Photovoltaic systems - Specification for solar trackers

IEC/TS 62727:2012(E) provides guidelines for the parameters to be specified for solar trackers for photovoltaic systems and provides recommendations for measurement techniques. The purpose of this test specification is to define the performance characteristics of trackers and describe the methods to calculate and/or measure critical parameters. This specification provides industry-wide definitions and parameters for solar trackers. Keywords: solar photovoltaic energy, solar trackers

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IEC/TS 62727
Edition 1.0 2012-05
TECHNICAL
SPECIFICATION
colour
inside
Photovoltaic systems – Specifications for solar trackers
IEC/TS 62727:2012(E)
---------------------- Page: 1 ----------------------
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IEC/TS 62727
Edition 1.0 2012-05
TECHNICAL
SPECIFICATION
colour
inside
Photovoltaic systems – Specifications for solar trackers
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
ICS 27.160 ISBN 978-2-83220-122-0

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

® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 3 ----------------------
– 2 – TS 62727 © IEC:2012(E)
CONTENTS

FOREWORD ........................................................................................................................... 5

1 Scope and object .............................................................................................................. 7

2 Terms and definitions ....................................................................................................... 7

2.1 Photovoltaics (PV) ................................................................................................... 7

2.2 Concentrating photovoltaics (CPV) .......................................................................... 7

2.3 Concentrator module (CPV module) ........................................................................ 7

2.4 Concentrator assembly ............................................................................................ 8

3 Specifications for solar trackers for PV applications .......................................................... 8

3.1 Specification template ............................................................................................. 8

4 Tracker definitions and taxonomy ................................................................................... 10

4.1 General ................................................................................................................. 10

4.2 Payload types ........................................................................................................ 10

4.2.1 Standard photovoltaic (PV) module trackers .............................................. 10

4.2.2 Concentrated photovoltaic (CPV) module trackers ..................................... 11

4.3 Rotational axes ..................................................................................................... 11

4.3.1 Single axis trackers ................................................................................... 11

4.3.2 Dual axis trackers ...................................................................................... 12

4.4 Actuation and control ............................................................................................. 14

4.4.1 Architecture ............................................................................................... 14

4.4.2 Drive types ................................................................................................ 14

4.5 Types of tracker control ......................................................................................... 15

4.5.1 Passive control .......................................................................................... 15

4.5.2 Active control............................................................................................. 15

4.5.3 Backtracking .............................................................................................. 15

4.6 Structural characteristics ....................................................................................... 16

4.6.1 Vertical supports........................................................................................ 16

4.6.2 Foundation types ....................................................................................... 16

4.6.3 Tracker positions ....................................................................................... 17

4.6.4 Stow time .................................................................................................. 17

4.7 Energy consumption .............................................................................................. 17

4.7.1 Daily energy consumption .......................................................................... 17

4.7.2 Stow energy consumption .......................................................................... 18

4.8 External elements and interfaces ........................................................................... 18

4.8.1 Foundation ................................................................................................ 18

4.8.2 Foundation interface .................................................................................. 18

4.8.3 Payload ..................................................................................................... 18

4.8.4 Payload interface ....................................................................................... 18

4.8.5 Payload mechanical interface .................................................................... 18

4.8.6 Payload electrical interface ........................................................................ 18

4.8.7 Grounding interface ................................................................................... 18

4.8.8 Installation effort ........................................................................................ 18

4.8.9 Control interface ........................................................................................ 19

4.9 Internal tolerances ................................................................................................. 19

4.9.1 Primary axis tolerance ............................................................................... 19

4.9.2 Secondary axis tolerance .......................................................................... 20

4.10 Tracker system elements ....................................................................................... 20

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TS 62727 © IEC:2012(E) – 3 –

4.10.1 Mechanical structure ................................................................................. 20

4.10.2 Tracker controller ...................................................................................... 20

4.10.3 Sensors ..................................................................................................... 20

4.11 Reliability terminology ........................................................................................... 20

4.11.1 Mean time between failures (MTBF) .......................................................... 20

4.11.2 Mean time between critical failures (MTBCF) ............................................. 21

4.11.3 Mean time to repair (MTTR) ....................................................................... 21

4.12 Environmental conditions ...................................................................................... 21

4.12.1 Operating temperature range ..................................................................... 21

4.12.2 Survival temperature range ........................................................................ 21

4.12.3 Maximum wind during operation ................................................................ 21

4.12.4 Maximum wind during stow ........................................................................ 21

4.12.5 Snow load ................................................................................................. 21

4.13 Functional tests ..................................................................................................... 22

4.13.1 Static load test .......................................................................................... 22

4.13.2 Moment testing .......................................................................................... 22

4.13.3 Limit switch operation ................................................................................ 22

4.13.4 Manual operation ....................................................................................... 22

5 Tracker accuracy characterization .................................................................................. 22

5.1 Overview ............................................................................................................... 22

5.2 Pointing error (instantaneous) ............................................................................... 22

5.3 Measurement ........................................................................................................ 23

5.3.1 Overview ................................................................................................... 23

5.3.2 Example of experimental method to measure pointing error ....................... 23

5.3.3 Calibration of pointing error measurement tool .......................................... 24

5.4 Calculation of tracker accuracy .............................................................................. 24

5.4.1 Overview ................................................................................................... 24

5.4.2 Data collection ........................................................................................... 25

5.4.3 Data binning by wind speed ....................................................................... 25

5.4.4 Data filtering .............................................................................................. 26

5.4.5 Data quantity ............................................................................................. 26

5.4.6 Accuracy calculations ................................................................................ 26

6 Mechanical characterization ........................................................................................... 27

6.1 General ................................................................................................................. 27

6.2 Backlash ............................................................................................................... 27

6.3 Stiffness ................................................................................................................ 27

7 Reliability testing ............................................................................................................ 28

7.1 Corrosion .............................................................................................................. 28

7.2 Component durability............................................................................................. 28

7.3 Extreme conditions tests ....................................................................................... 28

8 Additional optional accuracy calculations ........................................................................ 28

8.1 Typical tracking accuracy range ............................................................................ 28

8.2 Tracking error histogram ....................................................................................... 29

8.3 Percent of available irradiance as a function of pointing error ................................ 29

Figure 1 – θ = Altitude angle = 0° (zenith angle = 90°) occurs when a vector normal to

the module face is pointing to the horizon. Altitude angle = 90° (zenith angle = 0°)

occurs when the module is facing the sky ............................................................................. 13

Figure 2 – Illustration of primary axis tolerance for a polar tracking axis ............................... 19

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– 4 – TS 62727 © IEC:2012(E)

Figure 3 – General illustration of pointing error ..................................................................... 23

Figure 4 – Two flat parallel plates at a specified distance, one having a pin hole for

sunlight to be tracked on specified-diameter circles that ultimately measure 0,1°, 0,2°,

and 0,3° accuracy rings (more if necessary) ......................................................................... 24

Figure 5 – Pointing error frequency distribution for the entire test period ............................... 29

Figure 6 – Available irradiance as a function of pointing error ............................................... 30

Figure 7 – Available irradiance as a function of pointing error with binning by wind

speed ................................................................................................................................... 30

Table 1 – Tracker specification template ................................................................................. 8

Table 2 – Alternate tracking accuracy reporting template ...................................................... 27

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TS 62727 © IEC:2012(E) – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
PHOTOVOLTAIC SYSTEMS –
SPECIFICATIONS FOR SOLAR TRACKERS
FOREWORD

1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising

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The main task of IEC technical committees is to prepare International Standards. In

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Technical specifications are subject to review within three years of publication to decide

whether they can be transformed into International Standards.

IEC 62727, which is a technical specification, has been prepared by IEC technical committee 82:

Solar photovoltaic energy systems.
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– 6 – TS 62727 © IEC:2012(E)
The text of this technical specification is based on the following documents:
Enquiry draft Report on voting
82/651/DTS 82/711/RVC

Full information on the voting for the approval of this technical specification can be found in

the report on voting indicated in the above table.

