This study investigates the integration of a solar field using parabolic trough collectors into a binary geothermal plant with isopentane as the secondary fluid, employing the Engineering Equation Solver (EES) and System Advisor Model (SAM) for analysis. The investigation evaluates the performance of two Heat Transfer Fluids (HTFs)-Therminol VP -1 and molten salts-in hybrid configurations, emphasizing variations in solar field size and thermal storage capabilities. First, a direct correlation has been identified between second law efficiency and Levelized Cost of Energy (LCOE), demonstrating that increases in thermal storage from 0 to 12 h result in LCOE increments up to 33%. The study highlights that molten salts, achieving the lowest LCOE of 0.075 USD/kWh, enhance net energy output by up to 15.55% compared to Therminol VP -1, particularly under extended storage conditions. Additionally, the integration of larger solar fields and increased storage capacities significantly impacts the costs of high-pressure steam production, which rise from 33.02 to 50.55%. By expanding plant capacity factors up to 97% for Therminol and 93% for molten salts with optimal thermal storage and solar multiple configurations, the study demonstrates that molten salts enable greater annual power output despite lower capacity factors. This comprehensive analysis underscores the pivotal role of second law analysis in optimizing the economic and operational efficiencies of hybrid geothermal -solar power systems, offering significant insights for enhancing the design and economic viability of renewable energy integrations.