Solar racking systems: the base of a PV system on roofs

Solar racking systems: the base of a PV system on roofs

If you are looking into the topic of solar panels, quite often the term solar racking comes up. But the meaning of the term remains for most people unclear. So what is solar racking? Is it an essential part when it comes to the installation of solar panels? Are there any differences in solar racking systems?

What is solar racking and why is it important?

When a solar panel is installed on a roof, you just see the panels. But beneath the panels is a structure that holds the solar panels. This structure is called solar racking or solar mounting. The solar racking is therefore an integral part of every solar installation and certainly very important since it connects the solar panel system to the roof. The solar racking system has to be able to withstand heavy winds as well as extreme temperatures. Furthermore, the solar racking system is responsible to transfer the weight of the solar panels to the roof structure and it has to make sure, that the weight is distributed and not fixed on just some points because of the roofs static. Most of the time, these mounting systems are made out of aluminum because of the lightness of the material while being white strong, resistant and durable.

 Solar racking components

Not all solar racking systems are the same but there are several components that are commonly used in almost all solar mounting systems. These are flashings, mounts, rails and clamps.

Flashings

When solar panels are installed on a roof, holes have to be drilled in the roof. These holes are potential leaks and may cause water damage when not properly made. To prevent water damage on the house, flashings are used to seal up these holes. Flashings are aluminum rectangles that cover the holes and therefore prevent the penetration of water. When the roof is made of asphalt tiles, the flashing piece is installed underneath the shingles. If the roofing is made out of metal, rubber or wood, special flashing are used that perfectly fit the unique shape of the roof covering.

Mounts

Mounts are an essential part of every solar panel system. These holders are attached to the roof with a bolt to the rafter to secure the whole solar racking system. There is a huge variety of mounts depending on which racking system you choose. Before the installation of a solar panel system, a fitter will have a look at the roof and the attic to determine which mounts are the right choice for this particular roof.

Rails

Solar panels are held by rails that are fixed to the mounts. Most of the time, these rails are made out of aluminum because of the lightness of the material as well as the durability and strength. The rails are often long tracks that can be installed vertically or horizontally on the roof and mark the space, where the solar panels are installed on the roof. After the solar panels are put on top of the rails, you will not see anything of the rails because there are covered by the panels.

Clamps

When the racking is installed, solar panels are put on top of the racks. To make sure that the panels stay in place, they are linked to the racks with clamps. Most of the time mid-clamps as well as end-clamps are used for the installation of a solar system on a roof. Whereas mid-clamps come in handy for the place between panels, because they can hold panels on two sides, end-clamps sit on the end of solar arrays and can hold solar panels on only one side.

Flat roof PV systems versus pitched roof PV system – What is the difference?

As stated before, solar racking systems are an integral part of the installation of a PV system on a roof. When it comes to roof mounted systems, there are mainly two different systems that are used – the flat roof PV system and the pitched roof PV system.

Flat roof PV systems

Most of the times commercial and industrial buildings but also some private buildings have a flat roof. Because of the flat structure, when installing a solar panel system there are just a few fixing points in the roof truss needed. The solar panels are not in danger of slipping down from the roof due to the level surface. Quite often the racking system on flat roofs is installed on a few feet as the base. On top of these feet a rail system with the solar panels is put and the solar system is complete. But as easy as this may sound, the installation can be quite challenging because of the roof’s load limit. In some cases a roof might not be built to support a lot of extra weight and then some penetrations have to be put in place. Flat roof mounting systems come in different shapes and types. Older systems are most of the time made out of stainless steel or aluminum while more recent developed systems are consisting of plastic and polymer based materials due to the lightness of the material.

Advantages:

  • Just a few fixing points are needed
  • Optimal orientation of solar modules can be freely determined

Disadvantages:

  • Possible roof load might be limited and extra penetration has to be put in place
  • Statics: wind and snow loads must be considered

 Pitched roof PV systems

Especially when solar panels are installed on residential buildings, installers have to deal with sloped rooftops. For pitched roofs there are many different options when it comes to solar racking systems. Most of the time, railed and shared rail systems are put on the roof to hold the solar panels; but rail-less systems can also be found on the solar market. No matter which type the house owner chooses, all systems for pitched roofs have to be anchored into the roof in some way. Quite often this is done with a rail system, which secures the solar panels from falling down. Each rail has to be fixed to the roof and this concludes in several drillings in the rooftop. When it comes to rail-less systems the frame of the solar panel works as the rail, and no further rails have to be attached to the roof. But as a matter of fact, rail-less systems do not mean lesser drillings in the roof’s structure. Much handier are the shared-rail systems compared to the other railed and rail-less systems in regard to the drilling in the roof truss. Two rows of panels are put in a shared-rail system on one rail rather than two. Because of this, there have to be lesser fixing points in the roofs structure. An exiting alternative for pitched roofs are the relatively new ballasted and non-penetrating mounting systems. These systems are draped over the peak of the roof and distribute by that the weight of the system on the whole roof rather than on specific parts.

Advantages:

  • Many different options for solar racking systems
  • Old roof covering can remain unchanged

Disadvantages:

  • Have to be anchored to the roof
  • Lower yield compared to flat roof system due to the angle

 The price for a solar racking system

The solar racking system is an important part of any solar system but plays only a minor part when it comes to the cost of the whole solar system installation. If a flat roof is able to hold up a heavy load, then the price for the solar racking system is definitely cheaper than for a pitched roof. But if the flat roof has to be prepared for the weight of the solar panels the price is almost even or higher than for a pitched roof system. The National Renewable Energy Laboratory (NREL) in the USA stated that the cost for the racking system is approximately around $0.10 per Watt (W) which means that the racking makes up around 3% of the overall cost of a solar system. There is also the possibility to buy a used system because even when the solar panels are outdated, the racking system might be still perfectly fine.