Renewable Energy Technology Assessments - Kauai Island Utility ...

Kaua’i Island Utility Cooperative
Renewable Energy Technology Assessments
3.0 Renewable Energy Technology
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Oscillating Water Column devices generate electricity from the wave-induced rise
and fall of a water column. The energy in this water column is normally extracted via a
moving air column using an air turbine. The main disadvantage with onshore devices is
that their construction is very dependent on local conditions and the available wave
power is lower at the shoreline; the advantage is that power transmission and
maintenance access are much simpler. The most developed example is Wavegen’s
500 kW LIMPET device operating since 2001.
Near-shore devices that can often be built around existing breakwater structures
include the Energetech device that uses a parabolic wall to focus wave energy onto the
collector and a Dennis-Auld turbine. In general, near-shore devices have the advantage
that they can access higher wave power without the need for extensive electricity
transmission, however (as with onshore devices) their shoreline location may affect their
adoption due to their visual appearance.
Overtopping tapered channel (TAPCHAN) devices generate electricity using
conventional low head hydropower turbines. A tapering channel concentrates and
funnels waves up the channel and increases their height so that they then spill into the
reservoir. As these are driven by water flowing from a reservoir back to the sea, this
device produces a more stable power output. Onshore devices normally need a tidal
range of less than 3 feet, deep water near the shore, and a reservoir location.
There is a much greater diversity of offshore WECS. The most common offshore
WECS are: 1) pneumatic devices, 2) overtopping devices, 3) float-based devices, 4)
moving body devices. In general, offshore devices can access the highest wave power,
but will require extensive power transmission as well as survivability/maintenance
requirements based on a more extreme environment.
Pneumatic devices generate electricity using air movement, often using a similar
OWC concept to that of shore-based devices. Overtopping devices generate electricity
using the same basic methodology as the shore-based versions. Float-based devices
generate electricity using the vertical motion of a float rising and falling with each wave.
The float motion is reacted against an anchor or other structure so that power can be
extracted. Moving body devices use a solid body moving in response to wave action to
generate electricity.
Float-based devices are the most common of all proposed designs. The welldeveloped
European designs that are still under development include the recent
combination of the IPS Buoy and the Swedish Hose Pump as the AquaBuOY, for which a
1 MW demonstration plant consisting of four 250kW buoys is planned for 2006 at Makah
Bay, WA. A fully submerged device is the Archimedes Wave Swing of which a 2 MW
prototype was successfully installed in Portugal in May 2004 and is now undergoing
21 March 2005 3-52 Black & Veatch