a brief Synopsis
Athens, Greece 01/10/1994
DAEDALUS Informatics
10/9/2001*double click on empty space anywhere on page, to access pagetop
1. Introduction1.1. Historical Background
Probably the first ever patent for a wave energy device was filed in Paris in 1799 by the Girards, father and son. The translation by A. E. Hidden of Queen's University, Belfast, indicated that they envisaged a 'ship of the line' attached by a gigantic lever to the shore, with the oscillatory motion of the lever driving machinery directly or via pumps.
Leishman and Scobie 1811 have carefully documented the development of wave- powered devices from the first British patent in 1855 up to 1973, when there were already 340 patents.One of tile earliest and most informative papers on wave power was presented at a meeting of the American Society of Mechanical Engineers at San Francisco in 1892 by A. W. Stahl. Many wave energy devices were then described, although they were limited to floating structures or vertical flat vanes whose motions were transferred by ropes, levers, and racks and pinions to the "pumping or other suitable machinery". One device however consisted of a pair of floats whose relative angular motion was employed to operate a ratchet wheel, from which the power was transmitted to "any suitable mechanism". This idea was subsequently further developed by Masuda in Japan and by Wavepower Limited in the UK, as described later.
An early practical application of wave power in 1910 at Royan, near Bordeaux, France is described by Palme. M. Bochaux-Praceique supplied his house with 1 kW of light and power from a turbine, driven by air which was pumped by the oscillations of the sea water in a vertical bore hole in a cliff. This is claimed to be the first form of the device developed by Masuda in Japan from 1965 onwards and by the National Engineering laboratory more recently as a part of the UK wave energy prograrnme.
In 1947, Y. Masuda, developed a three float system at the Oceanographic Unit of the Japanese Defense Department. This utilized the relative angular motion between three floats, which has an overall length of one wavelength. The device produced 200W of power, but tests were abandoned after it had been overturned by a large wave. This device was further developed about 30 years later by Wavepower limited at Southampton, under the direction of Sir Christopher Cockerell, the inventor of the hovercraft.
In 1959 Walton Bott et al devised a scheme for the island of Mauritius in the Indian Ocean which made use of existing coral reefs. Breakers would fill the low head reservoir formed by the extended reefs and turbo-ram pumps would deliver the water to a high head reservoir and hence to the 5MW power station. The scheme was abandoned in 1966 as the price of oil decreased, but reviewed in 1976, when a 20 MW scheme appeared to be most viable.
In 1962, the AVCO Corporation, Research & Development Division, carried out tests at Buzzard's Bay, Massachusetts on a buoy with taut line mooring and an internal diaphragm which was deflected by the fluctuating pressure within the waves. The diaphragm operated a hydraulic piston and eventually about 1 watt was produced. The diaphragm was however ruptured during a hurricane.
By 1965, Masuda [941 had invented and the Ryokuseisha Corporation of Japan had patented and manufactured air-turbine buoys with an output of 60W. More than six hundred of these wave-powered navigation buoys have been in operation off Japan, USA, Canada, the Persian Gulf and the British isles. The principle of operation of this device was quite simple and robust. A container, open at the bottom is partially immersed in the water so that air is trapped in the upper part. The water in the container rises as a wave crest passes and causes air to be forced through valves at the top. The air passes through a turbine and so produces power. As the level of water falls in a trough, air is drawn through another set of valves and passes through the turbine in the original direction so continuing to develop power.
(see a model animation at: http://www.daedalus.gr/DAEI/PRODUCTS/RET/General/OWC/OWCsimulation2.htm)
In 1973, S. Salter of the Department of Mechanical Engineering at the University of Edinburgh initiated a series of experiments, first on a hinged plate and then on an oscillating cam shaped device usually referred to as a 'Nodding Duck'. The high efficiency of these ducks in model tests in the laboratory, combined with Stephen Salter's considerable engineering ability and conviction, undoubtedly played an important role in the formulation of the overall UK policy. Originally the duck oscillated back and forth about a 'spine: so that internal splines on the duck interacted with external splines on the spine to pump fluid which then drove hydraulic motors coupled to generators. In more recent designs gyroscopes are employed in the "beak" of the duck instead of the spline-pump system.
