IEC 62862-3-2:2018

Solar thermal electric plants - Part 3-2: Systems and components - General requirements and test methods for large-size parabolic-trough collectors

IEC 62862-3-2:2018 specifies the requirements and the test methods for the characterization of a large-size parabolic-trough collector. This document covers the determination of optical and thermal performance of parabolic-trough collectors, and the tracking accuracy of the collector one-axis tracking system. This test method is for outdoor testing only. This document applies to parabolic-trough collectors equipped with the manufacturer-supplied sun tracking mechanism.

Centrales électriques solaires thermodynamiques - Partie 3-2: Systèmes et composants - Exigences générales et méthodes d'essai des capteurs cylindro-paraboliques de grande taille

L'IEC 62862-3-2:2018 spécifie les exigences et méthodes d'essai pour la caractérisation d'un capteur cylindro-parabolique de grande taille. Le présent document couvre la détermination des performances optiques et thermiques des capteurs cylindro-paraboliques et la précision du système de suiveur à un axe du capteur. Cette méthode ne concerne que les essais en extérieur. Le présent document s'applique aux capteurs cylindro-paraboliques équipés d'un mécanisme suiveur du soleil fourni par le fabricant.

General Information

• Status: Published
• Publication Date: 09-Jul-2018
• ICS: 27.160 - Solar energy engineering
• ICS: 29.060.10 - Wires
• Technical Committee: TC 117 - Solar thermal electric plants
• Drafting Committee: PT 62862-3-2 - TC 117/PT 62862-3-2
• Current Stage: PPUB - Publication issued
• Start Date: 29-Jun-2018
• Completion Date: 10-Jul-2018

Overview

IEC 62862-3-2:2018 is an international standard developed by the International Electrotechnical Commission (IEC) that specifies general requirements and test methods for large-size parabolic-trough collectors used in solar thermal electric plants. This standard focuses on the optical and thermal performance characterization of these collectors, as well as the tracking accuracy of their one-axis solar tracking systems.

Designed solely for outdoor testing, IEC 62862-3-2:2018 applies to parabolic-trough collectors equipped with the manufacturer-supplied sun tracking mechanism. It excludes conditions involving phase-change of the working fluid. The document ensures consistent, reliable testing methodologies to evaluate the efficiency and accuracy of parabolic-trough solar collectors at large scales, supporting manufacturers, engineers, and researchers in quality assurance and development.

Key Topics

• Performance Testing Requirements
  The standard defines test procedures for measuring the thermal and optical efficiency of parabolic-trough collectors. This includes the collector's ability to convert solar radiation into usable thermal energy.

• Tracking Accuracy Evaluation
  It establishes methods to determine the precision of the one-axis solar tracking system, critical for maximizing solar energy capture by keeping the collector aligned with the sun.

• Instrumentation and Measurement
  Specific instrumentation requirements include measurement of:

  • Solar radiation
  • Fluid flow rate
  • Temperature at various points
  • Wind speed
  • Data acquisition systems for accurate result recording

• Test Setup and Procedures
  Guidelines for test equipment installation, sample descriptions, and cleanliness protocols ensure reliable and repeatable test conditions.

• Result Calculation and Reporting
  The standard details calculations for useful power output, incidence angle modifiers (IAMs), and validation of performance tests. It also includes templates for reporting results and uncertainties.

• Additional Technical Content
  Annexes provide detailed descriptions of collector components such as reflectors, receiver tubes, bearing structures, and tracking systems, ensuring comprehensive evaluation.

Applications

IEC 62862-3-2:2018 is essential for organizations and professionals involved in:

• Solar Thermal Power Generation
  Ensuring large-scale parabolic-trough collectors meet efficiency and operational standards for commercial solar power plants.

• Collector Design and Manufacturing
  Verifying the quality, performance, and tracking accuracy of solar thermal collector products before deployment.

• Research and Development
  Providing standardized methods to compare prototype and innovative collector designs under real outdoor conditions.

• Quality Assurance and Certification Bodies
  Facilitating independent verification of solar collector performance for product certification and regulatory compliance.

