To achieve the "dual carbon" goals, most newly built industrial plants in China are being designed and installed with solar photovoltaic panels on their roofs. Ensuring that roofs do not leak over the long lifespan of the panels and ensuring that the photovoltaic system and roof waterproofing systems have a matching service life is a key research area in the waterproofing industry. The Suzhou New Generation N-Type High-Efficiency Solar Cell Project, a plant for a photovoltaic panel manufacturer, originally included a rooftop installation of photovoltaic panels. This article uses this project as an example to explore the application of TPO composite functional panels in photovoltaic roofing projects for newly built industrial plants.
1 Project Overview
The Suzhou Next-Generation N-Type High-Efficiency Solar Cell Project is located at the intersection of Heshan Road and Yinhe Road in Suzhou, Anhui Province. The planned plant area is approximately 240 mu (approximately 240 mu). The total construction area for the first phase of the project is approximately 116,000 square meters, including approximately 70,000 square meters of waterproof metal roofing. Figure 1 shows a design rendering of the project.
Figure 1 Rendering of Suzhou's new generation N-type high-efficiency solar project
The original design structure of this project is as follows from bottom to top: steel purlins, steel wire mesh, 0.3 mm thick PE vapor barrier, 50 mm thick glass wool insulation layer, 1.5 mm thick TPO membrane waterproofing layer, and 0.6 mm thick metal roof cover.
This solution has the following two defects: 1) Because the waterproof membrane is under the metal roof panel, the waterproof membrane must be penetrated during the construction and fixing of the roof panel, resulting in the risk of leakage in the roof system;
2) The necessary leakage repair will shorten the stable service life of the photovoltaic system, thereby reducing the economic benefits of photovoltaic power generation.
After numerous technical discussions, demonstrations, and on-site exchanges, the decision was made to replace the original design's roof panels and waterproofing layer with Beixin Waterproof's OIPS-129 composite functional panels (TPO composite functional panels). The optimized roof structure, from bottom to top, consists of: steel purlins, steel mesh, 0.3 mm thick PE vapor barrier, 50 mm thick glass wool insulation, and 2.4 mm thick OIPS-129 composite functional panels (1.8 mm thick H-shaped TPO membrane + 0.6 mm thick galvanized steel sheet), as shown in Figure 2.
Figure 2 Roof structure layers
2. Requirements for the selection of main waterproof materials and supporting materials
The roof waterproofing layer for this project utilizes Beixin Waterproof's 2.4 mm thick OIPS-129 composite functional panels (1.8 mm thick H-shaped TPO membrane + 0.6 mm thick galvanized steel sheet). The membrane and steel sheet are thermoplastically welded before shipment. After profiling at the construction site, they are spliced and installed. The long seams are joined together using hot-air welding with the reserved TPO overlap, forming a single, integrated composite functional panel. Bolts secure the composite functional panel to the steel purlins, and the nail caps are sealed with prefabricated TPO membrane sections of the same material.
The roof waterproofing layer for this project utilizes Beixin Waterproof's 2.4 mm thick OIPS-129 composite functional panels (1.8 mm thick H-shaped TPO membrane + 0.6 mm thick galvanized steel sheet). The membrane and steel sheet are thermoplastically welded before shipment. After profiling at the construction site, they are spliced and installed. The long seams are joined together using hot-air welding with the reserved TPO overlap, forming a single, integrated composite functional panel. Bolts secure the composite functional panel to the steel purlins, and the nail caps are sealed with prefabricated TPO membrane sections of the same material.
3 Roof construction technology
3.1 Laying wire mesh
The wire mesh is laid out according to the spacing between the roof purlins and the size of the roof. The wire mesh is first fixed along the ends, and then the construction workers use a traction method to lay the wire mesh rolls. Other construction workers are simultaneously fixing the laid wire mesh.
3.2 Vapor barrier laying
A 0.3 mm thick PE vapor barrier layer was laid on the installed wire mesh. The vapor barrier layer was temporarily fixed at one end. The construction workers used a traction method to lay the vapor barrier layer. The overlapping edges of the vapor barrier layer were firmly adhered with double-sided butyl tape (Figure 3).
Figure 3 Vapor barrier layer laying
3.3 Laying of insulation layer
Lay the insulation layer on the vapor barrier layer. The insulation layer should be laid flat and with tight seams. Double-sided butyl tape should be used to firmly tape the equipment base, vents, and flip-up areas where disconnection is required.
3.4 Large surface laying of OIPS-129 composite functional panels
1) OIPS-129 composite functional panels can be profiled on-site or pre-profiled before shipment. Due to the large span of this roof, on-site profiling was used. The profiling equipment was lifted to the same height as the roof, and the profiling machine operated continuously, cutting the panels to the pre-designed profile length. The roof span was 25 meters, so the panels were profiled in one go to the desired span, avoiding overlap on the short side. Figure 4 shows the on-site profiling process for OIPS-129 composite functional panels.
