Different types of roof installation systems

①Sloping roof installation method
The inclined roof installation method is well ventilated, easy to install, and relatively cheap, so it is the most commonly used roof home system. This type of system is installed directly above the roof surface, and the inclination and orientation of the photovoltaic array and the roof are the same. Sloping roof installation systems are generally attached to structural elements of the roof, for example, attached to the rafters by lag bolts or fixing brackets.

Then, install the horizontal rails on these brackets, and fasten the modules on the rails with photovoltaic module clamps. In this way, the track lifts the photovoltaic modules above the roof surface, increasing air circulation under the array. The sloping roof is installed with some ventilation channels around the modules, and it is still quite close to the roof, so it is considered to be an outstanding solution that considers aesthetics and ventilation. The materials commonly used for inclined roof installation methods include aluminum, stainless steel, and galvanized steel.

Figure 1 An example of a sloping roof installation system, clearly showing the module fixture

(1) Sloping roof installation method suitable for tiled roofs
It takes more time to install a photovoltaic system on a tiled roof than a metal roof, because the tiles must be removed and then reinstalled in the area where the system and the roof are connected (attachment points), which is very expensive. Time. Installers usually use roof hooks to connect the brackets to the rafters under the tiles. This hook is shaped like a gooseneck and has a protruding arm for connecting to the rail system. When connecting the top or side of the rafters, different manufacturers have different designs, which can be used for different types of tiles.

When planning to install a tiled roof photovoltaic system, it is also very important to consider the reinstallation of tiles. Installers can easily damage the tiles when walking on the roof. These cracked and damaged tiles need to be repaired or replaced. Before starting the installation, it is better to reserve some roof tiles.

Figure 2 Tile hook for side rail connection

(2) Sloping roof installation method suitable for metal roof
Due to the electrical conductivity of metals, working on metal roofs presents safety risks. When working on a metal roof, always pay attention to the bare ends of live cables not to touch the roof. Dissimilar metals are forbidden to come into contact with each other, as this will cause galvanic corrosion, damage to roofing materials and installation systems, and bring significant safety risks to the occupants of the building. By inserting rubber between different metals, galvanic corrosion can be prevented. This technique is called electrical isolation (also known as electrical insulation). For this reason, manufacturers usually list the allowable fasteners in their photovoltaic module information and recommend the use of these fasteners.

Certain types of metal roofs also require installation techniques not to penetrate the roofing material. Such installation requirements are particularly common in places where it rains frequently and the roof must be absolutely waterproof.
Hot weather has a great impact on the metal roof. Metal roofs can become very hot in some areas, so ventilation needs to be increased to maintain a reasonable working temperature for photovoltaic modules. Information can be collected from local industry associations and experienced operators, which will help you understand the potential local temperature effects and how to best respond.

② Bracket installation method
When the roof slope or orientation deviates too far from the optimal angle, bracket installation (also called inclined installation) can be used. This method is commonly used on horizontal roofs or low-inclination roofs, and most of the mounting hardware used in bracket installation It is the same as the sloping roof installation method, but the main difference is that this method includes a triangular support structure for raising the array and increasing the inclination angle. If installed on a flat roof, scaffolding is usually not needed, and in some cases, safety ropes are not even needed (check the local regulations for working height requirements). Although this installation method is simple, the weight of the support structure is increased on the roof. As well as increasing the force of wind load, this method increases a lot of engineering costs. Before installing the rack-mounted photovoltaic array, the installer should consult the local authority or association about the local wind speed design requirements and other special design requirements that must be considered. Usually, this information can be found in the relevant local code/regulatory agency. It is difficult for designers to figure out which codes/regulations apply, and it is helpful to consult with local operators.

Figure 3 Installation method of wavy metal roof

In most places, the bracket installation method needs to be approved by the structural engineer to ensure that the wind load design is reasonable and feasible. When selecting the bracket method, the cost, calculation, and aesthetic impact should be removed from the increased power output (due to the best orientation and inclination).

Providers of photovoltaic array installation systems generally also provide a complete set of installation guidelines. Installing photovoltaic arrays in accordance with the guidelines will meet the wind load standards. The system manual should include a certification or statement that the installation conforms to the standard, and the system inspector can prove that it conforms to the corresponding standard when required.

Figure 4 Bracket mounting system

③Direct installation method
The direct installation method (also known as the embedded installation method) is a photovoltaic installation method in which the photovoltaic modules are directly installed on the roof surface, and the space between the roof surfaces of the modules is small. This installation method greatly meets the aesthetic requirements. However, there is a lack of ventilation space under the array, and the output power of the photovoltaic array is less than that of a sloping roof or bracket installation system.

Figure 5 This set of photovoltaic system is compactly integrated with the building structure by using a curved direct installation method

④Building integration system
Because building integrated photovoltaic (BIPV) systems are more beautiful than traditional roof-mounted systems, BIPV applications are becoming more and more common. BIPV can be seamlessly embedded in a building, becoming an integral part of the roof, embedded in skylights or glass, or directly installed on the surface of the building. Now ecologically conscious architects have begun to use BIPV flexibly.

Figure 6 Case of building integrated photovoltaic system

BIPV projects are often highly customized and are generally much more complex than standard rooftop photovoltaic systems. Usually, architects and engineers need to work closely together to ensure the safety and water tightness of the BIPV system, while being closely integrated into the structural style of the building.

Solar tiles and solar strips are a form of BIPV, and because they can replace traditional roof tiles, they are becoming more and more common in new house proposals. Unlike traditional photovoltaic installation systems, BIPV tiles do not rise above the roof surface, which makes the system more aesthetically pleasing.

Figure 7 The BIPV awning integrated with the parking lot, developed by Sunvie. This 1.15MWp system is located in Saint-Emes, France
Figure 8 A case of solar tiles as a component of the roof

There are also amorphous silicon components on the market. This is a long and narrow flexible photovoltaic module. The adhesive layer on the back can be used to fix the module to the roof. Amorphous silicon modules can be used for many different types of wide metal roof panels and roofing coils and other building materials. Because this form of BIPV exhibits extremely low wind resistance, it is particularly suitable for buildings in areas with high wind speeds.

Summarizing the related problems of installing photovoltaic systems on the roof, some installation systems may not be compatible with certain photovoltaic modules. Therefore, it is very important to check the installation guide provided by the photovoltaic module manufacturer before choosing the installation method. The manufacturer shall prescribe the installation requirements of photovoltaic modules, such as the clamping position of the clamp and the position of the support rail.

Most installation systems require two horizontal rails under each row of components. It is generally recommended to leave enough space between the tracks, so that 50% ~ 74% of the photovoltaic module part is located between the two tracks. Another important point is that if the rails are placed parallel to the rafters (under the roof), the space between the rails depends on the space between adjacent rafters, and it should be checked that the system does not violate the module manufacturer’s recommended installation method.

Manufacturers also usually recommend that the module clamps should be clamped on the longer side, because the structural integrity of the module may not allow it to be clamped on the shorter side. When the wind blows, the photovoltaic module cannot withstand strong force, which causes the photovoltaic module to bend and glass break. crack. The clamp should not cover the photovoltaic cells on the module, and only clamp on the frame of the photovoltaic module, and should not touch the glass, otherwise applying excessive force on the glass will cause the glass to break.