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Wind Actions on Flat-Roof-Mounted Photovoltaic Panels : a Comparison of Design Guidelines

Vestin, Jonas LU (2011) In TVBK VBK920 20101
Division of Structural Engingeering
Civil Engineering
Abstract
Wind actions on roof-mounted solar collectors dier from those on an open range-deployment,
due to turbulence and wind stream deection induced by the underlying building. As of
December 2010, no construction codes in eect describes the wind loads on such structures,
with the exception of the preliminary standard NVN 7250 from the Netherlands, with the
latest draft released in 2007.
The roofs considered for this type of plants often consists of large-surface at-roofed
industrial halls with tar-bitumen roof sheeting. Penetrating the roong for xtures of the
solar collectors is often not allowable, so instead, wind-induced uplift forces are counter-
acted by attaching ballast to the photovoltaic mounting systems. This practice causes... (More)
Wind actions on roof-mounted solar collectors dier from those on an open range-deployment,
due to turbulence and wind stream deection induced by the underlying building. As of
December 2010, no construction codes in eect describes the wind loads on such structures,
with the exception of the preliminary standard NVN 7250 from the Netherlands, with the
latest draft released in 2007.
The roofs considered for this type of plants often consists of large-surface at-roofed
industrial halls with tar-bitumen roof sheeting. Penetrating the roong for xtures of the
solar collectors is often not allowable, so instead, wind-induced uplift forces are counter-
acted by attaching ballast to the photovoltaic mounting systems. This practice causes the
need for both safe and economical wind action guidelines, since uneconomical dimensioning
causes the ballast quantities to exceed the residual load capacity of the roof, rendering the
construction infeasible.
A static model was developed for a typical photovoltaic mounting system. Results from
three wind tunnel investigations on roof-mounted photovoltaics for dierent roof geometries
were gathered, and the guidelines from the Dutch pre-standard NVN 7250 were adapted
to the geometric boundary conditions of the respective studies. For all approaches to the
wind loads, roofs are divided into dierent load areas, were modules situated in the dierent
load areas are assigned dierent wind loading coecients. The static model was used to
determine the ballast quantities needed for static equilibrium, using the results from the
wind tunnel investigations, and the adaptions from the NVN 7250 respectively.
The pre-standard was found to underestimate the ballast compared to one of the wind
tunnel investigations, while signicantly overestimating the ballast compared to the two
other results. Further, large dierences were found between the wind loading coecients
from the wind tunnel investigations, derived for seemingly similar module layouts and
mounting system geometries. This led to the conclusion that the aerodynamic properties of
the mounting system itself plays a large role in determining the wind loads. The description
of the mounting systems in the pre-standard, where the systems from the investigations
all fall into the same category, seems insuciently ne-grained, since the wind actions in
the end turned out both over- and underestimated. It is therefore not advisable to use the
pre-standard NVN 7250 to dimension mouting systems and verifying static equilibrium. (Less)
Please use this url to cite or link to this publication:
author
Vestin, Jonas LU
supervisor
organization
course
VBK920 20101
year
type
H3 - Professional qualifications (4 Years - )
subject
publication/series
TVBK
report number
TVBK-5195
ISSN
0349-4969
language
English
id
3358488
date added to LUP
2013-01-10 13:09:50
date last changed
2013-01-10 13:09:50
@misc{3358488,
  abstract     = {Wind actions on roof-mounted solar collectors dier from those on an open range-deployment,
due to turbulence and wind stream deection induced by the underlying building. As of
December 2010, no construction codes in eect describes the wind loads on such structures,
with the exception of the preliminary standard NVN 7250 from the Netherlands, with the
latest draft released in 2007.
The roofs considered for this type of plants often consists of large-surface at-roofed
industrial halls with tar-bitumen roof sheeting. Penetrating the roong for xtures of the
solar collectors is often not allowable, so instead, wind-induced uplift forces are counter-
acted by attaching ballast to the photovoltaic mounting systems. This practice causes the
need for both safe and economical wind action guidelines, since uneconomical dimensioning
causes the ballast quantities to exceed the residual load capacity of the roof, rendering the
construction infeasible.
A static model was developed for a typical photovoltaic mounting system. Results from
three wind tunnel investigations on roof-mounted photovoltaics for dierent roof geometries
were gathered, and the guidelines from the Dutch pre-standard NVN 7250 were adapted
to the geometric boundary conditions of the respective studies. For all approaches to the
wind loads, roofs are divided into dierent load areas, were modules situated in the dierent
load areas are assigned dierent wind loading coecients. The static model was used to
determine the ballast quantities needed for static equilibrium, using the results from the
wind tunnel investigations, and the adaptions from the NVN 7250 respectively.
The pre-standard was found to underestimate the ballast compared to one of the wind
tunnel investigations, while signicantly overestimating the ballast compared to the two
other results. Further, large dierences were found between the wind loading coecients
from the wind tunnel investigations, derived for seemingly similar module layouts and
mounting system geometries. This led to the conclusion that the aerodynamic properties of
the mounting system itself plays a large role in determining the wind loads. The description
of the mounting systems in the pre-standard, where the systems from the investigations
all fall into the same category, seems insuciently ne-grained, since the wind actions in
the end turned out both over- and underestimated. It is therefore not advisable to use the
pre-standard NVN 7250 to dimension mouting systems and verifying static equilibrium.},
  author       = {Vestin, Jonas},
  issn         = {0349-4969},
  language     = {eng},
  note         = {Student Paper},
  series       = {TVBK},
  title        = {Wind Actions on Flat-Roof-Mounted Photovoltaic Panels : a Comparison of Design Guidelines},
  year         = {2011},
}