Rooftop Solar Panels

Rooftop PV

The majority of our customers install PV on their roofs, rather than building integrated or ground mount systems. The benefits of rooftop solar panels are they make good use of otherwise empty space, while keeping the array safely beyond reach and out of most common shading. We’ll take a look at the different types of PV you can choose depending on the roof type.

Sloping roofs

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

• by attaching solar panels to the roof using on-roof mounting brackets which sit above the tiles;
• by removing tiles in the area in which the panels are to go, and mounting the panels directly onto the battens and rafters using in-roof mounting brackets;
• by installing solar tiles directly onto the roof.

Most people are installing systems to their existing house (‘retrofit’) and choose to attach panels onto the roof using mounting brackets.

For new build or re-roof situations, or where there may be an issue with planning (e.g. a conservation area), an in-roof mounting system or solar roof tiles may be the solution of choice.

On roof

Installing panels on roof is the most common method, making use of existing roof space. It’s cost effective and provides benefits for performance through ventilation around the back of the panels.

How are solar panels fitted to a tiled roof?

1. Once the area of the array is mapped out on the roof, a few select tiles are removed.

2. In these gaps, anchors or hooks are attached to the roof rafters.

3. A weatherproof seal is applied around these.

4. The tiles are put back into place, with the hooks coming out below them.

5. A metal frame or rails hooks onto the anchor points.

6. The PV panels are fitted to the frame.

7. The array’s wiring is connected.

In roof: integrated and complete roof

In-roof systems use the same panels as on-roof systems. The only difference is that the panels are mounted on the battens/rafters, not on the tiles (usually with a metal tray backing between the panels and the rafters). The roofer will then tile up to the panels, often using lead flashing to make a tight seal around the panels.

In general we don’t recommend in-roof systems for existing roofs, for several reasons:

• Customers often believe the top of the panels will sit flush with the tiles. This is not the case – usually tiles are a few centimetres thick whereas the brackets and panels stand 11cm off the rafters. So unless the rafters around the PV system have been deliberately built up (as could be the case with a new roof) the tiles will not sit flush with the roof.
• The performance of the system will be reduced by around 3% relative to an on-roof system due to the fact that to operate more efficiently, panels need a gap behind them for ventilation. The in-roof system doesn’t provide this ventilation and the performance of the system is compromised as a result.
• In order to create a watertight seal between the system and the surrounding tiles, lead flashing usually needs to be used. This is often ugly and defeats the point of using an in roof system in the first place which is usually to create an unobtrusive system blending with the rest of the roof.

On a new roof, however, integrated panels are well worth considering. They’ll save you money on roofing materials and can offer a more streamlined, intentional appearance. You may even choose to go for a complete solar panel roof.

Solar tiles

If you want your system to sit flush with the surrounding tiles and to blend seamlessly into the roof, you may prefer to use solar roof tiles. These are much more expensive than an on-roof or in-roof systems, but could be a better bet if you are particularly worried about aesthetics.

Flat roof solar

In some ways flat roofs offer a simpler starting point for installing a solar system than sloping roofs, but they come with their own considerations:

• Flat roof systems take up more space per kW than pitched roof systems.
• Flat roof solar mounting frames are not usually secured to the roof itself, so must be weighted down using ballast. The structure of the roof needs to be able to support the ballast.
• If the system is fixed to the roof, it is important to check the impact on the roof warranty and to ensure water tightness is maintained. 
• Optimal mounting angle and orientation.

Green roof PV

If you’re considering developing the eco credentials of your building with a green roof, you may be surprised to find you can also install PV on top. Together they form a biosolar roof, where the panels are fitted with specialist mounts, ballasted by the soil.

You won’t generate as much electricity as a standard rooftop system, since the panels need to be higher and spaced further apart to allow space for the vegetation. But the greenery will lower the ambient temperature, helping the PV work more efficiently. And in return, the panels will provide shading and concentrated areas of rainfall for greater biodiversity.

Solar rooftop system costs

The price of solar PV will vary depending on location, ease of access and wiring, panel type etc. But here is a rough guide to compare the cost per kW of different mounting systems, based on a 16 panel domestic array.

The range is estimated using polycrystalline panels, string inverters and standard access/labour costs at the lower end, to monocrystalline panels, optimisers and higher access/labour costs at the higher end. Please get in touch for an accurate quote.

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: