CEN/TR 16999:2019

Solar energy systems for roofs - Requirements for structural connections to solar panels

This Technical Report provides guidance on the principles and requirements of structural design for the safety and serviceability of the structural connection between solar energy panels (thermal or photovoltaic) that are mounted on flat or pitched roofs.
This Technical Report does not include requirements for:
-   weather tightness of the roof, solar panels and connections;
-   electrical, thermal or mechanical characteristics of the solar panels;
-   precautions against fire of the installation.

Solare Energiesysteme für Dächer - Anforderungen an konstruktive Verbindungen zu Sonnenkollektoren

Dieses Dokument enthält Leitlinien zu den Prinzipien für und Anforderungen an die Tragwerksplanung zur Sicherstellung der Sicherheit und Gebrauchstauglichkeit der konstruktiven Verbindung zwischen Sonnenkollektoren (thermisch oder photovoltaisch) und der Konstruktion von Flach  oder Schrägdächern.
Dieses Dokument enthält keine Anforderungen für:
- die Witterungsbeständigkeit des Daches, der Sonnenkollektoren und der Anschlüsse;
- elektrische, thermische oder mechanische Eigenschaften der Sonnenkollektoren;
- Vorkehrungen gegen einen Brand der Anlage.

Systèmes d'énergie solaire pour les toits : Exigences relatives aux raccordements des panneaux solaires à la charpente

Sončni energijski sistemi za strehe: zahteve za konstrukcijske povezave solarnih plošč

V tem tehničnem poročilu so podane smernice o načelih in zahtevah glede konstrukcijske zasnove za varnost in uporabnost konstrukcijske povezave med (toplotnimi ali fotonapetostnimi) solarnimi ploščami, ki so nameščene na ravnih ali poševnih strehah.
To tehnično poročilo ne vključuje zahtev za:
– odpornost strehe, solarnih plošč in priključkov na vremenske pogoje;
– električne, toplotne ali mehanske lastnosti solarnih plošč;
– varnostne ukrepe proti požaru v napeljavi.

General Information

• Status: Published
• Publication Date: 26-Feb-2019
• ICS: 27.160 - Solar energy engineering
• Technical Committee: CEN/TC 128 - Roof covering products for discontinuous laying and products for wall cladding
• Drafting Committee: CEN/TC 128/WG 3 - Renewable energy systems for roofs
• Current Stage: 6060 - Definitive text made available (DAV) - Publishing
• Start Date: 27-Feb-2019
• Due Date: 20-Sep-2016
• Completion Date: 27-Feb-2019
• Ref Project: SIST-TP CEN/TR 16999:2019 - Solar energy systems for roofs: Requirements for structural connections to solar panels

Overview

CEN/TR 16999:2019 - Solar energy systems for roofs: Requirements for structural connections to solar panels is a CEN Technical Report providing guidance on the structural design principles and requirements for the safety and serviceability of connections between roof-mounted solar panels (thermal collectors or photovoltaic modules) and roof structures. It covers installations on both flat and pitched roofs and focuses on the structural connection (mounting, anchors, frames and fixings).

Not included: weather tightness of roof or panel connections, electrical/thermal/mechanical characteristics of panels, and fire-precaution requirements.

Key topics and technical requirements

• Design principles: guidance on limit-state design including Ultimate Limit State (ULS) and Serviceability Limit State (SLS) to ensure safety and durability of connections.
• Actions and loads: determination of permanent actions (dead loads) and variable actions including imposed loads, snow loads and wind loads, plus critical load combinations and partial safety factors.
• Load combinations & factors: procedures for combining actions (ψ factors, partial factors) and assessing consequence classes for structural failure.
• Connection resistance: methods for verifying structural resistance of connectors by calculation and test-assisted design, including characterisation of connector types and configurations.
• Special design cases: guidance for accidental actions and seismic design of panel connections.
• Practical examples and annexes: Annex A contains worked examples for different mounting systems (hooks, ballast-stabilized flat-roof collectors, in-roof PV) and verification procedures; Annex B gives supplementary information on wind actions and related terminology.
• Design responsibility: delineation of roles and responsibilities for designers and manufacturers.

