Solar PV on Flat Roofs Design Considerations Overview
In the UK, solar photovoltaic (PV) is a popular renewable energy and its deployment is rising rapidly across the globe. With recent fluctuations in energy markets and carbon reductions initiatives coming to the fore, the number of flat roof installations will continue to rise as local authorities and businesses look to reduce their carbon footprint and gain energy security for the future.
All too often within the construction industry, photovoltaic specifications focus on energy generation and outputs of the solar system. Any solar designer or specifier should give the same focus to ensuring the rooftop array is installed with methods that have as little impact as possible on the building and its waterproofing and that the array works to its maximum potential for its entire lifespan.
Specifying PV on new buildings
There are numerous reasons for including a solar PV array on a new flat roof. Large commercial buildings can often have the most suitable energy usage profile to benefit from the electricity produced from a rooftop PV array.
Motives for retrofitting PV on existing buildings
Retrofitting photovoltaic panels brings all the benefits of low maintenance renewable energy generation to an existing building, with the ideal opportunity for the installation to take place when the roof covering is being replaced.
Considerations for retrofitting PV
When planning a PV array for an existing building the condition of the flat roof should always be considered before the mounting method and array location can be determined. These are some key points to consider and clarify before proceeding with the project.
Sizing of PV arrays
The size of a PV array can be determined by several elements that are often driven by the overall aim of the scheme.
Combining a green roof with the solar PV array
Environmental considerations such as carbon reduction, biodiversity loss and storm water management are driving the inclusion of both a green roof and a photovoltaic system for new buildings. This can bring challenges for designers on how to locate both within a limited roof area. Biosolar systems provide the solution through the layering the green roof and PV array so that they can co-habit the same area.
Weight loading
The weight loading of different systems and their installation methods should always be considered. A ballasted PV system on a building in an exposed location can impose loads as high as 60 kg/m² which can impact both structural stability and compress waterproofing membranes and insulation. This is compared to other methods of PV installation which could impose as low as 9 kg/m².
Fixing methods for solar PV arrays
There are two fundamental options for fixing a PV system to a flat roof, ballasted or mechanical. A ballasted system adds additional weight to anchor the array to the roof whereas mechanical installations cover two key methods, either they are fixed to the deck penetrating the roof covering or they do not and leave the waterproofing system intact.