Ocean Energy: State of the Art

Transcription

1 Ocean Energy: State of the Art

2 Glossary AC ADCP CAPEX CO 2 DC GHG GW GWh HVDC kw kwh MW MWh OEM OPEX OSWC OWC PCM PTO TEC TRL WEC Alternating Current Acoustic Doppler Current Profiler Capital Expenditure Carbon Dioxide Direct Current Greenhouse Gas Gigawatt Gigawatt hour High Voltage Direct Current Kilowatt Kilowatt Hour Megawatt Megawatt Hour Original Equipment Manufacturer Operational Expenditure Oscillating Wave Surge Converter Oscillating Water Column Power Conversion Module Power Take Off Tidal Energy Converter Technology Readiness Level Wave Energy Converter Definitions Term Array Capacity Factor Rated Power Theoretical Resource Technical Resource Definition A set of multiple devices connected to a common electrical grid connection. The ratio of the actual output of a power plant over a period of time compared to its theoretical power output if the plant was to operate at full load over the same period. Ocean energy technologies are designed to achieve a rated power output when design conditions are met. The rated power is the peak power output of the device, and each ocean energy device will be rated at a specific wave height and period (wave devices) or at a specific tidal current velocity (tidal devices). A high level overview of the theoretical maximum potentially extractable energy contained within the overall resource. The actual value of the theoretical resource that can be exploited using existing technology options, taking account of current technology Page 1

3 limitations. Constraints such as water depth, estimated spacing requirements, and device capture and conversion efficiency assumptions will need to be considered. Practical Resource Tidal Range Fetch Bathymetry Prime Mover Surge Heave Sway Roll Pitch Yaw Directionality Angle of Attack CAPEX OPEX The actual value of the technical resource that can be exploited once grid connection; military zone; shipping lane; wind energy development; fishing; environmental; economic constraints, etc. have been accounted for. The difference in height between high and low water. The length of water over which a wind has blown which, together with the strength of the wind, determines the size of the waves produced. Measurement and mapping of water depths, characterisation of depth profile of ocean floor. A mechanism that converts natural energy into mechanical work. Linear, horizontal (front/back) motion. Linear, vertical (up and down) motion Linear, horizontal (side to side) motion Rotation about the horizontal surge axis Rotation about the horizontal sway axis Rotation about the vertical heave axis At any point in the ocean, the wave climate is the result of waves arriving from different directions. Wave directionality refers to distribution of waves from different directions. In fluid dynamics, the Angle of Attack is the angle between a reference line on a body (such as the chord line of an airfoil or hydrofoil) and the vector representing the direction of the incoming fluid flow. Capital Expenditure. The funds required at the beginning of a project for the purchase and construction of operating assets and necessary infrastructure. Operating Expenditure. The financial cost of operating and maintaining the asset(s) over the lifetime of the project. Page 2

4 Table of Contents Glossary... 1 Definitions... 1 Table of Contents Introduction Ocean Energy Technical Components of Ocean Energy Array Projects Project and Component Overview PTO Permutations Grid Connection Development Steps and Technology Readiness Wave Energy Converters Types of WEC Attenuator (A) Point Absorber (B) Oscillating Wave Surge Converter (OWSC) (C) Oscillating Water Column (OWC) (D) Overtopping (E) Pressure Differential (F) Bulge Wave (G) Rotating Mass (H) Other (I) International Examples (Wave) Attenuator Point Absorber OWSC OWC Overtopping Pressure Differential Rotating Mass Evolution of Devices (Wave) Use of Advanced Materials Design Modifications Cost-Reduction in installation Radical New Concepts (Wave) Tidal Energy Converters Types of TEC Horizontal Axis Turbine (A) Vertical Axis Turbine (B) Oscillating Hydrofoil (C) Enclosed Tips (Ducted) (D) Helical Screw (E) Tidal Kite (F) Other (G) Further Permutations International Examples (Tidal) Horizontal Axis Vertical Axis Oscillating Hydrofoil Enclosed tips Page 3

5 Helical Screw Other Multiple Rotor Platforms Evolution of Devices (Tidal) Radical New Concepts (Tidal) Arrays Strategic Technology Challenges Introduction Building upon Existing Knowledge Key Challenge Areas Predictability Manufacturability Installability Operability Survivability Reliability Affordability Development Activities and Themes an Example Synergies with Other Sectors Aviation Construction Mining Defence Offshore Wind Oil and Gas Shipping Conclusion Bibliography Page 4

6 1. Introduction There is a global awareness of the need for transition to a lower carbon energy system. Carbon dioxide (CO 2 ) and other greenhouse gas (GHG) emissions are recognised factors in climate change, and as such, decarbonisation of the energy sector is receiving precedence in international energy policy. Low carbon technological innovation is fundamental in achieving the targets that have been set. Within the energy sector, renewable technologies face both opportunities and challenges. The ocean energy sector has attracted significant levels of political and industrial interest. Policymakers and investors are encouraged to actively support innovation when tangible and credible outcomes exist, but the drive for accelerated change can also present unrealistic short-term expectations. Concurrently, the requirement for accelerated development and deployment presents a very serious technical and financial challenge. The drivers and uncertainties that exist within the ocean energy sector need to be understood. There is also an urgent need to recognise the relative impact of these uncertainties on the management of the development strategy that will help accelerate deployment of ocean energy. There is a significant wave and tidal resource in Europe. There are, however, significant barriers and obstacles to large scale deployment of technology capable of harnessing this resource. Currently, the cost of ocean energy is significantly higher than that of offshore wind. In order to become a recognised and established part of the European energy mix, ocean energy generation will need to become competitive with alternative forms of renewable power. Technical potential is not perceived to be a significant barrier to global deployment, however, the cost reduction potential that results from innovation remains uncertain. This document presents an analysis of the existing technology concepts within ocean energy, and will identify drivers for future technology developments and identify areas for future cost reduction. Accelerated development of ocean energy could offer a wide range of long-term benefits including: enabling new routes to decarbonisation of the energy supply, creation of a diverse generation portfolio, greater security of supply, and potential economic opportunities for the development of a home and export market for device developers and supply chain industries. Meeting the targets will require coordination and cooperation amongst European member states to drive low carbon technology innovation investment made now could offer a substantial reward in the long-term. It is important to clarify here that the term ocean energy, in this project, applies only to the wave and tidal stream energy sectors. The wave and tidal stream sectors have been identified as technology with the potential to offer a significant contribution to the European energy system in the medium to long term. While the majority of the sector is still demonstrating operational performance and maintainability at an individual device level, the next stage of the development process will involve deployment of arrays of multiple devices. Given the nascent stage of ocean energy sector, it is necessary to investigate the future market potential, together with opportunities for cost reduction, in order to accelerate the rate of deployment. The content of this report draws extensively on existing literature. The report explores the existing wave and tidal energy technologies across a variety of design types that are currently being developed and deployed. Each design type has different means of power production and each concept has its own perceived advantages and disadvantages. International examples of wave and tidal energy converters for each design type are provided. Evolution of designs has, in some cases, allowed a more refined concept; the more advanced technologies may be in the second or third Page 5

7 iteration of device. Further permutations of sub-components are also possible within a certain design type, and this is considered within the report. A review of knowledge on the identified key technological concepts, both those presently installed or under development, is presented. The report seeks to set the scene for the identification of technical improvements that will make device designs more durable and cost effective, while exploring opportunities for radical new designs that could open up step change innovation within the wave or tidal sector. The SI Ocean project aims to enhance cooperation between key ocean energy stakeholders, and create long lasting partnerships within the industry. By establishing a set of firm recommendations to address non-technical barriers in ocean energy, SI Ocean will help to accelerate commercialisation of the wave and tidal industry, creating new jobs and providing a secure, sustainable and competitively priced renewable energy source for Europe by The report opens with a high level introduction to Ocean Energy in Chapter 2. This is followed in Chapter 3 with further detailed information on the technical components that make up an Ocean Energy array project. A brief introduction is then made into ocean energy arrays in Chapter 4 Once the introduction to the Ocean Energy sector as a whole has been made, the report proceeds to introduce the wave energy sector Chapter 4. A discussion of the different types of wave energy converter technology is presented in Chapter 4.1, which is followed by Chapter 4.2 examining international examples of each of the technology types. Chapter 4.3 discusses the evolution of wave energy converters, taking a number of examples from industry. The section on wave energy converters concludes with Chapter 4.4, which discusses radical new concepts in the field of wave energy. Chapter 5 introduces the tidal energy sector. This is followed by a discussion of the different types of tidal energy converter technology in Chapter 5.1. Chapter 5.3 examines international examples of each of the technology types and Chapter 5.4 discusses the evolution of tidal energy converters, taking a number of examples from industry. The section on tidal energy converters concludes with Chapter 5.5, which discusses radical new concepts in the field of tidal energy. A combined assessment of the strategic technology challenges for the ocean energy sector is then presented in Chapter 7, setting the scene for future work within the SI Ocean project. Page 6

8 2. Ocean Energy Approximately 70% of the surface of the earth is covered by water. Several countries in Western Europe are exposed to the Atlantic Ocean, which contains particularly energetic wave resource. Countries such as Denmark, UK, Ireland, France, Spain and Portugal (the Atlantic Arc region) are well placed to develop wave and tidal energy projects in their adjacent ocean, where specific priority sites can be identified. The ocean contains a vast energy resource, and there are a number of ways in which this energy can be harnessed. The scope of the SI Ocean project considers only wave and tidal stream energy. These two forms of ocean energy present very different resource characteristics and challenges. Wave energy forms as kinetic energy from the wind is transmitted to the upper surface of the ocean. The height and period of resulting waves will vary depending on the energy flux between the wind and the ocean surface. Much work has been carried out in the field of research and development of technology capable of harnessing energy from the waves. At present there is very little design consensus surrounding the design of wave energy technology, and there are several areas in which a wave energy converter can be placed in order to harness the energy most efficiently. With tidal energy, large bodies of water such as oceans and seas are acted upon by the gravitational forces of the sun and moon, which in combination with the rotation of the earth on its axis, cause movements of the oceans and seas, known as tides. The motion of the moon and sun relative to the earth causes a periodic variation in the forces that generate the tides. Vertical movement (range) can be seen in the difference in water level at high and low tide, and horizontal motion of water is known as a tidal current. In recent years, international interest and development activity within the wave and tidal energy sectors has increased. A range of scale and full scale ocean energy test centres have been constructed in Europe, the USA and Canada [1]. Plans for new test centres in Asia are also being progressed[2]. International interest and a vast potential for growth in the ocean energy sector has led to the development of protocols and guidelines for ocean energy device developers, and international standards specifically for the ocean energy sector are in the process of being written [3]. The wave and tidal energy sectors are at the cutting edge of engineering design, with positive steps towards commercial viability now being demonstrated. The most advanced device developers are now progressing beyond single devices and are planning multiple-device developments and multimegawatt projects. Further investment in ocean energy technologies is being made through the backing of major utilities and OEMs, some of whom are becoming major shareholders in device development companies. Page 7

9 3. Technical Components of Ocean Energy Array Projects Energy extraction from each resource type (wave or tide) will require very different principles of operation. There has been some convergence within devices in the tidal energy sector with many of the developers focussing on horizontal axis turbines; significant design diversity still exists within the wave energy sector. In order to give some context as to the components within an ocean energy project, the purpose of an ocean energy device must be defined, together with an explanation of the importance of arrays within ocean energy projects. Each of the key components that constitute an ocean energy array project will also be discussed. The purpose of an ocean energy device is to extract energy from the available resource and convert it into an energy form suitable for transportation and use - electricity. Although individual devices vary from developer to developer, several common systems are present within all ocean energy conversion device designs. As discussed by The Carbon Trust [4], the common systems within wave or tidal energy converters include: Structure and Prime Mover, Foundations and Moorings, Power Take Off (PTO), Control, Installation, Connection, and Operation and Maintenance (O&M) Project and Component Overview An overview of the key components and cost centres that require consideration for ocean energy array projects is provided below: Structure & Prime Mover: The physical structure of the device which captures energy and the main interface between the resource and the power take off equipment within the ocean energy converter. The predominant structural material is steel, although certain concepts are exploring alternatives. Prime movers such as turbine blades are made of composite materials. Foundations & Moorings: The method used to secure the device to the sea bed. This includes permanent foundation constructions such as gravity bases or pilepinned foundations, or could consist of moorings such as tight or slack moored systems. Power Take Off: The means by which the mechanical energy extracted from the waves or tides is converted into electrical energy. Several types of Power take Off (PTO) exist including mechanical, hydraulic, or direct drive using permanent magnet generators. Control: Systems and software to safeguard the device and optimise the performance under a range of operating conditions. Control systems may adjust certain parameters of the device autonomously in order to ensure favourable operation. Installation: The method of placing the structure and device at its power generating location. This includes all vessels and ancillary equipment needed to fully deploy an ocean energy device. Page 8

