Tidal Stream Energy Resource Assessment at Lac Ghoubet Grand Passe in Djibouti Through Experimental and Numerical Investigations

The region of Ghoubet-el-Kharab in Djibouti, East Africa, presents some very interesting characteristics regarding the possibility of exploiting different sources of renewable energy such as solar, wind, geothermal and tidal stream energy. This study is aimed at providing a preliminary assessment of the tidal Stream Energy potential at the Grand Passe site, Lac Ghoubet. A short-term measurement campaign was performed to estimate the tidal stream speed, direction and vertical profile, providing basic reference data to adjust and validate long-term tidal prediction models. The research aims to evaluate the energy resource available for potential hydrokinetic turbine farm installations. Following an initial literature-based analysis, a measurement campaign was undertaken with the purpose of gathering site-specific bathymetric and tidal stream flow characteristics. An innovative methodology is introduced in this article for the extrapolation of the measured current speed, based on the annual tidal height profile. The approach used is based on the assumption that the current speed can be correlated to the slope of the tidal height time profile. Finally, a preliminary assessment of the overall tidal energy resource and the expected energy yield for a specific tidal turbine design is presented, utilizing the proposed tidal stream model. The current speed predicted by the model reaches a peak of approximately 4 m/s. To preliminarily estimate the theoretically available resource, an idealized flat seabed cross-section, 300 m wide and 7 m deep, was considered, yielding an estimated total theoretical energy of about 36.88 GWh/year. Furthermore, assuming a single-array layout comprising 18 hydrokinetic turbines (each 5.5 m in diameter with a rated power of 85 kW at a rated speed of 2.5 m/s), the practically available resource was estimated at approximately 2.99 GWh/year, representing about 8.1% of the theoretical value.