Final report
(English)
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Several big buildings in Europe, Switzerland and in canton Ticino have flat roofs. At present, 20-25% of the flat roof European market employs plastic materials like FPO or PVC as covering waterproofing membranes. For standard crystalline silicon plants on flat roofs, modules are mounted on separated structures - optimally tilted and orientated - designed to withstand wind loads. The bearing structure is fixed by means of ballasts or the ballast itself functions as bearing structure. The natural ventilation of the modules is guaranteed by the open-rack bearing structure. The 15.4 kWp installation, composed of flexible amorphous silicon triple-junction modules, was at its creation the only one in Switzerland. In fact, the modules, placed nearly horizontally on the flat roof – with a 3° tilt –, are directly laminated to the flexible polyolefin (FPO) membranes. The resulting elements are so joined by means of hot air welding and form the waterproofing membrane covering the whole flat roof. This kind of PV module integration presents the advantage of being very easy to install with very well-known technologies from the installers of covering membranes on flat roofs. Besides, contrary to standard fixing systems currently in use for PV plant on flat roofs, this kind of plant doesn’t need either ballast loads or additional structures. Nevertheless the horizontal position implies a lower incident irradiation over the year with respect to the optimally tilted solution. The irradiation difference between a horizontal position and an optimal tilted one can reach -15%. The main objective of this study was to verify in which order of magnitude the better thermal behaviour of a-Si compared to c-Si technologies (annealing mechanism and lower temperature coefficients) can compensate for losses due to the quasi-horizontal roof integration (lower irradiation and higher reflection), and thus be competitive in the new build flat roof market and in the refurbishment market. The thermal insulation doesn’t allow a ventilation of the modules as usually required by crystalline silicon PV modules. This leads to a heating of the modules and consequently to changes in the operating PV parameters. The temperature of the modules reaches 80°C, typically 40-45°C higher then the ambient temperature, during hot sunny days. Thus it reaches the level where the main degradation mechanism can be reversed. The second level of complete module regeneration was practically never reached. On the other hand the modules of the reference plants, which were not thermally insulated, never went above 60°C for the 3° tilt and 64°C for the 20° tilt, in the same climate conditions.
Auftragnehmer/Contractant/Contraente/Contractor:
Istituto di Sostenibilità Applicata all'Ambiente Costruito, SUPSI
Autorschaft/Auteurs/Autori/Authors:
Bernasconi,Angelo
Pola,Ivano
Chianese,Domenico
Burà,Enrico
Cereghetti,Nerio
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