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Photovoltaic Structural System Design Points
- Apr 19, 2018 -

First, the general principles of structural design

1.1 The structure of photovoltaic panels can be divided into two categories as follows:

(1) Separate photovoltaic panels: only have the power generation function, not as the panel of the enclosure structure; when the building needs the enclosure function, it must be provided with a sealed daylight ceiling or curtain wall. This panel is provided with a separate bracket, which is attached to the main structure. Therefore, this type of photovoltaic building is an integrated design with two skins.

(2) One type of photovoltaic panel: It has both the power generation function and the lighting ceiling or curtain wall panel. Also known as building photovoltaic panels. Because of the combination of power generation and building functions, the building envelope only requires a set of panels and a set of supports. This photovoltaic building is an integrated design, a layer of skin. The integrated photovoltaic structure system is generally the same as the ordinary glass curtain wall and the lighting roof, and the design method of the glass curtain wall and the lighting roof can be applied. The separated photovoltaic structure system additionally has a separate structure on the outside of the ordinary glass curtain wall and the lighting roof. Different from the general curtain wall and lighting roof, special design must be carried out.

1.2 Photovoltaic structural systems shall be structurally designed and shall have specified load carrying capacity, stiffness, stability and deformation capability. The useful life of structural design should not be less than 25 years. Embedded parts are difficult to replace parts, and their structural design service life should be considered in 50 years. The structural design life span of large-span steel structures should be the same as that of the main structure.

1.3 The design goal of the photovoltaic structural system is: It should have good working performance under normal use. Earthquake-resistant PV system systems should be able to be used normally under the action of multiple earthquakes; they can still be used after being repaired under the action of seismic intensity earthquakes; under rare earthquakes, the support skeletons should not collapse or fall.

1.4 Non-seismic design of photovoltaic system should calculate the effects of gravity and wind loads, and if necessary, take into account the effect of temperature. For the photovoltaic structural system with seismic design, the effects of gravity load, wind load and earthquake action should be calculated, and the effect of temperature action can be included when necessary.

1.5 Photovoltaic Structures The effects of the construction phase and normal use phases can be calculated flexibly and a combination of effects can be performed.

 

1.6 The components and connections of the PV structure system shall be designed according to the most unfavourable combination of each effect combination.

1.7 Photovoltaic structural components and joints The design value of the bearing capacity should not be less than the design value of the load and effect. Deflection values calculated from load and standard values should not exceed the allowable deflection.

Second, the load and role

2.1 Photovoltaic structure systems should consider the following gravity loads under different conditions: (1) Self-weight of the faceplate and support structure (2) Overhaul load (3) Snow load.

2.2 The wind load of the photovoltaic structural system shall be adopted in accordance with the national standard "load specification of building structure" GB500092006. The design should be considered separately: (1) The wind load of the separated photovoltaic panel should be included in the wind load on the windward side and the wind load on the leeward surface; (2) The wind load on the support should be included in the wind load transmitted from the panel and directly supported by the bracket. Wind load; (3) The unitary panel system shall adopt the wind load of the light roof and the curtain wall, respectively, and shall be adopted according to the corresponding specifications.

2.3 Separation of photovoltaic systems should take into account the seismic force amplification of small roof structures. If necessary, it can be used as an independent particle, together with the main structure for seismic response analysis. The separated photovoltaic system structure on the roof has a certain quality and rigidity, which is equivalent to a small floor, but its quality and rigidity are far less than the mass and rigidity of the main structure. The earthquake response on the roof is much stronger than on the ground, called the whiplash effect. On the roof, the seismic force can be amplified by 3 to 5 times more than on the ground, depending on the mass ratio and the stiffness ratio of the main structure.

The seismic force calculation of the 2.4-in-one type photovoltaic structure panel and supporting structure is the same as that of general glass curtain wall, and can be performed in accordance with the provisions of the industry standard "Technical Specifications for Glass Curtain Wall Engineering" JGJ102-2003.

2.5 When the stent with separate photovoltaic structure is exposed outdoors, the effect of temperature should be considered. The temperature stress of the steel bracket can be calculated if necessary.