Practical applications and users

CEN/TR 16999:2019 is essential for professionals involved in the structural aspects of rooftop solar installations:

• Structural and civil engineers designing roof connections and assessing load paths.
• PV and thermal system designers selecting mounting systems compatible with roof structure capacity.
• Mounting-system manufacturers validating connector resistance by calculation and testing.
• Roofing contractors and installers ensuring safe attachment methods for flat and pitched roofs.
• Building regulators and certifiers reviewing compliance with structural safety practices.

Use cases include sizing and spacing of fixings, verification of uplift and shear resistance under wind/snow, specifying testing protocols for connectors, and integrating seismic/accidental considerations into rooftop solar projects.

Related standards

The report references relevant structural and meteorological design standards (for example, EN design standards for snow/wind loads and national annexes) and complements product- and installation-focused standards for PV and thermal systems. Use CEN/TR 16999 alongside applicable EN codes for complete structural design compliance.

Standards Content (Sample)

SLOVENSKI STANDARD
01-maj-2019
6RQþQLHQHUJLMVNLVLVWHPL]DVWUHKH]DKWHYH]DNRQVWUXNFLMVNHSRYH]DYHVRODUQLK
SORãþ
Solar energy systems for roofs: Requirements for structural connections to solar panels
Solare Energiesysteme für Dächer: Anforderungen an konstruktive Verbindungen zu
Sonnenkollektoren
Systèmes d'énergie solaire pour les toits : Exigences relatives aux raccordements des
panneaux solaires à la charpente
Ta slovenski standard je istoveten z: CEN/TR 16999:2019
ICS:
27.160 6RQþQDHQHUJLMD Solar energy engineering
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

CEN/TR 16999
TECHNICAL REPORT
RAPPORT TECHNIQUE
February 2019
TECHNISCHER BERICHT
ICS 27.160
English Version
Solar energy systems for roofs - Requirements for
structural connections to solar panels
Systèmes d'énergie solaire pour les toits : Exigences Solare Energiesysteme für Dächer: Anforderungen an
relatives aux raccordements des panneaux solaires à la konstruktive Verbindungen zu Sonnenkollektoren
charpente
This Technical Report was approved by CEN on 26 November 2018. It has been drawn up by the Technical Committee CEN/TC
128.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2019 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TR 16999:2019 E
worldwide for CEN national Members.

