tion networks, which amounts to 6-700 MW. Since the plants utilize geothermal heat with heat pumps, they will primarily be able to supply heat to the distribution grid, as it will be too expensive to provide heat at the high temperature required in the transmission grid. In autumn 2022, HOFOR/CTR/VEKS started contract negoti- ations with the company Innargi regarding establishing geo- thermal energy in the capital area from around 2030. Capture and storage of CO2 In the metropolitan area, there are several large point sources for CO2 capture from the combustion of biomass and waste at large cogeneration plants. If CO2 from biomass - or the bio- genic part of the waste - is stored underground, this results in negative CO2 emissions. The capture process requires a lot of energy, a large part of which ends up as surplus heat that can be used in the district heating system. Together with five other companies, HOFOR/CTR/Vestfor- brænding/VEKS work together in the cluster collaboration C4 - Carbon Capture Cluster Copenhagen - with a vision to reduce CO2 emissions in the capital city area by 3 million tons annually through CO2 capture. Here, the heating companies' interest is to utilize the surplus heat that is a consequence of CO2 capture - and VEKS has entered the first LOI with a heat producer in this regard. CCS (Carbon Capture and Storage) is an investment-heavy technology, and the costs of establishing and operating CCS are uncertain. For CCS to become economically feasible, the process - either in the form of subsidies or by capturing CO2 from the biogenic part of waste and biomass - must be priced as "negative emission." Transport of CO2 to underground storage can be done by truck, ship, or in pipes, and the actual storage can be done offshore or on land-based coastal storage. In connection with the transport, there will be activities that generate surplus
If the large heat pumps are to be used economically and technically in the best way, they must be placed close to the district heating network and a heat source (e.g., excess heat, groundwater, seawater, or sewage water). This requires reserved space in the metropolitan area and cooperation be- tween energy planning and physical planning in the munic- ipalities. The analysis has therefore investigated whether switching to low-temperature operation in both the transmission and distribution networks is possible. Today, flow temperature in winter is typically up to 115 °C in the transmission network and a maximum of 90 °C in the distribution network. In low-temperature operation, flow temperature is lowered to 90 °C in the transmission network and to 70 °C in the distri- bution network - in connection with new construction, flow temperature is reduced further. Return temperature must follow down. The analysis shows that it is technically possible to convert to a low-temperature level and to convert the transmission and distribution grids for relatively low costs. However, this requires a lot of additional technical and hydraulic analyzes as well as intensive cooperation between the district heating companies. Lowering the temperature is also estimated to provide signifi- cant savings in heat production costs - around 8% or DKK 250 million per year (€ 33 million/year). At the same time, lower Tf gives a smaller net loss; and the network's transport capacity is reduced by up to 25%. Therefore, it will be even more im- portant to see a temperature drop in connection with future decentralized production capacity placement. Geothermal Geothermal heat is a stable and suitable heat source for dist rict heating, and research indicates a sizeable geothermal po- tential in the underground area of Greater Copenhagen. The potential is limited by the quantities consumed in the distribu-
PTES - Pit Thermal Energy Storage - Høje Taastrup under construction.
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