1 Challenge the future

Miguel Prado, Henk Polinder

Direct Drive in Wave Energy Conversion

- AWS Full Scale Prototype Case Study

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Structure

1 Introduction

2 Wave Energy Overview

3 AWS Wave Energy Converter

4 PTO of AWS Pilot Plant

5 Conclusions

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Wave Energy is not new ...

Source: Christine Miller (www.outsidelands.org/wave-motor.php) and Power Magazine 1911

Holland Wave Motor

California, USA, 1895

US Wave Motor Corporation

New Jersey, USA, 1911

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Different technologies being developed

Pelamis, Scotland

Wavestar, Denmark OPT, USA

OWC Pico, Portugal

Source: www.wavec.org; www.emec.org.uk

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Wavedragon, Denmark

OEbuoy, Ireland

Wavebob, Ireland

Aquamarine, Scotland

Source: www.wavec.org; www.emec.org.uk

And many more …

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Only a few direct drive applications ...

Source: www.wavec.org; www.emec.org.uk

AWS 2MW, The Netherlands

Oregon Univ. 10kW, USA Uppsala Univ. 10kW, Sweden

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Structure

1 Introduction

2 Wave Energy Overview

2.1 Waves (Fundamentals & World Resource)

2.2 Wave Energy Conversion

3 AWS Wave Energy Converter

4 PTO of AWS Pilot Plant

5 Conclusions

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Waves, a byproduct of solar energy ...

Source: Hagerman, G., “Wave and Tidal Power: Projects and Prospects”, CEAG, 2005

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No net mass transport (particles follow elliptical orbits)

Skin effect (motion decays exponentially from surface)

Energy storage (kinetic & gravitational potential)

Dispersion in frequency (T=6-12s => Vg=5-10m/s)

Power transmission by pulses (2 x wave frequency)

P

Monochromatic Waves

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time

MAXPP 5.0

P

P

Monochromatic Waves

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Real Seas (Polychromatic)

P

MAXPP 1.0

P

time

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Source: “Wave Energy Utilization in Europe – Current Status and Perspectives”, CRES , 2002 ; Kinsman, B., “Wind Waves”, Prentice Hall, New Jersey, 1965

World Offshore Wave Resource ~2 TW

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~

~Wave

(variable heightand period)

Electricity - Grid(constant voltageand frequency)WEC

Wave Energy Conversion

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Wave(variable height

and period)

Captor PTO (Power Take Off)

2 ... N1

Electricity - Grid(constant voltageand frequency)

Wave Energy Conversion

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Structure

1 Introduction

2 Wave Energy Overview

3 AWS Wave Energy Converter

3.1 Concept

3.2 Pilot Plant

4 PTO of AWS Pilot Plant

5 Conclusions

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AWS Concept

• Submerged Device (better survivability)

• Variable Volume (higher performance)

• Adjustable Natural Period (higher performance)

• Direct Drive PTO (higher reliability & performance)

• Water Brakes (additional safety)

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• Captor diameter:9.5m

• Captor stroke: 7m

• Max. PTO Force: 1MN

• Nominal speed: 2.2m/s

• Deployment: easy & reversible

• Test Location: North Portugal (44m)

• Test Period: < 1 year

6 km ~

~

Landstation

15kVGrid

AWS Pilot Plant

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Pilot Plant Construction (2000-2001)

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Pilot Plant Final Submersion (2004)

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Structure

1 Introduction

2 Wave Energy Overview

3 AWS Wave Energy Converter

4 PTO of AWS Pilot Plant

4.1 Design

4.2 Construction & Installation

4.3 Offshore Tests Results

5 Conclusions

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Design Choices (Linear Generator)

• Topology:

3-phase longitudinal flux PM machine

Magnets on the translator

Materials:

NdFeB magnets

Copper windings

Laminated iron (stator core), solid back iron (translator)

• Geometry:

Flat, double-sided machine (balance of magnetic forces)

Translator > stator (higher overlap)

Slots/pole/phase: 1

• Cooling: water cooled

• Power electronics: current source inverter

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Design Options (Linear Generator)

T o p M id B o t t o m

T r a n s l a t o rS e g m e n t

S t a t o rS e g m e n t

T r a n s l a t o r P o s i t i o n

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Design Options (Converter)

Grid15kV, 50Hz

AC/AC Converter

Generator0-6kV, 0-21Hz

3kV/3kV/15kV2x1330kVA

AC/AC Converter

RDC

Generator0-6kV, 0-21Hz

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Construction (Translator)

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Construction (Stator)

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Installation (Stator)

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Installation (Stator)

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Installation (Translator)

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Installation (Translator)

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Installation (Land Station)

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Offshore Test Results (Resistor Bank)

~

~

15kVGrid

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Offshore Test Results (Grid Connected)

14:00 14:15 14:30 14:45 15:00 15:150

50

100

150

200

250

PD

C (

kW

)

14:00 14:15 14:30 14:45 15:00 15:150

20

40

60

80

100

120

RD

C (

)

~

~

15kVGrid

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Structure

1 Introduction

2 Wave Energy Overview

3 AWS Wave Energy Converter

4 PTO of AWS Pilot Plant

5 Conclusions

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Conclusions / Lessons learnt

• AWS designed, built and tested

• Test results demonstrate the operating principle

• Only test results at low power levels

• Difficulties of submersion operation underestimated

• The principle of AWS is very simple, but all kinds of secondary

systems compromise reliability

• Economic viability is not easy

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Thank you very much !