www.sunbeam-pv.com Fact Sheet Wind load and ballast calculation — April 2015

T H E P R O F E S S I O N A L P V M O U N T I N G S Y S T E M

Design principles

By combining well-established design principles with our own research

and wind tunnel testing we successfully created a light-weight design

for SUNBEAM, without the need to compromise on either safety or

durability.

Stiff matrix structure

The matrix-design, featuring beams in two directions, distributes the

wind load equally across the structure. Contrary to the construction

principles used in many competing products, the modules themselves

are not part of SUNBEAM’s load-bearing structure.

Reduced system height

SUNBEAM systems, which by default deploy a 15-degree panel angle

in landscape orientation, are lower than traditional systems deploying

30-degree panel angles or systems with panels in portrait orientation,

and thus are less susceptible to wind.

Wind deflectors

Wind deflector plates help guide the wind over the system and thus

reduce the pressure under the modules, which in turn reduces the bal-

last required. The SUNBEAM wind deflectors are positioned such that

one can still walk between the rows. The wind deflectors also enhance

the mechanical stability of the system as a whole.

Ballast where it counts

The wind load on a panel depends on its exact location on the roof.

For this reason SUNBEAM deploys ballast only in those places where

it is really needed: at the corners and edges of the array. For large

arrays ballast is deployed in the center area as well.

Lack of specific standards

Due to the complexity of the subject matter, which involves the unpredictable

behaviour of the wind over time and how it reacts to the shape of the system, it

is not feasible to manually calculate the ballast configuration for an integrated

system. In addition, there are no formal standards for ballast calculations that

can be applied to flat roofs. Although the new Dutch norm NEN7250 provides a

framework for calculating the ballast required for independently placed panels, it

also explicitly states that the norm is not valid for integrated systems. Integrated

systems always require model-specific wind tunnel testing.

SUNBEAM light-weight mounting systems are the perfect choice for roofs not designed to carry heavy loads.

The wind load for a project depends on the height of the building,

the size of its roof, its surroundings and the layout of the solar

power system. SUNBEAM developed their own method to weigh

each of these factors when calculating the appropriate ballast

configuration.

Eurocode

The starting point for all our calculations is Eurocode 1, which is the

European norm for determining the wind load on buildings

(EN 1991_1-4 including its National Annexes). Eurocode 1 can be

used to obtain a value for the maximum wind velocity pressure (for

example: 560 N/m2) as a function of the height of the building and

its surroundings, amongst other factors. This peak pressure value is

a measure for the maximum wind force that may statistically occur

once every 50 years. The Eurocode also

describes unambiguously how to calculate

the ‘safe’ distances to the edges of the

roof, for at the corners and at the eaves

the wind tends to be much stronger than

at the centre of the roof.

Wind tunnel testing

SUNBEAM combines the values obtained from our own wind tun-

nels tests — carried out according to Dutch wind tunnel standard

CUR 103 — with the basic values according to the Eurocode. These

measurements result in specific values for the ballast required for

various wind directions and loads. The fact that SUNBEAM is an

integrated system leads to a much lower average ballast weight as

compared to a system deploying independently installed panels.

Array form factor

The larger the array of solar panels, the more panels will be shel-

tered from the wind by a neighbouring

panel. The unique SUNBEAM calculator

automatically accounts for this shelter-

ing effect by dividing the array into zones

and assigning a specific wind load to each

individual zone.

Ballast configuration

SUNBEAM’s completely automated

calculations result in a project-

specific ballast configuration plan

that clearly indicates the position of

the required ballast, and how much

it should weigh. The client is free to

select the type of tiles to be used as ballast. The tiles are placed in

rugged ballast racks.

Fact Sheet Wind load and ballast calculation