Wojciech Zienkiewicz

CHARACTERISATION AND REVIEW OF AVAILABLE TIDAL ENERGY GENERATION SYSTEMS AND RESOURCES IN SCOTLAND. Author: Wojciech Zienkiewicz - Supervisor: Martin Askey Degree Dissertation submitted as a part of the requirements for (BEng) Energy and Environmental Engineering at the school of Engineering and the Built Environment, Edinburgh Napier University APRIL 1, 2015 EDINBURGH NAPIER UNIVERSITY Abstract The fallowing report briefly describes tidal energy potential in Scotland by identifying suitable resource sites with high current flow speeds. Generation systems were compared, indicating wide range of technology used for harvesting tidal energy. Calculation of potential power output for Kyle Rhea, Scotland using data set of current speeds, proves that tidal power systems could have significant contribution to renewable energy in Scotland. Financial evaluation of tidal energy farms is presented in rather theoretical form than calculation, due to early stages of tidal energy projects. Additionally, short environmental analysis was made to assess any potential environmental impacts. 2 Acknowledgements I would like to express my deepest gratitude to my supervisor, Mr. Martin Askey, for his patience, guidance and great atmosphere during the consultation meetings. I would also like to thank my parents for the love and support they gave me. Additionally I would like to thank to Montserrat Serra Romero for giving me the chance to study in quiet environment throughout all these years. 3 Contents Abstract ............................................................................................................................................................2 Acknowledgements ......................................................................................................................................3 Abbreviations .................................................................................................................................................6 List of Figures ................................................................................................................................................6 List of tables ...................................................................................................................................................7 List of equations ............................................................................................................................................7 1. Introduction ................................................................................................................................................8 2. Analysis of tidal energy potential in Scotland. .................................................................................8 2.1 Early estimations of the potential. .................................................................................................8 2.2 Early assessments in contrast to recent studies. ......................................................................9 2.3 Conclusion .........................................................................................................................................10 2.4 Identification of the areas with the most suitable flows for energy extraction in Scotland. ....................................................................................................................................................11 2.4.1 List of the potential sites in northern Scotland (Pentland Firth and Orkney waters) ..................................................................................................................................................................12 2.4.2 List of the potential sites in Scotland (different locations). ...........................................13 2.4.3 Test sites. ....................................................................................................................................13 2.5 Technically accessible resource ..................................................................................................16 3. Technology review- technical components of the tidal energy projects. ................................16 3.1 Structure & Prime Mover: ...............................................................................................................16 3.2 Foundations & Moorings: ...............................................................................................................16 3.3 Frequency converters......................................................................................................................17 3.4 Generators ..........................................................................................................................................18 3.4.1 Asynchronous (Induction) generator ...................................................................................18 3.4.2 Doubly- Fed Induction Generator..........................................................................................19 3.4.3 Synchronous generator ...........................................................................................................20 3.4.4 PMSG Permanent Magnetic Synchronous Generator .....................................................20 3.5 Power take- off types: ......................................................................................................................21 3.6 Grid connection.................................................................................................................................22 3.7 Tidal Energy Converter (TEC)........................................................................................................22 3.7.1 Horizontal Axis Turbine (Axial flow rotors) ........................................................................23 3.7.2 Vertical Axis Turbine ................................................................................................................23 3.7.3 Oscillating Hydrofoil .................................................................................................................23 3.7.4 Enclose Tips ...............................................................................................................................23 3.7.5 Archimedes screw .....................................................................................................................24 3.7.6 Tidal Kite ......................................................................................................................................24 4 4. Kyle Rhea site’s resource assessment .............................................................................................24 4.1 Characteristics of the Kyle Rhea ..................................................................................................25 4.2 Energy Conversion ...........................................................................................................................26 4.2.1 Methodology ...............................................................................................................................27 4.2.2 Results .........................................................................................................................................29 5. Detailed design evaluation ...................................................................................................................31 5.1 Sizing and array optimization ........................................................................................................31 5.2 Structure .............................................................................................................................................36 5.3 Foundations and moorings ............................................................................................................36 5.4 Installation ..........................................................................................................................................39 5.5 Grid connection.................................................................................................................................39 5.5.1 Cables type..................................................................................................................................39 5.5.2 Onshore substation and grid connection ...........................................................................40 5.5.3 Operation and Maintenance....................................................................................................41 6. Financial viability ....................................................................................................................................41 6.1 Lifetime levelised cost- methodology .........................................................................................41 6.2 Risk factors. .......................................................................................................................................42 6.3 Cost analysis. ....................................................................................................................................43 6.4 Assumptions and limitations: .......................................................................................................44 6.5 Capital expenditure (CAPEX) - cost of the tidal project deployment up to 40m depths. ......................................................................................................................................................................44 6.6 Operational expenditure (OPEX) - cost of the tidal project deployment up to 40m depths.........................................................................................................................................................45 6.7 Levelised Cost with Internal rate of return. ...............................................................................46 6.8 Tidal funding ......................................................................................................................................46 6.9 Financial support- ROC...................................................................................................................47 6.10 Potential cost reduction................................................................................................................48 6.11 Financial viability- discussion ....................................................................................................49 7. Environmental Impact ............................................................................................................................49 7.1 Results review from the EMP ........................................................................................................50 7.1.1 Marine mammals........................................................................................................................50 7.1.2 Benthic ecology .........................................................................................................................50 7.1.3 Tidal Flow regime: .....................................................................................................................51 7.1.4 Ornithology: ................................................................................................................................51 7.2 The Pentland Firth and Orkney waters .......................................................................................51 7.3 CO2 emissions....................................................................................................................................52 8. Planning, policy and legislation ..........................................................................................................52 8.1 Kyle Rhea licencing requirements: ..............................................................................................52 5 8.2 Renewable energy policy................................................................................................................52 8.3 Planning Legislation ........................................................................................................................52 