Session: 09-09-01: Hybrid Energy I

Submission Number: 157328

Complementarity of Brazil’s Ocean Thermal Gradient Energy and Offshore Wind
Power 

The study analyzes the complementarity potential between the resources of Ocean Thermal Energy Conversion (OTEC) and Offshore Wind energy, in the Potiguar Basin (North Brazil) and Campos Basin (Southeast Brazil). Combining OTEC and offshore wind energy can significantly reduce the intermittency of renewable energy systems, fostering a more reliable supply. Within the broader goals of energy transition and decarbonization, this synergy can bolster the energy supply for offshore platforms, like floating production, storage, and offloading units (FPSOs), which are progressively moving towards low-emission operations.

To evaluate the offshore wind resource, data from ERA5, the fifth generation of ECMWF's atmospheric reanalysis, with a horizontal resolution of 31 km, were used. For the OTEC resource, data from HYCOM (HYbrid Coordinate Ocean Model) with a spatial resolution of 9 km were utilized. Both datasets were analyzed on an hourly basis during the last 20 years (2000 -2020).

 The wind energy was calculated using FLOw Redirection and Induction in Steady State (FLORIS), which is developed by NREL and Delft University of Technology with support from the U.S. Department of Energy Wind Energy Technologies Office. The wind speed is measured at 150 m height, the cut-in speed is set to 3 m/s, the rated wind speed is 11 m/s and the cut-out wind speed is 25 m/s. The energy from OTEC was analyzed using a thermodynamic model based on the Rankine cycle. In this model, the Sequential Least Squares Programming (SLSQP) method was employed, an iterative optimization algorithm that solves nonlinear, constrained optimization problems. This approach is particularly suitable for scenarios where an objective function needs to be minimized (or maximized) under a set of equality and inequality constraints. In our case, to maximize the efficiency of the OTEC system, the optimization focused on the working fluid flow rates, hot and cold-water flow rates, operating temperatures in the evaporator and condenser, and the minimum temperature difference in the evaporator and condenser.

To assess the complementarity between resources, Pearson and Kendall correlation analyses were conducted. In these tests, a negative correlation indicates complementarity between resources, whereas a positive correlation suggests a synergistic relationship.

In the Potiguar Basin, the Pearson correlation was -0.63, and the Kendall correlation was -0.5, indicating a notable complementarity between the two resources. An additional statistical measure applied was the Coefficient of Variation (CV), a commonly used metric to represent the relative variability of a dataset in relation to its means. The annual CV for the wind resource was 82%, demonstrating high variability, while the CV for OTEC was only 6%, indicating low variability in the ocean thermal gradient resource.

 In the Campos Basin, the Pearson and Kendall correlations were -0.19 and -0.12, respectively, also indicating a complementary relationship between the resources. Here, the CV for offshore wind was 70%, while the CV for OTEC was 17%, reflecting the higher variability of the wind resource over the years. Together, these findings reinforce the potential for OTEC to complement the more variable offshore wind resource, providing a more stable energy supply across both basins.

 The choice of study locations is based on the fact that the Campos and Potiguar basins are two relevant oil-producing regions in Brazil, each with a strategic role in the national energy economy. The Campos Basin, located off the coast of Rio de Janeiro, is historically the largest oil producer in the country, accounting for a significant share of national production. The Potiguar Basin, located in northeastern Brazil, is the main sedimentary basin producing oil and natural gas on the Equatorial Margin.

Presenting Author: Daniela Corrêa Federal University of Rio de Janeiro

Presenting Author Biography: Oceanographer and PhD student in Ocean Engineering