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Special Issue "Tools and Techniques for Economic Delivery of Ocean Energy"

A special issue of Energies (ISSN 1996-1073).

Deadline for manuscript submissions: closed (31 October 2015)

Special Issue Editor

Guest Editor
Prof. Dr. John Ringwood

Centre for Ocean Energy Research (COER), National University of Ireland (NUI) Maynooth, Maynooth, Co. Kildare, Ireland
Website | E-Mail
Phone: +353 1 708 4766
Interests: wave and tidal energy; modeling and control of wave energy devices; energy forecasting; fault diagnostics and prognostics; techno-economic optimisation

Special Issue Information

Dear Colleagues,

Ocean (wave and tidal) energy is at a crucial stage of development, with few commercial deployments. The anticipated cost of wave and tidal energy is large compared to the cost of other renewables (especially wind) and conventional sources. There are also questions over the longevity of ocean energy technology projects and realistic maintenance requirements and costs. This special issue solicits articles describing algorithms, technologies and techniques which directly address improvements in the economic cost of wave energy. Studies can focus on the geometric design and hydrodynamic properties, power train efficiency optimization, optimization of wave/tidal farm layouts, electrical system optimization and optimal maintenance strategies or design for maintenance. Because they contribute to lower capital costs, survival strategies will also be relevant for wave devices.

Prof. Dr. John Ringwood
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Energies is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • ocean energy
  • economic optimization
  • control systems
  • efficiency maximization
  • energy storage
  • power smoothing
  • power quality
  • wave energy
  • tidal energy
  • array layout optimization

Published Papers (13 papers)

