University of Bristol



WAVE TECHNOLOGIES

This section of the report will investigate a number of wave energy devices, looking at the technology, and the potential to contribute to the UK’s energy requirements. The devices investigated here range from being fully working commercial devices such as the LIMPET through to devices in demonstration schemes such as the Wave Dragon. Due the difference in how advanced the technology is the range of information available is very large. This makes direct comparisons of the devices extremely hard. Therefore this section of the report only aims to narrate the current status of the devises. And make general high level suggestions or prediction of how wave energy devices can and should be used in the future to contribute to the UK’s energy requirements.

Oscillating Water Columns

An OWC comprises of a partly submerged structure called the collector, which has an opening below the water level. The column collector contains a column of water that oscillates up and down with the waves. Above the water within the column is some trapped air. The column of water acts like a piston displacing a trapped air as it oscillates. The movement of the air causes a turbine to rotate. The turbine is coupled to a generator to produce electricity. A schematic of an OWC is shown bellow.

[pic]

Schematic of an OWC device. [1]

There are two main variations of the OWC today, the LIMPET and the OSPREY both will be discussed in the following sections.

Limpet

The LIMPET, shown in the figures below is a shoreline OWC device located on the island of Islay, off the west coast of Scotland. The Limpet was installed in the 2000, by Wavegen and is connected to the national grid. The acronym LIMPET stands for Land Installed Marine Powered Energy Transformer.

[pic]

The LIMPET. [2]

Technology

The LIMPET comprises of three distinct components:

• a shoreline oscillating water column collector

• a turbo generation unit

• and a control and monitoring station

The LIMPET has an inclined shoreline oscillating water column collector, inclined at an angle of 40 degrees from the horizontal. An inclined collector has two main advantages:

• It offers an easier path for water ingress resulting in less turbulence and lower energy loss.

• It also increases the water plane area of the column for a given chamber cross section. This permits the primary water column resonance, which is influenced by the ratio of the water plane area to the entry area, to be better coupled to the predominant period of the incoming wave [3].

The collector has a width of 21m, this width has been divided up into three columns because:

• As the width of a column increases there is an increased risk of transverse wave excitation within the column. Which would reduce the energy capture performance of the devise.

• The design of the roof of the collector capable of spanning 21m without additional supports would have been too expensive.

The collector is made from BISTEEL a sandwich of steel-concrete-steel. And has been described as containing a higher density of steel than a nuclear bunker [4]. This is all to cope with the hostile environment of the shoreline. To construct the collector they used a technique called protective excavation. This involves excavating an area for the collector just behind the cliff edge, but leaving a protective bund between the mouth of the collector and the sea. This bund is removed once the construction is complete. The figure below illustrates this technique.

[pic]

Protective excavation technique. [5]

The air exits the collector and enters the turbo generation unit through two 2.6m diameter openings in the back wall of the collector. The turbo generation unit consist of two 500kW counter rotating Wells turbines. Each turbine has a flywheel to smooth out the energy supply, as well as a sluice gate offer protection in stormy seas.

Current Situation

The LIMPET was estimated to have an average net electrical output of 202kW, however only 21kW where being outputted in 2002. This is due to a number of factors being lower than expected as illustrated in the table below [6]. The lower than expected output is not due to any fundamental problems with the concept, but instead with the modelling used to predict the output.

| |Initially expected |Actually recorded |

|Wave Power (kW/m) |20 |12 |

|Pneumatic Efficiency (%) |80 |64 |

|Turbine Efficiency (%) |60 |40 |

Despite the lower than initially expected power output the LIMPET has been haled as a success. It is important to remember that this is still a developing technology and the lesions learnt here will help improve the next generation of LIMPETs. And it is still believed that this technology has the capability to output approximately 200kW.

Osprey

The OSPREY is nearshore OWC device, designed by Wavegen. The acronym OSPREY stands for Ocean Swell Powered Renewable EnergY.

History

In 1995 a prototype device called OSPREY1 was launched, towed and installed near Dounreay in Scotland. The steel structure comprised of a 20m wide collector, located between two ballast tanks. The tanks focused the waves towards the collector. Unfortunately during the installation phase when the ballast tanks where being filled with sand, a three-meter swell developed. Due to the ballast tanks not being filled the structure failed, and OSPREY1 never became operational.

Current Situation

OSPREY2 is now under development, but its structure differs greatly from OSPREY1. OSPREY2 is made from concrete and the ballast tanks are built into the walls of the collector. Above the collector there will be two stacks each containing a 500kW counter rotating Wells turbine.