10 Connection: The cables and electrical infrastructure for connecting the power output from the device to the electricity network. In order to export the generated electricity to the grid, power conditioning systems and transformers will be needed, which provide a grid code compliant electrical output. Operations & Maintenance: Periodic repair and reconditioning work will be required on all ocean energy devices. As well as the physical maintenance of mechanical and electrical components within the device, operation and maintenance will also have to consider access to the device, and device retrieval. Note: Other ongoing costs for ocean energy projects include site leases and insurance PTO Permutations The primary mechanisms for PTO within a wave energy converter are identified in Figure 1. Permutations in PTO can lead to similar device structures having significantly different mechanisms for energy conversion. The identified mechanisms have been categorised into three topics, Turbine, Hydraulic, and Linear Electrical Generators. The Turbine PTO uses air as the fluid through which energy extraction takes place. Changes in pressure due to a fluctuating wave height can be used to draw in or exhaust air from a chamber through a turbine. Hydraulic PTO requires some form of mechanical stroking motion in order to pump high pressure fluid through a motor. Direct drive systems also exist where relative movement between two bodies in most cases a linear motion - can be converted directly into electricity. Most wave devices under development today use a hydraulic or turbine PTO. Direct drive linear or rotary generators may provide a route to reduced costs within future generations of WEC. Figure 1: WEC PTO Permutations (Source [5]) These PTO design variations within a particular type of device can also be observed in tidal energy devices. There are subtle differences between tidal devices and that of wave energy converters, and the various PTO permutations for tidal energy converters are summarised in the following diagram. Page 9

11 Figure 2: TEC PTO Permutations Mechanical PTO utilises a gearbox and generator configuration similar to certain designs of wind turbine. Hydraulic PTO uses stroking or rotary motion to pump high pressure fluid thorough a motor. Direct drive generators can convert slow speed mechanical rotary motion directly into electricity without the need for a gear box. Most tidal turbines under development today use mechanical or direct drive PTO connected to a horizontal or vertical axis prime mover Grid Connection An important factor in any ocean energy project is the need for electrical connection between the generating device and the local grid network. The identifiable ocean energy resource is often situated away from densely populated areas; the resource far outweighs the demand from local communities in many cases. It is intended that electricity generated through ocean projects will be transported to regions where there is greater demand. For this to take place, the necessary infrastructure for electricity transportation is needed. There are two stages of grid connection in an ocean energy device. The first stage is to connect the device to an export cable, bringing electricity to shore. Device connection can be carried out using dry-mate or wet mate connectors. Dry mate connectors require the connector to be above the water surface when the connection is made. The connected cable is then lowered in to position. Wet-mate connectors allow a connection to be made sub-sea, which would allow an ocean energy device to be placed into position prior to the cable being connected. The second stage of grid connection involves voltage step-up and connection to the distribution and transmission grid network. On-shore substations and transformers will step up the voltage to the applicable level before connection to the distribution or transmission grid Development Steps and Technology Readiness There are several steps that developers must progress through on the journey between initial concept and commercial product. Figure 3 shows the different stages a concept will move through towards commercialisation and highlights how development costs increase progressively through the stages. Figure 3: The Technology Journey (Source: Carbon Trust [6]) Page 10

12 It would be pertinent to define here the term Technology Readiness Level. A number of steps have been set in place to pave the way for a staged growth of a new wave energy concept or design. Technology development, from first concept to commercial operation, is expected to progress through defined stages. In order to track the progress of ocean energy devices from concept through to final product a table of Technology Readiness Levels (TRL) has been produced [7]. These TRLs define the status of a particular technology, and can be useful in identifying the market readiness of a particular device, and is described in Table 1.The information contained within this table utilises definitions from the US DoE Marine and Hydrokinetic database [8], and information obtained through discussion within the SI Ocean partners. Page 11

13 Table 1: Technology Readiness Levels TRL Description Indicative Ocean Energy Device 1 Basic principles observed and reported Technology concept and/or application formulated Analytical and experimental critical function and/or characteristic proof of concept Component and/or partial system validation in a laboratory environment Component and/or partial system validation in a relevant environment System/subsystem model validation in a relevant environment System prototype demonstration in an operational environment Actual system completed and service qualified through test and demonstration Actual system proven through successful mission operation Discovery/Concept Definition; Scientific research begins to be translated into applied research and development where basic principles are observed and reported. Technology concept and application are formulated and investigated through analytic studies and in-depth investigations of principal design considerations. This stage is characterised by paper studies, concept exploration, and planning. Scale Guide 1:25 1:100 (Small Scale) Early Stage Development, Design and Engineering; Active research is initiated, including engineering studies and laboratory studies to physically validate analytical predictions of separate elements of the technology. Scale Guide 1:25 1:100 (Small Scale) Proof of Concept; Early stage proof-of-concept system or component development, testing and concept validation. Critical technology elements are developed and tested in a laboratory environment, and computer simulation of the device will be carried out. Scale Guide 1:10 1:25 (Medium Scale) Technology Laboratory Demonstration; Basic technological components are fabricated at a scale relevant to full scale and integrated to establish and verify subsystem and system level functionality and preparation for testing in a simulated environment. Subsystem level interfacing testing demonstrated at model scale. Scale Guide: 1:2 1:5 (Large Scale) System Integration and System Technology Laboratory Demonstration; System level interfacing/integration testing demonstrated at model or prototype scale. At this level, representative model or prototype system at a scale relevant to full scale, which is beyond that of TRL 5, is tested in a relevant environment, such as a test facility capable of producing simulated waves/currents and other operational conditions, while monitoring device response and performance. Furthermore, the devices foundation concept shall be incorporated and demonstrated. This stage represents a major step up in a technology's demonstrated readiness and risk mitigation and is the stage leading to open water testing. Scale Guide: 1:2 1:5 (Large Scale) Open Water System Testing and Demonstration; Testing may be initially performed in water at a relatively benign location, with the expectation that testing then be performed in a fully exposed, open water environment, where representative operating environments can be experienced. The final foundation/mooring design shall be incorporated into testing at this stage. Scale Guide: 1:1 1:3 (Large Scale) Open Water System Operation; The prototype in its final form (at or near full scale) is to be tested, and qualified in an open water environment under all expected operating conditions to demonstrate readiness for commercial deployment in a demonstration project. Testing should include extreme conditions. Production of GWh scale electricity, operating continuously for at least one year. Scale Guide: 1:1 1:2 (Pre Commercial Demonstrator) Commercial Scale Production / Operation; Final commercial unit, economic deploymentwhen the technology is ready for mass production and has proven to operate as designed for several years. Array scale projects. Scale Guide: 1:1 (Full Scale 1 ) 1 The term full-scale for each device is based on the developers stated full-scale. In some cases full-scale may be MW-scale, and in some cases it may be kw scale. Page 12

14 4. Wave Energy Converters This section provides an overview of the current status of Wave Energy Converters. It also introduces the different prime-mover concepts that are being developed for extracting useful energy from ocean waves. The wave energy sector is reaching a significant milestone in the development of the industry, with positive steps towards commercial viability being taken. The more advanced device developers are now progressing beyond single unit demonstration devices and are proceeding to array development and multi-megawatt projects. The backing of major utility companies is now manifesting itself through partnerships within the development process, unlocking further investment and, in some cases, international co-operation. At a simplified level, wave energy technology can be located near-shore and offshore. Wave energy converters can also be designed for operation in specific water depth conditions: deep water, intermediate water or shallow water. The fundamental device design will be dependant on the location of the device and the intended resource characteristics. Figure 4: Mooring and Foundation Configurations for WECs The energy contained within the waves manifests itself in the form of kinetic motion of water particles, with the energy imparted to the waves from the wind. The particle motion varies relative to the water depth. Far offshore, particle motion is circular. As the waves approach the shore, interference from the seabed (drag) causes the water particle motion to become more ellipsoidal in shape. At the shore, waves break as the upper surface of the wave begins to travel faster than the water particles closer to the sea bed. This is shown diagrammatically in Figure 5. The orbital particle motion decreases exponentially with increasing water depth, which can be seen in the reducing path size for water particles deeper within the water column. Page 13

15 Figure 5: Wave Particle Motion The near-shore environment is more benign and accessible than the deep water environment, but still allows access to a significant extractable wave energy resource. The near shore environment is shielded from the largest ocean waves, and offers an increased directionality with regards to force in the surge direction. As waves approach the shore, the wave speed and wave length decrease, resulting in an increased energy per unit area, known as wave shoaling. On the other hand, there is a trade-off, as compared to the deep offshore environment there is a lower resource in the near shore waves, as energy is lost due to drag with the seabed. Much of the European ocean wave energy resource lies in deeper waters, as wave energy levels increase predominantly with increasing westerly distance from shore [9]. The areas of deep water that are suitable for wave device deployment are significantly larger than the areas available for near-shore device deployment, and so there is probably a larger market for deep water devices. There are many more constraints to development in the near shore environment, including geotechnical constraints, which reduce the relative level of practical near shore resource. There are also challenges in the deep offshore environment, as water depth can increase costs significantly. Technology and financial limitations restrict the depth to which deployment can take place, but emerging technologies may open up markets in water depths of greater than 250m. Site characterisation is an essential part of the development process for any proposed site. Wave resource characterisation can be quantified using wave buoys or through use of land based wave radar systems. Ideally, two or three years of wave data could allow for an estimation of the wave climate at a particular site, although a larger data set consisting of ten years data would provide a more accurate estimation of extremes. The location of a wave energy device will largely influence the type of mooring used. Shoreline devices will typically require significant civil engineering works to integrate the device into a natural rock face or a man made breakwater. Near-shore devices will make use of either pinned pile foundations, or will rely on gravity mass to hold the device in place. Devices located off shore have the option of tight moorings or slack moorings, which may be dependant on the type and location of the structure and PTO system. A significant challenge for the wave energy industry is demonstrating the survivability of a device. The ratio of working loads to extreme loads is such that devices need to be over-engineered in comparison to the expected average operating conditions in order to survive the extreme load scenarios that could occur during storm conditions. As with other design decisions, the exact design of WECs will be the result of a cost-engineering exercise that aims to minimise the levelised cost of electricity from the WEC Page 14

16 4.1. Types of WEC Various international examples of technology that has been designed to extract energy from the waves will be discussed in following sections of this report, but first, the classification of devices must be defined. For the purpose of this report, classification will follow that used by EMEC[10], in which the following notation is used: Table 2: WEC Types Device Type Attenuator Point Absorber Oscillating Wave Surge Converter (OWSC) Oscillating Water Column (OWC) Overtopping/Terminator Submerged Pressure Differential Other - Bulge Wave Rotating Mass Other Classification (Wave) A B C D E F G H I Each type of device is designed to extract energy in different ways using the surge, heave or sway motions of the waves (or a combination of each). Descriptions on these wave motions, and the rotation around each axis (roll, pitch, and yaw) is provided in the Glossary and Definitions at the beginning of this report Attenuator (A) Description: Attenuator type wave energy converters use the energy within oncoming waves to induce an oscillatory motion between two (or more) adjacent structural components. The motion can be resisted by hydraulic rams which pump high pressure hydraulic fluid through a motor, or by a direct drive power take off system, to generate electricity. Attenuator type wave energy converters can be surface floating or fully submerged, the former is most common. Attenuators tend to yaw automatically to face the predominant wave direction. Image Source: Point Absorber (B) Description: Point Absorber type devices use buoyant forces to induce a heaving motion of one body relative to a secondary fixed body. The fixed body may be moored to the sea bed, or held in place by gravitational forces through a large foundation mass. Point absorbers are non-directional, as they can receive incoming waves from any incident angle. Image Source: Oscillating Wave Surge Converter (OWSC) (C) Description: A type of device that can use near-shore wave particle motion. Generally located in near-shore regions, where the water particle motion becomes more ellipsoidal in shape, these devices use the surge motion of the waves to induce oscillating motions of a body in the horizontal direction. OWSC are typically bottom mounted Page 15

