Monday, March 29, 2010

Anaconda





A radically different approach to harvesting wave power is by compressing water inside a rubber tube.

Technology:
  • Wave damper
  • During the high pressure part of the cycle, water passes through a set of non-return valves into an accumulator where pressure is allowed to build up.
  • A smoothed flow of water then passes from the accumulator into a conventional hydraulic turbine which drives an electrical generator.
  • On exit from the turbine, the water is accepted into a low pressure accumulator and is then drawn through another set of non-return valves back into the main tube during the low pressure part of the bulge wave cycle.
Advantages:
  • Floating device: easy to install, transport, maintain etc
  • Light weight rubber structure
  • Survivability, no "hard-limits"
  • Few parts, low maintenance
Disadvantages:
  • How much of the available energy is it able to capture?

Cost:
  • Unknown
Other info:

Links:
Video:

Wave Dragon




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.

Technology:
  • 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.
Advantages:
  • 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.
Disadvantages:
  • 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.
Cost:
  • Unknown
Other info:
  • 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
350 - 440 kW

16 - 24 x
460 - 700 kW

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
mooring system

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

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
during installation

Installation of the mooring arrangement and deployment of the Wave Dragon units will cause an increased amount of traffic. Can affect sea birds
• Moulting
• Breeding
• Resting
Comparable to the effect known from existing vessel traffic.

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
moored structures
at sea

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
• Will create a fishery exclusion zones
• Artificial reef effect will attract fish

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:
• Impact on coastal processes as erosion and sediment transport.
• Changes in the marine habitats
• Reduced recreational value, i.e. regarding surfing due to smaller waves.

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
subsea cables
in seabed

Electromagnetism.

The subsea cables will be buried in the sea bed.

Operation of
the turbines

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.
Impact level: Permanent – low.

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
arrangements

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
and substations
onshore

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
decommissioning
of WEC from site

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
mooring
arrangements

Will temporarily affect the nature of sub tidal habitats.

Available low impact techniques will be used.

Removal of
subsea cables

Will temporarily affect the nature of sub tidal habitats.

Available low impact techniques will be used.


Links:
Official Website: http://www.wavedragon.net

Wave Roller




Another idea, very similar to the Oyster is the WaveRoller.

Technology:
  • Wave damper
  • Simple mechanical hinged flap connected to the seabed at low depth
  • Each passing wave moves the flap, driving hydraulic pistons to deliver high pressure oil which moves a generator.
  • Instead of the floatation of the flap to recover the vertical position, the Wave Roller uses the back movement of the water
Advantages:
  • Simple and robust mechanical offshore component with innovative use of proven conventional onshore hydro-electric components
  • Minimal environmental footprint and is effectively silent in operation
Disadvantages:
  • How much of the available energy is it able to capture?
  • Joints between sections in contact with sea water

Cost:
  • Unknown. AW-Energy, a Finnish cleantech company developing WaveRoller, has signed a $4.4M (3 million euros) contract with the European Union to demonstrate its technology.
Other info:
  • October 2, 2009 The goal of the project is to manufacture and deploy the first grid-connected WaveRoller unit in the Portuguese waters. The exact installation site is located near the town of Peniche, which is famous of its wave resources and also known as "Capital of the waves." The nominal capacity of the WaveRoller unit is 300 kW and the project includes a one-year testing period.
Links:
Official Website: