Forward component of FLProduces the thrust which drives the blade forward
Wave Diagram
Phase Velocity (c)
The rate at which the phase of the wave propagates in space
Wave energy and power (eqn)
A water particle whose mean position below the surface z moves in a circle of radius:
Wave number (k)
Oscillating water column diagram
Oscillating water column
Wave motion induces pressure changes beneath the column
Pressure changes cause the water level in the chamber to oscillate
Oscillating water level cause airflow changes in the chamber
Wells Turbine
Consists of aerofoils whose symmetry directs the air in the same direction -> allows turbine to power generator regardless of airflow direction
Water density
Water is 800 times denser than air
Why offshore
The waves on the open sea have great energy potential
Negligible environmental impacts
Three locations of wave energy converters
Shore
Near shore
Offshore
Shore downside
Nearer the coastline the average energy intensity of a wave decreases due to interaction with the seabed.
Offshore sdvantage
Greater power available in the waves
Factors in Placement (6)
Engineering challenges
Construction costs
Maintenance and/or installation costs
Transmission costs and losses
Environmental impacts
The scale of electricity production
Basic methods for converting wave energy
Fixed (TAPCHAN and OWC)
Floating (floating devices and wave profile devices)
Fixed WEC Devices
Fixed WEC devices are either built into the shoreline or fixed to the seabedÂ
The number of suitable sites is limited.
TAPCHAN Diagram
TAPCHAN
tapered channel systems
consist of a tapered channel feeding into a reservoir that is constructed on a cliff
The narrowing of the channel causes the waves to increase their amplitude (wave height) as they move towards the cliff face
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 a water turbine to generate electricity.
TAPCHAN Advantages
Low maintenance costs
Reliable
Power on demand
TAPCHAN Disadvantages
Not suitable for all costal regions
TAPCHAN suitable locations:
COnsistent waves
Good average wave energy
Tidal range less than 1m
Deep water near shore
Location for a reservoir
OWC Advantages
Air velocity can be increased by reducing channel cross sectional area
Floating WEC Devices
systems that are floating in the ocean, either close to shore or offshore
Types of floating WEC devices
Powerbuoy
Wave Profile WEC devices (The Whale device, Pelamis, Salter duck)
PowerBuoy Diagram
PowerBuoy
Mechanical power is obtained by floats making use of the motion of water
Float moves up and down with the water
An air turbine is run by the compressed air which in turn drives an electrical generator producing electricity
The generated electricity is then transmitted to the shore through an underwater cable.
Wave Profile Devices
They float on or near the sea surface and move in response to the shape water rather than just the vertical displacement of water
Mighty Whale Device
OWC based device for offshore operation
A 120 kW prototype with 3 OWCs in a row has been operating since 1998 1.5 km off Nansei Town, Japan at 40 m depth
Pelamis (Sea Snake)
The Pelamis is a semi-submerged, articulated structure composed of sections linked by hinged joints
The wave induced motion of these joints is resisted by hydraulic rams which pump high pressure oil through hydraulic motors via smoothing accumulators
The hydraulic motors drive electrical generators to produce electricity
Salter Duck
Generates electricity through the harmonic motion of the floating part of the device
The devices rise and fall according to the motion of the wave and electricity is generated through the motion.
Salter Duck working principle
The Duck rotates with a nodding motion as the wave passes. This motion pumps a hydraulic fluid that drives a hydraulic motor, which in turn, drives an electrical generator
Advantages of offshore wave energy (6)
Sea waves have high energy densities
Clean source of renewable energy
Natural seasonal variability of wave energy follows the electricity demand
Negligible land use demand
Secure energy in remote regions
Stimulate declining industries
Disadvantages of offshore wave energy (4)
The peak-to-average load ratio in the sea is very high and difficult to predict
The structural loading in extreme weather conditions may be as high as 100 times the average loading
High construction costs
Cost of electricity transmission from deep ocean sites