Rooftop Solar Panels

Rooftop PV

The majority of our customers install solar panels on their roof rather than opting for ground-mounted or building-integrated systems. Rooftop solar makes good use of otherwise empty space, keeps the array safely out of reach, and is generally free from the shading that can affect ground-level installations.

The right approach depends on your roof type. Here is a guide to the main options.

Sloping roofs

There are three ways of installing solar on a pitched, tiled roof:

• On-roof: panels are attached to the roof surface using mounting brackets that sit above the tiles
• In-roof: tiles are removed and panels are mounted directly onto the battens and rafters using in-roof brackets, with the surrounding tiles brought up to meet them
• Solar tiles: purpose-made solar roof tiles replace conventional tiles entirely

Most customers installing on an existing roof choose the on-roof method using mounting brackets. For new builds, re-roofing projects, or where planning constraints apply, such as conservation areas, in-roof mounting or solar tiles may be the better option.

On-roof installation

On-roof is the most common mounting method and the one we recommend for the majority of installations. It makes use of the existing roof structure, is cost-effective, and performs well because the gap between the panels and the roof surface allows air to circulate behind the panels, keeping them cooler and improving output.

 How are solar panels fitted to a tiled roof? 

1. The area of the array is mapped out on the roof
2. A small number of tiles are removed at the anchor points
3. Hooks or anchors are fixed to the roof rafters
4. A weatherproof seal is applied around each fixing
5. The tiles are replaced, with the hooks sitting beneath them
6. Metal rails are attached to the anchor points
7. The panels are clipped to the rails
8. The wiring is connected and the system is commissioned

In-roof installation

In-roof systems use the same panels as on-roof systems. The difference is that the panels are mounted directly onto the battens and rafters, usually with a metal tray between the panels and the roof structure, and the surrounding tiles are brought up to meet them, with lead flashing used to create a weatherproof seal at the edges.

We do not generally recommend in-roof systems for existing roofs, for three reasons:

• The panels do not sit flush with the tiles. Tiles are typically a few centimetres thick, whereas the in-roof brackets and panels sit around 11cm above the rafters. Unless the surrounding roof structure has been deliberately built up, as might be the case with a new roof, the panels will stand proud of the tiles rather than sitting flush with them.
• Performance is reduced. Panels operate more efficiently when air can circulate behind them. In-roof systems do not provide this ventilation, which reduces output by around 3% compared to an equivalent on-roof system.
• The weatherproofing is often unsightly. Lead flashing is typically required to seal the system against the surrounding tiles. This is frequently considered the least attractive aspect of an in-roof installation and can defeat the purpose of choosing the system in the first place.

For new builds or re-roofing projects, integrated panels are well worth considering. You will save on roofing materials, the aesthetic result is cleaner, and the structural limitations of a retrofit do not apply. Our in-roof panel of choice for these situations is the Viridian Clearline Fusion, which is designed specifically for integrated installation.

Solar tiles

If you want your solar system to sit fully flush with the surrounding roof and blend seamlessly into the building's appearance, solar tiles are worth considering. Individual solar tiles replace conventional roof tiles entirely, with no visible mounting hardware or framing.

Solar tiles are significantly more expensive than on-roof or in-roof systems, but for customers where aesthetics are the priority, particularly on listed buildings, in conservation areas, or on high-specification new builds, they can be the right solution.

Flat roof solar

Flat roofs present a different set of considerations from pitched roofs, but can work very well for solar.

• More space is required per kW than on a pitched roof, as panels need to be tilted and spaced to avoid self-shading
• Frames are typically ballasted rather than fixed — most flat roof mounting systems are not attached to the roof itself but are weighted down with ballast blocks. The roof structure must be able to support the additional load
• If the system is fixed to the roof, it is important to check the impact on the roof warranty and to confirm that water tightness is maintained
• Orientation flexibility is one of the advantages of a flat roof — panels can be arranged in an east-west configuration to spread generation across the day and fit more panels into the available space
  
  

Green roof solar

If you are developing the ecological credentials of a building with a green roof, it is also possible to install solar on top. Together they form what is known as a biosolar roof, where panels are fitted with specialist mounts ballasted by the growing substrate.

Output will be lower than a standard rooftop system, as panels need to be raised and spaced further apart to allow space for the vegetation. However, the greenery reduces the ambient temperature around the panels, which improves their efficiency. In return, the panels provide shade and concentrate rainfall, which can benefit biodiversity on the roof.

Designing your rooftop system

Planning a rooftop array involves optimising for the current roof structure and surrounding environment (potential shading etc). Our expert team has designed thousands of systems and would be happy to assist you with your project. Give them a call on 0118 951 4490, email info@spiritenergy.co.uk or try our solar calculator to estimate what you could generate from your roof: