Preliminary bathymetric and interannual thermal stability screening for ocean thermal energy conversion (OTEC) along the eastern coast of Sorsogon Province, Philippines

Ocean Thermal Energy Conversion (OTEC) uses the temperature gradient between the warm surface and the cold deep water. Existing thermal resource screening studies rely only on short observational campaigns or multi-decadal climatologies that characterize seasonal conditions but not year-to-year continuity. This study screens the eastern coast of Sorsogon Province, Philippines, integrating a 20-year (2005–2024) CMEMS GLORYS12V1 reanalysis with GEBCO bathymetry, interpolated to 10–1000 m and analyzed across rainy, cool-dry, and hot-dry seasons. Sea surface temperature ranged 27.5–29.5 °C, deep water below 500 m remained 4–7 °C, and the vertical gradient exceeded the 20 °C OTEC threshold up to 21.5–25.3 °C. The interannual coefficient of variation, computed from 20 discrete annual fields, stayed below 1.7% at all depths and decreased with depth. Shoreline-to-1000 m contour distances ranged from 8.3 km (Prieto Diaz) to 53.9 km (Matnog). CMEMS was evaluated through spot-check against 20 independent World Ocean Database profiles drawn from only 6 of the 20 years of record and concentrated in the northern and central study domain, yielding RMSE of 0.21–0.32 °C below 500 m, comparable to the products' documented global accuracy. An Entropy-TOPSIS multi-criteria framework, combining thermal persistence, interannual stability, and bathymetric accessibility, identified Prieto Diaz as the most favorable site, and the ranking was robust across four weighting schemes, though entropy weighting assigned negligible weight to the thermal criteria, indicating the ranking is effectively dominated by bathymetric accessibility at the resolution of the available reanalysis. These findings indicate the preliminary screening-level OTEC potential and provide a basis for further hydrodynamic, environmental, and techno-economic assessment; they do not constitute an engineering feasibility or net power assessment.