Dielectric elastomers for wave energy harvesting

By Rocco Vertechy and Marco Fontana

Ocean-wave power is one of the most persistent, spatially-concentrated and predictable forms of intermittent renewable energies. The worldwide estimated resource amounts to nearly 3TW of yearly average power, and wave energy could cover a significant portion of the intermittent renewable energy mix in the future.

Harvesting energy from waves is very challenging and the sector is still immature, with only a few pre-commercial systems in operation around the world. Existing wave energy converters (WECs) are complex and costly to construct, install, and maintain. They are also vulnerable to the marine environment (experiencing large impulsive loads and corrosion) and show limited energy conversion efficiency.

In this context, dielectric elastomer generators (DEGs) could provide the technological breakthrough that is required to make wave energy exploitable. DEGs are deformable capacitors made with incompressible elastic dielectric layers and compliant electrodes that can be used to convert mechanical energy into electricity by variable capacitance electrostatic generation. Potential advantages of DEGs over conventional technologies are: large energy densities, direct-drive and cyclic operation, good and rate-independent efficiencies, good shock and corrosion resistance, silent operation, and moderate-to-low cost.

Vertechy and Fontana at University of Bologna investigated different concepts for DEG-based WECs and consider the polymeric oscillating water column (poly-OWC) the most promising. It performs well at capturing energy, is architecturally simple, and is applicable on- and off-shore, as well as along the shoreline (see Figure). The poly-OWC is an upgraded version of the turbogenerator-based OWC converter, which is currently the most studied and best developed type of WEC.

Their developed system was capable of harvesting energy with an average power of 670mW for water waves with 4.5cm height and 0.7Hz frequency with a wave-to-wire efficiency close to 20%. Energy density for the DEG was up to 109J/kg. (That corresponds to an equivalent full-scale system average power of 270kW for waves with 1.8m height and 9s period.) These results were confirmed by experiments on a floating 1:50 scale poly-OWC model in a 3D circular wave tank which also demonstrated the functionality of the system under irregular sea conditions.

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