Contents Page
European foreword . 7
Introduction . 8
1 Scope . 9
2 Normative references . 9
3 Terms and definitions . 10
4 Symbols . 10
5 Configuration of solar panel installation . 10
6 Design responsibility . 10
7 Thermal solar collectors and PV solar panels . 10
8 Principles of limit state structural design . 11
8.1 General . 11
8.2 Design situations . 11
8.3 Ultimate limit state . 11
8.4 Serviceability limit state . 11
9 Determination of actions . 11
9.1 Permanent actions (G) . 11
9.2 Variable actions (Q) . 11
9.2.1 General . 11
9.2.2 Imposed loads . 12
9.2.3 Snow loads . 12
9.2.4 Wind loads . 12
9.2.5 Critical load combinations . 13
9.2.6 Load combination factor ψ . 13
9.2.7 Partial safety factors for actions . 13
9.2.8 Consequence of structural failure . 13
10 Structural resistance of connections . 14
10.1 Configuration and type of connectors . 14
10.2 Design by calculation . 14
10.3 Design assisted by testing . 14
11 Design for accidental action . 15
12 Design for seismic action . 15
Annex A (informative) Examples of connection design . 17
A.1 Fixing hook for PV solar panels mounted above tiled roof . 17
A.1.1 Description of the system . 17
A.1.2 Climate zone . 17
A.1.3 Loads . 17
A.1.3.1 Dead loads. 17
A.1.3.2 Imposed load . 18
A.1.3.3 Wind and snow loads . 18
A.1.3.4 Calculation of the wind load acting on the panels . 18
A.1.3.5 Snow loads . 19
A.1.3.6 Summary of loads acting on a single panel, in directions normal to the roof and down the
roof . 19
A.1.4 Factored load combinations for the ultimate limit state . 20
A.1.5 Factored load combinations for the serviceability limit state . 21
A.1.6 Structural resistance (by test) . 22
A.1.6.1 General . 22
A.1.6.2 Characteristic Resistance . 23
A.1.6.3 Safety factors and design resistance . 24
A.1.6.3.1 General . 24
A.1.6.3.2 Ultimate Limit State for characteristic resistance by test . 24
A.1.6.3.3 Serviceability Limit State for resistance by test . 24
A.1.6.3.4 Design structural resistance values: . 24
A.1.7 Design verification – derivation of the number of hooks required . 25
A.2 Thermal solar collector on flat roof stabilized with dead weight . 27
A.2.1 Description of the system . 27
A.2.2 Climate zone . 27
A.2.3 Loads . 27
A.2.3.1 Dead loads . 27
A.2.3.2 Wind load at roof height Z . 27
A.2.4 Ultimate load case for uplift and sliding . 28
A.2.5 Serviceability limit state . 28
A.2.6 Ultimate resistance to uplift and sliding . 28
A.2.7 Design downward load on roof (concrete blocks + collector + downward wind + snow,
excluding self weight of roof structureConcrete blocks: 14x0,35x1,35 = 6,62kN
(γ = 1,35) . 29
G
A.2.8 Verify the design load and compression strength of the aluminium member BD . 30
A.2.8.1 Critical load case: Snow + downward wind . 30
A.2.8.1.1 Snow: In accordance with EN 1991-1-3: . 30
