Environmental Engineering Reference
In-Depth Information
Kingdom, and the United States. Quite a few pre-commercial ocean devices were
deployed. For example, a U.S. company, Ocean Power Technology, deployed one of
their 150-kW wave energy conversion (WEC) systems in Scotland in 2011 (Ocean
Power Technologies, 2011). An Irish company, Wavebob, tested a one-quarter model
in Galway Bay, Ireland, in 2006 (Wavebob, 2014). In Denmark, the half-scale 600-kW
Wavesta r
®
energy system was deployed at Hanstholm in 2009 (Wavestar, 2014), and
quarter- and half-size models of the Wave Dragon were tested at Nissum Bredning
in 2003 (Wave Dragon, 2014). Furthermore, international organizations, such as the
International Energy Agency and the International Electrotechnical Commission
(IEC), are heavily involved in the development of wave energy devices. In 2001, the
International Energy Agency established an Ocean Energy System Implementation
Agreement to facilitate the coordination of ocean energy studies between countries
(IEA, 2014). In 2007, the IEC established an Ocean Energy Technical Committee to
develop ocean energy standards (IEC, 2014).
In the early 1970s, the harnessing of wave power focused on using floating devices
such as Cockerell rafts (a wave power hydraulic device), Salter's duck (curved-cam-
like device that can capture 90% of waves for energy conversion), rectifiers (to con-
vert AC to DC electricity), and the clam (a floating, rigid, doughnut-shaped device
that converts wave energy to electrical energy). Wave energy converters can be clas-
sified in terms of their location: fixed to the seabed, generally in shallow water;
floating offshore in deep water; or tethered in intermediate depths. These floating
devices are not cost effective and significant mooring problems remain to be solved,
so current practice is to move closer to shore, sacrificing some energy. Fixed devices
do have several advantages, including (Tovey, 2005):
•
Easier maintenance
•
Easier to land on device
•
No mooring problems
•
Easier power transmission
•
Enhanced productivity
•
Better design life
Wave energy devices can be classified by means of their reaction system, but it is
often more instructive to discuss how they interact with the wave field. In this con-
text, each moving body may be labeled as either a displacer or a reactor:
•
A
displacer
is a body moved by the waves. It might be a buoyant vessel or a
mass of water. If buoyant, the displacer may pierce the surface of the waves
or be submerged.
•
A
reactor
is a body that provides reaction to the displacer. It could a body
fixed to the seabed, or the seabed itself. It could also be another structure or
mass that is not fixed but moves in such a way that reaction forces are cre-
ated (e.g., by moving by a different amount or at different times). A degree
of control over the forces acting on each body or acting between the bod-
ies (particularly stiffness and damping characteristics) is often required to
optimize the amount of energy captured.
