Environmental Engineering Reference
In-Depth Information
Marine Energy Centre on the Orkneys in Scotland, and there are plans for a version to be
installed in Alderney in the English Channel.
Although there may be advantages with ducted systems or complex annular rim systems,
these configurations have to use two-way turbines if they are to extract power from all four
tidal movements, which may increase costs and reduce their efficiency. It may be easier to
have rotors which can be turned 180 degrees to face the changed tidal flow direction, as with
MCT's Seaflow and Swansea University's 350kW Swanturbine propeller unit. SMD
Hydrovisions' twin rotor 500kW 'Tidel' device is held mid stream by tethers between a
floating pontoon and an anchor, so it can swivel through 180 degree when the tide changes
direction .
However there may also be cost attractions in having fixed units mounted on the sea bed,
as with Tidal Hydraulic Generator Ltd's rotor array, Tidal Generation's 500kW sea-bed
mounted propeller-type prototype, and Robert Gordon University's 150kW Sea Snail, which
has a propeller unit held in place on the sea bed by hydroplanes.
As can be seen, horizontal-axis propeller-type systems dominate. So far, despite the
attraction of being able to operate multi-directionally, on both tidal flows and ebbs, free
standing vertical-axis designs have not been favoured. However, vertical-axis rotors have
been used in the sea bed mounted fixed-duct Proteus system developed by Neptune
Renewables and the University of Hull, for use in shallow water.
Rather than using vertical or horizontal axis rotors, another approach is to make use of
hydroplanes designed to move up and down in the tidal flow. This idea was developed by The
Engineering Business in Northumbria, with a 150kW Stingray prototype tested in the
Shetlands Isles in Scotland in 2002. Subsequently, an oscillating hydroplane system called
Pulse Tidal has been developed and tested at the University of Hull, and a 100kW prototype
is being tested in the Humber estuary.
It should be clear from the sample above that many new ideas are being explored in the
UK. Given the it has the largest tidal stream resource in the country, it is not surprising that
Scotland has played a major role. Orkney- based Scotrenewables is testing a free-floating
rotor, and Tidal Stream have developed a cantilevered multi-turbine 'Semi-Submerged
Turbine' system, which allows the rotor blades to be swivelled out of the water for
maintenance. It is designed for use in the Pentand Firth. Another Scottish company have
developed the StarTider, a novel multi-rotor concept, with arrays of rotors mounted on
common axles. In addition, a Scottish consortium has developed the Tidal Delay system,
with a turbine which feeds power to a heat store, which is used to raise steam for continuous
power generation. That opens up a new approach: a system that can directly compensate for
the cyclic availability of tidal energy.
Tidal Current Turbines around the World
There are many tidal current turbine projects underway around the world, in
North
America
in particular. For example, six of Verdant Powers three bladed tidal turbines have
been on test in New York City's East River near Roosevelt Island, as part of a 10MW $7m
project, and the Massachusetts Tidal Energy Company is looking at the possibility of
installing up to 150 2MW devices at Vineyard Sound on the New England coast. Meanwhile,
Ocean Renewable Power Company is deploying its OCGen tidal turbine in Eastport, Maine.
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