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How to install solar panels on a flat roof: Plain talk
- Updated: Apr 15, 2025
- 10 min
Edited by: Andrei Gorichenskii
Some solar installers scratch their heads when it comes to putting solar panels on a flat roof — not everybody is ready to take on this job. Why though? Despite seeming simple, this type of roof has a few tricks to it. Let’s break down how to install solar panels on a flat roof the right way.
Key takeaways
- Flat roofs give you more room and choices for your solar panel system. Unlike slanted roofs, you can use the entire flat surface. This means you can often fit more panels to generate more electricity. Plus, you have the freedom to angle the panels perfectly towards the sun for the best energy collection throughout the day.
- Putting solar panels on a flat roof can sometimes be a simpler process. Instead of always drilling into the roof, installers can use heavy weights like concrete blocks to hold the panel frames in place. This method reduces the number of holes, which can help prevent future leaks in your roof. It can also make the initial installation quicker and less complicated. It may also be cheaper, ask for quotes to figure out the price.
- Taking care of solar panels on a flat roof is generally easier and safer. Because the roof is flat, you can walk on it without much trouble and special equipment. This makes it much simpler to clean the panels to keep them working efficiently. It also makes it easier for an installer to inspect the system for any issues or perform necessary repairs.
- However, there are a few potential problems with flat roofs and solar panels. Some companies might not offer the same warranty for panels on flat roofs due to the chance of water pooling. If you live in a windy place, you'll need extra strong support to keep the tilted panels from blowing over. Also, if you do need to drill any holes, they must be sealed very well to prevent water from leaking into your home.
- Flat roofs are definitely suitable for solar energy, and you can adjust the panel angles for the best sunlight. You'll need to think carefully about how far apart to space the rows of panels. This is important to avoid one row casting a shadow on the panels behind it, especially during the winter months when the sun is lower in the sky. Professionals can help you figure out the best layout for maximum energy production.
Flat roof and solar panels: Benefits and drawbacks
Solar panels can be installed on any type of roof, the only difference is how straightforward or complicated the installation process is. Flat roof is right in the middle, having both advantages and challenges. In some ways, putting a PV system on top of it is a lot like building a ground installation. Let’s look at the benefits of mounting solar panels on a flat roof..
✔ More space and power
With a flat roof, you can fit more panels, because you don’t just have one working slope facing south, but the whole roof at your disposal. Also, you can use bifacial solar panels to generate even more power.
✔ More freedom and flexibility
With a standard tilted roof, sometimes it is impossible to install solar panels facing strictly south at a perfect angle. When you build a solar system on a flat roof, you can turn the panels any way you want and adjust the angle to your preference.
Direction and angle of solar panels: How to get the most out of them✔ Easier installation
If you want to mount solar panels on a flat roof without drilling, the panel mounting structures can be secured with ballast alone, say, cinder or concrete blocks. This means not only a simpler installation, but also less problems with potential roof leaks.
✔ Easier maintenance
A flat roof also offers easier maintenance: You can walk safely, rather than crawling on it. This means your solar panels will be easier to clean, inspect, and repair if necessary.
What about the disadvantages of installing solar panels on a flat roof? There are quite a few:
✖ More warranty problems
Not every company gives a warranty for panels installed on a flat roof, because they tend to pool up rainwater, which can lead to breakage. Also not every company performs flat roof installation. This means you will have to spend more time searching and choose from a limited number of options.
✖ More anchoring required
Living in a windy region, you need to take extra care when securing your solar panels. In strong winds, angled solar panels will be like sails, which means that the support structure must not only support the panels, but also securely anchor them down to ensure they are not carried away by the wind.
✖ Higher risks of leakage
Most solar panels are made to withstand winds of at least 140 mph
Even without solar panels, flat roofs tend to collect water in certain areas. If you drill into the roof to attach the solar panels and don’t ensure a tight sealing, the water can easily get into the drill holes and make the situation even worse.
Can you put a solar panel on a flat roof?
Yes, you can definitely put solar panels on a flat roof. In fact, flat roofs offer some unique advantages for solar installations.
One of the main benefits is flexibility in panel orientation. Unlike sloped roofs where the panel angle is fixed by the roof's pitch, on a flat roof, you can use mounting systems to tilt the panels at the optimal angle to capture the most sunlight throughout the day, typically facing south. This can actually lead to better energy production compared to a sloped roof that doesn't face the ideal direction.
However, there are also considerations. Flat roof solar installations might require more space between rows of panels to prevent shading from one row to the next due to the tilt. Also, the cost of the mounting system to achieve the optimal tilt can sometimes be higher than for simple sloped roof mounts. Wind loading can also be a factor, requiring careful design and secure mounting. Despite these points, with proper planning and the right mounting system, flat roofs are a viable and often advantageous location for solar panels.
One of the main benefits is flexibility in panel orientation. Unlike sloped roofs where the panel angle is fixed by the roof's pitch, on a flat roof, you can use mounting systems to tilt the panels at the optimal angle to capture the most sunlight throughout the day, typically facing south. This can actually lead to better energy production compared to a sloped roof that doesn't face the ideal direction.