OWC UK Potential

In the UK shoreline resources have been estimated to be approximately 2TWh/yeat, and nearshore resources to be between 100-140TMh/year [9].

Below is a table showing the key data regarding both the LIMPET and the OSPREY [10]:

| |LIMPET |OSPREY |

|Wave Power (kW/m) |32 |30 |

|Annual Power Output (MWh) |2300 |4955 |

|Capital Cost (£k) |1400 |275 |

|Annual Operating Cost (£k) |29 |19 |

For the LIMPET the right geographic factors, i.e. the right combination of shoreline topography and geography, together with low tidal ranges and closeness to the grid, have been identified in 72 sites around the UK.

Overtopping

An overtopping device has three stages. The first stage is the absorption stage, this is where the wave energy is focused and the wave is allowed topple over the structure. The second stage is the storage stage, once the wave has toppled over the structure the water is stored in a reservoir above sea level. The third stage is the power take off stage the water is allowed to leave the reservoir via a hydro turbine. An example of an overtopping device is the Wave Dragon.

[pic]

Schematic of an overtopping device. [11]

Wave Dragon

Technology

The Wave Dragon, a floating overtopping device, can generate up to 7MW. A Wave Dragon power plant would be capable of producing 77MW, electricity for 60000 homes would consist of 11 individual devices [12]. Covering an area of 5.5km2. The mooring would be either by a concrete gravity base or a pile secured to the seabed. A Wave Dragon Prototype has been tested in Danish sea, a photo of which is shown in the figure bellow.

Current Situation

A Wave Dragon demonstration is due to be conducted off the Pembrokeshire Coast.. The demonstration will consist of one full size device. The Wave Dragon demonstration project will be in place for 3-5 years before the site is completely decommissioned.

UK Potential

This technology is very much in the early stages of development. But pending the results of the Wave Dragon demonstration project, an overtopping device has the potential to make a contribution to the UK energy requirements.

Point Absorbers

A point absorber is a device where one section moves with the waves, relative to a fixed sectioned, often secured by mooring. Point absorbers are often uni directional in their ability to pick up wave power, and they will only absorb energy in one plane of motion.

Salter Duck

Introduction

The Edinburgh Duck, or Salter Duck as it is commonly known, is one of the forerunners of wave power devices. It has been developed over many years by Stephen Salter and the Wave Energy Group at Edinburgh University. Falling under the category of a point absorber, the Duck faces into the direction of the waves and the “beak” moves up and down with the wave motion, while the “bottom” section remains stationary, anchored to the sea bed by a mooring device. An array of around 30 ducks would sit interconnected along a spine, all bobbing in differing phases. Since its conception in the 1970s the Duck has undergone various alterations in design and this report will look at some of the technical alterations between the 1982 Duck and the current day Duck. Although the Duck is one of the most famous offshore devices, as well as being the most highly developed, it has never seen any commercial success, although in the 80s it did come close to government funding.

The research on the Duck has so far been performed under lab conditions, with Stephen Salter saying he wants to solve all the problems before putting the device to sea. Some people are critical of this approach and believe it to be counter productive for the development of the Duck commercially.

The tests on the Duck have required the development of highly complex wave tank systems, designed by the Edinburgh Wave Energy Group. Many test tanks in use for other wave energy devices are developed by the Edinburgh Wave Energy Group, or using many of their revolutionary ideas.

There was one high profile use of a duck outside the laboratory environment, but this was infact a fake duck created by XXXX University [4]. This was tested on Loch Ness and showed good performance, until it sank. Steven Salter claims these tests to have damaged the Duck’s reputation, however many believe it highlighted the feasibility of wave power to the general population.

The main idea behind the Duck was for a device to gain the most energy available from the waves [4]. To achieve the highest power the Duck was optimised for use in depths of around 80m, far offshore. This approach meant that many inherent problems of the ocean environment would need to be tackled and it was understood from early stages that it would be a time intensive product development. Because the design was so innovative many new technologies have been developed by the Edinburgh wave research team for testing wave devices and for the functioning of them. If the Duck never manages to become commercially realised, no one can deny the invaluable contribution its development has brought to wave power technologies.

Technology

Gyroscope - The original idea for the Duck met problems in the power take of, because motion was slow and unstable. For the 1983 Duck design Salter had a breakthrough on the power take of in his idea for use of gyroscopes [7].

