Exergy-based flexibility cost indicator and spatio-temporal coordination principle of distributed multi-energy systems

Demand-side flexibility in distributed energy systems has aroused broad attention in recent years. However, existing researches concentrate on flexibility improvement based on the 1st law of thermodynamics or efficiency improvement based on the 2nd law of thermodynamics, but the insightful physical mechanism of how and at what expense the distributed energy system offers flexibility is still unclear, especially when it is involved with multi-energy converters and storage. This paper introduces an exergy-based indicator to quantify the cost associated with flexibility improvement of distributed energy systems, and then figures out different flexibility improvement mechanisms of multi-energy converters and storage contributing to the whole energy system. Finally, a spatio-temporal coordination principle for distributed energy systems is established. In the spatial dimension, distributed energy systems in the power grid offer power flexibility at the cost of additional exergy destruction to compensate for fluctuation of renewable power. In the temporal dimension, the thermal energy storage device in each distributed energy system offsets part of the flexibility cost by reallocating the heat loads at different periods. Results show that the proposed principle is in good agreement with directly solving the centralized optimization, and helps to protect privacy and clarify the contribution of each distributed energy system in terms of the 2nd law of thermodynamics.