Harvesting the energy from ocean waves is one of the greatest attractions for energy engineers and scientists. Till date, plenty of methods have been adopted to harvest the energy from the ocean waves. However, due to technological and economical complexity, it is intricate to involve the majority of these energy harvesters in the real ocean environment. Effective utilization and sustainability of any wave energy harvester depend upon its adaptability in the irregular seasonal waves, situation capability in maximum energy extraction and finally fulfilling the economic barriers. In this paper, the front end energy conversions are reviewed in detail which is positioned in the first stage of the wave energy converter among other stages such as power take off (PTO) and electrical energy conversion. If the recent development of these front end energy conversion is well known then developing wave energy converter with economic and commercial viability is possible. The aim of this review is to provide information on front end energy conversion of a point absorber and emphasize the strategies and calamity to be considered in designing such kinds of devices to improve the energy harvesting competence. This will be useful to the engineers for speeding up the development of a matured point absorbing type wave energy converter.
. [J]. Frontiers in Energy, 2015, 9(3): 297-310.
Nagulan SANTHOSH, Venkatesan BASKARAN, Arunachalam AMARKARTHIK. A review on front end conversion in ocean wave energy converters. Front. Energy, 2015, 9(3): 297-310.
Utilizing two buoys – one on the surface of the water – the other suspended underwater
A piston arrangement is placed between the two buoys to drive the onshore turbine
Pelamis [21]
Five tube sections linked by universal joints
Five tube sections linked by universal joints which flex in two directions to drive generator through hydraulic unit
Neptune wave power [22]
Floating buoy with pendulum interconnected
On board electric generator driven by oscillating pendulum
Dexawave [23]
Two hinged catamarans as floating buoys
Electric generator driven by the oscillations produced by two hinged catamarans
AWS [24]
Floating multi cell flexible membrane
Turbine- generator driven by pneumatic cell membrane activated by waves
Tab.1
Fig.4
Fig.5
Fig.6
Fig.7
Fig.8
Fig.9
Fig.10
Fig.11
Fig.12
Fig.13
Fig.14
Fig.15
Fig.16
Fig.17
Fig.18
Fig.19
Fig.20
Front end energy converter
Device
Significances
Comments
Buoys
Floating
Searaser [20]
Searaser harnesses almost constant power； On shore power generation and simplex structure
Less installation and maintenance cost and power fluctuation is minimum
Pelamis [21]
Power generation is smooth and continuous； The long, thin, streamlined shape of the machine minimizes the drag and slamming forces.
Machine response in storm is minimum
Neptune wave power [22]
The moving parts are not exposed to the sea water and preserved from corrosion and other calamity； Scalable and movable； Modular design for cost effective manufacturing； Interchangeable components for cost effective maintenance
Dynamically configurable for any offshore environment
Dexawave [23]
The converter can be easily relocated
Cost effective and no negative environment footprint
AWS [24]
Naturally discard load and de-tunes in large wave； Acquiescent mooring system reduces wave loadings； Sealed air system prevents exposure of moving parts to environment
Devices will be arranged in arrays or ‘farms’ and high range of power can be generated
Submerged
Submerged [28]
The device can be implemented in near-by shore applications； The device is totally submerged under water and it is prevented from the slamming forces of the waves
High efficiency is achieved by phase shift through appropriate feedback control
Buoy with reference frame
Sea floor mounted/anchored [6]
Provide high stability
Simple structure to mount the wave energy converter on sea bed
Submerged plates [30]
Efficient damping
Device is prevented from sea bed earthquakes since it is moored and not rigidly fixed
Other floating bodies [31−33]
More than one mode of oscillation can be achieved to extract maximum energy
Simple and reliable energy conversion is achieved by implementing direct drive rotary generators
Spar [34]
High structural stability； Prevent the energy conversion devices from ocean environment
Spar prevents the wave energy harvester from displacement during buoy movement
Non-buoyant wave energy converter
Non-buoyant near shore wave energy converter [35]
Maximum energy can be harvested due to high mass density of non-buoyant body； Prevent failure during extreme wave conditions and rough weather
These devices are suitable for near shore applications
Wave energy converter with different modes of motion
Heave [36,37]
Simple mode of motion； Continuous power generation is possible despite waves being periodic
Documented several years of continuous production in the sea
Surge [38]
Implemented to harvest energy in shallow wave； Surge type device is installed at a shorter distance to land thus the electricity can be delivered to the grid with lower power losses
These devices are suitable for near shore applications
Sway [39]
Implemented to harvest energy in deep sea； Enable optimal performance； Designed to avoid exposure to extreme wave conditions； Bio inspired structure
Power generated and supplied to the grid is stable and it is of utility-grade quality
Long cylinder/tube wave energy converter
Flexible tubes [40]
Hinges, joints are not present in these energy harvesters and hence life expectancy is more； Rubber tubes can sustain in sea environment for a longer period of time
Reasonable installation cost with acceptable performance
Rigid cylinder [41]
Energy extraction is increased by implementing each and every cylinder as energy harvester； Energy generation is maximized even in small waves； The energy converter is prevented from extreme conditions by reducing the system response
These device are suitable for offshore environment
Surfing Wave Energy Converter
Surfers [42]
Anticipated to be most applicable in near shore installations
Wave paddle which is incorporated in the system to harvest the wave energy is unable to remain in the wave front due to inertial and frictional loads； As the paddle passed through the wave crest negative power was absorbed from the wave field, reducing the average power capture
Inertial Sea Wave Energy Converter (ISWEC)
Gyro balancers [43−45]
Reliable and durable operation is achieved by operating the flywheel in a sealed floating body
Non-linear coupled model (mechanics+hydrodynamics) is implemented to improve the float shape in order to maximize the power absorption； The efficiency of the device is increased by modifying the float dimensions
Pendulum wave energy converter
Pendulums [46−48]
Pendulum device harvest wave energy in both strokes to generate power； The system is simple and has no complicated components
Continuous energy generation can be achieved using these devices
Tab.2
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