A New U-OWC Device to Produce Electrical Power from Ocean Waves: Some Applications to Italian Coasts

Several researchers have been involved in the design of marine structures devoted to the energy harvesting from water waves (Cruz, 2008). Actually, it is largely recognized that water waves can contribute extensively to the demand of energy supply. Indeed, it has been estimated that the total amount of available energy is of the same order of magnitude as world energy consumption. In this context, even if, according to Cruz (2008), a conservative exploitable limit is of 10-25%, the sea wave energy may be regarded as an attractive energy resource.

From a general perspective, three kinds of devices have been proposed in the past years: overtopping devices, single point absorbers and Oscillating Water Column (OWC) devices. The first devices are designed for exploiting the potential energy accumulated by reservoirs which collect the water coming from the largest waves. The conversion is performed via hydraulic turbines placed at the bottom of the reservoir. The single point absorbers are commonly of buoy-type. Thus, they are based on the use of a floating body which is connected to the sea bed via a cable. Such a cable interacts with a generator, so that the floating motion of the body is transmitted to the generator. The OWCs are based on the use of a large caisson with an open bottom. The caisson is partially immersed into the water, so that a closed air chamber is available over the mean water surface. Such a configuration fosters the sea wave propagation into the inner chamber of the structure. Thus, the air pocket inside the caisson is alternatively compressed and expanded. At the top of the chamber is located a tube with a small diameter, in which a turbine (commonly, a Wells turbine) is placed. The turbine is used for exploiting the energy due to the air flow generated by the compression/expansion of the air pocket.