Abstract
At the present time, the role of renewable energy in Brazil is significant as hydropower and other renewable energies, mainly biomass, contribute with 70.7% and 9,6%, respectively, towards the total offer for electric energy, as compared to the corresponding figures of 14,8% and 5,6% regarding worldwide averages. Nevertheless, there is already an increasing role which is played by wind energy, and a promising potential for tidal current energy. This paper is concerned with the assessment of the tidal current resource in São Marcos Bay, located on the north-eastern coast of Brazil in the state of Maranhão, and possesses a highly promising potential for the generation of electricity generation through the conversion of tidal current energy. Also, the impact of in-stream Hydrokinetic Energy Converter (HEC) arrays would have on the bay’s morphology is studied. Three potential zones for tidal power exploitation were identified employing SisBaHiA® finite element hydro-sedimentological model based on the sediment transport equation of Engelund & Hansen. Potential zones have surface areas of 1km² to 5 km², mean spring peak tidal currents in the range of 2–2.5 m/s and water depths range from 22m to 40m. An analytical power model applied for each zone defines HEC array characteristics and demonstrates an annually potential output in the range of 34-49 GWh. The analytical power model has, for simplification, a fix lateral spacing between TECs set in 3 rotor diameters and considers cut-in and cut-off velocities. An additional stress term was added to the model momentum equations in order to include TEC operation as a momentum sink taking into account thrust coefficient as a function of flow velocity. Six scenarios with full-scale TEC arrays are modelled to study hydrodynamic influences between arrays, as well as morphological effects. The hydrosedimentological scenarios include, initially, a simulation without TEC arrays to adjust bathymetry of possible data uncertainties to an equilibrium condition, afterward individual simulations of each array, followed by pairs of arrays and ending with the simulation of the three arrays case. Even though, the sediment transport model accepts differentiating granulometry and erosion limit at each calculating node of the domain, it was adopted a uniform granulometry consisting of five types of sediments distributed in an erodible layer of up to 5 m. Results for the hydrodynamic interference study indicate increases and decreases in power output up to 16.7% and 10.7% respectively. Morphological effects are studied in the proximities of the promising zones. Results, interpreted in a qualitative manner, indicate the formation of sand banks with heights lower than 0.75 m and regions experiencing levels of erosion of the same order. Future work is directed towards layout optimisation to maximise electric energy generation, minimising adverse effects in sediment dynamics.