This article looks at the various types of roof mounted solar photovoltaic (PV) systems, how to choose between them and how to get your system properly designed, specified and installed.
Depending on your energy requirements, sustainability objectives, and budget, a solar PV system can be placed anywhere, including on the ground or even on pitched walls. However, if the circumstances are correct, a roof is a good choice for siting solar PV as it can make use of an otherwise underutilized space.
There are solar PV systems available for all building types, from domestic to commercial, education to industrial buildings. The expanding solar market can be confusing. Specifiers should be aware of how to choose appropriately and what factors to consider when making that choice. As always, the team at AccuRoof are here to help.
Pitched Roof Solar PV Systems
There are two main types of solar PV systems available for pitched roofing; in-roof (commonly used for new build projects) and on-roof (commonly a retrofit product).
In Roof Solar PV
In roof solar PV, also called ‘roof-integrated solar’ the solar arrays are installed flush with the roof finish.
- Installed before the roof covering is applied, in-roof systems are suitable for new builds, but can be installed on an existing roof as part of a re-roofing project.
- Systems are compatible with many pitched roof coverings including clay and concrete tiles, natural and fibre cement slates, and even cedar shingles and shakes.
- As the system is part of the roof covering, less roof covering material is required than with an on-roof system.
- Without visible fixings or space underneath, the system does not require pest control measures to prevent nesting birds getting under the panels.
On Roof Solar PV
On roof solar PV is installed over an existing, serviceable pitched roof covering.
- A commonly used retrofit option for existing roofs.
- Systems are available for tiled and slated roofs but also for industrial roofing, standing seam and hard metal roofs, with the appropriate fixings.
- Panels sit above the roof surface and pest control measures may be required.
- On roof solar PV can be more cost effective than in-roof, where there is an existing suitable roof covering already installed.
Flat Roof Solar PV Systems
Solar PV systems for flat roofs can be divided into two types:
Penetrative flat roof PV systems
Flat roof mounted solar PV systems can be mounted on the roof structure via fixings which penetrate the waterproofing.
- The PV array is installed onto a rail system with hard point fixings into the structure, through the waterproofing layer.
- Engineered fixings are available for all common roof coverings. Some fixing systems incorporate matching membranes integrated into the fixing.
- The array sits above the roof covering, at a pitch and orientation suitable for the environment.
- Properly designed frame systems can carry large panels – at the time of writing the largest panels on the UK market are 2.384m long.
Ballasted flat roof PV Systems
Ballasted systems sit directly on the roof unfixed and are instead held down with additional weight.
- Ballasted systems involve less interference with the roof’s waterproofing and spread the load and wind uplift across the roof, rather that at fixed points.
- A ballasted system applies additional load to the roof beyond the weight of the arrays and frame.
- Ballast can take several forms, such as proprietary trays to carry paving slabs.
- One way to introduce ballast is in the form of green roof substrate, integrating a biodiverse green roof below and around the PV arrays. This is known as BioSolar and can contribute to a developments’ Urban Greening Factor (UGF).
Flat roofs are a particularly useful site for solar PV. However, it is important to be aware that even ballasted systems involve some penetrations and therefore it is wise to ensure the system is designed, installed and maintained correctly to avoid invalidating your roofing warranty.
How to Choose a Solar PV System
To ensure the most efficient use of the space available, a rooftop PV system should always be designed to be site-specific. This allows the design to take into account the site constraints, the nature and orientation of the existing roof and the requirements of the client.
Smaller projects and dwellings
On smaller projects such as single dwellings, SIG Roofing have developed a Solar Calculator. This online tool uses Google mapping data and Artificial Intelligence (AI) to enable a homeowner, installer or roofer to get a personalised, site-specific quotation.
The SIG Roofing calculator calculates what solar product is required, including any relevant fixings, provides the cost of materials, and estimates the energy the solar panels will generate each year. If the user also provides the current annual energy usage for the property in KWh, the calculator will also work out the payback period.
Larger projects – education, commercial, industrial
Some manufacturers of solar systems have the facility to create a standard design with a parts and cost list. However, for larger projects, such standard designs can be significantly improved with a more in depth and technical approach:
- Once the client’s requirements have been confirmed, a survey of the existing roof spaces will determine all the relevant constraints.
- The expected lifespan of existing roofs will be determined to ensure that if a new PV system is installed it won’t need to be removed early to replace a roof finish. A PV strategy can then be integrated into the client’s estate management plans.
- The load capacity of the roof may need to be calculated by a structural engineer to determine if a ballasted system must be ruled out, for example.
- Wind uplift calculations will be carried out, along with shade analysis and modelling where appropriate.
- A site-specific design can then be produced.
These steps ensure the design of a site-specific layout which is likely to be the most efficient and enables us to confirm the true yield of the array(s).
A solar PV scheme should always be installed by an MCS (Microgeneration Certification Scheme) registered installer. MCS registered installers work to British Standards, BRE and IEE codes and will sign off and commission the installation correctly.
Full Service for Solar PV Systems
Accuroof’s experience across a wide range of roofing types means we can take an integrated approach to incorporating solar PV systems into your project and provide you with system agnostic advice.
SIG Roofing, AccuRoof’s parent company, is a leading provider of roofing and construction materials, and distributes solar equipment and services throughout the UK from over 100 branches.
SIG Roofing also has a dedicated solar team to give advice on selecting the most appropriate products, ensuring the maximum efficiency of your solar PV installation. Speak to us about your Solar PV requirements.
