Building-integrated solar thermal systems based on vacuum-tube technology: Critical factors focusing on life-cycle environmental profile

The present study refers to Building-Integrated Solar Thermal (BIST) systems based on vacuum-tube collectors and it consists of two parts. In the first part, a literature review is presented, including studies about vacuum-tube technology (vacuum-tube/BIST systems, the environmental profile of vacuum-tube collectors, etc.). Critical issues, for example related to the integration of vacuum-tube collectors into the building, are highlighted. The review shows that most of the proposed vacuum-tube/BIST concepts are about façade-integration and there are few studies about the environmental profile of vacuum-tube collectors. As a continuity of the issues presented in the first part, the second part includes a case study about the environmental comparison of a vacuum-tube/BIST system with a flat-plate/BIST configuration, based on life cycle assessment. The systems are gutter-integrated, patented and they have been developed/tested at the University of Corsica, in France. Multiple life-cycle impact assessment methodologies, environmental indicators, scenarios and databases are adopted. The results reveal that the energy-payback time is 1.8 and 0.5 years, for the flat-plate/BIST and for the vacuum-tube/BIST, respectively, while by using recycling these values become 0.5 and 0.1 years, respectively. Energy-return-on-investment, greenhouse-gas payback time and avoided impact during use phase (by adopting USEtox, ecological footprint and France´s electricity as well as with reference domestic-gas-boiler CO2.eq emissions) are also presented. The findings of the present work: 1) are compared with the literature and good agreement is observed, 2) verify that considerably higher impact can be avoided by utilizing the vacuum-tube/BIST instead of the flat-plate/BIST system.

The authors would like to acknowledge networking support by the COST Action TU1205 Building Integration of Solar Thermal Systems. The authors would also like to thank “Ministerio de Economía y Competitividad” of Spain for the funding (grant reference ENE2013-48325-R).