Solar Module Installation on a Flat Roof

Figure 4.45 displays solar modules installed using solar flat roof elements (SOFRELs), which are mass – produced prefabricated concrete elements for mounting solar modules on flat roofs. These elements are not secured to the building in any way, so as to avoid sealing problems. The SOFREL system can be used for both laminates and framed modules. However, to avoid unduly severe wind load problems, the tilt angle is only adjustable from 18° to 25°.

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Figure 4.45 Flat-roof installation for framed 120 Wp solar modules using SOFRELs. Owing to the shallower tilt angle b = 18°, the wind forces are lower than for the installation shown in Figure 4.47, thus reducing (a) the load on the roof, (b) the need for additional weight and (c) the amount of spacing needed to avoid reciprocal shading Nonetheless, solar generators installed on flat roofs tend to become dirtier and produce less energy during the winter (Photo: Tritec)

Figure 4.46 displays another flat-roof solar generator with somewhat larger solar modules (approxi­mately as in Figure 4.4). The spacing between the concrete mounting elements and the roof is somewhat larger, which makes it easier for winter snow to slide off the modules.

Figure 4.47 displays the rear of a solar generator comprising framed modules mounted on a specially made and relatively heavy structure on a flat roof. Inasmuch as the only compensatory elements for the wind forces that the installation is exposed to are frictional force and specific gravity, the roof in such cases needs to exhibit the requisite load-bearing properties – namely, around 100 kg per square metre of solar generator area. In realizing such an installation, it must be ensured that the wind forces cannot tip over the mounting rack. This mounting method renders both the front and rear of the installation readily accessible.

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Figure 4.46 Relatively large solar generator (total of about 100 kWp) on the flat roof of an apartment block in Geneva. The framed approximately 215 Wp solar modules (as in Figure 4.4) were mounted using elements similar to those shown in Figure 4.45. However, the spacing between the modules and roof is somewhat larger, thus making it easier for snow to slide off the modules (Photo: Sunpower Corp./Suntechnics Fabrisolar AG)

The wind forces that the installation shown in Figure 4.47 is exposed to are counteracted by specific gravity and frictional force. The following additional features of this installation are also visible in the photo:

• The module frames and racking are connected to lightning protection installations.

• The modules are combined into series-connected strings via short wires, which exhibit a minor anomaly in that they are dangling rather than being fastened down.

• The installation contains junction boxes, where the strings are wired in parallel.

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Figure 4.47 Rear view of a flat-roof installation for a solar generator comprising framed Siemens M55 modules (55 Wp, tilt angle b = 35°) that are partly held in place by the force of gravity. The modules are mounted in groups of four on aluminium sections, which are secured to the prefabricated concrete elements on the roof and weighted down at the rear of the installation to avoid possible tipping induced by wind forces

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Figure 4.48 Flat-roof installation of a solar generator composed of 120 Wp Siemens M55 laminates that were mounted using Solgreen elements. Such laminates are less prone to grit accumulation and the consequent power loss, but are more vulnerable to lightning strikes (Photo: Basler & Hofmann AG)

PV systems are often installed on landscaped flat roofs. Figure 4.48 displays such an installation using Solgreen elements.

Updated: August 6, 2015 — 9:54 am