Integrated 4E evaluation and optimization of a hybrid solar–biogas gas turbine system for sustainable hydrogen and desalinated water production

Hybrid energy integration into gas turbine cycles (GTC) has gained attention in recent years, as it improves efficiency and reduces the drawbacks of relying on a single energy source, such as intermittency or high emissions. In this study, a hybrid configuration employing a solar power tower (SPT) and a biogas-fueled combustion chamber is proposed to drive a GTC. The system utilizes the waste heat from the GTC through a combination of an organic Rankine cycle (ORC), a heat recovery steam generator, and a modified Kalina cycle (MKC). Additionally, residual heat from the ORC and MKC is further recovered by a thermoelectric generator and an absorption chiller to enhance overall energy utilization. The electricity generated by the ORC and MKC is directed to a proton exchange membrane electrolyzer and a reverse osmosis desalination unit for the co-production of hydrogen and freshwater, effectively transforming the system into a novel poly-generation layout. A comprehensive mathematical model is developed to evaluate the system from energy, exergy, exergoeconomic, and environmental perspectives. The influence of key parameters on system performance is analyzed, followed by a multi-objective optimization targeting maximum exergy efficiency and minimum total cost rate. In the base scenario, the SPT represents the dominant component in the system, contributing 68.33 % to overall exergy destruction, 75.62 % to the total initial cost, and 68.93 % to the cost associated with exergy destruction. Optimization results yield an exergy efficiency of 30.491 % and a total cost rate of 5832.14 $/h, showing improvements of 4.3 % and 1.8 %, respectively, compared to base case outputs. Under optimal conditions, the system delivers 20,632 kW of electricity, 33,201 kW of heating, 3,003 kW of cooling, along with 6.399 kg/h of hydrogen and 16.07 kg/s of freshwater. Compared to existing designs, the proposed hybrid SPT–biogas GTC configuration demonstrates enhanced efficiency and cost-effectiveness, confirming its potential for integrated production of power, heat, cooling, hydrogen, and desalinated water.