12-11-2012, 01:42 PM
WAVE ENERGY CONVERTER
New Wave Energy Convertor REPORT.doc (Size: 273 KB / Downloads: 1,069)
INTRODUCTION
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.
TWO TYPES OF WAVE ENERGY CONVERTERS
A. 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.
Stator
The stator is made of laminated electrical steel, piled into one solid unit, The conductors are power cables with a circular cross-section and a conducting area of 16 mm2, insulated with a 1.1 mm PVC-layer, which adds up to an outer diameter of 7.2 mm. The coil winding is a three-phase winding with a slot per pole and phase ratio of 5/4. This winding configuration aims at minimizing the fluctuation in the output power caused by cogging. A three-phase LFM with a slot per pole and phase ratio equal to one is proposed as generator in the Archimedes Wave Swing.
Rotor
Two types of magnet fixation methods, surface mounting and burying magnets between pole efficiency and low material usage is desired. The electromagnetic efficiency includes hysteresis losses, eddy current losses and resistive losses. Furthermore, a low load angle is desired. A machine with inherently low load angle has better performance at both normal and transient conditions and is less affected by changing loads and varying frequencies. The four rotor concepts are simulated for different magnet dimensions and various pole widths. Output power, voltage and stator width are held constant in the simulation and the vertical length of the rotor is iterated to fulfill these conditions. Usage such as total magnet volume, stator steel.
Magnet dimensions
Different heights to width relations of the magnets have been investigated in order to seeif there is an optimum. The magnet volume of single magnet is kept constant and the electromagnetic efficiency and total magnet weight is plotted for different height to width relations of the magnets. As can be seen the electromagnetic efficiency is steadily increasing and the total magnet weight is decreasing with increasing magnet width for the surface mounted magnets. The pole width limits the magnet width and no optimum is reach for the surface mounted magnets. Only active power is converted
Wave Regeneration
In a system where a number of WEC-arrays are deployed over an ocean surface the “up wave” arrays will shadow the ones behind them, when there is a predominant wave direction in the same sense as the buoys instead the individual array as discussed,. However, this additional shadowing effect can be avoided through an ample distance between arrays, for regeneration of waves by the action of the wind. If the arrays are placed in straight rows perpendicular to a constant wind direction, as shown in Figure 2a, the necessary distances for wave regeneration can be calculated using a relation between the significant wave height, Hs, the wind speed, V, and the length of the fetch, F. A parameterization of this relation yields,
For a rectangular wave power plant, where the arrays are ordered side by side in long rows, as absorption by each buoy, a row of arrays will absorb 26% of the energy coming in over its width. This corresponds to a 14% attenuation of the wave height, neglecting array effects on wave period. An initial significant wave height of 2 m will thus be reduced to 1.7 m immediately behind the row.
FLOATING WAVE ENERGY EXTRACTER
Another variation of a wave energy converter, which uses the vertically exerted force of a wave, is a Floating wave energy extractor.
About the technology:
The floating wave energy extractor is also a method for the maximum exploitation of the wave energy and it is designed for distant offshore with very unstable sea surface. The system is consists of a rectangular shaped huge mass floating body supported by a large number of floating air columns. The air column’s extensions are connected to pistons. The pistons are placed its own cylinders and it can move up and down through the cylinders when the floating air columns moves with the up-down movements of the waves. The upper side of the cylinders has two valves. One to a high-pressure fluid pipe and it will open when the floating air column on crest. One valve is to the low-pressure fluid pipe it will open when the floating air column on the trough. The whole system is anchored to the sea bottom.
Working
When the wave moves through the floating air columns, it to oscillate the floating air columns. When some of the air columns (air columns that on the crest) move upward, the whole weight of the floating system will be supported through that air columns. Also, now some floating air columns (the air columns that on the trough) will move downward. As some of the air columns move upward, the pistons of those air columns to pressurize its corresponding cylinders and the hydraulic fluid inside of the cylinders rush to the high-pressure fluid pipe with high pressure (now the valves to the low-pressure fluid pipe will be closed). Since the whole of the high-pressure fluid pipes are interconnected, the net pressure will focus on the turbine and the turbine will rotate. As the floating air columns that on the trough move down ward because of the gravity, the valves to the high-pressure fluid pipe will be closed and the valves to the low-pressure fluid pipe (the low-pressure fluid pipes are also interconnected) will be open. Now the low-pressure fluid will enter to the cylinders and will be filled. As the turbine rotate, the generator connected to the turbine generates electricity.
CONCLUSION
Waves represent one of the most densely powered natural fluxes which can be directly used for renewable energy generation.Furthermore, it can have a relatively large utilization time as the power flux variations are attenuated when the waves are induced by winds which in turn originates from solar power. In this present scenario of injudicious use of natural resources wave energy will definitely play an important role in accounting for the future energy needs.