Maria Cristina Munari Probst, Christian Roecker, Andreas Schuler, Jean Louis Scartezzini Laboratoire d’Energie Solaire et Physique du Batiment — LESO-PB, Swiss Federal Institute of Technology-Lausanne,.

Integration of solar thermal collectors into facades has always been problematic for architects because of the lack of freedom in the choice of panels’ details, and consequently the hardly controllable visual impact these elements have.

The irremediably black colour, the visible piping, the absorber’s imperfections gleaming through the glass in the glazed collectors, together with the dimensions and the fixing details of the existing single panels may be acceptable for roof plants, but need to be redesigned for the use of the collectors in facades.

A recent study conducted in Austria by AEE INTEC shows that the large majority of architects are not satisfied with the black colour of the absorber and would prefer a choice of different colours even if that means a reduction in the yield of the collector.

The study also shows the importance of the dimensioning of the single panel in order to make the architectural integration with the other elements of the facade possible. This also explains the consequent inclination of the planners in using the collectors in new buildings rather than in the refurbishment of old buildings where boundary conditions are imposed.

Two recent developments in surface coating are leading to possible major innovations in the integration of these collectors into building facades.

The first consists in corrosion resistant, selective coloured coatings for steel absorbers developed within the European project SOLABS.

The second presents a promising option for the glazed collectors market with newly developed thin film interference filters deposited on glass. As they are reflecting only a small part of the sun’s spectrum, in the visible range, they are letting most of the energy pass through, allowing the use of a standard black collector hidden behind.