9. Discussion ................................................................................................................................................53 10. References..............................................................................................................................................55 Appendices A ...............................................................................................................................................57 Appendices B ...............................................................................................................................................58 Abbreviations AEP- Annual Energy Production. Array- A set of multiple devices connected to a common electrical grid connection. Availability- The proportion of the time the device is available to generate electricity. Discount rate- The percentage rate used to calculate the present value of a future cash flow. Hurdle rate- The minimum rate of return (discount rate) a developer will accept on a project. Load factor- The ratio of the actual output of a power plant over a period of time compared to its theoretical power output if the plant were to operate consistently at full load over the same period. Levelised Cost of Energy (LCOE) - Sum of discounted lifetime costs divided by sum of discounted lifetime electricity output. Lifetime costs include capital, operating and decommissioning costs. It is an expression of cost, not revenue or price. PTO- Power Take Off system which converts mechanical energy to hydraulic/electrical energy O&M- Operations and Maintenance. ROV- Remotely Operated Vehicle. Yield- Percentage of available energy converted. EMP- Environmental Monitoring Programme SAC- Special Area of Conservation TEC- Tidal Energy Converter EC- European Commission SSSI- Sites of Special Scientific Interest List of Figures Figure 1- UK's Peak flow for a mean spring tide (MER, 2008) ...............................................................10 Figure 2- Compared Spring and Neap Mean Tidal Power in Scotland. (MER, 2008) ........................11 Figure 3- Pentland Firth and Orkney waters development sites (orkneymarinerenewables, 2014) ...12 Figure 4- Strangford Lough testing site (aviationenterprises, 2010) .....................................................13 Figure 5- Common types of TEC foundations and moorings. (Whittaker, et al., 2003) ......................17 Figure 6- Asynchronous (Induction) generator with (Whitby, 2013) ......................................................19 Figure 7- DFIG (Whitby, 2013) ....................................................................................................................19 Figure 8- PMSG without gearbox (Whitby, 2013) .....................................................................................21 Figure 9- PTO types for Tidal Energy Converters (Whittaker, et al., 2003)..........................................21 6 Figure 10- Simplified UK power transmission system (Beardmore, 2011) ...........................................22 Figure 11- Kyle Rhea array project progress by MCT (BVG, 2011) ......................................................24 Figure 12- Kyle Rhea, investigated section (Haskoning, 2010) .............................................................25 Figure 13- Betz's limit, rotor efficiencies for a wind turbine, similar results should be expected for TEC, axial flow efficiency (Peter Fraenkel, 2010).....................................................................................27 Figure 14- Energy output and current speed relationship. ......................................................................29 Figure 15- The energy output at specific current speeds with cut-in and cut-off speed of the turbine. ..........................................................................................................................................................................30 Figure 16- Daily energy output. ...................................................................................................................30 Figure 17- Potential energy output from Kyle Rhea site during one week operation, using 2 x 16 rotor diameter turbine with Cop= 44% ........................................................................................................31 Figure 18- Extractable Power during spring tide by 6 and 36 turbine farms. (MET2014- Zhaoqing Yang, 2014) ....................................................................................................................................................32 Figure 19- [a]: velocity and [b]: turbulence intensity for three-turbine arrays with lateral and longitudinal spacing (in diameters) of [i]: 1.5 × 1.0; [ii]: 3.0 × 1.0; [iii]: 1.5 × 10.0; [iv]: 3.0 × 10.0. (Rami Malki, 2014) ........................................................................................................................................33 Figure 20- Velocity of the flow upstream of the downstream turbine in a three-turbine array compared to the inlet velocity. The lateral spacing of the upstream turbines is [a]: 1.5 diameters and [b]: 2.5 diameters. (Rami Malki, 2014)................................................................................................34 Figure 21- Power output of the downstream rotor in a three-rotor array with different longitudinal (×) and lateral spacing. (Rami Malki, 2014) .....................................................................................................34 Figure 22- Velocity contours for [a]: regular and [b]: modified rotor array layouts and [c]: power outputs for the two layouts. (Rami Malki, 2014) ........................................................................................35 Figure 23- Foundation arrangements for a single device. (MARINTEK, 2014) ...................................37 Figure 24- Mooring arrangements for a single device. (MARINTEK, 2014) .........................................39 Figure 25- Operation and maintenance breakdown. (BVG, 2011) ........................................................41 Figure 26- Tidal early array cost breakdown (SI OCEAN, 2013) ...........................................................43 Figure 27- Capital expenditure for Tidal shallow projects [£/MW] (Ernst&Young, 2010) ...................44 Figure 28- Operational cost in Tidal shallow projects (Ernst&Young, 2010) ........................................45 Figure 29- Levelised cost and IRRs to the date (Ernst&Young, 2010) .................................................46 Figure 30- Tidal stream ROCs/MWh required to meet IRRs at specific dates. (Ernst&Young, 2010) ..........................................................................................................................................................................47 List of tables Table 1- Site comparison............................................................................................................... 15 Table 2- TECs classification by EMEC .......................................................................................... 23 Table 3- Array arrangements (MET2014- Zhaoqing Yang, 2014) .................................................. 32 List of equations Equation 1- Mass flow rate ............................................................................................................ 26 Equation 2- Power from the tidal resource ..................................................................................... 26 Equation 3- Actual power extracted by energy converter ............................................................... 26 Equation 4- Omega ....................................................................................................................... 28 Equation 5- Power of the turbine ................................................................................................... 28 Equation 6- Load Factor ................................................................................................................ 41 Equation 7- Levelised cost of electricity ......................................................................................... 42 Equation 8- Levelised decommissioning cost ................................................................................ 42 7 1. Introduction Tidal energy is the one of the most promising marine energy source in Scotland. The new Scottish Renewables report shows that the government has already spent £217m to help this specific sector of energy generation to grow and improve the efficiency of technologies that are already in testing phase. Estimated 25% of the Europe’s tidal potential is in Scotland. Tidal flow is the motion of water caused by the gravity. Mass of water flowing through the channel has an enormous amount of kinetic energy flux; therefore it can be used to produce electricity by simply mounting similar devices to wind turbines across the channel. Tidal currents are consistent and they can be predicted, unlike the many other forms of renewable energy, thus this type of energy generation became attractive to many companies around the world. To estimate the amount of energy that can be harvest from the water movement, a detailed analysis of how tides work against time has to be performed. The aim of this project was to investigate the tidal energy potential in Scotland and to look into specific regions to find the best areas for the project deployment. By using tide range data, calculating estimated energy output and applying different technology solutions, it was possible to assess the feasibility of the tidal project in terms of energy resource availability in Kyle Rhea. This report contains an analysis of tidal energy potential in Scotland with the calculated estimation of energy that can be harvest from the 1.2 MW tidal energy converter. Review of tidal power technology was based on already existing analysis and reports made by developers and University researchers. Analysis is limited to tidal stream only, tidal barrages and lagoons will not be considered in the fallowing work. A large amount of assumptions was made due to the infancy of the tidal energy technology. 2. Analysis of tidal energy potential in Scotland. 2.1 Early estimations of the potential. In 1979 at International Conference on Future Energy Concepts (Fraenkel & Musgrove, 1979), provided an estimation of power available in major UK channels. This was obtained using approximated depth and width values. Later on, they were confirmed by the GEC Hirst Research Centre with the similar approach using Admiralty data. Comparison of estimated energy resources shows that the results vary and demonstrates difficulty due to the many sources of data and different methodology. Between- the new approach of numerical modelling was used to determine kinetic energy flux around Channel Islands. Two- dimensional model helped to simulate currents and water rises from the main semidiurnal harmonic constituent. Suitable sites were selected based on 8 minimum depth and average kinetic energy flux density over a one tidal period. To obtain approximated power output it was necessary to calculate the amount of kinetic energy flowing through the channels, rotor diameter of turbines and their number per unit surface area, surface power considered in the project and turbine’s coefficient of performance. In 1990s Energy Technology Support Unit (ETSU), has created a Tidal stream energy Review report, which helped the government and energy industry to assess the viability of tidal energy projects. That report identified 33 applicable areas around the UK. They were selected in terms of two factors i.e. current velocity (minimum of 2 m/s during mean spring tidal stream) and depth (greater than 20m). Velocity values were obtained from Admiralty charts and improved conforming to tidal range variation at Dover, each area was divided into sections based on the depth of the water. Finally ETSU made a histogram showing the relationship between velocity bins (0.5 knots) in time, consecutively, the annual energy output for each section was obtained using the method stated before. Later on, European Commission has