Device for checking the safety of profile rails

Abstract

Device (2) for checking the security of an adhesive joint of profile rails (20) or profile rail sections of a photovoltaic cell substructure on a roof covering (10) of a flat roof, comprising said profile rails (20) or profile rail sections, a force measuring device (60) arranged on a tripod (50) above the adhesive joint, and a load-bearing means (70) connected to the profile rail (20) or the profile rail section.

Description

Technical field

[0001] The invention relates to a device for fastening profile rails for substructures of photovoltaic cells on flat roofs. A flat roof refers to a roof with no or only a slight roof pitch, with a slight roof pitch meaning a roof pitch of up to 10 degrees from the horizontal. Background of the invention

[0002] In the conventional installation of PV systems on flat roofs, two main methods have emerged to protect the PV system from wind-induced uplift: bolting the substructure to the ground and ballasting the substructure. Regarding ballasting, several expert reports have already presented cases in which generator systems on flat roofs were displaced several meters from their original position. However, the bolting method is rarely used in expert circles, as any drilling through the sealed roof surface always carries a certain risk of losing the seal. While manufacturers offer system components for this purpose, these do not always comply with applicable regulations and some have not been fully tested in practice.

[0003] According to current DIN standards, bonding is generally prohibited because the load transfer falls on the roof waterproofing. In individual cases, bonding is permitted with a special manufacturer's approval. Direct specifications for this method can be found neither in the applicable professional regulations of the German roofing trade nor in the standards.

[0004] EP2362428A2 describes a method for bonding a profile rail or a profile rail section of a PV system to a flat roof. In this method, a laminate strip with fibers embedded in a matrix is ​​first applied to the flat roof before the profile rail or profile rail section is pressed into the strip. On the one hand, this bonding works purely through the adhesion of the laminate strip. On the other hand, the integrity of the bonded joint is not verified.

[0005] Previous approaches failed because the bonding of mounting systems on flat roofs neither complied with applicable standards nor with recognized engineering practices. In particular, reliable load transfer could not be guaranteed because the roof waterproofing is not designed as a load-bearing layer. Furthermore, there were no options for non-destructive testing of the adhesive bond, which called into question its long-term functional reliability. Weather influences, material aging, and thermal stress also led to a loss of adhesive strength. In practice, this approach lacked acceptance under building regulations and was not economically feasible. Object of the invention

[0006] The object of the invention is to provide a device for checking the safety of PV systems, which not only optimizes the load transfer to the roof waterproofing, but also offers effective protection against the lifting of the PV construction by wind and the otherwise occurring "floating" of the PV construction on the flat roof surface, without risking the waterproofing of the flat roof.

[0007] This object is achieved by the device according to claim 1. Advantageous further developments result from the devices of the subclaims.

[0008] According to the invention, a device for testing the safety of a photovoltaic (PV) cell substructure on a flat roof is provided. The device is designed to be used in the method initially discussed below: - Applying a first primer to the profile rail or the profile rail section, - Application of a fibre composite material, whereby the fibre composite material covers the profile rail or the profile rail section and is bonded to both the first primer and the underlying flat roof, - Attaching a load-carrying device to the profile rail or the profile rail section, whereby a force measuring device is connected to the load-carrying device, - applying a tensile force directed essentially upwards to the load-carrying device, whereby the tensile force is measured and successively increased without tearing off the profile rail or the profile rail section, and - Determine whether a design-dependent tensile force threshold has been exceeded.

[0009] The construction-dependent threshold is a site-, position-, and building-specific parameter. The site specificity is determined depending on the wind zone in which the building on which the PV cell substructure is / was mounted is located. Germany, for example, is divided into four wind zones (see DIN EN 1991-1-4 / NA). More precise assignments of individual districts and independent cities to wind zones are published by the German Institute for Building Technology (www.dibt.de Aktuelles / Technische Baubestimmungen). Depending on the height of the building, different velocity pressures (q(z e ) in kN / m 2 ) in the respective wind zone (WZ). WZ profile h≤10m 10m <h≤18m 18m <h≤25m 1 inland 0,5 0,65 0,75 2 inland 0,65 0,8 0,9 2 Coast and Baltic Sea islands 0,85 1,0 1,1 3 inland 0,8 0,95 1,1 3 Coast and Baltic Sea islands 1,05 1,2 1,3 4 inland 0,95 1,15 1,3 4 Coast and Baltic Sea islands 1,25 1,4 1,55

[0010] The design values ​​(w d,e in kN / m 2 ) for the wind load on the surfaces are then calculated using the velocity pressures, the partial safety factors (γ Q) for unfavourable variable actions (DIN EN 1990) and the shape and inclination dependent external pressure coefficients (c pe ) to calculate (w d,e = γ Q × c pe × q(z e )).

