This work evaluates the energetic performance of a maritime Natural Cave located in Cidade-Velha (Cabo-Verde) for the electricity production purpose. The selection of this Natural Cave results from deep studies conducted around Santiago Island and already published on a scientific journal. To carry on the measurements (done in June), we equipped the orifice of the Natural Cave with a 1.5 m height vertical rectangular tube connected to a fixed base on the rocky shoreline. For the tube cross-section area (15 cm x 30 cm), the highest and the average air velocity values were around 84.20m/s and 32.61m/s, respectively. The airflow throughout the tube is incompressible with maximum Mach Number close to 0.30. Since the peak power available for conversion (between 6.9 and 10 kW) was around eight times higher than average power (between 0.9 and 1.5 kW), it is necessary to design a smart control system to maximize energy conversion. All performances parameters are directly influenced by the four sea tides around Santiago Island. Through the Design Charts for Wells turbines, for a NACA0021 profile with N = 4 blades, producing 1.1 kW a Wells turbine was found with the following features: power coefficient C = 1550.55, solidity S = 0.72, pressure drop coefficient dp = 0.1, flow coefficient phi = 0.1275, Tip radius R-tip = 207 mm and chord c = 173 mm, working, in a 435mm x 435mm cross-section tube. The designed power plant besides supplying electricity to at least 13 houses with the consumption profile similar to that in Cidade-Velha, it represents an annual saving of 2412.9 L of diesel and 6314.56kg of CO2 not emitted to the environment.
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