01
Project Overview
This project is a roof renovation project for an industrial park.After the roof renovation, a photovoltaic power generation system will be installed,designed to generate 799 kWp.The overall power generation is relatively small,classifying it as a distributed photovoltaic system.The roofs of the three buildings to be renovated are flat concrete factory roofs,covering an area of approximately 10,000 m².Except for a few equipment bases,the overall structure of the roofs is simple and flat, with no other buildings currently obstructing the view,making it suitable for photovoltaic system installation.During the original use of the factory roofs,simple repairs were made by using self-adhesive modified bitumen waterproof membrane to cover the joints (Figure 1).
Figure 1. Original appearance of the roof base surface after renovation
02
Waterproofing process and selection of main waterproofing materials
For existing roofs with limited load capacity,waterproof materials that can be directly exposed and do not require a protective layer should be selected when upgrading the roof photovoltaic system.In addition,the operation of photovoltaic equipment will generate heat,which will further increase the ambient temperature around the components and may accelerate the aging of waterproof materials.Therefore,waterproof materials with excellent durability should be selected.In order to ensure the overall benefits of photovoltaic power generation projects, the exposed waterproof layer in the photovoltaic roof system often needs to maintain a service life of more than 10 years or even 20 to 30 years,thereby reducing the later maintenance costs.Taking into account the above factors,the recommended main waterproof material for photovoltaic roof systems is a single-layer roof waterproof system with good weather resistance,excellent high and low temperature resistance,and stable and reliable overlap sealing.Common processes for single-layer roof systems include loose laying,full adhesion,and mechanical fixing. Based on the actual situation,this project selected TPO waterproof membrane with butyl self-adhesive rubber layer as the main waterproof material for photovoltaic roofs.This type of membrane,when used with a special base treatment agent,can form a full adhesion with the concrete base layer without damaging the concrete base layer,reducing the application of auxiliary materials,reducing the construction difficulty and overall leakage risk,ensuring reliable waterproof quality,and high overall cost performance.After butyl rubber is bonded to the substrate,a strong, interwoven bond is formed between the rubber and the substrate.The bonding strength gradually increases over time,resulting in excellent adhesion.Figure 2 shows the bonding effect of butyl rubber with various substrates.
Figure 2. Bonding effect of butyl rubber to various substrates
03
Photovoltaic System Selection
When retrofitting existing factory roofs with photovoltaic (PV) systems,traditional through-support mounting requires drilling holes in the roof,penetrating the waterproofing layer.Poor waterproofing can lead to leaks and negatively impact the roof's lifespan.Furthermore,40% of existing factory roofs are low-load-bearing,typically old concrete or light steel structures with a load-bearing capacity of 5-10 kg/m².When the roof's load-bearing capacity is insufficient,PV systems weighing 15-30 kg/m² cannot be reliably supported.For these existing buildings,the industry offers various non-destructive PV module installation methods.Depending on the project's specific circumstances,a suitable PV system can be selected and installed while ensuring basic roof functions such as waterproofing and insulation.Common PV installation methods,prioritizing structural integrity and waterproofing,include:counterweight concrete supports,welded flexible supports,and flexible PV modules.
3.1 The counterweight concrete bearing uses concrete supports and stainless steel brackets.Its construction methods include precast cement foundations and direct casting foundations,and it is generally used for flat concrete roofs.This process is simple and convenient to construct,and has a strong load-bearing capacity for photovoltaic systems;however, its disadvantages are also obvious,namely,a significant increase in the load on the roof and a higher overall cost. Based on past project experience,the entire photovoltaic system using counterweight concrete bearings (Figure 3) has a relatively large load,ranging from 0.9 to 1.0 kN/m²,posing a challenge to the structural load of the roof to be modified.
Figure 3. Counterweight concrete support
3.2 Welded Flexible Support System:This system uses flexible supports that are directly welded to the exposed waterproof layer without damaging the waterproof layer,effectively ensuring the waterproof effect.Furthermore, the use of TPO material for the flexible supports further reduces the load compared to heavy-duty supports. However,the welded flexible support still needs to be combined with aluminum alloy guide rail brackets and panel photovoltaic power generation systems,resulting in limited overall system load reduction (Figure 4).
Figure 4. Welded flexible support (left) and guide rail installation (right)
3.3 Flexible photovoltaic modules There is a type of lightweight flexible photovoltaic module on the market. Flexible solar cell modules can be directly cold-bonded to the original roof metal plate or single-layer waterproof membrane with adhesive.No additional support system is required, and the roof and waterproof structure will not be damaged.Such photovoltaic modules have begun to be used in the renovation of existing building roofs. The self-weight of traditional photovoltaic modules is generally 12~16 kg/m2.After adding the guide rail and support,the overall weight is even greater,which is not suitable for existing building roofs with low load.Flexible module products have a lightweight design and a self-weight of only 4~5 kg/m2.Compared with conventional modules,the load-bearing requirements of the structure are greatly reduced.No support and purlins are required, which eliminates the cost increase caused by reinforcement and makes them more widely applicable.
