3 1. WAVESWaves are generated by wind passing over the sea: organized waves form from disorganized turbulence because wind pressure pushes down wave troughs and lifts up wave crests, the latter due to Bernoulli‘s principle.In general, large waves are more powerful.Wave size is determined by wind speed and fetch (the distance over which the wind excites the waves) and by the depth and topography of the seafloor (which can focus or disperse the energy of the waves). A given wind speed has a matching practical limit over which time or distance will not produce larger waves. This limit is called a "fully developed sea."
4 2. WAVE POWERWave power refers to the energy of ocean surface waves and the capture of that energy to do useful work- including electricity generation, desalination, and the pumping of water (into reservoirs). Wave power is a form of renewable energy. Though often co-mingled, wave power is distinct from the diurnal flux of tidal power and the steady gyre of ocean currents. Wave power generation is not a widely employed technology, and no commercial wave farm has yet been established
5 3. HOW IT WORKSThere are several methods of getting energy from waves, but one of the most effective works like a swimming pool wave machine in reverse. At a swimming pool, air is blown in and out of a chamber beside the pool, which makes the water outside bob up and down, causing waves. At a wave power station, the waves arriving cause the water in the chamber to rise and fall, which means that air is forced in and out of the hole in the top of the chamber.
6 4. OCEAN WAVE ENERGY TECHNOLOGIES A variety of technologies have been proposed to capture the energy from waves. Some of the more promising designs are undergoing demonstration testing at commercial scales.Wave technologies have been designed to be installed in nearshore, offshore, and far offshore locations. Offshore systems are situated in deep water, typically of more than 40 meters (131 feet).While all wave energy technologies are intended to be installed at or near the water's surface, they differ in their orientation to the waves with which they are interacting and in the manner in which they convert the energy of the waves into other energy forms, usually electricity. The following wave technologies have been the target of recent development.
7 Terminator devices extend perpendicular to the direction of wave travel and capture or reflect the power of the wave.Point Absorber Wave Energy FarmPoint absorberA point absorber is a floating structure with components that move relative to each other due to wave actionThe oscillating water column is a form of terminator in which water enters through a subsurface opening into a chamber with air trapped above it..Point Absorber Operation
8 "Wave Dragon" Prototype Overtopping Device Attenuators are long multisegment floating structures oriented parallel to the direction of the waves.Overtopping devices have reservoirs that are filled by incoming waves to levels above the average surrounding ocean.Attenuator Wave Energy DeviceSeagoing vessels capture the energy of offshore waves. These floating platforms create electricity by funneling waves through internal turbines and then back into the sea."Wave Dragon" Prototype Overtopping Device
9 MODERN TECHNOLOGYWave power devices are generally categorized by the method used to capture the energy of the waves. They can also be categorized by location and power take-off system. Method types are point absorber or buoy; surfacing following or attenuator terminator, lining perpendicular to wave propagation; oscillating water column; and overtopping. Locations are shoreline, nearshore and offshore. Types of power take-off include: hydraulic ram, elastomeric hose pump, pump-to-shore, hydroelectric turbine, air turbine and linear electrical generator. Some of these designs incorporate parabolic reflectors as a means of increasing the wave energy at the point of capture.
10 CURRENT TECHNOLOGY According to the DTI, there are three types of wave energy collector. These are: a. Buoyant Moored Devicb. Hinged Contour Device c. Oscillating Water Column
11 Buoyant Moored DeviceThis type of device floats on the surface of the water or below it. It is moored to the seabed by either a taught or loose mooring system. One example of this type of device will be discussed, the Edinburgh or Salter Duck. The Duck team is led by Professor Salter at Edinburgh University.The Duck is shown in the figure below. Ducks work by independently rotating about a long linkage; this maintains its stability by out spanning wave crests. The front edge of the duck matches the wave particle motion. In moderate seas, the more cylindrical back portion creates no stern waves but when the weather is bad these parts shed energy through wave making to the rear. The device requires a depth of at least 80 metres and uses a system of weights and floats to give almost constant tension in the mooring cables.
12 b. Hinged Contour Device This type of device follows the motion of the waves; it creates power using the motion at the joints. It is commonly moored slackly to hold it in place. One example of this type of device is the Pelamis WEC that is being developed by Ocean Power Delivery.As the Pelamis moves with the waves, the motion is resisted at the joints by hydraulic rams that pump high-pressure oil through hydraulic motors via smoothing accumulators. These motors are used to drive generators to create power. It has been said that a 750kW device would be 150m long and 3.5m in diameter and comprise five sections.
13 c. Oscillating Water Column (OWC) This method of generating power from the tide works by using a column of water as a piston to pump air and drive a turbine to generate power. This type of device can be fixed to the seabed or installed on shore.In Scotland, the Government awarded three wave energy projects under the Scottish Renewables Obligation. Only one of these projects has been realised and is generating power in Scotland as this pack is being written, this is the LIMPET 500 on the Island of Islay of the west coast, enabling the Island to take a step towards becoming self sufficient in renewable energy.
14 OCEAN WAVE POWER GENERATOR A while back, a Discover Circuits visitor wanted a simply way to demonstrate how electricity could be generated from the up and down movement of ocean waves. The system was to be part of a science fair project, showing different renewable energy sources. I gave this some thought and came up with the system shown below. It uses a simple plastic foam float attached to a lever arm, which is connected to the shaft of an inexpensive stepper motor, available fromWhen properly mounted in a tank of water, the motion of a wave in the tank causes the shaft of the stepper motor to move. That movement produces enough electricity to turn on the visible red LED.
15 ISLAY WAVE POWER STATION The Islay Wave Power Station will provide 0.5MW of electricity for the island of Islay's grid - enough to power around 500 homes. Known as LIMPET 500 (Land Installed Marine Powered Energy Transformer), it was designed and build by Wavegen and Queen's University, Belfast, with funding from the EU. Without getting into the technical details, waves enter a concrete capture chamber which is set into an excavated rock face on the island. As water enters and leaves the chamber with the arrival of each new wave, the pressure of the air within the chamber increases and decreases. It is this oscillation of the air pressure within the chamber which draws air in or pushes air out of the chamber passing through the turbine. Whether air is being forced through the turbine, or drawn back into the chamber through the turbine, electricity is generated.
16 5. POTENTIALGood wave power locations have a flux of about 50 kilowatts per meter of shoreline. Capturing 20 percent of this, or 10 kilowatts per meter, is plausible. Assuming very large scale deployment of (and investment in) wave power technology, coverage of 5000 kilometers of shoreline (worldwide) is plausible. Therefore, the potential for shoreline-based wave power is about 50 gigawatts. Deep water wave power resources are truly enormous, but perhaps impractical to capture.
17 These are some of the challenges to deploying wave power devices: Efficiently converting wave motion into electricity; generally speaking, wave power is available in low-speed, high forces, and the motion of forces is not in a single direction.2. Constructing devices that can survive storm damage and saltwater corrosion; likely sources of failure include seized bearings, broken welds, and snapped mooring lines.3. High total cost of electricity;wave power will only be competitive when the total cost of generation is reduced. The total cost includes the primary converter, the power takeoff system, the mooring system, installation & maintenance cost, and electricity delivery costs.
18 7. ADVANTAGES The energy is free - no fuel needed, no waste produced; Not expensive to operate and maintain;Can produce a great deal of energy.
19 8. DISADVANTAGESDepends on the waves - sometimes you'll get loads of energy, sometimes nothing.2. Needs a suitable site, where waves are consistently strong.3. Some designs are noisy.4. Must be able to withstand very rough weather.