The main problem with the gyroscopes was one of cost. It was a very complex system, to complex to explain in this report, and the parts were not only expensive, but difficult to protect from the elements, which drove the costs up very high. Also the gyroscopes weighed a great deal, which lowered the efficiency of power conversion.

Ring-cam pump - When Salter heard about a new material called Ceremax, which was a ceramic coating for offshore devices, he discarded the gyroscopes for a simpler Ring-cam pump design [7]. The ceremax prolongs the life of parts before corrosion sets in. With the ring-cam pump, the motion of the duck bobbing on the waves, relative to the stationary spine of the duck, forces a ring to move across a hydraulic fluid filled container, pumping the fluid into a digital hydraulic motor, known as the “wedding cake”. I believe this motor to be an early stage of the hydraulic motors developed for some modern wave technologies. This pump set-up allowed transfer of twice the torque of the gyroscope design, with only half the mass [4].

Current Situation

It is hard to asses the current position of the Duck technology, because there is little information about any recent development. As mentioned previously, there are many aspects of the Duck’s development that have contributed to other technologies. Perhaps the most the Duck it will ever contribute to a UK renewable energy solution is to be a source of ideas, but never more than a concept.

Attenuators

An attenuator works by the motion of one part relative to another moving part. Unlike in a point absorber there is no fixed part, also there is often no restriction to the direction of motion for power take off, although the amount of energy taken from the waves tends to be reduced.

Pelamis

Introduction

The Pelamis could be considered the most commercially developed of the UK’s offshore wave power devices, with a test device contributing up to 750 kW to the national grid. It looks much like a large snake floating on the sea, consisting of 4 sections held by 3 hinged joints, totalling 150m in length and 3.5m diameter. Power is generated through the motion of each section relative to the others as the wave crests roll by. The motion of the sections is resisted by hydraulic rams, which pump high pressure oil through a hydraulic motor, which in turn drives an electrical generator.

The company Ocean Power Development was set up in 1998 with the specific goal of developing the Pelamis wave power device. The concept of the Pelamis can perhaps be attributed back to Sir Christopher Cockerell, the inventor of the hovercraft. In the 1970s he came up with the idea of interconnected rafts, bucking in respect to one another due to the wave’s motion. Sir Cockerell has a long history working with ships and has spent a great deal of time working to stop boats buckling in the waves, which led to the ideas of designing the opposite. Cockerell’s design was the first device falling in the category of a hinged contour device and the design of the Pelamis is clearly along the same lines, although much of the technology and concepts are significantly moved on from Sir Cockerell’s original ideas.

Over the past 2 years Ocean Power Delivery have worked closely with Atkins, who verified their prototype against DNV offshore codes and used their extensive knowledge of offshore systems to support the development of Pelamis.

The Pelamis has been developed over many years, with several tests being performed on scaled prototypes, to assess, validate and optimize the device for power capture, survivability and mooring requirements. A total of 14-wave tank test programs were carried out at 1:80, 1:35, 1:33, and 1:20 scale.

Technology

In designing wave power devices, one main concern is survivability, as waves greatly vary in their power. Ocean Power Delivery saw survivability as the main design criterion and this can be seen in many features of the design. The low cross section of the Pelamis to the oncoming waves serves to reduce loads facing the waves, and control features, which stiffen the joints in powerful seas, serve to reduce loads normal to heavy waves.

The stiffening of the joints in strong seas also works in reverse in small seas. The Pelamis is designed to respond resonantly in small seas and joint stiffness can be altered to utilise this resonant response; this allows more power to be generated in smaller seas, which is important for wave energy to be a viable energy solution.

The concept behind the self referencing arrangement of the device is that it gives a very large dereferencing effect in long wavelength. This, coupled with 3 separate joints, further increases the energy available in small seas.

The device was developed using proven existing technologies from the offshore oil and gas industry. This eliminated the need for such extensive testing as was required for devices like the Salter Duck, for which most components were newly designed.

Each Pelamis consists of 4 sections and is 150m long and 3.5m diameter, weighing 700 tonnes in total, including ballasts. In the device there are 3 independent power conversion units, each of modular construction and can be removed individually for repair. The power converters each contain 4 hydraulic rams, 2 heave and 2 sway, which drive 2 variable displacement motors, via smoothing accumulators. The motors each drive a 125kW generator, which totals to 750kW across the whole Pelamis device.