17 devices, fixed directly to the sea bed, but concept floating OSWC devices are under development. Image Source: Oscillating Water Column (OWC) (D) Description: Oscillating water columns (OWC) use a chamber that is part filled with water to drive air through a turbine. Variations in the wave height cause the water in the column to rise and fall, acting like a large piston on the volume of air within the chamber. As the water level rises, the pressure in the chamber rises, and air is exhausted from the chamber driving a turbine. When the water level decreases, the air flow reverses and air is drawn into the chamber, once again driving a turbine. OWC devices can be contained within a fixed structure at the shoreline, located near shore bottom as a bottom mounted structure, contained within a man-made breakwater, or can moored in deeper water as a floating system. Image Source: Overtopping (E) Description: An overtopping device (also known as a terminator device) converts wave energy into potential energy. The design causes waves to break across the device, and the surge energy in the breakers allows water to be collected in a reservoir above the free water surface. Water contained in the reservoir can produce energy by flowing through a low-head hydraulic turbine. Overtopping devices can shore based as part of a shoreline structure or man-made breakwater, or they can be floating devices located in deeper water. Image Source: Pressure Differential (F) Description: Pressure Differential devices rely on oscillating hydrodynamic pressure caused by passing waves. The devices can be floating or fully submerged. Submerged devices experience an induced motion as waves pass over the device, creating a temporary vertical force on the body. Once the wave has passed, the reduced pressure differential causes the body to return down to its starting position. Floating pressure differential devices could utilise the increased pressure due to passing waves to compress air through a turbine. Image Source: Bulge Wave (G) Description: In bulge wave technology, a flexible tube filled with fluid is moored to the seabed, allowing the device to orientate into oncoming waves. As waves pass over the device, differential pressure will cause the water contained within the flexible tube to be squeezed, forming a bulge wave. This bulge wave travels along the device, at a speed proportional to the wave velocity and the flexibility of the tube, gaining energy as the bulge grows. This energy can be used to drive a turbine located at the end of the tube. Image Source: Rotating Mass (H) Description: Rotating mass devices utilise the wave motion to cause pitch and roll of a floating body. Within the floating body, an eccentric mass will be excited, and will begin to rotate. The rotation will drive an electrical generator contained within the device. A further permutation Page 16

18 of the rotating mass device uses gyroscopic effect. Image Source: Other (I) Description: Devices in the Other category do not fit into any of the above headings, but instead employ a novel or unconventional technique for extracting energy from the waves International Examples (Wave) At present, wave energy converters are in the R&D phase of technology development. Certain device developers have had a grid connected device for a number of years, but the sector as a whole does not have any commercially available production wave devices. There exist over 100 concepts, with development of devices taking place in over 30 countries across the globe. Projects within a visible development pipeline are now underway, and several test centres have increased the availability for grid connected berths in which to test wave energy conversion concepts. Test centres include the European Marine Energy Centre (EMEC), Wave Hub, Biscay Marine Energy Platform (BiMEP), and the Danish Wave Energy Centre (DanWEC). Several device developers have now experienced several months of at-sea testing, and certain devices are nearing a commercially viable stage. This section aims to present a review of the status of the wave energy sector, providing an overview of relevant technological developments that are adding to the knowledge and experience of the industry. A list of wave energy technologies and device developers, together with information on device type and technology readiness levels, can be found on the United States Department of Energy Marine Hydrokinetic Database [11]. This reference database is fully searchable, and there are advanced search options available for convenient site navigation. Information on devices and developers is also contained on the EMEC website [10]. This document includes a representative list of technologies in each WEC type. However, the list is not exhaustive, as other potential technologies have not being included due to the limitation of the report length. A summary of device developers within each of the technology types is shown in Table 3 below. Table 3: A Selection of WEC Device Developers Device Type Device Developers at Various Stages of Development Attenuator Pelamis, Dexa-Wave, AlbaTERN Point Absorber Ocean Power Technologies, Wavestar, Seatricity, CETO Wave Energy Technology, SeaRaser, SeaNergy Oscillating Wave Surge Converter Aquamarine Power, Waveroller, Langlee Wave Power (OWSC) Oscillating Water Column (OWC) Voith Hydro WaveGen, WavEC Pico Plant, Oceanlinx, Ocean Energy Overtopping/Terminator Wave Dragon, Waveplane Pressure Differential AWS Ocean Energy Rotating Mass Wello Oy Bulge Wave Checkmate Seaenergy A selection of these devices will now be discussed in greater detail in the sections that follow. The wave energy sector contains a number of devices that are at different levels of technology readiness. Advanced concepts have significant at sea testing, and this has been made clear throughout the section. In the individual device information, in the instance that a device is in the pre-deployment stages of development, the rated power output is indicated in parenthesis. Page 17

19 Attenuator Pelamis Wave Power Pelamis is a semi-submerged wave energy converter consisting of individual tubular sections, each linked to neighbouring segments by universal joints. Motion is induced in each section as a wave passes down the length of the device; movement between neighbouring segments will be resisted by hydraulic rams, which pump hydraulic fluid through pressure smoothing accumulators then on to a hydraulic motor. This motor is connected to a generator. Pelamis will be moored in water depths exceeding 50m, and the design of the device is such that it is able to weathervane to face oncoming waves - a self-referencing mechanism that allows the device to maintain a directional heading perpendicular to the oncoming wave direction. The weathervane concept also allows the Pelamis device to enter a survival mode in which the WEC rides underneath extreme waves which would otherwise impart extreme forces. Pelamis Wave Power (Source: The current model of device, the P2, has a rated power output of 750kW. At present, there are two Pelamis P2 machines undergoing grid-integrated testing at the European Marine Energy Centre in Orkney, UK. Two utility companies, E-On and ScottishPower Renewables, have entered into an agreement to carry out joint testing of their respective device, with knowledge gained over the course of the testing being shared between the two utilities. Pelamis have recently secured an order for a third device from Swedish utility company Vattenfall. Pelamis are involved in the development of array projects in the Pentland Firth (Marwick Head) and Shetland (Aegir) together with utility partners, in addition to the development of two sites autonomously, Farr Point and Bernera. Country of Origin UK Rated Power Output 750kW Water Depth Min/Max 50m / 250m Mooring Type Slack Moored TRL 7 Number of Deployed Devices 6 Target Market Deep offshore PTO Hydraulic Deployment Vessel Tug boat, Anchor handling vessel Maintenance Strategy Projects to Date Return to base Aguçadoura 3 x 750kW EMEC 2 x 750kW Page 18

20 Dexawave Dexawave is a Danish wave energy device developer producing a hinged raft WEC, where motion between the raft sections is resisted by hydraulic rams. Dexawave are participating in an FP7 project titled Aquagen. The aims of this project are to develop and demonstrate an environmentally friendly PTO system, with water replacing hydraulic oil as the working fluid. Investigation into alternative materials such as steel reinforced concrete is underway for future devices. Dexawave is also in the early stages of development of a wave farm project on the island of Malta in the Mediterranean Sea. Dexawave (Source: Country of Origin Denmark Rated Power Output 5kW, (250 kw) Water Depth Min/Max 25m / Unknown Mooring Type Slack moored TRL 6 Number of Deployed Devices 1 Target Market Intermediate offshore PTO Hydraulic Deployment Vessel Tug boat Maintenance Strategy Projects to Date Minor maintenance: on site Major maintenance: Return to base Hanstholm, Denmark 5kW Page 19

21 Point Absorber Ocean Power Technologies (OPT) OPT's PowerBuoy is a semi-submerged floating device consisting of a toroidal float that moves with respect to an inertially stable spar structure tethered to the sea bed. This device is a self reacting heaving buoy, slack moored in deep water. The mechanical stroking motion of the buoy relative to the spar is converted to an electrical output via a sophisticated power take-off driving an electrical generator. In extreme waves, the structure can lock up and cease movement, protecting the device in the event of storm waves. To date, OPT have deployed the 150kW variant of the PowerBuoy in various wave climates. OPT are currently developing a 500kW PowerBuoy device. Ocean Power Technologies (Source: Country of Origin USA Rated Power Output 150 kw, (500kW) Water Depth Min/Max 55m / 250m Mooring Type Slack moored TRL 7 Number of Deployed Devices 4 Target Market Deep offshore PTO Direct Drive Deployment Vessel Buoy tender, tug boat, crane or A- frame vessel Maintenance Strategy Projects to Date Return to base Atlantic City (USA) 1 x 40kW; Oahu (Hawaii) 1 x 40kW; Santoña (Spain) 1 x 40kW; Scotland, UK 1 x 150kW Page 20

22 Seabased Seabased are a Swedish device developer, developing a taut moored point absorber that utilises a float on the surface of the water to move a linear direct-drive neodymium-iron-boron magnet generator located within a tower on a sea bed foundation. End stops prevent the linear generator from exceeding the allowable travel. The sea bed mounted generators are anchored using a concrete gravity foundation. The dimensions of the foundation are designed to withstand the wave loading, and installation can take place without requirement for seabed preparation. Seabased (Image Source: Elforsk Rapport 11:02 [12]) A wave research project was initiated by Uppsala University in 2006, and it is anticipated that this project will remain in operation until Seabased have received funding from the EC and the Swedish Energy Agency to develop a 10MW demonstration array, which will consist of up to 420 units, deployed near Sotenäs, Sweden. Country of Origin Sweden Rated Power Output 30kW (50kW) Water Depth Min/Max 20m / 100m Mooring Type Taut moored TRL 7 Number of Deployed Devices 3 Target Market Intermediate offshore PTO Direct Drive Linear Generator Deployment Vessel Crane Barge Maintenance Strategy Return to base Projects to Date Lysekil, Sweden multiple 30kW devices Page 21

23 OWSC Aquamarine Power Oyster Oyster, developed by Aquamarine Power, is a near-shore hydroelectric wave energy converter. The main structure of the device is a buoyant, bottom-hinged flap. As waves approach the shore, a reduction in water depth and drag from the sea bed results in an ellipsoidal wave particle motion. Oyster uses this motion to oscillate the buoyant hinged flap backwards and forwards with the wave surges. The oscillation is used to pump fresh water through a high-pressure pipeline to an onshore hydroelectric power plant. Double acting hydraulic cylinders allow both the forward and backward motion to pump. The pressurised water drives a Pelton wheel turbine connected to an electrical generator, located on the shore. Multiple Oyster devices can be connected to a pipe manifold to allow the operation of a farm of devices requiring only a single onshore hydroelectric system. Aquamarine Power Oyster (Source: The current design water depth for Oyster is 10 to 15m, approximately 500m from the shore. A 315kW Oyster 1 proof-of-concept device operated at sea at the European Marine Energy Centre (EMEC) in northern Scotland between 2009 and The second-generation 800kW Oyster 800 began operation testing at sea in June 2012 when it produced first electrical power to the grid. Planned installation of a third-generation Oyster 801 machine is scheduled The first and second generation Oyster devices were constructed from steel. The next-generation Oyster 801 is to be constructed from fibre-reinforced polymer (FRP). Country of Origin UK Rated Power Output 800kW Water Depth Min/Max 10m / 15m Mooring Type Bottom fixed, pin pile TRL 7 Number of Deployed Devices 2 Target Market Near Shore PTO Hydraulic, high pressure water pumped from device to a shore based Pelton turbine. Deployment Vessel Tug boat Electrical PTO components and hydroelectric turbine Maintenance Strategy located onshore. Calm weather window required for any offshore maintenance work. Major maintenance: Return to base Projects to Date EMEC, UK 1 x 315kW, 1 x 800kW Page 22

24 AW Energy WaveRoller WaveRoller is a hinged flap, bottom mounted device consisting of three oscillating plates on a single gravity base foundation. The back and forth movement of surging waves moves the plate, and the kinetic energy that is produced can be converted to hydraulic pressure of a working fluid, using a piston pump. This energy can be converted to electricity by a closed hydraulic system in combination with a hydraulic motor/generator system. WaveRoller is a modular concept, which means that the plant capacity is formed by connecting multiple production modules into a WaveRoller plant. Each production module can consist of 3-5 wave flap elements installed into a common generation system. Waveroller (Source: Country of Origin Finland Rated Power Output 300kW (500kW 1MW per panel) Water Depth Min/Max 8m / 20m Mooring Type Bottom fixed, gravity mass, ballast water TRL 7 Number of Deployed Devices 1 Target Market Near Shore PTO Deployment Vessel Maintenance Strategy Projects to Date Hydraulic, high pressure fluid pumped through accumulators and hydraulic motor. Tug boat Return to base. Device will use pressurised air to remove ballast water, the device will then float to the surface and be towed to shore for maintenance Peniche, Portugal 1 x 300kW Page 23

25 Langlee Wave Power Langlee Wave Power, a Norwegian wave energy company, is developing a floating steel structure containing hinged wings that move backwards and forwards, synchronising their movement with the passing wave motion. The movement of the wings drives a hydraulic system to power electric generators. The wings are able to freely rotate through 360, and so there is no end stop that could cause damage to the structure or water wings. Langlee Wave Power (Source: At present, both the 50kW and 250kW prototypes are in the development phase, but it is hoped that the Langlee device will be ready for deployment in Country of Origin Norway Rated Power Output (50kW), (250 kw) Water Depth Min/Max 30m / 150m Mooring Type Slack Moored TRL 6 Number of Deployed Devices 0 Target Market Intermediate and deep offshore PTO Hydraulic Deployment Vessel Tug boat, Anchor handling vessel On site maintenance every 5 years: Service of generator, anode Maintenance Strategy replacement, mooring inspection, fatigue inspection Major Maintenance: Return to base Projects to Date N/A Page 24