At EXPO 1970 at Osaka in Japan, Masuda demonstrated 500W air-turbine generator units. Also in 1970, the Power Systems Company of Boston, Massachusetts, USA successfully completed tests on a small-scale sea-bed device consisiting of diaphragms in concrete troughs. The pressure fluctuations caused hydraulic fluid to be pumped to an accumulator on the adjacent shoreline.
CONTEMPORARY R&D IN THE UK AND INTERNATIONAL DOMAIN
More contemporary designs and intensive R&D in wave energy was mostly carried out in UK. The government interest in wave energy and subsequent further development of the UK prograrnme, began formally in 1974 with the publication by the Central Policy Review Staff of a report entitled Energy Conservation. The recommendation in that report was for a full technological and economic appraisal to be put ill hand. This preliminary evaluation was initiated in February 1974 at the National Engineering Laboratory (NEL) at East Kilbride, Scotland by the newly-fommed DOE, and resulted in the report by Leishtman & Scobie which assessed the situation up to February 1975. Following this detailed study, the government announced, in April 1976, the start of a two-year study costing about 1 million BP to establish the feasibility of the large scale extraction of wave power and to provide information to enable the cost of further development to be estimated. Four conversion devices were chosen initially for this two year programme, whilst research into a number of problems common to all devices was undertaken. This inluded the collection and analysis of wave data, the effects of wave forces on structures, the methods of anchoring a d mooring, and power generation and transmission, as well as environmental effects.
By April 1977 encouraging progress persuaded the government to increase the funding to 2.5 million BP and in June 1978 an additional 2.9 million BP was allocated, so as to allow development work at 1/10th scale in open water and the testing of vital components at a larger scale. In September 1980, the Minister with responsibility for renewable energy announced in a Press Notice, that 3 million BP had been spent on wave energy in the previous year and that the allocation for this present year would be 3.5 to 4 million BP. New contracts were awarded to Edinburgh University for work on spines and tank operation, to Vickers Umited for work on oscillating water columns, to Sea Energy Associates and Lanchester Polytechnic for work on spines and mooring systems and to Sir Robert McAlpines for work on the Bristol Cylinder device. As these new contracts indicated, further work on fundamental problems was required as well as work on the new generation of devices.
After the success of Masuda's air-turbine buoys, the Japan Marine Science and Technology Center initiated further studies in 1974 on large-scale wave power generation using the oscillating water column principle, Masuda himself being the Chief Scientist of the Marine Technology Department. In 1976, a prototype wave power machine, KAIMEI, was constructed. This long ship-like structure was chosen for ease of construction and safety of mooring, and in 1977 three turbine-generator units, constructed by the Fuji Electric Company, were installed, and the first sea tests completed between July 1978 and April 1979. Each impulse-type turbine was 1.4m in diameter and the a.c. generators were rated at 125 kW at 900 rev/min. Peak outputs of 260 kW were achieved, but average values were reported to be lower (~40kW). In 1979 the UK, with Canada, Eire and the USA, accepted an offer by the Japanese to participate in a joint programme of tests under the auspices of the International Energy Agency. Eventually seven Japanese units and one UK unit were installed and Miyazaki and Masuda reported the results of these latest tests, which indicated that generator number 9 (Japanese) recorded a maximum output of 291 kW, exceeding all expectations.
Salter's work at Edinburgh University, already mentioned in section 1.5, received governmental approval first as an award from the Mechanical Engineering & Machine Tools Requirements Board and later, in 1976, as one of the four first-generation devices of the UK programme supported by the Department of Energy. Dr. N. W. Bellamy Lanchester Polytechnic, Coventry carried out preliminary trials on a string of model Salter Ducks at 1/50th scale on Draycote Reservoir, Coventry, and then in 1977 was involved with the NEL in the manufacture of a modified Edinburgh design at 1/10th scale for tests on Loch Ness. Although there were many teething troubles, requiring several modifications, the device weighing 25 tonnes and measuring 50m long was returned to the loch in September 1978 for testing. Meanwhile, Salter was more concerned with "small-scale laboratory tests with increasing levels of hydrodynamic realism". To this end a new wide tank was completed at Edinburgh by the end of 1977. The tank is 27 m X 11 m and has 89 independently-controlled wave makers along one of the longer sides. Suitable programming allows the creation of a variety of wave conditions closely representing real sea states. Since the start of 1979, Salter has also been concerned with the problems of full-scale design. Gyroscopes, in the beak of the duck, now absorb the torque and the precession motions of these gyros drive ring-cam pumps which pressurise oil, which in turn drives a swash plate motor coupled to the electrical generator. This system not only provides a completely sealed power unit, but, by using contra-rotating gyros, torques can be cancelled and the loading of the spine reduced.