established study under its non- nuclear energy programme identifying 42 sites. There was a similar approach for the site selection but this time tidal stream velocities considered were lower (1.5 m/s). ETSU 93 and EC reports were based on one data set of velocities which result in uncertainty in determined power output values due to the lack of variation in velocities across site’s surface area. 2.2 Early assessments in contrast to recent studies. In 2004, Black and Veatch Consulting Ltd. released the document, in which authors disagreed with the methodology used in previous studies. ETSU 93 and EC 96 did not consider what could be the effect of the energy extraction on the tidal stream velocities. They propose the significant impact factor (SIF), which helps to recognize and quantify the impact of the tidal stream generation devices on characteristics of the flow. SIF helped to create layout of the turbines and realistic maximisation of energy potential from investigated sites. UK department of Trade and Industry carried out an assessment of the renewable resources in UK including tidal energy characteristics. Proudman Oceanographic Laboratory has made High Resolution Continental Shelf Model (HRCS) of tidal resources, which was later used in Atlas of UK Marine Renewable Energy Resources in 2004. It is known as one of the key reference documents providing the description of energy resources in offshore regions in UK with the grid resolution of approximately 1.8 km. It is also known to be a strategic sources of information for the tidal projects in UK, based on up-to-date data available at the time. Although, it is not fully comprehensive as it does not cover smaller regions like narrow straits or headlands, which have high velocity tide currents due to their shape. In 2007, Department of Business, Enterprise and Regulatory Reforms (BERR) and Strategic Environment Assessment (SEA) decided to keep improving Atlas with more updated and reliable data to deliver best possible map of tidal resources. BERR ordered a consortium controlled by Marine Environment Research 9 with support of Met Office and Proudman Oceanographic Laboratory to extend and improve the Atlas for the future projects deployment. Figure 1- UK's Peak flow for a mean spring tide (MER, 2008) 2.3 Conclusion It is very difficult to estimate accurate energy potential from tidal streams and analytical model delivers only an overview of it with a significant uncertainty in calculated results. Although, technology improvement, more detailed calculations and a grid map with even smaller resolution help to obtain results with smaller possible range of values for energy output from specific site. Previous assessments ignored important aspects like Significant Impact Factor (SIF) or by excluding narrow straits and headland’s tidal flow velocities in marine energy resources atlas, thus this type of assessment should be consider as a summary and should not be taken in to account while executing detailed regional analysis. At the moment there are several testing sites for tidal and wave energy in UK with 10MW capacity what makes UK a leader in marine energy projects. The Department of Energy and Climate Change estimated that tidal and wave energy can generate up to 50GW which makes approximated 20% of UK’s electricity demand. Scottish tidal energy make important contribution to that demand, forecasting 7.5GW available within tidal resources. In 2007 Scottish 10 Government announced a new target for electricity supply from renewable sources to reach 50% by 2020. New regulations fallow the Climate Change ACT from 2009, which indicates reduction of greenhouse gas emissions by 80% until 2050 with an interim target of 42% reduction by 2020. (Haskoning, 2010). 2.4 Identification of the areas with the most suitable flows for energy extraction in Scotland. Marine spatial framework report presents considered areas for tidal energy deployment in Pentland Firth and Orkney waters. Currently, there are 9 sites that have been investigated and assessment takes into account resource specification like: bathymetry and seabed, shipping and fishing, environment, tourism and cultural heritage. Figure 2- Compared Spring and Neap Mean Tidal Power in Scotland. (MER, 2008) This region contains most of the tidal potential in Scotland as declared by Scottish Government: “Seabed owners The Crown Estate expect the Pentland Firth and Orkney Waters commercial lease area to be generating up to 1.6GW (gigawatts) from tidal and wave device deployment by 2020. This area of sea off the northern coast of mainland Scotland, and encompassing the waters around the Orkney Islands, contains 50% of the UK’s tidal resource and 25% of Europe’s tidal resource.” (Estate, 2012) 11 2.4.1 List of the potential sites in northern Scotland (Pentland Firth and Orkney waters) Figure 3- Pentland Firth and Orkney waters development sites (orkneymarinerenewables, 2014)  Stroma Sound  Duncansby Head  Pentland Firth Outer Sound  Swona and South Ronaldsay  South Hoy/South Walls  Graemsay(Hoy Sound/Burra Sound)  Westray Firth to Stronsay Firth  Papa Westray (Mull Head)  Sanday and North Ronaldsay 12 2.4.2 List of the potential sites in Scotland (different locations).  Kyle Rhea  Islay/Mull of OA  West Islay  Mull of Kintyre  Mull of Galloway 2.4.3 Test sites.  Fall of Warness  Shapinsay Sound- Nursery test site Comparison of these site is shown in table 1. Figure 4- Strangford Lough testing site (aviationenterprises, 2010) 13 Name: Peak spring Interest conflicts Bathymetry Seabed Fishing/shipping Yes 30m-35m Incomplete: Little or no commercial flows velocities Stroma Sound 2.5m/s Old red sandstone Duncansby 4m/s, Head 6m/s up to Yes- area lies within Irregular, vertical wall, military practice area, horizontal beds, max. although depth 50m it “danger” is or not Rock, bank of sand Tankers, Cargo vessels a “Byelawed” area Pentland Firth Outer Sound ~4.6m/s the east ~4.1m/s from Yes- Ferry route and 80m-90m in the area of Folded and fractured with Tankers, Cargo vessels, Fishing vessels (agreement and commercial shipping, tidal race faults, for clearance for vessel passage required) from sediment deposit present the west Swona and 4m/s Yes- Ferry route, 60m-75m main channel, Faults and fractures, hard Ferry runs north- south, route depends on tide state to build foundations and weather conditions, low level of commercial fishing Incomplete data for near Ferry runs north- south, route depends on tide state South commercial shipping, Swona’s Ronaldsay area lies within military quickly to 50m depths practice coast drops area, although it “danger” is or not a “Byelawed” area South 3- 3.5m/s Yes- Ferry route, 50-80m depths, Hoy/South commercial shipping, shore area, fractures , faults and weather conditions, tankers and commercial Walls area lies within military bedrock vessel traffic is less than the other locations. Low level practice although “danger” area, it is or of commercial fishing not a “Byelawed” area 14 Graemsay (Hoy 2-2.5m/s (25m Yes- Ferry Sound/Burra depth) Fishing farms Sound) 4.4m/s route, Data unavailable. Partially blocked with ship Ferry route and small local ferry (Stromness to wrecks Graemsay), Fishing vessels, Finfish farms present Bed rock exposed in some Large area is used for Whelk and pot fishing; large areas, north and east have fishing vessels; inter-island ferries, routes depends on some weather and tidal conditions (10m depth) Westray Firth to 2.6m/s Stronsay Firth * 3.7m/s up to Yes- Ferry route, 30-35m Fishing vessels depends on location thick deposits of boulders, cobbles, gravel shelly sand, well covered with flora and fauna, sand deposit close to the shore Papa Westray 2.5-3m/s No data 30-50m Gravelly (Mull Head) Sanday sand-offshore seabed and 2.5-3m/s Yes- commercial 20-30m Offshore seabed- gravelly North shipping and fishing sand, inshore seabed- no Ronaldsay vessels data Name Shipping and Fishing vessels traffic is light Peak spring Interest conflicts Bathymetry Seabed flows velocities Table 1- Site comparison 15 Fishing vessels and commercial shipping high traffic Fishing/shipping 2.5 Technically accessible resource Quality of the seabed and surroundings as well as depth of the water play key role in tidal project deployment. If the seabed is fractured and irregular it makes it hard to build a foundation for the turbine and increased the potential cost of the project. Depth of water has to be taken into account and usually cost will increase due to difficulty of turbine installation and grid connection, which is also a crucial feature. Areas within water depth around 60m should be avoided. It will make offshore works not viable. Due to the fast current velocities there is likely to be bare rock at the bottom of the channel. It is a very problematic issue because of the very expensive drilling methods that have to be used while building a foundation and also setting up the cables and their protection will require challenging works. (N C Scott, 2009) Tidal current may cause scour development around foundations, which was described in HR Wallingford report, investigates effect of water depth, shape of the obstruction (foundation), reversal of the flow direction, tidal cycle duration and sediment size. The results have shown that water depth has a large influence on size and depth of the scour and with decreasing water depth, scour depth also decrease. This problem can be solved using designed protection. (M. Escarameia, 1999) 3. Technology review- technical components of the tidal energy projects. There is a wide range of tidal energy devices considered by developers, although they may be different and unique, the same systems and principles are still used. The most common are the Structure and prime mover, foundations and moorings, power take off (PTO) and frequency converter, control, installation, connection. 3.1 Structure & Prime Mover: The structure of the Tidal Energy Converter is usually made out of steel, although some parts like blades are made of composite. Seaflow’s 11m diameter turbine blades are made out of marine epoxy resin matrix with carbon-fiber spar joint and fiberglass ribs coated with fiberglass skin. (Marsh, 2004) For comparison Seagen made their blades by using carbon-fiber box shaped spar with carbon ribs covered by fiberglass composite with prepreg applied, which is pre-impregnated composite with high-performance fibers such as carbon, glass and Kevlar. (Fraenkel, 2008) 3.2 Foundations & Moorings: Tidal energy devices are subjected to considerable thrust and can experience forces of 1MN in tidal streams velocities of 2.3m/s for 1MW TEC. (Whittaker, et al., 2003). Therefore, foundation plays a crucial part in the system deployment. Various foundation and moorings 16 types exist and selection is made based on constraints of the seabed. Few foundation types are presented below. Figure 5- Common types of TEC foundations and moorings. (Whittaker, et al., 2003) Gravity bases are the steel and /or concrete structures with large diameter base, usually ballasted from the inside ones they are placed on the seabed. The other type widely considered by companies is mono- pile. Long steel tubes are put into the rock so drilled in the seabed or mounted using hydraulic pilling hammer. Piled jacket or space frame foundations are often used in gas and oil sector, frame is secured and attached to the seabed using piles. This way structure would experience less of the force acting on the system’s foundation due to decreased surface area. Floating systems create technical challenges in fast current streams. As the result of the movement, moorings tend to wear and are subjected to unevenly distributed stresses, thus flexibility of the material used, has to be considered because the failure of one part can cause the failure of the whole system. So-called “tension leg” can be the solution to keep moorings tensioned, thus protect them from unequally distributed tidal stream forces. (Whittaker, et al., 2003) 3.3 Frequency converters Frequency converter is an important component of tidal PTO system and it allows the generator frequency to be independent from the frequency in the grid. This is a necessary feature in generators, which operate at different speeds. The use of frequency converters in Tidal energy systems can be beneficial for the amount of power extracted. Types of frequency converters used in TEC’s generators.  