• Project Engineering and Plant Operation
  Supporting optimal design and performance assessment of solar thermal plants to maximize energy yield and operational reliability.

Related Standards

IEC 62862-3-2:2018 integrates with and references several related international standards to maintain coherence within the solar thermal and electrotechnical sectors:

• IEC TS 62862-1-1 – Solar thermal electric plants – Terminology: Ensures consistent use of technical terms across the solar thermal electric plant standards.

• ISO 9488:1999 – Solar energy – Vocabulary: Provides foundational solar energy terminology essential for clear communication.

• ISO 9806:2017 – Solar energy – Solar thermal collectors – Test methods: Offers additional standardized test methods related to solar thermal collectors, complementing IEC 62862-3-2.

By adhering to IEC 62862-3-2:2018, stakeholders can confidently assess the performance and operational precision of large-scale parabolic-trough collectors, advancing the adoption and optimization of solar thermal electric plants worldwide.

Keywords: IEC 62862-3-2, parabolic-trough collectors, solar thermal electric plants, solar collector testing, tracking accuracy, thermal performance, optical performance, solar energy standards, outdoor testing, solar thermal system components.

Standards Content (Sample)

IEC 62862-3-2 ®
Edition 1.0 2018-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Solar thermal electric plants –
Part 3-2: Systems and components – General requirements and test methods for
large-size parabolic-trough collectors

Centrales électriques solaires thermodynamiques –
Partie 3-2: Systèmes et composants – Exigences générales et méthodes d'essai
des capteurs cylindro-paraboliques de grande taille

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IEC 62862-3-2 ®
Edition 1.0 2018-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Solar thermal electric plants –

Part 3-2: Systems and components – General requirements and test methods for

large-size parabolic-trough collectors

Centrales électriques solaires thermodynamiques –

Partie 3-2: Systèmes et composants – Exigences générales et méthodes d'essai

des capteurs cylindro-paraboliques de grande taille

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 27.160 ISBN 978-2-8322-5790-6

– 2 – IEC 62862-3-2:2018 © IEC 2018
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Terms, definitions and symbols. 6
3.1 Terms and definitions . 6
3.2 Symbols . 7
4 Test requirements . 7
5 Instrumentation . 7
5.1 Solar radiation measurement . 7
5.2 Flow rate measurement . 7
5.3 Temperature measurements . 7
5.4 Wind speed measurement . 7
5.5 Data acquisition . 8
5.6 Tracking accuracy measurement . 8
6 Test procedure . 8
6.1 Sample description . 8
6.2 Test equipment (installation/mounting/cleanliness) . 8
6.2.1 Performance test . 8
6.2.2 Tracking error test . 10
6.3 Measurement procedure . 10
6.3.1 Performance test . 10
6.3.2 Tracking error test . 10
6.4 Calculation and test results . 11
6.4.1 General . 11
6.4.2 Useful power . 11
6.4.3 Incidence angle modifier (IAM) . 12
6.4.4 Validation performance test . 12
6.4.5 Tracking error test . 13
6.4.6 Uncertainty estimation . 14
7 Reporting format . 14
Annex A (informative) Parabolic-trough collector description/requirements . 15
A.1 General description . 15
A.1.1 General . 15
A.1.2 Bearing structure . 16
A.1.3 Drive pylon . 16
A.1.4 Middle, end and shared pylon . 16
A.1.5 Reflectors . 16
A.1.6 Receiver tube . 16
A.1.7 Tracking system . 17
A.2 Operation modes . 17
Annex B (normative) Documentation to be supplied by the collector manufacturer . 18
Annex C (normative) Test report . 21
C.1 General . 21
C.2 Collector characteristics . 21

C.3 Parabolic-trough collector limitations. 22
C.4 Description of the experimental setup . 22
C.5 Results . 22
Bibliography . 24

Figure 1 – Test equipment installation. 9
Figure 2 – Structure sketch of one module of parabolic-trough collector – Gross
aperture area definition . 12
Figure A.1 – General view of a parabolic-trough collector . 15

Table C.1 – Alternate tracking accuracy reporting template . 22

– 4 – IEC 62862-3-2:2018 © IEC 2018
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SOLAR THERMAL ELECTRIC PLANTS –

Part 3-2: Systems and components – General requirements and
test methods for large-size parabolic-trough collectors

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 62862-3-2 has been prepared by IEC technical committee 117:
Solar thermal electric plants.
The text of this International Standard is based on the following documents:
FDIS Report on voting
117/87/FDIS 117/89/RVD
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.

