Ultimate Guide To Flat Roof Solar Panels

Guide Overview: Installing Solar Panels On Flat Roof

This is a 10-minute read. Stuck for time? Bookmark our flat roof solar panel guide for later, and read this overview instead!

You can install solar panels on a flat roof. Using an adjustable mount, you can pitch your panels to an angle that leads to maximum electricity production. 

Costs to install solar panels on a flat roof such as a garage or extension are similar to fitting them on a pitched roof. Expect to pay £7,000 for a 3.5kW system, rising to £12,000 if you want a suitably sized solar battery.

Advantages of installing solar panels on a flat roof include: 

• Reduced hassle when it comes to maintenance, thanks to easy access in comparison to a pitched roof setup
• Unlike pitched roof panels, they’ll hardly be visible to passers-by
• Huge energy savings

However, there are some disadvantages to consider such as:

• Energy production can be compromised massively if they aren't installed correctly
• Installation can void certain new-build warranties
• They need more surface area in comparison to a pitched roof system of the same size (in kW)

Get quotes using our solar panel installation page here, or ask our experts if a flat roof or pitched roof installation will be most suited to your property.

Can I Install Solar Panels On A Flat Roof?

Solar panels can be installed on a flat roof, as long as the roof can support the weight. 

In many cases, installing them on a flat roof such as a garage, shed or extension is actually preferable. Adjustable mounts can be fitted to achieve optimum orientation (south facing) and angle (approximately 30 degrees), maximising their exposure to sunlight.

In the case of a normal installation using a pitched roof, you’re going to be limited by: 

• The exact pitch of your roof; some mounts only allow for minimal adjustment in pitch
• It’s orientation; south facing is always the best, so the orientation of your property’s roof directly relates to how much energy you can produce using solar panels

Jump over to our solar panel installation page here where you can configure your system.

You can also speak to an advisor here to determine if a flat or pitched roof installation is most suitable for your property.

Flat Roof Solar Panel Installation Costs

The typical cost to install flat roof solar panels is £7,000 for a 3.5kW system. This system size is suitable for a small 2-3 bedroom house, but the price does not include a solar battery. 

If you're using more electricity than your solar panels produce, you won't need a solar storage battery. In fact, any excess electricity you generate you can sell back to the grid via the Smart Export Guarantee (SEG). 

However, bear in mind the SEG scheme pays under 5p per kWh at time of writing. If you need to buy back electricity during times where your solar panels aren't producing much / anything at all (evenings / night time), expect to pay around 20p per kWh or more. 

That's where a solar battery comes in. To be self-sufficient, a suitable battery for a 3.5kW flat roof solar panel system like the one mentioned above, is likely to cost £5,000.

Next, we have labour costs. Labour costs to fit solar panels on a flat roof are lower than on a pitched roof, but materials can be slightly more expensive. 

Panels on a flat roof such as a garage or extension use a different process for mounting. In order to ensure they are secure in strong winds you'll need ballast; that's an additional material cost in comparison to a pitched roof installation.

As a side note, those receiving a means tested benefit may be eligible for grants such as ECO4. At the very least these will offer households substantial discounts on flat roof solar panel installation costs, and sometimes even free solar panel fitting!

The £7,000 cost estimate (or, £12,000 with a suitable storage battery) is exactly that, an estimate. There are plenty of variables that affect the price of your installation including: 

• Interest charged on finance
• The kW output of your system
• Quality, brand and efficiency of your solar panels
• Battery size
• Average labour costs in your county

Looking for further reading to understand the cost of flat roof solar panels? We’ve written a 10-minute guide to solar panel installation costs here. 

Alternatively, jump over to our clickable solar panel tool here, and configure the most suitable system for your property. 

Pros & Cons

Like installing solar panels on a pitched roof, there are both advantages and disadvantages to consider before making an investment of this size.

Pros 

Ease of Maintenance 

Accessing a pitched roof is difficult. Due to Working at Height Regulations 2005, certified MCS contractors would need to erect scaffolding in order to maintain your solar panels. 

