A Helicopter View of the Special Issue on Wave Energy Converters

Abstract

This paper intends to provide the reader with an overview of the Special Issue on Wave Energy Converters. Through 16 contributions from authors of 10 different countries, a number of key topics have been tackled, including resource assessment, engineering design, and financial analysis. As a whole, the Special Issue forms an interesting and helpful compendium on the state of the art of wave energy extraction and exploitation.Keywords: Wave Energy Converters; resource assessment; feasibility study; engineering design Wave Energy (WE) has the potential to be a valuable contributor to the renewable energy mix, as it is abundant, inexhaustible, and relatively well predictable compared to other sources. Accordingly, it has aroused considerable interest over the last twenty years and more than 1000 Wave Energy Converters (WECs) have been patented worldwide.Despite using a wide specter of variants, the working principles of WECs can be conveniently categorized into three groups, namely the Oscillating Water Column (OWC), Wave Activated Bodies (WAB), and OverTopping Devices (OTD). In the OWC technology, a cushion of air is trapped within a partly submerged chamber, where the water level rises and falls with the waves. The oscillating motion forces the air to pass through a turbine, which rotates in the same direction irrespective of the direction of flow. WABs exploit the relative motion of the different parts of the device; hydraulic systems are generally employed to compress oil, air, or water, which are then used to drive a generator. In the OTDs, a sloping plate leads the waves to overtop into a reservoir and the energy is extracted via a turbine that works with small head differences (below 3 m) and large flow volumes.In spite of the large body of work already carried out, WE is still far from being a real competitor of wind and photovoltaic energy, which are now commercially viable alternatives to fossil fuels. In view of this, the following research items deserve greater attention to speed up the development path:(a) Assessment of the available and exploitable resources; (b) New technical solutions to enhance the performance of the devices; (c) Development of engineering tools for reliable technical and economical design; (d) Analysis of the device impact on the marine environment; (e) Development of criteria for optimization of the projects and feasibility analysis; (f) Development of new technologies. This Special Issue includes 16 papers from authors of 10 different countries, which provide the reader with food for thought on each of these topics.