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.
– 6 – IEC 62862-3-2:2018 © IEC 2018
SOLAR THERMAL ELECTRIC PLANTS –

Part 3-2: Systems and components – General requirements and
test methods for large-size parabolic-trough collectors

1 Scope
This part of IEC 62862 specifies the requirements and the test methods for the
characterization of a large-size parabolic-trough collector.
This document covers the determination of optical and thermal performance of parabolic-
trough collectors, and the tracking accuracy of the collector one-axis tracking system. This
test method is for outdoor testing only.
This document applies to parabolic-trough collectors equipped with the manufacturer-supplied
sun tracking mechanism.
The test method in this document does not apply to any collector under operating conditions
where phase-change of the fluid occurs.
This document applies to the whole collector.
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 – Terminology
ISO 9488:1999, 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 and
IEC 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

3.2 Symbols
The following symbols are used in this document:
β elevation (measured by an inclinometer) (º)
real
ρ reflectance measured during the test (-)
test
reference value of the reflectance of the reflectors installed in the collector (-)
ρ
nom
θ
tracker elevation error (°)
T
F ratio between the product of the reflectors' reflectance and the glass envelope transmittance
c
during the test and the product of the reflectance and transmittance nominal values
ratio between the measured specular reflectance of reflector to the nominal specular
χ
reflector
reflectance of reflector
4 Test requirements
The parabolic-trough collector should be equipped with all the components supplied by the
manufacturer (such as bearing structure, reflector facets, receiver tubes, actuator system and
control) and mounted according to the manufacturer's instructions.
The different components/elements (such as the receiver, reflector, tracker, structure) should
be previously tested separately by current test methods or standards when available.The
documentation to be supplied by the manufacturer shall be according to Annex B.
5 Instrumentation
5.1 Solar radiation measurement
Solar radiation measurement shall be performed according to 21.1 of ISO 9806:2017.
Incidence angles will be determined by calculation or with sun position sensors with an
accuracy equal to or higher than ± 0,1º. In the case they are calculated from the sun position
equation, the accuracy of the calculation algorithm shall be equal to or higher than 0,025°.
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.
The collector inlet and outlet positions shall be defined by the manufacturer and the
temperature sensors shall be installed at no more than 200 mm from this point.
NOTE The problems caused by the concentrated light on the sensors if the sensors are mounted in the focus
zone are taken into consideration.
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 at a distance from the collector extremity (end pylon as shown in Figure A.1)
not higher than 100 m. If there is no wind speed sensor close enough to the meteorological
station of the plant, one temporary sensor should be added close to the collector.

– 8 – IEC 62862-3-2:2018 © IEC 2018
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. Accuracy
of the inclinometers 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) and another one at one of the collector's end.
6 Test procedure
6.1 Sample description
A general description and requirements of the parabolic-trough collector are given in Annex A.
The collector description 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 be selected randomly from the
production.
All the serial numbers and identification of those components should be reported in the test
report.
6.2 Test equipment (installation/mounting/cleanliness)
6.2.1 Performance test
The sensors shall be mounted according to ISO 9806:2017. A basic diagram of the test
installation is presented in Figure 1.