Full active converter  Passive Generator Bridge  Doubly fed generator converter 17 In the document presented by EC- funded consortium, 3 different frequency converters approaches were described and analysed. SeaGen horizontal axis turbine system contains Double Fed Induction Generator (DFIG) that operates in variable speeds. The next system considered was vertical axis Kobold turbine with permanent magnet synchronous generator (PMSG) connected to a grid through full power converter. Clean current’s horizontal axis turbine with a direct drive and variable- speed PMSG also has a grid connection via full power converter. (Marinet: Jamie Grimwade, 2014) 3.4 Generators The choice of right generator depends on design application and environment within it will operate. Synchronous generators are usually more expensive but a gearbox is not required. In synchronous generators, sinusoidal waveform of the voltage corresponds to the speed of the rotor. Asynchronous generators are cheaper and the gearbox is required. This can result in additional repairs, as the mechanical parts are located under the water. Although in some application this issue can be neglected. Usually large synchronous generators are more efficient and easily adaptable to variations in power load. In addition, aspects like maintenance, control, size, grid connection have to be considered during design process. 3.4.1 Asynchronous (Induction) generator In these types of generators, rotor speed is not the same as the synchronous speed of the grid. They are relatively simple and require little maintenance; although there is no speed regulation and range of the speed is only 4-5% of the synchronous speed. This may affect the efficiency of the system but applying frequency converters can solve this problem. The rotor magnetic field is supplied from stator magnetic field through electromagnetic induction. In wind turbines the rotor is connected to grid via bidirectional power converter (which is described later), which makes positive input into the system by reducing the size of the power electronics and allowing for active and reactive power control. Converters can be controlled individually, what helps to control the power factor from the grid side but also requires use of electromechanical devices that allow the transmission from a stationary structure to the rotor, called slip rings (additional maintenance). By using full power bidirectional converter no slip rings are required or reactive power compensation parts. (Marinet: Jamie Grimwade, 2014). 18 Figure 6- Asynchronous (Induction) generator with (Whitby,- Doubly- Fed Induction Generator In this case stator is directly connected to the grid and power converter supplies the rotor. It is an alternative way of achieving variable speeds, where full-power converter replaces the external resistors. Power flows via doubly-fed induction generator and it is proportional to the speed fluctuations (+/- 30 %), it occurs when rotor’s current is proportional to the rotor’s resistance and thus increasing the rotor resistance, by reducing the current it will increase the slip. When the rotor is not operating at required speed, converter takes power from the power line and supplies the stator. During the situation in which speed of the rotor exceeds the synchronous speed, the converter will take up the power and transmit it to the power line. By using this type of generator, wide range of speed variation can be obtained and it can operate at insufficient and exceeded synchronous speed. Figure 7- DFIG (Whitby, 2013) 19 3.4.3 Synchronous generator Synchronous generators are quite popular solution in renewable energy extraction technology. The magnetic field is created by exciter, which gives Dc current in the coil located in the generator. It can be also generated in permanent magnet rotor, where magnetic field occurs in the shaft of the permanent magnet mechanism. In these type of the generator the armature coil is directly connected to the grid and no slip occurs. In tidal devices, power available from the resource is a non- linear function; therefore the power should be extract at maximum rate in all circumstances, which can be controlled by optimizing the speed. Because of fixed speed of the turbine, variations in resource current velocity affect Drive train and gearbox applying large mechanical stresses, thus during the design process, heavy load conditions have to be considered. These variations are also affecting the power quality received by the grid. Using power converters, which are described later, can solve this problem. 3.4.4 PMSG Permanent Magnetic Synchronous Generator It does not require gearbox to operate, because the turbine rotor turns a permanent synchronous generator. Usually rotor shaft is connected directly to prime mover, so rotation speed of the blades is transmitted to the permanent magnets creating magnetic field. Due to the absence of the winding excitation, a supply of the field magnetizing current is unnecessary. Also less refrigeration is needed, as there are no slip rings and rotor copper losses cease. In this kind of generator number of poles can be increased and that results in ability to build devices, which can operate in slower range of speeds. In addition of full- power converter the grid receives alternating current form the generator, through AC- DC- AC conversion. Benefits of PMSG: - Operation without connection to the network (self- excited) - No winding losses - High efficiency and improved power curve - No mechanical losses linked to the gearbox - Full-power converter- optimization of rotational speed, followed by maximization of energy extraction, thus reduction in transmission losses. - Reliability and low maintenance cost. - Less number of components - No gearbox- no controlled lubrication needed. Due to the exposure to the high temperatures, magnets like Neodymium tend to demagnetize. They are wildly used in the generators because they are light and stronger than samarium- 20 cobalt magnets (highly resistant to demagnetization). The main producer of neodymium is China and price may vary, what causes doubts to use it or not, due to political and economic factor, shortage of that material can be expected (Purma, brak daty). That issue mostly applies when generator is used in the wind turbines. Submerged device should experience cooling effect from the water. (Marinet: Jamie Grimwade, 2014) Figure 8- PMSG without gearbox (Whitby, 2013) 3.5 Power take- off types: PTO is the mechanism that converts the motion of the prime mover into a useful form of energy. Figure 9- PTO types for Tidal Energy Converters (Whittaker, et al., 2003) 21 Mechanical PTO is a common system used in horizontal and vertical axis turbines. Hydraulic PTO is used in hydrofoil concept of TEC and uses high-pressure fluid to drive hydraulic motor and electrical generator. Direct drive converts rotary motion directly in to electricity. 3.6 Grid connection The TEC has to be connected to the grid, therefore two steps have to be considered. First is the connection of the device with the onshore substation and can be done by using dry or wet mate connectors. Dry mate connectors required connection to be made above the water surface while wet mate connectors allow connection at sub sea level, thus the device can be mounted into position before connection is made. Next, cables have to be connected to the main grid but before that sub-station with a transformer have to step up the generator voltage output so it matches grid voltage. It is important to transfer the electrical power at the highest voltage with significantly low current to avoid losses, hence necessity of power transformation at sub-station level. Figure 10- Simplified UK power transmission system (Beardmore, 2011) 3.7 Tidal Energy Converter (TEC) Tidal energy sector developed few main technologies used for power extraction. Different concepts of tidal systems allowed distinguishing most efficient technologies that can be used. Energy collected from tidal stream is proportional to the stream’s velocity; therefore it is crucial for the developer to find most appropriate system design, which will efficiently operate in site’s 22 specific conditions. EMEC classifies TECs according to their technical designs but they can be also grouped by depth of water in which they are design to operate. TEC name Classification Horizontal Axis A Vertical Axis B Oscillating hydrofoil C Enclose Tips D Helical Screw E Tidal Kite F Other G Table 2- TECs classification by EMEC 3.7.1 Horizontal Axis Turbine (Axial flow rotors) Rotor hub axis is aligned with the flow of the water and contains blades radially mounted with the rounded leading edge and sharp trailing edge Power is extracted from the lift of the rotor blades that are moved by the tidal stream. Prime mover is mounted on the horizontal axis and by converting movement of the rotor through the generator, produces electricity. 3.7.2 Vertical Axis Turbine It operates on the same principle as Horizontal Axis Turbines. Rotor is mounted on vertical axis and tidal stream spins the blades, which extract the energy. 3.7.3 Oscillating Hydrofoil The oscillating hydrofoil cause a hydrodynamic lift and drag forces as a result of pressure difference on the top and bottom surface of the foil caused by tidal stream motion. These forces move the device arm to run hydraulic ram pump, which then turn the motor and generator. 3.7.4 Enclose Tips This type of the devices, contain their rotor in encased structure, which can have positive or negative impact on the performance. Positive aspect of that design is that the flow may be aligned and accelerated through the turbine, decreasing the turbulence affecting the flow, thus the size of the rotor diameter is smaller than in un-ducted TECs. 23 3.7.5 Archimedes screw It is a device with cylindrical shaft and helical surface. The water flow, which strikes against the surface, pushes it up creating drag force and turns the turbine. 3.7.6 Tidal Kite Tidal kites contain the turbine that is mounted underneath them and the device is attached to the seabed. Kite moves in a figure of eight shape to increase the water velocity going through the attached turbine. As stated by one of the leaders in Tidal kite systems, the secret lies in that figure of eight- shape movement, resulting in 10 times faster current speed. By principle of tidal power generation, velocity of the stream is cubed; hence it has large and positive impact on power output. Systems are design to operate on depths up to 120m. 4. Kyle Rhea site’s resource assessment Kyle Rhea is the narrow strait between Isle of Skye and Scottish mainland with north stream velocity up to 7 knots and south stream velocity up to 8 knots during spring tides. Figure 11- Kyle Rhea array project progress by MCT (BVG, 2011) 24 4.1 Characteristics of the Kyle Rhea Figure 12- Kyle Rhea, investigated section (Haskoning, 2010) In this project, area of approximately 2km2 will be considered and the Boundaries are shown in fig. 11. Investigated site’s boundary coordinates: •-°, -5.66358° •-°, -5.66099° •-°, -5.66102° •-°, -5.66361° For the project deployment purposes, substation was built to connect the device to the National grid, through already existing infrastructure. There is a high possibility for the array farm to be build, thus increase the amount of energy captured from the resource. Although, to determine exact layout of the array, site’s constraints have to be investigated. The site is accessible form the mainland, using Old military road to Glenelg off the A87 south of Loch Duich and from Isle of Skye from A87 at Ashaig to the Settlement of Kyle Rhea. The closest airports are located in Inverness and Isle of Skye. Transport cost will have significant impact on capital cost of the project, thus it is necessary to evaluate good road connection with the site. Maximum depth of the channel is 36m and the north and south strait’s entrances depths reach 16m and 11.4m respectively. The most suitable place for array installation is in deep waters closer to the southern end of the channel. 