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Research

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Open AccessArticle Methodology to Calculate the Costs of a Floating Offshore Renewable Energy Farm
Energies 2016, 9(5), 324; https://doi.org/10.3390/en9050324
Received: 6 October 2015 / Revised: 16 March 2016 / Accepted: 12 April 2016 / Published: 28 April 2016
Cited by 5 | PDF Full-text (6110 KB) | HTML Full-text | XML Full-text
Abstract
This paper establishes a general methodology to calculate the life-cycle cost of floating offshore renewable energy devices, applying it to wave energy and wind energy devices. It is accounts for the contributions of the six main phases of their life-cycle: concept definition, design
[...] Read more.
This paper establishes a general methodology to calculate the life-cycle cost of floating offshore renewable energy devices, applying it to wave energy and wind energy devices. It is accounts for the contributions of the six main phases of their life-cycle: concept definition, design and development, manufacturing, installation, exploitation and dismantling, the costs of which have been defined. Moreover, the energy produced is also taken into account to calculate the Levelized Cost of Energy of a floating offshore renewable energy farm. The methodology proposed has been applied to two renewable energy devices: a floating offshore wave energy device and a floating offshore wind energy device. Two locations have been considered: Aguçadoura and São Pedro de Moel, both in Portugal. Results indicate that the most important cost in terms of the life-cycle of a floating offshore renewable energy farm is the exploitation cost, followed by the manufacturing and the installation cost. In addition, the best area in terms of costs is the same independently of the type of floating offshore renewable energy considered: Aguçadoura. However, the results in terms of Levelized Cost of Energy are different: Aguçadoura is better when considering wave energy technology and the São Pedro de Moel region is the best option when considering floating wind energy technology. The method proposed aims to give a direct approach to calculate the main life-cycle cost of a floating offshore renewable energy farm. It helps to assess its feasibility and evaluating the relevant characteristics that influence it the most. Full article
(This article belongs to the Special Issue Tools and Techniques for Economic Delivery of Ocean Energy)
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Open AccessArticle Evaluation of the Fluid Model Approach for the Sizing of Energy Storage in Wave-Wind Energy Systems
Energies 2016, 9(3), 162; https://doi.org/10.3390/en9030162
Received: 8 October 2015 / Revised: 6 February 2016 / Accepted: 19 February 2016 / Published: 4 March 2016
Cited by 1 | PDF Full-text (2857 KB) | HTML Full-text | XML Full-text
Abstract
The application of energy storage in offshore renewable generation systems allows managing the intrinsic uncertainty of the resources and improving the utilization factor of the electrical network. Optimal storage design algorithms generally have to evaluate the behavior of the whole system thousands times
[...] Read more.
The application of energy storage in offshore renewable generation systems allows managing the intrinsic uncertainty of the resources and improving the utilization factor of the electrical network. Optimal storage design algorithms generally have to evaluate the behavior of the whole system thousands times before converging to the optimal solution and the reliability of the results obviously depends on the quality of input data. On the other hand, the utilization of simplified storage models in the design stage can reduce the simulation time drastically, while still providing useful information. The goal of this paper is to evaluate the applicability of a methodology for sizing the energy storage system in a hybrid wind and wave farm, which is based on fluid models. The description and performance of this modeling approach will be introduced and compared to standard design procedures based on extensive simulations. Advantages and limitations of each approach will be underlined and the impact of input data quality will be discussed. Full article
(This article belongs to the Special Issue Tools and Techniques for Economic Delivery of Ocean Energy)
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Open AccessFeature PaperArticle Wave Energy Resource along the Coast of Santa Catarina (Brazil)
Energies 2015, 8(12), 14219-14243; https://doi.org/10.3390/en81212423
Received: 24 September 2015 / Revised: 5 December 2015 / Accepted: 10 December 2015 / Published: 17 December 2015
Cited by 25 | PDF Full-text (7658 KB) | HTML Full-text | XML Full-text
Abstract
Brazil has one of the largest electricity markets in South America, which needs to add 6000 MW of capacity every year in order to satisfy growing the demand from an increasing and more prosperous population. Apart from biomass, no other renewable energy sources,
[...] Read more.
Brazil has one of the largest electricity markets in South America, which needs to add 6000 MW of capacity every year in order to satisfy growing the demand from an increasing and more prosperous population. Apart from biomass, no other renewable energy sources, besides hydroelectricity, play a relevant role in the energy mix. The potential for wind and wave energy is very large. Brazil's Santa Catarina state government is starting a clean energy program in the state, which is expected to bring more than 1 GW of capacity. Assessment of wave energy resources is needed along the coastline. This work studied the potential wave energy along the north-central coasts of Santa Catarina, in Southern Brazil, by analysis of the hindcast data from the European Centre for Medium-Range Weather Forecasts (ECMWF). The annual offshore wave power was found to be equal to 15.25 kW/m, the bulk of which is provided by southeastern waves. The nearshore energetic patterns were studied by means of a numerical coastal propagation model (Mike21 SW). The mean wave power of 20 m isobaths is 11.43 kW/m. Supplementary considerations are drawn on realistic perspectives for wave energy converters installations. Full article
(This article belongs to the Special Issue Tools and Techniques for Economic Delivery of Ocean Energy)
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Open AccessArticle Control-Informed Geometric Optimization of Wave Energy Converters: The Impact of Device Motion and Force Constraints
