EN 
PT_BR 
In my solar energy courses at UNICAMP (http://www.cursosolar.com.br) I always repeat to students that any adaptation to adjust the inclination angle or orientation of photovoltaic modules installed on roofs, in addition to being unnecessary, can be dangerous. The best thing is to always install the modules on the roof slope itself. This recommendation applies to residential, commercial or industrial systems, in any type of tile: ceramic, metallic, calhetão or any other.
Studies with PVSyst can be carried out to determine the correct angle for installing photovoltaic modules. In cities like São Paulo, for example, the ideal is to place modules with an inclination of 25O relative to the horizontal plane. Residential roofs, with colonial or Portuguese-style tiles, typically have slopes not much greater than 15O. Metal roofs usually have slopes between 5O and 10O.
Adaptations with metal structures to tilt the modules by a few degrees or to try to orient the modules towards the North add unnecessary cost to photovoltaic installations on rooftops. The result is poor, producing little practical effect in increasing energy generation.
On roofs, due to area limitations, the spacing between the rows of modules is small, which prevents installation with a very high inclination angle — which would produce losses due to shading in the modules. The solution would be to tilt the modules at a reduced angle, with little or no advantage in this.
When, then, the modules must be inclined at the ideal angle for the location (for example: 25O in Sao Paulo)? This “shed” type of installation should only be used when there is a lot of area available, allowing the rows of modules to be adequately spaced. This is the case for solar plants built on land, as illustrated in Figure 1.
On flat roofs or very large slabs, normally found in commercial buildings, the installation of sheds can also be done, but with caveats: on slabs, the sheds must be solidly supported on concrete shoes fixed to the slab with chemical glue. In addition to preventing holes in the slab, the shoes add additional weight to the structure, making it more resistant to wind force. If the installation is carried out on a roof, the modules' fixing supports must necessarily be fixed to the roof structures and not to the tiles.
Installations like the one in Figures 2 and 3, for example, do not offer adequate fixation in the event of windstorms. The drill screws (which we see in detail in Figure 3) are weakly fixed to the tiles, offering no resistance to vertical tearing in the event of a gale.
In systems like those shown in Figures 2 and 3, no incident may ever occur. However, in extreme (and yet predictable) situations, results such as those shown in Figures 4 and 5 below may occur.
In short, it is not recommended to use structures to increase the slope of modules when they are installed on roofs. The best strategy is to follow the slope of the tiles, even if it is small.
Below are some more examples of installations that are not recommended – ugly and dysfunctional:
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