25 4.2 Energy Conversion Extraction of the kinetic energy from the tidal flow, works on the same principle as for wind turbines. The amount of power in a fluid can be described as the function of the mass flow rate, which is the mass of the fluid passing through specific cross-section per unit time. 𝑑𝑚 = 𝜌𝐴𝑉𝑓𝑙𝑜𝑤 𝑑𝑡 Equation 1- Mass flow rate Where: 𝜌- Density of the sea water [1027kg/m3] 𝐴- Swept Area of the rotor [m] V – Tidal current velocity [m/s] m- Mass [kg] t- Time [s] To measure amount of power that could be generated per unit area from the tidal resource, assuming 100% efficiency, the fallowing formula is used: 𝑃= 1 𝑑𝑚 2 1 3 𝑉𝑓𝑙𝑜𝑤 = 𝜌𝐴𝑉𝑓𝑙𝑜𝑤 2 𝑑𝑡 2 Equation 2- Power from the tidal resource Where: P- Power of the turbine [W] Although in real life, only fraction of the tidal current energy will be captured, thus the above formula has to be improved: 1 3 𝑃 = 𝜌𝐴𝑉𝑓𝑙𝑜𝑤 ∗ 𝐶𝑝 2 Equation 3- Actual power extracted by energy converter Where: 𝐶𝑝 - Overall Coefficient of performance of the system Betz limit also applies in tidal power, thus only 59.3% of the total kinetic energy from the source can be extracted (maximum of Cp= 0.593). Due to the transmission and mechanical losses in 26 the system, maximum efficiency drops even lower and it is usually in the range of 40-50%. (Fraenkel, 2008) Figure 13- Betz's limit, rotor efficiencies for a wind turbine, similar results should be expected for TEC, axial flow efficiency (Peter Fraenkel,- Methodology Data: 1. Tidal range data for Kyle Rhea was obtained from tides.willyweather.co.uk 2. Data range: Two months, October and November 2014 3. Two different range data per day was considered. Two different HW and LW in one tidal cycle, means two different maximum velocities daily. 4. Two different maximum velocities were obtained (each day) using computation of rates table, by creating computation tool in Excel. This method gives fair estimation of realistic tidal stream velocities that occur during different tides. 5. From two daily velocities, an average velocity was taken for each day as the reference for energy output calculation. 6. Daily tidal stream average velocity profile for two months was generated. 27 Energy output: 1. To create a detailed (every 30min) daily velocity estimation profile the trigonometric interpolation was used. 2. Period is considered to be a half of the tidal cycle i.e. approximately 12 hours and 25min, which is equal to 44700 seconds. 3. Omega: Ω= 2𝜋 = 1.40563 ∗ 10−4 44700 Equation 4- Omega 4. Ω*time Omega was multiplied by every 30min period of time (t) 5. Sin (Ωt) 6. Average velocity was then multiplied by the assigned sin (Ωt) value. 7. Set of velocity data was generated for 2 months period with 30min accuracy. Cut-in and Cut- off velocity limits for the turbine were applied for power generation calculation purposes. 8. Power calculation for the turbine: From cut-in speed when power is first generated at low currents, output power rises as a cube index of speed in accordance with the formula: 𝑃𝑡 = 1 ∗ 𝜌 ∗ 𝐴 ∗ (𝑉 3 ) ∗ 𝐶𝑝 2 Equation 5- Power of the turbine Where: 𝑃𝑡 - Power of the turbine [W] 𝜌- Density of the sea water [1027kg/m3] 𝐴- Swept Area of the rotor [401.92m] 𝐶𝑝 - Overall Coefficient of performance of the system [0.44] 28 V – Tidal current velocity [m/s] 9. Power of the turbine has to be taken as an absolute value to create appropriate output graph. Due to the sinusoidal interpolation of values, data set shows negative values for the power output, although these negative values in reality corresponds to positive power generated. 10. Power output for each 30min period, during two months of turbine operation was then multiplied by 0.5 to obtain the amount of energy generated. 11. Some of the periods show 0 kWh of the energy harvest, it is a consequence of applying Cut- in and Cut- off limits for turbine to generate the power. 4.2.2 Results The fallowing results show potential energy output from Kyle Rhea site, using 2 x 16m rotor diameter turbine. It has to be noted that this analysis was based on and compared to MCTs turbine, already operating in Strangford, Northern Ireland. Calculation spreadsheet is available in appendices C MCT turbine specification: See Appendices A 3.5 800 3 700 600 2.5 500 2 400 1.5 300 1 200 0.5 |Energy output [kWh] current speed [m/s] Energy output and current speed relationship 100 0 0 Velocity Energy output [Kwh] Figure 14- Energy output and current speed relationship. Fluctuation seen on the graphs is due to the Cut-Off speed limitation applied in calculation, essentially the Cut- Off speed was assumed to be 2.4 m/s, wherever in data set there is a 29 speed range between 2.40-2.49 it will occur as fluctuation on the graph. It is considered as an error. Energy output at specific current speeds 800 700 Energy [kWh] - 0.5 1 1.5 2 2.5 3 3.5 Current speed [m/s] Figure 15- The energy output at specific current speeds with cut-in and cut-off speed of the turbine. Daily energy output 800 700 Energy [kWh] - - 0 Time [h] Figure 16- Daily energy output. Daily energy output correlate with tide phases. 0 kWh on the curve indicates slack periods at which flow speed is equal to zero or is too slow to turn rotor’s blades. Points on the curve with over 600kWh represents highest flow speed and constant power generation. 30 800 Energy [kWh] - - 0 Time [h]- 1 week Figure 17- Potential energy output from Kyle Rhea site during one week operation, using 2 x 16 rotor diameter turbine with Cop= 44% The annual energy output form 2 x 16m rotor diameter turbine. The result is subjected to considerable error, due to the stated limitations and assumptions (see appendices B). Results shown below refer to different locations; thus different current speed; although the size of the rotor swept area is the same.  Amount of energy captured, Kyle Rhea assessment: 7567.02 MWh  Amount of energy captured by MCT turbine in Strangford Lough: 7600 MWh The annual energy output will also depend on device availability, meaning, time at which TEC is fully operating. Any operations and maintenance, repairs will have a large impact on the amount of the energy captured. 5. Detailed design evaluation 5.1 Sizing and array optimization The total amount of energy that can be generated from the site resources, depends on number of the TECs that can be installed and size of their rotors. During the Marine Energy Technology Symposium (MET2014), eight different cases of array layout was investigated using Hydrodynamic Model with Tidal Turbine Module. Arrays with 6 and 36 turbines were studied with regard to four types of the layout: cantered, staggered, lateral, and longitudinal. Results present very similar power output for every design. Lateral layout shows slightly smaller output value than other design and the reason for that might be the fact that turbines are located in the region of the channel close the shore where current speed decrease. (MET2014- Zhaoqing Yang, 2014) 31 Table 3- Array arrangements (MET2014- Zhaoqing Yang, 2014) Results shown below, include array of 6 TECs and 36 TECs in for different layout designs. Figure 18- Extractable Power during spring tide by 6 and 36 turbine farms. (MET2014Zhaoqing Yang, 2014) It is clear that extractable power from 36- turbine array is lower than form 6- turbine arrays. Although the overall energy captured from the 36- turbine array would be many times greater than just from 6 turbines. Lower rate of power generation could be the result of small distances between the turbines and influence of Significant Impact Factor and longer rejuvenation distance of current stream. Thus, more detailed analysis should be made in term of water 32 depth variation, current speed variation, SIF and impact of power extraction from the stream, which will affect the current speed across the channel. Figure 19- [a]: velocity and [b]: turbulence intensity for three-turbine arrays with lateral and longitudinal spacing (in diameters) of [i]: 1.5 × 1.0; [ii]: 3.0 × 1.0; [iii]: 1.5 × 10.0; [iv]: 3.0 × 10.0. (Rami Malki, 2014) i. Lat., long. (1.5,1.0) ii. Lat., long. (3.0,1.0) iii. Lat., long. (1.5,10.0) iv. Lat., long. (3.0,10.0) In example “a/b-i” and “a/b-iii” with lateral spacing of 1.5 diameters, the downstream rotor will experience lower velocity of the current and will be exposed to the turbulence caused by the disturbed current flow form the upstream rotors. Less turbulence occur when the downstream turbine is located within short longitudinal distance. In case “b-iii” would most definitely affect turbine performance and durability of blades due to unequally distributed forces. the could also r In case “a-ii” and “a-iv”, where lateral spacing is 3 diameters, downstream turbine will be in high current velocity region caused by flow acceleration between two upstream turbines. 33 Figure 20- Velocity of the flow upstream of the downstream turbine in a three-turbine array compared to the inlet velocity. The lateral spacing of the upstream turbines is [a]: 1.5 diameters and [b]: 2.5 diameters. (Rami Malki, 2014) From the results presented above it is seen that turbine separation distance of 2.5 diameter would affect in higher than freestream velocity, due to accelerated flow between two first line rotors. Downstream rotor would essentially receive faster current and thus improve the performance and power output. Distance of 1.5 diameter between the rotors would have significant impact on the centreline velocities, thus decreased upstream velocity, which moves towards downstream turbine, hence less power extracted. (Rami Malki, 2014) Figure 21- Power output of the downstream rotor in a three-rotor array with different longitudinal (×) and lateral spacing. (Rami Malki, 2014) 34 In power output analysis of the downstream rotor, Fig. 11 shows evidently the impact on amount of power extracted related to insufficient spacing between the rotors. In lateral spacing below 3 diameters, turbulence from turbines will disturb the flow between them, decreasing its velocity. By placing the devices in lateral distance lower than 3 diameters will affect the stream velocity along the central line between them. Stream will slow down resulting in lower downstream turbine performance. Small velocity variation occur in TEC layout with lateral distances above 3 diameters. Reduction in Longitudinal distances may have a positive effect from two leading turbines by accelerating the flow towards downstream rotor, thus increasing its power generation potential. Figure 22- Velocity contours for [a]: regular and [b]: modified rotor array layouts and [c]: power outputs for the two layouts. (Rami Malki, 2014) Figure 12. Shows deployment of 14- turbine array and compare two different arrangements. In case (b) turbines in second row will experience reduction in flow velocity. It can be clearly seen (c) that array performance is better in layout shown in (b) due to the sufficient longitudinal distance between two rows, for the flow to recover and lateral spacing which in this case increase the flow velocity between the turbines. In the work presented by international journal of Renewable Energy the fourteen turbine array standard arrangement i.e. four rows with lateral and longitudinal spacing of 3 and 10 diameters respectively was investigated. After rearranging the array and taking into account all observations and conclusions made from the influence of spacing on tidal array performance, the power output was 10% greater of that from standard arrangement. This is a great improvement of potential power output and return on invested capital. 35 Spacing suggestions: -Longitudinal distance up to 40 diameters was investigated and results shown indicate that even with distances greater than 40 diameters, downstream turbine receives only 82.8 % of the upstream turbine flow velocity. -Decreasing longitudinal distance between turbines greatly improves downstream performance, due to accelerated flow. -Lateral spacing of 3 diameter or greater should be used to avoid decreased velocity along the central line between upstream devices reaching downstream TEC -Lateral spacing lower than 3 diameters can result in long flow recovery distance. Final farm layout should be evaluated considering lateral and longitudinal distances with detailed analysis of turbines arrangement and their effect on the current flow within the farm boundaries. This type of analysis can be made using blade element momentum – computational fluid dynamics (BEM–CFD) model. 