Now and into the future: Modelling and analysis of Danish urban energy systems

The global population is growing and so is the urbanisation share - currently over half of the world population lives in urban areas. Urban energy and transport systems are responsible for up to 70% of worldwide greenhouse gas (GHG) emissions, therefore the climate action on the local level is crucial if the objectives of the Paris Agreement are to be fulfilled.

Owing to the relatively stable political situation of local governments, as well as their closeness to citizens, cities and towns are recognizing the challenge and increasingly becoming the drivers of sustainable energy transition. In Denmark, many municipalities implement ambitious climate and energy policy aiming to reach carbon neutrality within next decades.

Planners and decision-makers need decision support tools for devising their strategic energy plans. Energy system models could play such a role by helping assess the feasibility of renewable energy and energy savings projects on a system level and identify scenarios for cost-efficient reduction of CO2 emissions.

Nonetheless, there is still not enough research concerning the identification and evaluation of least-cost sustainable energy scenarios for specific local urban energy systems, the suitability assessment of potential tools to be used and their usefulness from the municipal planners' perspective. Therefore, this PhD thesis investigates the methods for representing urban energy systems and assesses what changes are feasible in urban energy systems in order to reduce CO2 emissions.

The PhD thesis employs mathematical modelling of energy scenarios for three Danish cases: the Greater Copenhagen area, and two middle-sized municipalities: Helsingør (Elsinore) in eastern Denmark and Sønderborg in western Denmark. The dissertation also examines relations between the technical changes in energy systems caused by increased share of renewables and energy efficiency, and selected economic characteristics, such as system costs.

Moreover, it explores the role of energy system modelling in municipal planning using qualitative research consisting of expert interviews and content analysis. The PhD thesis comprises four papers, focusing on climate mitigation actions in the energy infrastructure and the built environment, and improvements of modelling tools and the modelling process of urban energy systems.

This PhD thesis finds that it is possible to significantly reduce CO2 emissions from urban energy systems in a cost-effective way by implementing a mix of different energy conversion pathways and energy storage, and a balance between district heating expansion and heat savings. Whereas the detailed findings are applicable mainly for Copenhagen, Helsingør and Sønderborg, on a more general level they are indicative for other areas with similar climatic conditions, population and natural resources.

This dissertation considers three different energy modelling tools and three different energy systems as case studies. Out of the modelling tools used, Sifre and Balmorel are found suitable to analyse integrated energy systems, while energyPRO and the spreadsheet tool LCT - to analyse heating and heat savings.

Among the weaknesses of quantitative energy scenario modelling is the inability to depict complex and non-linear stakeholder interactions. Therefore, to better portray sustainability transitions, energy system modelling should be, and often is, supplemented by other types of analysis. The qualitative analysis shows that municipalities are not active model users, but are involved in the modelling process together with consultancy firms, heat supply companies or academia.

Yet still, the modelling process can be improved by putting more effort into sharing data, assumptions and models, interand cross-municipal collaboration, as well as a constant dialogue on how to make tools useful for planning and implementing sustainability measures. Overall, the findings of this PhD thesis can support planners and decision-makers in the transition towards a more sustainably-planned energy system of a city, allowing achieving technical, environmental, social and economic benefits.