7 8 9
2 3 4 5 6
Power block / Balance of plant

IEC
Key
1 pump 6 temperature sensor (t )
out
2 flow meter (test) 7 ambient temperature sensor (t )
a
3 temperature sensor 8 pyrheliometer
4 temperature sensor (t ) 9 anemometer
in
5 parabolic-trough collector unit
Figure 1 – Test equipment installation
During the tests of a parabolic-trough collector it will be necessary to guarantee that the
reflectors and glass envelopes of the receivers are kept clean. It shall be ensured that the
< 1,0. For testing purposes, the
collector’s cleanliness factor is within the range 0,95 < F
c
cleanliness factor is defined as the ratio between the product of the reflectors reflectance and
the glass envelope transmittance during the test and the product of the reflectance and
transmittance nominal values.
There is currently no field instrumentation available to determine the degree of dirt in the
receiver cover once installed in the collector; a good approach is to assume that the same
percentage of reduction in the reflectors reflectance and in transmittance of the glass
envelope is produced due to dirt. The reflectors cleanliness factor χ will be measured
reflector
with a portable reflectometer in each sequence of the test, at least in five positions per
module. The number and position of points measured should be reported in the test report. If
the mean cleanliness factor is lower than 0,95, the collector (both reflectors and glass tube)

should be cleaned.
– 10 – IEC 62862-3-2:2018 © IEC 2018
Therefore, the global cleanliness is given by Equation (1):
 ρ 
1,5
test
F χ (1)
( )
 
C reflector
ρ
 nom 
where ρ is the specular reflectance measured during the test and ρ is the reference
test nom
value of the specular reflectance of the reflectors installed in the collector.
ρ and ρ should be measured with the same equipment.
nom test
6.2.2 Tracking error test
The solar tracker should be installed according to the manufacturer's recommendations. The
collector should have all the necessary components (receiver tube, reflector, structure, etc.).
One inclinometer or other angular sensor should be mounted on the centre of the parabola or
on the reflector, close to the drive pylon.
The minimum number of measurement devices is two, one close to the drive pylon and one
mounted in the collector end. It is recommended to install an additional sensor in the other
collector end. If the sensor is not perfectly parallel to the concentrator aperture an offset
should be subtracted to the tracking error calculated.
6.3 Measurement procedure
6.3.1 Performance test
The thermal performance test to determine peak optical efficiency, heat losses and incidence
angle modifier shall be performed according to ISO 9806:2017 using the quasi-dynamic test
method. The wind speed shall be less than 5,5 m/s for each point measured.
6.3.2 Tracking error test
The tracking test is performed over the full available tracking range (e.g. from sunrise to
sunset), by manually set tracking angles in steps of 10 degrees. The data shall be recorded
and evaluated for all the steps. Deviations between measured values and set values at the
drive have to be analysed. Also deviation between measured values at collector end and
collector centre have to be analysed. The recorded data should include:
• the tracker elevation error recorded in 1 min average intervals and calculated as
Equation (2):
θ ββ− (2)
T set
with the set tracking angles β and the real β (measured with an inclinometer);
set
• direct normal irradiance (DNI) recorded in 1 min average intervals (only if tracking system
with sun sensor);
• wind speed reported in 1 min increments for the 10 min mean speed at 10 m height
(terrain for the wind measurement and tracker location shall have a slope of less than
3 %);
• date and time.
The date and location of the test should be reported to facilitate assessment of adequacy of
the data collection, particularly with respect to the range of motion.
=
==
6.4 Calculation and test results
6.4.1 General
Calculation of the test results shall be performed according to Clause 24 of ISO 9806:2017 for
the quasi-dynamic test method.
The increase of specific enthalpy of the fluid Δh is equal to ∆=hh − h . Polynomial
out in
approximations or interpolation of tabulated values can be used for the specific enthalpy h(T)
of the heat transfer fluid.
It is not recommended to use the specific heat capacity, because it depends on both inlet and
outlet temperature.
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 or any other
independent body. This data shall be perfectly documented and referenced.
6.4.2 Useful power
The model of the collector should be according to Formula (13) from ISO 9806:2017.
Additional requirements are set for collectors with a transparent cover and a concentration
ratio higher than 3, or for evacuated concentrating collectors: the wind speed dependency can
be neglected. So, some parameters (a , a and a ) may be set to 0.
3 6 7
Additionally, for collectors with a concentration ratio higher than 20, the parameters a and K
4 d
may also be set to 0. In this case the collector model would be given by Equation (3) or
Equation (4) assuming that with a good tracking, θ = 0º.
T
⋅
  dt 
m
Q= m∆=h A ηθK G F − a tt− − a tt− − a (3)
( ) ( ) ( )
 
G 0,b b L b C 1 ma 8 ma 5
dt
 
⋅
  dt 
m
Q= m∆=h A ηθK G F − a tt− − a tt− − a (4)
( ) ( ) ( )
G  0,b b L b C 1 ma 2 m a 5 
dt
 
A : should be the solar collector gross aperture area (see definition in IEC TS 62862-1-1), as
G
shown in Figure 2. A = L × W × N, where L and W are the gross length and width and N is the
G
number of modules, respectively.

