Air-based photovoltaic-thermal (PVT) systems offer a sustainable solution for generating combined electrical and thermal energy. Still, their performance is hindered by high operating temperatures in water-scarce, high-irradiation regions like Port Said, Egypt. This study is significant for developing a cost-effective, passive cooling solution to enhance PVT efficiency and longevity, supporting renewable energy adoption in arid climates. The purpose is to design and validate an air-based PVT system with a novel cooling chimney (40.0 cm height) and four-inlet design (1.0 cm principal, 2.0-4.0-cm secondary inlets) using computational fluid dynamics (CFD). This novel design outperforms conventional single-inlet air-cooling systems by achieving uniform heat dissipation and higher thermal efficiencies. Major novel findings include thermal efficiencies of 25.0-35.0%, electrical efficiencies of 1.0-3.0%, and reduced PVT surface temperatures to 340.0 K at 1100 W m-2, achieved through buoyancy-driven airflow (mass flow rate of 0.0010-0.0050 kg s-1, Reynolds number of 500-2000) via the chimney effect. CFD simulations in ANSYS 2025 validate these results using a 988,200 hexahedral cell mesh with the Boussinesq approximation and k-epsilon turbulence model. This passive cooling design, incorporating a front glass, PV module, and absorber, offers a low-maintenance alternative for building-integrated or solar farm applications in arid regions.