Existing Wave Energy Converters Assessment Engineering Essay

Chapter 4

4.0. Introduction

Most current moving ridge energy convertors are in the design stage, proving stage or early commercial stage. The taking and more mature engineerings abroad every bit good as local WECs from Mauritanian discoverers were assessed. The assessment procedure was made more ambitious due to the reluctance of companies to supply more elaborate technology information sing their WECs in order to protect their Intellectual Property rights.

4.1. Appraisal Standards

The standards used for measuring the WECs are rather similar to that used by the Electric Power Research Institute ( EPRI ) in 2004 to measure offshore WECs. Below are listed the appraisal standard classified into different classs and subcategories:

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Technical Issues

This class will chiefly concentrate on measuring the design adulthood and the functionality of the device. The devices will be analysed on these undermentioned issues:

Structural Elementss

Power Take Off


Survivability/Failure Manners


Installation and Deployment

Operation and Care

Life Expectancy




This class will cover with the capital investing needed to buy the device from the maker. This cost estimation does non include the cost for developing and set uping the needed substructure ( such as moorage, grid connexion and power overseas telegrams ) on site, site deployment costs, care and operation costs.

Development Status

This standard will measure the preparedness of the design to be deployed.

Environmental Impact

The environmental impact the device may hold during operation or during the building stage will be assessed.

4.2. Appraisal of WECs from Leading Companies

In Table 4.1 are listed the WECs that were assessed.

Device Name

Manufacturer Name



Device Type


Pelamis Wave Power Ltd.

United Kingdom



Wave Dragon

Wave Dragon ApS





Carnegie Wave Energy Limited



Submerged force per unit area derived function

Table 4.1 Wave Energy Conversion Devices Assessed.

4.2.1. Appraisal of the Pelamis

Figure 4.1 The Pelamis

( Beginning: Pelamis Wave Power Ltd. ) Device Description

Manufacturer ‘s Description: The Pelamis is a semi-submerged, articulated construction composed of cylindrical subdivisions linked by hinged articulations. The wave-induced gesture of these articulations is resisted by hydraulic random-access memories, which pump high-pressure fluid through hydraulic motors via smoothing collectors. The hydraulic motors drive electrical generators to bring forth electricity. Power from all the articulations is fed down a individual umbilical overseas telegram to a junction on the sea bed. Several devices can be connected together and linked to shore through a individual ocean floor overseas telegram. Specifications

Device Name: Pelamis P1


Overall length: 150m

Diameter: 3.5m

Supplanting: 700 metric tons ( including ballast )

Nose: 5m long, drooped conelike

Power take-off: 3 independent power transition units

Power Conversion Unit:

Power take-off: 4 x hydraulic random-access memories ( 2 heaving, 2 sway )

Ram velocity: 0 – 0.1m/s

Power smoothing/storage: High force per unit area collectors

Working force per unit area: 100 – 350 Barroom

Power transition: 2 ten variable supplanting motors

Generator: 2 x 157kVA / 125kW

Speed: 1500rpm


Overall power evaluation: 750kW

Annual end product: 2.7GWh

Nominal moving ridge power: 55kW/m

Hydrostatic power modification: & A ; gt ; 6 – 7m important moving ridge tallness

Generator type: Asynchronous

System electromotive force: 3-phase, 415/690Vac 50/60Hz

Transformer: 950kVA measure up to typ. 11kV or 33kV

Site Mooring:

Depth: & A ; gt ; 50m

Current: & A ; lt ; 1 knot

Mooring system: Compliant, slack moored Technical Issues

Structural Elementss

The organic structure of the Pelamis is a cylindrical steel construction that can be comparatively easy built utilizing standard equipment and building techniques available at most modern shipyards.

Power Take Off

The Pelamis snake-like construction is made up of 4 cylindrical subdivisions connected by 3 hinged articulations. The wave-induced gesture causes these articulations to power hydraulic random-access memories which pump high force per unit area fluid through hydraulic motors via smoothing collectors. The hydraulic motors will drive the electrical generators to bring forth electricity. The power is fed down an umbilical overseas telegram to a junction on the ocean floor connected to a individual sub-sea overseas telegram to shore. The umbilical overseas telegram is besides connected to a transformer found in the olfactory organ.

Figure 4.2

( Beginning: Pelamis Wave Power Ltd. )

Figure 4.3

( Beginning: Pelamis Wave Power Ltd. )


The Pelamis is slack moored and as a consequence it acts against itself instead than the moorage to absorb power. The Pelamis is slack-moored at 3 points leting it to turn into wave waies within its moorages restraints. There are 3 berthing weights resting on the ocean floor. The slack moorage system will add to the survivability accomplishments of the Pelamis.