26 OWC Voith Hydro Wavegen Voith Wavegen has successfully completed two OWC projects, the LIMPET device, and an OWC contained within a breakwater in Mutriku, Spain. LIMPET (Land Installed Marine Powered Energy Transformer) is a shoreline based Oscillating Water Column energy converter located on the island of Islay, on the west coast of Scotland. The rise and fall of water height within the water column causes air to flow in and out of the structure through a turbine. Installed in 2000, the device has a peak power output of 500kW and is grid connected. A breakwater was constructed in the town Mutriku, Basque country, Northern Spain, which incorporated a 300kW power generation system. This system comprises of 16 individual OWC wave energy units, contained within a 100m section of the breakwater. Whilst the breakwater was deemed necessary for additional protection to both fishing and recreational boats, incorporating a wave energy generation plant into the breakwater maximised the utility of the project. Voith Wavegen (Source: Country of Origin UK, Germany Rated Power Output 300kW, 500kW Water Depth Min/Max 15m nominal mean Mooring Type Shore based structure TRL 7 Number of Deployed Devices 2 Target Market Near Shore PTO Pneumatic, Wells turbine and induction generator Deployment Vessel N/A Maintenance Strategy Due to the location of the device, all maintenance and major repair works can be carried out on shore Projects to Date Islay, UK; Mutriku, Basque Country, Spain Page 25

27 WavEC Pico Plant The WavEC Pico Demonstrator is also a shoreline oscillating water column structure, equipped with a horizontal-axis Wells turbine-generator set and a guide vane stator installed on each side of the rotor. To avoid over pressure within the air chamber, a pressure relief valve controls the pressure, ensuring that the turbine does not stall. This system has been operated and maintained by WavEC. WavEC Pico Plant (Source: The Pico North coast was chosen as the location of the WavEC OWC device, due to the high energy levels and suitable geographic conditions for this type of device. Suitable water depths in front of the WEC, in addition to ease of access from local roads and a suitable grid connecting point, were present at the chosen location. The goal of the project was to demonstrate the viability of OWC technology for production of electricity to a small grid. Since 2006, WavEC has been responsible for the maintenance and operation of the plant. Significant improvements such as a reduction in turbine-generator vibrations have been achieved since 2009, helping the plant to achieve better levels of efficiency. After further upgrades, the Pico plant is now ready to accommodate two turbine ducts of equal size (suitable for testing equipment between 100KW and 700kW). Between 2007 and 2012, the Pico plant produced over 51MWh of electricity during 2730 hours of operation. Country of Origin Spain Rated Power Output 400kW Water Depth Min/Max Unknown Mooring Type Shore based structure TRL 7 Number of Deployed Devices 1 Target Market Near Shore PTO Pneumatic, Wells turbine and induction generator Deployment Vessel N/A Maintenance Strategy Projects to Date Due to the location of the device, all maintenance and major repair works can be carried out on shore Pico, Azores Page 26

28 Ocean Energy Limited Within the OWC family, an Irish developer is currently undergoing testing of a floating platform OWC. The OEBuoy device uses wave energy to compress air in a plenum chamber and pump it through an air turbine. The power conversion system is therefore isolated from the seawater. The device is a floating system with the opening of the OWC facing away from the oncoming wave direction. The OE Buoy has undergone three full phases of scaled testing, from 1:50 scale to 1:4 scale. Initial testing of the OE Buoy concept was carried out at the Hydraulics and Maritime Research Centre (HMRC) in University College Cork, Ireland. The three-quarter scale OEBuoy is deployed at the scale test site in Spiddle, near Galway, Ireland, for data collection purposes as part of the EU funded CORES project. OE Buoy has only one moving part and has completed over 3 years of testing in Atlantic waves. A full scale OE Buoy is planned for deployment at the Wave Hub test facility in Cornwall, UK. Ocean Energy Limited (Source: Country of Origin Ireland Rated Power Output Unknown Water Depth Min/Max Unknown Mooring type Slack moored TRL 6 Number of Deployed Devices 1 Target Market Deep Offshore PTO Pneumatic, Wells turbine and induction generator Deployment Vessel Tug boat Maintenance Strategy Minor maintenance: on site Major maintenance: Return to base Projects to Date Spiddle, Galway, Ireland Page 27

29 Overtopping Wave Dragon Wave Dragon is an overtopping type floating wave energy converter. The structure comprises of a reservoir, which stores water at a height above the sea level. Two reflector arms focus oncoming waves onto a ramp, which directs some of the water from the oncoming waves up into the reservoir. Water in the reservoir is used to drive a hydro electric turbine, making use of the pressure head between the water in the reservoir and the surrounding sea. Wave Dragon (Source: Wave Dragon deployed a 58 m wide prototype in 2003 off the coast of Denmark at Nissum Bredning. A modified prototype was deployed in 2006 in a more energetic wave climate. In total, Wave Dragon accumulated over 20,000 hours of operational experience between 2003 and 2009, with grid connection allowing generated electricity to be supplied to domestic homes. There are plans for a full scale demonstration device to be deployed off the coast of Wales, and a wave farm off the coast of Portugal is also in the development pipeline. Country of Origin Denmark Rated Power Output 20kW, (4MW) Water Depth Min/Max 25m / unknown Mooring Type Slack moored TRL 6 Number of Deployed Devices 1 Target Market Intermediate offshore PTO Direct drive permanent magnet generator Deployment Vessel Tug boat Maintenance Strategy Projects to Date Maintenance and major repair works can be carried out at site Nissum Bredning, Denmark Page 28

30 Pressure Differential AWS Ocean Energy AWS Ocean Energy is developing a multi-cell array of flexible membrane absorbers, which operate by converting the pressure differential from passing waves into pneumatic power, the AWS-III. By compressing air within a cell, the compressed air can be used to drive an air turbine. The cells are inter-connected in order to allow air to flow between cells in anti-phase. A typical device will be made up of 12 cells, with the full scale device anticipated to be more than 60m in diameter. The AWS-III will be slack moored in water depths of around 100m using standard mooring spreads. The AWS-III is designed for ease of operation and maintenance. The large structure provides an inherently stable platform allowing safe on-site maintenance. The modular design allows rapid removal and replacement of the flexible wave absorber cells. AWS Ocean Energy (Source: Country of Origin UK Rated Power Output (2.5MW) Water Depth Min/Max 70m / 150m Mooring Type Slack moored TRL 6 Number of Deployed Devices 1 Target Market Deep offshore PTO Pneumatic, Wells turbine and induction generator Deployment Vessel Tug boat Maintenance Strategy Projects to Date Maintenance and major repair works can be carried out at site Loch Ness, Scotland Page 29

31 Rotating Mass Wello Oy Penguin Wello Oy is a Finnish company Founded in The Penguin WEC is designed to capture rotational energy generated by the movement of its asymmetrically shaped hull, which rolls, heaves and pitches with each passing wave. This motion is used to accelerate and maintain the revolutions of a spinning eccentric mass housed inside the hull, which in turn drives an electric generator to produce electricity that can be exported via a sub sea cable. Fabricated in Riga, Latvia, the Penguin device is a 220-tonne structure (excluding ballast) that is around 30 meters in length, and has a draft of seven metres. The device has been undergoing testing at Lyness since arriving in Orkney in June 2011 and was first deployed at the Billia Croo wave test site in summer Wello Oy Penguin (Source: Country of Origin Finland Rated Power Output 500kW Water Depth Min/Max 50m / 200m Mooring Type Slack moored TRL 7 Number of Deployed Devices 1 Target Market Deep Offshore PTO Deployment Vessel Maintenance Strategy Projects to Date Eccentric rotating mass connected to a direct drive permanent magnet generator Tug boat Minor maintenance: On site Major maintenance: Return to base EMEC, UK Page 30

32 4.3. Evolution of Devices (Wave) Device evolution is a necessary part of the cost reduction process in order to bring the total levelised cost of energy to a level which competes with other, more mature, sources of renewable energy such as wind; typical first generation technology will require substantial reductions in cost in order to attain a level of cost-competitiveness. More radical changes to the principles of operation of a device may result in step change performance or cost of energy improvements, and this will be discussed in greater detain within Section 4.4. Progression can be made through successive iterations to the design to create performance improvements: This may be to increase the maximum power output of each device, to improve the capacity factor, or to increase the range of operating conditions in which the device can produce grid compliant electricity. The evolution could involve a radical overhaul of the design of a major component, such as the mooring system. Alternatively, the evolution may take place in the form of a component change or upgrade; a sub-system change, but the overall design of the device would not be fundamentally altered. Three examples will be considered here: Evolution through use of advanced materials; design modification; and cost-reduction in installation techniques Use of Advanced Materials The majority of ocean energy converters are fabricated from steel, a metal that offers good (and well understood) fatigue and stress limits. Some device developers are investigating the use of Steel Reinforced Concrete, or Fibre Reinforced Polymer (FRP) for certain components. FRP offers some cost and weight saving advantages over steel, but the fatigue and stress limits are not yet well understood in comparison to steel. This material has been proven in the marine environment, albeit in a very different application to ocean renewable energy, and is used extensively in other applications such as civil infrastructure and boat design. Aquamarine Power plans to use FRP in their next generation Oyster flap device, and Pelamis are considering the use of concrete tubes in their next prototype. Other wave devices are being designed to use rubber or other flexible materials as the main structural component Design Modifications Pelamis Wave Power (see Section 4.2.1) made structural design changes to their 750kW P1 device, which was deployed initially at EMEC in 2006 and then the Aguçadoura wave power project in Portugal. The Power Conversion Modules (PCM) in the original device, housing the hydraulic PTO components, were located as separate segments contained between the longer steel tubular segments. Single axis hinge joints at each end of the PCM facilitated heave or sway motion. In the next generation P2 device, the PCM was incorporated into the main tubular steel segment, and a universal joint allowing heave, sway and rotational movement connected neighbouring steel segments. This revised set up allows a more efficient power take off and greater device flexibility. Pelamis Wave Power P1 (left) and P2 (right) Devices (Source: Page 31

33 The design of improved control systems could also increase the level of energy extraction achieved for certain devices, without the need for new hardware. This will be discussed in further detail within Section 7. Device developers continue to research routes for design optimisation, and progression on to further generations of device are likely to see additional reductions in the levelised cost of energy. By modifying the structural material from steel to concrete, Pelamis hope to achieve some further cost improvements without affecting the performance of the device. It is likely that there will be a phased transition in to the use of concrete within future devices, until the material has proven its capability through long term operation and reliability Cost-Reduction in installation Sea bed preparation techniques are sometimes necessary for certain device foundations; it is sometimes necessary to use sea bed piling methods to secure devices against unwanted movement. In the OWSC design, Aquamarine Power designed a hinged flap that oscillates with the wave motion, called Oyster (see Section 4.2.3). In the first deployment of the technology, foundation requirements resulted in the need for four drilled piles. Any sea bed operations such as piling require expensive vessel operations. In order to reduce the costs of successive designs, the second iteration of the Aquamarine Power Oyster was designed for installation using only two piles. Further iterations of the device may enable installation costs to reduce further still by designing for a single monopole per device. Further cost reductions could be made, as drilling operations for multiple devices could take place in one vessel mobilisation, mitigating the need for multiple vessel mobilisations and expensive cost overruns. First, Second and conceptual Third Generation Aquamarine Power Oyster WEC (Source: [13]) However it is achieved, device evolution is fundamental to the commercialisation of wave energy technology; without device evolution and subsequent cost reductions, the market for wave energy will not develop. The three examples outlined above only represent some of the methods that have been adopted within the industry, but represent the challenges that the sector as a whole faces in the drive to reach cost-competitiveness with more mature forms of renewable energy Radical New Concepts (Wave) There are some innovative new concepts emerging in the wave energy sector. The idea of a radical concept may challenge the fundamental principles of operation of a wave energy converter, or it may look at revolutionary materials that have not yet been used within the sector. A radical concept must open up potential routes to significant step change cost reduction. By their very nature, radical concepts are not necessarily proven technologies, and they must be distinguished from fully fledged, working, demonstration prototypes. Page 32

34 One such radical concept in the wave energy sector is the Anaconda, a device being developed by Checkmate Seaenergy. Anaconda uses bulge wave technology, a concept that does not fall under any of the previous wave energy device types discussed. The device is essentially a large rubber tube filled with water, moored to the sea bed. Anaconda will float just below the surface of the water, and will align itself to face the incident wave direction. As a wave passes the device, the rubber tube will lift and become squeezed by the surrounding wave, and a bulge of water will form within the rubber tube. This bulge will travel the length of the device, gathering energy from the wave as it progresses through the tube. Resonance can be achieved by ensuring that the speed of the bulge wave is identical to the speed of the forcing ocean wave, this ensures that high power capture is achieved. The bulge wave will drive a generator located at the stern of the device. Anaconda has been through a rigorous testing procedure at scale, providing proof of concept, at QinetiQ s Haslar Marine Technology Park at Gosport, Hampshire. The next phase of development will require significant funding investment in order to produce a full scale prototype. A full scale Anaconda is anticipated to be around 200m long, with a diameter of 5.5mand power output of 1MW. Conceptual Seaenergy Anaconda WEC (Source: Another new concept under development is the AlbaTERN Squid, a device that has been underpinned by extensive laboratory testing at scale level. A central buoyant absorber is filled with water so that it sits just below the surface. The absorber is moved by the passing waves, and the relative motion between the absorber and the link arms is used to pump hydraulic fluid through a generator, producing electricity. Progression of the concept has taken it into a scale deployment at sea, at one of the nursery berths at the EMEC test facility in Orkney, UK. This device is rated at 7.5kW, with an opportunity for modular deployment in what the developers call a WaveNET array, which will consist of several Squid devices moored to a common platform. AlbaTERN Squid WEC (Source: The current project has paved the way for a larger, more powerful, version of the Squid device, rated at 75kW, to enter the development process. Development of this device will take place in Inevitably radical new concepts will require refining, a development process likely to take a number of years. Recent advances in computational modelling have also accelerated the rate at which designs can be tested in a wide range of simulated conditions. Innovative technology could be gamechanging in the challenge to achieve a cost effective ocean energy converter, however this is not a near term solution, and much work is required to progress the design from concept to commercial operation. Page 33

