Potential analysis of the integration of flexibly operated Direct Air Capture (DAC) plants in the heat and power system using the example of Hamburg

Abstract

For climate neutrality by 2045, Germany must compensate unavoidable residual greenhouse gas emissions by negative emission technologies such as direct air capture (DAC) technology. This study explores the technical feasibility and economic viability of implementing flexibly operated DAC plants in Hamburg’s district heating system in 2045. Literature about DAC technology requests high full-load operation hours (FLOH) to achieve the economic feasibility of DAC plants. In this work, scenarios of different DAC plant scales on both flat rooftops and open fields are developed considering a range of demand-related costs and various district heating (DH) system designs with deviating short-term and seasonal thermal energy storage capacities. Construction sites for DAC plants are identified on open spaces and rooftops near the DH grid. Unused heat generation capacities in the DH system are identified. The DAC application, along with heat pumps, shall operate during periods of negative residual loads in the power system. Results of a mixed-integer linear programming optimization indicate that DAC plants on rooftops and open fields are technically feasible for different DH system designs. The proposed carbon dioxide removal rate for Hamburg in 2045 is achievable in a flexible operation mode. The DAC application can efficiently utilize surplus heat and unused heat pump capacities from the DH system. Economically, large-scale DAC plants on open fields prove more feasible than on rooftops, with levelized costs of CO2 removal below 100 €/tCO2, dependent on the DH system design and demandrelated costs. A flexibly driven DAC plant with lower FLOHs on an open field has an achievable economic break-even point if the demand-related costs can be partially compensated through e.g., political incentives such as industrial DR or dynamic electricity pricing. The findings suggest that economically viable DAC plants in Hamburg’s DH system depend mostly on the specific investment costs rather than the final DH system design.