The main goal of the project consists in the deployment of a prototype of the GEMSTAR system, a tidal energy device, for a sufficiently long period in order to validate previous design studies and to assess the reliability and economic effectiveness of the system, in view of a final commercial development.
The GEMSTAR system represents the second generation of the former GEM system, the prototype of which was deployed for short time on 2012 in Venice Lagoon (max current speed 3 knots). It is composed of a pair of hydrokinetic turbines mounted at the sides of a floating underwater support body. The support structure is linked to the seabed through a mooring cable and can turn around the vertical axis following flow direction changes, as happens, for example, in reversing tidal currents. A proper winch device allows both the deployment of the system at the proper operating depth and its recovery to surface for easier maintenance intervention.
The development of the project is still underway. A first large-scale prototype was installed in the Venice lagoon in 2012. Since then, the project is still evolving and a major revision of the design is planned in view of an expected installation in a site located within the Strait of Messina, in southern Italy. GEMSTAR system, expected to be deployed in the Strait of Messina, differently from first prototype will not use the rotor shrouds, it will use fixed pitch blades and it will have a rotor radius of about 6 m, yielding a rated power of 300 kW at a rated speed of 2 m/s and it will have a rated rotational speed of 16 rpm. An innovative control for above rated speed conditions will be employed.
A preliminary investigation of potential installation sites is necessary to determine a suitable choice of the plant location. A proper choice of the installation site needs to take into account several considerations about the site characteristics. Thus, a preliminary survey is currently ongoing, aiming at the evaluation of the following features:
- a proper bathymetry
- with a depth comprised in a range allowing for system operation with a proper clearance both from the seabed and the free surface;
- with a relatively flat seabed area to allow for safe system orientation;
- suitable geotechnical properties of the seabed to accommodate the anchoring foundation structures;
- amount of available energy resource (through current profile measurements).
Installation is planned in the Strait of Messina, Italy.
An in-deep survey is still undergoing on several possible sites of installation, taking into account bathymetric, geomorphologic and tidal current characteristics. Details on installation site will be available after the end of the survey. However Seapower had already started the permit procedures back in 2013 in order to obtain a permit on Italian side of the Strait, in Villa S. Giovanni, and the final permit will be soon released.
GEMSTAR technology belongs to Seapower Scarl and some attempts are being conducted to involve large industrial companies. The most promising one involves SAIPEM which is a large offshore company. Licenses as well as agreements to constitute Newco are possible for industrialization and commercialization of the system.
A previous experimental campaign on a large-scale model was performed in real sea environment on the initial system configuration. As said, a first prototype of a previous project, named GEM, with 3 m diameter shrouded turbines was deployed in a low speed site of the Venice lagoon for a short time period. Currently, a survey on Sicilian coasts has been started in January 2019 and is still undergoing. A long period ADCP measurement campaign of the tidal current speed is planned.
No direct study about the environmental aspects of the plant installation has yet been performed at this stage of the development. The area of the Strait of Messina has, however, a very rich and differentiated ecosystem, with peculiar characteristics within the Mediterranean Sea. Moreover, the Strait is placed along a migration route of several species, comprising Cetacean and marine mammals. Thus, the development of the project can be an opportunity for the investigation of the possible interference of the system operation on the surrounding environment. The planned prototype deployment in real operating conditions can provide information on such possible environmental issues. Another potential subject is related to the pollution of oil (mainly used in the transmission system). The use of proper sealing systems or of lubricants with reduced environmental impact can have a mitigative effect. Further studies are planned involving also CNR (Italian National Research Council) especially for acoustic impact evaluation.