As everyone knows, the Adriatic Sea is characterised by low wave power; moreover, the wave climate is strongly bidirectional, since both North-East wind and South-East wind are rather frequent. Thus, a wave energy converter (WEC) that can take full advantage of the available wave energy is needed. A floating WEC could be the best option in this case, since these devices can be placed offshore, where more wave energy is available. In particular, we propose a WEC of the point-absorber type, which means a device that produces energy regardless of the direction of waves. The device we are developing at the University of Bologna is small, modular and wholly made of recycled and eco-friendly materials. It can be easily installed in farms with the minimum occupation of space. Moreover, its structure could serve as support for different offshore activities if installed in the proximity of a decommissioned platform. Many offshore platforms have been or are going to be decommissioned off the Adriatic Coast. These structures could be converted to different uses, among which the exploitation of renewable energies. Keeping in mind that wave energy alone is not yet cost-effective and completely reliable, at the present time a hybrid plant combining wind, wave and solar energy is likely to be a trustworthy solution to provide energy to ports and coastal communities in any season and in any weather conditions.
Based on our experience, we propose the installation of a floating device which would have many advantages in the case of a tourist harbour on the Adriatic coast. The main advantage is the possibility of fully exploiting the wave energy available offshore, since the Adriatic Sea is characterized by a very low available wave power and therefore an onshore device would be likely to have a very low producibility. Other advantages of floating WECs are the following: no need to rebuilt harbour structures, therefore avoiding any visual impact and major structural work; no large fixed structure onshore or on the seabed and therefore reduced visual and environmental impact; greater social acceptance since the installation would only require anchors on the seabed. Moreover, we propose a WEC of the type “point absorber”, which, compared to other devices, has the additional benefit of harvesting energy regardless of wave direction, therefore maximizing the production in the case of multidirectional sea states, like that of the Adriatic Sea. Our device, in particular, is small, with a minor part emerging from the water, and ensures a minimum occupation of space in case of multiple installation. It will be realized with only recycled and eco-friendly materials in the context of circular economy. The device has already been successfully tested through numerical simulations with different wave conditions, while the experimental test campaign is planned for the next months in the new wave basin that has recently been inaugurated at the University of Bologna. The experimental tests will allow the assessment of the producibility with the Power-take-Off (PTO) system supplied by Umbra Group, a leading company in this field. Moreover, the wave farm could be integrated with other renewable energy sources in order to cover the variable energy demand during the whole year, minimizing the need of fossil-fuels. We have a great experience on the installation of WECs in the Adriatic Sea and on the combination of different renewables (in particular wave, wind and solar energy) to supply energy for specific activities, since the University of Bologna is involved in the PON project PlaCE (https://bluegrowth-place.eu/). The scope of our activity within the project is to demonstrate the first pilot system for wave energy production integrated in an Oil&Gas (O&G) offshore platform and also to explore the integration of renewable energy sources within a hybrid generation solution for self-powering the Multi-Use Platform (MUP). The Viviana platform for gas extraction, object of the project PlaCE, is only twenty kilometres north of Marina di Pescara and is just one of the several offshore platforms off the coast of Abruzzo, and in the Adriatic Sea in general, that have been or are going to be decommissioned and can be allocated to different activities, among which the exploitation of renewable energies, and could therefore provide clean energy also to ports and coastal communities.
It is undeniable that wave energy in itself is still far from being economically feasible, mainly due to the low efficient technologies of power conversion and to the design challenges such as the mooring design. The Adriatic Sea, in particular, is characterized by a very low available wave power (a yearly average of 1-2 kW/m); this means that WECs, which are mainly designed for regions with higher available power (e.g. 20-30 kW/m, as in Northern Europe), need to be conveniently scaled to match the typical wave climate of the Mediterranean area. In other words, the dimensions of the WEC and its Power-Take-Off (PTO) system need to be specifically designed to produce energy with lower wave heights. Also, since the Adriatic Sea is characterized by gentle slopes of the seabed and shallow waters, it would be favourable to place the WECs offshore in order to take advantage of the higher available wave power that we have in the open sea.
