Marine Energy Introduction
The combination of grid-tied Marine Energy test centres and the visibly improved investor interest for marine energy technologies has meant that 2005 saw a leap of activity for those engaged in the design of marine energy converters. Portugal has agreed terms for its first grid-connected wave energy farm with Scotland's OPD. A number of island and coastal nations are awaiting the arrival of working devices on the market. Those countries that offer the best feed in tariffs for electricity derived from marine energy are proving most attractive for developers. The issue of grid connection and new interconnectors is likely to prove an important factor in where the early marine energy developments will be located.
Tidal Energy Devices
The first era of enthusiasm for tidal energy plants focused on large tidal barrage power stations and it was this work that has given birth to the hybrid concepts of artificial tidal lagoons and impoundments under discussion. Patents and prototypes of technologies aimed at extracting energy from the tidal currents, known as "tidal stream" are being reported globally. Companies from the UK and Scandinavia already have large prototypes in the water. Models include horizontal axis turbines (very similar to marinised wind turbines) fixed to towers buried in the seabed, to those designed to free stand on the seabed and harvest energy by means of hydro foils.
Wave Energy Devices
The ground breaking work of several Scottish teams over the last 20 years can be seen in much of the technology incorporated into today's new devices. Wavegen have successfully promoted the use of shore-based wave energy converters, their grid connected installation on Islay has led on to similar Oscillating Water Column (OWC) devices being considered for incorporation into future sea defences. Technologies first used in Salter's Duck can be identified in the sinuously articulated floating wave energy converter Pelamis, for which Pelamis Wave Power have taken orders for three 750kW devices from Portugal.
Additional to the currents caused by the tidal action, there are the much larger scale ocean current circulatory systems which mix the seas of all the oceans. These currents are driven by gradients in temperature and salinity levels and draw their energy from the extremes between the cold fresh water provided by the Polar Regions and the much warmer and more saline tropical seas which can absorb such large levels of solar radiation. These deep water currents offer reasonably predictable currents which could possibly be harvested once tidal stream technologies advance to provide cross over engineering concepts.
Ocean Thermal Energy Conversion
The mechanisms that drive the ocean's currents act like a slow motion natural heat pump. In tropical seas where there is much colder water available deep down, it is possible to replicate this natural system by pumping up the cooler water and using large heat exchangers to extract energy from the temperature extremes between the surface and the depths. One such OTEC scheme was built onshore in Hawaii and there are ambitious designs for large floating OTEC ships. Certainly, this technology offers great potential, especially where the additional synergies of using the high levels of nutrients contained in the rich cool deep water.