5.2 Structure Kyle Rhea is treated as a shallow water channel with a maximum depth below 40m. Current velocity can reach 5m/s during the spring tides. During the peak velocities, submerged tidal device would experience thrust force about the same as the land structure during approximately 500km/h wind speed. Thrust acting on SeaGen turbine structure with 16m diameter rotor is approximately 1500kN (150 tonne) when the stream velocity reach 2.4 m/s. The key issue is to build the structure which can withstand such a strong force in harsh sea environment. Next structural aspect is the ability to resist the frequency of the load i.e. magnitude which can cause the fatigue of the structure and material. Welds are usually the most affected parts of the structure and are critical during the design stage. The whole structure should have streamline shape or build in the way that current flow is not disturbed so that rest of the turbines on the site could receive the current flow with satisfactory velocity without major turbulences. 5.3 Foundations and moorings The key requirements for foundations and moorings can be specified using factors like: life expectancy, loadings, and installation. Most of the renewable power plant life expectancy is around 20 years, thus, unless foundation replacement is planned, the material used should withstand heavy loadings for a time period excessing 20 years limit. Well design structure should perform in such way where the load of the current is transmitted into the seabed. On the other hand, in the open channels with high current velocities, seabed 36 is a usually a rock which has a critical load limit. Seabed rock could also have gaps, empty cavities and crack which could affect this limit significantly. Large bonding area between the foundations or moorings and the seabed is required to avoid disintegration and rock crumbling. Due to the fact that tidal current changes direction, structural alignment with the stream is critical for power generation as well as safety of the device. Tidal flow direction vary, thus the situation where the TEC is out of alignment should be avoided. Turbulence of the stream and flow induced vibrations cannot be overlooked during potential hazard analysis and can decrease lifetime of the foundations, moorings, rotor blades or the whole structure. Current flow can also develop scours around the foundations and flow could carry rubbish or debris which could mechanically damage the parts. Seabed in Kyle Rhea channel is mainly composed of Lewisian Gneisses and Torridon sandstones (Gemma Bedford, 2010). Recent study shows slopping bedrock covered by pebbles, boulders and coarse sediment. These two type of the sandstones are soft but usually thick layered on the seabed (Maarten Krabbendam, 2011). From the Carbon Trust’s review about foundations and moorings, in which table represent adequate mounting type accordingly to the site’s seabed geology and bathymetry (Cordah, 2009), appropriate foundation type can be evaluated. Figure 23- Foundation arrangements for a single device. (MARINTEK, 2014) Most suitable foundation type in Kyle Rhea:  Gravity base Benefits: Simple installation method, thus low cost. It is suitable for rock, sandstone and provides stable structure. Limiting factor: Low lateral load resistance and cannot be installed on the slopping seabed. High construction cost, size is limited by transportation and installation method. 37  Mono- pile, method: drilling Benefits: High vertical lateral load resistance, load transmitted to the seabed, small mooring footprint. Limiting factor: Deep water- still possible although complexity of the installation will increase with increasing depth of the water. Installation can be made after sufficient site data is collected. In case of a pull- out, there is no anchoring system that could secure the structure (design improvement can be developed).  Pin- piled structures, method: drilling  Benefits: High axial loads resistance, load transmitted to the seabed, well known installation methodology and wide range of seabed types. Limiting factor: Deep water- installation process could be too difficult and too complex. In the shallow water projects, it requires large amount of the equipment and detailed survey, high cost. Two types of foundation structure are taken into account in Kyle rhea tidal project. Tripod or quadro-pod pin-piled to the seabed with each pin-pile between 1-2m diameters. The rock sockets could be up to 11m in depth and up to 2.2m in diameter, where seabed footprint area can reach 15.2m2 in the worst scenario and using quadropod construction. Foundation also includes ladders, J- tubes to prevent the cabling from mechanical damage and a platform for maintenances boat. Final design is yet to be announced and will depend on geotechnical and geophysical surveys, metocean conditions analysis, life cycle cost and installation method. Most suitable mooring types in Kyle Rhea:  Catenary Limiting factor: none  Vertical Lift Limiting factor: none Anchoring:  Pile  Pin- pile  Gravity 38 Mooring is not deliberate here as the site is more suitable for seabed foundation, despite the fact, future project improvement does not exclude this type of attaching TEC to the seabed. Figure 24- Mooring arrangements for a single device. (MARINTEK, 2014) Figure 17. From the left: taut moored system, basic catenary system, catenary system with auxiliary surface buoy and lazy- wave system with subsea floater and sinker. As described by the Marintek, synthetic ropes and chains system, blue and black ropes respectively, can reduce highest loads acting on the mooring. 5.4 Installation Crucial requirements for the installation process have to specify and are dependable on site characteristics and technology used. Design stage should indicate the total allowable weight of the structure including TEC. This will help to determine type and size of the vessel according to the weight of the whole structure. Type of the vessel will also depend on the foundation type. For example installation of mono-pile structure would require boat equipped with large crane, where floating device could be towed. Site should be checked if any preparation is required before installation. Preparation of the site could include levelling the seabed (rock removal) or any type of rearrangement to make it suitable for the deployment. Number of tidal devices, seabed condition, weather conditions on the site, time at which installation can be made and stages of the deployment can result in different installation methodology. Depth of the water will have a major influence on complexity of the installation and the distance to the site from the onshore base should be relatively short to avoid additional costs related to installation vessels rental. 5.5 Grid connection 5.5.1 Cables type Intra- array AC cabling to be used in the Kyle Rhea array project. Cable made of 3-core copper conductors insulated with polypropylene and a steel- wiring protection rated at 33kV will deliver electricity directly from the array to the substation. The external diameter will be around 39 140mm and will include optical fibres for communication and control purposes. Total length of the cable is up to 500m (MCT, 2014). For the future array development with higher power capacity, 66kV 3-core inter-array cables can be used with aluminium conductors as presented by Nexans, which is currently trying to accelerate OWA program in UK. Technology of connecting tidal array to the grid was initially taken from offshore wind array grid connection solution. 66kV voltage cables allow for more power capacity, smaller dimensions and low current. This type of cables also have lower lifecycle cost and more optimized inter- array layout. (Nexans, 2014) 3- Core subsea cables will essentially transmit the electricity to land- located subsea cable joints, where they will switch to 3 single core cables and connect the array with 33kV switching substation and 33kV Grid Substation. The most appealing place for cable landing, in offshore projects, would be mud flat or a beach, although that requires survey of the coast (EMEC, 2013). Rock cutting method would be the most suitable for subsea cabling in Kyle Rhea, although areas with mobile sediment should be avoided. 5.5.2 Onshore substation and grid connection According to MCT Ltd analysis the grid connection is most suitable on Isle of Skye rather than on the west part of Scottish mainland. Although there is a plan to upgrade the transmission network with a high voltage direct current connecting with the Western Isles. This will allow for adequate capacity on Isle of Skye. Also a substation is planned to be built with approximately 18m2 footprint. Each device has its own transformer, thus the substation will only contain a switchgear (MCT, 2014). Substation will be linked with the closest power lines which are located at Broadford, Isle of Skye, Scotland. 40 5.5.3 Operation and Maintenance Figure 25- Operation and maintenance breakdown. (BVG, 2011) 6. Financial viability 6.1 Lifetime levelised cost- methodology To calculate the lifetime cost of energy from the TEC array, capital and operating costs as well as cumulative energy yield for the array have to be considered. To obtain the future cash flow, discount rate has to be accounted.  Capital cost: devices, foundations, moorings, installation, project costs, decommissioning  Operating cost: maintenance, operations, seabed rent, transmission charges, and insurance  Annual energy production: device energy capture, availability of the resource. Some of the costs are bring upon the project in the early stage while costs like insurance or operations are spread over the lifetime of the tidal devices deployment. The yield of the tidal array will have a significant impact on the cost per kWh and it depends on the amount of the electricity generated, resource availability, and performance of the TECs and proportion of the time when the device is available. Load Factor: 𝐿𝐹 = 𝐴𝐸𝑃 87.6 𝑥 𝑅 Equation 6- Load Factor R- Rated power of the device in MW 41 LCOE is calculated using the formula: 𝐿𝐶𝑂𝐸 = 𝑆𝐶𝐼 + 𝑆𝐿𝐷 𝑟 ∗ (1 + 𝑟)𝑛 𝑂𝑀 ∗ + 𝑛 87.6 ∗ 𝐿𝐹 (1 + 𝑟) − 1 87.6 ∗ 𝐿𝐹 Equation 7- Levelised cost of electricity LCOE: Levelised cost of electricity [c£/kWh] SCI: Capital cost of the power plant [£/kW] SLD: Specific levelised decommissioning cost [£/kW] LF: Load factor of the facility r: Discount rate n: Facility lifetime [years] OM: Annualized O&M costs [£/kW] Levelised decommissioning cost is calculated using formula: 𝑆𝐿𝐷 = 𝑆𝐷𝐶 (1 + 𝑟)𝑛 Equation 8- Levelised decommissioning cost SDC: Specific decommissioning costs at end of lifetime [£/kW] r: Discount rate n: Facility lifetime [year] 6.2 Risk factors. Risk is an important factor that has to be taken into account while calculating viability of the project. Projects, which are considered having a high risk of overspend or lower than expected revenue, should have higher rate of return to attract potential Investors. The minimum rate of return is the hurdle rate and projects internal rate of return must be equal or higher than hurdle rate. Project Risk: - Extreme Installation and O&M conditions, damage to the equipment, delays. Technical Risk: - New technology, lack of experience in design, operation and maintenance, reliability of the device Other Risks: 42 - Uncertainty in cost reduction, learning rate predictions, lack of data for full array deployment Risk reduction: - Accurate estimation of resource availability - Accurate estimation of the device availability - Accurate CAPEX and OPEX cost estimation - Accurate Energy output form device/ array 6.3 Cost analysis. As seen in Figure 26, the large part of total cost of the project is installation and foundations/moorings due to the complexity of attaching the TEC in to the seabed in fast flow sea environment. SI OCEAN has created an early array cost breakdown to visualise cost distribution. Figure 26- Tidal early array cost breakdown (SI OCEAN, 2013) The early stage of the technology development and project deployment solutions is the reason of uncertainties in cost evaluation, says SI OCEAN after interviewing the developers. For some developers data from already operating site is not enough to estimate the realistic cost as there is no detailed information about maintenance cost and long term operation. Foundation cost is what really bothers the developers. Each site will require different foundation type, thus different cost of the project, what significantly affect the total cost. Lack of resource site characteristic, seabed surveys, analysis of environmental impact deter the developers from proceeding with the projects. (SI OCEAN, 2013) 43 6.4 Assumptions and limitations: Fallowing cost analysis is based on Ernst&Young and Black&Veatch report on costs related and financial support for tidal projects. - Costs have been applied for an average date at which the defined global deployment stage is achieved.  