Elsevier

Ocean Engineering

Volume 178, 15 April 2019, Pages 204-214
Ocean Engineering

Wave energy converter configuration in dual wave farms

https://doi.org/10.1016/j.oceaneng.2019.03.001Get rights and content

Highlights

  • We analyse the effects of wave energy converter (WEC) configuration in dual wave farms.

  • Case study with wave farms formed by WaveCat WECs off a beach in southern Spain.

  • Laboratory tests to characterize wave-WEC interaction, various configurations & sea states.

  • Coupled numerical scheme applied to the case study with input from laboratory.

  • For optimum performance, WEC configuration should be adapted dynamically to sea state.

Abstract

Wave farms, i.e., arrays of Wave Energy Converters (WECs), have recently been proven to be effective in fulfilling the dual function of carbon-free energy generation and coastal protection. In this paper these dual-function wave farms are referred as dual wave farms. The objective of this work is to investigate the influence of the WEC configuration on the performance of these dual wave farms through a case study: a dual wave farm consisting of WaveCat WECs deployed off an eroding beach. WaveCat is a floating overtopping WEC consisting of two hulls joined by their stern, forming a wedge. Two configurations are considered, with wedge angles of 30° and 60°. To characterize wave-WEC interaction, laboratory tests of a 1:30 WaveCat model are conducted using the two configurations and low-, mid- and high-energy sea states characteristic of the study area. The reflection and transmission coefficients obtained from the laboratory tests are inputted into a suite of numerical models to investigate the hydro- and morphodynamics of the beach. We find that the smaller wedge angle (30°) WECs afford more (less) coastal protection - quantified in terms of dry beach area availability - for short (long) peak periods than WECs with 60. These results allow us to conclude that, for optimum performance of dual wave farms, WEC geometry should be adapted dynamically to the sea state.

Introduction

The development of renewable energy is one of the most relevant targets confronting society in the coming decades (European Commission, 2007, 2009), due to the finite nature of fossil fuels, their high costs and, last but not least, the environmental impacts of their exploration and use (Asif and Muneer, 2007; Shafiee and Topal, 2009). Among the carbon-free energy sources, marine energy resources offer a vast potential and comparatively low effects on the environment (Falnes, 2007; Cornett, 2008; Cruz, 2008; Panwar et al., 2011; Rinaldi et al., 2017). In particular, the worldwide potential of wave energy was assessed as 17 TW h/year (Lund, 2007). These facts contrast with the low degree of development and utilization of wave energy compared to other renewable sources, such as hydroelectric, biomass or wind energy (U. E. I. Administrationet al., 2011; Eurostat, 2016).

For these reasons, increasing research efforts have focused on wave energy over the last years. The objectives of the investigations carried out so far have been: (1) the assessment and characterization of wave energy resources (Iglesias et al., 2009; Iglesias and Carballo, 2011; Vicinanza et al., 2013a; Carballo et al., 2015, 2018; Contestabile et al., 2015; López et al., 2015a; Silva et al., 2015; Veigas et al., 2014, 2015; Iuppa et al., 2015a; Viviano et al., 2016; Prieto et al., 2019), (2) the study and optimization of possible locations (Carballo et al., 2014; Iuppa et al., 2015b; López-Ruiz et al., 2016, 2018a, 2018b; Elginoz and Bas, 2017; Alifdini et al., 2018; Khojasteh et al., 2018), (3) the economic viability of wave energy (Astariz and Iglesias, 2015a, 2016a; Astariz et al., 2015a; Contestabile et al., 2017a; Frost et al., 2018), (4) the combined implementation with other ocean energies, most notably, wind (Azzellino et al., 2013; Astariz and Iglesias, 2015b, 2016b; Astariz et al., 2015b; Pérez-Collazo et al., 2015; Wang et al., 2018), and (5) the development of wave energy technologies and devices (Viviano et al., 2016; Vicinanza et al., 2012, 2013b, 2014; Falcão, 2007; Margheritini et al., 2009; Fernandez et al., 2012a; López et al., 2014, 2015b, 2015c, 2016, 2017a, 2017b, 2018, 2018; López and Iglesias, 2014; Day et al., 2015; Buccino et al., 2015; Contestabile et al., 2017b; Elhanafi et al., 2017; Medina-López et al., 2017, 2019; López et al., 2018; Moñino et al., 2018; Ramos et al., 2018; Barambones et al., 2018; Chao et al., 2018; Do et al., 2018; Halder et al., 2018; Kolios et al., 2018; Sergiienko et al., 2018; Wu et al., 2018; Yang et al., 2018; Zheng and Zhang, 2018).

