Showing papers on "Wave power published in 2013"

Review of wave energy technologies and the necessary power-equipment

Abstract: The wave energy is having more and more interest and support as a promising renewable resource to replace part of the energy supply, although it is still immature compared to other renewable technologies. This work presents a complete analysis of the wave energy technology, starting with the characterisation of this global resource in which the most suitable places to be exploited are showed, and the classification of the different types of wave energy converters in according to several features. It is also described in detail each of the stages that are part in the energy conversion, that is, from the capture of the energy from the waves to the extraction of a proper electrical signal to be injected to the grid. Likewise, existing offshore energy transmission alternatives and possible layouts are described.

Discrete Displacement Hydraulic Power Take-Off System for the Wavestar Wave Energy Converter

Abstract: The Wavestar Wave Energy Converter (WEC) is a multiple absorber concept, consisting of 20 hemisphere shaped floats attached to a single platform. The heart of the Wavestar WEC is the Power Take-Off (PTO) system, converting the wave induced motion of the floats into a steady power output to the grid. In the present work, a PTO based on a novel discrete displacement fluid power technology is explored for the Wavestar WEC. Absorption of power from the floats is performed by hydraulic cylinders, supplying power to a common fixed pressure system with accumulators for energy smoothing. The stored pressure energy is converted into electricity at a steady pace by hydraulic motors and generators. The storage, thereby, decouples the complicated process of wave power absorption from power generation. The core for enabling this PTO technology is implementing a near loss-free force control of the energy absorbing cylinders. This is achieved by using special multi-chambered cylinders, where the different chambers may be connected to the available system pressures using fast on/off valves. Resultantly, a Discrete Displacement Cylinder (DDC) is created, allowing near loss free discrete force control. This paper presents a complete PTO system for a 20 float Wavestar based on the DDC. The WEC and PTO is rigorously modeled from incident waves to the electric output to the grid. The resulting model of +600 states is simulated in different irregular seas, showing that power conversion efficiencies above 70% from input power to electrical power is achievable for all relevant sea conditions.

Joint Environmental Data at Five European Offshore Sites for Design of Combined Wind and Wave Energy Devices

Abstract: The costs for an offshore wind farm, especially with bottom fixed foundations increase significantly with increasing water depth If costs can be reduced to a competitive level, the potential for wind farms in deep water is huge One way of reducing costs might be to combine offshore wind with wave energy facilities at sites where these resources are concentratedIn order to design combined renewable energy concepts, it is important to choose sites where both wind and wave energy resources are substantial Such facilities might be designed in ultimate limit states based on load effects corresponding to 50-year wind and wave conditions This requires a long-term joint probabilistic model for the wind and wave parameters at potential sitesIn this paper, five European offshore sites are selected for analysis and comparison of combined renewable energy concepts developed in the EU FP7 project – MARINA Platform The five sites cover both shallow water ( 200m), with three sites facing the Atlantic Ocean and the other two sites in the North Sea The selection of the sites is carried out by considering average wind and wave energy resources, as well as extreme environmental conditions which indicate the cost of the systemLong-term joint distributions of mean wind speed at 10-meter height (Uw), significant wave height (Hs) and spectral peak period (Tp) are presented for selected sites Simultaneous hourly wind and wave hindcast data from 2001–2010 are used as a database, which are obtained from the National and Kapodistrian University of AthensThe joint distributions are estimated by fitting analytical distributions to the hindcast data following a procedure suggested by Johannessen et al (2001) The long-term joint distributions can be used to estimate the wind and wave power output from each combined concept, and to estimate the fatigue lifetime of the structure For estimation of the wind and wave power separately, the marginal distributions of wind and wave are also providedBased on the joint distributions, contour surfaces are established for combined wind and wave parameters for which the probability of exceedance corresponds to a return period of 50 years The design points on the 50-year contour surfaces are suggested for extreme response analysis of combined concepts The analytical long-term distributions established could also be applied for design analysis of other offshore structures with similar environmental considerations of these sitesCopyright © 2013 by ASME

Analysis of a Two-Body Floating Wave Energy Converter With Particular Focus on the Effects of Power Take-Off and Mooring Systems on Energy Capture

