In recent years, Power to Gas, which converts surplus renewable energy into gaseous fuels for storage and utilization, has been attracting attention. One such Power to Gas project involves hydrocarbon production technology. In this paper, a hydrocarbon production system using Solid Oxide Electrolysis Cell (SOEC) co-electrolysis was devised and the effects of the system components on efficiency were investigated. First, we conducted a comparative analysis of energy efficiency at different SOEC operating temperatures: 750°C, 800°C, and 850°C. The results indicate that operating the SOEC at 750°C yields the highest energy efficiency. Secondly, we compared the effects of H₂O and CO₂ utilization, as well as the heat loss rates of the SOEC, with the thermal and heat loss rates of the heat exchanger on overall efficiency. The findings highlight that variations in heat loss rates within the SOEC have the most significant impact on energy efficiency. Additionally, when comparing the heat loss per heat exchanger in our study, we observed that the steam generator and heat exchanger for air introduced from outside exhibited high heat loss rates within the system. Furthermore, we investigated the influence of the supplied air quantity on energy efficiency, revealing that reducing the amount of supplied air is essential for achieving high efficiency.