Public defence in Power Systems and High Voltage Engineering, M.Sc.(Tech.) Niina Helistö

The title of the thesis: Analysing flexibility in energy system investment planning

Doctoral student: Niina Helistö
Opponent: Prof. Sami Repo, Tampere University, Finland
Custos: Prof. Matti Lehtonen, Aalto University School of Electrical Engineering, Department of Electrical Engineering and Automation

The growth of renewables from weather-dependent sources, such as wind and solar, increases the need for flexibility in power systems. The lack of flexibility results in high electricity price variations, as seen already today. Flexibility can be provided by several technologies in electricity supply and demand side. However, correctly planning for investments into these technologies requires methods that can correctly capture the need for flexibility. Two important aspects in this regard are the temporal structures and techno-economic operational constraints of investment planning models. 

This doctoral thesis aimed at analysing the flexibility needs of energy systems, as well as exploring and developing methods for improving the temporal representations and operational detail of investment planning models. Interestingly, the results show significant dependence on system characteristics. Therefore, the modelling tools that are used in investment planning need to be adaptable in terms of their temporal structures and operational constraints. The results underline the role of the temporal structure of planning models and how its comprehensiveness becomes increasingly important alongside the growth of renewables. In addition, the results highlight the benefits of batteries and smart charging of electric vehicles in solar-dominated power systems and the benefits of electricity interconnections, power and heating system integration and thermal storage in wind-dominated power systems. The results also underline the benefits of shifting from base load power plants to power plants that can provide flexibility and economically cope with lower utilisation as the share of wind and solar grows. 

The results on the role of the flexible technologies offer useful information for investment planners, technology manufacturers and policy makers. The analysis related to the temporal structures and operational constraint configurations, on the other hand, may help those who are developing and using energy system investment planning tools. 

The thesis advances the methodologies in energy system investment planning and demonstrates interactions of energy technologies in power systems with different characteristics.

Keywords: energy system modelling, energy system optimisation, operational constraints, power system planning, solar energy, time series reduction, wind power

Thesis available for public display 10 days prior to the defence at: https://aaltodoc.aalto.fi/doc_public/eonly/riiputus/

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Doctoral theses in the School of Electrical Engineering: https://aaltodoc.aalto.fi/handle/123456789/53