Energies 2015, 8(12), 13672-13687; https://doi.org/10.3390/en81212386
Received: 27 August 2015 / Revised: 9 November 2015 / Accepted: 23 November 2015 / Published: 2 December 2015
Cited by 5 | PDF Full-text (450 KB) | HTML Full-text | XML Full-text
Abstract
The energy cost for producing electricity via wave energy converters (WECs) is still not competitive with other renewable energy sources, especially wind energy. It is well known that energy maximising control plays an important role to improve the performance of WECs, allowing the
[...] Read more.
The energy cost for producing electricity via wave energy converters (WECs) is still not competitive with other renewable energy sources, especially wind energy. It is well known that energy maximising control plays an important role to improve the performance of WECs, allowing the energy conversion to be performed as economically as possible. The control strategies are usually subsequently employed on a device that was designed and optimized in the absence of control for the prevailing sea conditions in a particular location. If an optimal unconstrained control strategy, such as pseudo-spectral optimal control (PSOC), is adopted, an overall optimized system can be obtained no matter whether the control design is incorporated at the geometry optimization stage or not. Nonetheless, strategies, such as latching control (LC), must be incorporated at the optimization design stage of the WEC geometry if an overall optimized system is to be realised. In this paper, the impact of device motion and force constraints in the design of control-informed optimized WEC geometries is addressed. The aim is to verify to what extent the constraints modify the connection between the control and the optimal device design. Intuitively, one might expect that if the constraints are very tight, the optimal device shape is the same regardless of incorporating or not the constrained control at the geometry optimization stage. However, this paper tests the hypothesis that the imposition of constraints will limit the control influence on the optimal device shape. PSOC, LC and passive control (PC) are considered in this study. In addition, constrained versions of LC and PC are presented. Full article
(This article belongs to the Special Issue Tools and Techniques for Economic Delivery of Ocean Energy)
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Open AccessArticle Towards a Low-Cost Modelling System for Optimising the Layout of Tidal Turbine Arrays
Energies 2015, 8(12), 13521-13539; https://doi.org/10.3390/en81212380
Received: 28 September 2015 / Revised: 6 November 2015 / Accepted: 16 November 2015 / Published: 30 November 2015
Cited by 3 | PDF Full-text (5201 KB) | HTML Full-text | XML Full-text
Abstract
In the long-term, tidal turbines will most likely be deployed in farms/arrays where energy extraction by one turbine may significantly affect the energy available to another turbine. Given the prohibitive cost of experimental and/or field investigations of such turbine interactions, numerical models can
[...] Read more.
In the long-term, tidal turbines will most likely be deployed in farms/arrays where energy extraction by one turbine may significantly affect the energy available to another turbine. Given the prohibitive cost of experimental and/or field investigations of such turbine interactions, numerical models can play a significant role in determining the optimum layout of tidal turbine arrays with respect to energy capture. In the present research, a low-cost modelling solution for optimising turbine array layouts is presented and assessed. Nesting is used in a far-field model to telescope spatial resolution down to the scale of the turbines within the turbine array, allowing simulation of the interactions between adjacent turbines as well as the hydrodynamic impacts of individual turbines. The turbines are incorporated as momentum sinks. The results show that the model can compute turbine wakes with similar far-field spatial extents and velocity deficits to those measured in published experimental studies. The results show that optimum spacings for multi-row arrays with regard to power yield are 3–4 rotor diameters (RD) across-stream and 1–4 RD along-stream, and that turbines in downstream rows should be staggered to avoid wake effects of upstream turbines and to make use of the accelerated flows induced by adjacent upstream turbines. Full article
(This article belongs to the Special Issue Tools and Techniques for Economic Delivery of Ocean Energy)
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Open AccessArticle Development of an Active Power Reserve Management Method for DC Applied Wave-Wind Combined Generation Systems
Energies 2015, 8(11), 12488-12504; https://doi.org/10.3390/en81112321
Received: 27 August 2015 / Revised: 22 October 2015 / Accepted: 22 October 2015 / Published: 4 November 2015
Cited by 1 | PDF Full-text (2604 KB) | HTML Full-text | XML Full-text
Abstract
A system that combines a wind turbine and a wave generator can share the off-shore platform and therefore mix the advantages of the transmission system construction and the power conversion system. The current hybrid generation system considers output limitation according to the instructions
[...] Read more.
A system that combines a wind turbine and a wave generator can share the off-shore platform and therefore mix the advantages of the transmission system construction and the power conversion system. The current hybrid generation system considers output limitation according to the instructions of the transmission system operator (TSO), and controls the profile using wind turbine pitch control. However, the integrated wave generation system utilizing a DC network does not adapt a power limitation scheme due to its mechanical constraints. In this paper, a control plan focusing on the electrical section of wave generators is formed in order to effectively manage the output profile of the hybrid generation system. The plan pays attention to power reserve flexibility for the utility grid using the analysis of the controllable elements. Comparison with the existing system is performed based on real offshore conditions. With the help of power system computer aided design (PSCAD) simulation, the ability of the novel technique is estimated by proposing the real power control based on the reference signal of TSO and the reactive power capacity it produces. Full article
