Abstract
The growing interest in renewable energy depends on the perceived risks of using fossil fuels. In recent years many resources are focused in the renewable energy field such as solar, wind and ocean energy. In this thesis I will focus on energy harvesting from ocean waves, one of the most promising alternative energy source. In the literature, devices with power take off (PTO) systems employing a combination of electromechanical generators and hydraulic systems have been proposed, however these PTOs do not adapt easily to the sea environment and sea frequency. Current wave energy converters (WEC) exhibit a number of technical limitations such as: 1) large number of heavy and expensive components; 2) complex architecture.
This thesis introduces and evaluates the performance of a novel concept of point absorber converter. The new device (called STEWEC: STEwart Wave Energy Converter) involves the use of a Stewart platform equipped with Dielectric Elastomer Generators (DEGs) as a PTO system. It is formed by a cylindrical buoy, which represents the mobile part, connected to a fixed submerged Y-shaped structure by six hollow cylinders, each with a mobile inner axis. The relative movement between the two components of the cylinder deforms a stack of dielectric elastomer membranes connecting the cylinder to the inner rod. Each membrane undergoes an electromechanical cycle due to the sea motion converting mechanical to electrical energy. The performance analysis of the system has been assessed mainly considering the motions of heaving, surging and pitching.
This study describes the principle of operation of the entire innovative system, the workspace and the nonlinear out-of-plane deformation of the DEG. Compared to the current PTO systems, the use of DEGs entail substantial advantages such as i) large energy densities, ii) low cost, iii) high energy conversion efficiency that is independent of sea wave period, iv) easiness of manufacturing, and v) silent operation. The work evaluates the energy generated in common Mediterranean sea conditions for a STEWEC with a buoy of 5 m in diameter.
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