[0011] The location and building specificity depends on the direction from which the wind flows onto the roof surface. Depending on the direction of the wind, the roof is divided into different zones – F, G, H, and I. The F-zones (F-zone) are located at the corners of the front (side facing the wind flow). Their dimension is e / 10 in the direction of the wind flow, where e is the smaller of twice the height of the building (h) and the width of the front (b) (e = min{2h, b}). From the sides of the building to the center, they are e / 4. The area between the F-zones up to the same depth of e / 10 is the G-zone. Between e / 10 and e / 2 in the direction of the wind flow (across the entire width of the building) lies the H-zone, and behind it the I-zone. The magnitude of the stress in the respective areas also depends on the design of the roof edge (e.g., whether with or without a parapet). Depending on the zone, different values ​​for the external pressure coefficients (c) result.pe ): flat roof F G H I Sharp-edged roof edge -2,5 -2,0 -1,2 -0,6 Roof edge with parapet h p / h = 0,025 -2,2 -1,8 -1,2 -0,6 h p / h = 0,05 -2,0 -1,6 -1,2 -0,6 h p / h = 0,1 -1,8 -1,4 -1,2 -0,6

[0012] Protection against wind loads is achieved, for example, by applying a load (e.g., gravel). The design value of the dead weight of loads is 16 / 32 g of gravel. d = 0.18 kN / (cm x m 2 ). In order to withstand the wind load, the thickness of the load would have to be d = abs[w d,e ] / G d [cm] - of course, provided that the additional weight on the roof structure is permissible and complies with the technical building regulations.

[0013] For example, for a 12 m high building with a length of 26 m and a width of 16 m at a location in wind zone 2 with a parapet height of 0.3 m, the following values ​​result: q=0.8 kN / m2 cpe(F)=−2.2 cpe(G)=−1.8 cpe(H)=−1.2 cpe(I)=−0.6 wd,e(F)=−2.64[kN / m2] wd,e(G)=−2.16[kN / m2] wd,e(H)=−1.44[kN / m2] wd,e(I)=−0.72[kN / m2]

[0014] The dimensions of the zones depend on the direction from which the building is approached. If the wind blows towards the 16 m long side (e = min{16 m, 2x12 m} = 16 m), the edge zones (width; depth) are: F = (4 m; 1.6 m), G = (9 m; 1.6 m). If the wind blows towards the 26 m long side (e = min{26 m, 24 m} = 24 m), the edge zones have the following dimensions (width; depth): F = (6 m; 2.4 m), G = (14 m; 2.4 m). The remaining rectangular section inside (H-zone) therefore has an area of ​​(26 m - 2 × 1.6 m) × (16 m - 2 × 2.4 m) = 255.36 m 2 . Following the above explanations, the roof in the respective zones would have to be d(F)=2.64 / 0.18 cm=14.7 cm d(G)=2.16 / 0.18 cm=12 cm d(H)=1.44 / 0.18 cm=8 cm be weighted down with gravel.

[0015] Following previous considerations, it has been empirically shown that particularly high levels of safety for PV substructures on flat roofs are achieved when the PV substructures inside the roof (H and I zones) can withstand a vertical tensile force of 2 kN. This is sufficient for secure attachment even at roof heights of > 25 m. In the edge areas of the roofs (F and G zones), it is desirable for the PV substructures to withstand a tensile force of 2.5 kN, preferably a tensile force of 3 kN. These values ​​result in a particularly safe arrangement for PV systems on flat roofs.

[0016] This method not only checks whether the structure can withstand the conditions, the layer arrangement also allows the bonded joints to be touched up if adhesion is insufficient. This could arise precisely because the liquid plastic and the fleece / or fiber reinforcement are applied from "above". The first primer can be a polyvinyl butyral-based primer or similar, for example. When applying this primer, the flash-off times must be observed. The fiber composite is, for example, polyurethane-based. General liquid plastics in combination with fleece inserts or fiber reinforcements can be considered. The load-bearing device can be, for example, a clamp, a loop or a shaped part specially designed for the profile of the profile rail or profile rail section.