04.
Special Project Design
The flexible photovoltaic modules used in this project have external dimensions of 2319 mm × 777 mm × 4 mm, with a weight of approximately 6 kg per m².They utilize a 1.6 mm reinforced glass layer and have passed an ice ball impact test at a diameter of 25 mm (7~8 g) and a speed of 23 m/s,demonstrating their ability to protect the power generation modules from impact.The cell type is monocrystalline PERC,with a theoretical power generation exceeding 160 W/m²,and a theoretical power generation exceeding 9000 kW·h over 30 years.In traditional installation processes for flexible photovoltaic modules,lightweight photovoltaic modules are often directly and fully bonded to the roof waterproofing layer. However,photovoltaic modules continuously generate heat during power generation,and this close-fitting installation process poses a severe challenge to the high-temperature resistance of the waterproofing material.Furthermore,in adhesive methods,the long-term bonding ability of the adhesive is questionable after prolonged exposure to the high temperatures generated by the modules.A new type of photovoltaic (PV) module has emerged on the market,prefabricated in factories and integrated with the roof waterproofing membrane.On-site,the module is fixed to the roof waterproofing membrane via hot air welding along its short side,achieving integrated PV and waterproofing installation.To improve the module's heat dissipation capacity and ensure the roof membrane doesn't age prematurely due to heat generated by PV power generation,a TPO square tube heat dissipation grille is used as a support structure between the module and the TPO waterproofing membrane.The softness of TPO provides some resilience,reducing damage from frontal impacts.The TPO square tube heat dissipation grille is further secured to the TPO waterproofing membrane using 25 mm × 25 mm spot welding to prevent wind-induced vibration.
05
Construction Process
5.1 Waterproofing Construction Flow:Base cleaning→Spraying primer onto concrete base surface→Applying 2142 adhesive to existing membrane surface→Marking lines for positioning→Detail node treatment→Pre-laying butyl self-adhesive TPO membrane→Laying butyl self-adhesive TPO membrane→Welding membrane joints→Fixing and edge pressing→Waterproofing layer acceptance.
5.2 Waterproofing Base Surface Treatment: If the roof concrete is severely weathered,powdery,or delaminated, use a chisel or small shovel to remove loose fragments detached from the base.Then sweep away the debris and foreign objects with a broom,and fill with cement mortar. Allow it to dry before proceeding with subsequent construction.Spray the special primer onto the base surface,ensuring even coverage without any exposed substrate or accumulation (Figure 5).The membrane can only be installed after the primer has been sprayed and reached a dry, non-sticky state.The membrane should be laid on the base as soon as possible after applying the primer to prevent secondary dust contamination.Since the original roof joints are covered with self-adhesive bitumen waterproof membrane,a special 2142 adhesive should be applied to the surface of the original self-adhesive bitumen membrane to improve the adhesion between the butyl self-adhesive TPO membrane and the base layer (self-adhesive bitumen membrane) and reduce hollow areas (Figure 6).
Figure 5. Spraying primer Figure 6. Applying 2142 adhesive to the original roll surface
5.3 Waterproofing Layer Construction 1) Pre-laying of the membrane: Based on the on-site dimensions of the roof, the height of the surrounding walls,and the width of the membrane,lay out the TPO membrane on the roof for 15-20 minutes to release internal stress.The membrane should be flat, straight,and loose, and should not be folded; the membrane should preferably be laid parallel to the ridge direction,and construction should proceed from the lowest point to the highest point (Figure 7).
Figure 7. Pre-laying of butyl self-adhesive TPO roll material
2) Applying the membrane:Peel off the release film from the main membrane area.After applying the membrane, use a hand roller to press and remove air bubbles,ensuring a firm bond between the membrane and the substrate.Avoid stepping on the rolled membrane surface.When laying adjacent membranes,pre-lay the membrane and align it with the long side overlap guide line of the previous membrane,ensuring an overlap width of at least 80 mm.The short side overlaps of the two membranes should be staggered by at least 300 mm.
3) Welding the membrane:Use an automatic welding machine for welding the main membrane areas,and use manual welding for short sides,detailed nodes,or vertical surfaces.The joint surfaces of the weld seams should be clean,free of water,oil,and other contaminants.Ideally, the membrane laid on the same day should be welded on the same day.For joints left after each day's construction,effective protection methods must be used to prevent rain and moisture.
