Towards low-carbon cities with envelope-integrated photovoltaic-thermal systems: A multi-scale techno-economic appraisal

Envelope-integrated photovoltaic-thermal (EIPV/T) system is a new double-layer building envelope for roofs and façades. It features an operable air channel that supplies warm air to indoor spaces during winter. By providing electricity and heat, EIPV/T systems show strong potential for carbon-neutral urban buildings or blocks. However, the evaluation of its performance remains challenging, as the solar resources are significantly influenced by local solar radiation, topography, and urban feature. To facilitate the deployment of EIPV/T system, a multi-scale appraisal framework was developed to evaluate the EIPV/T's potential of power generation, heating, and carbon reductions, considering the effects of topography and urban canopy. This appraisal framework was validated with PV output data from our pilot EIPV/T building. The analysis focused on Shaanxi Province, China, a region spanning a wide latitudinal range and encompassing both mountainous and flat urban landscapes with distinct solar resource conditions. At the urban scale, the simulation results show that over 70% of the buildings in the simulated area have the potential to become the energy plus building (EPB). Based on the hourly analysis of typical block, combined with optimized energy storage, the EIPV/T system can achieve an internal rate of return (IRR) of 3-4% and meet 10-20% of the heating load. The carbon emissions can be reduced by 25-65% throughout the lifecycle. This study aims to demonstrate how EIPV/T systems can enhance the efficiency of urban carbon mitigation and local energy supply by aligning solar resources, energy demand, and energy storage within a multi-scale appraisal framework.