Another different concept is the Wave Dragon: it converts the wave energy into potential energy, storing water above the sea level and the passing it through standar turbines.
- Overtopping
- Overtopping (absorption) -> Storage (reservoir) -> power-take-off (low-head hydro turbines).
- The Wave Dragon overtopping device elevates ocean waves to a reservoir above sea level where water is let out through a number of turbines and in this way transformed into electricity.
- Power generation on the Wave Dragon is based on the potential energy in the water that overtops the ramp and is temporarily stored in the reservoir. This reservoir contains approximately 8,000 m3 water that has to be let out through the Kaplan turbines in between two waves.
- The rotation of the hydro turbines is transformed to electricity via a Permanent Magnet Generator on each turbine.
- Floating device: easy to install, transport, maintain etc
- Simple construction and has only one kind of moving parts: the turbines.
- Moored (like a ship) on relatively deep water, i.e. more than 25 m and preferably +40 m to take advantage of the ocean waves before they lose energy as they reach the coastal area.
- Wave Reflecting Wings. As the waves reach the reflectors they elevate and reflect towards the ramp increasing the amount of overtopping water thereby increasing the possible energy output
- Wave Dragon is constructed with open-air chambers where a pressurized air system makes the floating height of the Wave Dragon adjustable. This is used to adjust to varying wave heights as overtopping efficiency depends on choosing the right ramp height.
- Extreme waves will not be a problem. Model tests have shown that high waves simply run over the rig.
- How much of the available energy is it able to capture?
- Turbines in direct contact with sea water.
- The more water is stored, the more it weigths and thus lower potential energy.
- Wave Dragons turbines will rotate with a variable and low speed.
- Unknown
- The first prototype connected to the grid is currently deployed in Nissum Bredning, Denmark.
Wave Dragon key figures: | Nissum Bredning prototype 0.4 kW/m | 24 kW/m | 36 kW/m | 48 kW/m |
Weight, a combination of re-inforced concrete, ballast and steel | 237 t | 22,000 t | 33,000 t | 54,000 t |
Total width and length | 58 x 33 m | 260 x 150 m | 300 x 170 m | 390 x 220 m |
Wave reflector length | 28 m | 126 m | 145 m | 190 m |
Height | 3.6 m | 16 m | 17.5 m | 19 m |
Reservoir | 55 m3 | 5,000 m | 8,000 m3 | 14,000 m3 |
Number of low-head Kaplan turbines | 7 | 16 | 16 - 20 | 16 - 24 |
Permanent magnet generators | 7 x 2.3 kW | 16 x 250 kW | 16 - 20 x | 16 - 24 x |
Rated power/unit | 20 kW | 4 MW | 7 MW | 11 MW |
Annual power production/unit | - | 12 GWh/y | 20 GWh/y | 35 GWh/y |
Water depth | 6 m | > 20 m | > 25 m | > 30 m |
Construction
Activities | Potential impacts | Mitigation measures |
Subsea cables | Temporarily affect the nature of sub tidal habitats in the cable duct. Comparable to effects known from e.g. offshore wind projects. | Identification of important habitats for fisheries, benthos etc. and avoiding laying cables in these areas. |
| Damage to archaeology sites. | Identify potential sites and avoid these. |
Onshore cables | Temporarily affect the nature of shore habitats. Comparable to effects known from e.g. onshore wind. | Identification of important habitat or scenic places and avoid going onshore at these locations. |
Installation of | Temporarily affect the nature of sub tidal habitats. Effects are known from mooring of ships. | Identification of important habitats for fisheries, benthos etc. and avoiding deployment of mooring blocks in these areas. |
Construction of | Wave Dragon will not be constructed on site but towed to the site from the dry dock where it is constructed. | A separate EIA will be made if a purpose build dry-dock is established. Sensitive areas will be avoided and the area re-established after use. |
Vessels traffic | Installation of the mooring arrangement and deployment of the Wave Dragon units will cause an increased amount of traffic. Can affect sea birds | Installation will be carried out with respect to the breeding, resting and moulting periods of sea birds species. |
Operation and Maintenance
Activities | Potential impacts | Mitigation measures |
Physical presence of
| Will have some impact on landscape and be visible. | The colour and design of the Wave Dragon structure will – to the extend possible with regard to marking requirements and to the operation of the Wave Dragon - be adjusted to minimise visual impact. Compared to wind turbines the visual impact will be low. |
