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Installing Solar Panels Completely Flat - The Pros And Cons

By Kristy Hoare on in How Solar Power Works

Installing Solar Panels Completely Flat - The Pros And Cons

You must have seen arrays of solar panels installed at an angle to the ground, happily looking at the sun like fields of sunflowers. And when contemplating going solar, you would have probably also wondered if you can just lay them flat on your flat roof.  

There are advantages and disadvantages to installing solar panels completely parallel to a flat roof vs tilting them up. But the cons outweigh the pros, therefore our best advice for most circumstances is to install solar panels with a tilt of at least 10 degrees from horizontal. Let’s find out why.

Up until recently, the general rule within the solar industry has been to tilt solar panels to at least 10 degrees, for two main reasons.  Firstly, solar panels can self-clean in the rain at that angle, and keeping solar panels clean is important, because even a small amount of dirt or debris can cause substantial loss in solar generation.

Secondly, tilting solar panels towards the sun means that more solar electricity can be generated. The reason? Panels generate the highest power when sun rays fall perpendicular on the surface. We hence need to optimize the panel angle to the angle of the sun.

In the last few years, new types of solar panels have entered the market claiming to be suitable for flat-mounting..  This includes frameless solar panels and panels with rainwater channels.  Note: Solar panels with rain water channels are not available from NZ distributors at present.

Some companies have picked up and ran with the marketing hype around frameless solar panels, claiming that it’s all good to install these panels flat.  But a few years on, experience is revealing that it’s not that simple to install these specialised panels flat and treat them as normal.

Let’s go ahead and find out: 

What Are The Advantages To Installing Solar Panels Flat i.e. Horizontal?

  • No spacing is required between rows of solar panels (if the panels are tilted they need space from each other because the tilted panels cause shading).
  • This means you can install more solar panels on a flat roof if you are limited for space
  • Avoid your roof from looking ugly (apparently) because of angled solar panels sticking out above the roof line.
  • Avoid the cost of tilting solar panels (but beware, the “specialised” flat solar panel cost might outweigh these savings).
  • There may be an argument for installing solar panels flat where there is a lot of wind, but this can normally be mitigated with extra bracings.

If you are still enticed with the concept of installing panels flat, your best bet, as we discussed above, would be going for frameless solar panels. In that case, it’s important to know them better, which is why you need to read the following section.

The Pros And Cons Of Frameless Solar Panels

Standard solar panels are made up of a single sheet of glass and a lightweight aluminium frame.  The frame strengthens the panel and is also used as the point of contact to clamp the solar panels to the roof mounting.  Frameless solar panels instead of the frame have two sheets of glass, and as the name suggests, no frame.  Frameless solar panels use rubber coated clamps to attach the panels to the roof mounting. Plus, at 24 kg, frameless panels weigh significantly more vs standard solar panels, which weigh around 17kg.

Since they don’t have frames, the claim is that rain water will run off the panels and take dirt with it, known as self-cleaning.  While it is true that frameless solar panels will self-clean better when laid flat compared to standard solar panels, the panels can’t completely avoid pools of water, attracting dirt and dust.  Therefore the recommendation is to clean flat laying frameless solar panels every two months.  Whereas framed solar panels at a tilt of 10 degrees or more only requires a clean once a year or if necessary.

Frameless solar panels also require more regular maintenance from a professional, as manufacturers recommend checking the torque of terminal screws once a year.  The torque can change due to the rubber used in the clamps.  

A large commercial sized solar power system might be better suited for flat solar panels, since the asset is so large, the extra cleaning and maintenance is worth the trouble.  Whereas, when selling residential solar power systems, the claim is that they are virtually maintenance free.  Choosing frameless solar panels would take away this valuable perk.

Are Flat Solar Panels Cheaper To Install?

Yes, there is a cost to tilt solar panels on a flat roof, it will add around $800 to the cost of installing a standard residential 5kW system.  But in the case of panels installed flat, the cost of maintenance is higher, as it is recommended that a solar expert inspects the clamps of a frameless solar panel system once a year.  Also they need to be cleaned more often.  The ongoing cost, hassle and worry about accumulated dirt outweighs the cost of tilting up the panels.

The Best Orientation And Tilt For Solar Panels In New Zealand

To get maximum solar generation in New Zealand, over a year, solar panels need to be facing north, tilted to a  25-degree slope in the North Island, and 30 degrees in the South Island.

Facing solar panels east or west is ok too, but the total solar generation over the year will be slightly less.  Additionally, east facing panels should be preferred if more electricity is used in the morning, as the peak generation time for solar panels facing east is before 12-noon.  Vice versa for west facing solar panels, where the solar generation peaks after lunch.

Naturally, self-cleaning is also optimal at a higher angle - tilted solar panels ensure rain water runs off and takes dirt and debris with it. When it comes to self-cleaning, even solar panels tilted at 6 or 7 degrees is better than being laid flat.

Solar Generation Results When Installing Solar Panels Flat

Depending on your location within New Zealand, a solar power system could generate a striking 10-15% more power if they are tilted to 25 degrees versus being laid flat.

On the other hand, flat solar panels can be an advantage to those who need more solar power during the summer months, December through to February. However, they will produce less power in winter months.

More commonly, people want a more consistent flow of generation all year round which is what you’ll get from tilted solar panels. 

To illustrate the points above, I have used an example of a 5kW solar power system in Nelson, to show the month to month generation of solar power in the winter versus summer.


Flat roof in nelson, 5kW system - Annual solar generation= 6751 kWh


Tilted 25 degrees, Nelson, 5kW system. Annual solar generation= 7632 kWh

The first graph shows slightly higher solar generation in the summer months, which is outweighed by the extra solar power produced in the winter months on the tilted solar panel system.

The options for configuring a solar power system seem to be endless, with the options of brands, size, and as talked about today - tilting solar panels vs laying them flat. Finally, making the perfect decision is a complex task, and we just hope that the decisions faced when going solar are made a little easier with the information above.

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