The hydraulic rams are set up with 2 driving each variable displacement motor. They are set up one in the heave direction, which takes power from vertical flexing of the Pelamis, and one in the sway direction, which takes power from horizontal flexing. There are 2 motors in each power module, therefore 4 rams, so that as one ram in being compressed, the coupled ram is being expanded.

The power from the pistons is converted into rotational motion by hydraulic motors, developed by Artemis Intelligent Power. For electricity generation a constant rotational speed and torque is required. The hydraulic motor converts an irregular and slow moving input into this required motion.

Assisting the smoothness of the hydraulic motor is an accumulator, which stores the unevenly input fluid and releases a smooth output flow. Figure xx

The energy from the hydraulic motor is converted into electricity by 125kW ABB electrical generators [5]. The hydraulic motors are developed by Artemis technologies and allow slow irregular input from the waves to be converted into a high speed stable rotation, utilising a constantly varying transmission ratio. This varying transmission is controlled by Digital DisplacementTM technology, developed by Artemis. Using a hydraulic motor also serves to limit impact of high loads, inherent in waves, by sharing the load across many pumping modules, rather than single contact points in gear box transmissions. [6]

The power from all 3 generators will be transmitted down one umbilical cable, most likely to a sea bed junction, as will be the case for off the coast of Cornwall in the Wave Hub initiative mentioned later in this report.

Deployment of the Pelamis is by a rapid release deployment system, which allows for the device to be quickly towed from its deployment position to a sheltered quayside location for any maintenance work. All internal aspects of the device are modular, and removable by a standard 5T mobile crane, ensuring easy maintenance when the device is back onshore. The downside of this near shore maintenance is that the device is out of service for the whole maintenance period, although in a wave power farm one device out of service would have minimal impact, and additional spare devices could be on standby at limited overheads.

Optimum Conditions

Like all wave power devices the efficiency of the Pelamis is dependant on the wave conditions. The optimum positioning for the device is around 5-10km offshore in depths of 50-70m, although Ocean Power Delivery claim it also performs in depths up to 100m. At these depths the device can maximise the potential of the larger wave whilst still remaining close enough to shore to reduce the costs of submarine cables. The optimum wave height is 6-7m, at which height the maximum output of 750 kW will be obtained and any extra power will be shed to protect the device. Wave heights below 1m will generate no power, and there is a fairly linear rise from the lowest to the highest power rating. Figure.

The power rating is not solely influenced by the wave height, but also the wave period. The power matrix in figure shows wave heights around 6-7m with periods around 7-10s to give highly effective power outputs, although for these conditions to be consistent is very optimistic. Positioning of the Pelamis will need to be in an area where the optimum wave conditions can be successfully achieved through much of the year.

The power matrix provided by Pelamis can be used to predict annual power production by looking at site specific data over a few years, as shown in figure.

Efficiency

The predicted efficiency of the Pelamis is 25-40% of the rated power across the year. This will clearly vary across the year, depending on the quality of the waves. From figure xx it can be seen that in the winter months output is closer to 50-60% of rate power, whereas in the summer months it is much less. A convenient aspect of wave power is that in winter the UK sees stronger seas, which is the time of year that a greater energy demand is placed on the grid.

Looking at the actual efficiency of the device in converting wave power to electrical power the Pelamis appears less effective. Because the primary design objective was survivability its efficiency is high power waves is greatly reduced. Although I have found no data to support this I am inclined to believe that the power conversion efficiency is at its highest at low to medium wave sizes, trailing of rapidly in large waves. I wouldn’t consider the loss of conversion efficiency as a big problem with the Pelamis; the main thing is the amount of its rated power it achieves. As Stephen Salter said, “efficiency itself is of no concern when the gods pay for the waves”[4].

Current Situation

Currently the Pelamis device is undergoing a trial connection to the grid at the European Marine Energy Centre in Scotland. It is the first deep water grid connected terminal in the UK, and tests have been successful enough for interest to be shown by many companies.

Enersis in Portugal acquired 3 Pelamis devices for a 2.25MW in the Port of Peniche, with potential plans for a further 28 devices to expand to 22.5MW. E-on, in conjunction with Ocean Prospect have laid out plans for acquiring 7 Pelamis for use off the coast of Cornwall and are one of the 4 companies agreed to make use of the Wave Hub, which was given planning permission in September 2007. ScottishPower have secured investment to go ahead with plans for a large scale instalment of 4 devices at the EMEC site in Orkney, which will provide 3MW to the grid, enough for 2000 homes.