This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

The committee has decided that the contents of this publication will remain unchanged until

the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data

related to the specific publication. At this date, the publication will be
• transformed into an International standard,
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

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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TS 62727 © IEC:2012(E) – 7 –
PHOTOVOLTAIC SYSTEMS –
SPECIFICATIONS FOR SOLAR TRACKERS
1 Scope and object

This technical specification provides guidelines for the parameters to be specified for solar

trackers for photovoltaic systems and provides recommendations for measurement
techniques. No attempt is made to determine pass/fail criteria for trackers.

The purpose of this test specification is to define the performance characteristics of trackers

and describe the methods to calculate and/or measure critical parameters.

This specification provides industry-wide definitions and parameters for solar trackers. Each

vendor can design, build, and specify the functionality and accuracy with uniform definition.

This allows consistency in specifying the requirements for purchasing, comparing the products

from different vendors, and verifying the quality of the products. In addition, this specification

will clarify terminology and definitions for trackers and provide examples of measurement

techniques.

This technical specification will be a foundation for other standards to follow, including (but

not limited to) design qualification and reliability.
2 Terms and definitions

For the purposes of this document, the following terms and definitions apply. For additional

tracker-specific terminology, see Clause 5.
2.1
photovoltaics
devices that use solar radiation to generate electrical energy
2.2
concentrating photovoltaics
CPV

devices that focus magnified sunlight on photovoltaics to generate electrical energy. The

sunlight could be magnified by various different methods, such as reflective or refractive

optics, in dish, trough, lens, or other configurations.
2.3
concentrator module
CPV module

a group of receivers (PV cells mounted in some way), optics, and other related components,

such as interconnections and mechanical enclosures, integrated together into a modular

package. The module is typically assembled in a factory and shipped to an installation site to

be installed along with other modules on a solar tracker.

Note 1 to entry: A CPV module typically does not have a field-adjustable focus point. In addition, a module could

be made of several sub-modules. The sub-module is a smaller, modular portion of the full-size module, which might

be assembled into the full module either in a factory or in the field.
---------------------- Page: 9 ----------------------
– 8 – TS 62727 © IEC:2012(E)
2.4
concentrator assembly

a concentrator assembly consists of receivers, optics, and other related components that have

a field-adjustable focus point and are typically assembled and aligned in field

EXAMPLE: A system that combines a single large dish with a receiver unit which must be

aligned with the focal point of the disk.

Note 1 to entry: This term is used to differentiate certain CPV designs from the CPV modules mentioned above.

3 Specifications for solar trackers for PV applications
a) Specification template

All trackers complying with this specification should provide, as part of their product marking

and documentation, a table in the form specified below (see Table 1). See later clauses and

subclauses of this Technical Specification for further explanation of individual specifications.

Some of the specifications within the table are optional; however, if a tracker manufacturer

chooses to include optional information, it should be reported and measured in the specific

way shown in Table 1 (and in some cases, also described later in this Technical
Specification).

Engineering safety factors should be dictated by appropriate local standards and applications

details and documented by the tracker manufacturer.

The specification template below is a visual example only and should not be read as a list of

