convert thesea wave energy in electric energymaking it immediately available for offshore plants or by feeding it into the electricity grid to power coastal communities. This is what the sistema Iswec – Inertial Sea Wave Energy Converter – sviluppato da Eni with Wave for Energy S.r.l., spin-off del Turin Polytechnic.
Wave motion is one of the main sources of renewable energy currently not exploited. Sea waves have high predictability, reduced variability and have an extremely high energy density, because they concentrate that produced by the wind and that deriving from the heating of the atmosphere due to the sun. These characteristics make them a promising energy source for the future, suitable for the decarbonization of offshore O&G activities and to ensure theenergy autonomy of small islands.
The Iswec system consists of a watertight floating hull with, inside, a pair of gyroscopic systems connected to as many generators. The waves cause the unit to pitch, anchored to the seabed, but free to move and rock. The pitch is intercepted by the two gyroscopic systems connected to generators which transform it into electrical energy.
Iswec is perfect for supplying electricity to off-shore plants, in particular to Oil&Gas platforms. The first pilot plant was installed at Ravenna in March 2019, connected to the Eni PC80 platform and integrated with a photovoltaic system. The rig was then decommissioned in September 2022 following its test period in the offshore operating environment. These applications make it possible to increase the energy self-sufficiency of structures located offshore, far from the coast and perhaps in geographical contexts where the electricity supply is not obvious.
The technical challenge
The problematic aspects to be solved in the development of the technology were substantially two: the corrosion due to salt air not variations in the intensity of the waves. In the Iswec system, however, the mobile and delicate parts are inside the sealed hull, completely isolated from the salt water, while the operation of the gyroscopic systems that power the two generators is optimized through an active control system to respond to the different weather and sea conditions. Iswec converts wave motion into electricity thanks to an inertial system based on the classical physics principle of conservation of angular momentum: the waves cause the hull to oscillate which is transmitted to a flywheel rotating on an axis perpendicular to the pitch axis. This, due to the gyroscopic effect, produces a third motion, perpendicular to both, consisting in the precession of the gyroscope shaft, which can be used to generate electricity.
Iswec also has an active component in the process energy capture, which is regulated by the rotation speed of the flywheel and allows the inertia of the hull to be adapted to the wavelength of the sea hitting it; this feature, implemented for the first time in the world by Eni on an industrial prototype, is the real point of discontinuity with respect to other capture systems: in fact, it is possible to vary the inertia of the device as if we were changing its dimensions, effectively obtaining a virtual variable geometry system and thus maximizing energy conversion.