Assessing ocean renewable energy off Brazil

Climatic change mitigation strategies include the reduction of fossil fuels dependency and the increase of energy mix contribution from renewable sources. Oceanic renewable energy sources emerge as a promising alternative to diversify the energy mix. In the southwestern tropical Atlantic off Brazil, the Ocean Thermal Energy Conversion (OTEC) and the potential energy from surface currents were investigated. Time series of 40 years (1983 - 2022) of water temperature data (surface and 1000 m depth) were used to estimate thermal gradients. The temporal gradients showed no significant differences between the months over the annual cycle, with maximum thermal gradients >20ºC throughout the study region. The spatial gradient showed high thermal efficiency coefficients throughout the study region (h > 0.8), mainly in the North and Northeastern. The combined analysis of thermal efficiency and distance from the coast showed three points with the highest thermal efficiency ratings (h > 0.85) and the shortest distance (<30 km) for the effective implementation of an Ocean Thermal Energy Conversion-OTEC projects. Furthermore, the presence of the strong western boundary subsurface North Brazil Undercurrent (NBUC) in this region lead to the investigation of the current power density (CPD) at different vertical levels. The results showed four hotspots for marine current energy exploitation with CPD higher than 1000 W m^-2, two of them related to the NBUC at depths between 150 and 250 m. All the hotspots identified were a consequence of flow-topography interactions, in particular because of changes in current dynamics due to coastline and shelf-break isobaths direction changes. We compared the hotspots in terms of closeness to the coast, closeness to oil and gas exploration blocks, stability of current core and absence of deep reef system at the subjacent shelf. Our results indicate that, besides the challenges of current core being in deeper layers, the undercurrent provides a stronger and seasonally stabler CPD than the surface currents. Finally, current and OTEC technologies can promotes access to clean, non-intermittent and sustainable energy sources, reducing greenhouse gas emissions and contributing to the mitigation of climate change.