A.2.8.1.2 Wind: Downward pressure coefficient c = +1,2 . 30
p,net
A.2.8.1.3 Factored snow, wind and dead loads . 30
A.2.8.2 Compression strength of member BD . 33
A.2.9 Summary of design verification for compression member BD . 34
A.3 Connections for an in-roof solar PV system. 35
A.3.1 Description of the system . 35
A.3.2 Climate zone . 35
A.3.3 Loads . 35
A.3.3.1 Dead load . 35
A.3.3.2 Imposed loads . 35
A.3.3.3 Wind loads . 35
A.3.3.3.1 General . 35
A.3.3.3.2 External pressure coefficient . 35
A.3.3.4 Snow loads . 36
A.3.3.5 Thermal loads . 36
A.3.4 Vector load components . 37
A.3.5 Ultimate limit state load combinations . 37
A.3.5.1 Ultimate limit state criteria . 37
A.3.5.2 Load cases . 37
A.3.5.3 Vectorial load . 38
A.3.6 Serviceability limit state load combinations . 39
A.3.6.1 Serviceability limit state criteria . 39
A.3.7 Structural resistance of connections . 39
A.3.7.1 Lower side of module . 39
A.3.7.1.1 General . 39
A.3.7.1.2 Axial load . 39
A.3.7.1.3 Shear Load . 40
A.3.7.2 Upper edge of module . 41
A.3.8 Design verification (resistance ≥ loads) . 42
A.3.8.1 Lower edge of module . 42
A.3.8.2 Upper interlocking profile . 43
A.4 Earthquake resistant design of solar PV panel connections . 43
A.4.1 Description of the system . 43
A.4.2 Seismic zone . 43
A.4.3 Calculation of the seismic load acting on the panels . 43
A.4.4 Seismic load and other loads acting on a single panel . 45
A.4.5 Load Combination . 45
Annex B (normative) Supplementary information on wind actions . 47
B.1 General . 47
B.2 Terms and definitions (NEN 7250:2014/A1:2015 3.0) . 47
B.2.1 back panel (NEN 7250:2014/A1:2015 3.1) . 47
B.2.2 building construction (NEN 7250:2014/A1:2015 3.2) . 47
B.2.3 eave height (NEN 7250:2014/A1:2015 3.3) . 47
B.2.4 photovoltaic element (NEN 7250:2014/A1:2015 3.4) . 47
B.2.5 combined element (NEN 7250:2014/A1:2015 3.5) . 47
B.2.6 closed substructure (NEN 7250:2014/A1:2015 3.6) . 47
B.2.7 façade (NEN 7250:2014/A1:2015 3.7) . 47
B.2.8 sloping roof (NEN 7250:2014/A1:2015 3.8) . 48
B.2.9 high side (NEN 7250:2014/A1:2015 3.9) . 48
B.2.10 mounting method (NEN 7250:2014/A1:2015 3.10) . 48
B.2.11 mounting method 1 (NEN 7250:2014/A1:2015 3.11) . 48
B.2.12 mounting method 2 (NEN 7250:2014/A1:2015 3.12) . 49
B.2.13 mounting method 3 (NEN 7250:2014/A1:2015 3.13) . 50
B.2.14 mounting method 4 (NEN 7250:2014/A1:2015 3.14) . 51
B.2.15 mounting method 5 (NEN 7250:2014/A1:2015 3.15) . 52
B.2.16 low side (NEN 7250:2014/A1:2015 3.16) . 53
B.2.17 substructure (NEN 7250:2014/A1:2015 3.17) . 53
B.2.18 open substructure (NEN 7250:2014/A1:2015 3.18) . 53
B.2.19 flat roof (NEN 7250:2014/A1:2015 3.19) . 53
B.2.20 thermal element (NEN 7250:2014/A1:2015 3.20) . 53
B.2.21 external dividing construction (NEN 7250:2014/A1:2015 3.21) . 54