The second of the first-generation devices supported by the DOE in 1976 was the Oscillating Water Column (OWC) unit, developed by the National Engineering Laboratory (NEL), East Kilbride, Scotland. Initial experiments described by Meir were concerned with achieving the optlmum shape and size, comparing two and three- dimensional devices, and assessing the performance of fixed and floating systems. Consideration was also given to the type of air turbine required and a Francis type recommended. In a later report, Moody explained that a free floating concrete structure was selected in 1978 because of its low material cost even though some slight loss of hydrodynamic performance compared with a steel structure resulted. The Francis turbine would drive an a.c. generator, but, after transforming and rectifying, transmission ashore would be via a high voltage d.c. link. Moody also indicated that a seabed mounted OWC in shallow water (~15m) was possible. These NEL devices were arranged in line to face the oncoming waves and were classified as'temminators'. An alternative arrangement in line and perpendicular to the line of the wave crests and with side openings has also been designed and tested as a model in the Edinburgh wave tank. This device, classified as an 'attenuator' would be at least 1.5 wavelengths long for cost effectiveness and productivity.
The third of the first generation of devices was the wave-contouring raft developed by Sir Christopher Cockerell since 1971. Early experimental work in 1974 by his company Wavepower Limited, indicated that high efficiencies could be obtained and in 1976 the DOE provided financial support. Although early models had up to seven sections with six hinge lines, it was soon found that there was little gain in power from having more than two hinge lines. In 1978, trials with a three raft system at 1/10th scale were conducted in the Solent with the centre raft of the three fully instrumented to measure the loads on the structure. An oil hydraulic system was employed with double-acting rams mounted above the hinges. The pressurized oil operated a piston-type motor which drove an automotive altemator. Based on the initial testing and experience a full-size system was designed. This consisted of a rear section 50m wide with two separate front sections each 25m wide connected along a single hinge line. The pump, extending fully across the raft and forming an integral part of the structure, was a double-acting oscillating vane type, with appropriate flap valves to allow sea water to be pumped to a reservoir on the rear raft section. The water then flowed from the reservoir through an axial flow Kaplan-type turbine and discharged to sea below the raft. The generator was rim-mounted to the turbine, although it was also possible to use a bulb-type unit. Two materials were considered for the rafts, steel and concrete, with the latter more durable, and with a better corrosion resistance, but heavier. In their paper of 1978, Cockerell, Platte & Comyns-Carr suggested a programme of manufacture commencing in 1990 with 50 rafts per year, and rising to 300 rafts per year in 1995. This programme would ensure a final installed capacity of about 19GW by 2020. However, the estimated cost of electricity produced by rafts has not yet been demonstrated to be competitive, so that future development by Wavepower Limited continues as a private enterprise.
The fourth first-generation device was the HRS Rectifier, initiated at the Hydraulics Research Station by R.C.H. Russell in 1975 and described by Rance. The Hydralics Research Station had first been involved with wave power in the late 1950s with the Mauritius scheme mentioned in section 1.5. The Rectifier is a large rectangular hollow caisson with a series of narrow compartments (<10m wide). The narrow front faces of alternative compartments are fitted with non-return flap valves, allowing water entry under the pressure of wave crests, whilst the intervening compartments have flap valves which open to allow discharge into a wave trough. To avoid valve closure due to wave reflections from the rear face of the device the front-toback dimension must be 4:1/4 wavelength (~25 to 50m). To avoid problems with torsional strength, buoyancy and mooring, a seabed location in about 30m of water was selected. Water flowed from the higher level in the inlet compartments through a Kaplan turbine to the outflow compartments. To inhibit the intrusion of sediment a new design was considered with a 1 in 3 ramp leading to the inlet chambers. This device was to be located in 15m of water and use a bulb-turbine. The difficulties in alligning the device to face the oncoming waves because of the sea-bed contours near the Hebrides and the size and hence cost per unit output have resulted in this scheme falling from favour. With the realisation in 1978 that the first generation of devices were costly, ETSU considered a number of second generation devices and three of these received support from the DOE.
