SEA HEART CONVERTOR
Renewable marine energies (EnRM) are mentioned among the objectives of the European Union Horizon 2020 program as one of the European energetic Mix components (20% of the used energy must be generated from renewable sources). Ocean waves energy represents a resource that every European citizen has imagined one day to tame, but this energy source remains not that easily amenable. The oceans receive annually from the Sun an amount of energy greater than 1000 times the global demand. They redistribute this energy in multiple forms such as offshore wind, sea current, wave’s power, etc...
The marine energy potential could represent a net inflow of 17.2 TWh/year (2030 prospective study, Ifremer, 2008) which represents 13,230 times the nuclear reactor production, thus contributing to the goal of the renewable energy. The sea is the first lung of the planet; it can become its energy heart.
Our approach is divided into two parts: an approach for the buoy and another for the energy convertor producing the electrical energy with constant frequency.
The SHC consortium proposes to study, develop and build a semi-submerged buoy cage generator using the wave’s water mass displacement associated with the marine surface current.
This hybridization increases the recoverable power by reducing the size of the buoy and thus limiting the hydraulic effects.
The buoy is used to disrupt the natural water movement (wave and current) which gives a moving and a restraining force. The buoy moves slower than the wave or the current. This displacement is transmitted by hawsers to the convertor system located on the sea floor.
Overview and hybridization of moving
The combined action of the surge and the current increases by between 10 and 20% the extracted power from a 2 m medium wave.
The hybridization aspect of the system reflects its ability to use sea currents as an energetic benefit. Two types of hybridization are possible:
- The direct hybridization: using the current going in the direction of the surge, that is the drift current of wave.
- The complex hybridization: it consists in the creation of an oscillation of the buoy from a continuous surface current regardless of its direction.
A direct hybridization using the drift current of the waves will allow an energy saving of about 10%. In addition, a more complex hybridization transforming surface current into buoy oscillation, even in absence of waves, would generate an extra 25% average power (for usual surface sea currents of 0.5 m/s). Hence, the hybridization of the system allows a total gain of 35% in power.
The main gain of this wave/current hybridization is primarily to permit the generation of electricity in the presence of waves or current, or both; which means an interesting flexibility of use.
The second challenge is the recovery of the energy itself generated from marine waves or oscillating motion of the buoy. In this type of movement, only the rising phase can generate energy. It makes necessary to have a smoothing system for the connection of the energy before its release on a power grid (central generators should not have frequency variation exceeding 1.5%).
Our converter system is inspired from heart in its philosophy, with a suction and discharge of a water volume at low pressure but with a high flow rate. This particularity permits to directly smooth the energy flow and use a submerged and inboard turbine. Moreover, thanks to its hybridization between waves and sea currents, the system will have an unbeatable use rate with components operating either by waves or by currents. Thus, our concept will resist to a higher life cycle; which coupled with its many other benefits will emerge as a revolution compared to current systems.
Waves and currents directions are not constant; it is one of the reasons that made us prioritize the star configuration.
Presentation of the power management following the different directions of the surge and the current
Depending on the waves and sea current direction and intensity, each converter will extract a different amount of energy. However the global energy extracted corresponds to the available wave energy and current energy collected by the buoy.
Due to sea current, flaps becomes inclined up to touch their stoppers. In such position flaps generate rotation load on the buoy. So the buoy turns. However, flaps automatically change orientation when the buoy reaches a certain angle regarding the sea current. Thus the flap direction is alternated as well as the generated rotation of the buoy.
With such concept of hybridization, the oscillating movements of the buoy (rotation due to sea current) permit to pull the hawsers with an oscillating movement, like the waves do. Thus the converter which is linked to the hawser will be directly able to extract this sea current energy without knowing if it comes from wave or sea current.
This alternating rotation generates an alternating tension on the hawsers, as generated by the waves. Thus it enables the generation of current with constant frequency using the oscillating movement of the buoy rotation.
Electrical Energy Converter
The aim of our concept is to produce electrical energy at constant power and frequency from a punctual energy source taken directly to the source in order to get the best return.
The aim of our concept is to adapt the pick of energy taken by the buoy, to smooth it prior convert it into electricity. Its objective is to enable the generation of electricity at constant frequency directly from the source (submerged system) and to have the best power return.
All these systems are expected to provide a very important and global efficiency : 60% to 70%. this level of efficacy is permitted by the success to smooth energy before extract it :
The principle is:
- Divide traction energy taken from the buoy in a double thrust and aspiration cycle
A mass can store energy into potential energy and work with the suction and discharge pump, in order to divide the peak of the energy source in two.
- Processed mechanical energy extracted by the buoy into hydraulic energy under a high flow with low pressure.
- Smoothing hydraulic flow generated: Accumulators will ensure a regular flow in the turbine; either buoy in ascending or descending phase.
- and 5. Energy extraction and conversion into electricity with continuous frequency.
The flywheel will ensure the final energy smoothing when occurs the reversal of the water flow in the turbine or possible quiescent phases. This system can be optional if overcapacities are provided to the hydraulic energy storage.