Showing papers on "Marine energy published in 2012"

A review of oscillating water columns

Abstract: This paper considers the history of oscillating water column (OWC) systems from whistling buoys to grid-connected power generation systems. The power conversion from the wave resource through to electricity via pneumatic and shaft power is discussed in general terms and with specific reference to Voith Hydro Wavegen's land installed marine energy transformer (LIMPET) plant on the Scottish island of Islay and OWC breakwater systems. A report on the progress of other OWC systems and power take-off units under commercial development is given, and the particular challenges faced by OWC developers reviewed.

Measurements of Turbulence at Two Tidal Energy Sites in Puget Sound, WA

Abstract: Field measurements of turbulence are presented from two sites in Puget Sound, WA, that are proposed for electrical power generation using tidal current turbines. Time series data from multiple acoustic Doppler instruments are analyzed to obtain statistical measures of fluctuations in both the magnitude and direction of the tidal currents. The resulting turbulence intensities (i.e., the turbulent velocity fluctuations normalized by the deterministic tidal currents) are typically 10% at the hub heights (i.e., the relevant depth) of the proposed turbines. Length and time scales of the turbulence are also analyzed. Large-scale, anisotropic eddies dominate the turbulent kinetic energy (TKE) spectra, which may be the result of proximity to headlands at each site. At small scales, an isotropic turbulent cascade is observed and used to estimate the dissipation rate of TKE, which is shown to balance with shear production. Data quality and sampling parameters are discussed, with an emphasis on the removal of Doppler noise from turbulence statistics. The results are relevant to estimating the performance and fatigue of tidal turbines.

A synthesis of numerical methods for modeling wave energy converter-point absorbers

Abstract: During the past few decades, wave energy has received significant attention for harnessing ocean energy. Industry has proposed many technologies and, based on their working principle, these technologies generally can be categorized into oscillating water columns, point absorbers, overtopping systems, and bottom-hinged systems. In particular, many researchers have focused on modeling the point absorber, which is thought to be the most cost-efficient technology to extract wave energy. To model such devices, several modeling methods have been used such as analytical methods, boundary integral equation methods and Navier–Stokes equation methods. The first two are generally combined with the use of empirical solution to represent the viscous damping effect, while the last one is directly included in the solution. To assist the development of wave energy conversion (WEC) technologies, this paper extensively reviews the methods for modeling point absorbers.

Nearshore oscillating wave surge converters and the development of Oyster.

Abstract: Oscillating wave surge converters (OWSCs) are a class of wave power technology that exploits the enhanced horizontal fluid particle movement of waves in the nearshore coastal zone with water depths of 10–20 m. OWSCs predominantly oscillate horizontally in surge as opposed to the majority of wave devices, which oscillate vertically in heave and usually are deployed in deeper water. The characteristics of the nearshore wave resource are described along with the hydrodynamics of OWSCs. The variables in the OWSC design space are discussed together with a presentation of some of their effects on capture width, frequency bandwidth response and power take-off characteristics. There are notable differences between the different OWSCs under development worldwide, and these are highlighted. The final section of the paper describes Aquamarine Power’s 315 kW Oyster 1 prototype, which was deployed at the European Marine Energy Centre in August 2009. Its place in the OWSC design space is described along with the practical experience gained. This has led to the design of Oyster 2, which was deployed in August 2011. It is concluded that nearshore OWSCs are serious contenders in the mix of wave power technologies. The nearshore wave climate has a narrower directional spread than the offshore, the largest waves are filtered out and the exploitable resource is typically only 10–20% less in 10 m depth compared with 50 m depth. Regarding the devices, a key conclusion is that OWSCs such as Oyster primarily respond in the working frequency range to the horizontal fluid acceleration; Oyster is not a drag device responding to horizontal fluid velocity. The hydrodynamics of Oyster is dominated by inertia with added inertia being a very significant contributor. It is unlikely that individual flap modules will exceed 1 MW in installed capacity owing to wave resource, hydrodynamic and economic constraints. Generating stations will be made up of line arrays of flaps with communal secondary power conversion every 5–10 units.