One promising device, created by Professor French, at Lancaster University was funded initially by the Science Research Council and consisted of a long beam of prestressed concrete aligned perpendicular to the wave crests, and kept afloat by flexible air bags attached along the top of the beam. As a wave crest rises round a bag, the air is forced through non-retom valves into a high pressure duct, from which it flows through a turbine and then back during a wave trough to the bag, via non retum valves and a low pressure duct. This device was found to be close to cost competitiveness - less than 5p/kWh generated at 1980 prices compared with 2p/kWh for conventional means - and is now being developed by Lancaster University and by Wavepower Limited with DOE funding. The original design dimensions were 190m long, 6m beam and 8m deep, but a shorter length is now considered more economical. The air bags, made of flexible material 8 mm thick were arranged in two groups, either side of the central turbine housing; each group being formed by dividing tile continuous outer cover Irto about 10 separate bags by transverse membranes of the same material. Two single-stage air turbines with adjustable nozzle blades were employed; the nozzle blades being closed for high waves to give a low reaction stage and opened to give about 50% reaction for low waves.
Several of these Wave Energy Converters would be moored side-by-side with sufficient spacing to clear each other even under the most adverb conditions. Although waves would obviously pass through the gap between the devices, the absorption of energy from the water adjacent to the bags would cause some refraction and energy would be drawn in towards the converter to be absorbed towards the stem. Theoretical analysis by Budal and Ambli have indicated that this interaction between a row of absorbers may be expected and experiments by Budal have verified that the interaction factor increases linearly with the absorber spacing-to-wavelength ratio (d/L) up to pi as d/L approaches unity
The second of the new generation of devices was invented by a mathematician, Dr. D V. Evans of Bristol University early in 1978 and funded initially by the Science Research Council. Evans used the theory of Ogilvie, who predicted that when a submerged circular cylinder rotates on an eccentric axis parallel to its own, the waves produced on the free surface travel away from the cylinder in one direction only; this being the direction of motion of the top of the cylinder at the top of its orbit. Evans showed that the reverse was true, so that by loading the cylinder with appropriate spring and damper forces all the energy can be extracted from small amplitude regular incident waves, under tuned conditions, of the correct ratio of cylinder radius to wavelength. Experiments using Salter's test rig at Edinburgh confirmed the theory for small waves and clearly demonstrated the achievement of acceptable efficiencies over a reasonable range of wavelengths. In their experiments, the cylinder was positively buoyant and held down by cables passing round pulleys at the bottom of the wave tank. The cables were then attached to leaf springs above the surface so that the system resonated at wave frequency. The load on the cylinder was controlled by printed armature motors with integral tachometers. Strain gauges in the cables near to the cylinder measured the oscillating forces on the cylinder and together with measurements of cylinder velocity enabled the power absorption to be evaluated. In the original scheme, for power generation in real seas, the cables passed round torsionally-loaded drums at the sea bed and the power take off mechanism was included with the drum housing. Subsequently the mooring lines for the cylinder actuated a spring and damper system which pumped fluid to a turbogenerator.
The third new device was developed by the Design & Projects Division of Vickers Limited and described by Chester-Browne. The design considerations were the avoidance of the hostile air/water interface, the avoidance of mooring problems, and the selection of the simplest of generation mechanisms with the minimum of moving parts. The operating principle involved the use of a resonant oscillating water column, as suggested by Professor Sir James Lighthill, with flow rectification achieved by allowing some of the water in the column to overflow, at the top of each oscillation, into a reservoir which included a trapped act volume. The pressurized air then forced a controlled flow of the overspill water through a towhead hydraulic turbine which drove the generator. The device was located on the sea bed to meet the first two design conditions and had an upward facing inlet close enough to the surface to capture most of the wave energy. A model of the device was tested in a small wave tank at Lancaster University and at the resonant frequency had an efficiency of 93%.
Additional research and development in the UK has been supported by the Science Research Council (SRC) and has included an isolated hydro-pneumatic buoy system initiated by A. E. Hidden in 1973 at Belfast University, a stationary cylindrical converter developed by Professor J. O. Flower and Dr. G. F. Knott at the University of Sussex in 1977, a twin chamber air buoy devised by Professor J. G. Morley at Nottingham University and a triplate converter created by Dr. F. M. Parley at the Royal Military College of Science, Shrivenham in 1977.
