Energy from the sea – Beppe Grillo’s Blog

by Domenico P. Coiro – Energy from the sea represents an enormous source of renewable energy that is still little exploited today, even if numerous companies and research groups in Italy and around the world are working to make the exploitation of this enormous resource feasible.

In Italy it is possible to exploit the energy contained in the motion of the waves and that contained in the tidal currents. The availability of the wave motion is more widespread but the technological maturity of the systems that exploit the wave motion is lower than the systems that exploit the tidal currents. These, in Italy, are present only in the Strait of Messina and in the Venetian Lagoon with the former much more intense than the latter.

It is therefore extremely important to support the development of these innovative technologies with appropriate incentive mechanisms, including the all-inclusive fixed tariff for each kilowatt hour of energy produced and fed into the grid; it is the most effective and democratic since it offers everyone the opportunity to exploit it and above all it allows to attract Italian and foreign investments for the development and installation of systems. In fact, to be effective, the development of renewables must be linked to the development of a virtuous industrial chain with consequent job creation. Think of the large wind turbines installed in Italy to date: they have all been purchased abroad and, in fact, we have financed German, Danish, Spanish companies etc. funding their industries and increasing their workforce.

We now have an incredible opportunity with offshore wind on a floating platform which is the only technology that can be installed in our seas, due to the great depth. It is a not yet fully mature technology in which many industrial and research groups are investing. Therefore, to avoid the same mistake made in the past, an entirely Italian product chain should be organized and developed which would favor the development of large port infrastructures; our steel and mechanical engineering companies and would lead to the creation of numerous jobs, otherwise we risk favoring other European companies again.

Consider that a single 10 Megawatts offshore floating wind turbine employs around 3000 tons of steel and therefore imagine installing 33 Gigawatts of these turbines in future years, which is about half of what is needed to meet our renewable energy needs by 2030. , the amount of steel needed is about 100 million tons! And we know very well how it is necessary to best support the Italian steel industry: do we want to miss this opportunity again?

The main advantages of systems that exploit the energy of tidal currents compared to those that exploit the wind are:

  • The tidal currents are perfectly known at the beginning of the year since they depend on the phases of the moon and therefore also the electricity that is collected at the end of the year is perfectly predictable as opposed to what happens with the wind and with many other renewables since they depend on the meteorological trend.
  • In air, compared to water, the area swept by the turbine must have an area about 15 times larger to produce the same electrical power! For example, let’s assume two turbines in the Strait of Messina, one of which is moved by the wind and the other is moved by tidal currents. To produce 1000 kW of electrical power (1 MegaWatt), the turbine in the water would have to have an area equal to about 180 square meters – a quarter of the surface of a football field – with a diameter of about 15 meters, while the one operating in the air, to produce the same power, it should have an area equal to about 2800 square meters – equal to the surface of 4 football fields – with a diameter of about 60 meters!

DIMENSIONS OF TURBINES IN AIR AND IN WATER

ELECTRIC POWER = 1000 kW = 1 MegaWatt
TURBINE IN AIR (Wind speed = 12 m / s = 43 Km / h – Diameter = 60 m – Area = 2800 m2)
TURBINE IN WATER (Water speed = 3 m / s = 6 knots = 11 km / h – Diameter = 15 meters – Area = 180 m2)

As mentioned, in the Strait of Messina, there is a strong tidal current that can reach up to 3 m / s (6 knots) of speed.

Considering only the area adjacent to Punta Pezzo, on the Calabrian side, it is possible to install marine turbines up to a power of about 19 MW and these can produce a total annual energy of 46 GWh (energy capable of powering about 18,500 homes). The energy available throughout the Strait is enormously higher.

The first vertical axis turbine in the world, the KOBOLD, was developed, patented and installed by us in the Strait of Messina in 1999 in collaboration with the company Ponte di Archimede, now liquidated, and also has the longest stay in water in the world since it was decommissioned in 2016.

The GEMSTAR project, the Sea Kite, represents the second generation and evolution of the first GEM prototype which was patented and developed starting from 2005 in an initial collaboration between the former Department of Aerospace Engineering of the “Federico II” of Naples and the Molise Science and Technology Park. Since 2012, all development has been conducted in collaboration with the non-profit research consortium in renewable energy SEAPOWER Scarl (www.seapowerscrl.com) which is participated by the same University of Naples “Federico II”. The GEMSTAR is a system for generating electricity from the motion of water such as tidal currents, sea currents or the motion of rivers.

GEMSTAR consists of two marine turbines connected to a float that a cable binds to the seabed. GEMSTAR, by means of an on-board winch, drags itself under the surface of the water to the predetermined depth (about 15 meters) and, in the presence of current, it aligns itself with it floating in mid-water just like a kite does in the air. When the tidal current changes direction, GEMSTAR follows it in complete autonomy. The visual impact of the GEMSTAR, being this under the sea surface, is therefore zero, it allows the transit of ships above it and when maintenance is required, just let go of the winch and the GEMSTAR rises to the surface to facilitate operations.

From L: GEMSTAR WITHOUT CURRENT, WHILE PRODUCING, UNDER MAINTENANCE

After a series of tests in the naval tank of our University on two small-scale models with excellent results in terms of performance and system stability, in 2012 a first full-scale prototype was built and installed for a short period in the Venetian Lagoon thanks to to a loan from the Veneto Region to a group of Veneto companies. In the lagoon the tidal current is not particularly fast and reaches a maximum of 1.4 m / s (about 3 knots) while in the Strait of Messina it reaches 6 knots (3 meters per second). And it is precisely in the Strait of Messina that the next full-scale prototype of 300 kW (kilowatts) will be installed. This will have two turbines which, with a diameter of about 12 meters each, will develop a total power of about 300 kW and will produce about 1 million kilowatt hours per year capable of powering about 500 homes. If the incentive rate of 30 cents per kilowatt hour were active, which ended in 2017, the system would pay for itself in a few years.

THE AUTHOR

Domenico P. Coiro – Full professor at the Department of Industrial Engineering of the Federico II University and President of the non-profit applied research consortium Seapower Scrl which employs about twenty researchers. He is also the editor and author of the text: Renewable Energy from The Oceans: from wave, tidal and gradient systems to offshore wind and solar – [email protected]


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