• Energy Research

Martifer Energia is developing a concept of a wave energy converter (WEC) to be used at near shore locations with water depths starting at around 40m. It is a floating device composed of two bodies connected by a one degree of freedom articulation. The energy is extracted at the articulation by a power takeoff system actuated by the relative motion between the bodies. One of the important components of many WECs is the mooring system, since usually the cost is large compared global cost of the device. In this case the WEC will be moored by a spread mooring that allows the device to weathervane with the environmental loads. The paper presents one design solution for the mooring system investigated during the development stage of the concept. It is composed of four hybrid lines, each one with a segment of nylon rope connected to the floating device and a part of chain that contacts with the sea bottom and ends at the anchor. The wave frequency hydrodynamics are first calculated with a frequency domain boundary element method. The nonlinear cable dynamics problem, which is coupled to the slow drift motions of the floater, is solved in the time domain by a finite difference method. The design considers the climatology of the future area of operation of the prototype. Since the loads on the lines depend on the characteristics of the lines themselves, the design solution is obtained iteratively. Appropriate safety factors are considered. The result is the number of mooring lines, their angular separation, length and diameter of each line component.

Abstract The Sea-wave Slot-cone Generator (SSG) is a multi-level overtopping based wave energy converter that can be installed either nearshore or offshore. The installation in harbor breakwaters and in the shoreline presents several advantages despite the usual exposure to smaller waves than at offshore locations. This work analyzes the effect of wave focusing walls ( i.e ., wave concentrators) on the performance of isolated SSG units using a physical model built on a geometric scale of 1/40. Seven configurations were defined by changing the opening angle and the crest level of those elements. The use of wave concentrators proved to be advantageous since a wider wave front is captured and the run-up and overtopping phenomena are enhanced on the SSG ramp owing to the wave energy concentration (walls tapering effect). In fact, the total mean power captured increased for all SSG configurations with concentrators in comparison to the base configuration (without concentrators), regardless of the sea state considered. In terms of hydraulic performance, the gain associated to the use of wave concentrators depends on the characteristics of incident waves, being higher for the smaller significant wave heights and the shorter peak wave periods. The hydraulic efficiency, defined as the ratio between the total mean power captured per meter of SSG width and the wave power per meter width of the incident waves, increases with the significant wave height and reduces with the peak wave period in all tested SSG configurations. In addition, in comparison to the base configuration, the hydraulic efficiencies with concentrators were higher for the smaller significant wave heights, but smaller for the other sea conditions. The use of wave concentrators increased the annual energy production approximately to the double. Overall, the application of the SSG technology in breakwaters presents itself as promising considering the characteristics of the wave resource nearshore or even in onshore locations.

Sea ports are infrastructures with substantial energy demands and often responsible for air pollution and other environmental problems, which may be minimized by using renewable energy, namely electricity harvested from ocean waves. In this regard, a wide variety of concepts to harvest wave energy are available and some shoreline technologies are already in an advanced development phase. The SE@PORTS project aims to assess the suitability and viability of existing wave energy conversion technologies to be integrated in harbor breakwaters, in order to take advantage of their high exposure to ocean waves. This paper describes the experimental study carried out to assess the performance of a hybrid wave energy converter (WEC) integrated in the rubble-mound structure that was proposed for the extension of the North breakwater of the Port of Leixões, Portugal. The hybrid concept combines the overtopping and the oscillating water column principles and was tested on a geometric scale of 1/50. This paper is focused on the assessment of the effects of the hybrid WEC integration on the case-study breakwater, both in terms of its stability and functionality. The 2D physical model included the reproduction of the seabed bathymetry in front of the breakwater and the generation of a wide range of irregular sea states, including extreme wave conditions. The experimental results shown that the integration of the hybrid WEC in the breakwater does not worsens the stability of its toe berm blocks and reduces the magnitude of the overtopping events. The conclusions obtained are therefore favorable to the integration of this type of devices on harbor breakwaters.

Abstract Ocean waves constitute an abundant source of clean and predictable energy, with the potential to partly replace carbon intensive energy sources. At present, several technologies to convert wave energy into electricity are being developed, but those suitable for integration into port breakwaters present additional advantages. This paper presents a novel concept that combines two well-known wave energy conversion principles, an oscillating water column and a multi-reservoir overtopping system. This hybrid concept was designed to be integrated in rubble-mound breakwaters, having as case study Leixoes’ northern breakwater, Portugal. The performance and efficiency of the single components were assessed separately as well as that of the hybrid module as a whole, to demonstrate the advantages of their combination into a single unit. Furthermore, the annual energy production was estimated for a 20 m wide hybrid module considering the local metocean conditions. Results showed that overall efficiency amounted to circa 44.4%, the wave-to-wire efficiency to 27.3% and the annual electricity production was estimated at 35 MWh/m. Considering that 240 m of the reference breakwater are used, the developed hybrid module could provide approximately 50% of the electricity consumption of the Port of Leixoes, which demonstrates the potential and interest of the developed technology.

This review details the groundwork made in the most recent years on the development of TENGs for wave energy conversion systems and discusses future perspectives in the scope of autonomous, self-powered sensor buoys and other offshore floating platforms.

Seaports are highly energy demanding infrastructures and are exposed to wave energy, which is an abundant resource and largely unexploited. As a result, there has been a rising interest in integrating wave energy converters (WEC) into the breakwaters of seaports. The present work analyzes the performance of an innovative hybrid WEC module combining an oscillating water column (OWC) and an overtopping device (OWEC) integrated into a rubble mound breakwater, based on results of a physical model study carried out at a geometrical scale of 1:50. Before the experimental tests, the device’s performance was numerically optimized using ANSYS Fluent and WOPSim v3.11. The wave power captured by the hybrid WEC was calculated and the performance of the two harvesting principles discussed. It was demonstrated that hybridization could lead to systems with higher efficiencies than its individual components, for a broader range of wave conditions. The chosen concepts were found to complement each other: the OWEC was more efficient for the lower wave periods tested and the OWC for the higher. Consequently, the power production of the hybrid WEC was found to be less dependent on the wave’s characteristics.