The use of carbon dioxide as a high-performance working-fluid in advanced thermodynamic cycles provides a compelling route for developing low-carbon, multi-output renewable-energy systems. The study develops and assesses an advanced hybrid solar-geothermal polygeneration facility designed to produce electricity, hydrogen, and freshwater under the real resource conditions of the Harrat Rahat geothermal zone in Saudi Arabia. The configuration combines a double-flash geothermal cycle with a Transcritical CO2 Rankine cycle, a Kalina cycle, an alkaline electrolyser, and a reverse-osmosis desalination unit, supported by parabolic trough solar thermal augmentation. A full 3E+S evaluation-covering energy, exergy, economic, and sustainability metrics-is carried out alongside multi-objective optimization using the Secretary Bird metaheuristic algorithm. Under the real resource inputs of the Harrat Rahat site-geothermal reservoir temperatures exceeding 220 degrees C and mean solar irradiance of similar to 6.6 kWh m(-2) day(-1), the results show the system could deliver 3.65 MW of net electricity, 9.35 kg.h(-1) of hydrogen, and 10.23 m(3).h(-1) of freshwater, with overall energy and exergy efficiencies of 42.7 % and 38.18 %. Optimization enhances exergy efficiency by about 1.54 % and lowers the levelized cost of energy by roughly 2.2 %, yielding an LCOE of 0.04039 USD/MJ and a sustainability index of 0.238. Exergy-destruction profiling shows that condensers (approximate to 47 %) and the solar thermal subsystem (approximate to 16 %) are the main contributors to irreversibility. Overall, the results indicate that integrating high-enthalpy geothermal resources with concentrated solar power and advanced thermodynamic cycles can deliver a robust, efficient, and economically competitive polygeneration pathway suited to arid regions with strong energy and water needs.