 
c 2
(11)
HH+
eff   rec
 
Alternatively to a linear interpolation it may be possible to use for each 1D incidence modifier
function a polynomial in incidence angle or incidence angle cosine. The order of the polynomial
has to be high enough to be able to represent the angular function. This can be tested by
varying the order and check the variation of the functions.
Alternatively to measuring experimentally the IAM in the range of incidence angles θ and θ
T LS
accessible for the location of the test, it is possible also to calculate the complete two-
dimensional range of IAM from ray-tracing, using the geometry of the collector and the optical
properties of mirror and receiver materials. and then check for a selection of minimum 5 defined
pairs of angles and measure the IAM there. The difference between experimental and
theoretical IAM should be less than 5 % points.
6.5.4 Evaluation for the quasi-dynamic test method QDT
The QDT method is based on measurements taken in approximately steady state over a certain
time period and a determination of collector parameters according to the basic test Formula (3)
using least-square fitting methods (multi-linear regression MLR), which is a fast matrix method
that allows a non-iterative parameter fit. Formulas (3) to (11) are used to adapt the general
formula for the specific case. The MLR is used to minimize the difference between the power
output measured and the power output calculated using the parameters a , IAM values, and
i
end-loss factor. Note that the IAM values that can be determined with the QDT method are
related to the accessible angles during the testing days, due to the Sun’s diurnal paths.
Without the loss of generality, no well-known physical model exists for the incident angle
modifier on longitudinal solar plane K (θ ) and on the transversal solar plane K (θ ). The
L LS T T
complexity that represents a two-dimensional model of the IAM, as compared to simpler models,
is commonly solved by complementing the adjustment of the MLR with an additional
mathematical formulation. Sallaberry et al. [5] used the so called “dummy variables” method
with angular ranges of ±1º. Hofer et al. [3] expanded the MLR-method with an iterative
procedure to be able to determine the IAM-values in the longitudinal and transversal directions.
Note that the IAM values
...