Erecting scaffolding for an average property is typically £800 per week.

Maintenance for the parts of the system situated on your flat roof includes the likes of:

• Cleaning panels; dirty solar panels can see a huge drop in efficiency of up to 25%
• Checking all wiring and connections are secure and safe

A maintenance check for your flat roof solar panel system is generally only needed once a year. However, you should aim to have your solar panels cleaned every 3-6 months. 

One cost-effective option here is to employ a window / solar panel cleaning company that uses a water-fed-pole system. Using extendable poles, they remove the need to erect scaffolding, drastically reducing the cost of cleaning in the process.

Aesthetics 

Not everyone likes the look of solar panels. Fitted on a pitched roof, they’re visible not just from a distance, but even when walking by a property. 

Even when flat roof solar panels are pitched, the majority of the system is out of view to passers by. 

If aesthetics are important to you and you have spare space, installing solar panels on a flat roof is a great alternative to using your pitched roof.

Energy Savings

Although generating clean energy is important, most people that install solar panels on a flat roof do it to save money. According to the Energy Saving Trust, you can save anywhere between £510-£600 per year. 

The figures below include rough estimates of utilising the Smart Export Guarantee (selling excess energy produced back to the National Grid).

Cons

Reduced Efficiency When Installed Incorrectly

Solar panels work at their best when south facing and when installed at around 30 degrees. 

Having a flat roof gives you the opportunity to optimise the performance of your solar panels by adjusting their pitch and orientation. Of course, not all installers work to the same standards. 

If your installer doesn’t fit your solar panels to the above specs, it’s going to reduce your electricity production, and increase the overall payback period dramatically.

To minimise mistakes during installation, use an MCS registered installer. All of Dwellow’s installers are MCS certified; you can get solar panel installation quotes here. 

Roof Warranty For New-Builds

New-builds in the UK typically come with a 10-year warranty from the NHBC (New Homes Building Control). Your roof will be covered as part of this warranty. 

However, not all homebuilders will cover your roof if you install solar panels. 

At approximately 25 kg per panel plus mounting hardware, a typical 10-panel system can weigh well over 300 kg. If your flat roof isn't weight bearing, that's going to be a big problem. 

Contact your homebuilder, check the fine print of your warranty, or contact our experts here to determine if installing solar panels on a flat roof will void your warranty.

More Surface Area Needed Compared With Pitched Roofs

Solar panels on a flat roof will need to be spaced differently to those on a pitched roof. This isn’t just due to the need to install ballast and mounts that tilt, it’s also because panels on a flat roof will shade other panels if they’re too close.

What does this mean for you? You’ll be limited when it comes to the size (in kW) solar panel system you can install on a flat roof; it might not be big enough to power your home completely.

What’s The Best Angle For Flat Roof Solar Panels?

The best angle for solar panels on a flat roof varies from 20-50 degrees. 

The exact angle you need to set your solar panels to depends on the time of year and where in the UK you’re based; 30 degrees is the most common angle for solar panels.

What To Do Before Installing Solar Panels On A Flat Roof

Planning Permission

In general, you don’t need planning permission for solar panels. However, it’s worth checking before forking out thousands of pounds (typical installation costs are £7,000 for a 3.5kW system). 

If you’re unsure whether you need planning permission, contact our solar panel experts here. 

Roof Assessment 

Before installation, your flat roof will need to be assessed to ensure it can hold the weight of solar panels without compromising its integrity. 

A typical solar panel system can weigh over 300 kg. Old and poorly constructed flat roofs on garages, sheds and extensions may not be suitable. 

Check whether your roof is suitable for solar panels by contacting our experts here. 

Check Your Roof Warranty

If you live in a new-build, it’s likely you’ll have a 10-year warranty thanks to the NHBC. 

Check your contract to ensure that fitting solar panels on your flat roof doesn’t compromise your warranty. 

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