(This article belongs to the Special Issue Tools and Techniques for Economic Delivery of Ocean Energy)
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Open AccessArticle Estimation of Downtime and of Missed Energy Associated with a Wave Energy Converter by the Equivalent Power Storm Model
Energies 2015, 8(10), 11575-11591; https://doi.org/10.3390/en81011575
Received: 1 September 2015 / Revised: 7 October 2015 / Accepted: 10 October 2015 / Published: 15 October 2015
PDF Full-text (380 KB) | HTML Full-text | XML Full-text
Abstract
The design of any wave energy converter involves the determination of relevant statistical data on the wave energy resource oriented to the evaluation of the structural reliability and energy performance of the device. Currently, limited discussions concern the estimation of parameters connected to
[...] Read more.
The design of any wave energy converter involves the determination of relevant statistical data on the wave energy resource oriented to the evaluation of the structural reliability and energy performance of the device. Currently, limited discussions concern the estimation of parameters connected to the energy performance of a device. Thus, this paper proposes a methodology for determining average downtime and average missed energy, which is the energy that is not harvested because of device deactivations during severe sea storms. These quantities are fundamental for evaluating the expected inactivity of a device during a year or during its lifetime and are relevant for assessing the effectiveness of a device working at a certain site. For this purpose, the equivalent power storm method is used for their derivation, starting from concepts pertaining to long-term statistical analysis. The paper shows that the proposed solutions provide reliable estimations via comparison with results obtained by processing long wave data. Full article
(This article belongs to the Special Issue Tools and Techniques for Economic Delivery of Ocean Energy)
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Open AccessArticle Design Parameters Analysis of Point Absorber WEC via an evolutionary-algorithm-based Dimensioning Tool
Energies 2015, 8(10), 11203-11233; https://doi.org/10.3390/en81011203
Received: 6 July 2015 / Revised: 28 September 2015 / Accepted: 29 September 2015 / Published: 12 October 2015
Cited by 4 | PDF Full-text (3211 KB) | HTML Full-text | XML Full-text
Abstract
Wave energy conversion has an essential difference from other renewable energies since the dependence between the devices design and the energy resource is stronger. Dimensioning is therefore considered a key stage when a design project of Wave Energy Converters (WEC) is undertaken. Location,
[...] Read more.
Wave energy conversion has an essential difference from other renewable energies since the dependence between the devices design and the energy resource is stronger. Dimensioning is therefore considered a key stage when a design project of Wave Energy Converters (WEC) is undertaken. Location, WEC concept, Power Take-Off (PTO) type, control strategy and hydrodynamic resonance considerations are some of the critical aspects to take into account to achieve a good performance. The paper proposes an automatic dimensioning methodology to be accomplished at the initial design project stages and the following elements are described to carry out the study: an optimization design algorithm, its objective functions and restrictions, a PTO model, as well as a procedure to evaluate the WEC energy production. After that, a parametric analysis is included considering different combinations of the key parameters previously introduced. A variety of study cases are analysed from the point of view of energy production for different design-parameters and all of them are compared with a reference case. Finally, a discussion is presented based on the results obtained, and some recommendations to face the WEC design stage are given. Full article
(This article belongs to the Special Issue Tools and Techniques for Economic Delivery of Ocean Energy)
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Open AccessArticle Assessment of the Wave Energy in the Black Sea Based on a 15-Year Hindcast with Data Assimilation
Energies 2015, 8(9), 10370-10388; https://doi.org/10.3390/en80910370
Received: 25 June 2015 / Revised: 20 July 2015 / Accepted: 9 September 2015 / Published: 21 September 2015
Cited by 19 | PDF Full-text (2260 KB) | HTML Full-text | XML Full-text
Abstract
The principal target of the present work is to assess the wave energy potential in the Black Sea, identifying also some relevant energetic features and possible patterns. A wave prediction system based on the Simulating Waves Nearshore model (SWAN) has been implemented and
[...] Read more.
The principal target of the present work is to assess the wave energy potential in the Black Sea, identifying also some relevant energetic features and possible patterns. A wave prediction system based on the Simulating Waves Nearshore model (SWAN) has been implemented and intensively tested in the entire sea basin. Moreover, considering an optimal interpolation technique, an assimilation scheme of the satellite data has been developed, leading to a visible improvement of the wave model predictions in terms of significant wave heights and, consequently, also in terms of wave power. Using this wave prediction system with data assimilation, simulations have been performed for a 15-year period (1999–2013). Considering the results of this 15-year wave hindcast, an analysis of the wave energy conditions in the basin of the Black Sea has been carried out. This provided a more comprehensive picture concerning the wave energy patterns in the coastal environment of the Black Sea focused on the average wave conditions that might be expected in this sea. Following the results presented, it can be concluded that the wave energy extraction in the Black Sea can become an issue of interest, especially from the perspective of the hybrid solutions. Full article
(This article belongs to the Special Issue Tools and Techniques for Economic Delivery of Ocean Energy)
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Open AccessArticle Computational Fluid Dynamics and Visualisation of Coastal Flows in Tidal Channels Supporting Ocean Energy Development
Energies 2015, 8(6), 5997-6012; https://doi.org/10.3390/en8065997