In this context, the Marina di Pescara wants to test systems to generate electricity from waves to accomplish an energy transition to renewables and is looking for trustworthy solutions to supply the demand of the Marina, that at present takes energy from the electricity grid and uses natural gas. Our opinion is that a hybrid plant combining offshore floating WECs and other more mature technologies (wind and solar plants) could be the best option, both from a reliability and from an economic point of view. In fact, although fixed onshore devices that could be integrated in the harbour structures are very promising (see for example the OBREC in Naples), their installation would require the removal of the rubble-mound breakwater, replaced by a concrete dam, which could have a low social acceptance in the case of a touristic port, due to the visual impact. Moreover, these WECs can harvest energy for only a few wave directions, a fact that, together with the lower wave power nearshore, would take little advantage of the already low available energy of the Adriatic Sea. Those considerations done, our team proposes the installation of a floating device, in particular a so-called point absorber, that can be placed offshore (eventually in the proximity of one of the several offshore platforms under decommissioning, in combination with a wind or solar plant) and can harvest energy regardless of waves direction, a characteristic that is particularly indicated in the case of multidirectional sea states, like that of the Adriatic Sea, where both North-East wind and South-East wind are frequent. It would have no aesthetic impact on the Marina (since it would be anchored far from shore and it wouldn’t require the modification of the existing harbour structures) and it could take full advantage of the available wave energy offshore.
Concept and innovation
In particular, we propose an innovative device which is currently under development at the University of Bologna. It is square-shaped and its dimensions can be specifically designed basing on the wave climate: at the considered location, it could have a side length of approximately 2.5 m and a height at its highest point of about 1.5 m, only the half of which would be visible above the surface, as a maximum. Following the principles of the circular economy, it is essential for us to realize our WEC with only recycled and eco-friendly materials, which are currently under evaluation with internationally renowned companies. The PTO system will be provided by Umbra Group, an Italian company of great success in this field: their innovative generator can be tuned on different wave states and has already proven its effectiveness with several point-absorber WECs chrachterized by different operating principles. Our device has been tested through numerical simulations in Ansys-AQWA with different mooring system configurations and different wave conditions typical of the Adriatic Sea and it has proven to be stable with a return time up to 10 years. The experimental test campaign is planned for the next months in the brand-new wave basin (https://site.unibo.it/vasca-marittima/it) that has recently been inaugurated at the University of Bologna and will hopefully lead to a patent. Moreover, compared to other point absorbers, which have a great footprint if installed in farms because of the necessary distance between one and the other, our device could be installed in a modular way, with a checkerboard pattern (sharing its sides with the adjacent devices), thus optimising the use of space. For example, a farm of 32 devices (4×8) would occupy an area of approximately 9x18m, almost like a medium size boat at anchor off the coast. The number of devices to be installed depends on the energy requirements to be satisfied. Being the project in a development phase, the estimation of produced energy is still uncertain. Anyway, our previous experience and international literature provide some general indication on point absorbers producibility. For example, an AquaBuoy device conveniently scaled based on the Adriatic climate could produce from 3 to 5 MWh/y depending on the location (personal elaborations within the PON project PlaCe, not yet published). A small farm could be installed in the waters off the Marina di Pescara, with low impact since there are yet many other business activities in this area, or a wider farm with higher producibility could be installed farther away from shore in deeper waters, eventually in the proximity of a decommissioned offshore platform, where wave energy could be integrated with other renewable energy sources, like small wind turbines or solar plants, in order to ensure the continuity of power supply for enhanced safety and reliability. The University of Bologna has a wide experience in this field and has proposed, within the PON project PlaCE, a criterion for the optimal energy mixing, proving the feasibility of the combination of different renewable sources to supply energy for specific activities (Dallavalle et al., Towards green transition of touristic islands through hybrid renewable energy systems. A case study in Tenerife, Canary Islands, Renewable Energy, 2021). A hybrid installation could take advantage of the seasonal variability of various renewable energy sources (sun, wind, waves) combining them in order to minimize the need of fossil-based back-up system. This kind of installations are likely to be economically advantageous in case of government incentives on renewable energy.