Cost

It is difficult to fully assess the costs of the Pelamis, especially as it is not yet on full scale production, however to gain an insight, the 4 Pelamis at the EMEC site in Orkney are requiring an investment of around £4 million[2], so roughly £1 million per device. These costs will obviously decrease in time and for larger scale projects, but at this cost the cost for electricity from the Pelamis can be roughly calculated. If a 30MW plant requires 40 Pelamis, this would cost £40 million, and operating at 40% efficiency it would generate 0.1TWh in 1 year. If the plant were 100% available through the year there would be a positive return in 1 year if the electricity were sold at 0.5p/kWh. This seems really low, and is probably due to an error in the initial cost of each Pelamis, however it does show that if the Pelamis only ran at 25% rated power on average through the year the increased cost for positive return would only increase by about 25%, so if costs we an order of magnitude higher electricity could still cost as little as 5-7.5 p/kWh. This is obviously very much a ballpark figure and the cost will need to be increased to incorporate lower availability of the plant, maintenance costs and other factors.

Potential Sites

To assess the potential sites for the wave devices the average wave heights need to be taken into account, as do the extreme weather conditions. As the Pelamis also works best on long wavelengths its optimum positioning will need to take this into account.

As discussed in an earlier section the west coast of England sees the highest power waves through the year, with the West of Ireland and Outer Hebrides gaining most and Southwest Wales and western Cornwall second highest. With the highest power also comes the highest extreme conditions, with Shetland have a 100 times more powerful 100 year design wave than Cornwall, at around 25m.

The Pelamis was designed for survivability and as such can withstand some large waves. Its 100 year design wave is……. This makes it suitable for all areas off the UK coast. To get maximum potential it should be placed further from shore, to maximise exposure to the larger waves and more importantly the longer wavelengths it is designed for. It would also be more effective placed along the Irish coast and northern England, although the Wales and Cornwall areas would still be effective, especially in the winter months.

More specific decisions regarding the sighting of a Pelamis wave farm would be determined with use of various assessments of the area, including finding the area with the most consistent mean wave direction and determining the best sea bed type to accommodate the devices mooring.

Production Scalability

With regards to scalability the Pelamis can work at a 30MW maximum capacity from a site of 1 square kilometre, which would be enough to power 20,000 homes. The UK energy usage is roughly 350TWh per year; therefore a kilometre square Pelamis site would provide 0.25TWh per year, which is a percentage contribution to the UK grid of roughly 7.5x104%. There is a predicted convertible wave capacity of at least 50TWh per year [1], about 15% of demand, which is roughly what the government requires from renewable sources by 2015. For Pelamis to meet this demand it would require 200km2 running at full capacity; however the predicted yearly output of a Pelamis in the best locations around the UK is 25-40%, which would increase the area covered by Pelamis devices to 500-800km2.

Powerbuoy

Introduction

The Powerbuoy has been developed in USA by Dr George W Taylor and Dr Joseph R Burns in Ocean Power Technologies. It is a large floating buoy which bobs up and down with the waves. The Powerbuoy is a classical example of a buoyant moored device, where the central section is held rigid by mooring on the sea bed, and power is generated by motion of the buoy relative to this fixed section. There are 3 main Powerbuoy models, with different power ratings each, the largest providing 40kW per buoy.

The Powerbuoy began its development in 1997 with prototype tests off the coast of New Jersey. Since then it has seen major interest and financial backing, now having several future development plans, including a 1.39MW build planned with Iberdrola S.A of Spain [8].

Technology

The main advantage of the Powerbuoy is the use of an existing device, the buoy. The technology for power take off was designed to fit into existing structures, simplifying the testing process as the structure is already tried and tested. Because buoys have been in use for decades, techniques for the mooring and installation of the Powerbuoy need very little work and no specialist technology is required.

Simplicity is key for the Powerbuoy and the device is designed to have a simple, modular construction. The only parts with any real complexity would be the power take off and control systems, which are all patented new technologies.

As the waves roll past the Powerbuoy its buoyancy causes the main body to move up and down, causing mechanical stroking of a piston like structure, fixed by mooring to the sea bed. The power from this is converted into electricity via a High Temp Superconductor Linear Generator, developed by Converteam Ltd.

The HTS linear generator has improved efficiency, reliability and maintainability over conventional linear permanent magnet based systems, this is also combined with lower cost and lower weight, making OPTs working partnership with Converteam highly advantageous for the Powerbuoy.

Converteam have done extensive work developing power take of for renewable technologies, focussing on HTS rotational generators and have applied much of this technology to their linear generator, particularly developments in higher operational temperatures, allowing use of cheaper coolants [9].

