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District heating should be expanded In Heat Plan Denmark 2021, we also analyze where DH should be utilized. We do this by using the estimates for heat demands for all buildings in Denmark and finding the heat density for each area without DH. We then make five scenarios for DH ex- pansion. Specifically, in Heat Plan Denmark 2021, we analyze the following expansion scenarios:

In Heat Plan Denmark 2021, we both map the geography of the heating demand and supply, as well as relate these to the integration potential in the Danish energy system. The map- ping involves seven different detailed geographical informa- tion system analyses covering all of Denmark. These include estimates for annual heat demands and energy saving poten- tials of all Danish buildings and costs and heat loss of DH grids in about 3,000 areas, which currently are without DH. These mapping data provided input for making over 1,000 hour-by- hour energy system simulations for a future Danish decarbon- ized energy system. Heat savings in the building stock In Heat Plan Denmark 2021, heat-saving options are estimated for each building in Denmark. This is done based on the Danish heat atlas, a detailed GIS mapping of estimated annual heat demands in nearly 2 million Danish buildings 1 . The estimates for each building’s demand are based on a heat consumption model that uses average heating needs based on the build- ings’ use, age, and size. The heat consumption model is linked to the building-specific data from the national Building and Housing Register. The main principle behind heat savings in buildings is that they should only be implemented until the cost of decarbonizing the heat supply is cheaper than the cost of increased heat savings. In Heat Plan Denmark 2021, we find that heat savings should be done regardless of whether DH is expanded or not. The reason is that heat savings are important for reducing costs in the energy system and keeping biomass consumption at a sustainable level. The results show that the costs in the energy system are lowest, with heat savings between 32% and 36% in the building stock. These are flat optimums, and a sensitivity analysis shows that increasing heat savings to 40% can result in further reductions in biomass consumption with only a mar- ginal increase in the energy system’s cost. The heat savings can include improvements of the buildings’ climate screen (exterior walls, roofs, etc.) and a more optimized operation of the heating systems through, e.g., intelligent me- ters and control equipment.

Buildings currently registered with DH (~ 50%)

All buildings in areas designated for DH (~ 59%)

Extensions to urban areas with heat density above 15 kWh/m2 (~ 63%)

Extensions to urban areas with heat density above 10 kWh/m2 (~ 70%)

Extensions to urban areas with heat density above 5 kWh/m2 (~ 74%)

More than 3,000 areas without DH are evaluated, and for each area, a DH grid layout is modelled, including pipe sizes, costs, and grid losses. The five expansion scenarios have been simulated in a national energy system analysis tool, simulating the entire energy sys- tem hour-by-hour. This is done to identify how the different expansion levels affect a future Danish energy systembased on 100% renewable energy sources. We find that expanding DH from the current approx. 50% of the total heat demand in buildings to 63-70% will most bene- fit the energy system. The expansion is primarily at the expense of individual heating with natural gas, but also oil, biomass, and direct electric heating. In Heating Plan Denmark 2021, we propose an expansion to 70% as the main suggested expan- sion. 70% provides the lowest costs in the energy system while reducing the pressure on the need for biomass and wind pow- er in the overall energy system.

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