Active renovation strategies with building-integrated photovoltaics (BIPV). Application on an early 20th century multi-family building

Tomorrow's cities are already largely built, as much of the existing building stock – with a low level of energy performance – will still be standing in 2050. Urban renewal processes therefore play an essential role towards the sustainable transition of European cities. In this context, building-integrated photovoltaic (BIPV) systems can potentially provide a crucial response to achieve current energy and mid- to long-term carbon targets. Functioning both as envelope material and electricity generator, BIPV systems can simultaneously reduce the use of fossil fuels and greenhouse gas (GHG) emissions, while providing savings in materials and electricity costs. These are precisely the objectives of most European energy directives, from zero- to positive-energy buildings. However, despite continuous technological progress and increasingly favourable economic conditions, the significant assets of BIPV remain broadly undervalued in the current practice. Focusing on the architectural design, this paper presents the results of a multi-criteria evaluation in terms of Life-Cycle Assessment (LCA) and Cost (LCC) of different renovation and energy-use scenarios, showing which strategies can allow to achieve the ambitious targets for the 2050 horizon by integrating into the design process: (1) Passive strategies, to improve the envelope through low-embodied energy materials and construction systems; (2) BIPV strategies, using innovative photovoltaic products as a new construction material for façades and roofs, and by selecting the BIPV surfaces in order to synchronize on-site generation with the building consumption profile; (3) Active strategies, adapting the HVAC system to improve its efficiency and maximize PV self-consumption, thus reducing the dependence on feed-in-tariffs to ensure the profitability of investments. The research methodology, presented in this paper through the comparison of different renovation scenarios applied on a 1900’s archetype building in Neuchâtel (Switzerland), proposes a new way to address rehabilitation projects of existing buildings in urban environments towards Low Carbon Buildings. The main outcome provides - to architects and engineers - advanced BIPV renovation strategies depending on the building typology, the architectural design goals, and the level of intervention.