Abstract
Sustainable and renewable energy resources have gained interest the past decades, as a result of the increasing energy demand, the shrinking fossil fuel reserves and the climate change. The need to reduce greenhouse gas emissions has led to measures that are being taken at European level, as well as by Member States at national level, so that the EU succeeds in meeting its targets under the Kyoto Protocol and the "20/20/20" objectives.
Ocean wave energy is one of the intensively developing renewable energy resources with great potential. Energy from ocean waves can be utilized by installing Wave Energy Converters (abbreviated as WECs) in the sea, which are devices that convert the kinetic and/or potential energy of waves into electricity. Many concepts of WECs have already been developed, mainly distinguished based on the conversion principle, in (i) oscillating water columns and wave-activated bodies, which oscillate under incident waves, and (ii) overtopping devices, which capture the overtopped waves in a basin above sea level that creates a hydraulic head.
Most importantly, in order to extract a considerable amount of energy at a specific site location, and to make the commercial exploitation of wave energy possible, installation of large numbers of WECs (e.g. tens of WECs simultaneously) will be required. The WECs will have to be arranged in an array (or a farm or park) using a particular geometric layout. However, power production of the array may be smaller or larger than the sum of the power produced by the equivalent number of individual WECs, due to hydrodynamic interactions between the WECs within an array (so-called intra-array interactions or park effect). Moreover, as a result of the large number of WECs within an array, usually wave height attenuation is observed numerically and in scale model experiments with small WEC arrays. This wave height dissipation is observed mostly between the WEC array installation site and a downwave location, e.g. the shoreline (so-called extra-array effects). These wave field modifications can influence neighbouring activities in the sea, other marine (energy) projects, coastal eco-systems and even the coastline and the coastal defence conditions and parameters.
Therefore, an accurate understanding is required of the WEC array effects, which consist of the intra-array interactions between WECs in a wave farm and the extra-array effects on the environment. With this understanding, the optimal geometric layout of the WEC array can be determined, changes to wave conditions can be quantified and ultimately the cost of energy will be reduced significantly.