The Belfast device, which is essentially an air-turbine buoy, was unique because the turbine, devised by Professor A. A. Wells, was seIf-rectifying. The blades of the turbine were symmetrical uncambered aerofoils which generated a lift force with a forward component whether the absolute air velocity is from above or below the axis of symmetry.The Sussex converter depends on the pressure wave which rotates around the circumference of a stationary immersed cylinder in synchronism with the regular incident waves. The original device consisted of a deformable layer of fluid-filled bags completely surrounding the cylinder, but eventually discrete pulsating sources and sinks were used, in the form of pistons fitted to two of three cylindrical openings arranged at 120o to each other and perpendicular to the main cylinder axis.
The Nottingham device, consisting of a twin chamber air buoy, was an interesting development of the Masuda air buoy, because the two chambers were designed to resonate at different frequencies, whilst pitching and heaving occurred at still different frequencies. It was thereby proposed to accommodate the range of frequencies encountered in a real sea.
The Triplate Converter employed the horizontal component of the wave motion. The two rear plates are fixed rigidly together half a wavelength apart and, as a result of a resonant wave between them, they do not move horizontally. The front plate, in three separate sections, was located one quarter wavelength in front of the rear pair, at the point of maximum horizontal motion, caused by the full reflection from the stationary rear pair. This horizontal motion has an.amplitude of oscillation twice that of the incident wave, but by suitable loading of the front plate the amplitude can be restored to that of the incident wave, with full energy absorption. In 1980, Dr. Parley proposed a Flexible Resonant Raft device, "Porpoise", consisting of a long slender flexible raft floating on the water and aligned with the direction of wave propagation. The thin elastic structure was designed to oscillate with waves and an internal pumping mechanism was proposed for power generation.
Another device in the same period, is the 'Clam' devised by Dr. Bellamy at Lanchester Polytechnic and developed by Sea Energy Associates, a consortium led by the Ready Mixed Concrete and Cawood groups and including Faitclough Construction whose associated company Howard Doris has built concrete structures for the offshore oil industry. The 'Clam' wave energy converter is a spine-based pneumatic terminator, as is the Salter Duck. Such devices have high capture efficiency and relatively low mooring forces. The Clam uses air as the working fluid. It consists of flaps attached at the bottom to a floating concrete spine with flexible air bags located between the two parts. Waves impinge on the flaps and the resultant oscillatory motion forces the entrapped air through seIf rectifying turbines. The air is contained in a closed circuit and returns to the bags when the flaps move out in wave troughs.
In the original concept a 10 MW generator unit consisted of 10 clam elements each 30 m long, with the rectangular spine 15 m deep by 10 m wide. A 2.5 MW unit, 180m X 10m X 8m, and displacing 18,000 tonnes could be built initially at a cost of 10 million BP and eventually it is envisaged that 320 units each 275m long could generate 2GW.Later inventions in the US include the Dam-Atoll device evolved at the Lockheed Rye Canyon Research Laboratory, Saugus, California in 1973 and demonstrated successfully as a 1/100th scale model on 1977. This device was patented by L. S. Win of Lockheed Corporation. The principle employed is that of wave refraction caused by change of water depth. Waves travel slower in shallower water, so that the direction of propagation (the ray path) is bent towards the shallower water. This phenomenon has long been observed with nature atolls where unidirectional waves bend around to approach the beaches of the atoll radially from all directions. Furthermore as the waler becomes shallower, the waves steepen and eventually break. Provided that the beach is correctly designed, the breakers are of the surger type and all the wave energy is converted to kinetic energy. In the Dam-Atoll, guide vanes direct this irregular radial motion of the breakers tangentiadly towards the perimeter of a vertical cylindrical chamber. This produces a vortex, which acts as a fluid flywheel, from which energy is continuously and steadily withdrawn by a turbine, which drives a generator.