4) Detailed treatment of nodes:
① Pipes penetrating the roof:Wrap them with H-type TPO membrane,with a height of not less than 250 mm. Secure the top with a stainless steel hoop and seal with sealant.Weld the bottom to the main TPO membrane (Figure 8).
② Straight drain outlet:Weld the H-type TPO membrane into a cylindrical shape and place it inside the rainwater pipe.Seal the bottom with silicone sealant and hot-air weld the top to the roof TPO waterproofing layer (Figure 9).
Figure 8. Roof pipe Figure 9. Straight drain outlet
③ Roofing equipment:For equipment that needs to be exposed,use H-type TPO rolls to turn up,fix the top with a sealing strip and seal with sealant,with a height of not less than 250 mm,and weld the bottom to the large TPO roll (Figure 10);for equipment that does not need to be exposed,use H-type TPO to bond and wrap the whole, and use homogeneous H-type TPO to reinforce the middle waist belt (Figure 11).
Figure 10 Equipment base Figure 11 Roof water tank
④ Gutters:Butyl self-adhesive TPO rolls are used for both the plane and vertical surfaces of the gutters.A long U-shaped strip is used to fix the bottom two internal corners,and the top is covered with 150 mm wide H-type TPO rolls (Figure 12).
Figure 12 Shallow Gutter Node Treatment
5) The finished effect of the TPO waterproof layer after the large surface is completed is shown in Figure 13.
Figure 13. Effect after waterproofing layer is completed
5.4 Photovoltaic System Installation and Fixing 1) Process Flow Overview:TPO waterproof membrane surface cleaning → grid positioning and pre-laying → grid welding and fixing → butyl tape laying → module bonding and fixing → membrane cleaning at welding points → module and membrane welding and fixing → inspection and acceptance → electrical testing → site cleanup upon completion.
2) Square Tube Heat Dissipation Grid Fixing: After the large-area waterproof layer is completed,clean the membrane surface and position and arrange it according to the design requirements.Four TPO square tubes (25 mm × 25 mm cross-section) are installed under each module,with a spacing of 425 mm between the tubes.The lower part of the TPO square tubes is spot-welded to the large-area TPO membrane according to the area.Each square tube is welded at least 6 points,with each point having a welding area of approximately 25 mm × 25 mm (Figure 14).
Figure 14. TPO square tube heat dissipation grille setup
3) Butyl tape is applied to the square tube. Double-sided self-adhesive butyl tape is pasted on the upper surface of the square tube and then bonded to the flexible photovoltaic module to play an auxiliary fixing role (Figure 15).
Figure 15 Butyl tape bonding and fixing
4) When laying and installing photovoltaic modules,grasp the four corners of the lightweight photovoltaic module product, vertically carry the module to the predetermined position,and then let the front of the module face up.Use double-sided butyl tape to bond the back of the lightweight module product to the square tube.Use a soft tool to press gently to ensure that the photovoltaic module and the butyl tape are in full contact and bonded (Figure 16).
Figure 16. Adhesion and fixing of flexible photovoltaic modules
5) Photovoltaic module welding is performed by using a handheld welding gun to weld the TPO material on the short side of the module to the TPO waterproof layer on the large side.The joint surfaces to be welded should be cleaned with a cleaning solvent in advance (Figure 17).
Figure 17 Flexible photovoltaic module welding
5.5 Finished Result After the roof construction is completed,pay attention to keeping the roof clean.Clean up construction parts and generated waste promptly to avoid damaging the photovoltaic modules or forming hot spots, which would affect power generation efficiency.The finished roof photovoltaic system is shown in Figure 18.
Figure 18. Effect of the photovoltaic system after completion
Conclusion
Traditional photovoltaic (PV) module systems are mostly rigid products,while PV roof systems,designed for overall waterproofing effectiveness and lifespan,often use flexible polymer waterproofing materials. Managing the connection between rigid and flexible components has always been a challenge in the on-site application of PV roof systems.This project adopted a"butyl self-adhesive TPO membrane+flexible PV module"system solution, significantly reducing structural load and simplifying installation.Installing this integrated PV waterproofing system on old or even leaking concrete roofs allows the self-adhesive TPO membrane to solve leakage problems while providing waterproofing protection for over 30 years.The use of TPO square tube heat dissipation grilles simplifies installation steps,greatly improving construction efficiency while enhancing the heat dissipation performance of the PV system and preventing accelerated aging of the roof membrane due to heat generated by PV power generation.This combined solution demonstrates excellent performance in both waterproofing and PV aspects,making it particularly suitable for existing light-load roof PV retrofit projects and worthy of widespread promotion.
