Study on the technical and economic requirements to secure a stable and continuous energy supply for fuel cells in buildings in Seoul

•The techno-economic conditions under which the fuel cell system of a building in Seoul would become a stable source of energy were derived.•The Energy Saving Ratio vary by 1–10% depending on the heat energy use rate.•In the research model, if fuel cells handle 30% of the electricity consumption of the building and the building uses 100% of the generating heat of fuel cells, it can be the most stable energy performance and economy.•If the electricity rate rises by more than 5 %, the initial investment cost can be recovered within 10 years, and if the 10 % increase, the economic feasibility is met by meeting the Benefit-Cost Ratio > 1, Net Present Value > 0.