Photovoltaic Training Course - Module 2.2 - Mechanical assembly
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Mechanical parts in PV plants
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Photovoltaic Training Course - Module 2.2 - Mechanical assembly
- 1. Photovoltaic Systems Training Execution and Commissioning 2.2 MECHANICAL WORKS www.leonardo-energy.org/
- 2. Flat Tilted No wind action Important wind action Worse cooling Best natural cooling Lower cost (Both for structure & mounting) Higher cost (Both for structure & mounting) Mechanical works Fixed installations can be installed parallel to the surface (flat), or with the optimum tilt for the particular latitude (tilted) Photo: Krannich www.leonardo-energy.org Flat Tilted No wind action Important wind action Worse cooling Best natural cooling Lower cost (Both for structure & mounting) Higher cost (Both for structure & mounting) Structure type Weight Anticorrosion protection Mechanical performance Galvanized steel Resistant rooftops 8 years (non salty atmosphere) Good Hot galvanized steel Resistant rooftops More than 25 years Good Anodizing Aluminum Light rooftops More than 20 years Medium No structure Light rooftops - -
- 3. Mechanical works Structures for ground installations can be anchored in a number of different ways. Ground anchor Screws of 1 – 1.6 meters in length Easy to dismount Easy to adapt to terrain Cannot be used in rocky terrain Concrete base Can be installed above or below ground Require a flat surface Easy to dismounted if above ground Source: Conectavol www.leonardo-energy.org
- 4. Roof anchorage Metal roof anchors Two options: Tile roof anchorage Typical solution: U-shaped piece anchored directly to the roof (avoiding drilling the tile) Alternatively: A special piece through the tile (where drilling the tile is unavoidable, despite the threat that the tile will break). Anchored directly on to purlins Anchored to the roof sheathing Direct-to-purlin anchorage is recommended if a tilted structure is being installed Roof sheathing Purlins Roof truss www.leonardo-energy.org
- 5. PV Roofs Evaluate the roof’s: Safety Install: Lifelines; and Skylight networks where necessary Type Be careful of asbestos roofs. Consider changing the roof where necessary. Sealing Use sealants with good elasticity and mechanical resistance to avoid leakages. Consider using EPDM* bands * a type of synthetic rubber (ethylene propylene diene Monomer)
- 6. Element Weight Structure 2KG Crystalline panels 15KG Thin filmglass‐glass panel 22KG Thin film laminated panel 6KG PV Roofs Loads on the roof Material weight (average weight per square meter) Wind effect Both panel height and exposed surface must be considered Consider the effect of extra loads during installation: tools, workers, materials… Access Accesses should be distributed along the roof surface, guaranteeing worker safety and allowing easy supply of materials and tools www.leonardo-energy.org
Hinweis der Redaktion
- The main mechanical work to be done during the construction phase is the installation of a structure to hold and support the PV modules.
- Different structures are appropriate for different uses and lifetimes – as illustrated in the table above. On rooftops the structure is often fixed parallel to the surface where it is installed. Even if the roof is inclined, modules installed parallel to the roof are called flat. As we learnt in the first webinar a flat does module will not suffer from the effects of the wind, while, at the same time, taking advantage of the slope of the roof. Installing flat is simpler and cheaper. A tilted structure is more expensive to install, but the tilt can be optimised to give maximum output over the year. The decision on whether to install flat or tilted modules is a balance of price and the expected economic performance of the installed modules.
- Anchoring the strcuture to the ground or roof is critical. For ground-mounted racks of modules, there are two possibilities: a ground anchoring system or installation on a concrete base. The main advantage of ground-anchoring is that it is easy to dismount and the structure can be more easily adapted to the terrain. Normally, for these types of structure screws of 1 to 1.6 meters are driven into the ground. Howeve,r this type of structure cant be used in rocky terrain. The concrete base structure will require a flat surface. It can also be easily dismounted, especially if a structure raised above the ground is selected.
- There are different fitting systems for metal and tile roofs. . For metal roofs there are two options, anchoring the array directly to the structural framing of the roof (known as the purlins) or specially designed anchors can be used that anchors the modules to roof’s sheathing – that is the board or sheet material fastened to the rafters on which the metal or tile roof covering is laid. For tile roofs, the common method is a system that anchors the modules to the purlins. An advantage with this approach is that it avoids having to drill through tiles for fittings. However, sometimes tiles have to be removed resulting in a danger of roof leakages – or worse. There are solutions where tiles are drilled, but that runs the repeated risk of tiles breaking.
- For all solutions, consider: Safety, the roof type and the ceiling. For safety it is important to install a lifeline or a skylight network where there there is any possibility of falling or if the roof might crack. When planning to drill or cut to install an anchoring system, make sure there is no asbestos in the roof. On occasion, it is best to change the roof to a metal one. This decision should be made at the design and calculation stage. Finally the ceiling is important for leak avoidance.
- At the design stage, take into account the loads on the roof. See the table for the main loads in a PV project. The load is particularly important when considering the effect of the wind, wheb both the panel height and the exposed surface must be considered. And don’t forget to take account of the extra loads that the roof must endure during installation. Acess pointsshould be distributed all along the roof’s surface.