Abstract: The present paper summarizes analyses of a two-body floating wave energy converter (WEC) to determine the mooring tension and the effect of the mooring system on energy capture. Also, the effect of the power take-off (PTO) is assessed. An axisymmetric Wavebob-type WEC is chosen as the object of investigation. However, the PTO system is modeled in a simplified manner as ideal linear damping and spring terms that couple the motions of the two bodies. The analysis is performed using SIMO, which is a time domain simulation tool that accommodates the simulation of multibody systems with hydrodynamic interactions. In SIMO, docking cone features between the two bodies allow movement as per actual operation, and fenders are applied to represent end stops. Six alternative mooring configurations are applied to investigate the effect of mooring on power capture. Mooring analysis is performed to determine the necessary capacity of mooring lines for each configuration to carry the tension due to the WEC motion in extreme conditions. Hydrodynamic loads are determined using WAMIT. We assumed that the WEC will be operated to capture wave power at the Yeu site in France. The analysis is performed for several regular and irregular wave conditions according to wave data available for that site. Simulations are performed to study the effect of the PTO system, end stops settings and several mooring configurations on power capture.

Radiation belt electron acceleration by ULF wave drift resonance: Simulation of 1997 and 1998 storms

Abstract: Pc 5 ULF waves are seen concurrently with the rise in radiation belt fluxes associated with CME-magnetic cloud events. Four such geomagnetic storm periods in 1997 and 1998, 10-11 January and 14-15 May, 1997; 1-4 May and 26-28 August, 1998, have been simulated with a 3D global MHD code driven by L1-measured solar wind parameters. The field output has been used to advance electron guiding center trajectories in the equatorial plane. The time series has also been analyzed for ULF wave mode structure. Toroidal field line resonances with low azimuthal mode number and frequencies commensurate with the electron drift period are identified in the radial electric field component, along with enhanced power in the poloidal (azimuthal) electric field component. The simulated time scale for inward radial transport of electrons in the several hundred keV to MeV energy range, from geosynchronous orbit to L=3-4, varies with the level of ULF wave power and overall energy input to the magnetosphere. Of the four events studied, the May 1998 storm period was most geoeffective and the January 1997 least so, in terms of simulated radial transport and energization of electrons. This transport rate is consistent with the level of ULF waves excited in the simulations, and the proposed drift resonant acceleration mechanism.

Investigation of a low-power, double-sided switched reluctance generator for wave energy conversion

Abstract: In this paper, a low-power, direct-drive, double-sided linear switched reluctance generator (LSRG) is designed and constructed as one of the components of generator matrix for wave power utilizations by direct energy conversion. This machine has the characteristics of simple construction, mechanical robustness, and maintenance free. Following the theoretical background of linear power generation, characteristic investigation is performed by finite element analysis, which shows that each phase can be controlled individually and normal forces can be approximately counteracted from the double-sided structure. Both preliminary power simulation and experimental results show that there is an optimized generation region for turn-on and turn-off position control strategy. The closed loop test based on Pulse Width Modulation (PWM) of current waveforms also demonstrate that for a wide range of wave speed excitations, PWM scheme should be combined with other control strategies for uniform current level regulations.

Characteristics of the Operational Noise from Full Scale Wave Energy Converters in the Lysekil Project: Estimation of Potential Environmental Impacts

Abstract: Wave energy conversion is a clean electric power production technology. During operation there are no emissions in the form of harmful gases. However there are unsolved issues considering environmental impacts such as: electromagnetism; the artificial reef effect and underwater noise. Anthropogenic noise is increasing in the oceans worldwide and wave power will contribute to this sound pollution in the oceans; but to what extent? The main purpose of this study was to examine the noise emitted by a full scale operating Wave Energy Converter (WEC) in the Lysekil project at Uppsala University in Sweden. A minor review of the hearing capabilities of fish and marine mammals is presented to aid in the conclusions of impact from anthropogenic sound. A hydrophone was deployed to the seabed in the Lysekil research site park at distance of 20 and 40 m away from two operational WECs. The measurements were performed in the spring of 2011. The results showed that the main noise was a transient noise with most of its energy in frequencies below 1 kHz. These results indicate that several marine organisms (fish and mammals) will be able to hear the operating WECs of a distance of at least 20 m.

Predictability and Variability of Wave and Wind: wave and wind forecasting and diversified energy systems in the Danish North Sea

