An offshore floating farm for sustainable transport in areas of great natural interest.

No need of fixed and impacting structures onshore or on the seabed: we believe that floating wave energy converters (WECs), characterised by dimensions and mooring system like those of a boat, could be the best option in the case of areas of great natural interest. 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 classified as a point-absorber, which means a WEC, symmetric in shape, that produces energy regardless of the direction of waves, allowing the highest possible exploitation of the wave resource with the lowest space requirement. Our compact floating WEC could be placed far from the coast, since the seabed in the area off San Felice Circeo is characterized by very gentle slopes: even 5 kilometres away from shore, it is only 30-40 meters deep. This would have two main benefits with respect to onshore devices: avoiding any visual impact and exploiting the much higher wave energy amount available offshore.

We propose the installation of a floating device which, based on our experience, would have many advantages in the case of an area of great natural interest like San Felice Circeo: 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 case of multidirectional sea states. 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. In the case of San Felice Circeo, the device could be placed far from the coast, since the seabed is still only 30-40 meters deep even 5 kilometres off the shore; this would allow to avoid visual impact and to harvest more energy with respect to onshore devices. The energy could be transferred to shore through a submerged cable which wouldn’t have an excessive environmental impact. 

Context and objective

The national park of Circeo is one of earliest natural protected areas in Italy, thus it is no surprise that the Municipality of San Felice Circeo has always been attentive towards the sustainability of the town. In particular, they are looking for Blue Energy devices that can be integrated with existing infrastructures onshore (harbour docks or breakwater barriers) in order to supply energy to recharging stations for electric vehicles and other public services. Actually, our opinion is that offshore renewable energies, and specifically wave energy, might represent a better option for areas of great natural interest, since they could provide clean energy with no occupation of space onshore and exploiting the marine space instead. In fact, although fixed onshore devices that could be integrated in port 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 small touristic port or tourist beaches, due to the visual impact. Moreover, these WECs can harvest energy for only a few wave directions (front waves). Those considerations done, our team proposes the installation of a floating device, in particular a so-called point absorber, that compared to other types of devices have smaller dimensions and can harvest energy regardless of waves direction. The main advantages of a floating device would be: the absence of impacting fixed structures, since these devices are anchored on the seabed in a similar way to that of boats; the possibility of exploiting the much higher wave energy amount available offshore. In addition, the number of WECs can be easily adapted to the current and future energy needs, with no need of impacting and disturbing structural works onshore; this would be positive in a perspective of progressive improvement of the services for tourists and of the sustainable mobility policies.

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 colours of the WECs, as for markers buoys, have to be bright for safety reasons, however, a great deal of attention will be paid to the design of the device in order to make it easier to the eyes. 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 (4x8) would occupy an area of approximately 9x18m, almost like a medium size boat at anchor off the coast.

Landscape and environmental framework

The seabed off the coast of San Felice Circeo is characterized by very gentle slopes and even 5 kilometres away from shore, it is only 30-40 meters deep, that is an ideal depth for the installation of a floating farm. Being the device not so far from the coast and from the urban centre, although almost not visible from the beach, it would be quite easy to bring the energy onshore through a submerged cable with low environmental impact.

Possible advantages and production

The number of devices to be installed depends on the energy requirements to be satisfied and can be easily adapted to the current and future demand of San Felice Circeo, with no need of impacting and disturbing structural works onshore: this would be positive in a perspective of progressive improvement of the services for tourists and of the sustainable mobility policies.

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) while, in the Thyrrenian Sea, it could produce 10 MWh/y in Mazara del Vallo, Sicily, and up to 14 MWh/y in Alghero, Sardinia (Bozzi et al., Wave electricity production in Italian offshore: A preliminary investigation, Renweable Energy, 2014). Therefore, we might hypothesize an average yearly energy production of 6-7 MWh/y for a single floating device off the coast of San Felice Circeo.

Lastly, a further possible advantage of a farm of floating WECs could be an additional protection of the beach against sea storms, as indicated in the literature (Nørgaard et al., Wave Dragon wave energy converters used as coastal protection, Coastal Structures, 2011; Zanuttigh and Angelelli, Experimental investigation of floating wave energy converters for coastal protection purpose, Coastal Engineering, 2013).

Future development

Thinking ahead, a wider farm with higher producibility could be installed farther away from shore in deeper waters or wave energy could be integrated with other renewable energy sources, like small wind turbines or solar plants, in order to make the city energy independent. The University of Bologna has a wide experience in this field and has proposed a criterion for the optimal energy mixing, proving the feasibility of the combination of different renewable sources to supply energy 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 can take advantage of the seasonal variability of different 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 more likely than wave energy alone to become economically advantageous, in particular when government incentives on renewable energies are available.

Example of floating point-absorber WEC with mooring lines.

Newly inaugurated wave basin at the Laboratory of hydraulic Engineering, University of Bologna.

San Felice Circeo 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.

-        Modularity: the number of WECs can be easily adapted to the current and future energy needs, with no need of impacting and disturbing structural works onshore.

-        Possibility to exploit the higher amount of wave energy offshore and to take advantage of the waves from every direction.

-        Almost no visual impact, almost no impact on nature and small marine space requirement.

-        Greater social acceptance on the grounds that the installation does not require permanent structural works but only anchors on the seabed.

-        Additional protection of the beach against sea storms.

-        Possibility of integration with other renewable energy sources in order to cover the variable energy demand during the whole year.

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.