Assessing the long-term feasibility of net-zero energy houses in Slovenia: Impacts of climate scenarios, roof design, and technological progress

This study assesses the long-term viability of high-performance detached houses in Slovenia as net-zero energy buildings (NZEBs) under future climate change. Using a bottom-up approach, over one million energy models—calibrated against a sample of 78 real houses—were simulated across 12 Slovenian cities. The analysis integrated future climate projections from a 20-model ensemble (SSP2-4.5 and SSP3-7.0) with scenarios for technological advancements in HVAC and photovoltaic (PV) systems. Our findings demonstrate that, under optimistic technology development scenarios, projected efficiency gains significantly outweigh the climate-driven rise in cooling demand. Specifically, the solar-ready roof area required to achieve winter energy balance is projected to decrease by a factor of up to 6.5 by 2080, making long-term NZEB status attainable. However, achieving a year-round energy balance remains a critical challenge, particularly during winter in colder regions, where gable roofs perform poorly for PV generation compared to pitched or flat roofs. The results highlight that roof design is a decisive factor for NZEB feasibility. We conclude that realizing Slovenia's NZEB potential requires a shift away from restrictive, one-size-fits-all urban planning guidelines towards more flexible, site-specific design frameworks that optimize on-site renewable energy generation.