Demonstration projects:-  Commercial projects:- - Low level of project deployment is expected until 2020 - Cost analysis is subjected to high degree of uncertainty - Total capital expenditure: Construction cost: 80%, O&M cost: 50% - Learning cost evaluated via logarithmic correlation to the global deployment forecast - Tidal stream cost is expected to fall by 70% - Learning rate from the first commercial deployment: 12.5% - Overall capex learning rate: 17.1 % - Deployment trajectories and learning rate uncertainties may have a major impact on levelized cost. 6.5 Capital expenditure (CAPEX) - cost of the tidal project deployment up to 40m depths. Tidal- shallow (Capex- Cost- 11193 - 4292 3220 Tidal- shallow (Capex) £k/MW 0 Figure 27- Capital expenditure for Tidal shallow projects [£/MW] (Ernst&Young, 2010) Capital cost is highly dependable on the cost of foundation and installation and device technology. After demonstration stage will finish and commercialization will begin, CAPEX cost should decline drastically. Due to large amount of assumptions and uncertainties in cost evaluation, values in Fig. 26 should be subjected to considerable error, at least 30%. 44 6.6 Operational expenditure (OPEX) - cost of the tidal project deployment up to 40m depths. Fallowing analysis shows OPEX cost decreasing after finalizing certain stages. Cost of the electricity produced by pre- demonstration project will always be the highest and unattractive to the investor. When the Tidal Energy industry will reach a market maturity and develop new technologies and solutions, operational cost will decrease and stabilize. Due to large amount of assumptions and uncertainties in cost evaluation, values in Fig. 27 should be subjected to considerable error, at least 30%. Tidal- shallow (Opex- Cost) £/MWh/Year- 472 310 Tidal- shallow (Opex) £/MWh/Year 150 Pre-demonstartion Demonstration Commercial Figure 28- Operational cost in Tidal shallow projects (Ernst&Young, 2010) 45 6.7 Levelised Cost with Internal rate of return. Levelised cost £/MWh- Levelised cost £/MWh Figure 29- Levelised cost and IRRs to the date (Ernst&Young, 2010) The levelised cost is a primary unit to calculate the cost of electricity produced by a generator. It includes all components of the renewable energy generation project and their lifetime cost. LCOE is then divided by expected energy output from the power plant. It also includes market inflation and discount for the time- value of money. Internal rate of return (IRR) represent the attractiveness of the project, higher the IRRs, then better for the investor to undertake the project. 6.8 Tidal funding In the growing industry of tidal energy there is a need for investments from private sector. Government is trying to promote new technologies to build up an attractive market for the investors. The new policy called Contract- for – Difference made by the Department of Energy & Climate Change (DECC) as a part of electricity reform and low carbon technologies, provides grant funding for the new renewable technology solutions and components. (Change, 2014). In 2014, £51 million has been received for the deployment of four 1.5MW devices in Meygen project in the Petland Firth to process with the next stage. The analysis made by Catapult Company, between 30%-50% of the funding are yet to be granted to some projects (Catapult, 2014). Recently, Skerries project (MCT) has lost £10 million fund, due to the delay on the deadlines, which was initially granted by The DECC. The Crown Estate also participate in supporting the Tidal industry and will be giving £10 Million for two leading tidal array projects. Further analysis shows that if the project developer is likely to invest up to £20 million for the 46 10 x 1MW array with a capital cost of £8 million/MW, there is still between £24- £43 million of the total project cost, to be received in form of grants. (Catapult, 2014). Tidal sector seems to be attractive for the investors as the power generation is constant in this case, they should expect relatively fast cost return. 6.9 Financial support- ROC ROC is the Renewables Obligation Certificate, which is issued to an accredited generator for eligible renewable power generated and utilised by the costumers via electricity supplier. Renewables Obligation is the support scheme for renewable projects in UK and the main task is to place an obligation on UK electricity suppliers to increase the amount of electricity generated by renewable systems. Some technologies can benefit from multiple ROCs per each MWh generated. (Ernst&Young, 2010) Electricity suppliers use ROCs to prove that they have met their obligation. In 2014-15 the obligation in Scotland is equal to 0.244 ROCs/MWh (OFGEM, 2014) if the obligation is not met and the number of ROCs is less than required, company has to pay the equivalent amount to RO fund. The fund is used to cover an administration cost and to pay the suppliers amount, which is equivalent to the number of ROCs they produced. In 2014-15 the buy-out price is £43.30 per ROC (OFGEM, 2014). Tidal energy is eligible for ROCs. Figure 30- Tidal stream ROCs/MWh required to meet IRRs at specific dates. (Ernst&Young, 2010) Values presented above are subjected to an error due to the effect of high and low CAPEX and OPEX capital cost estimation uncertainties. 47 6.10 Potential cost reduction Cost reduction possibilities according to SI OCEAN. After first demonstration sites will start to operate, the designers will learn more about the device performance in realistic conditions. This will allow to decrease the design margins and thus reduction in component and material cost, which can lead to standardization of certain design concepts. Performance observation may help to indicate alternative materials. It will help to redesign components and optimize the weight. Although tidal technology is well understood as it is similar power extraction method as wind turbines. Potential cost reduction according to the component. Foundations and moorings:  Contribution: Around 14 % of the lifetime cost (for the seabed mounted tidal devices). - Development of new techniques of pin-pilling from remote- operated submarine. - Using multiple small pins, instead of single piles and gravity bases. - Floating devices moored to the seabed in deep water tidal projects. - Shared foundations between multiple devices Power take- off:  Contribution: 10% of lifetime cost. - Permanent magnet generators- reduction in losses, absence of the gearbox - Development of the power electronics industry - Reactive control mechanism- By controlling the production, flow and absorption of reactive power at all levels in the tidal system improves the voltage profile and reduces the transmission losses. Control: - Blade control system, pitch control- improvement expected as in the case of wind turbines. Increase in yield and safety system reducing structural loads. - Minimal capital cost increase results in increase energy production. Connection:  Contribution: 5% (depends on the site) of lifetime cost. - Sub-sea hubs integrating arrays. - Wet mate connectors (described in 5.6”Grid Connection”). - Future development of high voltage cables could also decrease the cost. - More substations with grid connection. 48 Installation:  Contribution: 27% of lifetime cost. - Use of lower cost vessels due to improvements in installation methods. - Developing the subsea drilling technique instead of using jack- up vessels. - Shared foundation also reduces cost of installation (multiple power plants). - Developing method of installation under variety of weather conditions. - Subsea remote operated vehicles, which are able to operate in high flow velocities. - Installation of floating devices and floating platforms, should be cheaper than bottom mounted devices. Operation and maintenance:  Contribution: 19% of lifetime cost. - Design improvement in terms of device reliability. - Onshore O&M, only for floating devices. - Lifting mechanism- submerged devices, which can be accessed on the sea surface. - Suitable local port, distance between the O&M base and site should be as short as possible. - Predictive condition monitoring and use of sensors to detect potential system failures. - Development of large scale array will result in offshore O&M establishment. 6.11 Financial viability- discussion To decrease the future cost of the tidal power generation projects, it is necessary to improve technology and installation method of TEC. More detailed and advanced resource analysis could prevent the investor from additional costs or doubts in terms of resource energy potential. Most of the projects are expected to have at least 20 years of lifetime in order to achieve this, technology must be reliable and ready to operate within the extreme marine environment, which will result in future cost reduction in CAPEX and OPEX. Increasing learning rate will essentially decrease cost of the technology and cost of the electricity, reassuring appreciable industry growth. 7. Environmental Impact Tidal energy projects may have an impact on the environment. Before the deployment of the array detailed survey about existing flora and fauna and potential hazardous impact of the project, should be made. During the deployment of first TEC in Strangford Lough, SeaGen began an environmental monitoring of the site, to provide details for Environmental Impact Assessment (EIA). In 2008, SeaGen S technology was awarded with temporary licence allowing for the deployment. 