Wave Energy Converter

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We know that our earth is made up of water and oceans will never run out of waves it is important to extract this wave energy as alternative source of energy since the fossil fuels are becoming extinct and if it continues like this then it is definite that everything in one or the other day therefore it is very much important to think of the alternative sources of energy.
??????????? Here let us consider the device (OEC) that extracts the ocean wave energy. Generally there are three devices used they are

  • Oscillating water column
  • Ramped surge device
  • Nodding float

?Out of these three devices the Oscillating water column is the one which extracts the most power. So in this paper we are describing the OWC?s design, material required and the procedure followed.
Oscillating water columns moves water up and down inside a vertical cylinder when the waves pass by.  The oscillating water column is one of the most successful ocean wave energy converters.  They are the most modern wave energy converters and they are also known as OWC.  The water moving up and down inside acts like a piston inside a cylinder, moving the air forward and back through a turbine connected to a generator.  The air inside can only moves one direction at a time through the machine.  OWC are built in many different shapes, sizes, and designs.  Large ones are anchored out at sea in the ocean swells.  Medium ones are placed between the shore and far of the coast.  Some are even built on shore in skinny tapered channels that utilize the wave power to its full potential.

The WEC is a new, highly efficient technology that harnesses the immense, renewable energy contained in ocean waves. Its unique ability to extract and convert energy from both the rising and falling of waves represents a technological breakthrough.

A wave energy conversion apparatus comprises at least two devices, each comprising a surface float , at least one of the surface floats being rigidly attached to a submerged body . The movement between the at least two devices preferably effects an energy generation which is harnessed by the linkages.

The apparatus may also include mooring systems that maintain the complete apparatus in a position that is consistent with statutory requirements and not significantly inhibit its efficient operation.

Today more than 80 per cent of the world?s electric power production comes from fossil-fuelled plants. As the demand for electricity is forecasted to increase, there is an urgent need to find new methods to extract electric energy from renewable sources. Renewable electric energy supply is today one of the highest priorities in many parts of the world.
The Kyoto declaration 1997 and the last agreement at Marrakech 2002 are significant proof of this. Both the EU and the US have set their targets on future greenhouse emissions. Ocean waves represent a vast unexplored source of renewable energy. The wave energy potential in the EU has been estimated conservatively as 120?190 TWh/year offshore and an additional 34?46 TWh/year at near shore locations.
However, these estimations depend on assumptions of technology and energy cost. The actual resource could be a magnitude larger. In any case, it will be a challenging task to convert the vast energies in the ocean waves into electric energy. When approaching sustainable electric power production for the future, attention must be paid to the economical constraints.
The social, ecological and environmental impacts also need to be addressed. The need for research and investigations in this area must not be underestimated.
Today, several countries have national efforts within wave energy. The dominating countries in the development of wave power have so far been Denmark, India, Ireland, Japan, Norway, Portugal, The Netherlands, Australia, UK and USA.
The Swedish waters have been estimated to contain too little wave energy and the general opinion has been that it could not be motivated to do research on small 5?50 kW conversion devices. From the mid eighties the area has been considered difficult and uneconomical. Despite this, one of the more tested technologies has been developed in Sweden, the so-called IPS OWEC Buoy with a power of 100 kW or more. It is now further developed in the

 

USA and UK. The device is pumping water up and down, thereby driving a traditional generator.
The ocean wave?s behaviors have been the objectives for many investigations. However, apart from some tests, mechanical solutions with a traditional rotating generator (1,500 r.p.m.) have been predominant for the conversion. Most of the projects remain in the research stage, but a substantial number of plants have been deployed in the sea as demonstration schemes.
Several ways of classifying wave energy devices have been proposed, based on the energy extraction method, the size of the device and so on. A group of devices, classified as ?Point Absorbers?, appears to have the approach a performance where commercial exploitation is possible.
Available Energy from the ocean
Potential Energy:? PE = mh
Kinetic Energy:? KE = ? mv2 or ? mu2
Wave energy is proportional to wave length times wave height squared per wave length per unit of crest length
A four-foot (1.2 m), ten-second wave striking a coast expends more than 35, 000 HP per mile of coast.