Abstract: This project covers two fields of study: a) Wave energy predictability and electricity markets. b) Variability of the power output of WECs in diversified systems: diversified renewable systems with wave and offshore wind production. The issue of the first part of this research project is: 1) Quantify how accurately waves can be predicted and compare that value to winds predictability. 2) Estimate WECs and wind turbines power productions predictability. 3) Estimate the errors incurred in the bids to the day-ahead market, both for wave and for wind energy, if the productions had been traded in day-ahead electricity markets. 4) Evaluate economically the errors of day-ahead bids and assess the economic benefits, in terms of reduction in balancing costs, of including wave energy in a system based on wind energy solely. On the whole, the research focus has been the economic value of waves' predictability. To the authors knowledge, it is the most comprehensive study on wave power forecasting in the North Sea waters, both for waves and for WECs power productions. Results suggest that for day-ahead forecasts, waves are 23% more predictable than winds, the power output of WECs is 35% more predictable than for wind turbines, and the inclusion of wave energy in a wind-only system reduces balancing costs up to 35%. This would imply annual savings to the Danish system of 13 MEUR (i.e. 95 MDKK/y) and a balancing premium tariff for wave energy of 1.8 EUR/MWh (compared to the current premium tariff of wind turbines of 3 EUR/MWh). In a nutshell, results have shown the benefits of waves' predictability. The second research study has focused on the opportunities of combining the power production of different technologies in the same site to provide a continuous power output. Particularly, it has investigated the combined power production of WECs and of wind turbines. The study has focused on the benefits of a combined wave and wind power output compared to the individual productions. This is investigated through theoretical and real case studies that analyse the individual power productions of WECs and of wind turbines and compares them to the combined power production. To the authors best knowledge the study comprises the first research investigating and comparing real power productions of WECs and of wind turbines. The most indicative finding is that the combined power output is smoother and provides higher availability than the individual productions: both the peaks and the fast changes found in the individual productions reduce when these are combined, and the percentage of time with null production reduces to a minimum. Variability reduces up to 31% and the percentage of time with zero production decreases to 6%. Overall, the project has carried out an optimisation analysis which has sought to find the mix of WECs and of wind turbines and WECs, that resulted in an optimal electricity supply from the WEC system. The most predictable and most constant energy output has been chosen as the optimisation parameter. (LN)

Analysis of linear wave power generator model with real sea experimental results

Abstract: This study presents the dynamic modelling of a linear permanent magnet generator for extracting energy from ocean waves. Translator position, calculated from measured generator voltage, is used as input for the simulation model. Instantaneous power from the simulation model has been compared with the measurements from the Lysekil research site. The power output from the model considering the air gap flux variation is precisely matching with the measured values before core saturation. The generator dynamic model is modified by including the saturation effect. Although a simple mathematical expression is considered for representing the saturation, the model gives accurate power spectrum close to the experimental results. The presented model is a first step towards the system model that can simulate the entire electric system including electric grid. As such, the generator model can be used for further analysis of the wave energy conversion system.

Wave power potential at a few shallow- water locations around Indian coast

Abstract: Variations in nearshore wave power at four shallowwater locations along the east and west coast of India are examined based on the measured wave data for one-year period. The study shows that along the west coast of India, 83–85% of the annual wave power is during the summer monsoon period (June–September), whereas at Visakhapatnam (on the east coast), 55% of the annual wave power is during the summer monsoon period. Along Puducherry coast in the east, wave power is relatively less with maximum value of 31.8 kW m. The average wave power during the summer monsoon is high (15.5–19.3 kW m) along the west coast of India. The study shows that the annual average wave power (1.8–7.6 kW m) along the locations studied is much lower than that available for temperate zones.

Wave Power Extraction by an Oscillating Wave Surge Converter in Random Seas

Abstract: This paper investigates the behaviour of a bottom hinged flap-type wave energy converter (WEC), namely the Oscillating Wave Surge Converter (OWSC), in random seas. The semi-analytical model of Renzi and Dias (2013b) for an OWSC in the open ocean is considered to analyze the performance of the device in random incident waves. The modelling is performed within the framework of a linear potential flow theory, by means of Green’s integral theorem. The resultant hypersingular integral equation for the velocity potential obtained from the above formulation is solved using a series expansion in terms of Chebyshev polynomials of the second kind.The behaviour of the device is investigated for six different sea states, generally representative of the wave climate in the North Atlantic Ocean at the European Marine Energy Centre test site. A Bretschneider spectrum is considered in order to reproduce the sea climate. The analysis is made for sea states where the spectral energy contribution from large periods, which cause excitation of body resonance of the flap — not modelled by the linear theory — is almost negligible. The power take-off damping is optimised for each individual sea state to calculate the captured power.The investigation is undertaken for two flaps of different widths, resembling the Oyster1 and the new Oyster800 version of the Oyster WEC, respectively. Comparison is made between the performances of the two converters. The effect of varying the width and the characteristic parameters of the flap on the capture factor in random seas is then discussed.The results of the analysis show that the performance of the device is fairly consistent for the sea states considered. Also an enhancement in the overall average capture factor is shown for the latest version of the wave energy conversion device.© 2013 ASME