35 5. Tidal Energy Converters This section gives an overview of the current status of Tidal Energy Converters. It also introduces the different prime-mover concepts that are being developed for extracting useful energy from ocean tidal currents. As with the wave energy sector, the tidal energy sector is reaching a significant milestone in the development of the industry; tidal technologies are taking a step towards commercial viability, with the more advanced device developers now progressing beyond single unit demonstration devices and proceeding to array development and multi-megawatt projects. The backing of major OEMs will enhance the ability of technology developers to continue to optimise the development process, potentially unlocking further investment from utilities as array scale projects enter the planning phase. There are three principal hydraulic mechanisms by which tidal currents operate: Tidal streaming, hydraulic current and resonant basins. Tidal streaming occurs as a result of the need for continuity within a fluid flow: As water flows through a constriction, the flow is accelerated. Hydraulic currents occur when two large bodies of water are connected, but are out of phase or have non-concurrent tidal ranges; the difference in water level in each body of water creates a pressure head, and the flow of water from one body of water into the other results. The third mechanism, a resonant basin, occurs when constructive interference between an incoming tidal wave and a reflected tidal wave generates a standing wave. The energy within a tidal stream is proportional to the cube of the velocity. The desire for developers is therefore to harness energy from sites where the velocity is large enough to make deployments economical. Although a one-seventh power law is often used to approximate the velocity profile within a tidal flow, this is not always an accurate representation of the true flow at all points during the tidal cycle. The velocity flow profile is dependant on local site conditions such as seabed roughness, bathymetry and surrounding land mass topography. Tidal energy offers some advantages over other renewable resources such as wind and wave. The fluid medium, sea water, is over 800 times denser than air, so tidal power offers a greater energy density than wind for a given turbine rotor swept area. As the movement of tides result from gravitational forcing, the tides flow with a predictable intermittency. That is the variability is deterministic (and not stochastic like wave or wind), so this eases the integration of tidal energy into existing electricity networks. Providing a sufficiently long data set exists (35 days is the recommended duration), predictability of the tides is possible through a process known as harmonic analysis, hence tidal velocities can be predicted to a good accuracy indefinitely, both future and retrospectively. The operating principle behind tidal energy converters is that the energy contained within the moving current is harnessed by a device that extracts kinetic energy from the flow and imparts this into a mechanical motion of a rotor or foil. The device then converts the mechanical motion of the structure into electrical energy by means of a power take-off system. Before connection to the electricity grid, the electrical power output from the device will need to be conditioned in order to make it compliant with grid code regulations. In essence, tidal device operation is synonymous to that of a wind turbine, albeit operating within a different fluid medium. The following section will discuss in more detail each of the types of tidal energy converter, and their principles of operation. Page 34

36 5.1. Types of TEC In a similar manner to wave energy devices, several classifications have been created that define the variety of tidal energy converters by type, covering primarily the technical concepts behind the device operation. Tidal energy converters can also be designed for operation in specific water depth conditions: deep water, intermediate water or shallow water. Various international examples of technology that has been designed to extract energy from the tides will be discussed in following sections of this report, but first, the classification of devices must be defined. For the purpose of this report, classification will follow that used by EMEC, in which the following notation is used: Table 4: TEC Types Device Type Classification (Tidal) Horizontal Axis Turbine A Vertical Axis Turbine B Oscillating Hydrofoil C Enclosed Tips (Ducted) D Helical Screw E Tidal Kite F Other G Although, strictly speaking, most enclosed tips (ducted) turbines fall under the same horizontal axis design principle, the addition of a duct can have both positive and negative impacts when compared to an un-ducted device. A duct can accelerate the flow into the rotor, and could also align flow whilst reducing the turbulence of the flow within the duct. This is more favourable in terms of reducing fatigue on the rotor. Where ebb and flood tides are not perfectly bi-directional, a ducted turbine could be an advantage. By placing a duct around a rotor, a structure is put in place that will make it more difficult for marine mammals to evade the rotating components of the turbine. Some turbine designers have tried to address this by creating an opening at the centre of the turbine through which marine life can pass safely through. One significant disadvantage of a ducted structure is the additional drag penalty that will be faced. This drag penalty will extract energy from the flow that will not be recoverable down stream. Device developers need to be aware of minimising the energy dissipation through interaction with the foundation structure of the device Horizontal Axis Turbine (A) Description: Horizontal axis turbines utilise lift generated by blades to turn a rotor. Energy is extracted from the tidal flow and causes the rotation of a turbine mounted on a horizontal axis. The rotation is converted to electrical energy through use of a generator. Image Source: Vertical Axis Turbine (B) Description: Vertical axis turbines, similar to the above, utilise lift generated by blades to turn a rotor. Energy is extracted from the tidal flow and causes the rotation of a turbine mounted on a vertical axis. The rotation is converted to electrical energy through use of a generator. Image Source: Page 35

37 Oscillating Hydrofoil (C) Description: The oscillating hydrofoil device consists of a hydrofoil located at the end of a swing arm. Control systems alter the pitch of the foil to create either lift or downforce, moving the foil in an oscillatory motion. This motion can be used to pump hydraulic fluid through a motor. The rotational motion that results can be converted to electricity though a generator. Image Source: Enclosed Tips (Ducted) (D) Description: Enclosed Tips (Ducted) devices are essentially contained within a shrouded structure. The duct may be used to accelerate and concentrate the fluid flow, allowing the use of smaller rotor diameters. Other ducted structures could help to minimise turbulence and align the flow of water into the turbine. Image Source: Helical Screw (E) Helical screw type turbines are a variation on vertical axis turbines that draw power from the tidal stream as the water flows up through the helix. Image Source: Tidal Kite (F) Tidal kite designs, in which a tethered kite flies a small turbine through the flow, effectively increase the relative velocity entering the turbine. These dynamic devices could generate electricity from significantly lower-velocity currents, or use much less material than static TECs. Image Source: Other (G) Description: There may be other novel tidal turbine concepts in the development process, which utilise different means of extracting energy from the flow of fluid, and do not fit into any of the categories defined above. These can be classified in the other category Further Permutations In addition to the different turbine designs, there are several mooring options that can be considered for fixing a tidal turbine to the sea floor. Monopile: A single tubular steel tower can be drilled and grouted into a deep socket in the sea bed. Surface piercing foundation types of this design are generally limited to approximately 30m water depth. Monopile foundations could be used for fully submerged devices as an alternative to gravity or pinned foundations. Page 36

38 Pinned: Foundation structures can be pinned by drilling and grouting small sockets in the sea bed. These anchor points may utilise pins of several metres in length, but will generally be shorter than the drill depth required for monopole foundations. These foundations are suitable for turbines mounted close to the bottom of the water column. Gravity Base: This foundation type will hold a tidal energy converter to the sea bed by means of a substantial mass, with the gravitational forces keeping the device fixed in place. These foundations are suitable for turbines mounted close to the bottom of the water column. Floating: Buoyant turbine devices can be moored to the sea bed using either flexible or rigid moorings. There may also be an option of mounting multiple devices on one floating platform. Designs of this type can access the faster flowing currents located higher within the water column, but it is possible that there may be some increased cyclic loading and fatigue stress caused by complex interactions due to the circular wave particle motion discussed in Section 4 and Figure 5. Figure 6: Tidal energy converter foundation types Many of the tidal energy converter concepts at the forefront of the industry have adopted a horizontal axis device. While this concept has received the greatest attention, there is little convergence in the design of foundation and support structures. While horizontal axis devices are more common, the vertical axis and oscillating hydrofoil designs intersect a larger area for a given rotor diameter than horizontal axis designs. The swept area for given device designs are indicated in Figure 7. The tidal energy resource is very site specific. Much of the existing identified resource lies in close proximity to a significant land mass, although there are limited grid connection opportunities at present, and grid reinforcement will be necessary to take advantage of the available resource. A significant challenge for the tidal energy industry is demonstrating the survivability of a device. The marine environment is far harsher than that of other onshore renewables, with extremely high loading due to the density of water. Although certain aspects of device loading can be predicted, the effect of turbulence on devices is still an area of research. In order to survive the extreme load scenarios that could occur during storm conditions, the device must be carefully engineered to protect it from damage. Page 37

39 Figure 7: Tidal energy converter swept area Yaw: Horizontal axis tidal devices may contain systems that allow orientation of the device to face the oncoming tidal flow. This is known as yaw. Devices with yaw capabilities may have an active yaw system, in which motors turn the device (about the vertical yaw axis) to face the oncoming tidal flow. Generally, yaw movements will be carried out at slack tides, where the forces on the turbine are at the lowest value. A device with passive yawing makes use of hydrodynamic forces to align the device with the flow. Figure 8: Yaw and Pitch Pitch: In order regulate the loading faced by the rotor, and to optimise the efficiency of the rotor over a wide range of flow speeds, certain rotor designs incorporate pitching blades. Pitch systems allow control of the angle of attack of the blades, giving greater control over the rotor loading. Certain devices have blades that can pitch 180 to allow for the changing direction of the tide therefore allowing the blade to face both ebb and flood tidal flow directions. This 180 pitch mechanism is generally found on devices without the ability to yaw. Yaw and blade pitch mechanisms add mechanical complexity to system design. Additional components increase the chance of failure, so removal of yaw or blade pitch system could increase system reliability. Devices without pitching blades will require a means of carrying out an emergency stop of the device to protect the components from damage, for situations such as loss of grid connection. The force on a fixed pitch blade in an emergency situation will require substantial braking power in order to prevent movement of the rotor. There are both positives and negatives for the implementation of a pitch or yaw system, and these need to be considered carefully in system design to ensure that the added cost and complexity if offset by increased yield. While the sector is still demonstrating operational performance and maintainability at an individual device level, the next stage of the development process will involve deployment of arrays of multiple devices. Page 38

40 5.3. International Examples (Tidal) The tidal energy sector has several front-running devices. A number of device developers have deployed single unit demonstration devices, and substantial operational experience has been gained, the industry is yet to progress beyond deployment of single devices. Array projects are well into the planning phase and in March 2011 the Scottish Government gave planning consent for a 10MW tidal array in the Sound of Islay, Scotland. If funding negotiations are successful, construction is planned to take place between 2013 and 2015, and the project will be the first of its kind within Europe. As with the wave energy sector, the backing of major utility companies is now manifesting itself through partnerships within the development process, unlocking further investment and in some cases international co-operation. Significant investment from OEMs has also allowed the tidal industry to take a step towards commerciality. Several tidal device developers have received the backing of an industrial partner such as a major OEM. With the OEM experience in other sectors such as wind power or hydro power, there is the potential for good knowledge transfer and accelerated development of technology. This section aims to present a review of the status of the tidal energy sector, identifying and highlighting front-running technology, whilst providing an overview of relevant technological developments that are adding to the knowledge and experience of the industry. A list of tidal energy technologies and device developers, together with information on device type and technology readiness levels, can be found on the United States Department of Energy Marine Hydrokinetic Database [11]. This reference database is fully searchable, and there are advanced search options available for convenient site navigation. Information on devices and developers is also contained on the EMEC website [10]. In order to avoid repetition of work that has been carried out elsewhere, this document will identify the most advanced technology developer(s) in each tidal energy converter type, together with detailing the technology readiness level and the level of testing that has been carried out by the device developers. At present, most tidal energy converters are in the R&D phase of technology development, however a small number of devices have reached an extensive level of at sea testing using a full scale demonstration device. This document includes a representative list of technologies in each TEC type. However, the list is not exhaustive, as other potential technologies have not being included due to the limitation of the report length. A summary of device developers within each of the technology types is shown in Table 5 below. Device Type Horizontal Axis Vertical Axis Oscillating Hydrofoil Enclosed Tips (Ducted) Helical Screw Tidal Kite Table 5: A Selection of TEC Device Developers Device Developers at Various Stages of Development Siemens MCT, Andritz Hydro Hammerfest, TGL, Atlantis, Voith Hydro, Verdant Power, Scotrenewables, Tocardo, Straum Hydra Tidal, Oceanflow Energy Neptune Renewable Energy, Ponte de Archimede Pulse Tidal OpenHydro, Clean Current Flumill Minesto The tidal energy sector has experienced far greater design convergence than the wave energy sector. Many of the tidal energy converter concepts at the forefront of the industry have adopted a horizontal axis turbine. There are a significant number of design permutations within the horizontal axis design type, but there are a number of designs that deviate from the conventional approach. These will be discussed further within this section. The tidal energy sector contains a number of Page 39

