Based on our experience, we propose the
installation of a floating device which would have many advantages in the case
of a small tourist island: 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 an island. 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
Samos Island, the device could be placed offshore, outside the narrow gulf of Samos
in order to harvest more energy and avoid usage conflicts, and could directly supply
energy to the port. Moreover, the wave farm could be integrated with other
renewable energy sources in order to cover the variable energy demand of the
Island as a whole throughout the year in the different seasons, minimizing the
need of fossil-fuels.
Context
Samos Island, in the Eastern Aegean Sea, is one
of the most popular islands in Greece, an unspoiled place of great natural
interest, where there are also many archaeological sites, beautiful beaches and
quaint fishing villages. At the same time, like the majority of small island of
the Mediterranean region, it depends on polluting and expensive imported fossil
fuels for its electricity needs, despite the large availability of renewable
sources. Thus, renewable energies, and specifically wave and tidal energy,
represent a great opportunity for small islands, since they could ensure energy
self-sufficiency exploiting the vast marine space.
Objective
In this context, the Municipality of Eastern
Samos is looking for Blue Energy technologies that could help to reach energy
autonomy of the port of Samos while respecting the environment and the natural
landscape. Our opinion is that small floating offshore devices might be a viable
option. In fact, although fixed onshore devices that could be integrated in the
structures of the port 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, 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 advantage 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.
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 gulf of Samos is approximately 1 kilometre
wide, thus there is little space for a floating installation in the proximity
of the port. Moreover, the interval of wave directions that could be exploited
inside the narrow gulf would be very limited. A possible location for the installation,
only considering the surroundings of the port of Samos, could be the west side
of the gulf, between Floka and Kedro or better between Kedro and Kokkari,
300-500 metres off the coast, were the depth of the seabed varies from 20 to 40
m (that is the ideal depth for the installation of a floating device) and the
interval of possible wave directions is wider. A particular attention should also
be paid to the placement of the anchors, which could be located in the most
convenient positions, following the recommendations of biologists and
ecologists. The selected area, although relatively close to shore, seem to be
out of the ferry routes and pretty far from the beaches. Being the device not
so far from the coast and from the urban centre, it would be quite easy to
bring the energy onshore through a submerged cable.
Possible advantages and production
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) 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).
Future development
Moreover, thinking ahead, a wider farm with higher producibility could be installed farther away from shore in deeper waters or, more easily, wave energy could be integrated with other renewable energy sources onshore, like small wind turbines or solar plants, in order to make the island energy independent, as in the case of the island of El Hierro (Canary Islands), Samso (Denmark) and many others. The University of Bologna has a wide experience in this field and has proposed a criterion for the optimal energy mixing and proved the feasibility of the combination of different renewable sources to supply a desalination plant in Tenerife Island (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.
Samos 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
Impact
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.
-
Possibility
to harvest a greater amount of energy taking advantage of the higher and
multidirectional waves offshore, outside the Gulf of Samos.
-
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 integration with other renewable energy sources in order to cover the
variable energy demand of the port and of the island in general during the
whole year, minimizing the need of a fossil-based back-up system.
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.