B.2.22 solar element (NEN 7250:2014/A1:2015 3.22) . 54
B.2.23 solar energy system (NEN 7250:2014/A1:2015 3.23) . 54
B.3 Requirements for the construction (NEN 7250:2014/A1:2015 6) . 54
B.3.1 General (NEN 7250:2014/A1:2015 6.1). 54
B.3.2 Wind load (NEN 7250:2014/A1:2015 6.2) . 54
B.3.2.1 General (NEN 7250:2014/A1:2015 6.2.1) . 54
B.3.2.2 Net pressure coefficient for mounting method 1 (NEN 7250:2014/A1:2015 6.2.2) . 55
B.3.2.2.1 External pressure coefficient c , mounting method 1 (NEN 7250:2014/A1:2015
pe
6.2.2.1) . 55
B.3.2.2.2 Internal pressure coefficient, c , mounting method 1 (NEN 7250:2014/A1:2015
pi
6.2.2.2) . 55
B.3.2.2.3 Pressure equalization factor c mounting method 1, sloping roof (NEN 6.2.2.3) . 55
eq
B.3.2.2.4 Pressure equalization factor c , mounting method 1, wall (NEN 7250:2014/A1:2015
eq
6.2.2.4) . 57
B.3.2.3 Net pressure coefficients for mounting method 2 (NEN 7250:2014/A1:2015 6.2.3) . 59
B.3.2.3.1 Net Pressure Coefficient, cp,net, pitched roof, parallel (NEN 7250:2014/A1:2015
6.2.3.1) . 59
B.3.2.3.2 Net Pressure Coefficient, c , pitched roof, not-parallel (NEN 7250:2014/A1:2015
p net
6.2.3.2) . 60
B.3.2.3.3 Net Pressure Coefficient, c , of Mounting method 2, façade (NEN
p net
7250:2014/A1:2015 6.2.3.3) . 61
B.3.2.3.4 Net Pressure coefficient c , for mounting method 2, flat roof (NEN
p, net
7250:2014/A1:2015 6.2.3.4) . 61
B.3.2.4 Net pressure coefficient c , for mounting method 3 (NEN 7250:2014/A1:2015 6.2.4) 62
p net
B.3.2.4.1 General (NEN 7250:2014/A1:2015 6.2.4.1) . 62
B.3.2.4.2 Open support structure (NEN 7250:2014/A1:2015 6.2.4.2) . 62
B.3.2.4.3 Closed under construction (NEN 7250:2014/A1:2015 6.2.4.3) . 65
B.3.2.4.4 Load Zones (NEN 7250:2014/A1:2015 6.2.4.4) . 66
B.3.2.4.5 Roof areas (NEN 7250:2014/A1:2015 6.2.4.5) . 67
B.3.2.5 Net pressure coefficient mounting methods 4 and 5 (NEN 7250:2014/A1:2015 6.2.5) . 69
B.3.3 Determination of the design value for wind load resistance of solar energy systems
according to assembly method1 and 2 by testing (research prototype) (NEN
7250:2014/A1:2015 11.2) . 69
B.3.3.1 General (NEN 7250:2014/A1:2015 11.2.1) . 69
B.3.3.2 Principle (NEN 7250:2014/A1:2015 11.2.2) . 70
B.3.3.3 Sampling (NEN 7250:2014/A1:2015 11.2.3) . 70
B.3.3.4 Test Conditions (NEN 7250:2014/A1:2015 11.2.4) . 70
B.3.3.5 Specimen (NEN 7250:2014/A1:2015 11.2.5) . 70
B.3.3.5.1 Test Samples (NEN 7250:2014/A1:2015 11.2.5.1) . 70
B.3.3.5.2 Dimensions of the test specimen (NEN 7250:2014/A1:2015 11.2.5.2) . 70
B.3.3.5.3 Number of tests (NEN 7250:2014/A1:2015 11.2.5.3) . 70
B.3.3.5.4 Composition of the test piece (NEN 7250:2014/A1:2015 11.2.5.4) . 70
B.3.3.5.5 Equipment and apparatus (NEN 7250:2014/A1:2015 11.2.6) . 70
. 70
B.3.3.5.6 Test Procedure and evaluation (NEN 7250:2014/A1:2015 11.2.7) .
Bibliography . 73