– 12 – IEC 62862-3-2:2018 © IEC 2018
L
Reflector
Receiver
Driver
Bearing
structure
Pedestal
IEC
Figure 2 – Structure sketch of one module of parabolic-trough collector –
Gross aperture area definition
Equation (3) will be preferred, with a parameter for heat losses. If the r of the regression is
better with Equation (4), and the t-ratio (parameter value/standard deviation of parameter) of
the a parameter is less than 3, then Equation (4) will be used, with a parameter for heat
8 2
losses.
6.4.3 Incidence angle modifier (IAM)
When the incidence angle is different from 0° (θ ≠ 0°), the value of the incidence angle
L
modifier, K(θ), is obtained from Equation (5). The set of values K(θ) obtained as a function of
the different incidence angles θ shall be set to a curve type such as:
2 n
b ⋅+θθb ⋅ + . + b ⋅θ
12 n
K θ 1− (5)
( )
cos θ
( )
where parameters b , b and b will be determined by least-square fitting.
1 2 n
NOTE In general a quadratic or cubic polynomial is adequate.
6.4.4 Validation performance test
6.4.4.1 Power output
The test consists in keeping the collector in operation for two days (for at least four hours, two
hours before noon and two hours after noon) at two different fluid inlet temperatures, T ,
in
(different by at least 10 K) with the daily average environment ambient temperature different
from no more than 5 ºC and steady within the normal working temperature range of the
collector, with the transversal incidence angle at θ = (0 ± 0,1)º and the longitudinal incidence
T
angle varying during the whole day.
Stability of the measurements and other requirements of the global efficiency test will be the
same as in the thermal performance test.
To validate the former characterization, the useful power output from the collector shall be
calculated according to Equation (3) or Equation (4) considering the determined parameters.
The average difference between the calculated and measured power should be within ± 5 %.
W
=
6.4.4.2 Peak optical efficiency (optional)
The peak optical efficiency should be calculated theoretically using the intercept factor
measured by deflectometry, close-range photogrammetry, or other techniques, and the optical
properties provided from the receiver and reflectors manufacturers (transmittance of glass
cover, absorptance of receiver tube and reflectance of the reflector).
The formula to calculate the peak optical efficiency from the solar components manufacturers
specifications is:
η = ργ⋅ ⋅⋅τ α (6)
opt,0º T,0º
Where ρ is the near-normal reflectors solar reflectance, γ is the near-normal overall
T,0º
intercept factor, which is the product of the intercept factor of the solar concentrator γ and
C
the effective length factor of the receiver tubes installed in the parabolic-trough collector γ ; τ
R
is the near-normal transmittance of the receiver glass envelope, and α is the near-normal
absorptance of the receiver metallic tube.
The difference between the determined optical efficiency (Equation (3) or Equation (4)) and
measured (Equation (6)) should be within ± 5 %. If the difference is higher, at least the test
results, data provided by the manufacturers of the single components and the overall intercept
factor measurements should be analysed and reported.
6.4.5 Tracking error test
6.4.5.1 Data binning by wind speed
If necessary, the data have to be at least separated into low and high measured wind speed
bins using 4 m/s as the threshold value.
Two bins represent a compromise to minimize test duration, complexity, and cost. The
manufacturer may choose to report tracking accuracy statistics for additional wind speed bins
and include its relationship with wind direction.
If the solar tracker has a sun sensor filter for minimum irradiance (optional), all data recorded
with a direct normal irradiance that is less than 250 W/m should be removed.
6.4.5.2 Data quantity
For each of the data sets (“low wind, minimum error measurement”, “high wind, maximum
error measurement”, and so on), ensure there are a sufficient number of data points.
The data from each tracking error sensor should satisfy these criteria:
• at least 360 data points after the above filtering;
• at least five separate days, with at least 50 data points per day;
• at least 180 points at high wind speed;
• at least 50 data points before noon and 50 points after noon.