Received: 31 March 2015 / Revised: 20 May 2015 / Accepted: 9 June 2015 / Published: 18 June 2015
Cited by 4 | PDF Full-text (5425 KB) | HTML Full-text | XML Full-text
Abstract
Flow characteristics in coastal regions are strongly influenced by the topography of the seabed and understanding the fluid dynamics is necessary before installation of tidal stream turbines (TST). In this paper, the bathymetry of a potential TST deployment site is used in the
[...] Read more.
Flow characteristics in coastal regions are strongly influenced by the topography of the seabed and understanding the fluid dynamics is necessary before installation of tidal stream turbines (TST). In this paper, the bathymetry of a potential TST deployment site is used in the development of the a CFD (Computational Fluid Dynamics) model. The steady state k-ϵ and transient Large Eddy Simulation (LES) turbulence methods are employed and compared. The simulations are conducted with a fixed representation of the ocean surface, i.e., a rigid lid representation. In the vicinity of Horse Rock a study of the pressure difference shows that the small change in height of the water column is negligible, providing confidence in the simulation results. The stream surface method employed to visualise the results has important inherent characteristics that can enhance the visual perception of complex flow structures. The results of all cases are compared with the flow data transect gathered by an Acoustic Doppler Current Profiler (ADCP). It has been understood that the k-ϵ method can predict the flow pattern relatively well near the main features of the domain and the LES model has the ability to simulate some important flow patterns caused by the bathymetry. Full article
(This article belongs to the Special Issue Tools and Techniques for Economic Delivery of Ocean Energy)
Open AccessArticle Nearshore Tests of the Tidal Compensation System for Point-Absorbing Wave Energy Converters
Energies 2015, 8(4), 3272-3291; https://doi.org/10.3390/en8043272
Received: 16 February 2015 / Revised: 1 April 2015 / Accepted: 3 April 2015 / Published: 22 April 2015
Cited by 6 | PDF Full-text (19114 KB) | HTML Full-text | XML Full-text
Abstract
The power production of the linear generator wave energy converter developed at Uppsala University is affected by variations of mean sea level. The reason is that these variations change the distance between the point absorber located on the surface and the linear generator
[...] Read more.
The power production of the linear generator wave energy converter developed at Uppsala University is affected by variations of mean sea level. The reason is that these variations change the distance between the point absorber located on the surface and the linear generator located on the seabed. This shifts the average position of the translator with respect to the center of the stator, thereby reducing the generator output power. A device mounted on the point absorber that compensates for tides of small range by regulating the length of the connection line between the buoy at the surface and the linear generator has been constructed and tested. This paper describes the electro-mechanical, measurement, communication and control systems installed on the buoy and shows the results obtained before its connection to the generator. The adjustment of the line was achieved through a linear actuator, which shortens the line during low tides and vice versa. The motor that drives the mechanical device was activated remotely via SMS. The measurement system that was mounted on the buoy consisted of current and voltage sensors, accelerometers, strain gauges and inductive and laser sensors. The data collected were transferred via Internet to a Dropbox server. As described within the paper, after the calibration of the sensors, the buoy was assembled and tested in the waters of Lysekil harbor, a few kilometers from the Uppsala University research site. Moreover, the performance of the sensors, the motion of the mechanical device, the power consumption, the current control strategy and the communication system are discussed. Full article
(This article belongs to the Special Issue Tools and Techniques for Economic Delivery of Ocean Energy)
Open AccessArticle Influence of Model Simplifications Excitation Force in Surge for a Floating Foundation for Offshore Wind Turbines
Energies 2015, 8(4), 3212-3224; https://doi.org/10.3390/en8043212
Received: 10 December 2014 / Revised: 10 April 2015 / Accepted: 14 April 2015 / Published: 22 April 2015
Cited by 3 | PDF Full-text (986 KB) | HTML Full-text | XML Full-text
Abstract
As offshore wind turbines move towards deeper and more distant sites, the concept of floating foundations is a potential technically and economically attractive alternative to the traditional fixed foundations. Unlike the well-studied monopile, the geometry of a floating foundation is complex and, thereby,
[...] Read more.
As offshore wind turbines move towards deeper and more distant sites, the concept of floating foundations is a potential technically and economically attractive alternative to the traditional fixed foundations. Unlike the well-studied monopile, the geometry of a floating foundation is complex and, thereby, increases the difficulty in wave force determination due to limitations of the commonly used simplified methods. This paper deals with a physical model test of the hydrodynamic excitation force in surge on a fixed three-columned structure intended as a floating foundation for offshore wind turbines. The experiments were conducted in a wave basin at Aalborg University. The test results are compared with a Boundary Element Method code based on linear diffraction theory for different wave force regimes defined by the column diameter, wave heights and lengths. Furthermore, the study investigates the influence of incident wave direction and stabilizing heave-plates. The structure can be divided into primary, secondary and tertiary parts, defined by the columns, heave-plates and braces to determine the excitation force in surge. The test results are in good agreement with the numerical computation for the primary parts only, which leads to simplified determination of peak frequencies and corresponding dominant force regime. Full article
(This article belongs to the Special Issue Tools and Techniques for Economic Delivery of Ocean Energy)
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Review