[0017] The method is suitable for reliably testing the safety and integrity of the connection of profile rails or profile rail sections on flat roofs without compromising the roof's sealing properties or damaging the existing fastening. Since no ballasting needs to be tested, the focus when assessing the area utilization is on the orientation, tilt angle, and possible shading from neighboring modules. The profile rails or profile rail sections to be tested are typically U-, trapezoidal-, or omega-shaped perforated sheets made of galvanized sheet metal, stainless steel, or aluminum. They feature means for connecting to the rest of the substructure of the PV system.It features a support surface for connection to the roof surface, as well as upward-facing flanks curved inward for reinforcement, which, together with a fastening slot, allow connection to the substructure. The method can also be applied to other types of profile rails familiar to the specialist, provided they are already connected to the roof surface.

[0018] The procedure can also be used, for example, in the installation / assembly of PV systems. In this case, the following steps precede the verification procedure: - Applying a primer to a roof covering of the flat roof, - Placing a test / profile rail or a profile rail section of the PV cell substructure on a part of the first primer.

[0019] The primer can be a polyurethane-based primer, for example. It serves as both a primer and a bonding agent and is applied in a layer that covers the base of the profile rail and surrounds it with a width of preferably at least 5 cm in all directions.

[0020] The primer can be applied, for example, in an area where a profile rail is to be installed and beyond. The primer can be selected depending on the material of the roof covering, for example. Experts are familiar with common combinations for this.

[0021] The orientation of a PV system on a flat roof is a fundamental factor that influences the amount of sunlight the solar cells can capture. In Germany, the ideal orientation is south-facing, as this allows for maximum solar radiation throughout the day. The tilt angle of the PV modules on flat roofs, achieved through mounting systems, is another key factor.

[0022] Theoretically, PV modules can be mounted completely flat on flat roofs, which would be the most cost-effective solution. In this case, the rails glued to the flat roof are used directly to attach the modules, and clamps are used to hold them in place. However, there are some challenges regarding heat buildup and snow load. With flat mounting, heat can build up under the modules, reducing efficiency. Furthermore, unlike with sloped mounting, snow (and other debris) accumulates on flat-mounted modules instead of simply sliding off. This would result in the loss of self-cleaning properties.

[0023] One solution to overcome the challenges of flat installation is a one-sided south-facing mounting. This involves mounting the solar modules at the optimal inclination and orientation. A south-facing orientation is ideal if there is sufficient space available on the roof. However, it should be noted that the entire roof area can only be utilized if the modules are arranged parallel to the roof, with the modules reaching right up to the roof edges. The ideal angle of inclination for one-sided south-facing mounting is around 35 degrees, similar to a sloping roof. However, it is not necessary to adjust the angle precisely, as small deviations have only a minimal impact on energy generation. More important is avoiding self-shading, the shadows cast by the mounted modules. The greater the angle of inclination, the greater the distance between the module rows must be.

[0024] For some roof situations, a double-sided east- and west-facing installation offers advantages. The modules are tilted head-on, with one facing west and the other facing east. Due to the daily and annual course of the sun, the modules should be positioned more flatly. The optimal tilt angle is slightly over 10 degrees, with a maximum of 15 degrees. This angle is flat enough to prevent shadows, but steep enough to maintain the self-cleaning effect. Although the yield of a single module is lower than with a south-facing installation, the roof area can be covered more densely with modules, ultimately resulting in a positive impact on yield.

[0025] External shading effects can also significantly impair the performance of PV systems on flat roofs. Trees, surrounding buildings, or even ventilation shafts can cast shadows on the solar cells. Therefore, a careful site analysis is essential. PV modules should be positioned in such a way that (self-)shading effects are minimized.

[0026] The fiber composite material can be based on polyurethane, for example. Liquid plastics combined with a fleece insert or fiber reinforcement are generally conceivable. During this step, the fiber composite material must essentially cover the profile rail or profile rail section, preferably completely. Care must be taken to ensure that no air bubbles are trapped under the fleece or reinforcement. When cutting the fleece to size, the geometry of the profile rail or profile rail section must be taken into account. Furthermore, the fiber composite material must be dimensioned so that it extends beyond the profile rail or profile rail section to essentially completely cover a first primer applied to the roof membrane. This arrangement is particularly advantageous because it increases the adhesion. Furthermore, the shape can be adjusted and further reinforced with additional fleece layers or reinforcements.

[0027] During the tensile test, a force gauge is positioned on a tripod above the area to be tested, and a load-bearing device is used to apply a tensile load to the substructure at a point between two adhesive points. The tensile force is essentially orthogonal to the flat roof plane (upwards). The load-bearing device can be, for example, a clamp, a shaped part for the respective substructure (the profile rail or the profile rail section), or even a loop. Once the load-bearing device has been attached and connected to the force gauge, the tensile load is continuously increased. Care must be taken not to pull beyond the point at which the waterproofing begins to detach. The measured values ​​are then documented and compared, for example, with predefined thresholds. The comparison tells the installer whether additional fastening is necessary.The tensile test step serves as an additional safety measure for bonded PV substructures.