Figure 4.4

( Beginning: Pelamis Wave Power Ltd. )

Survivability/Failure Manners

The Pelamis is a narrow and flexible construction, giving it good survivability features. It is besides slack-moored which should diminish the emphasis on the moorage system in instance of utmost conditions.


The Pelamis is rated at 750kW. Depending on the moving ridge resource at the site location, end product is typically 25-40 % of rated power over the class of the twelvemonth. The Pelamis is designed to bring forth power optimally in high frequence conditions ( low periods ) with maximal gesture between its cannular subdivisions. It is hence be less suitable to long period moving ridge conditions.

For the moving ridge clime at Blue Bay, with a moving ridge tallness of 3.06m and a period of 9s, about 292kW of power will be produced for most of the clip from a rated 750kW device, and the moving ridge clime of Riambel, with a moving ridge tallness of 2.14m and a period of 8.6s, about 147kW of power will be produced. These represent one-year productions of 2,558MWh and 1,288MWh of electricity severally.

Table 4.2 Pelamis Power Table

( Beginning: Pelamis Wave Power Ltd. )

Installation and Deployment

For installing at a site, Pelamis machines are towed or constituents are shipped by land or sea, for local assembly. There is no demand for frogmans for the chief installing work. However, there are sometimes installation work that require diver intercession during the initial installing, and during the quayside commissioning procedure.

Operation and Care

Once Pelamis machines have been installed on site, operation of the machines is handed over to shore control.

For its care, merely modest installations are required:

A quayside or pontoon that the Pelamis can be moored to

A caducous storage

A little Crane for raising modular constituents out of the machine should they necessitate replacing.

For care intents, the Pelamis is towed back to sheltered H2O for all care actions to be carried out in safety on a quayside. No frogmans are needed for operation and care intents.

Life Expectancy

Pelamis is designed to last the life of the undertaking, which is usually in the order of 20 old ages harmonizing to the maker.


Project boundary markers, as stipulated by the regulating navigational authorization, will necessitate to be installed prior to Pelamis associated equipment in order to define the country to be avoided by Marine traffic. Usually central marker buoys are the standard method to tag out the boundaries of offshore renewable undertakings. The sites are delineated with navigational markers with visible radiations and radio detection and ranging reflectors. Wave Farm sites are evidently non located in transporting lanes. In the improbable event that the Pelamis gets free, the Pelamis has a GPS ( Global Positioning System ) that is monitored 24/7 so any evident ‘out of place ‘ event would be instantly investigated.


The Pelamis needs to be towed back to sheltered H2O for care. The system is designed to avoid the usage of human intercession. In both connexion and disjunction, the lone manual intercession is the connexion of slack man-made ropes on the surface prior to commanding the latching and unlatching mechanisms by distant Wi-Fi nexus from the tow vas. Pelamis has successfully performed these operations in moving ridges of over 2m important tallness and is presently technology developments to stretch the restricting conditions standards for recovery to 3.5m important moving ridge tallness. Cost

The cost of a individual device is reported to be at $ 2 to $ 3 million USD ( 2004 Prices ) ( ERPI 2004 ) . Assuming an initial cost of $ 3million USD, the cost is $ 4000/kW. Taking into history rising prices rates, 2011 monetary values should match to about $ 4,700/kW.

Calculating the electricity coevals cost per kWh for the Pelamis

The entire electricity coevals cost of a undertaking per kWh = per kWh building cost + per kWh production cost


Useful life = 20 old ages

Capacity Factor is assumed 0.40

Per kWh production cost is assumed nothing


Per kWh building cost = _______________Device Cost_________________

( kW Rating x Useful Life x Capacity Factor x 8,760 )

= _______3,500,000____

( 750 x 20 ten 0.40 ten 8,760 )

= $ 0.067/kWh ( 2011 monetary values )

Per kWh production costs = ______________Production Cost_______________

( kW Rating x Useful Life x Capacity Factor x 8,760 )

= assumed nothing

The entire electricity coevals cost of the Pelamis per kWh = $ 0.067/kWh ( 2011 monetary values ) . Development Status

The Pelamis is a promising and comparatively mature engineering which is one of the few WECs presently in the commercial phase. The first ‘next coevals ‘ Pelamis P2 machine was constructed in 2010, presently in the first phases of deployment to be tested at the European Marine Energy Centre ( EMEC ) in 2011. Environmental Impact