A review of the potential water quality impacts of tidal renewable energy systems

Abstract: The continued increase in the demand for energy, growing recognition of climate change impacts, high oil and gas prices and the rapid depletion of fossil fuel reserves have led to an increased interest in the mass generation of electricity from renewable sources. Traditionally, this has been pursed through riverine hydropower plants, with onshore wind systems growing steadily in popularity and importance over the years. Other renewable energy resources, which were previously not economically attractive or technically feasible for large scale exploitation, are now being considered to form a significant part of the energy mix. Amongst these, marine and in particular, tidal energy resource has become a serious candidate for undergoing mass exploitation in the near future, particularly in places with a tidal range of 4 m or more. Tidal renewable energy systems are designed to extract the kinetic or potential energy flow and convert it into electricity. This can be achieved by placing tidal stream turbines in the path of high speed tidal currents or through tidal range schemes, where low head turbines are encapsulated in impoundment structures, much like in low head riverine hydropower schemes. It is thought that these systems, when implemented at scales required to generate substantial amounts of electricity, have the potential to significantly alter the tidal flow characteristics, which could have knock-on impacts on the hydro-environment. This review gathers together knowledge from different research areas to facilitate an evaluation of the potential hydro-environmental impacts of tidal renewable energy systems, with a particular focus on water quality. It highlights the relevance of hydroenvironmental modelling in assessing potential impacts of proposed schemes and identifies areas where further research is needed. A case study is presented of recent modelling studies undertaken for the Severn Estuary.

On the Wind Power Input to the Ocean General Circulation

Abstract: The wind power input to the ocean general circulation is usually calculated from the time-averaged wind products. Here, this wind power input is reexamined using available observations, focusing on the role of the synoptically varying wind. Power input to the ocean general circulation is found to increase by over 70% when 6-hourly winds are used instead of monthly winds. Much of the increase occurs in the storm-track regions of the Southern Ocean, Gulf Stream, and Kuroshio Extension. This result holds irrespective of whether the ocean surface velocity is accounted for in the wind stress calculation. Depending on the fate of the highfrequency wind power input, the power input to the ocean general circulation relevant to deep-ocean mixing may be less than previously thought. This study emphasizes the difficulty of choosing appropriate forcing for ocean-only models.

Sliding-Mode Control of Wave Power Generation Plants

Abstract: The worldwide demand for energy requires alternatives to fossil fuels and nuclear fission, so renewable resources, particularly ocean energy, are called to play a relevant role in a near future. In particular, the oscillating water column (OWC) is one of the most promising devices to harness energy from the sea, as it is the case of the Nereida project plant, located in the Basque coast of Mutriku. This kind of devices consists of a particular type of turbine and a doubly fed induction generator. The turbogenerator module is usually controlled using a traditional proportional-integral (PI)-based vector control scheme, which requires an accurate knowledge of the system parameters and lacks of robustness, limiting, in some cases, the power extraction. To avoid these drawbacks, a novel sliding-mode-control-based vector control scheme for the OWC plant is presented in this paper. This variable-structure control is intrinsically robust under parameter uncertainties, which always appear in real systems, and presents a convenient disturbance rejection. The stability of the proposed controller is analyzed using the Lyapunov theory. The performance of the control scheme presented is proved by comparing it to the traditional PI-based vector control scheme in a series of representative maximum power generation case studies. Both numerical simulations and experimental results show that the proposed solution provides high-performance dynamic characteristics, improving the power extraction in spite of parameter uncertainties and system disturbances.

An overview of ocean renewable energy resources in Korea

Abstract: Korea relies on imported fossil fuels to meet its energy consumption demands As such, there is a need to investigate alternative energy resources such as renewable energy In this paper, assessments of the potential of various ocean renewable energy resources in the sea around Korea; potential sources of energy including wave energy, tidal energy, tidal current energy and ocean thermal energy Tidal energy and tidal current energy are likely to play an important role in meeting the future energy needs of Korea, whereas the potentials of wave energy and ocean thermal energy for the same are relatively low The level of technical development and the renewable energy market in Korea is currently in an early stage The government will have to be more aggressive in the promotion of renewable energy to achieve sustainable development in Korea