European foreword
This document (CEN/TR 16999:2019) has been prepared by Technical Committee CEN/TC 128 “Roof
covering products for discontinuous laying and products for wall cladding”, the secretariat of which is held by
NBN in co-operation with CEN/TC250 “Structural Eurocodes”, CEN/TC254 “Flexible sheets for
waterproofing”; CEN/TC312 “Thermal solar systems and components” and CLC/TC82 “Solar photovoltaic
energy systems”.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN shall not be held responsible for identifying any or all such patent rights.
Introduction
The following is a summary of the requirements for structural design of the structural connection between
solar energy panels and the roof structure as detailed in this Technical Report.
a) Type of solar panel: Thermal or photovoltaic solar panels which comply with the mechanical resistance
requirements of EN 12975-1 (solar thermal collectors) or EN 61215 (solar PV panels).
b) Determining of the loads and load combinations: self-weight of the solar panels and relevant imposed
snow and wind actions in accordance with EN 1991-1-1, EN 1991-1-3 and EN 1991-1-4. Referring to
French Standard NF P78−116 and Dutch Standard NEN 7250 for additional data on snow and wind loads
on solar panels.
c) Determining the design loads for the solar panels: multiplication of each of the loads by their respective
partial factor γ or γ for the ultimate limit state, and separately for the serviceability limit state in
G Q
accordance with EN 1990.
d) Identifying combinations of most unfavourable design loads which act together at the same time, for the
ultimate and serviceability limit states. Modifying the loads by applying a load combination factor ψ to
one of the two variable loads which act at the same time.
e) Determining of the structural resistance of the connections between the solar panels and the roof
structure in accordance with calculation methods of one or more of the following European Standards:
EN 1992 series to EN 1996 series, and EN 1999 series for the ultimate and serviceability limit states:
1) For the serviceability limit state, determining of the resistance at the specified maximum deformation
limiting the function of the connection;
or
2) determine the resistance by serviceability and ultimate load tests.
f) Verifying the design by confirming that the factored structural resistance is not less than the critical
combinations of factored actions for both limit states.
Four examples of design calculations for different solar panel connections are given in Annex A.
1 Scope
This document provides guidance on the principles and requirements of structural design for the safety and
serviceability of the structural connection between solar energy panels (thermal or photovoltaic) and the
structure of flat or pitched roofs.
This document does not include requirements for:
— weather tightness of the roof, solar panels and connections;
— electrical, thermal or mechanical characteristics of the solar panels;
— precautions against fire of the installation.
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.
1)
EN 1990:2002, Eurocode - Basis of structural design
EN 1991-1-1, Eurocode 1: Actions on structures - Part 1-1: General actions - Densities, self-weight, imposed loads
for buildings
EN 1991-1-3:2003, Eurocode 1 - Actions on structures - Part 1-3: General actions - Snow loads
EN 1991-1-4:2005, Eurocode 1: Actions on structures - Part 1-4: General actions - Wind actions
EN 1992 (all parts), Eurocode 2 - Design of concrete structures
EN 1993 (all parts), Eurocode 3 - Design of steel structures
EN 1994 (all parts), Eurocode 4 - Design of composite steel and concrete structures
EN 1995 (all parts), Eurocode 5 - Design of timber structures
EN 1996 (all parts), Eurocode 6 - Design of masonry structures
EN 1998-1:2004, Eurocode 8: Design of structures for earthquake resistance - Part 1: General rules, seismic
2)
actions and rules for buildings
EN 1998 (all parts), Eurocode 8: Design of structures for earthquake resistance
EN 1999 (all parts), Eurocode 9: Design of aluminium structures
3)
EN 1999-1-1:2007, Eurocode 9: Design of aluminium structures - Part 1-1: General structural rules

