Abstract:
Extraction of sea wave energy' at the shore is cheap compared to doing it off shore
because offshore structures and operations are relatively costly. See waves gain
kinetic energy when the wave approaches the shore. This research aims at extracting
both kinetic energy and the potential energy of the sea wave at the shore.
A device called “Pendulor” was invented in Japan and has proven 40%-50% of
wave energy conversion efficiency at the sea of Muroran, Japan. The low waveT
energy density oceanic climate of Sri Lanka makes this device more preferred,
because of its high energy conversion capability. Only kinetic energy of the moving
wave could be extracted by such pendulors alone. In this research, a float has been
attached to the pendulor (flap) to extract potential energy of the wave, while the
kinetic energy is extracted by pendulor flap. The rotation of the heavy flap about its
hinge axis is a measure of extracted energy.
The device was tested at a location in the shore where the sea waves frequently
break. The flap was gradually loaded with extra weights in addition to its own
weight to check the device’s ability to extract energy from the waves. The
experiment also helps to prove the necessity of a float to extract potential energy
component of the breaking waves.' It was found that the device performed
satisfactorily extracting a significant amount of energy from the sea waves. At
certain instances the extracted energy exceeded lOkJ per wave. In average, the lm
long device extracted 100W of power from the sea waves.
It is clear that the combined profile of the flap and the float influences the energy
extraction. Therefore maximum energy extraction can be done by an optimized
profile which best suitable for extracting both kinetic & potential energies. The
other factors affecting the energy extraction are; water level with respect to axis of
the flap, back flow of the water and self weight of the flap.
It is obvious from the results that the wave energy can be extracted by this device
and can be used as the reciprocating shaft power. Since the waves occur
intermittently, additional devices are required to continuously use the energy
extracted by a torsionaly reciprocating shaft. The device can be used in arrays to
catch more and more waves so that the array could continuously produce useful
power.