Example of floating point-absorber WEC with mooring lines.
Newly inaugurated wave basin at the Laboratory of hydraulic Engineering, University of Bologna.
Marina di Pescara bathymetry.
Visual impact of a wave energy converted (e.g. OBREC) integrated in the harbour structure. Realistically, many units like this should be installed in order to produce a sufficient amount of energy.
The possible advantages and positive effects of the project would be:
– Absence of large fixed structures onshore or on the seabed.
– No need to alter or rebuilt the existing harbour structures.
– Reduced visual impact, almost no impact on nature and small space requirement.
– Greater social acceptance on the grounds that the installation does not require permanent structural works but only anchors on the seabed.
– Possibility of installation in the proximity of a decommissioned offshore platform.
– Possibility of integration with other renewable energy sources (offshore wind and solar plants) in order to cover the variable energy demand during the whole year, minimizing the need of a fossil-based back-up system and ensuring a greater reliability.
The WEC has been conceived and designed by:
Barbara Zanuttigh, Associate Professor at the Department of Civil, Chemical, Environmental, and Materials Engineering (https://www.unibo.it/sitoweb/barbara.zanuttigh/research). Research topics: wave energy converters – design optimisation for combined energy production and coastal protection purposes or installation in off-shore platforms; analysis and development of cost-efficient and eco-compatible interventions for beach defence planning, through interdisciplinary works; wave-structure interaction with the development of new formulae, neural networks, conceptual, physical and numerical models; coastal flooding and erosion risk, with the support of numerical and conceptual models.
Elisa Dallavalle, PhD Student at the Department of Civil, Chemical, Environmental, and Materials Engineering (https://www.unibo.it/sitoweb/elisa.dallavalle3/en). Research topics: wave energy converters; mooring systems; optimal mixing of renewable energy sources; green transition of isolated communities; offshore platforms decommissioning.
The PTO system will be provided by:
Umbra Group (https://www.umbragroup.com), founded in 1972 in Foligno, Italy. The company proposes innovative solutions in several market sectors: automation, automotive, biomedical, deformation, energy, machine tool, plastic, railway.
The following Professors could eventually contribute to the project with their expertise, ensuring an interdisciplinary approach:
Fabio Zagonari, Associate Professor at the Department for Life Quality Studies (https://www.unibo.it/sitoweb/fabio.zagonari/research). Research topics: Environmental Economics, Ethics and Sustainability, Decision Support Systems.
Luca Pietrantoni, Full Professor at the Department of Psychology “Renzo Canestrari” (https://www.unibo.it/sitoweb/luca.pietrantoni/research). Research topics: Human-technology and human-automation interaction; Human and organisational factors in safety critical organisations; Crisis and disaster psychology; Accident analysis, safety and risk management; Behaviour change programs.
Carlo Alberto Nucci, Full Professor at the Department of Electrical, Electronic, and Information Engineering “Guglielmo Marconi” (https://www.unibo.it/sitoweb/carloalberto.nucci/cv-en). Research topics: Dynamics of electric power plants and of power systems, with particular reference to power system restoration after blackouts and to the influence of load modelling on voltage collapse simulations; Electromagnetic transients of power systems, with particular reference to lightning originated ones; Smart Grids and Distribution networks operation in presence of small-scale generating plants; Fault location in distribution networks; Smart Cities and Local Energy Communities.
Marina Antonia Colangelo, Assistant Professor at the Department of Biological, Geological, and Environmental Sciences (https://www.unibo.it/sitoweb/marina.colangelo/cv-en). Research topics: Meiobenthos; Experimental designs and data analysis; marine communities; Macrobenthos; Coastal management; Sandy shores; Complexity; Disturbance.