Energy Supply Modelling in Cities, Illustrated Using Data from the Municipality of Sønderborg in Denmark

In the ongoing transition towards a fully sustainable energy system, maximizing the system efficiency and the integration across its sectors while minimizing the costs of the system and carefully prioritizing the usage of energy resources are key issues. Denmark aims at becoming independent of fossil fuels for electricity and heat generation by 2035 and at having a fully renewable energy system by 2050.

Harmonized national and regional efforts are required in order to meet these goals. As the majority of the demand for energy services is located in cities, and because the density of energy transmission networks is highest within cities, it is useful to focus on city areas when seeking to optimize the system efficiency, economy and integration.

We have performed a case study using data from the Danish municipality of Sønderborg, which has the goal of becoming CO2 neutral by 2029. We have developed and modeled different scenarios for Sønderborg’s energy system in 2029, containing various different energy conversion pathways. These include e.g. biogas production and upgrade using hydrogen from electrolysis, scenarios with biomass gasification and local transport fuel production and scenarios in which gas turbines for reserve electricity generation have been displaced by reversible electrolysis/fuel cell systems.

The aim of the case study was to identify if and how new energy conversion technologies can be integrated in the future energy system to meet the demand for energy services in an economical, efficient and sustainable way on a regional scale. The results show that the gas and district-heating systems, along with utility-scale heat pumps, will serve as valuable system integrators for the large amounts of fluctuating electricity supply from wind and PV.

The overall system efficiency can be enhanced by supplying surplus process heat to the district-heating network and by using electrolysis to produce hydrogen for upgrading of biomass-derived gases. The results also pinpoint the importance of prioritizing biomass for the production of synthetic hydrocarbon transport fuels rather than for heat and power generation.

The work was carried out using the Sifre energy systems analysis software developed by Energinet.dk (the Danish electricity and gas TSO). It is a linear optimization model that seeks a least-cost solution for the hour-by-hour operation of the specified energy system. The work was carried out as part of CITIES, funded by Innovation Fund Denmark.