The second US device was developed at the Scripps institution of Oceanography by Professor J. D. Isaacs and depends on the inertia interaction between two integrated systems, a buoy connected to a long vertical pipe filled with water. The water is accelerated upwards by the motion of the buoy and the low natural frequency of the water column ensures that the water continues to flow upwards, even as the buoy and pipe drop. This pressurizes a hydraulic reservoir, from which the water is allowed to flow steadily to a turbine.In Norway at the University of Trondheim a smalI group, including Mr. K. Buda and Dr. J. Falnes, have studied wave power devices theoreticalIy since 1973, and more recently have conducted supporting experiments on heaving buoys, whose motion was controlled for maximum power absorption. For regular waves, maximum power is obtained at resonance, when the force on the buoy and its velocity are always in phase. Experimentally this was achieved by adjusting the mass of the buoy and the counter-weight located on the opposite side of the power absorption pulley. For irregular waves, enhanced performance was achieved by locking the buoy by means of an electronically controlled electromagnet when the velocity was zero at the lowest and highest positions. The buoy was then subsequently released after one quarter of the natural period, which was arranged to be slightly less than the wave period. The buoy velocity was then in phase with the heave excitation force and approximately fulfilled the conditions for maximum power absorption. Budal et al. also experimentalIy confirmed the theoretical prediction of a beneficial interaction between point absorbers in a linear row. They defined an interaction factor q as the maximum power absorption, with interaction, divided by the maximum power absorption of an isolated buoy and showed that this increased linearly with the ratio of the spacing of the buoys to the wavelength (d/L) up to q = pi as d/L approached unity. They also demonstrated that 50% of the incident wave power may be absorbed by a single row of heaving buoys, whilst 100% capture efficiency can be achieved when a reflector is placed behind the buoys.
This work at Trondheim was supported by the Norwegian government to the extent of 0.4 million BP in 1980, whost a further 1 million BP was provided for work on the focusing of ocean swells by Dr. E. Mehlum and Mr. J. Stamnes at the Centra Institute for Industrial Research in Oslo.Work in other European countries and in Canada has also been described in the Proceedings of the First Symposium on Wave Energy Utilization held at Chalmers University of Technology, Gothenburg, Sweden in October-November 1979.
R&D DURING THE LAST DECADE
More recent development has produced third generation devices focused at both off-shore and coastal wave energy exploitation. Large scale offshore devices and small scale shoreline devices have been ocean tested. The Commission for Wave Power was established by Greenpeace to study how Scotland can pursue ocean wave generated electricity. The market is estimated at $32 billion in the United Kingdom and $800 billion worldwide -as a most conservative estimation. Progress has been substantial -yet still on explorative industrial stages- and concerned with both evolution and refinement of older principles and devices, along with development of new ones. Along line of the former category, the Salters lab, Edinburgh, has produced a reformed version of the original ‘Duck’ device first invented in the 70’s and has undergone continual development since. The latest ‘Duck’ consists of dozens of pistons fixed inside a cylinder which are pushed in and out by a ring of cams fixed to the moving float. This arrangement works by using highly specialised digital hydraulics which juggles the pressure inside many hydraulic circuits, turning the slow bi-directional movement of the float into the constant high speed rotation of a generator. The recent device has an efficiency of approximately 65% and is claimed to be more reliable than ever. Up to 24 ducks can be laid out in series along a concrete spine which will require a structure or the seabed as a mooring point.
Another concept continually developed by Stephen Salter, Technocean (Sweden) & OPT America, is the IPS Buoy .This concept consists of a float connected below to a weighted vertical tube. Inside the tube, which is open to the sea at both ends, is a piston which extends upwards to the float. Out at sea, the float and tube move up and down more vigorously than the piston and again the difference in motion is converted to electricity. Stephen Salter has found that by locating the buoys at an angle from the vertical can increase the machines efficiency. Sea trials of 10 x 30 kW Technocean devices is expected to be carried out in the Greek Island of Amorgos this year.
Further development in Edinburgh produced some third generation devices, along with improvements in 2nd generation devices. These are briefly described bellow:Bending Spine WPT-375 (designer Richard Yemm). This new concept unveiled his new design for the first time at the 1998 IWEC. The device generates electricity from differential motion from 10 buoyant tubes (stabilised by denser material attached to the underside) placed end to end to form a spine measuring 120 m long. Each device is expected to generate 375 kW of electricity and sea trials will be taking place in the near future to determine the overall effectiveness of such a system.
