Techno-economic analysis of Ocean Thermal Energy Conversion (OTEC): The influence of cold seawater depth

Ocean Thermal Energy Conversion (OTEC) is a promising renewable energy technology that utilizes the temperature difference between surface and deep seawater to generate electricity. However, its implementation faces significant challenges, particularly related to the design and cost of cold seawater intake infrastructure. This study investigates the influence of deep seawater intake depth (350, 400, 500, 600, and 700 m) on the technical performance and economic feasibility of an OTEC system using Manado Bay, Indonesia, as a case study. Temperature profiles derived from HYCOM data were combined with a single-stage Rankine cycle model to evaluate system efficiency, component sizing, and the Levelized Cost of Electricity (LCOE). The thermodynamic model was validated against experimental results reported in the literature, showing good agreement and confirming the reliability of the adopted approach. The results indicate that increasing the intake depth enhances the thermal gradient, which improves system performance and reduces the required mass flow rates of seawater and working fluid. Consequently, the heat exchanger area and associated capital costs decrease with increasing depth. The system operating with a 700 m intake depth achieved the highest thermal efficiency of 3.75% and the lowest LCOE of 8.31 USD cents/kWh. Sensitivity analysis further shows that LCOE is strongly affected by variations in CAPEX and OPEX, particularly those associated with platform and heat exchanger costs. These findings provide useful insights for optimizing OTEC system design and improving the economic feasibility of renewable energy deployment in tropical coastal regions. • Temperature difference increased from ∼21.5°C at 350 m to ∼24.9°C at 700 m depth. • Iteration method was used to reach mass and heat balance for 100 MW net power output. • Economic evaluation included CAPEX, OPEX, and LCOE calculations for each intake depth. • Deeper intake improved efficiency and reduced component sizes and seawater flow rates. • At 700 m depth, system achieved 3.75% efficiency and lowest LCOE of 8.31 USD cent/kWh.