– 14 – IEC 62862-3-2:2018 © IEC 2018
6.4.5.3 Accuracy calculations
For each of the data sets, calculate the following two values:
• Typical accuracy: the median value of the tracking error over the filtered data set. As all
recorded tracking error values will be positive values, the “typical accuracy” will be a value
greater than zero but less than the 95th percentile accuracy.
• 95th percentile accuracy: the 95th percentile value of the tracking error over the filtered
data set. That is, 95 % of the measured data points fall below this error.
NOTE 95th percentile accuracy in no way implies that the tracking accuracy statistics follow rules for a normal
distribution.
6.4.6 Uncertainty estimation
The calculation of standard uncertainty of the characteristic parameters describing the optical
and thermal performance, calculated applying the test method described in this document,
follows the rules established in Annex D of ISO 9806:2017.
7 Reporting format
The final report on the optical and thermal performance of the tested parabolic-trough
collector shall include detailed information of:
• The tested parabolic-trough collector description.
• The test setup (description of the test facility where the collector has been tested, sensors
and other equipment used to measure the variables needed to apply this test method).
• The result of the determined model parameters accompanied with their corresponding
uncertainty values.
• The result of tracking error characterization.
• The graph to show the data set of the variables measured during the tests leading to the
final result, according to ISO 9806:2017, Figure 9 (in this case, t – t versus DNI) and
m a
Figure 10 (DNI versus θi).
The contents of the report shall be structured according to Annex C.

Annex A
(informative)
Parabolic-trough collector description/requirements
A.1 General description
A.1.1 General
A parabolic-trough collector is a line-focus solar collector that concentrates the solar radiation
by means of a reflector with a parabolic cross section. It is composed of a set of modules
connected in series driven by a common drive unit and with only one sun-tracking system
(see IEC TS 62862-1-1). A receiver tube is located at the focus of the parabola. The reflector-
receiver trough is mounted on a mechanical support system that includes steel pylons and
bearings. Each parabolic-trough collector includes local instruments, a hydraulic drive system,
and its own local controller via which it independently tracks the sun, and maintains the
reflector focused on the receiver.
The parabolic-trough collector is the basic functional unit which forms a collector loop in a
solar field (Figure A.1). Each collector loop is formed by parabolic-trough collectors. Each
collector contains the following elements:
• several modules,
• one drive pylon,
• several middle pylons,
• end pylons, if applicable,
• shared pylons, if applicable.
Shared pylon
Module
Middle pylon
Drive pylon
End pylon
IEC
Figure A.1 – General view of a parabolic-trough collector
The basic characteristics of a parabolic-trough collector are detailed below:
• focal distance,
• aperture width,
• number of modules per collector,
• module/collector length,
• number of reflectors per module/collector,
• receiver tubes per module/collector,
• maximum operational wind speed,
• maximum survival wind speed.

