Utilizing maritime caves for wave energy: wells turbine performance and household power supply from cave-generated electricity

<p class="06Abstract"><span lang="EN-US">Maritime Natural Caves (MNCs) are coastal infrastructures that harness ocean wave energy to generate pneumatic power, which drives a turbo-generator to produce electricity. This study focuses on the use of MNCs for wave energy extraction, with the Cidade-Velha MNC identified as the most promising one. The research involved constructing several Wells turbines with varying rotor blade orientations (β) to analyze their impact on energy production during high-energy conditions within the MNC. The characteristic curves of the turbines show a linear trend, with determination coefficients exceeding 75%. However, non-linear behavior was observed at higher flow rates probably due to boundary layer separation on the turbine blades. Quadratic data approximations provided a better fit, with determination coefficients over 93%. Among the turbines tested, the one with a 15° blade inclination (β=15°) was more effective under extreme conditions, while the turbine with a 0° inclination (β=0°) was less suitable. Despite its better performance in high-energy conditions, the turbine with β=15° encountered more start-up difficulties and longer downtime compared to the β=0° turbine, which performed better under low to moderate energy levels. The MNC demonstrated hysteresis, leading to significant inaccuracies in efficiency evaluations. Additionally, the turbines experienced operational issues at high rotational speeds. The initial attempt to use the MNC for household electricity generation revealed several challenges that need to be addressed before MNCs can be considered a reliable energy source.</span> <p class="06Abstract"><span lang="EN-US"><br /></span> <p class="06Abstract"><strong><span lang="EN-US">Received: 17 September 2024 </span></strong> <p class="06Abstract"><strong><span lang="EN-US">Accepted: 31 October 2024 </span></strong> <p class="06Abstract"><strong><span lang="EN-US">Published: 27 November 2024</span></strong>