49 Environmental Monitoring Programme (EMP) cost MCT around £3 million and it included mammal monitoring, bird and benthic surveys. At the end of the program, conclusion was made that TEC device has no major impact on the environment. EMP was controlled by Royal Haskoning DHV, which is a leading environmental consultancy. Also a science research group was established, which task was to observe and advise programme leaders on various aspects with intension to improve investigation methods. Sea Mammal Research Unit also contributed during the monitoring with no objections relevant to project. To fully understand the surrounding environment and potential impact from tidal array, vary detailed survey has to be made, considering many possible hazardous aspects. List of the environmental aspects to consider for EIA:  Marine physical environment and coastal processes  Hydrology, geology and surface water  Marine water quality  Terrestrial and intertidal ecology  Ornithology  Marine mammals and basking shark  Benthic ecology  Fish and shellfish 7.1 Results review from the EMP 7.1.1 Marine mammals Marine mammals spend most of the time under the water therefore they are hard to detect. With an increasing distance from the observation point, probability of mammal detection decrease. These two issues make impossible to agree on excluding potential impact on the mammals, nevertheless insufficient amount data does not prove it. All abundance estimation are under-estimates and are subjected to considerable uncertainty. Monitoring will continue to collect more data and to evaluate more accurate survey. (Haskoning,- Benthic ecology Due the fast tidal currents within the strait, high level of natural variation of benthic organisms inhabiting the seabed was expected. Tidal currents can move boulders, rock and sediment which contains benthic colonies, thus seabed is in constant succession. Using the acoustic 50 surveys methods, Seagen created a map showing dominant biotope within studied area. Foundation of the structure will definitely affect some amount of benthic communities, it has an installation footprint of 36.3m2, which takes around 0.0097% of the estimated abundance of CR.HCR.FaT.Bal.Tub (most popular biotope, covering surface of approximately 373000m2 within the Strangford Narrows). The structure itself, after installation, provided around 75.2 m2 of habitable surface. The video collected in 2010 shows that this surface is covered in around 50% by mentioned biotope. This gives surface replacement of 37.6m2. It is likely that since last examination, surface area covered by CR.HCR.FaT.Bal.Tub increased. The mussel biotope which also occur in the Narrows, provides a food source for some fish, echinoderms and crustaceans, which is considered as a positive impact. Further surveys will take place during the operational stage. (Haskoning, 2011) 7.1.3 Tidal Flow regime: In this part of monitoring the limiting factor was the amount of data collected and time period. Fast tidal current can cover up potential impact of the turbine on flow regime. Although acceptable results were gathered form pre and post surveys showing no evidence of flow deviations caused by the turbine. Any changes noticed were within the limit of natural variations. (Haskoning, 2011) 7.1.4 Ornithology: From the key findings related to bird’s activity, it was stated that tidal cycle is a significant factor in the number of bird sightings and it decreases with ebb tidal phase. Turbine operation significantly decrease number of birds observed within the area and increase when the turbine is turned off. Even though, after more detailed analysis it was noticed that it mostly a change in distribution rather than number of birds. There was a decline in cormorant sightings by approximately 25% during TEC operation. From the further analysis made by University of Exeter in 2010, few minor statistically significant variations were noticed related to birds distribution and no other hazards, which could meaningfully disturb birds species. (Haskoning, 2011) 7.2 The Pentland Firth and Orkney waters The Pentland Firth and Orkney waters are inhabited by important and rare species which makes this area rich in biodiversity. This marine and coastal variety of animals is listed in EC Habitats Directive (92/42/EEC) annex I and they have been protected by Special Areas of Conservation (SACs). 51 There are seven SAC sites around considered areas and habitats are also protected under National Legislation through the Sites of Special Scientific Interest (SSSI). There is also an extensive range of mammals living in these waters, including whales, seals, dolphins and porpoise. Approximately 43% of Europe’s seal populations and 85% of Europe’s grey seal populations live around Orkney Islands. Whales, dolphins and porpoise are often seen and are protected under Annex IV of the Habitats Directive and Wildlife and Countryside Act (1981). (Government, n.d.) 7.3 CO2 emissions Tidal power generation does not produce CO2 emissions. Although it is associated with 1.8g of CO2/kWh. (Rule BM, 2009) This includes emission during building the components of the system, installation process and O&M. 8. Planning, policy and legislation 8.1 Kyle Rhea licencing requirements:  Section 36 (Electricity Act), Authority: Consent Scottish Ministers  Marine Licence (Marine (Scotland) Act), Authority: Consent Marine Scotland  Licence to Disturb Marine Species, Authority: Marine Scotland  Licence to Disturb Basking Shark, Authority: Marine Scotland  Town and County Planning Permission, Authority: District of Skye and Lochalsh – Highland Council 8.2 Renewable energy policy Scottish planning policy 6: Renewable energy (2009), determines the components that will go under consideration of appropriate authorities, during renewable energy applications. 8.3 Planning Legislation Any planning application has to be followed by Environmental Statement (ES). Legislation required for tidal energy generation project:  Electricity Act, 1989, Section 36 Tidal energy array deployment with capacity of 1MW or more and electricity generation will require a consent from Scottish Ministers. Although the Marine Act allows for the application to be made under section 36 as a one application including Marine Licence.  EIA Directive, 1985 (amended 1999) It insures that appropriate assessment was made to identify all potential environmental impact cause by the project. Public opinion is taken into account as a valuable factor in this case. 52  The Electricity Works (Environmental Impact Assessment) (Scotland) regulations, 2000 Outlined requirements for assessment of the effect of the projects on environment. It is related to Electricity Act, and give the regulatory of installing overhead power lines; construction, extension and operation of power plant.  Marine Act Marine Act Scotland was enact in 2010, and it aims to improve seas management and interest variety of marine users. Marine Scotland was established in 2009 as a directorate of the Scottish Government to control marine environment. This act shows framework for marine environment protection combined with economic progress of marine industry. Marine Act will also simplify consent requirements of Food and Environment Protection Act, 1985, Section 5 Part II and Coast Protection Act, 1949, Section 34  Town and Country Planning (Scotland) Act, 1997, Section 57 It is a request to the Scottish Government for planning permission.  Energy Act 2004 Act which provides regulations for offshore project developers. It also gives rights to The Crown Estate to licence generation of renewable energy, applying limits to 12nm and 200nm when the site is within the Renewable Energy Zone.  Water Environment and Water Services Act Saturator controls and regulations in relation to low risk deployments like cable landing, preventing from pollution of the water.  Lease of the Seabed The Crown Estate has to be contacted regarding lease to deploy a tidal project. 9. Discussion Significant progress was made in tidal energy technology in last years, including first operating test turbines showing convincing amount of power that can be generated from the current flow. Few companies have already moved forward with tidal array deployment, which is important step towards commercialisation of marine energy industry. Tidal energy is a constant source of electricity, which can be predicted to satisfactory levels. Nevertheless more detailed and accurate surveys are yet to be develop. There is a need to build up decent level of reliability 53 of the TEC devices as well as improve methodology and technique in assessing the tidal resources. Future streamline manufacturing of devices and improved installation processes as well as maintenance routines will reduce the cost and increase attractiveness for potential investors. If the next demonstration stages will prove the financial viability of the tidal projects, Scotland may become marine energy leader in the world. Analysis of first prototypes has already proved cost reduction after certain amount of the TEC will be deployed. Developers are able to demonstrate ways to reduce the capital and operating cost while increasing energy yield. Experience needed to expand range of applicability, improve reliability of the tidal devices and simply to strengthen the industry can be taken from others, like offshore wind sites. Supply chain could be more integrated with other manufacturers, creating wide web, thus decreasing the cost. Development of new ways to predict potential power output from the tidal array project could result in higher integration level with already existing grid infrastructures. It is crucial to fully understand TEC performance with connection to other devices under variety of resource conditions. Tidal energy generation is in its infancy but soon it will make a big step, moving forward from demonstration sites with a single device to arrays with several devices. Renewable marine energy experiences a wide range of challenges and difficulties in technology along with forecasting its own future. It will have to overcome these challenges in order to achieve market maturity, which will stabilize the future of the industry. The group of investors, which are already actively participating in race against time, will determine future aspects of the marine energy industry. Their task is to engage public interest with supportive information and to promote clean energy. From overall environmental perspective, it is too early to affirm low environmental impact. Several assessment were made for single devices deployment but unfortunately there is no existing tidal array to be a investigated in terms of a large scale tidal power extraction site and its impact on inhabiting species of the resource. Additional surveys will be carry out to thoroughly understand the potential hazards linked to TEC and TEC array projects. Kyle Rhea resource assessment proved feasibility of the site deployment. During one year operation, 2 x 16m rotor diameter turbine, placed within the strait of Kyle Rhea, could supply around 1645 UK houses with electricity (assuming 4.6MWh energy demand per UK’s household). Although this number is just an estimation and potential error should be considered. 54 10. References aviationenterprises, 2010. http://www.aviationenterprises.co.uk/P6%20Renewables.html. [Online] Available at: http://www.aviationenterprises.co.uk/P6%20Renewables.html [Accessed 2015]. Beardmore, R., 2011. http://www.roymech.co.uk. 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T., Fraenkel, P. L., Morton, A. B. –. K. M. & Lugg, L., 2003. THE POTENTIAL FOR THE USE OF MARINE CURRENT ENERGY IN NORTHERN IRELAND, s.l.: s.n. Appendices A THE SEAGEN TURBINE 1st commercial scale marine current turbine to extract energy from UK tidal flows. Power Rated Power – 1.2MW Power to grid per year – 3800MWh/yr Equivalent houses – 1140 (based on 3.33MWh per house per year (0.38kW continuous)) Equivalent Carbon – 1695 tonnes CO2/year (based on 0.446 kg CO2/kWh) Tower Total height above Seabed – 40.7m Diameter – 3.025m Crossbeam Crossbeam length – 29m Distance between Drivetrains – 27m Weight with Drivetrains – 151 tonnes Water Depth Depth of Water Lowest Astronomical Tide (LAT) – 24m Depth of Water Mean Sea Level (MSL) – 26.2m Depth of Water Highest Astronomical Tide (HAT) – 28.3m Maximum Range – 4.3m Drivetrain Diameter of Rotor – 16m Drivetrain weight – 27 tonnes Gearbox ratio – 69.9:1 Nominal Generator Speed – 1000rpm Nominal Rotor Speed – 14.3rpm Tip Speed – 12m/s Rated Power – 2 x 600kW = 1200kW Nominal Rated Rotor Thrust – 431kN each (Rated Speed, Rated Current) Equivalent Trent 900 engines (70000llbs thrust) – 1.38 per drivetrain Independent Pitch Motors – 8.4 kW continuous Current Mean Spring Current – 3.7m/s or 7.2knots Max Current – 4.8m/s or 9.3knots (1yr) Rated Speed – 2.4m/s or 4.7knots Lift Mechanism Weight to lift – 170 tonnes Lift Leg weight – 9.0 tonne each Lift Distance – 16.9m Speed – 0.38 m/min Hydraulic Rams, 2 * 280mm bore 57 Appendices B Assumptions and limitations of Kyle Rhea resource assessment 1. Energy output does not consider downtime of the device. 2. Methodology of calculation allows for considerable error. 3. Only two months data used to estimate annual energy output. 4. Energy output does not include any potential losses. 5. Power curve was generated using sinusoidal interpolation method. In real life, more detailed calculation has to be made using harmonic constituents. 5. Calculation does not consider Significant Impact Factor. Appendices C CD-R with Excel workbook “Energy output” File navigation guide: “30 min” sheet: 1. Input rotor diameter = B5 2. Input rotor swept area= C5 3. Input cross section area= B4 Note: allows to see power from the flow through specific CSA 4. Input CoP= B6 5. Output annual energy= T2 and T3 6. Output power of the flow in specific CSA= column O (every 30 min) 7. Output Energy= column R (every 30 min) 58