Thermal storage vs. battery storage in urban microgrids: A techno-economic assessment of hybrid PV–PTC–ORC systems with storage

This study evaluates the techno-economic performance of hybrid solar energy systems designed for urban microgrids, with a particular focus on the role of thermal energy storage (TES) as an alternative to battery energy storage systems (BESS). A detailed thermo-economic model integrating photovoltaics (PV), parabolic trough collectors (PTC), thermal storage, and an organic Rankine cycle (ORC) is developed and coupled with a hybrid PSO-GA optimization framework. The main goal is to minimize the weighted average cost of energy (waCOE) while maintaining a target share of renewable energy (FRES). Realistic operating conditions are considered by analyzing flow rates of both heat transfer and working fluids, the ORC efficiency variations, and partial load effects on turbine behavior. This formulation creates a high-dimensional (9D), non-linear optimization problem that explicitly couples thermodynamic off-design performance with economic dispatch strategies. To address this nonlinearity and multi-variable optimization, a hybrid metaheuristic algorithm combining Particle Swarm Optimization (PSO) and the Genetic Algorithm (GA) is employed to determine the optimal sizes of system components, such as the PTC, PV field, TES, turbine, condenser, pump, evaporator, and heat exchangers. Three different setups, PV + BESS, PTC + TES + ORC, and PV + BESS + PTC + TES + ORC, are evaluated from both technical and economic viewpoints. The optimized PV + BESS + PTC + TES + ORC hybrid configuration (14×38MW PTC, 1.76MW PV, 121.53MWh TES, and 774.65kW ORC) with zero BESS capacity, suggesting displacing BESS with TES for PV-PTC-ORC hybrid systems. This optimized system delivers the lowest waCOE of 0.2378€/kWh, achieving a demand supply fraction (DSF) of 57.18% and a FRES of 82.00%. Finally, a sensitivity analysis of waCOE and FRES with respect to system component capacities is performed, which confirms the robustness and adaptability of the proposed hybrid design. These findings offer quantitative evidence that hybrid solar-thermal systems with TES can enhance urban energy resilience, reduce reliance on battery materials, and support cost-effective decarbonization strategies for cities.