2.6 The load combination of the photovoltaic structural system can be carried out in accordance with the industry standard "Technical Specifications for Glass Curtain Wall Engineering" JGJ102-2003. The gravity load of the PV roof and slanted wall will produce a force component in the out-of-plane direction, which is superimposed with the effects of wind load and seismic force. Care should be taken when calculating. The combination of gravity loads from the control function, the partial coefficient of the gravity load should be taken as 1.35. The combination of the main effects of the wind load, the combined value of the seismic action coefficient should be taken as 0.5.

Third, the panel design

3.1 The glass of the panel shall be able to withstand the loads, seismic effects and temperature effects exerted on the panel. In addition to the thickness determined by the calculation, it should still meet the minimum thickness requirements.

3.2 Monolithic glass in separated panel laminated glass, the thickness should not be less than 4mm.

3.3 As a unified panel for daylighting ceiling and curtain wall, the thickness of monolithic glass in laminated glass shall not be less than 5mm; when the inner side of curtain wall insulating glass is monolithic, the thickness shall not be less than 6mm.

3.4 Laminated glass with photovoltaic cells. Ultra-white glass should be used for the outer sheet. Inside and outside the laminated glass, the thickness difference should not be greater than 3mm.

3.5 Low-E coating is not suitable for single sheet laminated glass without hollow layer; laminated hollow glass with hollow layer, Low-E coating should face hollow layer.

The 3.6-in-one panel shall be PVB laminated film; the split panel may be PVB-laminated or EVA-laminated. Amorphous silicon battery laminated glass should adopt PVB laminated film.

3.7 When using insulating glass for roof lighting, laminated glass should also be used for indoor side; when using insulating glass for inclined glass curtain wall, laminated glass should be used toward the ground.

3.8 laminated glass should use semi-tempered glass or float glass, tempered glass can be used. Point support panel should use tempered glass. Tempered glass has a self-detonation rate of 1% to 3%, and even after the secondary heat treatment, there is an implosion rate of 0.1% to 0.3%. The semi-tempered glass and float glass do not blew themselves up, and become safe glass after being laminated. Therefore, if the bearing capacity is sufficient, it is not necessary to use tempered laminated glass to avoid the difficulty of replacing the glass after use. The local stress of the point-supporting glass opening is very large, and only the toughened glass with high strength can meet the requirements of the bearing capacity.

3.9 The structural calculation of the panel should be carried out in accordance with the "Technical Specifications for Glass Curtain Wall Engineering" JGJ102-2003. Specifications and calculation tables for edge support glass and point support glass sheets have been listed in the specification and can be used directly.

3.10 The deflection of the panel caused by the load and the standard value of action, the side support panel should not be larger than 1/60 of the short side; the point support panel should not be larger than 1/60 of the spacing between the long side support points along the larger side.

Fourth, support structure design

4.1 The design of the support structure shall comply with the provisions of the "Code for the Design of Steel Structures" GB50017-2003 and the "Specifications for the Design of Structures for Aluminum Alloys" GB50429-2007. The

4.2 The section thickness of the steel bracket components of the separated panels shall not be less than 3.0mm. The steel grade, grade and quality grade of the steel bracket components shall comply with the provisions of current national standards and industry standards. When welding between steels, the provisions of current national standards and industry standards shall be complied with. The

4.3 The steel brackets of the separated panels shall adopt effective anti-corrosion measures. When using hot dip zinc antiseptic treatment, the zinc film thickness should not be less than 80 microns. When using fluorocarbon spray coating thickness should not be less than 40 microns. When using anti-rust paint or other anti-corrosion paint, the corresponding technical regulations shall be followed. Steel brackets in heavily corroded areas can be provided with a corrosion thickness of the section if necessary. In addition, closed-end steel profiles such as round tubes and square tubes are difficult to carry out anti-corrosion treatment on the inner surface and can also leave a corrosive thickness. Under normal conditions, the corrosion rate of the steel section does not exceed approximately 0.02 mm per year. This increases the section thickness of the steel section by an additional 1.0 mm, leaving a margin of 50 years for single-sided corrosion or 25 years for double-sided corrosion. The

4.4 Under the action of the wind load standard value, the horizontal displacement of the apex of the split panel bracket should not be greater than 1/150 of its height.

4.5 The support structure design of a one-piece panel shall be carried out in accordance with the "Technical Specifications for Glass Curtain Wall Engineering" JGJ102-2003.