Our proposal is to install a particular wave energy converter (WEC) designed for the nearshore zone, the Energy Double System (EDS), to produce clean electric energy. Its name is because it can harness both vertical and horizontal wave forces, through two different bodies placed in the same structure: a heaving float and a surging paddle. This allows to maximize the energy absorbed from each wave, since EDS can proficiently exploit both the vertical force of all the waves (through the float) and the huge horizontal force of the waves that are about to break (through the paddle). EDS can be attached to existing structures, and it is modular. Please visit our websites http://www.fluidlab.polimi.it/main-topics/wave-energy-converter and https://www.tecnomac.it/it/eds-energy-double-system.html.
Waves in the nearshore are directionally focused and have a huge horizontal force because of the effect of the sea bottom. The EDS is designed for dealing with such wave characteristics. The EDS combines a heaving float, supported by an arm hinged on a fixed structure, and a surging paddle, top-hinged on the same arm, between the float and the fixed hinge. The supporting arm is aligned along the wave propagation direction.
The EDS is scalable according to the available wave power, with typical float diameter ranging from 3 to 8 m.
The energy is extracted by a PTO (Power take-off) connected to the arms of the bodies. This works through the rotation of a single main shaft to which is connected a permanent magnet generator controlled by an A.F.E. system.
Tests on the scale model of the EDS, carried out at the Hydraulics Laboratory of the Politecnico di Milano, have revealed a maximum capture width ratio CWR (efficiency) of more than 40%, measured as the rate between the power absorbed by the EDS and the oncoming wave power. The main publications on the EDS are:
– Marchesi E., Negri M., Malavasi S., 2020. Development and analysis of a numerical model for a two-oscillating-body wave energy converter in shallow water. Ocean Engineering 214, 107765. https://doi.org/10.1016/j.oceaneng.2020.107765
– Negri M., Malavasi S., 2018. Wave energy harnessing through oscillating bodies. Energies 11, 2730. https://doi.org/10.3390/en11102730.
– Malavasi S., Negri M., 2015. Double system wave energy converter for the breaker zone. Special Issue Ocean energy: Ongoing research in Italy. Rivista EAI, ENEA. https://doi.org/10.12910/EAI2015-047
One or more modules of EDS can be installed outside the breakwaters of the port at a sufficient water depth (about one diameter D of the float). The number of EDS to install will depend on the need of electricity.
A preliminary simple estimate of the mean annual power Pout that can be produced with the EDS, utilizing a section of breakwater of length L, is the following:
Pout= Pw ∙ L/2 ∙CWR
– Pw [kW/m] is the mean annual available wave power for unit crest width [kW/m]
– L [m] is the length of the coast occupied (the factor ½ is because some space between the EDS modules is needed). Therefore, the total available wave power is Pw ∙ L/2
– CWR is the mean annual capture width ratio of the EDS, which can be interpreted as the mean annual absorption efficiency of the EDS.
The mean annual available wave power Pw at the port is included in the range 1—2 kW/m (see the references). The table below reports two examples of calculation, assuming different values of the mean annual available wave power. It is assumed an annual mean efficiency CWR=30%. The optimal diameter D of the EDS increases as available wave power increases. The calculations are made considering a section L=100 m of the breakwaters.
Although this is a first estimation and must be refined, it gives an idea of the power that can be produced. This calculation considers the annual mean power. Actually, the power extracted will present oscillations during the year, and a large part of the energy will be produced in winter.
|Case 1||Case 2|
|Mean annual wave power available||PW [kW/m]||1||2|
|Mean annual power produced||Pout [kW]||15||30|
|Energy produced in a year||Eout [MWh/year]||131||263|
|Diameter of the float||D [m]||3||4|
|Number of EDS modules||n||17||13|
– Ponce de Leon S., Orﬁla A., Simarro G., 2016. Wave energy in the Balearic Sea. Evolution from a 29 year spectral wave hindcast. Renewable Energy 85,1192-1200. http://dx.doi.org/10.1016/j.renene.2015.07.076
– Cascajo R., García E., Quiles E., Morant F., Correcher A. 2020. Wave Energy Assessment at Valencia Gulf and Comparison of Energy Production of Most Suitable Wave Energy Converters. Int. J. Environ. Res. Public Health 2020, 17, 8473; http://dx.doi.org/ijerph17228473
Waves are a clean, renewable source of energy. Excluding the phases of construction and installation of the EDS, the transformation of wave energy into electricity does not involve CO2 emissions. The EDS has a minimal impact on the landscape and on the marine environment. The mechanical and electrical parts of the energy transformation are not in contact with the water.
Tecnomac S.r.l. has patented and developed the EDS. Tecnomac was born in 1990 and has always been active in the field of innovation. Tecnomac is specialized in designing and building special equipment and multiple toolinh and special machines to run production processes automatically.
The scientific investigation of the EDS has been made at the Department of Civil and Environmental Engineering of Politecnico di Milano. A laboratory scale model and a numerical model of the EDS have been developed. The scale model of EDS has been tested at the Hydraulics laboratory of Politecnico di Milano.
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