Energy, exergy, and environmental performance of a solar-assisted hybrid cogeneration system for off-grid residential heating

Abstract

Off-grid rural dwellings still rely heavily on fossil-fuel generators for heating and electricity, yet experimental studies that couple energy, exergy, and environmental assessments of solar-assisted alternatives under real operating conditions remain scarce. To address this gap, this study experimentally and theoretically investigates the performance of a solar-assisted hybrid cogeneration system (SAHCS) designed for residential heating applications in off-grid rural areas. The proposed system integrates a photovoltaic (PV) panel, a vacuum tube solar collector, thermal energy storage, a battery-inverter unit, and a backup gasoline generator to meet both electrical and thermal energy demands. Experimental measurements were conducted in a residential space in Elaz & imath;& gbreve;, T & uuml;rkiye, during four different periods in 2023 under varying climatic and solar radiation conditions. The results showed that a substantial portion of the heating demand was supplied by solar energy, maintaining indoor temperatures within the thermal comfort range of 18-24 degrees C. The PV system achieved an electrical efficiency of 17-19%, while the solar thermal collector exhibited an energy efficiency of approximately 80-82%. The corresponding exergy efficiencies ranged from approximately 10-17% for the PV panel and 42-86% for the solar collector, depending on irradiance and operating temperature. The hybrid configuration reduced generator fuel consumption, yielding a CO2 emission reduction of 84-92% compared to generator-only operation. Based on extrapolation of the four measurement periods to a representative heating season, the annual CO2 saving potential was estimated to be on the order of 1.2 t year-1; this value should be regarded as an approximate estimate pending full-season monitoring. A preliminary techno-economic assessment indicated a simple payback period of approximately three years for the renewable components. The proposed SAHCS thus offers a reliable and sustainable solution for reducing fossil-fuel dependence in off-grid residential applications.