The Pelamis is one of the most environmentally friendly signifiers of electricity coevals in footings of emanations during their operational life-time. Initial life rhythm analyses that have been carried out for Pelamis, taking into consideration energy use in industry of the machine and its constituents every bit good as energy use through its operational and decommissioning stage, indicates that a Pelamis machine operating in a good moving ridge resource ( 40kW/m one-year mean wave energy degree ) will hold an energy payback period of less than 20 months with a life rhythm emanation of about 25g/kWhr ( Pelamis Wave Power Ltd. , 2011 ) . Under these conditions a Pelamis machine will countervail the production of about 2,000 metric tons of CO2 from a conventional combined rhythm gas power station each twelvemonth. Decision

This is presently considered as the most advanced and mature wave energy engineering. The survivability accomplishments of the Pelamis make it highly attractive in footings of establishing it in unsmooth seas, the form of the Pelamis shoul let it to survice even the most utmost conditions.

4.2.2. Appraisal of the Wave Dragon

Figure 4.5 The Wave Dragon

( Beginning: Wave Dragon ApS ) Device Description

Manufacturer ‘s Description: The Wave Dragon is a drifting slack-moored moving ridge energy convertor of the dominating type. It fundamentally consists of two wave reflectors concentrating the moving ridges towards a incline. Behind the incline there is a big reservoir where the H2O that runs up the incline is collected and temporarily stored. The H2O leaves the reservoir through hydro turbines that utilise the caput between the degree of the reservoir and the sea degree. This consequences in a three-step energy transition:

Dominating ( soaking up )

Storage ( reservoir )

Power-take-off ( low-head hydro turbines ) .

Figures 4.5 and 4.6 show the Wave Dragon and its operating rules.

Figure 4.6 Operating Principles of the Wave Dragon

( Beginning: Wave Dragon ApS )

The chief constituents that make up a Wave Dragon are:

Main organic structure with a double curved ( egg-shaped + handbill ) incline.

Two wave reflectors in steel and/or reinforced concrete.

Mooring system.

Propeller turbines with lasting magnet generators. Specifications

The physical dimensions of a Wave Dragon are optimised to the moving ridge clime at the deployment site as shown in Table 4.3.

Table 4.3 Wave Dragon Dimensions Harmonizing to Wave Climate

( Beginning: Wave Dragon ApS ) Technical Issues

Structural Elementss

The chief organic structure or platform is one big drifting reservoir made of a combination of strengthened concrete and steel home bases. The Wave Dragon needs to be big and heavy to guarantee stableness of the construction, in order to obtain the coveted weight, H2O ballast is added. The H2O reservoir is located on the top of the Wave Dragon ‘s chief organic structure.

To maximize H2O dominating efficiency a combination of moving ridge reflectors are attached to the chief organic structure are two wave reflectors besides made of a combination of strengthened concrete and steel.

Power Take Off

The Wave Dragon has merely one sort of traveling parts: the turbines. This is an advantage the Wave Dragon possesses, the deficiency of traveling parts will intend less opportunity of failure. Propeller turbines are used in the Wave Dragon. As the Wave Dragon ‘s turbines will revolve with a variable and low velocity, lasting magnet generators are used. In this manner no gear-box is needed, thereby cut downing both losingss in power and care costs significantly.


The Wave Dragon is a drifting slack-moored WEC. The device needs to be slack moored as its drifting tallness is adjustable. The Wave Dragon is constructed with alfresco Chamberss where a pressurized air system makes the drifting tallness of the Wave Dragon adjustable. This is used to set to changing wave highs as dominating efficiency depends on taking the right incline tallness. Figure 4.7 and 4.8 show the moorage constellation of the Wave Dragon.

Figure 4.7 Side View of the Mooring System of the Wave Dragon

( Beginning: Wave Dragon ApS )

Figure 4.8 Top View of the Mooring System of the Wave Dragon

( Beginning: Wave Dragon ApS )

Survivability/Failure Manners

The Wave Dragon is basically a big drifting platform. Bing freely drifting, there is small concern that the device will neglect under utmost conditions. The worst instance would be that the moorage system fails and the device interruptions free and starts floating. Backup berthing lines should be installed to forestall the device from floating off in instance of failure.

The Wave Dragon has multiple Kaplan Turbines running in analogue ; the device will most probably have a really high dependability evaluation. Even in instance that one turbine fails, the device will go on to bring forth power. Critical elements from a survivability position are the moorages system and the structural unity of the organic structure.


