When it comes to solar panel installations, flat roofs can sometimes get overlooked. However, just because they don’t have any natural angle doesn’t mean they can’t be suitable for solar panels.
In fact, in some ways installing solar panels on a flat roof can offer advantages for homeowners when compared to a sloped roof.
This article will take a look at flat roof solar installations, how to make the most out of them and what to look out for.
Can you install solar panels on a flat roof?
Yes, you certainly can install solar panels on a flat roof. Whilst the term ‘flat roof’ paints an image of panels lying horizontally against the surface, that’s not quite how they work.
To maximise efficiency when generating electricity from sunlight, solar panels on flat roofs should be installed using mounting systems or brackets that tilt the panels towards the sun at the optimal angle.
Solar panels on flat roofs tend to be set at an angle between 20 and 50 degrees, with 35 degrees considered the sweet spot for most UK installations. This set-up mirrors what you might see in solar farms on fields or with ground-mounted systems, where each panel is carefully angled to catch the most sunlight. Installing on a flat roof is no different.
In addition to the standard considerations of a solar panel install, it’s worth noting that there are a few extra things to bear in mind flat roof solar panel installations. For example, they often require a little more space per kilowatt than pitched roofs to make sure each panel has adequate ventilation and to stop the panels from self-shading.
Do you need planning permission for solar panels on flat roofs?
There’s good news for those considering flat roof solar installations. In December 2023, the government introduced changes to UK planning regulations to make it easier to install solar panels on flat roofs.
Under the new permitted development rights, solar panels on flat roofs can now project up to 60cm above the roof surface, which is an increase from the previous 20cm limit. This brings the rules for homes in line with those for businesses.
This means that for most cases, you won’t need to apply for planning permission.
However, planning permission will apply if your home is located in a conservation area or if it’s a listed building. It’s always worth checking in with your local planning authority before you go ahead and install.
Advantages of flat roof solar installations
Although they aren’t as popular as sloped roofs, flat roof solar systems bring with them a number of benefits that shouldn’t be dismissed.
- Flexibility in orientation and tilt – Unlike pitched roofs, flat surfaces allow for optimal panel positioning to maximise sun exposure throughout the day.
- Easier installation and maintenance – There’s no need for scaffolding with flat roof solar panels. This makes installation much easier, as well as any future maintenance. An installation without scaffolding also means it should be cheaper.
- Less visible – Flat roof installations are usually less visible from street level, making them a great option for those concerned about aesthetics.
- Energy savings – Like all solar installations, flat roof systems can significantly cut your energy bills. With a well-placed installation, your energy bill can drop by around 70%.
- Reduced carbon footprint – No matter where you install solar panels, if they are generated electricity from the sunlight, you’ll be reducing your carbon footprint. According to the Energy Savings Trust, the average carbon savings from solar panels is between 1.3-1.6 tonnes per year.
Drawbacks of flat roof solar panels
Whilst flat roof solar installations do offer a number of advantages as you’ve seen, there are a few drawbacks that you need to consider.
- Roof integrity – It’s crucial to make sure your roof is structurally sound and can support the additional weight of the solar system. If your roof is on the newer side, it shouldn’t be a problem, but if it’s an old house and the roof’s been standing for a while, it will need a professional assessment before installation.
- Shading – Being flat and lower down to the ground, a flat roof is more prone to shading. Consider potential shading from nearby trees, walls and big buildings. There’s also the problem of self-shading by the other panels in the array if they are too close together. This is why flat roof installations require more space between panels.
- Waterproofing – Flat roofs are more likely to have water pooling issues. You need to be aware of this as it can accumulate over time. Your installer also needs to make sure that the mounting system doesn’t compromise your roof’s waterproofing when it’s drilled in. Any breaks in the roof surface need to be properly sealed afterwards.
Optimising panel angle and orientation
One of the most crucial aspects of any flat roof solar panel installation is getting the angle right. Without the natural gradient of a sloped roof, the angle has to be created by the mounting system.
In the UK, a tilt angle of between 30-40 degrees is generally considered optimal for flat roof installations. This will help the solar panels to absorb the maximum amount of sunlight they can across the day and year. The tilt also helps with rainwater run-off to naturally clean your solar panels.
There are some high-tech mounting systems that can automatically adjust the angle throughout the day, but these are super expensive at this moment in time.
Alongside the angle is orientation. On a flat roof, you have much more flexibility over the positioning of each solar panel compared to a sloped roof where there’s only one choice.
In the UK, south-facing panels capture the most sunlight over the course of a year. Tests show that panels facing south at an angle of 35 degrees can capture about 95% of available sunlight energy annually.
Second to south-facing panels are east-west orientations. These can also be effective, especially for properties that use more energy in the mornings and evenings. Although they may be about 20% less efficient than south-facing panels, they can still capture over 60% of available sunlight when angled at 35 degrees.
Mounting systems for flat roof solar panels
For flat roof solar panel systems to work effectively, you need to get the mounting system right. This makes sure the solar panels are secured to or on the roof and are at a good angle to capture sunlight. The system you go for will depend on the type of roof you have, for example tiled, felt or slate.
It’s most common for mounting systems to be fixed directly to the roof with a metal structure. This offers an extra-secure installation, but it does mean drilling into the roof material. This requires careful waterproofing and sealing afterwards.
On some flat roofs, it’s possible to mount solar panels onto simple plastic tubs that are weighed down with heavy materials, such as stones and slabs. The benefit of this installation is that you don’t need to drill into the roof.
To lessen the impact of wind, it’s often recommended to install solar panels at least 1m away from the edge of a flat roof.
How much do flat roof solar panels cost?
Like other solar panels installations, the cost of a flat roof system can vary. Prices are dependent on how many panels are installed, the types of panels, the mounting system used and the labour costs.Â
That said, a good rule of thumb to bear in mind is that you can expect to pay between £750 and £900 per kilowatt (kW) of capacity.
For an average 3-bedroom house with a 3-5kW solar system, the total cost may range from £5,000 to £9,000. Although installation costs can be similar to pitched roof systems, you’re likely to save a little on labour costs with flat roof installations thanks to the easier access.
We think solar panel installations are well worth it. They can help the average 2 to 3-bedroom house save between £440 and £1,000 a year on energy bills with solar panels, giving them a rough break even point of 7 to 10 years. Even if you don’t plan to be in your current property for that long, it’s thought solar panels can add 4-14% onto your home’s resale value, meaning you’ll recoup any spend when you come to sell.
For us, solar panels on flat roofs are a great opportunity to generate your own renewable energy, save on electricity bills and reduce your carbon footprint. With recent changes to planning regulations making installation easier than ever, there’s never been a better time to consider flat roof solar panels.
