Utilizing the flexibility provided by the thermal system components, for example, pipelines in the district heating network (DHN), building envelopes as well as thermal energy storage (TES) devices, can be an effective way for power system to solve the wind curtailment problem which closely relates to the limited flexibility of combined heat and power (CHP). However, almost all the previous studies ignored heat transfer (HT) constraints when modelling these abovementioned thermal system components. HT constraint is one of the most important constraints in thermal system analysis, without considering it may result in infeasibility for the dispatch results. Hence in this study we propose a detailed model for these three components, namely DHN, building envelopes as well as TES devices, with consideration of HT constraints. This model can be further simplified to consider different combinations of these components by setting relevant model parameters. An iteration solution to deal with such nonlinear HT constraints is put forward. The effectiveness of the proposed model is verified by case studies. The simulation results demonstrate that considering HT constraints is necessary when try to exploit the flexibility provided by these thermal system components, or we may overestimate their benefit

Due to the coupling of its heat and power output, combined heat and power (CHP) has limited flexibility, which is one of the main reasons for variable renewable energy source (RES) curtailment problem in Northern China. Almost all the existing studies have modelled the CHP's output characteristics as a feasible operation region of electric power and heat power. However, only the extraction steam of a CHP unit that used for district heating can be controlled directly, without considering the extraction steam's heat transfer process, the actual heat power output cannot be precisely decided. Thus this paper proposes a detailed CHP dispatch model based on the principles of heat transfer. A three-stage heat transfer model of the extraction steam is used to describe the heating process. Then, a joint dispatch model concerning CHP units, conventional thermal power units, and RESs is given. Finally, the impacts of different factors on the extraction steam's heat transfer process and its influence for RES accommodation are analyzed. Results show that considering heat transfer process is essential in modelling the CHP plant that used for district heating, especially when the CHP plant is working at a status that deviates from the rated one significantly.

Distributed energy system, a decentralized low-carbon energy system arranged at the customer side, is characterized by multi-energy complementarity, multi-energy flow synergy, multi-process coupling, and multi-temporal scales (n-M characteristics). This review provides a systematic and comprehensive summary and presents the current research on distributed energy systems in three dimensions: system planning and evaluation, modeling and optimization, and operation and control. Under the regional environmental, resource, and policy constraints, planning distributed energy systems should fully integrate technical, economic, environmental, and social factors and consider device characteristics, system architecture, and source-load uncertainties. Further, this review presents four modeling perspectives for optimizing and analyzing distributed energy systems, including energy hub, thermodynamics, heat current, and data-driven. The system’s optimal operation and scheduling strategies, disturbance analysis, and related control methods are also discussed from the power system and thermal system, respectively. In all, more research is required for distributed energy systems based on an integrated energy perspective in optimal system structure, hybrid modeling approaches, data-driven system state estimation, cross-system disturbance spread, and multi-subject interaction control.