Optimizing the integration of power-to-heat technologies in district energy infrastructures in Turku, Finland, using an MILP formulation

Efforts to decarbonize district thermal energy networks are underway in Europe, with a focus on replacing coal and gas-fired installations with biomass and power-to-heat technologies such as heat pumps and electric boilers. An optimization model was developed to assess ideal degrees of power-to-heat technology integration in district thermal energy networks in the city of Turku, Finland. Large heat pumps capable of producing district heating and cooling, high-temperature heat pumps capable of producing steam, and electric boilers were considered. The optimization simulated the ability of the production units to meet network demands in Turku during 2023, with the option to expand unit capacities at specific investment costs. Results show that optimal investments could reduce operating costs by 12 % under 2023 fuel and electricity price conditions. Heat pumps could increase the share of the annual district heat coverage from 16 % to 39 %, electric boilers could cover 3.7 %, and high-temperature heat pumps could cover 27 % of the steam network demands. The need for increased electricity production is highlighted, as the annual electricity demand of the optimized network would increase from 236 GWh to 327 GWh. Meanwhile, the production profile of the existing biomass combined heat and power plant would partially shift toward operating primarily when electricity production is profitable, with annual heat production decreasing from 1 087 GWh to 836 GWh, and electricity production decreasing marginally from 456 GWh to 431 GWh.