The SEATURNS solution is the result of a benchmarking of existing WEC (wave energy converter) technologies with the various obstacles that prevent their commercial development.
This study resulted in five research objectives:
– resisting different sea conditions,
– efficiently converting energy, according to different types of swell,
– minimizing and facilitating maintenance operations,
– ease of setting up,
– offering different possibilities of use in different market segments.
The chosen solution is a compact, small, simple solution that uses the free water ballast technique.
With a global deposit of 18 500 TWh/yr, WEC have a more regularly strong development potential than other RME (renewable marine energy) systems.
The free water ballast technique will alternatively presurise / depresurise two volumes connected by a turbine system set in motion by the generated air flow.
Several outlets exist, the provision of point-source electricity in isolated or insular coastal areas or the generation of electricity in networks.
Three-quarters of the planet is covered with sea water, an inexhaustible but salty source, and freshwater needs for irrigation, industry and drinking water are constantly growing.
The free water ballast technique producing pressure variation is very effective in pressuring sea water and provokes the reverse osmosis principle.
There are several outlets, the production of point freshwater in isolated or insular coastal areas or the mass decarbonate production of freshwater.
INNOVATIVE ANCHORING SYSTEM
The anchoring system, in particular the peripheral fastening of the mooring line to the float bodies, allows it to associate the pitch movement with a pitch motion that oscillates the free water ballast.
This system allows the ballast to produce on different types of swell even on the longest surges.
THE FLOAT IS A SET OF BASIC ELEMENTS
The steel float consists of two coaxial cylinders, of rigid bulkheads and a separate bulkhead, all soldered to each other, the only moving element being the free water ballast, consisting of sea water collected on the spot (80 % of the mass of the float).
THE POWER TAKE-OFF (PTO) IS A MODULE
To produce electricity, the extraction module (PTO) is an air turbine coupled with an alternator.
To produce fresh water, the extraction module (PTO) is a pressure converter, which pressurizes sea water to reach the reverse osmosis plant.
In both cases, the module is compact and can be extracted simply and easily for control or maintenance.
This WEC device does not contain any “problem-introducing” devices affecting the longevity of WEC.
No hinges, in contact with sea water, with oscillating arms and cylinders.
No end stops, impossible to size to withstand tens of millions of swell cycles.
No large forces and small velocities.
No superstructures sets to extract energy from long waves.
The WEC has the shape of a marine beacon, known for its resistance to difficult conditions and longevity.
This shape is also the one of tanks containing gases or liquids with low or high pressure.
This design is the most suitable to withstand storms, exceptional or unusual waves.
ALONE OR IN A GROUP
The Seaturns device may operate individually for the supply of electricity or the supply of fresh water, occasionally in isolated or insular coastal areas or can be used in groups in production areas by sharing the mooring lines in an optimal way.
This small size allows profitability similar to large WEC, is easier and more flexible to carry onhore and offshore and to set up.
THE PROOF OF CONCEPT
The tests at the central LHEEA Nantes wave basin have shown that the concept is able to absorb much of the incident energy of the waves and convert it into pneumatic power.
From the simple proof-of-concept phase a “capture width ratio” larger than 20 % could be observed, an easily improved value by optimization studies.