[0028] After the force measurement, if it is determined that the profile rail or profile rail section does not reach the specified threshold, the process can be continued with refastening the profile rail or profile rail section. The profile rail or profile rail section is then subjected to tensile force again in the manner described above and it is determined whether the design-dependent threshold is now exceeded or reached. During refastening, for example, another layer of liquid plastic with a fleece insert or fiber reinforcement is applied over the existing fiber composite layer, as before. In particular, refastening can also mean applying another primer to the edge of the fiber composite layer on the roof skin and applying another layer of fiber composite material with an overlap, for example 5 cm, over the edge of the existing fiber composite layer.If damage has occurred at the joint during the previous tensile test, the refastening step also serves to repair this damage.

[0029] In this process, the profile rail or profile rail section can be prepared by degreasing, cleaning, and roughening before applying the next coat of primer to improve the primer's adhesion. For example, acetone cleaner is used to degrease and clean the surface of the profile rail or profile rail section. Roughening can be done using 80-grit sandpaper, for example.

[0030] The invention relates to a device (2) for checking the security of an adhesive joint between profile rails (20) or profile rail sections of a photovoltaic cell substructure on a roof covering (10) of a flat roof, wherein the profile rails (20) or the profile rail sections are adhesively bonded to the flat roof. The device (2) comprises said profile rails (20) or profile rail sections, a force measuring device (60) arranged on a tripod (50) above the adhesive joint, and a load-bearing device (70) connected to the profile rail (20) or the profile rail section. The profile rails (20) or profile rail sections are covered by a fiber composite material (40) on the flat roof for adhesive bonding to the flat roof. The profile rails (20) or profile rail sections are adhesively bonded to the flat roof in such a way that the adhesive joint withstands at least a construction-dependent threshold value of a tensile force.

[0031] The PV modules can be mounted either flat on the profile rails or profile rail sections, or they can be mounted on supports, for example, in rows facing south or alternating east-west. The advantages and disadvantages of the various arrangements are known to those skilled in the art and were discussed at the beginning. The optimal setting of the tilt angle should be determined according to known criteria and is generally approximately 35 degrees for a south-facing orientation and approximately 10 to 15 degrees for an east-west orientation.

[0032] A first coat of primer, such as a polyurethane-based primer, is applied to the roof membrane, beneath the profile rail or profile rail section, and in the peripheral area around the profile rail or profile rail section. This primer serves as both a primer and an adhesion primer.

[0033] A further primer is applied to the profile rail or profile rail section, which may be the same material as the first primer. Additionally or alternatively, polyvinyl butyral-based primers can be used to protect the profile rail or profile rail section from corrosion.

[0034] The fiber composite material can, for example, be polyurethane-based and comprise a liquid plastic combined with a fleece insert or fiber reinforcement. The fiber composite material essentially completely covers the profile rail or profile rail section and the first primer applied to the roof membrane. This arrangement is particularly advantageous because it increases the adhesion. Furthermore, the shape can be adjusted and further reinforced with additional fleece layers or reinforcements.

[0035] According to an advantageous embodiment of the invention, the load-bearing device is a clamp, a shaped piece for the profile rail or profile rail section, or a loop. This enables a versatile and secure connection to the profile rail or profile rail section during the inspection of the bonded joint.

[0036] According to an advantageous embodiment of the invention, the profile rail or profile rail section is a U-, trapezoidal-, or omega-shaped perforated sheet. This ensures a robust and adaptable shape of the structure.

[0037] According to an advantageous embodiment of the invention, the profile rail or profile rail section is made of galvanized sheet metal, stainless steel, or aluminum. This provides high corrosion resistance and durability for the profile rail or profile rail section.

[0038] According to an advantageous embodiment of the invention, the fiber composite is polyurethane-based. This results in excellent adhesion and durability of the fiber composite.

[0039] According to an advantageous embodiment of the invention, the fiber composite is a liquid plastic combined with a nonwoven insert or fiber reinforcement. This enables improved mechanical strength and flexibility of the fiber composite.

[0040] According to an advantageous embodiment of the invention, a primer is applied to the roof skin beneath the profile rail or profile rail section and in an edge area around the profile rail or profile rail section. This significantly improves the adhesion of the bonded joint.

