Techno-Economic Analysis and Sizing of a Hybrid PV-Geothermal System for Building Energy Sustainability: A Case Study under Egyptian Climatic Conditions

This study presents a techno-economic and environmental assessment of a hybrid Earth-Air Heat Exchanger (EAHE) and photovoltaic (PV) system for a residential F2-type building under the hot-arid conditions of Cairo, Egypt (ASHRAE 2B and Köppen-Geiger BWh). The analysis combines Meteonorm Typical Meteorological Year weather data, DesignBuilder/EnergyPlus building-load simulation, and EAHE/soil-temperature models validated against measured literature data; internal gains and operating schedules are standard-based assumptions rather than field-measured inputs. Results show that the EAHE moderates ambient air temperature, achieving an average air-temperature reduction of 5.18 °C during the cooling season and an average increase of 6.62 °C during the heating season. The EAHE reduces the July baseline cooling demand by 233.34 kWh (15.4%) and supplies 298.09 kWh of thermal energy in January, covering 92.0% of the heating demand. A year-1 PV capacity of 7.64 kWp was selected to cover the post-EAHE July demand using fourteen 550 W-class modules, requiring approximately 38.5 m 2 of roof area. If the same coverage is required at the end of a 25-year PV lifetime under 0.5%/year degradation, the required design capacity increases to approximately 8.62 kWp. The economic results are scenario-dependent: the simple payback period is 3.8 years under a high avoided-cost tariff of 0.18 USD/kWh, whereas it increases to approximately 15.9 years when the official upper residential tariff in Egypt is used. Environmentally, the hybrid system reduces grid electricity use and associated CO 2 emissions, although the long-term EAHE performance should be verified experimentally because multi-year soil thermal saturation was not modeled.