•A concept of a novel solar façade system for building energy retrofit is proposed.•A UST collector as component of a façade system by merging different technologies.•Selection of buildings suitable for the solar façade system.•Investigation of thermal behaviour of thermal active elements integrated in façade.•Investigation of energy potentiality of a combisystem through dynamic simulation. In the perspective of the Net Zero Energy Buildings as specified in the EPBD 2010/31/EU, we propose the concept and design of a modular unglazed solar thermal (UST) façade component for facilitating the installation of active solar façades. The renovation of existing buildings offers an opportunity to improve the energy efficiency when using such a system and a novel design methodology tackled via a parametric approach is here proposed. We analysed a variety of building typologies as potential application targets of the UST collector, properly sizing the collector field for each typology to match the heat loads profile. We investigated the thermal behaviour of the novel thermal façade component and the energy potentiality in covering the heat demand using the TRNSYS software’s model of the UST collector field as a part of a combisystem. We concluded with the definition of rules of thumb for early design stage. The work here presented demonstrates that the low-cost, the versatile modularity and the easy installation make this active solar façade an innovative and promising technology for the building stock transformation, despite of the low quality of the produced energy due to the low outcome temperature of the unglazed collector.