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
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.