Solar Panels on a Flat Roof (7 Ways to Improve Performance)

In this article, you will learn about installing solar panels on a flat including the top ways to improve the output of an array.

The good news is that it is completely possible to put solar panels on a flat roof. It is very common to do but requires a different approach to a pitched roof you usually see on houses. 

You’ll see many large commercial buildings that have flat roofs with dozens of solar panels on top. As long as your structure is strong enough you should be able to add a solar array. 

Below we will discuss the key factors to consider and discuss with your installer to get the best results. 


Tilt Angle

The most important factor in generating the most electricity possible is the angle at which the panels are mounted. This is because a solar panel tilted towards the sun will capture more energy than one laid flat.

tilted solar panel

A solar panel laid flat will have a ‘tilt angle’ of 0 degrees. Even small increments from this can have a dramatic effect output. The optimum angle for solar panels is between 30 – 45 degrees. This improves power output by 10% to 15% compared to a panel laid flat. A tilt angle mount should be used on a flat roof.

solar panel on tilt on a flat roof
Solar panels on tilt mounts

Orientation

It is critical to orientate solar panels in the correct direction. This means making sure they point facing the sun. As they are mounted at a tilted angle we want to make sure this is then directed at the strongest direct sunlight through the middle of the day. 

In the northern hemisphere, like the USA, Canada, and UK, this should be south facing. (But north facing in the southern hemisphere).

solar panels at angle
Face solar panels towards sun

Orienting a solar panel to true south will give it the maximum performance. As you move away from this direction you will lose performance. For example, facing a solar panel east or west can result in a 15% output reduction. Plus, north facing would reduce energy production by 30% or more.


Placement and Shading

You should measure out exactly where your solar panels will be mounted in relation to the sun. It can be a costly error to mount rows equipment too close together, particularly if they are drilled into the roof. 

You should account for the angle of the sun and shadow created in your particular location. Any shade covering solar cells can severely affect performance. Panels mounted in a front-row could shade ones mounted behind! Don’t forget, the sun will sit at different heights in the sky throughout the year.


Mounting System

There’s various mounting options for houses with flat roofs. This allows you to put solar panels on virtually any flat roof including structures like garages and extensions. You must ensure it is strong enough to bear the weight.

You will find these systems are placed into two categories – Penetrated and Ballast. 

Penetrated Roof Mount – This involves drilling holes and securing the mount directly to the roof. Flashing is then added to ensure it remains waterproof.

Ballast Roof Mount – This uses weight to hold the solar mount in position. Hence the name ‘ballast’. The benefit is that there is no drilling required so there are no risks of leaking. Of course, it adds significant weight to the overall installation. 

solar panel ballast
Concrete ballast on solar mount

Water Leaks

The risk of leaking is increased on a flat roof compared to a flat roof. This is because there is a higher potential for water to pool and find a way through the hole created by drilling. This is only an issue when using penetrated mounting systems.

You should check your installer has experience in working on flat rooftops and that they are following the best practices. Any holes need to be sealed correctly and flashing should be used to divert water away efficiently.


Accounting for Wind

Wind is not always a concern as solar panels are incredibly durable made from aluminum and tempered glass. But when mounted at an angle it can become a problem in very strong winds.

A flat roof solar panel system will be able to withstand gusts of up to 100mph (160kph). That should be enough in most areas. If you live in a place that can see wind conditions higher than this then you should reconsider and discuss the issue with your installer. You should specify this type of wind information to help in selecting mounting and installation methods.


Other Objects

Shading can be a big problem for solar panels and can come as a shock to people with flat roofs. Afterall, how can flat surfaces produce shadows?

Well, there might be other components and objects on the roof that create shade. This can include chimneys, watertacks, vents, ducts, AC, and more. Take these into account and check where they deliver shade or might interfere with a solar array. 


Are Solar Panels Effective on a Flat Roof?

Yes, solar panels can be just as effective and even perform better than a pitched roof. This is because you can control the tilt angle and orientation. You can’t move or adjust the angle of a pitched roof with panels mounted flush.

You can use a mounting system where the tilt angle can be adjusted to suit your region and specific needs. In addition, orientation can be measured to make sure everything is facing the perfect direction. These two things can make a huge improvement to performance to increase your total electricity generation.


Does a Flat Roof Need Planning Permission for Solar Panels?

If you are looking to install solar panels on a flat roof you will need to comply with local building regulations. A local solar installer should have in-depth knowledge of the city building codes in your area. It should design your array to fall within these requirements. 

There are several checks that are carried out by local authorities to check you are compliant too. Plus your utility company will have to approve the installation and give permission to operate. All of this means it can take 3 – 6 month for a system to be installed and switched on.


Solar Panels on a Flat Roof Summary

I hope this page about solar panels on a flat roof gives you a clear idea of what is required for an efficient system.

As you discovered, there are many factors to take into account to ensure the best performance. Keep in mind that every system will need to be customized and altered depending on your location and property. You can use these tips above to discuss with an installer what is best for your situation.

Wondering what type of roof is best for solar panels? Read the complete guide