As part of the “Façade-integrated photovoltaic systems” research project funded by the German Federal Ministry for Economic Affairs and Energy, the properties of building-integrated photo-voltaics (BIPV), especially CIGS façades, are being investigated in comparison to PV rooftop systems.
A limiting factor for using PV rooftop systems on industrial and administrative buildings is that the roof surface is also needed for building infrastructure equipment – such as heat exchangers, ventilation systems or solar thermal collectors, which fragment the roof surface as shading elements. In addition, there may be competing use as an accessible roof garden or for locally prescribed extensive roof greening. It is often not possible to realise PV rooftop systems on halls or warehouses because the permissible area load is exceeded. In addition, the PV rooftop system’s share in covering the building’s energy requirement decreases as the number of floors increases, as the energy generated is distributed over more and more floors.
In contrast, the use of PV in façades offers several advantages: the orientation of the PV systems stabilises the energy production over the course of a day. The typical midday peak generated by PV rooftop systems is eliminated and thus the proportion of self-consumed electricity increases by including power generated during the morning and evening hours as well as in the winter half-year. Façade systems are therefore both grid-supportive and advantageous for system users. In addition, the PV façade system grows in proportion to the number of storeys (see graph below).