Roof solar installations - is your structure up for it?

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07 April 2020

Are you looking to put solar panels on your roof; install panels on someone else’s roof; or looking to develop a solar panel system?  If your answer is “yes” to any of those, chances are that you won’t just need a Renewable Energy Engineer, but also a Structural Engineer with plenty of experience in the solar industry.

Over the last 15 years, Partridge has been involved in many areas of the solar industry ranging from existing roof adequacy assessments, to the design of roof-mounted solar framing, to the design of large-scale solar farms.  Our role as structural engineers is to ensure that your roof, the supporting frames, the solar array itself, and the many other components are all safe and strong enough for the loads that they might experience in their service lifetime.

One of the great features of modern solar arrays (a fancy term for the photo-voltaic cells or PVC panels) is that they’re surprisingly lightweight.  This leads many folks to mistakenly assume that they can be safely installed on any existing roof without undue stress or impacting the roof’s capacity to withstand the load.

Unfortunately, nothing could be further from the truth!  Whether it’s a homeowner looking to install solar to their tiled roof at home or a warehouse/building owner looking at a more commercial installation on their structure, the addition of a solar array to a roof can have a very significant impact on the roof’s strength and capacity, and failures are surprisingly common.

The reason for this is usually not the simple additional self-weight of the array but, more commonly, how the installation of the array changes the roof’s susceptibility to adverse wind pressures.  Even if you can walk, run, jump, and dance on your roof, putting the extra few kilograms of solar panels on your roof may cause problems because of how they change wind behaviour.  Wind pressures are usually the highest loads a roof structure will see in its lifetime, and – depending on a host of different variables and parameters – many solar array installations can significantly worsen and increase the magnitude of these wind pressures.  Unfortunately, not every structure is able to support solar panels when assessed by the most current Australian Standards, and strengthening is occasionally required.

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For most buildings, engineers need to assess the structure for a 1-in-500-year wind event, which for most of Australia means windspeeds of around 160km/h.  These windspeeds are even higher in places that can receive tropical storms such as Brisbane (205km/h), Darwin (250km/h), and Exmouth (315km/h).  For context, a person is barely able to stand up straight in a 60km/h wind, so you can imagine just how enormous the stresses are that wind imparts on to your house’s roof and other building structures!

Not only does your engineer need to know what windspeeds to design and assess for, but also, they must know how the wind behaves with the structure and the solar panels.  Even for the same exact windspeed, a solar panel in the middle of a land based solar farm is going to experience a different load to a solar panel mounted onto a roof in suburban Sydney.  Think of an aeroplane’s wings: The pilot is able to change the amount of uplift acting on the wings by making a few adjustments to the control surfaces, which changes the way that the air flows over the wings.  In the same way that the wind forces on an aeroplane can be increased by angling the flaps on a wing, so too can the forces on a roof be increased by tilting solar panels.  Sometimes, a roof might only just have enough strength to resist the wind (sometimes it doesn’t have enough strength), so any amount of tilting (or even any solar panels at all) might not be able to be accommodated, at least without strengthening works being carried out first.

So, in order to achieve the most efficient design or to ensure that detrimental factors aren’t overlooked, your engineer needs to have a sound understanding of the Australian Standard wind loads, how to use them, and how to correctly assess and calculate all of the many different variables and parameters.

Needless to say, using as little material as possible is key to a successful project, so having an appropriate structural engineer who listens, thinks, engages and delivers and who knows where and how to make reductions can be a crucial investment in your project.   Partridge has the experience and ethos and we’re always happy to help.  If you’re about to embark on a solar installation project, be sure to give us a call.

 

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Source:  Partridge - www.partridge.com.au

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