Jump to: Research

Open AccessReview Enhancing Wave Energy Competitiveness through Co-Located Wind and Wave Energy Farms. A Review on the Shadow Effect
Energies 2015, 8(7), 7344-7366; https://doi.org/10.3390/en8077344
Received: 30 April 2015 / Revised: 25 June 2015 / Accepted: 13 July 2015 / Published: 21 July 2015
Cited by 14 | PDF Full-text (801 KB) | HTML Full-text | XML Full-text
Abstract
Wave energy is one of the most promising alternatives to fossil fuels due to the enormous available resource; however, its development may be slowed as it is often regarded as uneconomical. The largest cost reductions are expected to be obtained through economies of
[...] Read more.
Wave energy is one of the most promising alternatives to fossil fuels due to the enormous available resource; however, its development may be slowed as it is often regarded as uneconomical. The largest cost reductions are expected to be obtained through economies of scale and technological progress. In this sense, the incorporation of wave energy systems into offshore wind energy farms is an opportunity to foster the development of wave energy. The synergies between both renewables can be realised through these co-located energy farms and, thus, some challenges of offshore wind energy can be met. Among them, this paper focuses on the longer non-operational periods of offshore wind turbines—relative to their onshore counterparts—typically caused by delays in maintenance due to the harsh marine conditions. Co-located wave energy converters would act as a barrier extracting energy from the waves and resulting in a shielding effect over the wind farm. On this basis, the aim of this paper is to analyse wave energy economics in a holistic way, as well as the synergies between wave and offshore wind energy, focusing on the shadow effect and the associated increase in the accessibility to the wind turbines. Full article
(This article belongs to the Special Issue Tools and Techniques for Economic Delivery of Ocean Energy)
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