One of the wave energy converters (WECs) under development is WaveCat (Iglesias et al., 2009, 2011). A floating, overtopping WEC, it comprises two hulls joined at the stern by a hinge – for a detailed description of the device, the reader is referred to (Fernandez et al., 2012a, 2012b). Wave farms consisting of WaveCat WECs have been proven to fulfil a dual function as wave energy generators and coastal defence elements on both sandy beaches (Abanades et al., 2014a, 2014b, 2015, 2018) and gravel-dominated coasts (Bergillos et al., 2018a, 2019; Rodriguez-Delgado et al., 2018a, 2018b, 2019).

So far, the effects of the WEC configuration on the hydro- and morphodynamics of the coast in the lee of the wave farm have not been studied. The main objective of the present research is to analyse the effects of the configuration of WaveCat, in particular, the wedge angle or angle between the twin hulls, on wave propagation, longshore sediment transport (LST) and shoreline dynamics, considering the varying transmission and reflection coefficients obtained from laboratory experiments under different sea states.

The laboratory experiments were conducted in the Ocean Basin of the University of Plymouth (Section 3.1). In addition, this research involved the application of a wave propagation model (Section 3.2.1), an LST formulation (Section 3.2.2) and a one-line model (Section 3.2.3) to a study site in southern Spain (Section 2).

Section snippets

Study site

Playa Granada is a gravel-dominated deltaic beach located on the Mediterranean coastline of southern Spain (Fig. 1a). The beach, which is bounded by the Guadalfeo River mouth to the west and by Punta del Santo to the east (Fig. 1b), has been experiencing shoreline retreat and terminal erosion in recent years (Bergillos et al., 2015a, 2016a, 2018b), partly due to anthropogenic interventions in the Guadalfeo River basin (Bergillos et al., 2015b, 2016b; Bergillos and Ortega-Sánchez, 2017).

Two

Laboratory experiments

Laboratory tests were performed in the Ocean Basin of the University of Plymouth to measure the reflection (Kr) and transmission (Kt) coefficients for two different wedge angles, i.e., angles between the hulls of WaveCat (α=30 and α=60, Fig. 2). The experiments were carried out at a 1:30 scale and the dimensions of the model were 3 m (length) and 0.6 m (height) (Fig. 2).

The selection of the two wedge angle values was done to represent two different types of operation of WaveCat corresponding

Significant wave heights at breaking

This section details the influence of the wave farm on wave propagation – in particular, on the significant wave heights at breaking – depending on the wedge of the WECs. The alongshore variation of the differences between breaking significant wave heights for α=30 and α=60 (ΔHm,br) are indicated in Fig. 3.

Under SW waves, it is shown that the differences are generally negative for short wave periods (Tp=7 s) and positive for long periods (Tp=11 s and Tp=13 s). In all the cases, the maximum

Conclusions

Wave energy is one of the renewables with the greatest potential for development due to the resource availability and low visual pollution. Recent research has highlighted the possibility of using wave farms for a dual function, i.e., renewable energy generation and coastal protection.

This paper presents the first study on the influence of WEC configuration on the performance of dual wave farms. In particular, the effects of two values of the wedge angle, i.e., the angle between the twin hulls

Acknowledgements

This paper was carried out in the framework of research grants WAVEIMPACT (PCIG-13-GA-2013-618556, European Commission, Marie Curie fellowship, fellow GI) and ICE (Intelligent Community Energy, European Commision, Contract no. 5025). RB was funded by the Spanish Ministry of Science, Innovation and Universities (Programa Juan de la Cierva 2017; FJCI-2017-31781). Wave and bathymetric data were provided by Puertos del Estado (Spain) and the Spanish Ministry of Agriculture, Fisheries and Food,

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