Marine Renewables
Wave Energy
Waves are created by the interaction of winds with the sea surface, and possess both kinetic energy (in the forward movement of water) and potential energy (due to the amount of water displaced from the mean sea level). The highest concentration of wave energy occurs between 40 degrees and 60 degrees latitudes, in each hemisphere. This is due to the prevailing trade winds.
The power P (in W/m) in an idealized ocean (deep-water) wave is given by the following expression:
P = pg2H2T/(32*pi) watts per metre wave front
or approximately H2T kilowatts per metre wave front
where, |
p is the water density H is the wave height in metres (the vertical distance from wave trough to wave crest) T is the wave period in seconds |
Working Principles of Wave Power Devices
The major types of wave power generation technology are described below.
(a) Oscillating water column wave power device generates electricity from the wave-driven rise and fall of water in a cylindrical shaft or caisson. The rising and falling water column drives air out of and draws air into the shaft, which then turns an air-driven turbine and drives an electric generator to produce electricity. This type of system is also called pneumatic system.
Above: Working principle of an Oscillating Water Column Wave Energy Recovery Device
(b) A tapered channel (TAPCHAN) system for wave power generation consists of a tapered channel to channel and concentrate the waves into an elevated reservoir several metres above mean sea level. As the waves enter further into the tapered channel, their amplitudes (wave heights) increase as they approach the elevated reservoir. The water will eventually spill over the walls of the channel and into the elevated reservoir. The kinetic energy of the moving wave is converted into potential energy, as the water is stored in the reservoir. The stored water is then fed through Kaplan turbines to produce
TAPCHAN System
(c) A floating wave power devices employ the harmonic motion of the floating part of the device to produce energy. The rise and fall of the floating object according to the waves produce a motion that could generate electricity directly or drive a seabed mounted piston or hose pump, which in turn could operate a turbine and generator to produce electricity indirectly.
Above: PowerBuoy wave power device developed by Ocean Power Technologies
(d) The Pelamis Wave Energy Converter is a semi-submerged and floating, sea-snake-like structure made up of cylindrical steel sections linked by hinged joints, with each joint of the Pelamis containing a hydraulic pump. The wave-induced motion of the joints is resisted by hydraulic rams, which pump high-pressure oil through hydraulic motors via smoothing accumulators. The hydraulic motors then drive the generators to produce electricity. The machine is held in position by a mooring system, comprising of a combination of floats and weights which prevent the mooring cables becoming taut.
Above: Pelamis wave power device