Harmonizing to the maker, one Wave Dragon unit will bring forth electricity matching to the moving ridge clime nowadays:

Wave Climate [ kW/m ]

Annual Power Production [ GWh ]











Table 4.4 Annual Power Production Harmonizing to Wave Climate

( Beginning: Wave Dragon ApS )

The above information has been plotted in Figure 4.9 to be able to obtain an approximative power production appraisal for local moving ridge climes. With wave climes of 46.6kW/m at Blue Bay, expected one-year power production from a rated 11MW unit will be about 32GWh. The moving ridge clime of 21.7kW/m at Riambel will bring forth about 10GWh ( if we consider the secret plan as a additive line in Figure 4.7 ) from a rated unit of 4MW.

Figure 4.9 Annual Power Production Harmonizing to Wave Climate

Installation and Deployment

The installing may be slippery as it is an highly big device. The deployment should be done in unagitated sea conditions. Multiple jerks will be required for towing operations.

Operation and Care

Most of the operation and care activities should be comparatively easy carried out on the device itself as the Wave Dragon is a big and stable platform. Access to the platform can be done by boats or even choppers during utmost conditions.

Life Expectancy

Most wave energy devices have a life anticipation of at least 20 old ages. The most critical constituent that has the highest hazard of failure is the moorage system.


Cardinal marker buoys are the standard method to tag out the boundaries of offshore renewable undertakings. It will be deployed out of the manner of major transporting lanes. In instance the Wave Dragon interruptions free from its restraints, the device should be equipped with a GPS so that rapid intercession may be carried out before any more harm occurs.


The chief construction and the two wave reflectors will necessitate to be disassembled offshore so towed individually into a nearby port/shipyard. Cost

The cost for a individual 4MW unit is estimated to be in the scope of $ 10 – $ 12 million USD ( 2004 monetary values ) ( ERPI 2004 ) . This is merely the device cost. Mooring and electrical interconnectedness are non included. Assuming a cost of $ 12million USD, the monetary value per kilowatt is $ 3000 per kilowatt ( 2004 monetary values ) . Taking into history rising prices rates, this should match to about $ 3,500/kW in 2011 monetary values.

Harmonizing to the maker, in a moving ridge clime of 24kW/m, an electricity coevals cost of ˆ0.052/kWh is expected and in a 36kW/m moving ridge clime the corresponding cost of energy will be ˆ0.04/kWh. Assuming an exchange rate of 1 Euro is equal to $ 1.4 USDs, the expected coevals costs in USDs corresponds to $ 0.073/kWh and $ 0.056/kWh severally in 2011 monetary values.

Calculating the electricity coevals cost per kWh for the Wave Dragon of a 4MW Device

The entire electricity coevals cost of a undertaking per kWh = per kWh building cost + per kWh production cost


Useful life = 20 old ages

Capacity Factor = 0.34

per kWh production cost is assumed nothing


Per kWh building cost = _______________Device Cost_________________

( kW Rating x Useful Life x Capacity Factor x 8,760 )

= _______14,000,000____

( 4000 x 20 ten 0.34 ten 8,760 )

= $ 0.059/kWh ( 2011 monetary values )

Per kWh production costs = ______________Production Cost_______________

( kW Rating x Useful Life x Capacity Factor x 8,760 )

= assumed nothing

The entire electricity coevals cost of a 4MW Wave Dragon per kWh = $ 0.059/kWh ( 2011 monetary values ) Development Status

The Wave Dragon is still in the presentation stage with a 7MW demonstrator undertaking in Wales presently delayed due to the recent fiscal crisis. Environmental Impact

The Wave Dragon has comparatively small environmental impact. The biggest impact the Wave Dragon has on the environment is through its moorage system installing and the submerged overseas telegrams deployment. The effects are negligible. Marine life may besides be physically harmed as they go through the turbines. Decision

The chief issue with the Wave Dragon is that it is a low efficiency device as most of the energy contained in the moving ridges is dissipated as they climb the incline to eventually travel through turbines with merely the possible energy gained converted to kinetic energy. The survivability of the Wave Dragon should be of small concern if the moorage is good overdesigned every bit good as being equipped with backup overseas telegrams in instance of failure.

4.2.3. Appraisal of the CETO

Figure 4.10 A CETO unit runing offshore at Fremantle, Western Australia

( Beginning: Carnegie Wave Energy Ltd. ) Device Description

Manufacturer ‘s Description: Unlike other wave energy systems presently under development around the universe, the CETO wave power convertor is the first unit to be fully-submerged and to bring forth high force per unit area H2O from the power of moving ridges. By presenting high force per unit area H2O ashore, the engineering allows either zero-emission electricity to be produced ( similar to hydroelectricity ) or zero-emission fresh water ( utilising criterion contrary osmosis desalinization engineering ) . The system can besides be used for co-production of zero-emission electricity and fresh water. It besides means that there is no demand for submarine grids or high electromotive force transmittal nor dearly-won Marine qualified workss.

