Analysing flexibility in energy system investment planning: Impact of variable renewable energy, temporal structures and operational constraints

needs of power systems on multiple temporal and spatial scales. While various technologies exist and are being developed that can provide flexibility, exploring the interactions and roles of new and existing technologies in flexibility provision requires investment planning models which can correctly capture temporal, spatial, sectoral and technological diversity, and detail. Being aware of the most important details and the state-of-the-art methods for modelling them will facilitate higher quality planning results and help avoid misguided investment decisions.
This dissertation focuses on developing and exploring methods and frameworks for assessing the need for and provision of flexibility when planning energy system investments. The methods should be able to capture important temporal variations, as well as the necessary operational constraints of energy systems. In addition, a number of case studies were carried out to explore the sensitivity of electricity prices, the role of conventional thermal power plants and the benefits of different energy technologies in future energy systems. The case studies provide insight into the type of power system flexibility needed with increasing shares of wind and solar energy, as well as insight into further modelling needs.
The temporal representation of the investment planning model is shown to significantly impact the total system costs resulting from the planning outcome. Correctly capturing extreme periods and interannual variations in weather are key to enhancing resource adequacy considerations. Similarly, intra-annual variations need to be captured using, for example, appropriately selected representative days or weeks. According to the results, the best selection method and the sufficient number of selected periods depend on system characteristics. The results also suggest that the modelling of power plant start-ups and shutdowns, ramp rates, as well as simplified stability requirements and reserve products generally has less impact on total costs than the various possible temporal representations. However, correctly capturing the flexibility of sector-coupling technologies is demonstrated to have a significant impact.
Investment planning capabilities and additional features related to flexibility were included in Backbone, an adaptable energy system modelling framework, which is also available as opensource software. Backbone can be utilised to create models for studying the design and operation of high-level large-scale and fully detailed smaller-scale energy systems from various perspectives.