Figure 4 On-site profiling construction of OIPS-129 composite functional panels
2) OIPS-129 composite functional board fixing
OIPS-129 composite functional panels should be secured with screws. Screw material requirements are as described above. Screw spacing should be the same as steel purlin spacing. Plant spacing should meet the requirements of the wind-uplift load calculation document issued by the design firm. Typically, screws are secured trough by trough or every other trough. For this project, screw spacing is trough by trough. After screwing, install prefabricated screw caps and seal them with TPO sheeting.
3) OIPS-129 composite functional board overlap construction
The OIPS-129 composite functional panels have a TPO sheet overlap along the long sides. This overlap is then welded securely to the adjacent sheet using a hot air welder. The welder temperature and creep speed should be adjusted according to the on-site temperature and humidity to ensure weld quality. The weld strength should be higher than the sheet's own strength, and the weld should be dense and continuous.
For industrial plant metal roofs with a span of less than 18 meters on one side, OIPS-129 composite functional panels can be laid full length without overlapping the short sides. For larger spans, overlapping edges may be reserved to mitigate deformation caused by temperature differences. The overlap arrangement should be tailored to the project's specific needs. The distance between adjacent short-side overlaps should be no less than 500 mm. The joints between the upper and lower panels should overlap in the direction of water flow, and the overlaps should be securely sealed with welded TPO membrane of the same material.
3.5 Processing methods for each detail node
1) Roof ridge treatment
At the ridge, steel ridge tiles are screwed to the OIPS-129 composite functional panels on both sides. Once securely connected, a homogeneous TPO membrane (Type H) of the same material is cut to completely cover the ridge tiles and welded to the OIPS-129 composite functional panels on both sides. The effective weld width should be at least 25 mm, and the weld strength should be greater than the membrane's own strength. Fusiform patches should be cut to reinforce the crests.
2) Parapet wall gutters
This project utilizes stainless steel gutters, and waterproofing is achieved with backing-type TPO membrane (Type L) for full gutter adhesion. H-type TPO membrane is welded at the junction of the OIPS-129 composite functional panels and the backing-type TPO membrane (Type L) for the gutters to ensure the integrity of the waterproofing layer. The parapet wall gutter joint construction is shown in Figure 5.
Figure 5 Details of the inner gutter of the parapet
3) Siphonic Drain
A prefabricated siphonic drain is used for the gutter drain. At the drain outlet, the pre-laid TPO membrane is cut. After the prefabricated siphonic drain is installed, the TPO membrane at this location is welded to the larger TPO membrane. Welding should ensure a strong and tight weld to eliminate the risk of leakage at this joint. The siphonic drain joint construction is shown in Figure 6.
Figure 6 Siphon downspout node construction
3.6 PV Mount Installation
This project utilizes horizontal, flip-type anchor supports, as shown in Figure 7. Before installation, the construction location should be marked out, and a hole drill should be used to pre-drill holes between the OIPS-129 composite functional panels and the steel purlins. Once the holes are drilled, the supports are inserted into the steel purlins, and the support bolts are rotated until the flip-type anchor supports are securely fastened to the steel purlins. After the bolts are tightened, the pre-bolted TPO sheet is hot-air welded to the large-surface TPO membrane, allowing the photovoltaic panels to be subsequently connected to the bolts. This secure connection ensures the installation reliability of both the photovoltaic panels and the waterproofing layer.
Figure 7 Horizontal flip anchor support
4. Product Protection and Safety Measures
1) Do not walk on OIPS-129 composite functional panels while wearing spiked shoes.
2) Do not stack heavy objects on OIPS-129 composite functional panels.
3) Do not scratch OIPS-129 composite functional panels during material lifting and handling.
4) Avoid contact between OIPS-129 composite functional panels and organic solvents, oils, and grease.
5) When working on roofs, construction workers must wear a five-point safety harness; three-point harnesses are strictly prohibited.
5. Conclusion
The application of distributed photovoltaic roof systems has put new demands on the waterproofing of steel roofs. Beixin Waterproof's OIPS-129 composite functional panels, an innovative metal roofing technology, replace the steel roof panels and waterproofing layer in the original design. This solves the problem of requiring penetration of the underlying waterproofing layer when securing the steel roof panels, which can create leakage risks. This innovative technology is being gradually refined in actual projects to form a systematic solution. We welcome colleagues to explore the application of this new technology and promote innovative development of waterproofing technology in the metal roofing field.
