Multi-objective optimization of solar-coupled energy systems with physical storage and virtual multi-energy interaction

Interconnected solar driven integrated energy systems (IESs) can exploit complementary energy demands and solar resources across multiple subsystems. However, existing studies generally treat intersystem energy exchange as conventional energy sharing or trading, while its storage equivalent coordination with physical storage remains insufficiently quantified. This study develops a tri-objective optimization framework for two interconnected solar driven IESs. Battery, thermal, and chilled water storage are coordinated with bidirectional electricity, heating, and cooling exchanges. Virtual multi energy storage is defined as the system level flexibility obtained when one IES accesses the complementary generation, conversion, and storage capabilities of another through coordinated energy exchange. Economic cost, primary energy consumption, and environmental impact are simultaneously minimized over four typical days using the epsilon constraint method, and representative compromise solutions are identified using the Technique for Order Preference by Similarity to Ideal Solution. The framework is evaluated through four physical and virtual storage configurations, comparisons with existing optimization and dispatch strategies, Pareto quality indicators, and sensitivity analyses. The combined physical and virtual storage configuration achieves an economic cost of 646,224.51 USD, primary energy consumption of 12,852,834.68 kWh, and environmental impact of 3,024,247.05 kg. Compared with physical storage alone, these objectives are reduced by 3.32%, 6.95%, and 9.68%, respectively, while the corresponding reductions relative to the no storage configuration are 5.19%, 9.36%, and 10.56%. The combined configuration also achieves the highest hypervolume of 0.9227, which is 42.24% higher than that of physical storage alone. Increasing the photovoltaic capacity coefficient from 0.5 to 1.5 reduces the three compromise objectives by 6.26%, 29.21%, and 29.69%, respectively, whereas the benefit of additional solar thermal capacity becomes negligible beyond a coefficient of approximately 0.8. Moreover, variations in the three compromise objectives remain within 0.70%, 1.67%, and 2.61% when the storage degradation cost coefficient varies from 0.5 to 1.5. These results demonstrate that physical storage provides temporal regulation, while coordinated multi energy interaction supplies complementary spatial flexibility, enabling improved economic, energy, and environmental performance.