Energy evaluation and life cycle assessment of an innovative building integrated technology: the smart window-luminescent solar concentrator

Luminescent Solar Concentrators (LSC) represent one of the innovative and potentially most versatile technologies related to Building Integrated Photovoltaics (BIPV). The peculiarity of these devices lies in the fact that they can be integrated into the surface of the building to replace openings such as skylights or windows, thanks to their characteristic of being semi-transparent and of functioning both with direct and diffused radiation. Eni developed the own technology Eni Ray Plus® based on LSC and integrated it in a multifunctional smart window-LSC (SW-LSC) prototype. The device uses the energy produced by LSC modules to power an autonomous and passive shading system, exploiting irradiation sensors, motors and batteries. It independently regulates the movement of the shading system and allows energy surplus, through the electricity generated by modules. The final aim of this thesis is to explore the energy performances of the SW-LSC prototype into the building and to determinate the life cycle environmental impacts of the device through the application of the Life Cycle Assessment methodology. In addition, the focus is to highlight the impacts of the LSC modules only, assuming that they can be applied into glazed buildings, and to compare them with those of other PV technologies on the market. The first part of the work is focused on SW-LSC optical, thermal and electrical performances, comparing them with those of a traditional window. The analysis followed an experimental approach that involved lighting and electrical monitoring studies in a real test room, in order to create validated models for conducting simulations in larger buildings. The results were expressed through the study of illuminance maps, electricity generation obtainable from the integrated photovoltaic technology and in terms of energy savings. In conclusion, the models created allowed to evaluate the performances of the new technology, providing useful information for energy saving strategies in buildings. The second part of the work regarded the evaluation of the life cycle impacts. The functional unit (FU) chosen was the whole SW-LSC (5,27 m2) considering its thermal and optical characteristics (Uw = 1,6 -1,8 W/m2K, tvis = 77% and g = 85% of LSC modules) and the possibility to produce about 1.5 kWh/year. The system boundary was from cradle to gate considering the assembly and maintenance phase, while the end of life (EOL) was considered separately through a recycling/landfill scenario. Results showed that global warming potential (100 years) for SW-LSC was 5.91E+03 kg CO2eq and the production phase had the greatest impact (about 96%). The EOL recycling/landfill scenario results showed the possibility to reduce impacts by an average of 45%. The dominance analysis of SW-LSC components showed that the aluminum frame was the main hotspot (about 60% contribution) in all categories (except in abiotic depletion potential, 16% contribution), followed by the light-shelf (about 19% contribution). The batteries and motors for the shading system were the biggest contributors in the abiotic depletion potential category (36% and 30%, respectively). Since the materials of the SW-LSC prototype are not yet optimized in an eco-design context, it is important to underline that other alternative materials will be taken into consideration during the marketing phase (such as the use of wood or a wood-aluminum combination for the frame). The alternative scenario, which involved the use of 75% recycled aluminum for the window frame, showed that it is possible to reduce environmental impacts from 3% to 46% (with a mean value of 33.6%). Finally, the results for the SW-LSC were compared with those of the EPDs of some traditional windows (the functional unit for the comparison was the m2). A further comparative study was carried out between the LSC modules and some building integrated photovoltaic technologies, using 1 kWh of electricity generation as a functional unit. LSC modules impacts were on average 870% lower than that of various PV technologies when compared on the basis of m2; the only exception concerned the comparison with CIS and a-Si technologies, where LSC modules impacts were about 150% higher in some categories (global warming potential, ozone layer depletion potential and photochemical oxidation potential). LSC modules had highest impacts in all categories (from 200% to 1900%) if compared with other PV technologies on the basis 1 kWh of energy generated. The results based on energy generation are easily interpretable considering the lower performance of LSC modules compared to other technologies; however, LSC modules show greater versatility and different possible applications due to the their transparency. The SW-LSC could represent an option for the future efficiency of the built environment: in this sense, even if the power output from LSC modules integrated into the window is limited, it is sufficient to cover the energy demand of an efficient system of Venetian blinds that allow regulating the internal loads autonomously and independently, with a consequent energy saving. Furthermore, thanks to the thermal characteristics of the frame and the regulation of the light inside the environment, the SW-LSC represents an element designed to improve thermal and lighting comfort inside buildings.