Effects on sea birds in periods of breeding, moulting and resting. | Due to the non-motional nature of the Wave Dragon negative effects are not likely. Impacts are studied in the present prototype project situated in a RAMSAR and EU bird protection area. | |
Positive effects on fish resources | No mitigating measures needed. See below. | |
Negative effect on fisheries. | Locations have to be chosen with respect to commercial and recreational fisheries. | |
Effects on mammals;both the back side of the arms, mooring buoys, the ramp and horizontal trash rag covering the reservoir will attract resting seals | Design will be adapted to the optimal solution for the seals. | |
Effect on navigation: Will affect the navigational use by commercial ships, fishing vessels and recreational boating. | Standard marking of the structures and the area: lights, colours, radar reflection. Wave Dragon farms will be located out of traffic zones. | |
Reduce marine debris and spill of oil from ships washed on shore. A substantial part of this debris will end in the reservoir. | No environmental mitigating measures needed. | |
Changes in the hydro physical regime due to extraction of energy from the waves may cause: | Wave Dragon farms will extract energy from waves and to some extend changes the hydrodynamics behind a farm. Wave heights are initially estimated to be between 37 % to 22 % lower 1 km behind a Wave Dragon farm. Effect will be subject to generic and site specific hydrodynamic studies and the results from these will act as guidance in the site selection process. | |
Presence of | Electromagnetism. | The subsea cables will be buried in the sea bed. |
Operation of
| Fish and mammals will to some extend travel with the overtopping sea water into the reservoir. This may cause physical damages on fish and mammals from passage through hydro turbines. | Establishing of a trash rag covering the total reservoir preventing fish and mammal access to the reservoir and turbine system (as known from traditional hydro power stations). Fish smaller than the openings in the trash rag will pass through the operating turbines. A turbine with a slow turning (300 rpm) propeller has been chosen. |
Increased level of noise and vibrations may affects mammals dependent on sound for navigation. | Noise and vibration impact level will be low. If necessary measures to dampen these effects will be taken. | |
| Areas with abundance of cetaceans will be avoided. | |
Leaking of hydraulic fluids. | Water hydraulic has been chosen to eliminate any possibility for leaks of oil to sea water. No other potential polluting fluids etc. onboard. | |
Presence of
| Mooring blocks on sea bed will locally affect the nature of sub tidal habitats | Identification of important habitats for fisheries, benthos etc. and avoiding deployment of mooring blocks in these areas. |
Mooring chains moving on the seabed may damage the nature of sub tidal habitats | Design mooring arrangement in a way that chains are kept free of the sea bed. | |
Mooring arrangement – blocks, chains and buoys – may have an artificial reef effect with locally increased wildlife in quantity and diversity. | No mitigating measures needed. | |
Overhead-lines | Can reduce the aesthetic value of the landscape. | Landscape and visual assessment to identify route and location of infrastructure. |
Maintenance
| Offshore installations and machinery require regular maintenance. Wave Dragon is modularly built and components as turbines will be replaced on a regular basis for maintenance onshore. This will generate vessel traffic. | Maintenance will be carried out with highest possible respect to the breeding, resting and moulting period of sea birds species. |
Maintenance on mooring arrangements, marking equipment and the Wave Dragon structure will be performed on site. This will generate vessel traffic. | Maintenance will be carried out with highest possible respect to the breeding, resting and moulting period of sea birds species. | |
Anti fouling | There will be emission from any toxic antifouling. | Toxic antifouling is not used, as the weight from fouling is not a problem. A non-toxic silicone based slippery coating is tested in the turbine system (turbine outlet) in the present prototype project. |
Decommissioning
Activities | Potential impacts | Mitigation measures |
Removal and | No impact near the deployment site. | The structure will be towed to an appropriate site for re-cycling and decommissioning. Wave Dragon is designed and constructed in a way to ease recycling. |
Removal of | Will temporarily affect the nature of sub tidal habitats. | Available low impact techniques will be used. |
Removal of | Will temporarily affect the nature of sub tidal habitats. | Available low impact techniques will be used. |
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