A series of sensors are used to control the bobbing motion of the device, for 2 reasons. Firstly the system will lock up when the severity of the waves is too great and could damage the device. The second control is more complex and is used to control the frequency of the bobbing buoy to best match the waves. If it were left to bob on its own it would do so at a greater frequency than the waves which were driving it [ref], the result of this being analogous to pushing a child on a swing. As you push the child, more energy is transferred if you push when they have finished the backswing. If you push when they are still swinging back they will end up pushing you and losing energy. If the buoy were to be moving downwards when the wave was trying to push it up, a great deal of energy would be lost in trying to change the direction of motion.

I have found no information on the specific control systems use by Ocean Power Technologies, but the suggested technique by thingy would be to combine a method of predicting wave behaviour and altering motion to meet the prediction, with a mechanical means of self rectifying the devices motion to suit the waves[4]. A method of achieving the same motion from the buoy and waves would be to hold the buoy at the end of each stroke until the motion of the wave has caught up, measured perhaps by the force of the wave on the buoy being above a certain threshold level [4].

The electricity generated in the Powerbuoy will be transmitted to shore via an underwater cable, and like Pelamis, Powerbuoys will be tested on the Wave Hub off the coast of Cornwall.

The Powerbuoy technology is developed for use in depth of 30-50m with minimum wave power of 20kW/m, but development is still going on, so more detailed data on optimum wave heights is not currently available.

Efficiency

Again, detailed data on efficiency is not currently available, but it can be estimated to be around a 30-40% yearly average of the rated power. This is because they will have been designed to withstand a certain sized design wave, so can take large forces, but operating close to these large forces will greatly increase the costs of the device, so for safety and reduction of maintenance it is best to operate at lower levels.

Current Situation

At present the Powerbuoy has been on trial since 1997 of the shore of New Jersey. Future plans include a 1.39MW installation off the coast of Northern Spain, for which the first stages of installation have been completed.

Ocean Power Technologies are also one of the 4 companies which will utilise the Wave Hub off the coast of Cornwall, with plans for an installation of 5MW capacity.

Cost

I have been unable to find accurate costing of the Powerbuoy, and like the Pelamis have had to make calculations based on the funding received by the company. The Scottish Executive awarded roughly £1 million for the construction and testing of a 150kW Powerbuoy. On the same criteria as the Pelamis, to generate 0.1 TWh in a year, assuming 40% average of rated power, would require 200 Powerbuoys, costing £200 million, so to make a positive return electricity would need to be sold at around 2p/kWh. This cost would again vary as the device is further developed and with additional costs factored in.

UK Potential

The potential sites for the Powerbuoy would be very similar to that of the Pelamis, although the devices survivability is not quite as high and the size of waves it is offline in are lower than that of the Pelamis, so it is perhaps better suited to the Wales and Cornwall regions.

The Powerbuoy can be moved around easily, with commonly available technologies used to move standard buoys. This manoeuvrability could be utilised to position the Powerbuoy in differing places to take advantage of seasonal wave sizes, for instance the Cornwall Wave Hub in winter, then Northern regions in summer when Cornwall suffers from very low wave heights.

Production Scalability

The Powerbuoy is claimed to scale up to 10MW on a site which would take up 0.125 square kilometres, so 1 square kilometre could potentially produce 80MW, enough for around 70,000 homes. This would be a percentage contribution of 2x103% to the grid. Using the same data as for the Pelamis it would require roughly 70km2 for Powerbuoy to meet the governmental legislation of 15% renewable contribution by 2015. As with the Pelamis, the Powerbuoy doesn’t run at maximum capacity at all times, with a yearly rating of…..

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Wave Dragon Prototype. [13]

Wave Dragon demonstration device. [14]

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Figure xx: Outline of the 1983 Duck [7]

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Figure xx: Pelamis on sea trials in Orkney [10]

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Figure xx: Instantaneous pressure and smoothed pressure by accumulators[2]

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Figure xx: Pelamis being towed into position [11], the tow bar detaches when on site.

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Figure xx: Limiting power at wave height of 6m[2]

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Figure xx: Power matrix for Pelamis[2]

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Figure xx: Wave power across the year and Pelamis power conversion [2]

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Figure xx: Wave power across Europe

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Figure xx: Powerbuoy [8]

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Figure xx: Array of multiple Powerbuoys [8]

Fig Sketch of the OSPREY

Fig Schematic of OSPREY2

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