However, there are also considerations. Flat roof solar installations might require more space between rows of panels to prevent shading from one row to the next due to the tilt. Also, the cost of the mounting system to achieve the optimal tilt can sometimes be higher than for simple sloped roof mounts. Wind loading can also be a factor, requiring careful design and secure mounting. Despite these points, with proper planning and the right mounting system, flat roofs are a viable and often advantageous location for solar panels.
Installing solar panels on flat roof: Options
How to position solar panels on a flat roof?
Positioning solar panels on a flat roof involves aiming for the best sunlight capture while considering space and potential shading. Here's a breakdown of the key considerations:
The most important factor is the direction the panels face. In the Northern Hemisphere, the optimal direction is generally south to maximize direct sunlight throughout the day. If a true south-facing orientation isn't possible, aiming for southeast or southwest can still provide good results.
Next is the tilt angle. Unlike sloped roofs, you have control over this on a flat roof using mounting systems. The ideal tilt angle depends on your latitude and energy goals. A steeper angle captures more sun in winter when the sun is lower in the sky, while a shallower angle can be better for summer. A common rule of thumb is to use a tilt angle roughly equal to your latitude minus 15 degrees for optimal year-round production, or consider optimizing for summer or winter depending on your energy needs.
Finally, think about potential obstructions and maintenance access. Avoid placing panels near anything that could cast a shadow, such as chimneys, vents, or taller buildings. Leave enough space around the edges of the roof and between panel arrays for maintenance, cleaning, and potential repairs. Planning the layout carefully ensures efficient energy generation and easy access for upkeep.
The most important factor is the direction the panels face. In the Northern Hemisphere, the optimal direction is generally south to maximize direct sunlight throughout the day. If a true south-facing orientation isn't possible, aiming for southeast or southwest can still provide good results.
Next is the tilt angle. Unlike sloped roofs, you have control over this on a flat roof using mounting systems. The ideal tilt angle depends on your latitude and energy goals. A steeper angle captures more sun in winter when the sun is lower in the sky, while a shallower angle can be better for summer. A common rule of thumb is to use a tilt angle roughly equal to your latitude minus 15 degrees for optimal year-round production, or consider optimizing for summer or winter depending on your energy needs.
Finally, think about potential obstructions and maintenance access. Avoid placing panels near anything that could cast a shadow, such as chimneys, vents, or taller buildings. Leave enough space around the edges of the roof and between panel arrays for maintenance, cleaning, and potential repairs. Planning the layout carefully ensures efficient energy generation and easy access for upkeep.
Flat roof solar panels can be mounted onto a special tub either weighed down by concrete or cinder blocks or screwed down to the roof. The panels can also be installed on metal frames, which can also either be ballasted with heavy blocks or attached directly to the roof.
Have your roof inspected before you install solar panels. If you choose to screw your panels down, provide proper sealing. Flat roofs do not have a drainage system and tend to pool rainwater. If the roof starts leaking, repairing it will be much more problematic. If you opt for concrete blocks, make sure the roof can support both the blocks and the panels, especially if your home is not a new one.
How to space solar panels on a flat roof?
You want your solar panels to catch as much of that light as possible all day long, especially when the sun is low in the sky during winter. Think of your tilted solar panels casting shadows, just like anything else in the sun. You don't want one row of panels to block the sunlight from reaching the panels behind it. So, to figure out how far apart to put the rows:
Tilt angle: The steeper your panels are tilted, the longer the shadow they will cast.
Winter sun: The sun is lower in the sky in winter, meaning shadows will be longer then too.
Basically, you need to leave enough space between the rows so that the shadow from one row doesn't fall on the next row during the shortest day of the year (winter solstice) when the sun is at its lowest point in the sky.
A simple way to think about it: The taller the back of your tilted panel is, and the lower the winter sun is in the sky, the more space you'll need between rows.
While there's a math way to figure this out exactly, a good rule is to leave enough room so that if you look at the panels from the side on a winter afternoon, one row isn't blocking the sun from the row behind it. Solar installers have rules and tools to help them figure this out properly for your specific location and panel setup. They'll make sure you get the most sunlight possible without panels shading each other.
Tilt angle: The steeper your panels are tilted, the longer the shadow they will cast.
Winter sun: The sun is lower in the sky in winter, meaning shadows will be longer then too.
Basically, you need to leave enough space between the rows so that the shadow from one row doesn't fall on the next row during the shortest day of the year (winter solstice) when the sun is at its lowest point in the sky.
A simple way to think about it: The taller the back of your tilted panel is, and the lower the winter sun is in the sky, the more space you'll need between rows.
While there's a math way to figure this out exactly, a good rule is to leave enough room so that if you look at the panels from the side on a winter afternoon, one row isn't blocking the sun from the row behind it. Solar installers have rules and tools to help them figure this out properly for your specific location and panel setup. They'll make sure you get the most sunlight possible without panels shading each other.
Have a different roof type or want to learn more about solar panel installation? Read our article on how to install solar panels on a roof.
Julia Zaraeva
Author
Years of experience in translation and a love of nature help Julia find the right words to encourage going solar. She joined the team in 2023 and is happy to make her contribution to a greener future.
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