Bringing colours to solar collectors: a contribution to an increased building “integrability” Maria Cristina MUNARI PROBST, Andreas SCHUELER, Christian ROECKER Ecole Polytechnique Fédérale de Lausanne (EPFL), LESO-PB Bât. LE, Station 18, CH-1015 Lausanne, Switzerland E-mail: mariacristina.munariprobst@epfl.ch, andreas.schueler@epfl.ch, christian.roecker@epfl.ch ABSTRACT One main obstacle to facade integration of solar thermal collectors lies in the formal characteristics and low flexibility of available products. Major problems are the black and irregular appearance of their absorbers, their low dimensional flexibility and large size at the façade scale, and finally the lack of dummy elements. This paper presents a revolutionary though simple solution to all these problems, consisting in a novel coloured glass, able to mask absorber and piping while letting the solar energy pass through. Different colours can be produced and combined with different diffusing surface treatments on the glass outer side, finally offering a broad palette of novel glazing. These resulting glazing not only hide the black colour of the absorber and its imperfections, but can also be used as facade cladding on the non exposed areas of the building envelope, opening the way to the concept of active solar facades and offering a new level of freedom to architects. Keywords : Architectural integration, Colour, Multifunctionality, Solar collectors, Thin film 1. INTRODUCTION Façade integration of solar thermal collectors is still very rare, even though it would greatly increase the potential area available for solar thermal installations. One main obstacle to façade use can be seen in the difficulty to architecturally integrate presently available collectors which have not been developed with this implementation in mind. Fundamental integration issues lie in the black and irregular appearance of the collector absorber visible through the transparent glazing, in the low dimensional flexibility of available products and in the lack of dummies* (*non active elements having the same appearance, and able to complete the façade system. Dummies are common in the photovoltaic field) (Fig.1). Such specificities are a real barrier to façade integration, especially if we consider the size of collector fields at the façade scale: easily a third of the whole façade area! Finding novel solutions is then urgent considering the high interest of façade applications for solar heat production, especially when aiming at high solar fractions, The work presented here is one of the possible answers, and is based on the new vision of solar collectors seen as multifunctional building elements for façade cladding and heat collection. 2. THE COLOUR IDEA 2.1 Coloring the absorber One first idea to overcome the problem of the absorbers’ black colour, imposed to maximize the solar energy absorption, is to choose a lighter colour, thus accepting some efficiency reduction. This approach has been taken by some manufacturers, but the colours remain still very dark (dark blue, dark green, brownish reflection). Another approach is to use TISS (thickness Insensitive Spectrally Selective) paints, which offer a much broader colour palette, but at the cost of a higher efficiency loss. These approaches have either limited coloured improvement, or significant efficiency impact. Moreover, they don’t solve the problems of absorber surface irregularities or visible piping, nor the missing dummies.