[0041] According to an advantageous embodiment of the invention, which relates to the aforementioned primer, it is polyurethane-based. This ensures optimal adhesion and serves as a primer.

[0042] According to an advantageous embodiment of the invention, the fiber composite material essentially completely covers the profile rail or profile rail section and the first primer applied to the roof membrane. This arrangement maximizes the adhesion effect and also allows for subsequent adjustments and reinforcements with additional layers. Short description of the characters

[0043] From the pictures shows: Fig. 1 a cross-section of an arrangement according to the invention, and Fig. 2 an arrangement for checking the strength of a fastening. Detailed description of the characters

[0044] Fig.Figure 1 shows a cross-section of an assembly 1 with a profile rail 20 for photovoltaic systems on a roof covering 10 of a flat roof, with the profile rail 20 being glued to the flat roof. The profile rail is a U-shaped perforated sheet made of galvanized sheet metal, stainless steel sheet, or aluminum sheet. The profile rail 20 has a support surface with which it rests on a primer layer, as well as upwardly extending straight flanks, which are symmetrically bent inward again at their free ends for reinforcement, forming a fastening slot for connection to the remaining substructure. The profile rails 20 are installed as follows: - Applying a primer to a roof covering 10 of the flat roof, - Place and press the profile rail 20 of the PV cell substructure onto a part of the first primer, - Applying another primer 30 to the profile rail, - Applying a fiber composite material 40, wherein the fiber composite material covers the profile rail and is bonded to both the first and the further primer 30.

[0045] The primer, for example, is a polyurethane-based liquid plastic. The second primer 30, for example, is a polyvinyl butyral-based primer. The fiber composite material is, for example, a liquid plastic with a fleece insert or fiber reinforcement. As can be seen from Fig. As can be seen in Figure 1, the fiber composite material covers the profile rail 20 from above and from the sides, as well as the first primer coat, without any air pockets. The first primer coat is located between the profile rail 20 and on the roof skin 10 and is not shown separately.

[0046] In Fig.2 shows a device 2 for checking the fastening strength of the arrangement 1 according to the invention. Fig. 1. A shaped piece 70 matching the profile rail 20 serves as a load-bearing device and is wedged or fastened on the inside in the fastening slot of the profile rail 20. A force measuring device 60 is positioned on a tripod 50 above the fastening point and connected to the load-bearing device 70. The load-bearing device 70 is subjected to a tensile force. The tensile force is gradually increased without tearing the profile rail 20 away from the roof skin 10. The applied forces are measured and stored, and then compared with a design-dependent threshold value. If it is determined that the threshold value has not been exceeded, the arrangement is adjusted.

[0047] The embodiments shown here are merely examples of the present invention and should therefore not be considered limiting. Alternative embodiments contemplated by those skilled in the art are equally encompassed within the scope of the present invention. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] EP 2362428A2

[0004] Cited non-patent literature

[0000] DIN EN 1991-1-4 / NA

[0009] www.dibt.de

[0009]

Claims

[1] Device (2) for checking the safety of an adhesive joint of profile rails (20) or profile rail sections of a photovoltaic cell substructure on a roof covering (10) of a flat roof, comprising said profile rails (20) or profile rail sections, a force measuring device (60) arranged on a tripod (50) above the adhesive joint, and a load-bearing means (70) connected to the profile rail (20) or the profile rail section. [2] Device according to claim 1, characterized by that the load-carrying means (70) is a clamp, a shaped piece for the profile rail (20) or the profile rail section or a loop. [3] Device (2) according to claim 1, characterized by that the profile rail (20) or the profile rail section is a U-, trapezoidal or omega-shaped perforated sheet. [4] Device (2) according to claim 1 or 2, characterized bythat the profile rail (20) or the profile rail section is made of galvanized sheet metal, stainless steel or aluminum. [5] Device (2) according to one of the preceding claims, characterized by that the fiber composite (40) is polyurethane-based. [6] Device (2) according to one of the preceding claims, characterized by that the fiber composite material (40) is a liquid plastic in combination with a fleece insert or a fiber reinforcement. [7] Device (2) according to one of the preceding claims, characterized by that a primer is applied to the roof skin (10) under the profile rail (20) or the profile rail section and in an edge area around the profile rail (20) or the profile rail section. [8] Device (2) according to claim 7, characterized by that the primer is polyurethane-based. [9] Device (2) according to one of the preceding claims, characterized bythat the fiber composite material (40) essentially completely covers the profile rail (20) or the profile rail section and the first primer (30) applied to the roof skin (10).

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