Long-term energy-system optimization models – on generation adequacy, capacity credits and the representation of cross-border trade

Name: Tim Mertens

Erik Delarue

Introduction / Objective
The focus of this PhD dissertation is on energy-system optimization models (ESOMs), i.e., partial equilibrium, bottom-up, optimization models that model the energy system from the perspective of a benevolent, central planner. These models use total system cost minimization as a decision strategy and have been widely used to analyze and guide the ongoing transitions in the energy sector. To maintain computational tractability, the level of detail included in the model is often restricted and some model dimensions (e.g., temporal, technical, spatial) are represented in a simplified manner. This restricted level of detail has implications on the accuracy of planning model outcomes. As such, this dissertation investigates two aspects of ESOMs that are directly affected by a restricted level of detail, namely (i) the ability of ESOMs to ensure generation adequacy, and (ii) the modeling of cross-border trade exchanges of electricity with neighboring countries.

Research Methodology
- An optimization-based calculation procedure is proposed to calculate the capacity credit of storage technologies.

- Two strategies are pursued to improve the adequacy awareness of ESOMs
1. Using dynamic planning reserve margin constraints that forces the model to install a minimum amount of firm capacity. All relevant parameters, i.e., capacity credits of the different technologies and capacity targets, are updated in between investment periods.
2. Increasing the level of detail with which critical peak periods are modeled (SAC approach)

- To improve the modeling of cross-border trade exchanges, two methods are investigated.
1. Endogenizing foreign dispatch decisions 2. Constructing import/export curves

Results & Conclusions

- The capacity credit of a storage unit starts to decrease when the unit’s energy capacity becomes binding.
- Increasing the level of detail with which critical peak periods are modelled is the preferred approach to increase the adequacy awareness of ESOMs. (see Figure)
- Endogenizing foreign dispatch decisions is the preferred approach to model cross-border trade exchanges of electricity.