1) This document is impacted by the amendment EN 1990:2002/A1:2005.
2) This document is impacted by the amendment EN 1998-1:2004/A1:2013.
3) This document is impacted by the amendments EN 1999-1-1:2007/A1:2009 and EN 1999-1-1:2007/A2:2013.
3 Terms and definitions
For the purposes of this document, the terms and definitions for structural design given in EN 1990, the
EN 1991 series, the EN 1992 series, the EN 1993 series, the EN 1994 series, the EN 1995 series, the EN 1996
series, the EN 1998 series, and the EN 1999 series apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
4 Symbols
For the purposes of this document, the symbols for structural design given in EN 1990, the EN 1991 series,
the EN 1992 series, the EN 1993 series, the EN 1994 series, the EN 1995 series, the EN 1996 series, the
EN 1998 series, and the EN 1999 series apply.
5 Configuration of solar panel installation
The configuration of solar panel installations is classified by the method of mounting on the roof structure, as
given in Annex B.
6 Design responsibility
The designer should ensure that:
— the choice of the structural system and the design of the structural connections are made by appropriately
qualified and experienced personnel;
— adequate supervision and quality control are provided in design offices, factories and on site;
— the structure will be adequately maintained;
— the structure will be used according to the design assumptions;
— the building structure can safely support the solar panels according to Eurocode standards of design;
building retrofitted with solar panels should also be checked.
7 Thermal solar collectors and PV solar panels
Thermal solar collectors and PV solar panels are collectively called solar panels in this Technical Report.
Thermal solar collectors should comply with EN 12975-1, according to the manufacturer’s declared
requirements.
PV solar panels should comply with the requirements of EN 61215 or EN 61646.
The structural resistance of the body of solar panels is not considered in this Technical Report. It is assumed
that their structural resistance is adequate. Attention is drawn to high snow loads in certain areas of Central
and Northern Europe (see EN 1991-1-3:2003, Annex C), acting together with downward wind loads, which
should be compared with the structural resistance of solar panels determined by ‘mechanical load tests’
incorporating adequate safety factors.
8 Principles of limit state structural design
8.1 General
Structural design should be carried out according to the principles of limit states of EN 1990. The ultimate
limit state and the serviceability limit state should both be considered, for relevant design situations.
For each limit state:
— the design value of an action is its characteristic value multiplied by the appropriate partial safety factor
for the action;
— the design value of the resistance is its characteristic value divided by the appropriate partial safety factor
for the material, which should be not less than the design value of the action.
8.2 Design situations
Design situations to be considered are actions which are:
— persistent (conditions of normal use, from dead loads, wind and snow loads, and other imposed loads);
— induced loads from thermal action due to temperature variation (e.g. for mounting beams of solar panels);
— transient loads (e.g. during execution or repair);
— accidental actions (for exceptional conditions e.g. explosion, impact, disproportionate consequence of
local failure);
— seismic actions (in seismic locations only).
The most unfavourable combinations of actions which act together at the same time should be considered in
design. They may include loads which are applied in different directions.
8.3 Ultimate limit state
The ultimate limit state concerns the safety of people and/or the structure when failure of the structure occurs
by excessive deformation, transformation into a mechanism or loss of stability.
8.4 Serviceability limit state
The serviceability limit state concerns the deformation, vibration or damage of the structure under normal
use which affect its function, appearance, or discomfort to people.
9 Determination of actions
9.1 Permanent actions (G)
The characteristic value of self-weight of the solar panel and its structural connection should be taken as its
mean value.
Indirect actions, e.g. caused by irreversible deformation, are also classed as permanent actions.
9.2 Variable actions (Q)
9.2.1 General
Variable actions are imposed loads, wind and snow loads, and loads induced by thermal movement (e.g. for
mounting beams).
The characteristic load values for snow and wind speeds may vary with location and may be given in National
Annexes to the standard.
9.2.2 Imposed loads
Imposed loads are in accordance with EN 1991-1-1.
9.2.3 Snow loads
9.2.3.1 General
Snow loads are in accordance with EN 1991-1-3 and the relevant National Annex. Supplementary information
on increased snow load on solar panels at the eaves of pitched roofs in climatic conditions where melting,
sliding and re-freezing of snow can occur, is given in NF P78-116 (for France only).
9.2.3.2 Return period
The ground snow load value may be adjusted according to the return period adopted (see EN 1991-1-3:2003,
Annex D), if specified by the National Annex. The return period may be based on the expected design life of
the solar panel connections.
9.2.3.3 Sliding snow loads on pitched roofs
Sliding snow loads which act on the framework and connections of solar panels which project above the
pitched roof surface should be determined according to EN 1991-1-3:2003, 6.4. They may occur at the same