– 16 – IEC 62862-3-2:2018 © IEC 2018
The collector is basically formed by the following elements.
A.1.2 Bearing structure
The function of the bearing structure is to support the reflectors, provide the final parabolic-
trough surface, and ensure they are positioned correctly to track the sun. It has the adequate
strength to withstand external loads, and high stiffness to provide good optical performance.
In general, the bearing structure of a module consists of a main body, which is typically a
torque tube or a space frame made of steel, aluminum or other materials, reflector support
points installed in metallic struts (on the space frame structure) or in cantilever arms (e.g.
torque tube structure), and receiver supports, which shall allow the displacements generated
by the thermal expansion, so they are joined to the bearing structure by a flexible connection
(e.g. a flexible metal sheet).
A.1.3 Drive pylon
It is the central pylon of a parabolic-trough collector. It is a structural element fixed to the
ground, where the sun tracking system is mounted, and that supports the collector itself and
also the internal and external loads applied to the collector. In its interior it has a hydraulic
drive or electrical gear unit that allow it to drive the set of modules assembled, which
compose the parabolic-trough collector. In the case of hydraulic units it usually consists of the
two hydraulic cylinders, but also includes a hydraulic group, electrovalves, deposit, filter and
other actuation elements.
A.1.4 Middle, end and shared pylon
All these pylons are designed to support the shaft of the modules.
• Middle pylons are situated between two modules that belong to the same parabolic-trough
collector.
• Shared pylons are situated between two modules that belong to different parabolic-trough
collectors.
• End pylons are situated at the end of the parabolic-trough collectors.
A.1.5 Reflectors
The reflector panel is the element reflecting the solar radiation onto the receiver tubes. It shall
have high precision, high specular reflectivity and large durability.
It is possible to use parabolic reflectors, which are directly manufactured with the appropriate
curvature for a specific design of parabolic-trough collector, i.e. with the dimensions and focal
distance for a specific geometry, or to use flat thin reflectors, which are curved during the
construction of the whole parabolic-trough collector.
The reflectors can be silver coated glass reflectors or can be of alternative reflector materials.
A.1.6 Receiver tube
The receiver tube is another key component of the parabolic-trough collector that converts the
radiation concentrated by the reflectors into heat. This receiver tube consists of an inner
metallic tube (usually made of stainless steel), an outer glass tube (glass envelope) and
metallic expansion bellows on both sides, which form the joint between the inner metallic tube
and the outer glass tube. The inner tube is covered by a selective coating to maximize the
absorptance of the concentrated radiation and minimize the re-radiation of the infrared
radiation (thermal emittance). The glass envelope on both ends is joined with the metallic
bellows by a sophisticated glass-to-metal seal, resistant to operating temperatures and
sealing the enclosed vacuum. On the other side, the metallic bellows are welded to the inner
receiver tubes. The elasticity of these connecting bellows compensates the difference of the

thermal expansion of the inner metallic and the outer glass envelope during warming up and
cooling down of the receiver tubes. The sensitive glass-to-metal seal is protected from
damage due to overheating by solar radiation by a sleeve called bellow shield.
The energy of the concentrated radiation is converted into thermal energy at the absorber
surface of the inner metallic tube, which transfers the circulating heat transfer fluid and heats
it up. The glass envelope works as an additional barrier to the infrared re-radiation and
reduces thermal losses like a greenhouse made of glass. It is usually covered by an
antireflective coating.
A.1.7 Tracking system
The parabolic-trough collector has to track the sun to reach a continuous concentration of the
direct solar irradiance on the receiver tube from sunrise to sunset.
The parabolic-trough collector is a line-focus solar collector and has a one-axis tracking
system. Each collector rotates during its daily tracking of the sun around its rotation axis
driven by a drive unit composed of hydraulic actuators or electric gear drives which move the
bearing structure, reflectors and receiver tubes.
The tracking is controlled by a local controller, which needs information about the sun
position. This information is usually calculated with a mathematical algorithm that calculates
the sun position very accurately.
The sun position is compared to the collector axis position and any difference is corrected
using the drive unit. It is also possible to use sun sensors composed of lens and photocells.
A.2 Operation modes
There are different operation modes of the parabolic-trough collector when it is installed in a
solar field. The basic operation modes are:
– Track position: position of the collector when it is focused, i.e. when it is tracking the sun
and the concentrated solar radiation is impinging on the receiver.
– Stow position: rest or defense position of the collector. It is the position that the collector
has during the night, when the solar field is not running, or when there are strong wind
conditions.
– Desteer (defocusing) position: position of the collector when it is tracking the sun but
partially defocused, so the concentrated solar radiation is not impinging on the receiver.

– 18 – IEC 62862-3-2:2018 © IEC 2018
Annex B
(normative)
Documentation to be supplied by the collector manufacturer
The minimum information to be supplied by the manufacturer shall be:
1) General configuration of the parabolic-trough collector
a) Model and manufacturer
b) Axes and movemen
...