Figures 4.11 and 4.12 show the rule of operation of the CETO device.

Figure 4.11 CETO Power Schematic

( Beginning: Carnegie Wave Energy Ltd. )

Figure 4.12 CETO Fresh Water Schematic

( Beginning: Carnegie Wave Energy Ltd. ) Specifications

Device Name: CETO III

Buoyant actuator ( BA )

The BA is the energy aggregation system of the CETO engineering. It is a spherical construction 7m in diameter and 5m high It is manufactured chiefly from steel and gum elastic and weighs about 25 metric tons. The perkiness is provided by both internal fixed and variable perkiness. In operation, the BA will typically sit one to two meters below the ocean surface. The BA contains a proprietary system within it to cut down energy in really high moving ridge energy climes

The CETO device operates in Waterss of deepness & A ; gt ; 25m.

Figure 4.13 shows a more elaborate position of the CETO III device.

Figure 4.13 CETO III

( Beginning: Carnegie Wave Energy Ltd. ) Technical Issues

Structural Elementss

CETO units are manufactured from steel, gum elastic and hypalon® stuffs. These stuffs are all suited for usage in marine environments.

Power Take Off

The BA pumps H2O onshore that goes through Pelton turbines to bring forth electricity.


The CETO units are for good anchored to the sea floor to let for better opposition to beckon gesture therefore capturing more energy compared to slack moored WECs. The building of the foundation on the sea bed may be a spot slippery as it involves high cost and disputing civil technology plants.

Survivability/Failure Manners

The CETO engineering should hold no issues with survivability as they are wholly submerged. It should last even the most utmost conditions.


The maker confirmed that the paradigm successfully produced electricity every bit good as desalinated H2O.

Installation and Deployment

The building of the foundation may affect local site considerations such as ocean floor belongingss. Each site may necessitate customisation of the moorage system. The device will likely be towed to the site and with controlled perkiness the device will place itself at the right deepness so that frogmans may attach the device to the foundation.situate a

Operation and Care

Divers would most likely be needed to set about any care work.

Life Expectancy

Most wave energy devices are expected to last at least 20 old ages.


Marine safety markers will be located around the devices.


The device must foremost be detached from its moorage system so brought into port by towing. Cost

There are presently no cost estimations for the cost of a individual device. Development Status

Prototypes of 1/3rd graduated table have been tested with success in 2006. The commercial graduated table CETO III unit ( 3rd coevals CETO ) was unveiled in October 2010 and its testing in the Waterss off Garden Island in Western Australia. The company is presently set abouting the deployment of a individual independent unit to be followed by a 2MW works and a farther enlargement to a nominal 15MW. The company is besides transporting out probes for attractive sites to implement the CETO engineering, Mauritius being one of them. Environmental Impact

The CETO device will non hold any ocular impact and it should even pull marine life although the building of the CETO device may hold deductions on marine life. Decision

The CETO engineering is surely a really attractive engineering as it addresses two of the universe ‘s major issues: clean electricity production and drinkable H2O production. The survivability of the device should non be a concerned as it is a wholly submersed device that should be protected and easy survive unsmooth conditions. Although the building of the foundation will hold deductions on marine life, the CETO engineering remains an highly environment friendly energy beginning.

4.3.6. Decision

Wave energy is still presently an immature engineering, without a clear consensus on which are finally likely to turn out the successful devices. Additionally, in many states there is a high cost associated with obtaining licenses, deriving licenses and transporting out environmental impact appraisals, which little companies normally find hard to run into unless they benefit from economic inducements. The protection of Intellectual Property for commercial grounds is besides forestalling the rapid advancement of moving ridge energy as research and thoughts are largely kept secret by most companies. Furthermore, one time deployed in free energy markets, wave energy has to vie with established renewable energy engineerings that have benefited from decennaries of research and one million millions of dollars of cumulative investing. Table 4.5 shows a sum-up of costs involved for WECs assessed and it can be deduced that wave energy still remains an expensive manner to bring forth electricity although it is expected that the costs will diminish significantly in the hereafter.


Electricity Generation Cost [ $ /kWh ]

Capital Cost per kW [ $ /kW ]


$ 0.067

$ 4,700

Wave Dragon

$ 0.059

$ 3,500




Table 4.5 Summary of Costss Involved for WECs assessed.



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