Renewable ocean energy in the Western Indian Ocean

Abstract: Several African countries in the Western Indian Ocean (WIO) endure insufficiencies in the power sector, including both generation and distribution. One important step towards increasing energy security and availability is to intensify the use of renewable energy sources. The access to cost-efficient hydropower is low in coastal and island regions and combinations of different renewable energy sources will play an increasingly important role. In this study the physical preconditions for renewable ocean energy are investigated, considering the specific context of the WIO countries. Global-level resource assessments and oceanographic literature and data have been compiled in an analysis of the match between technology-specific requirements for ocean energy technologies (wave power, ocean thermal energy conversion (OTEC), tidal barrages, tidal current turbines, and ocean current power) and the physical resources in 13 WIO regions Kenya, Seychelles, Northern Tanzania and Zanzibar, Southern Tanzania, Comoros and Mayotte, Northern-, Central-, and Southern Mozambique, Western-, Eastern-, and Southern Madagascar, Reunion, and Mauritius. The results show high potential for wave power over vast coastal stretches in southern parts of the WIO and high potential for OTEC at specific locations in Mozambique, Comoros, Reunion, and Mauritius. The potential for tidal power and ocean current power is more restricted but may be of interest at some locations. The findings are discussed in relation to currently used electricity sources and the potential for solar photovoltaic and wind power. Temporal variations in resource intensity as well as the differences between small-scale and large-scale applications are considered.

Tides, sea-level rise and tidal power extraction on the European shelf

Abstract: An established numerical tidal model has been used to investigate the impact of various sea-level rise (SLR) scenarios, as well as SLR in combination with large-scale tidal power plants on European shelf tidal dynamics. Even moderate and realistic levels of future SLR are shown to have significant impacts on the tidal dynamics of the area. These changes are further enhanced when SLR and tidal power plants are considered in combination, resulting in changes to tidal amplitudes, currents and associated tidal dissipation and bed shear stresses. Sea-level rise is the dominant influence on any far-field impacts, whereas tidal power plants are shown to have the prevailing influence over any changes close to the point of energy extraction. The spatial extent of the impacts of energy extraction is shown to be affected by the sea level when more than one tidal power plant in the Irish Sea was considered. Different ways to implement SLR in the model are also discussed and shown to be of great significance for the response of the tides.

The effect of boundary proximity upon the wake structure of horizontal axis marine current turbines

Abstract: An experimental and theoretical investigation of the flow field around small-scale mesh disk rotor simulators is presented. The downstream wake flow field of the rotor simulators has been observed and measured in the 21m tilting flume at the Chilworth hydraulics laboratory, University of Southampton. The focus of this work is the proximity of flow boundaries (sea bed and surface) to the rotor disks and the constrained nature of the flow. A three-dimensional Eddy-viscosity numerical model based on an established wind turbine wake model has been modified to account for the change in fluid and the presence of a bounding free surface. This work has shown that previous axi-symmetric modeling approaches may not hold for marine current energy technology and a novel approach is required for simulation of the downstream flow field. Such modeling solutions are discussed and resultant simulation results are given. In addition, the presented work has been conducted as part of a UK Government funded project to develop validated numerical modeling tools which can predict the flow onto a marine current turbine within an array. The work feeds into the marine energy program at Southampton to assist developers with layout designs of arrays which are optimally spaced and arranged to achieve the maximum possible energy yield at a given tidal energy site.

Development of a Wave Energy Converter Using a Two Chamber Oscillating Water Column

Abstract: This paper presents the development and system analysis of segmented oscillating water columns (OWC) for wave energy conversion based on the wave conditions around Taiwan. The OWC chambers are designed for a target site and the power converted by each component (i.e., the chambers, turbine and generator) in the power chain is analyzed so that the overall power output and efficiency can be calculated. The characteristic match between the turbine and the generator is also discussed. The developed OWC is side-mounted and this allows the waves to penetrate and continue propagating after transferring power to the chambers. The OWC consists of two adjacent chambers which are aligned in the direction of the wave propagation. Each chamber has one Savonius turbine on top to convert the chamber power into mechanical shaft power. The two turbines are connected in-line and the individual chambers transfer power to the turbines with a phase difference, so that the power output can be smoothed. A brushless permanent-magnet generator is used to convert the turbine output power into electricity. Experiments are conducted on a scaled-down model in a wave tank to evaluate the performance and the results verify the design. It is also found that the successive chamber should have a different design to the first one as it suffers slight wave attenuation.