3. TWO TYPES OF WAVE ENERGY CONVERTERS
3.1. Point absorber driven linear generator
??????? 3.2. Floating wave energy extractor

3.1. POINT ABSORBER DRIVEN LINEAR GENERATOR
Linear generators for wave power conversion have previously been considered but where concluded as impossible, since low velocities were believed to give too slow flux changes and thereby large and expensive electromagnetic converters. However, renewed activities have been reported from England and the Netherlands. Furthermore, recent electromagnetic simulations revile a neglected opportunity.
We work with a concept that combines Faraday?s law of induction, Newton?s laws of motion, and the even older principle of Archimedes with relative recent advancement in materials technology. In the spirit of minimizing mechanics by adapting generator to wave motion a design with a buoy absorbing ocean wave energy at the surface driving a linear generator at the sea floor is studied as in fig 1


The rising and falling of the waves off shore causes the buoy to move freely up and down.

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The resultant mechanical stroking drives the electrical generator.

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The generated AC power is converted into high voltage DC and transmitted ashore via an underwater power cable.???????????????

??????????????????????????????????? ??????????????SCHEMATIC DIAGRAM

 

Wave Energy Converter, Seminar Report Wave Energy Converter
Fig: 1.The wave energy converter (WEC) consists of a buoy coupled directly to the rotor of a linear generator by a rope. The tension of the rope is maintained with a spring pulling the rotor downwards. The rotor will move up and down at approximately the same speed as the wave. The linear generator has a uniquely low pole height and generates electricity at low wave amplitudes and slow wave speeds.?
Wave energy is directly converted into electricity by a linear generator consisting of insulated conductors; NdFeB permanent magnet and steel of different quality like electroplate and construction steel. Detailed modeling and simulations, as opposed to the traditional rule of thumb estimates, with a full account of design in full physics simulation gives detailed data on performance, as illustrated in Figure 2.
The buoy, which drives the linear generator, can be built from different materials having good resistance to corrosion and which can withstand high stress caused by the ocean waves and in different forms.
However, a cylindrical shape is preferred as a uni-directional point absorber is desired. Buoy dynamics and its behaviors during ocean wave exposure have been described elsewhere. A buoy connected with a stiff rope will drive the generator piston as the wave is rising. When the wave subsides a spring that has stored energy mechanically will drive the generator. Thus allowing for generation of electricity during both up and down travel.

When the flux from the piston circumvents its coils induction will occur in the generators stator, as the piston ideally moves up and down. Dependent on several parameters, generator design, wave shape, buoy size, weight, load and springs etc., different voltages with varying frequencies will be induced in the stator windings.
For open circuit conditions, the generator AC-voltage starts at zero, when the buoy is momentarily at rest in its lowest position, increases as the buoy accelerates towards the top of the wave, where it again reaches zero as the buoy stops.
For a relatively small wave energy converter (WEC) in the regime of 10?20 kW the buoy will have a diameter of three to five meters depending on wave climate and power rating. The buoy will have a weight in the regime of a few hundred kg to one metric ton depending on size and material. The buoy is connected to the generator with modern synthetic rope (possible of stretched polyethylene) trade names such as Dyneema and Spectra, with an optional cover for handling of fouling. Housing encloses the generator, as indicted in Figure 1. This could be made of concrete or steel with and integrated bottom concrete slab.
The total weight of the generator is in the range of a few tons whereas the bottom slab must have a weight surpassing the floatation of the buoy, in the range of 10 to 30 metric tons. The slab can be positioned directly at the bottom and kept in place by gravity.
Wave Energy Converter, Seminar Report Wave Energy ConverterWave Energy Converter, Seminar Report Wave Energy Converter
Fig2.An individual wave energy converter under deployment

 

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