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Published in: Applied EnergyLink to article, DOI: 10.1016DOI: 10. /j.apenergy.2016 Publication date: 2016 Document VersionPeer reviewed version Link back to DTU Orbit Citation (APA): Dominkovic, D. F., Baekovi, I., osi, B., Krajai, G., Pukšec, T., Dui, N., & Markovska, N. (2016 features, various climates and significant differences in gross domestic product per capita, so the 39 integration of their energy systems is considered to be a challenging task. Large differences 40 between energy mixes, still largely dominated by fossil-fuel consumption, make this task even more 41 demanding. 42This paper presents the transition steps to a 100 % renewable energy system which need to be 43 carried out until the year 2050 in order to achieve zero carbon energy society. Novelty of this paper 44 compared to other papers with similar research goals is the assumed sustainable use of biomass in 45 the 100% renewable energy system of the region considered. It is important to emphasize here that 46 only the sustainable use of biomass can be considered carbon-neutral. The resulting biomass 47 consumption of the model was 725.94 PJ for the entire region, which is in line with the biomass 48 potential of the region. Modelling the zero-carbon energy system was carried out using the smart 49 energy system concept, together with its main integration pillars, i.e. power-to-heat and power-to-50 gas technologies. The resulting power generation mix shows that a wide variety of energy sources 51 need to be utilized and no single energy source has more than a 30 % share, which also increases 52 the security of supply. Wind turbines and photovoltaics are the main technologies with shares of 53 28.9 % and 22.5 %, followed by hydro power, concentrated solar power, biomass (mainly used in 54 cogeneration units) and geothermal energy sources. To keep the biomass consumption within the 55 sustainability limits, there is a need for some type of synthetic fuel in the transportation sector. 56Nevertheless, achieving 100 % renewable energy system also promises to be financially beneficial, 57 as the total calculated annual socio-economic cost of the region is approximately 20 billion euros 58 lower in the year 2050 than in the base year. Finally, energy efficiency measures will play an 59 important role in the transition to the zero-carbon energy society: the model shows that primary 60 energy supply will be 50.9 % lower than in the base year. 61Keywords: smart energy system; renewable energy system; zero carbon; South East Europe; 62 sustainable biomass; energy efficiency 63 64

A linear continuous optimization model with an hourly time resolution was developed in order to model the impact of subsequent interconnections of different DH grids. The municipality of Sønderborg was chosen for a case study and interconnections of five currently disconnected DH grids were assessed. Moreover, the impact of industrial waste heat on the DH supply was also assessed. In the reference year (2013) two out of four interconnections proved to be economically viable. The results for the future energy system (2029) showed that interconnecting geographically distributed DH grids reduces primary energy supply by 9.5%, CO 2 emissions by 11.1% and total system costs by 6.3%. Inclusion of industrial waste heat in the fully interconnected DH grid reduced primary energy supply for an additional 3%, CO 2 emissions for an additional 2.2% and total system costs for an additional 1.3%. The case of the future energy supply system with interconnected DH grids and installed industrial waste heat recuperation results in the lowest primary energy demand, emissions and costs. Finally, the benefits of the interconnected DH grid, in terms of system flexibility, CO 2 emissions, total costs and energy efficiency, proved to be much greater in the future energy system.

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