Sea Water Ageing of Composites for Ocean Energy Conversion Systems: Influence of Glass Fibre Type on Static Behaviour

Abstract: Composite material components will be an essential part of ocean energy recovery devices, and their long term durability in sea water must be guaranteed. Despite extensive experience for boat structures and wind turbines few data exist to design structures subjected to a combination of mechanical loads and sea water immersion. This paper presents the first results from an experimental study, performed jointly with fibre manufacturers, and a resin supplier, to fill this gap. The experimental study is completed by numerical modelling to simulate the coupling between water absorption and mechanical behaviour. Sea water ageing is shown to result in a drop in quasi-static mechanical properties and a change in flexural mode from compression to tension at longer ageing times, which is consistent with results from the numerical simulations.

An Assessment of the Hydrokinetic Energy Resource of the Florida Current

Abstract: Available ocean model and physically measured data from the Florida Current are analyzed to provide a detailed assessment of the hydrokinetic energy resource of the Florida Current, in support of harnessing a portion of it using ocean energy conversion devices. It has been estimated that approximately 25 GW of hydrokinetic power is available in the Florida Current. Fluctuations in this energy resource are described. Based on the analysis, realistic parameters governing where hydrokinetic energy extraction devices-turbines-may be ideally installed are discussed. An energy resource assessment methodology that has been developed is described. It can be used as a design tool for implementation of arrays of ocean energy extraction devices.

Assessing mechanical loading regimes and fatigue life of marine power cables in marine energy applications

Abstract: Reliable marine power cables are imperative for the cost-effective operation of marine energy conversion systems. There is considerable experience with marine power cables under static and dynamic ...

A Marine Spatial Planning Approach to Select Suitable Areas for Installing Wave Energy Converters (WECs), on the Basque Continental Shelf (Bay of Biscay)

Abstract: Recently, considerable interest has been generated in the wave energy production. As a new use of the ocean, a Spatial Planning approach is proposed to provide a mechanism to achieve consensus among the sectors operating at present, together with the identification of the most suitable locations to accommodate the Wave Energy Converters (WECs), in the near future. In this contribution: (a) a methodology for the establishment of a Suitability Index (SI) for WECs installation location selection is proposed; (b) the spatial distribution of the SI is mapped; and finally, (c) the accessible wave energy potential has been calculated for the entire Basque continental shelf. As the SI represents the appropriateness of several locations for WECs installation, while minimizing the conflict with other marine uses, the first step in the development of the analysis involved gathering all such information that may be likely to determine, or influence, the decision-making process. Seventeen information layers (among the...

Tidal current turbines glance at the past and look into future prospects in Malaysia

Abstract: Periodic changes of water levels, and associated tidal currents, are due to the gravitational attraction forces between the Earth, the Sun and the Moon. These changes can be transformed to a renewable energy resource called Tidal Current Energy. A number of resource quantization and demonstration studies have been performed throughout the world and it is believed that offshore ocean energy sector will benefit from this emerging technology. In this study, a set of basic definitions which are relevant to this technology are presented with an overview on the main tidal turbine schemes and the mooring methods that in use. A review of the current development and their fields of applications are outlined. The Blade Element Momentum BEM method and the Computational Fluid Dynamics CFD are discussed. The last section highlights the importance of this technology and its applicability in Malaysia. Other renewable energy resources in Malaysia are highlighted and discussed as well.

