Exploiting Flexibility of Integrated Energy Systems - Modelling, Operation and Balancing

This thesis addresses the development of an integrated energy system by exploring the requirements and potential benefits of a joint and coordinated operation of the electric power system, district heating system and gas system. In the present state, each of the energy systems is operated individually. However, several linking units, such as combined heat and power units, power-to-gas units, electric boilers and heat pumps allow to exchange energy between the systems. By increasing the capacity of the linking units and coordinating the operation of the different sectors, the synergies between the different energy carriers can be exploited. Such an integrated energy system is envisioned to provide the flexibility, economic and energy efficiency needed to fulfil the ambitious decarbonisation targets that have been formulated in order to counteract climate change.

One major requirement for further research in the field of integrated energy systems is the development of appropriate models that allow to test and validate proposed methods in a realistic environment. In this thesis, a detailed model of the Danish gas, electricity and heating system is introduced that incorporates real data from the system operator. Based on the current system, the amount of available flexibility that can be gained by operating the system as an integrated energy system is assessed and several operational strategies that optimize the performance of the whole system are discussed. It is shown that the coordinated operation and synergy of multiple energy systems allow the optimal economic operation of the entire integrated energy system with maximum utilization of renewable energy.

One main barrier for the decarbonised integrated energy system is its balancing and operation once highly fluctuating renewable sources are integrated. As the share of renewable energy sources is increasing, the intermittency and volatility are increasing. Currently employed deterministic day-ahead forecasting models fail to capture the uncertainties in the energy systems adequately, and therefore, no longer provide an optimal solution for real-time operation. Therefore, a stochastic- based day-ahead approach is applied that achieves more flexibility and reduces the mismatch between the day-ahead and real-time stage.

To eliminate the mismatch between generation and demand in the real-time stage, a framework for managing such imbalances in an integrated energy system is described. The proposed framework is applied to the model of the Danish system using historical data. It is shown that the linking units have a great potential in increasing the overall energy efficiency of the system by utilizing the excess power from renewable energy sources. Moreover, they improve the capability of the system to balance these uncertainties.

The gas system allows to store gas in both pipelines as well as storages, and both can be major providers of flexibility for the entire integrated energy system. However, the major part of the gas system is fossil fuel-based, and decarbonisation through electrification is hard to achieve. Motivated by the decarbonisation targets and lack of renewables in the gas system, the requirements to transform the gas system into a green-based system are explored. The missing link towards a green-based integrated energy system is establishing a green gas system and a new balancing model to incorporate the challenges that the future will bring.