Several design elements are involved in the setting up of an efficient solar PV power plant and among them is the Module mounting structure (MMS) that withholds the heart i.e. PV modules over its lifetime.MMS allows the PV modules to be held firmly to the surface of installation (can be a roof of groud), capable of battling strong winds that could, without the careful design can damage the entire installation.
MMS also becomes highly important as the generation of PV modules depend on the right tilt angle on which it is to be installed in order to raise the overall efficiency and generation capabilities of the PV power plant and this positioning based on geographical location is not possible without having a right MMS design.
MMS Design Considerations
Generally, module mounting structures are of three types:
- Hot Dip Galvanized Iron (GI)
- Mild Steel (MS)
Some of the design considerations to be taken care off for the construction/Installation of MMS are as follows:
- Comply with the applicable structural, building code and safety requirements.
- Meet standards and module manufacturer’s mounting requirements.
- Enhance array performance – allowing airflow to minimize operating temperature
- Provide reasonable accessibility for installation and maintenance
- Make the system aesthetically appropriate for the site and application.
- Thermal aspects – to allow expansion/contraction of modules/ structure
- Wind – shall be rated for the maximum expected wind speeds
- Material accumulation on PV array – Snow, ice, or dust
- Corrosion – corrosion resistant materials suitable for the lifetime and duty of the system
- Structural Standards to follow ASCE 7 (American Society of Civil Engineers): minimum design loads for building and other structures and IS: 875 (Part3): Wind Loads on Buildings and Structures.
Type of MMS for Rooftop Solar PV Installations
In case of roof or ground mount PV power plant installations, the type of MMS design changes based on the surface of installation. In rooftop solar PV installations, a tilted roof and a flat roof have different design approach. The MMS design and requirements changes based on the examination of roofs i.e. reinforced cement concrete (RCC), metal sheet, round seam, corrugated fibre cement or asbestous (some of them are shown in the image below).
Module Mounting structure Categories
Belo explained a few common MMS categories:
1. Flat concrete roof: For a flat concrete roof, an MMS is of immense importance, as it is the MMS that allows the modules to be tilted at an angle optimal to the particular installation.
- Penetrating method: In Penetrating methods, drilling or chipping is done in the existing roof. In this method, the substructure is prepared by simply drilling in the existing roof then anchor fasteners are inserted in the drill hole with the help of chemical grouting. Such MMs is not usually preferred these days as it experiences roof leakages, cracks and hampers roof strength.
- Non Penetrating method: In Non-penetrating methods, the substructure is prepared by reinforced cement concrete or plain cement concrete foundation is prepared above the existing roof. The image below shows some of the commonly used non-penetrating MMS used for RCC roofs. The told angle may vary based on geographical location.
2. GI Sheet roof: Such MMS are usually installed on the roof similar to its existing title angle.
- Trapezoidal: For a trapezoidal roof, running aluminium rails, that may be affixed using an industrial-grade adhesive or long-tapping screws, are used. The modules are then fixed with suitable end and middle clamps.
- Standing Seam: Aluminium rails, to which the modules are affixed, are held to the roof using specific types of standing seam clips, based on the roof itself. The modules are affixed to these rails using suitable end and middle clamps.
4. Tiled Roof: Not so common in India In case of a tiled roof, where the entire area of the roof is lined with tiles, the MMS is fixed to the roof by using screws that hold the MMS to the purlin, below the roof. Suitable end and middle clamps are then used to hold the modules to the structures themselves.
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