41 devices that are at different levels of technology readiness. Advanced concepts have significant at sea testing, and this has been made clear throughout the section. In the individual device information, in the instance that a device is in the pre-deployment stages of development, the rated power output is indicated in parenthesis. Page 40

42 Horizontal Axis Siemens Marine Current Turbines SeaGen is a horizontal axis tidal turbine. The rotor of each SeaGen turbine is connected to a generator through a gearbox, stepping up the speed of rotation, much in the same way as a conventional wind turbine. The blades on each rotor are pitch controlled and can be pitched through 180 when the direction of the tide reverses. There is no yaw mechanism on the SeaGen device. SeaGen in raised position (Source: The existing SeaGen device is a twin rotor tidal turbine, located in Strangford Lough, Northern Ireland. Installed in 2008, the device exceeded 5GWh of electricity production during Future SeaGen S devices will have an increased rotor diameter of 20m, and a power output of 1MW per rotor, increasing the rated power of each SeaGen S device to 2MW. A mechanical lifting mechanism makes it possible for turbines to be raised above the water allowing on-site maintenance: The main spar, upon which the twin rotors are connected, can be hoisted up the tubular steel foundation structure, allowing access to the mechanical components of the turbine. The same on-site access and maintenance design principle will be applied to future device designs. Country of Origin UK Rated Power Output 1.2MW (2MW) Water Depth Min/Max 20m / 30m Cut in Velocity (m/s) 0.8 Rated Velocity (m/s) 2.4 TRL 8 Number of Deployed Devices 2 Foundation Type Monopile or pinned quadropod PTO Mechanical, gearbox connected to generator Heavy lift vessel with Dynamic Deployment Vessel Positioning capability, or heavy lift barge Maintenance Strategy On site, turbines raised above water level Lynmouth, Devon, UK 1 x 300kW; Projects to Date Strangford Lough, UK twin 600kW rotors Page 41

43 Andritz Hydro Hammerfest Andritz Hydro Hammerfest develops the HS1000 device - a three-bladed rotor which is coupled to a generator through a gearbox. The blades are capable of pitching and at slack tide; the blades can be pitched through 180. There is no yaw mechanism in place on the HS1000 device. Andritz Hydro Hammerfest HS1000 (Source: The company deployed its first prototype tidal stream turbine in Kvalsund, Northern Norway, in The 300kW HS300 device became the first grid connected turbine to successfully export electricity in Although designed for a three year test period, the HS300 device was retrieved for inspection after four years of testing. After inspection and maintenance, the turbine was redeployed in 2009 for a period of further testing. Andritz Hydro Hammerfest report that the HS300 had an availability of 98% during the testing phase, during which over 1.5GWh of electricity was exported to the grid. The HS300 device provided a base for the up-scaled HS1000 1MW device, which is now undergoing extensive testing at EMEC in Orkney, UK. Andritz Hydro successfully completed an installation in some of the most hostile waters in the UK, during the winter climate. Country of Origin Norway / UK Rated Power Output 1MW Water Depth Min/Max 40m / 100m Cut in Velocity (m/s) 1.1 Rated Velocity (m/s) 2.2 TRL 8 Number of Deployed Devices 2 Foundation Type Gravity base PTO Mechanical, gearbox connected to generator Deployment Vessel Heavy lift vessel with Dynamic Positioning capability Maintenance Strategy Retrieval of nacelle, return to base Projects to Date Kvalsund, Norway 1 x 300kW; EMEC, UK 1 x 1MW Page 42

44 Tidal Generation Limited The TGL Deep Gen device has full yaw capability, in addition to pitching blades. During slack tides, the nacelle can be orientated to face the oncoming tidal flow. TGL installed a 500kW prototype at EMEC in the UK during This device, together with a 1MW unit currently under development, has been part of an Energy Technologies Institute (ETI) funded project called PerAWaT. TGL nacelle (Source: The existing 500kW device has an 18m rotor diameter. The nacelle is buoyant, and can be towed to the installation site using a tug boat. The nacelle is then winched into place on top of a pre-installed foundation. With the buoyant nacelle design, installation and retrieval can take place in under 20 minutes. In September 2012, Alstom signed an agreement with Rolls-Royce to acquire Tidal Generation Limited (TGL) Country of Origin UK Rated Power Output 500kW, (1MW) Water Depth Min/Max 35m / 80m Cut in Velocity (m/s) 1 Rated Velocity (m/s) 2.7 TRL 7 Number of Deployed Devices Foundation Type PTO Deployment Vessel Maintenance Strategy Projects to Date 1 Pinned tripod Mechanical, gearbox connected to generator Heavy lift vessel with Dynamic Positioning capability for foundation. Nacelle is buoyant and can be towed to location using a tug boat Retrieval of nacelle, return to base EMEC, UK 1 x 500kW Page 43

45 Atlantis Resources Corporation Atlantis Resources Corporation have designed and developed three families of tidal turbine, the AN series, the AS series, and the AR series. The largest of these, the Atlantis AR series, is a fixed pitch 1MW device. The turbine has the ability to yaw and at slack tide the device will be orientated to face the oncoming tidal flow. Atlantis has deployed and retrieved the 18m rotor diameter AR1000 device, and it is currently undertaking further development and testing in a controlled environment at the NaREC test facility in UK. Atlantis is working in partnership with global aerospace, defence, and emerging technology company Lockheed Martin to develop future iterations of the device. Atlantis Resources Corporation AR1000 (Source: Country of Origin Australia Rated Power Output 100kW, 500kW, 1MW Water Depth Min/Max Unknown Cut in Velocity (m/s) 1 Rated Velocity (m/s) 2.65 TRL 7 Number of Deployed Devices Foundation Type PTO Deployment Vessel Maintenance Strategy Projects to Date 1 Gravity base Mechanical, gearbox connected to generator Heavy lift vessel with Dynamic Positioning capability Retrieval of nacelle, return to base San Remo, Australia 1 x 5kW; San Remo, Australia 1 x 150kW; EMEC, UK 1 x 1MW Page 44

46 Voith Hydro Voith Hydro is developing a fixed pitch, horizontal axis turbine, designed to be mounted on the sea bed. The rotor consists of three symmetrical blades, which can capture energy from the ebb or flood movements of the tide without the device requiring pitch, or yaw, mechanisms. The rotor is coupled to a direct drive permanent magnet generator, and the rotor shaft bearings are lubricated by sea water. Voith hydro installed a 110kW 1:3 scale prototype device known as HyTide in Jindo, South Korea, in early The operation of this device will feed into preparation for a full-scale 1MW prototype. Voith Hydro commissioned Bauer Renewables to install a grouted pile foundation in preparation for deployment of the full-scale device. This work was carried out using a novel sea bed drilling technique developed by Bauer; a sea bed mounted drill carried out operations without the need for a jack up barge. A template with an automatic levelling system allows the accurate location of the drill, which can be remote controlled from a launch vessel. Voith Hydro HyTide (Source: Country of Origin Germany Rated Power Output 110kW, (1MW) Water Depth Min/Max 30m / unknown Cut in Velocity (m/s) unknown Rated Velocity (m/s) 2.9 TRL 7 Number of Deployed Devices Foundation Type PTO Deployment Vessel Maintenance Strategy Projects to Date 1 Gravity base or monopile foundation Permanent magnet direct drive generator Heavy lift vessel with Dynamic Positioning capability Retrieval of nacelle, return to base Jindo, South Korea 1 x 110kW Page 45

47 Scotrenewables The Scotrenewables tidal turbine is a second generation floating tidal turbine, consisting of a cylindrical tube to which two horizontal axis rotors are connected. The rotor blades are fixed pitch, but the entire rotor mechanism can be raised in a survival mode during storm sea states, or for transportation. Scotrenewables have deployed a 250kW scale prototype at EMEC, UK. Upon successful demonstration of the device, a 2MW full-scale demonstration device with a 16m rotor diameter will be constructed for testing at EMEC. This device will be four times the mass of the existing 250kW prototype, but will generate eight times the power. The Scotrenewables turbine is designed for transportation, installation and maintenance using only a multi-cat work boat. This keeps installation costs significantly lower than would be incurred if a heavy lift vessel was required. Scotrenewables SRTT250 (Source: Country of Origin UK Rated Power Output 250kW, (2MW) Water Depth Min/Max 25m / 120m + Cut in Velocity (m/s) unknown Rated Velocity (m/s) 2.5 TRL 7 Number of Deployed Devices Foundation Type PTO Deployment Vessel Maintenance Strategy Projects to Date 1 Floating moored structure Gearbox and variable speed induction generator Multi purpose workboat (multicat) Return to base EMEC, UK 1 x 250kW Page 46

48 Tocardo Tocardo are a tidal stream device developer based in the Netherlands. Their turbine contains a direct-drive generator that eliminates the need for a mechanical gearbox. The device uses a twin blade fixed pitch rotor with intelligent speed tuning (stall control). The first 100kW turbine was installed in the Afsluitdijk, a large dam between Waddensea and the Ijsselmeer during The device has operated successfully, exporting electricity to the grid since installed. The technology has been proven at small scale, and is highly scaleable. 200kW units have been tested and installed, and this is being followed by the development of large 500kW and 1MW turbines. It is anticipated that these could be installed in the Pentland Firth. The 50kW and 150kW variations are already commercially available, and are ready for implementation in run-of-river and inshore applications. Tocardo Conceptual 500kW Device (Source: Country of Origin Netherlands Rated Power Output 100kW, 200kW, (500kW), (1MW) Water Depth Min/Max 5.5m / 25m Cut in Velocity (m/s) (variable design conditions) Rated Velocity (m/s) 2 4 (variable design conditions) TRL 6 Number of Deployed Devices 1 Foundation Type Multiple foundation options PTO Direct drive permanent magnet generator Deployment Vessel Dependant on foundation To Date Retrieval of nacelle, return to base Projects in Operation Den Oever, Netherlands 1 x 100kW Page 47

49 Verdant Power Verdant Power s Kinetic Hydropower System (KHPS) is a water-to-wire system that consists of a three-bladed fixed pitch horizontal-axis turbine. The support structure of the turbine is hydrodynamically designed to allow the turbine to self-rotate into the prevailing current (weathervane) in order to face the oncoming flow of current. The rotor rotates at approximately 40rpm, and the nacelle is sealed from the marine environment. The development of the KHPS turbine has led to a proposed range of turbines from 5m rotor diameter (56kW) to 10m rotor diameter (500kW). Verdant Power ( Country of Origin USA Rated Power Output 50kW, (500kW) Water Depth Min/Max 10m / unknown Cut in Velocity (m/s) 1 Rated Velocity (m/s) Unknown TRL 6 Number of Deployed Devices Foundation Type PTO Deployment Vessel Maintenance Strategy Projects in Operation 6 Gravity base Planetary gearbox and induction generator Crane barge Retrieval of nacelle, return to base East River, New York City, USA Page 48

50 Hydra Tidal Morlid II Hydra Tidal s Morild II tidal power plant technology is a floating tidal power plant. The technology consists of a floating platform and two twin turbine units with blades fabricated from pine wood. The Morlid II turbine can be anchored in different water depths, and the floating platform opens up opportunities for deployment in deeper waters. The plant carries sea vessel verification, and it can be towed between the docks and the deployment location. The floating structure allows maintenance to be carried out on site. PTO is via hydraulic transmission to two synchronous generators. The blades can be pitched 180 to operate efficiently in both ebb and flood tides. Each turbine in the existing prototype has a rotor diameter of 23m, and the blades can pitch, offering optimised performance in a range of current velocities. The prototype has an installed capacity of 1.5 MW. Hydra Tidal Morlid (Source: Country of Origin Norway Rated Power Output 1.5MW Water Depth Min/Max Unknown Cut in Velocity (m/s) Unknown Rated Velocity (m/s) Unknown TRL 7 Number of Deployed Devices Foundation Type PTO Deployment Vessel Maintenance Strategy Projects to Date 1 Floating moored Hydraulic motor and synchronous generator Tug boat Maintenance carried out on site when in surfaced position; for major maintenance: return to base Gimsoy Stream, Lofoten, Norway Page 49