Osprey (designer ART, Inverness). This stand alone wave machine is a second generation device based on the original OSPREY design. The original OSPREY was a 2 MW device but was unfortunately wrecked by waves during 1995 when it was taken out on its first sea trial. Sea trials for the second generation machine will be carried out shortly.
Powerbuoy (ART, Inverness, Scotland). This device is expected on the market in the near future and the design cannot be revealed until patents are secured. The minimum depth required for deployment is 150 feet, while there is theoretically no maximum. It is reckoned that they can produce several megawatts of power, depending on location. One potential use for the Powerbuoy as suggested by Lee-Young (Oil & Gas Journal 19th October 1998) could be to provide power to oil and gas installations, where conventional gas or diesel generation would prove prohibitvely expensive.
The above principles have been recently carried under the the trademark of the UK based enterprise Wavegen, which is one of two wave energy companies participating in the Commission study under a 15 year British government contract. Wavegen's products use submerged turbine generators in the Limpet 500 0.5MW shoreline wave power station, the prefabricated steel caisson Osprey 2000 2MW near shore gravity anchored wave station deployed off Scotland in 1995, and the WOSP 3500 3.5MW near shore combined wave and wind station. All modules are designed to be installed individually, harnessing up to 3.5MW of energy, or in multiple units when larger quantities of electricity are required. Wind turbines can also be added to individual Osprey modules or to Limpet.
In Japan the 'Kaimei', 'BBDB' and the 'Mighty Whale' OWC devices have been undergoing continual evolution, yet on the same line of principles. Systems that demonstrate performance under grid connection, include a 350 kW Norwegian Tapered Channel plant and an Indian 150 kW oscillating water column. Japanese plants of 20, 30, 60 kW, and a 75 kW Scottish project put estimates of existing worldwide capacity at about 700 kW. A 500 KW OWC was also commissioned in the Azores island.
Other projects and variations of devices have been demonstrated at scales of hundreads of Watts and, up to several hundred kW. The United States has exhibited a slow responce, when compared to overseas projects in Norway, Denmark, Japan and the United Kingdom. Among notable exceptions have been Demi-Tek Inc., West Caldwell NJ, and Ocean Power Technologies, Princeton, NJ.
The former proposed a "Monitor" hybrid tide, wave, and wind electrical generation system in the ocean off Asbury Park. The invention is in service, August 1999, generating enough energy to light the boardwalk and Convention Hall.
The latter, has developed a "hydropiezoelectric" generator consisting of a slender panel tethered between a float and anchor. Panel models are 50’ long, 1’ wide, about 1’ thick, and consist of 50 to 100 thin sheets of a polyvinylidene fluoride trifluoroethylene copolymer. Electricity is generated from applied pressure as this piezoelectric material is stretched and released by rising and falling buoys. The inventors claim that an array of generators covering five square kilometers could supply electricity for 250,000 people at a cost of one to three cents per kWh, yet economic feasibility remains highly arguable. Japan's Penta-Ocean Construction Company Ltd. has contributed an undisclosed sum to fund the construction of a 1-kilowatt (kW) prototype in the Gulf of Mexico.Another USA based company, OWECO, suggests a principle resembling a "crackling carpet" for efficient sea anchorage while synergetically generating electricity on selected modules. Larry Bergren wave tank tested a wave energy device consisting of a floating buoy and a submerged plate. Both buoy and plate are vertical, straight, circular cylinders of equal radius connected to a power take-off mechanism.
In Greece, DAEDALUS Informatics has been developing a 3rd generation device, based on original R&D sourcing back to 1980s. The WECA device operates on a different than the OWC, defined as the CMW.
(see more info at:
http://www.daedalus.gr/DAEI/PRODUCTS/RET/General/RETWW2.html)A 30m 300KW platform is currently under pilot implementation, comprising a dual wave action principle incorporating the CMW principle along with OWC. Among considerable innovations is the employment of a radical power uptake mechanism for utilizations of the compressed air delivery, as well as a purpose built turbine for simultaneous capturing of off-shore wind potential, in tandem to the wave energy capture cycle.
The descriptions of the most important above-described devices, generally indicate major historic trends, and do not exhaust the great variety of potential designs and propositions offered so-far by the international community of researchers. The aim is to offer a concise introduction to the prevailing methods and scientific trends in the field of wave energy conversion techniques.
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