An Assessment of the Feasibility and Energy Potential of Subterranean Oscillating Water Column (OWC) Wave Energy Converters in Ireland
The Oscillating Water Column (OWC) wave energy converter is considered to be one of the most common concepts in use for wave energy capture. However it has yet to be demonstrated that energy can be extracted from ocean waves at an economic rate using OWC technology. This is predominantly due to the initial capital cost of the structure. Previous research has established that the approach of using a subterranean chamber for an OWC held considerable promise for the shoreline capture of ocean wave energy. This involves the implementation of underground technology to construct the chamber within an ocean facing cliff. This form of construction could potentially prove more economically viable than conventional methods of shoreline OWC manufacture. Previous research has also validated the design concepts of constructing an OWC within rock and proved that such a technique could produce acceptable hydrodynamic and pneumatic conversion efficiencies.
This study aims to contribute to information on the feasibility and energy potential of this OWC wave energy concept in Ireland. The methodology adopted to achieve this objective comprises four stages, (i) Site selection study, (ii) Site visit (iii) Wave climate modelling of the selected site, using DHI’s MIKE 21 Spectral Wave Model, and (iv) Hydrodynamic analysis of the subterranean OWC wave energy converter, using the boundary element method (BEM) code, WAMIT v6.4PC.
Loop Head, Co. Clare was selected as a result of the site evaluation process. Wave climate modelling of this site is being carried out to investigate the variation of wave energy around this headland and to determine the available wave energy resource where a subterranean OWC wave energy converter could potentially be located. A plan view of the Loop Head wave climate model can be seen in the attached figure. Hydrodynamic analysis of numerous chamber configurations has been initiated to assess performance and ultimately, will be used to estimate the annual energy production at Loop Head.
Artificial Reefs for coastal protection and enhanced surfing conditions
In the past, extensive modelling has been carried out on the effects of emergent and submerged breakwaters in the near-shore zone with regards to sediment transport. Recent developments in the geotextile industry have afforded new possibilities for shoreline protection. One of these possibilities is the use of Artificial Reefs for coastal protection. Artificial reefs work by inducing natural wave breaking over the reef which is located offshore, thus reducing wave energy in the near-shore zone and reducing sediment transport. This study aims to investigate these alternatives to traditional coastal protection methods by testing the efficacy of artificial reefs for shoreline protection. Furthermore the deliberate manipulation of reef shape is being investigated for proficiency in creating a controlled wave environment suitable for surfing. As part of an existing study within the group, extensive mathematical modelling is being carried out to approximate wave breaking, hydrodynamics and shoreline response to the presence of artificial reefs using DHI’s MIKE21 software suite (Figure - MIKE21 simulation of pocket beach with Artificial Reef).
Garrettstown Strand in County Cork in south-west Ireland is being modelled as a case study since it has been suffering from severe erosion which has become particularly acute in recent years. As one of the potential mitigation schemes under consideration, submerged breakwaters are being examined as one of the potential solutions to the beach erosion which include the idea of incorporating a recreational value to the coastal protection scheme in the form of surfing and other beach-based activities. This has involved a bathymetry survey of the bay being carried out and the analysis of the long term off-shore wave climate of the area. Different submerged breakwater geometric designs have then been developed to promote optimal plunging waves at a peel angle of 450. The theoretical affect of the submerged structure on the adjusted near-shore wave climate and littoral response was then modelled numerically at various different positions within the bay. The optimum position was thus defined in order to minimise the existing beach erosion and also to promote sand accretion. The results were compared against the ongoing effects of the current situation and also against other possible erosion mitigation schemes such as groynes and submerged breakwaters.
Project coordinator: Prof. Laurence Gill