51 Vertical Axis Neptune Renewable Energy Neptune Renewable Energy has developed the Proteus tidal stream power generator, a vertical axis turbine designed to harness the kinetic energy found in estuarine tidal flows. The Proteus demonstrator structure forms a venturi duct which accelerates the tidal flow onto a vertical axis, cross-flow rotor. The upper end of the rotor is connected to a gearbox and DC generator. All power conditioning equipment is located above the water line. Flow onto the rotor can be optimised by using computer controlled shutters. Each production Proteus turbine will have an installed capacity of 1.25MW, resulting in an annual power output of up to 6 GWh/year at sites where the mean spring peak tidal stream currents reach 3 m/s. Neptune Renewable Energy have identified at least ten British estuaries where the spring peak currents are suitable for Proteus device deployment. Pilot testing has been carried out in the Humber estuary, UK, where the demonstrator device is providing electricity for a visitor attraction and research centre in Hull called The Deep. Neptune Renewable Energy Proteus (Source: Country of Origin UK Rated Power Output 250kW (1.25MW) Water Depth Min/Max 6/ 8 (designed for estuarine use) Cut in Velocity (m/s) 1 Rated Velocity (m/s) 3 TRL 7 Number of Deployed Devices Foundation Type PTO Deployment Vessel To Date Projects in Operation 1 Floating moored Mechanical gearbox and synchronous generator Tug boat Minor maintenance carried out on site; for major maintenance return to base Humber Estuary, UK Page 50

52 Ponte di Archimede International (Kobald Turbine) A vertical axis Kobald Turbine has been developed by Ponte di Archimede International. The vertical axis design rotates independently of the current direction, and no yawing mechanism is required. The Kobold turbine generates a high torque that permits self starting once the cut in tidal velocity is reached. The pilot unit was launched in 2001 in the Strait of Messina, by the coast of Sicily, where the peak velocity of the tidal current can reach 3m/s. The device is located 150m from shore and is held on station by means of four catenary mooring lines. Ponte di Archimede is working in partnership with Bluewater Energy Services to deploy a fourturbine floating platform at the EMEC test facility in the UK. Ponte di Archimede (Source: Country of Origin Italy Rated Power Output 30kW, (250kW) Water Depth Min/Max 18m / 35m Cut in Velocity (m/s) 1 Rated Velocity (m/s) 2 TRL 6 Number of Deployed Devices Foundation Type PTO Deployment Vessel Maintenance Strategy Projects in Operation 1 Floating moored Mechanical gearbox and synchronous generator Tug boat Minor maintenance carried out on site; for major maintenance return to base Strait of Messina, Italy Page 51

53 Oscillating Hydrofoil Pulse Tidal The Pulse Tidal device uses oscillating hydrofoils, which lie horizontally in the water, to sweep vertically through the water column. This motion is used to drive a crankshaft, and the rotary motion that results is stepped up through a gearbox before connection to an induction generator. In 2009, Pulse Tidal deployed a 100kW "Pulse-Stream 100" oscillating hydrofoil device into the mouth of the River Humber, UK. Pulse Tidal (Source: Country of Origin UK Rated Power Output 100kW Water Depth Min/Max 10m / unknown Cut in Velocity (m/s) 1 Rated Velocity (m/s) 2.5 TRL 6 Number of Deployed Devices Foundation Type PTO Deployment Vessel Maintenance Strategy Projects in Operation 1 Piled or Gravity Base Mechanical gearbox and synchronous generator Crane barge, tug boat for future deployments Minor maintenance carried out on site; for major maintenance return to base Humber Estuary, UK Page 52

54 Enclosed tips Clean Current The Clean Current device is a ducted horizontal axis turbine with fixed pitch blades. The flooded permanent magnet generator is lubricated by the water flow, and allows variable speed operation. There is only one rotating part to the turbine. Commercial devices for shallower waters (less than 20m) such as rivers are under development. This will allow Clean Current to incrementally scale up the technology. Factory testing of the full scale river demonstration unit is intended to take place before deployment in Manitoba, Canada. The tidal devices will build upon the river units and incorporate a passive yaw mechanism allowing the device to rotate into the flow. It is anticipated that deployment in shallow tidal sites will take place shortly after the full scale river deployment. Clean Current (Source: Country of Origin Canada Rated Power Output 12kW, 33kW, 65kW, 85kW, (125kW, 285kW, 500kW) Water Depth Min/Max 5.5m / 20m Cut in Velocity (m/s) 1.5 Rated Velocity (m/s) 3.5 TRL 6 Number of Deployed Devices Foundation Type PTO Deployment Vessel Maintenance Strategy Projects to Date 1 Pinned or Gravity Base Permanent magnet generator - rotor attached to the blades and stator located in the central duct Crane barge Removal of nacelle, return to base Race Rocks, Victoria, Canada 1 x 65kW Page 53

55 OpenHydro The OpenHydro device is a ducted horizontal axis turbine, with a central opening that allows safe passage for marine life. The permanent magnet generator is located within the duct of the device. The rotor is attached to the blades, while the stator is fixed within the duct. OpenHydro was the first company to use one of the test berths at the EMEC test facility in the UK.A 6m diameter turbine rated at 250kW was installed and grid connected in Further device testing took place in Nova Scotia, where testing of a 10m diameter Open Centre Turbine took place. More recently, Electricite de France and OpenHydro have started ocean testing of the 2MW Open Centre Turbine at Paimpol-Brehat. OpenHydro (Source: Country of Origin Ireland Rated Power Output 1MW, 2MW Water Depth Min/Max 35m / Unknown Cut in Velocity (m/s) Unknown Rated Velocity (m/s) 2.65 (for 1MW device) TRL 7 Number of Deployed Devices Foundation Type PTO Deployment Vessel Maintenance Strategy Projects to Date 3 Gravity Base Permanent magnet generator - Circumferential generator with rotor attached to the blades and the stator located in the surrounding duct. Specialist installation barge Removal of nacelle, maintenance carried out on shore EMEC, UK 1 x 250kW; Bay of Fundy, Canada 1 x 1MW; Paimpol-Brehat, France 2MW Page 54

56 Helical Screw Flumill The Flumill tidal energy converter is influenced by the design of a helical excess flow control valve used in the gas industry. Glass reinforced plastic (GRP) is used for the construction of the helix, and buoyancy allows the system to be towed to location of deployment. The Flumill system is able to align passively into the flow, and the device is capable of accommodating offset tidal flows where the ebb and flood flow directions are not perfectly bi-directional. The rotational speed of the outer edge of the helix never exceeds the speed of the water flow, so there is no cavitation of the water. This also means that marine life will be able to safely negotiate around the device without risk of harm from fast moving blades. Counter rotating helical screws allow torque loading on the foundation to be cancelled out, ensuring a hydrodynamically stable device design. The device is self-regulating in strong tidal flows. A prototype of the smallest commercial Flumill device has been deployed at the EMEC nursery test site in the UK, and plans for a fully grid connected, larger diameter device is planned for Rystraumen near Tromsø. Country of Origin Rated Power Output Water Depth Min/Max Flumill 2 (Source: Cut in Velocity (m/s) 1 Rated Velocity (m/s) Unknown TRL 6 Number of Deployed Devices Foundation Type PTO Deployment Vessel Maintenance Strategy Projects to Date Norway 600kW, (2MW) Suitable for shallow water (mounted horizontally) or deep water (mounted vertically) 1 Gravity Base or pin pile Mechanical gearbox and synchronous generator Multi-cat workboat Removal of device from foundation, return to base EMEC, UK twin 300kW helix Page 55

57 Other There are certain device developers working on technologies that differ from the above mentioned categories. Some of these technologies operate using similar principles to that of existing device designs, but there are novel technologies introducing new methods of harnessing the tidal energy resource. Ocean Renewable Power Company Although very similar in design to vertical axis turbines, cross-axis (transverse horizontal axis) turbines are modular in construction and can be installed in groups to suit the operating environment to which it will be installed. Ocean Renewable Power Company is developing a cross axis turbine that can be deployed in river, shallow tidal and deep tidal environments. The ORPC turbine is constructed primarily from composite materials, which can resist corrosion. Ocean Renewable Power Company (Source: Country of Origin USA Rated Power Output 180kW Water Depth Min/Max 15m / 30m Cut in Velocity (m/s) Unknown Rated Velocity (m/s) 3 TRL 7 Number of Deployed Devices Foundation Type PTO Deployment Vessel Maintenance Strategy Projects in Operation 1 Gravity Base Permanent magnet generator Tug boat Removal of turbine generator unit, return to base Cobscook Bay, USA 1 x 180kW Page 56

58 Multiple Rotor Platforms Multi-rotor platforms are designed to house multiple devices on a common mooring or foundation. The designs are generally technology neutral, and could allow for a variety of different device designs to be mounted. The buoyancy of such platforms may allow multiple devices to be supported in the upper section of the water column, where the highest tidal velocities are located. While multi rotor platform design is yet to be demonstrated at large scale, there are several mooring platforms under development, with testing at model scale underway. The implementation of multiple rotors on a common mooring could open the door to significant cost reductions. BlueWater Bluewater is an offshore engineering firm with experience within the oil & gas sector. Bluewater has developed a floating structure for tidal turbines called BlueTEC. The structure is an openarchitecture system and may be equipped with either horizontal or vertical axis tidal turbines of any type. The BlueTEC design accommodates all electrical equipment above the waterline and allows ease of access for maintenance. Bluewater has secured a berth at EMEC for a full-scale demonstration. Several different turbines, both vertical and horizontal axis, will be tested on this device. Bluewater Bluetec Floating Platform (Source: Bluewater) Tidal Stream Tidal Stream is in the process of developing three and six-rotor foundation structures. The hollow steel spars are designed to be buoyant, so that the entire structure can be towed to site. Once on location the spars can be partially flooded, allowing horizontal alignment of the turbines. The turbines can be orientated to face the oncoming flow through passive yaw, induced by drag on the structure. Tidal Stream Triton Floating Platform (Source: Page 57

59 Sustainable Marine Technologies Plat-O is a submerged buoyant platform designed to accommodate up to five rotors. The buoyant design allows the structure to be towed to the deployment site, and the device can be held in place using mooring lines. The design makes it possible for individual rotors to be retrieved without the need to surface the entire structure. Sustainable Marine Technologies PLAT-O Floating Platform (Source: There exist other novel tidal energy converter technologies, but these will be discussed further in Section Evolution of Devices (Tidal) Tidal energy converters are now experiencing large scale demonstration and testing; some manufacturers have progressed beyond their original design concept and are looking into engineering solutions that will help to further reduce their cost of energy. Tidal energy converters can be classified into different generations of design as device developers and technologies progress beyond the first prototype concept: First generation technology has experienced significant levels of testing in ocean conditions, such as the horizontal axis type tidal turbines. As a general rule, first generation devices are fixed on sea bed mounted foundation structures with one or, possibly, two devices per foundation. Second generation technology offers novel ideas and solutions to moorings (for example buoyant turbines or foundations), allowing access to the faster flowing water higher in the water column and reducing foundation costs. Second generation technologies may also achieve step change cost reductions by mounting multiple rotors on one foundation structure, maximising the energy output per marine operation. Second generation platforms are already under development, although not necessarily by companies with existing first generation technology. Third generation tidal devices consist of designs that radically change the way in which energy is harnessed by a given device, or allows access to many sites that were previously thought to be uneconomical. This may be a radical overhaul within the structure and PTO components of a device. Third generation technology may produce energy in tidal currents of much lower velocity than can be considered at present by moving the PTO through the current, rather than relying on an area swept by a static prime mover. It must be noted that while the majority of developers are starting with bottom mounted first generation devices, certain device developers have moved directly in to second generation foundations by nature of their design. As development progresses, additional next generation technology may begin to appear in the sector. In the short to medium term, only areas in which the spring peak tide velocity exceeds 2.5 m/s will be economically suitable for development, utilising first generation devices [4]. Page 58

60 Figure 9: Generations of tidal energy converter (Based on Carbon Trust [4]) a) First Generation (Bottom mounted) b) Second Generation (floating) c) Second Generation (mid water column) d) Third Generation innovation allowing additional resource to become economical Second and third generation devices are still in the early stages of development, and there is limited operational experience in tidal flow conditions. There is a real need for next generation devices, which provide significant opportunities for cost reduction or performance and efficiency improvements. Using first generation technology, the cost of tidal energy is likely to be significantly higher than that of offshore wind. In order to become a recognised and established part of the European energy mix, tidal energy generation will need to become competitive with alternative forms of renewable power. The evolution of devices will play a fundamental role in achieving this goal. Although many first generation devices are focusing on deploying demonstration units, there are examples of where consideration has been made as to how further device deployments can harness the resource more efficiently. Marine Current Turbines, have a prototype evolution of their existing SeaGen S device. The existing device is fixed to the sea bed through use of a pinned quadropod foundation. The two rotors are attached to a spar that can be raised out of the water for maintenance. This method of raising the turbines from the current allows certain maintenance work to be carried out on site. This ease of access and multiple rotor configuration heavily influences the next generation of SeaGen U device, whereby an additional third rotor increases the swept area (and hence power output) of the installed system. The device will also have the ability to be raised and lowered through use of a buoyant structure. By increasing the number of turbines per foundation, the cost of energy can be reduced. Similarly, by ensuring the ease of accessibility of the devices, O&M costs can be minimised. SeaGen device evolution: First Generation (left), Conceptual Second Generation (right) (Source: Page 59