requirements.
Table 1 – Tracker specification template
Characteristic Example Notes/Clause/Subclause
Manufacturer The XYZ Company
Model number XX1090
Type of tracker CPV Tracker, Dual Axis 4.2, 4.3
Payload characteristics
Minimum/maximum mass 100/1 025 kg 4.8.3
supported
Payload center of mass 0-30 cm distance perpendicular to 4.8.3
restrictions mounting surface
Maximum dynamic torques Azimuth (Θ ): 10 kN⋅m 4.13.2, 7.3
allowed while moving
Θ , Θ : 5 kN⋅m
x y
[ should provide a set of diagrams to
clarify torques and which axes they
are relative to ]
Maximum static torques allowed [ should provide a set of diagrams ] 4.13.1, 7.3
while in stow position
Installation characteristics
Allowable foundation Reinforced concrete 4.6.2
Foundation tolerance in primary 4.9
± 0,5°
axis
Foundation tolerance in secondary ± 0,5° 4.9
axis
Electrical characteristics
Includes backup power? No N/A
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TS 62727 © IEC:2012(E) – 9 –
Characteristic Example Notes/Clause/Subclause
Daily energy consumption 1 kWh typical 4.7.1
5 kWh maximum
Stow energy consumption kWh typical 4.7.2
1 kWh maximum
Input power requirements 100-240 VAC, 50-60 Hz, 5 A No specifics defined
Tracking accuracy
Accuracy, typical 0,1° 5.4.6
(low wind, min deflect point)
Accuracy, typical 0,3° 5.4.6
(low wind, max deflect point)
Accuracy, 95 percentile 0,5° 5.4.6
(low wind, min deflect point)
Accuracy, 95 percentile 0,8° 5.4.6
(low wind, max deflect point)
Mean wind speed during the “low 3 km/h 5.4.6
wind” test conditions
Accuracy, typical 0,7° 5.4.6
(high wind, min deflect point)
Accuracy, typical 1,0° 5.4.6
(high wind, max deflect point)
Accuracy, 95 percentile 1,1 5.4.6
(high wind, min deflect point)
Accuracy, 95 percentile 1,6° 5.4.6
(high wind, max deflect point)
Mean wind speed during the “high 12 km/h 5.4.6
wind” test conditions
Weight and area of payload 500 kg payload evenly distributed 5.4.2.1
installed during testing over a 50 m area
Payload center of mass installed Payload center of mass 20 cm above 5.4.2.1
during testing the module mounting surface
Control characteristics
Control algorithm Hybrid 4.5
Control interface None 4.8.9
External communication interface Ethernet/TCP-IP No specific description
Emergency stow provided? Yes, at wind speeds 100 km/h 4.6.4, 4.12.3
Stow time 4 minutes 4.6.4
Clock accuracy 1 second per year N/A
Mechanical design
Range of motion, primary axis ± 160° azimuth 4.6.3.3
Range of motion, secondary axis 10°-90° elevation 4.6.3.3
System stiffness Azimuth (Θ ): 0,05º / 1 000 N⋅m, Θ : 6.3
z x
0,1º / 1 000 N⋅m
Diagrams attached show applied
loads and observed deflection
Backlash 0,1° maximum 6.2
Environmental conditions
Maximum allowable wind speed Design values: 4.12.3
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– 10 – TS 62727 © IEC:2012(E)
Characteristic Example Notes/Clause/Subclause
during tracking
80 km/h with 0 % terrain slope, open
country,
60 km/h with 8 % terrain slope,
suburban, urban
Tested to:
60 km/h with 0 % terrain slope, open
country
Maximum allowable wind speed in Design values: 4.12.4
stow
150 km/h horizontal wind,
120 km/h with 10 % slope
Tested to:
80 km/h with 0 % slope
Temperature operational range –20 °C to +50 °C 4.12.1
Temperature survival range –40 °C to +60 °C 4.12.2
Snow rating Up to 20 kg/m of snow load allowed 4.12.5

For an alternate template for the presentation of accuracy specifications see Table 2.

4 Tracker definitions and taxonomy
4.1 General

Solar trackers are mechanical devices used to point PV modules towards the sun or to direct

sunlight on PV cells or modules. Photovoltaic trackers can be classified into two types:

standard photovoltaic (PV) trackers and concentrated photovoltaic (CPV) trackers. Each of

these tracker types can be further categorized by the number and orientation of their axes,

their actuation architecture and drive type, their intended applications, and their vertical

supports and foundation type.
4.2 Payload types
4.2.1 Standard photovoltaic (PV) module trackers
4.2.1.1 Uses

Standard photovoltaic trackers are used to minimize the angle of incidence between incoming

light and a photovoltaic module. This increases the amount of energy produced from a fixed

amount of power generating capacity.
4.2.1.2 Type of light accepted

Photovoltaic modules accept both direct and diffuse light from all angles. This means that

systems implementing standard photovoltaic trackers produce energy even when not directly

pointed at the sun. Tracking in standard photovoltaic systems is used to increase the amount

of energy produced by the direct component of the incoming light.
4.2.1.3 Accuracy requirements

In standard photovoltaic systems, the energy contributed by the direct beam drops off with the

cosine of the angle between the incoming light and the module. Thus trackers that have

accuracies of ± 5° can deliver more than 99,6 % of the energy supplied by the direct beam. As

a result, high-accuracy tracking is not typically used.
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TS 62727 © IEC:2012(E) – 11 –
4.2.2 Co
...

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