Tidal energy resource complexity in a large strait: The Karori Rip, Cook Strait

Abstract: Successful extraction of tidal stream energy will require a good understanding of flow at a range of scales, including those relating to average energy, variability in energy supply and fatigue. Current and turbulence measurements from the Karori Rip area of Cook Strait, the prime focal region of open-water tidal stream electricity generation in New Zealand, are described. A key issue is that a significant portion of the energy is contained in waters deeper than normally considered for energy extraction. Here we compare shallow and deep sites. Velocity data were derived from acoustic Doppler current profiler moorings, as well as spatial surveys and show flow magnitudes reaching 3.4 m s −1 in the shallow regions. The maximum speeds in both shallow and deep sites were typically located in the upper part of the measured water column although moored acoustic Doppler current profiler (ADCP) observations showed some complexity in this regard. Benthic boundary-layers were resolved in the bottom ∼20 m of the water column. Measured turbulent kinetic energy dissipation rates e exceeded 10 −5 m 2 s −3 and estimated maximum e is a factor of 10 greater. This was not distributed evenly through the water column, with stratification and velocity shear clearly persisting, especially around the turn of the tide. The implications for tidal stream energy are that (i) there is sufficient energy resource in the region for a moderate sized array of turbines, (ii) the vertical variability in the flow speed suggests turbines that can operate near the surface would be more effective at accessing the resource, (iii) stratification may persist and influence the scales of turbulence and (iv) wave–current interaction effects will influence any near-surface structure as well as vessel operations.

Iswec: A Gyroscopic Wave Energy Converter

Abstract: Wave Power: how to produce clean electric energy from sea waves. Thousands of patents have been filed, hundreds of devices have been studied and tested in labs and tens of prototypes of Wave Energy Converters (WECs) have been deployed to the sea successfully harvesting wave power. The main research work has been carried out for the oceans, the most relevant source of wave energy. Closed seas, like the Mediterranean Sea, have smaller energy availability, but they have a particular feature: short waves. Short waves have higher frequency and can activate a WEC in a very effective way. For instance a WEC carrying a gyroscope-based energy conversion system harvests power proportionally to the square of the wave frequency. Gyroscopic effects can keep a spinning top in a quasi vertical position, guide airplanes, stabilize ships and, with some different architecture and strategy, harvest energy from sea waves!

Conceptual design of ocean compressed air energy storage system

Abstract: In this paper, an ocean compressed air energy storage (OCAES) system is introduced as a utility scale energy storage option for electricity generated by wind, ocean currents, tides, and waves off the coast of North Carolina. Geographically, a location from 40km to 70km off the coast of Cape Hatteras is shown to be a good location for an OCAES system. Based on existing compressed air energy storage (CAES) system designs, a conceptual design of an OCAES system with thermal energy storage (TES) is presented. A simple thermodynamic analysis is presented for an adiabatic CAES system which shows that the overall efficiency is 65.9%. In addition, finite element simulations are presented which show the flow induced loads which will be experienced by OCAES air containers on the ocean floor. We discuss the fact that the combination of the buoyancy force and the flow induced lift forces (due to ocean currents) generates a periodic loading on the storage container and seabed, and how this presents engineering challenges related to the development of adequate anchoring systems. We also present a system, based on hydrolysis, which can be used for storing energy (in the form of oxygen and hydrogen gas) in containers on the ocean floor.

Shipboard Propulsion, Power Electronics, and Ocean Energy

Abstract: Shipboard Propulsion, Power Electronics, and Ocean Energy fills the need for a comprehensive book that covers modern shipboard propulsion and the power electronics and ocean energy technologies that drive it. With a breadth and depth not found in other books, it examines the power electronics systems for ship propulsion and for extracting ocean ene

Marine tidal current systems: State of the art

Abstract: The Ocean, which covers two-thirds of the world, captures and stores huge amounts of energy. Several sources of energy can be used. This paper presents a brief review of state of the art on the marine tidal current generation technology. The purposes are as follow: the first part concerns the conversion of marine current energy into mechanical energy, a synthesis of the existing methods of the modeling of the resource and of the marine current turbine are presented. The second part is dedicated to the conversion of the mechanical energy to electrical energy by taking into account the power converters for the control and the grid connection. Some simulation results are briefly shown for each part.

Ocean energy power take-off using oscillating paddle

Abstract: This paper presents an ocean energy power take-off system using paddle like wave energy converter (WEC), magnetic gear and efficient power converter architecture. As the WEC oscillates at a low speed of about 5–25 rpm, the direct drive generator is not an efficient design. To increase the generator speed a cost effective flux focusing magnetic gear is proposed. Power converter architecture is discussed and integration of energy storage in the system to smooth the power output is elaborated. Super-capacitor is chosen as energy storage for its better oscillatory power absorbing capability than battery. WEC is emulated in hardware using motor generator set-up and energy storage integration in the system is demonstrated.