61 Although many device developers appear to be converging on a horizontal axis turbine, there are several variations within this design type that can be considered. The wind industry has converged on a three-bladed rotor design, and for many tidal energy converters, this design has been adopted as a standard for tidal energy. There are, however, several examples where the number of blades on a rotor deviates from the wind turbine design principles. Twin bladed rotors have been used by Marine Current Turbines on their existing SeaGen device. Tocardo are using a twin bladed, fixed pitch rotor design. Examples of devices with greater than three blades include Oceanflow Energy, where a four-bladed rotor is used in their current scale Evopod device, with four blades also present on the design of their 35kW community scale device under development. Variation in number of blades (Source: In most tidal devices, steel is the predominant material for foundation and structural components. Blades are often made from Glass Fibre Reinforced Plastic (GFRP). Steel properties are well known in terms of yield and tensile strength, and certain grades of steel have a proven track record in the marine environment. Steels can be protected from corrosion through use of paints, or by using cathodic protection. The use of alternate materials such as composites and plastics may become more widespread in systems which utilise buoyant structures. With a few exceptions, the majority of tidal device developers are currently developing and demonstrating single rotor devices. Whilst this is appropriate for testing and developing a concept, there are some interesting advantages that can be gained through use of contra-rotating rotors (two rotors moving in opposite directions on the same axis of rotation) or counter rotating rotors (two rotors moving in opposite directions on two different axis of rotation). Figure 10: Contra-rotation (left) and Counter-rotation (right) By having an equal number of rotors spinning in opposite directions, the torque loading on a foundation structure can be cancelled out. This has been used in industries such as aviation to great effect. Balance of torques could allow for reduced structural requirements for foundations, and may provide opportunities for cost reduction. Page 60

62 5.5. Radical New Concepts (Tidal) Innovation within the tidal energy sector is pushing the boundaries of engineering. New concepts are opening up the possibility of commercially viable energy production from tidal flows previously thought to be uneconomical. The idea of a radical concept may challenge the fundamental principles of operation of a tidal energy converter, or it may look at revolutionary materials that have not yet been used within the sector. A radical concept must open up potential routes to significant step change cost reduction. Current first generation concepts use sea bed mounted devices, but radical new concepts are looking to remove the need for large foundation structures, making greater use of buoyancy and tensioned cables. There are also some designs that are challenging the conventional horizontal axis turbine approach. These radical concepts may open up routes to significant step change cost reduction. By their very nature, radical concepts are not necessarily proven technologies, and may require significant development before a definitive judgement can be made on whether they do, in fact, reduce the cost of energy. Nautricity have utilised buoyancy and contra-rotation in their Contra Rotating Marine Turbine (CoRMaT) to reduce the foundation loading, allowing a single point mooring system to be used. The rotor torque from contra-rotating rotors cancels out in order to leave a negligible net total torque on the mooring and foundation. The use of buoyancy is a significant feature of second generation tidal turbines, allowing the rotor to be located higher in the water column in order to access the higher flow speeds. Nautricity are also developing HydraGlide, a surface float for the CoRMaT device that will allow the turbine to maintain an optimal position within the water column. Nautricity CoRMaT (Source: The Minesto Deep Green tidal kite design has the potential to unlock deep water sites with a lower velocity than is currently considered economically feasible. By fixing a turbine and generator into a nacelle underneath a wing structure, the wing can use lift to accelerate the device through the water at speeds of up to ten times the flow speed of the surrounding water, therefore increasing the relative velocity of water entering the turbine. The device can be tethered to the seabed, and rudder control surfaces at the rear of the device will allow it to be steered in a figure-of-eight path. In 2012, a one-tenth scale prototype was deployed in Strangford Lough, Northern Ireland, UK. Plans to upscale the technology could lead to a range of devices between 120kW and 850kW depending on the flow speed into which the turbine will be placed. Anticipated water depth range for the 150kW device is 50-65m. This could increase to between 90m and 120m for the 850kW variant. Minesto Deep Green (Source: Page 61

63 6. Arrays Ocean energy devices are generally modular in design, each device utilising only a small portion of the total resource potential at a given site. If the ocean energy sector is to reach the deployment targets set in the National Renewable Energy Action Plan of each Member State [14], and make a meaningful contribution to the European and global energy mix, the obvious route forward is technology deployment in multiple device arrays. At an array scale, projects are likely to consist of multiple marine energy converters, connected by sub sea cables providing a means of transporting electricity to a common transformer or grid connection, much in the same way as wind farms are currently developed. While an understanding of device design is important, it is fundamental to the ocean energy sector that the focus does not remain on individual devices. Configurations involving multiple devices, or arrays, will provide the route to commercialisation, and growth of the industry. Array projects can benefit from the economies of scale. A move towards larger scale manufacturing, as opposed to single unit production, will unlock cost savings in the form of a reduced unit cost and increased repeatability within component manufacture. Cost reduction through sharing of significant infrastructure systems expenses between multiple devices, as opposed to those costs being borne by a single device deployment, can also help to make array projects more economical. The move from single device to arrays represents a considerable shift from current practice as developing, demonstrating, testing, and refining first-of-a-kind autonomous devices has been the predominant focus of the industry, with very little collaboration between the individual device developers. Little is known about the impacts of array deployments, such as how each device will interact with the wake from adjacent devices, or the combined ecological impact of a farm of devices. The structural optimisation of arrays, the placement of individual devices, the operation and maintenance of multiple devices, device performance and array interactions, and the combined array environmental impact represent areas of significant research need. A number of policies and funding programmes have been set in place to reflect this, as the sector seeks to progress closer to commercialisation. In order to successfully make the transition from single device to array deployment, several technology challenges need to be met. In addition, there is a need for continued cost and risk reduction to facilitate increased investor confidence. Reports such as the Low Carbon Innovation Coordination Group Technology Innovation Needs Assessment (TINA) [15] on marine energy, produced by a collaboration of the UK s major public sector backed funding and delivery bodies in the area of low carbon innovation, have identified targeted R&D requirements in order to address the challenges associated with the transition to initial array deployments, together with identifying how the industry can bring into place the cost and risk reductions necessary in order to make further array deployments possible. With the ocean energy sector in the nascent stages, very few dedicated suppliers to ocean renewable energy exist. There is the potential for significant overspill from related technology sectors such as oil and gas or offshore wind. While the present technology within demonstration devices can utilise one-off custom made components, this lends itself to high production costs due to the design, development and fabrication on first-of-a-kind components. As single deployments turn into demonstration array deployments and full-scale arrays, mass production of components could lead to significant cost, and component lead time, reductions. With regards to grid connection configurations, knowledge transfer from the offshore wind sector may play a prominent role. Several electrical connection issues have been identified in the Equimar Page 62

64 Protocol Chapter II.C [16], which will require guidance and consideration at an early stage of any array project. There is also the issue of Grid and Distribution Codes, which must be adhered to for the relevant country in which the array connection is made. Within an array, the maximum number of devices that can be connected in one circuit is limited, due to voltage drop across a length of cable and the maximum capacity of a given cable. There are several options available for arrangement of device layout, each of which will result in different levels of power loss, reliability and overall cost. It should be noted that the actual layout of the ocean energy array will be determined by the geotechnical conditions at the proposed site, and the resource itself. This will have an impact on the electrical infrastructure and grid architecture. The layout options for arrays are known as clusters, and are highlighted in the diagram below: Figure 11: Possible Ocean Energy Converter Array Layouts (Source [16]) a) String Series Cluster - Medium and large farms AC and DC b) Star (Radial) Cluster Large unit farms AC and DC c) Full String Cluster Small farms AC and DC d) Redundant String Cluster High risk farms AC and DC e) Series DC Cluster Small and medium farms DC The spacing of devices will become increasingly important as arrays grow in size. Although the ocean energy sector is at a demonstration stage, very little research has taken place in the field to demonstrate the physical interaction between devices in close proximity. On one level, the lack of array projects means that no one developer has achieved a level of installation by which they can collect significant data to fully understand the interaction. Much effort is taking place at a computational level to understand the array effects of devices, waves and energy extraction. Once array deployment takes place, this area should receive attention in order to better understand the complex relationships between adjacent devices. Whilst it is desirable to minimise the overall electrical infrastructure required for a given array project, it must be noted that hydrodynamic interaction could lead to reductions in the overall Page 63

65 power output. It is therefore necessary to consider a wide range of parameters when configuring an array and the end result will be a compromise to achieve the lowest levelised cost of energy. The electrical configuration of offshore wind farm arrays may influence the design of ocean energy arrays. The wave or tidal arrays will require grid connection that will likely require transformers, electrical switchgear, and back up generators and batteries. Purpose built sub stations located offshore may be a requirement for future ocean energy arrays, and will bring added complexity and cost to the design of a project. Although no array deployment has yet taken place, the effect of shadowing from devices at the front of the farm is likely to impact the overall output from a farm of devices. There will be complicated hydrodynamic interactions that are, at present, little understood; so significant effort must be made in data collection to help identify and clarify the likely effects on downstream tidal devices, or secondary rows of wave devices that are located behind another row of wave devices, relative to the oncoming wave front. The challenges outlined above must be met if the ocean energy sector is to grow and, with increasing support from European Member States [17], utilities and OEM investors, array deployments are likely to become a reality within the next few years. Figure 12: Ocean Energy Arrays (Source: Page 64

66 7. Strategic Technology Challenges 7.1. Introduction The strategic technology challenges section of this report sets out to provide a summary of the challenges faced by the ocean energy sector, providing a foundation which will be built upon in future SI Ocean reports. A high level overview of the sector challenges will set the scene for the status of ocean energy development. While technical recommendations that can identify solutions to the technical challenges will be covered in future SI Ocean reports, the purpose of this section is to identify the over-arching themes that are shaping the challenges faced by the ocean energy sector today. Identification of these challenges is of significant importance, as it highlights the sector needs at a European level, indicating the specific action areas that require a unified and coordinated approach from the industry in order to secure reliable and cost effective ocean energy devices. While certain elements of the identified technology challenges may be targeted by individual technology developers, for credibility in the wider energy sector, it is essential that the ocean energy sector as a whole demonstrates that it is capable of adopting a unified approach to the technical challenges and their solutions. This section also highlights the specific action areas in which the ocean energy sector will seek to see continuous and sustained progress beyond current state of the art, ensuring that technology development does not remain constrained behind the same barriers that are presently identified, and that ocean energy technology can move beyond single device demonstration and into a commercial manufacturing phase. This will be of benefit to individual technology developers, and also wider manufacturing, supply chain, and research facilities within the EU. It must be reinforced that the fundamental challenge for WEC and TEC developers is reduction in the levelised cost of energy. The technical challenges that exist all relate, in some way, to this: Improving yield, increasing reliability, and reducing CAPEX and OPEX costs. However it is achieved, cost reduction is an essential requirement for accelerated and sustained deployment of ocean energy Building upon Existing Knowledge This section draws on a number of reports that have identified technology challenges for the marine energy industry at a European level. The ORECCA project [18] has identified specific challenges for the ocean energy sector and has highlighted generic areas where collaboration with offshore wind may help to address some of the challenges faced by the ocean energy sector at an EU level. The EU- OEA Ocean Energy roadmap [19] and the IEA Ocean Energy Systems Vision document [20] discuss challenges in the European and international context. A specific target for SI Ocean is to project the technology challenges faced by the ocean renewable energy industry on to a European level. The Carbon Trust report Accelerating Marine Energy [4] investigates the current and future cost of marine energy, based on detailed interviews with device developers based within the UK. Ambitious but achievable target for cost reduction have been set, and a plausible cost trajectory has been presented within the UK Low Carbon Innovation Coordination Group Marine Energy Technology Innovation Needs Assessment [15]. In Figure 13 the cost of ocean energy technology is anticipated to reduce to a stage at which commercialisation could occur (Point 1). Following on from commercialisation, three scenarios are shown: Page 65

67 A) No further cost reductions are seen once the technology has entered a commercial phase B) Costs are estimated to reduce with learning rates similar to that anticipated by the offshore wind sector through learning-by-doing mechanisms C) Costs are estimated to reduce through both learning-by-doing and technological innovation, whereby an improved cost reduction pathway can be achieved. Figure 13: Potential Impact of Innovation on Levelised Costs - Medium global deployment (Source: Carbon Trust [15]) The Accelerating Marine Energy report and the Marine Energy TINA highlight the role that innovation could play in order to reduce the technology and development costs. Innovation could be in the form of incremental enabling technology development, improving certain aspects of economic performance or efficiency, or innovation could be through radical new concepts opening up larger areas of resource, or creating a step change in device deployment costs. Key areas for public sector support for innovation have been identified in the Marine Energy TINA [15], such as supply chain optimisation and identifying appropriate funding mechanisms. While a more detailed investigation of the means through which the sector challenges can be addressed will be discussed in future SI Ocean reports, the most prominent challenges facing the industry are summarised in Figure 14. Figure 14: High Level Sector Challenges (Adapted from ORECCA Roadmap [18]) Page 66