time as vertical snow loads and snow drift loads. Solar panel elements are not designed to resist sliding snow
load.
To protect solar panels projecting above the roof surface from heavy sliding snow loads from a long length of
pitched roof, snow guards are recommended to be installed up-slope of the solar panels. Where the projected
height of the solar panels is greater than that of the snow guard, snow drift loads should be assumed to act on
the difference in projected height.
9.2.4 Wind loads
9.2.4.1 General
The modelling of wind velocity and peak velocity pressure is given in EN 1991-1-4. For site-specific data on
climatic information, wind speed distribution maps and altitudes, refer to the relevant National Annex to
EN 1991-1-4.
The dynamic pressure of the wind should be derived in accordance with EN 1991-1-4 based on the peak
velocity pressure. The characteristic wind load is the dynamic pressure modified by terrain, height and wind
pressure coefficients according to the shape and orientation of the structure.
Pressure coefficients for roofs of certain building configurations are given in EN 1991-1-4. Information from
the Dutch Standard NEN 7250:2014/A1:2015 on pressure coefficients for various mounting configurations of
solar panels on roofs and façades is given in Annex B.
The effect of wind loads on the roof surface with solar panels installed above it should be considered.
9.2.4.2 Return period
The wind speed may be adjusted according to the return period adopted (see EN 1991-1-4), which is normally
assumed to be not less than 25 years, unless otherwise specified by the National Annex.
9.2.5 Critical load combinations
The following are load combinations which may act together at the same time on solar panels and their
connections:
— dead load + imposed load;
— dead load + snow load (including sliding snow for pitched roofs) + wind (downward);
— dead load + wind load (upward);
— loads induced by thermal action [for mounting beams].
The most unfavourable load combinations in magnitude and load direction should be adopted for design.
9.2.6 Load combination factor ψ
Where the leading variable action occurs at the same time as other variable actions, the value of the other
variable actions may be reduced by multiplying by combination factors ψ (See EN 1990 and design examples
in A.1 and A.2).
9.2.7 Partial safety factors for actions
The design value of an action is the characteristic value multiplied by partial safety factor γ or γ
G Q.
For the ultimate limit state:
— permanent actions: in favourable load combination γ = 1,0;
G
— in equilibrium condition, e.g. dead load solely providing stability γ = 0,9;
G
— in unfavourable load combination γ = 1,35;
G
— variable actions: γ = 1,50.
Q
Where design is assisted by wind tunnel testing using an appropriate model of the structure and of the natural
wind (see EN 1991–1-4), the value of γ for wind action may be taken as 1,35.
Q
For the serviceability limit state:
— permanent and variable actions, γ = 1,0; γ = 1,0.
G Q
9.2.8 Consequence of structural failure
Where permitted nationally, solar panels installed on buildings in normal conditions of use may be designated
with a consequence class CC1 (EN 1990:2002, Table B.1) corresponding to Reliability Class RC1.
For RC1, a multiplying consequence factor K = 0,9 should be applied to unfavourable actions (ultimate limit
FI
state only).
For installations requiring consideration of higher risk, see EN 1990:2002, B.3.
10 Structural resistance of connections
10.1 Configuration and type of connectors
The arrangement in number, position and spacing of connectors to solar panels should be not less favourable
than the arrangement adopted in the mechanical load test for the body of the solar panel.
10.2 Design by calculation
The structural resistance should be determined by calculation in accordance with one or more Eurocodes the
EN 1992 series, the EN 1993 series, the EN 1994 series, the EN 1995 series, the EN 1996 series and the
EN 1999 series, for both the ultimate and serviceability limit states, to support adequately the most
unfavourable load combinations.
The design resistance is the lesser of the characteristic strength at the ultimate limit state, or at the
serviceability limit state, divided by a material partial factor γ
M.
Values of γ at the ultimate limit state are specified in the relevant Eurocode for structural materials: the
M
EN 1992 series, the EN 1993 series, the EN 1994 series, the EN 1995 series, the EN 1996 series and the
EN 1999 series (see design examples in Annex A). The value of γ for the serviceability limit state is 1,0.
M
10.3 Design assisted by testing
In accordance with EN 1990:2002, Annex D, design may be based on a combination of tests and calculations.
Testing to determine the resistance of the structure or part of the structure may be carried out, for example,
in the following circumstances if:
— adequate calculation models are not available;
— a large number of components are to be used;
— it is necessary to confirm, by control checks, assumptions made in the design.
Test specimens should be specified or obtained by sampling in such a way as to represent the conditions of
the real structure, and to obtain a statistically representative sample.
The rate of loading should where possible reflect actual conditions. Where the material of the structure has
significant time dependent effects on strength and deformation (e.g. timber – see EN 1995-1-1), the test
results should be modified to take into account the difference in load durations between testing and the
design conditions. Tests should be continued until failure
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