Optimal dispatch of a novel integrated energy system combined with multi-output organic Rankine cycle and hybrid energy storage

Abstract

Integrated energy system (IES) is characterized as a heterogeneous system, providing energetic, economic and environmental benefits by cooperating with multiple energy carriers. However, current studies rarely focus on utilizing hybrid electric/thermal storage in coordination with harvesting heat flexibly in IES, which should be further considered in the planning period. To this end, a novel IES combined with hybrid electric/thermal storage and multi-output organic Rankine cycle (ORC) is proposed. Considering operating modes of gas turbine, ORC’s working manners, and converting patterns of harvesting heat in IES, comparisons of case study and operating characteristics on typical season days are analyzed. A bi-level optimal planning model of hybrid electric/thermal storage with ORC is proposed, consisting of a lower-level operating model and an upper-level planning model. Results show that there is the least operating cost of IES on typical season days under the off-design mode of gas turbine, ORC’s combined heat and power (CHP) mode and harvesting heat flexibly, when enabling multi-flows to adjust thermoelectric ratio effectively. ORC’s pure power generating mode in IES with low electrical load is not economically attractive, while ORC’s CHP mode is beneficial to enhance ORC’s consistent dispatching time and electricity producing amount. State of charge of battery energy storage system has similar varying patterns, while heat storage degree and cold storage degree of thermal energy storage system change differently owing to varying thermal loads. The IES is thermodynamically feasible and economically attractive thanks to the bi-level optimization, achieving optimal battery energy storage system capacity of 1773 kWh, thermal energy storage system capacity of 4823 kWh and ORC capacity of 91.25 kW.