Advances in Applied Energy (May 2021)
Modelling and deploying multi-energy flexibility: The energy lattice framework
Abstract
This work proposes a novel modelling framework and an associated optimization methodology for short-term operational planning to deploy multi-energy system (MES) flexibility, with application to district energy systems and participation in energy and frequency control ancillary services (FCAS). In this paper, the proposed flexibility framework, based on the concept of multi-energy lattice, models a MES by several energy layers, each one associated with a specific energy carrier. The identified energy layers are linked by specific conversion nodes associated with coupling devices that operate across several energy carriers. After illustrating in detail the main features of the multi-energy lattice methodology and, particularly, how it enables to clearly describe and quantify how flexibility arises from both single-layer and cross-layer energy balancing, different features of the concept of multi-energy flexibility are defined and discussed. An associated operational optimization methodology to deploy multi-energy flexibility in a market environment is then introduced. This methodology is based on a two-step mixed integer linear programming approach, namely, (i) definition of a multi-energy baseline to cope with the energy demand across multiple energy vectors and (ii) identification of flexibility margins and economic convenience to offer different FCAS by deploying multi-energy flexibility. The multi-energy lattice concept is then demonstrated on the Milan district heating system. This MES plant exploits its flexibility for participation in multiple FCAS markets besides day-ahead energy trading, and it is shown how the proposed methodology is able to optimize the flexibility arising from different devices and optimally combine these contributions across multiple energy layers for business case purposes, in line with the general theory of the multi-energy lattice.
