Abstract
This study computed thermal efficiency in Brazilian coastal areas between 5.0°N and 35.0°S and 25.0°W–55.0°W using a 40-year (1983–2022) water temperature dataset (surface and 1000 m). Thermal gradients showed no significant monthly differences over the annual cycle (Kruskal–Wallis test; p > 0.05). Maximum gradients exceeded 20 °C across the study region, with high thermal efficiency coefficients (η > 0.07) particularly in the Northeast. Combining efficiency and coastal proximity identified five optimal sites (P11, P6, P8, P9, P10) with η > 0.07 (∼7.3 %) and distances <35 km, favoring Ocean Thermal Energy Conversion (OTEC) implementation. The Northeast exhibited the greatest potential, with efficiency from 6.1 % to 7.8 %, comparable to the Caribbean Sea and exceeding values from other tropical Pacific and Atlantic areas. The results highlight the strategic advantage of the northeastern coast for OTEC, offering favorable thermal conditions and short offshore distances, reducing infrastructure costs. Harnessing this potential could enhance access to clean, sustainable energy, reduce greenhouse gas emissions, and support climate change mitigation efforts. This work contributes valuable spatial and temporal insights for future renewable energy planning in Brazil's coastal regions, emphasizing the relevance of long-term thermal data analysis for marine energy exploitation.