Integration of water electrolysis and district heating through waste heat recovery in Nordic conditions: Techno-economic impacts of lowering the district heating network temperature

The future cost competitiveness of district heating (DH) has been acknowledged as facing challenges against individual heat pump (HP) systems, which are already highly competitive in the Nordic countries. An important factor identified for improving cost competitiveness is the reduction of temperature levels in DH networks (DHNs), which facilitates the integration of low-temperature waste heat (WH). This work investigates how the techno-economic indicators of WH recovery from a wind- and solar-power-based alkaline water electrolyzer (AWE) plant change when the temperature of a DHN is reduced. A WH recovery system including HPs, a pit thermal energy storage, and an electric boiler is cost-optimized in high-temperature DHN (HTDHN) and low-temperature DHN (LTDHN) cases. The WH generation of the AWE plant and the DH demand are based on measured data from southeastern Finland. It was found that the required HP capacity and electricity consumption of the HPs can be significantly reduced in the LTDHN compared with the HTDHN case. The electricity demand of the WH recovery system and its peak power can be reduced by at least 67 % and 53 %, respectively as the temperature of the DHN is lowered. The lower HP capacity and electricity demand are also highly reflected in the levelized cost of heat, which is reduced by at least 43 %. The key message of this study is that lowering the temperature levels in DHNs would enhance the profitability of WH- and HP-based DH generation while significantly reducing stress on the electricity system as the DH generation becomes electrified. • Waste heat from water electrolysis is recovered for DH using heat pumps and PTES. • Levelized cost of heat (LCOH) was optimized for two DH supply temperature levels. • LCOH can be reduced by at least 43% with the lower DH supply temperature. • Reducing DH network temperatures significantly benefits the electricity system.