Water Power Devices
Water Power Devices
Oscillating
Water Column
The Mighty Whale prototype
is 50 m long and 30 m wide and carries three air turbine generator
units:
one with a rated output of 50 kW + 10 kW and two of 30 kW.
After being towed to its mooring about 1.5 km from the mouth of Gokasho Bay, the Mighty Whale was anchored to the bottom of the sea (about 40 m deep) with six mooring lines; four lines on the seaward side and two on the lee side. The moorings are designed to withstand even typhoon strength wind and waves.
The Mighty Whale can be remotely controlled from on-shore. In the demonstration prototype, the energy produced is mostly used by the instruments carried on board; any surplus is used to charge a storage battery or, when this is fully charged, is used by a loading resistor. A safety valve protects the air turbines from stormy weather by shutting off the flow of air if the rotation speed of the turbines exceeds a predetermined level. So that it can be used in the future to improve water quality, the prototype is also equipped with an air compressor to provide aeration.
During the demonstration project, instruments aboard the Mighty Whale are monitoring the various factors that might affect its operation (see data in Tables 1, 2 and 3). The data are stored on board, but those relating to the safety of the Mighty Whale, and the operation of the monitoring equipment are transmitted to the on-shore control station.
The World's largest offshore
floating wave power device was launched in July 1998 by the Japan
Marine
Science and Technology Center. The full-scale prototype will be
demonstrated
and tested over a two-year period at the mouth of Gokasho Bay facing
the
Pacific Ocean.
The principle
The Mighty Whale converts
wave energy to electricity by using oscillating columns of water to
drive
air turbines. As shown in the figure above, waves flowing in and out of
the air chambers at the 'mouth' of the Mighty Whale make the water
level
in the chambers rise and fall. The water forces air into and out of the
chambers through nozzles on the tops of the chambers. The resulting
high-speed
air-flows rotate air turbines which drive the generators.
Because
it has absorbed and converted most of the energy in the wave, the
Mightly
Whale also creates calm sea space behind it, and this feature can be
utilised;
for example, to make areas suitable for fish farming and water sports.
The structure of the Mighty Whale itself can be used as a weather
monitoring
station, a temporary mooring for small vessels or a recreational
fishing
platform. As well as generating energy for use on-shore, the Mighty
Whale
can provide an intermediate energy source for aeration to improve water
quality.
The
Oscillating Water Column generates electricity in a two step process.
As
a wave enters the column, it forces the air in the column up the closed
column past a turbine, and increases the pressure within the column. As
the wave retreats, the air is drawn back past the turbine due to the
reduced
air pressure on the ocean side of turbine.
Much research is occurring
internationally to develop oscillating water columns which require less
stringent siting conditions, including the OSPREY and floating columns,
such as the Japanese Mighty Whale.
The Salter Duck, Clam,
Archimedes wave swing and other floating wave energy devices generate
electricity
through the harmonic motion of the floating part of the device, as
opposed
to fixed systems which use a fixed turbine which is powered by the
motion
of the wave. In these systems, the devices rise and fall according to
the
motion of the wave and electricity is generated through there motion.
The Salter Duck is able
to produce energy extremely efficiently, however its development was
stalled
during the 1980s due to a miscalculation in the cost of energy
production
by a factor of 10 and it has only been in recent years when the
technology
was reassessed and the error identified.
