Home' Ships and Shipping : June 2011 Contents earth's rotation and thermal layers in the oceans provide steady
current flows. Both can be harvested to provide substantial
amounts of energy.
The use of water power is not new. Waterwheels, using the
gravitational effects of streams, have been around since the First
Century BC. Barrage power generation dates back to before the
1920s. But the technology that is in place today and which offers
promise tomorrow is a far cry, technologically, from that. The
world's oceans contain more than 5,000 times the current global
total energy consumption, rated at 100 Petawatt hours or 100
million Terawatt hours. So there is much to play for.
In 2008, Strangford Lough in Northern Ireland became home to
the birth of a new industry, as the world's first commercial tidal
power station was installed in the narrows that separate the lake
from the Irish Sea. Water flows at speeds up to four metres per
second (m/s), generating 1.2 Megawatts (MW), enough to power
around 1,000 homes.
Twin 43-metre-diameter rotors generate electricity once the tide
runs faster than one metre per second. At maximum speed, the tips
move at around 12m/s. The two rotating blades turn at 14
revolutions per minute and drive the generators via gears. The
rotors and generators can be raised and lowered on the central
three-metre-diameter supporting pile for inspection and
maintenance. Future plans include the installation of more
turbines to provide a power "farm", as yet unspecified.
US-based Verdant Power uses five-metre-diameter, three-bladed
turbines to generate up to 70 Megawatt hours (MWh) of electricity
from New York's East River and, in 2009 was the world's first
grid-connected array of tidal turbines. Future plans include the
Cornwall River Energy Project in Ontario Canada, which will
generate an estimated 15MW of power supply locally.
Britain' Lunar Energy, has partnered with Korean Midland
Power Co (KOMIPO), to create a 300-turbine field in the Wando
Hoenggan Water Way off the South Korean coast. The plant plans
to provide 300MW to by December 2015. Each 1MW unit has a
turbine diameter of 11.5 m and a fully ballasted weight in excess of
2500 metric tonnes (mt).
The UK's Atlantis Resources has identified that, in the UK, there
is 18TWh/year of technically extractable tidal current resource, of
which 40 percent is concentrated in the far north of Scotland
(Pentland Firth and Orkney Islands). The challenge remains the
remoteness from consumers, although it is conceivable that, in
future, energy hungry industries will move to remote locations
with potential energy surplus. The Atlantis designs are based on
horizontal axis turbines featuring a twin rotor set with fixed pitch
blades and are rated at 2.6m/s with output up to 2MW.
Other designs feature ducted horizontal axis turbines with
mono-directional blades for use in river environments and
bi-directional blades in diurnal tidal locations.
A shallow water turbine design is in operation in San Remo,
Victoria, Australia, which has been grid connected. The turbine
uses "Aquafoils" to capture momentum from the flow of water to
drive a chain perpendicular to the flow. This design can withstand
water flow containing significant debris.
In an alternative configuration, the University of Oxford, UK
has developed a concept based on biaxial turbines. This technology
is proven for small wind turbines, typically mounted vertically on
buildings. It is particularly good at capturing wind from any
direction, so the same principle applies to sea currents.
Tidal Barrages also offer huge potential. The Tidal Power Plant
at La Rance in Brittany, France, is the world's only large scale
commercial tidal station, developing 240MW over 40 years with
no mechanical failures. The barrage is 330m long, the tide up to
13.5m (8m average) entering a basin of 22km2. Twenty-four bulb
type turbine generators of 5.35-metres-diameter, providing up to
10MW each, generate 600 million kWh annually or four percent of
the homes in Brittany.
The UK's shelved Severn Barrage project concept would involve
construction of a 16km dam between England and Wales. With a
tidal range up to 14 metres, this would be the world's currently
largest renewable energy project. The plan provides for 214 ten MW
turbines, generating up to 8.6 Gigawatts (GW) peak (2GW mean).
This would generate five to six percent of current electricity usage
in England and Wales, the equivalent of three nuclear or eight coal
power stations and providing a reduction in carbon emissions of 16
million tonnes or three percent. It is hard to imagine with such
opportunities, that the Severn Barrage will remain mothballed
forever, but many environmental challenges will need to be
addressed for the project to succeed.
Another conceptual design involves the capture of steady
currents. In the proposed hydrokinetic energy transfer system, the
flow of water current drives rotating turbine blades. Rotational
speed is increased through a gearbox, which drives high-pressure
fluid pumps. The high-pressure fluid is transported though flexible
tubes to a larger pipe and then on to an onshore hydroelectric
Continued next month
* James Ashworth is chairman of the joint branch of RINA and
Verdant Power's 3-blade turbines generate 70 MWh of electricity from New
York's East River
"Aquafoils" are used in shallow water with high levels of debris.
The Tidal Power Plant at La Rance has generated 240MW over 40 years with
no mechanical failures.
SHIPS AND SHIPPING June 2011 17
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