Electrical Systems for Wave Energy Converter Arrays

Fergus SharkeySchool of Electrical and Electronic Engineering

Supervisors: Michael Conlon and Kevin Gaughan

May 17th 2013

Outline

• Introduction and Motivation for Research

• Wave Energy, Wave Energy Converters and Arrays

• Challenges for WEC Array electrical systems

• Techno-economic optimisation and design tools

• Publications

• Future Research

• Conclusions

Introduction

• Graduate of DIT Kevin Street • Employed by ESBI since 2005• Seconded to Wavebob (TPA) 2010 - 2011• Part of ESB Ocean Energy Team• PhD Research in DIT Kevin Street since 2010

Motivation for Research• Lack of industry experience of electrical

systems for WEC arrays – convergence required

• Technology developing before application understood

• WEC developers lack electrical knowledge and can develop devices with inherent electrical issues

4

Wave Energy and Wave Energy Converters (WECs)

• There are numerous ways described to convert wave energy (mostly to electrical power)

• Devices are classed on location (onshore, near-shore, deepwater)

• And capture method (point absorber, terminator, attenuator, oscillating water column)

0o

30o

60o

30o

60o

Up to 6GW ‘practical accessible’ installed capacity

“Wave Farms”

Offshore Wind and Wave Test Sites

Wave Farm Requirements / Challenges• Individual device ratings are lower (~1MW)

• Devices are divergent and may have low capacity factors

• Water depth and distance from shore is larger

• Devices require connection and disconnection for installation and maintenance

• Devices are not fixed structure therefore interface to network is complex

• Array spacing is driven by different factors

• Sites are high energy and cable installation and protection may be a challenge

• Test site experience can help up to a point

Techno-Economic Optimisation

1. State of the art – Offshore Wind and Wave Test Sites

2. Wave Farm Electrical Network Roadmap

3. Key Interfaces

4. Economics of WEC Array Electrical Networks

5. System Issues – Flicker and Grid Access

Macro and Micro Perspective0.1-0.4Hz

Techno-Economic Optimisation and

Design Issues

PublicationsConference Title Date

WREC 2011 Investigation of Wave Farm Electrical Network Configurations May 2011

EWTEC 2011 Dynamic Electrical Ratings and the Economics of Capacity Factor for Wave Energy Converter Arrays

Sept 2011

ICOE 2012 Practical Analysis of Key Electrical Interfaces for Wave Energy Converter Arrays Oct 2012

ICOE 2012 Voltage Flicker Evaluation for Wave Energy Converters – Assessment Guidelines Oct 2012

EWTEC 2013 Impacts on the Electrical System Economics from Critical Design Factors of Wave Energy Converters and Arrays

Sept 2013

UPEC 2013 The Domestic and Export Market for Large Scale Wave Energy in Ireland and the Economics of Export Transmission

Sept 2013

Journal

IET RPG Resource Induced Voltage Flicker for Wave Energy Converters – Assessment Tools May 2013

IJME Maximising Value of Electrical Networks for Wave Energy Converter Arrays June 2013

IET – Ocean Energy Electrical Systems Book

‘Economic Challenges for Ocean Energy Electrical Systems’ July 2013

6 Conference Papers, 2 Journal

Papers and 1 Book Chapter

Selection of Results

0

0.5

1

1.5

2

2.5

3

0% 10% 20% 30% 40% 50% 60% 70%

Rela

tive

Cost

Capacity Factor (%)

Relative Cost of 40 Device Farm Electrical Cabling by MEC Capacity Factor

Relative Cost (20kV)

Relative Cost (33kV)

Network Configuration

Relat. Cost

Radial Network (A) 1.0

Single Return Ring Network (B)

2.58

Single Sided Ring Network (C)

1.8

Double Sided Ring Network (D)

1.69

Star Cluster Network (E)

1.54

Results… continued0.1-0.4Hz

Maximum ΔS/Sk :- Pst = 1, f = 0.4Hz

0.00%

2.00%

4.00%

6.00%

8.00%

10.00%

12.00%

14.00%

16.00%

18.00%

20.00%

22.00%

24.00%

0 2 4 6 8 10 12 14 16 18 20 22 24

X/R Ratio

ΔS/S

k Ra

tio

cosθ : 1

cosθ : 0.95 Lagging

cosθ : 0.95 Leading

Ongoing / Planned Research• Main focus is on completing outstanding papers• EWTEC Paper complete and submitted

– Impacts on the Electrical System Economics from Critical Design Factors of Wave Energy Converters and Arrays

• UPEC Paper ongoing with assistance from DIT undergrad student– The Domestic and Export Market for Large Scale Wave

Energy in Ireland and the Economics of Export Transmission• IJME Journal Paper Revisions due May 2013• Plan to prepare and submit Thesis by end 2013

Conclusions• Organised, comprehensive top-down approach taken to

research.– Electrical Networks for WEC Arrays– Key Interfaces– Economics– System Issues such as PQ and Grid Access

• Disseminated through multiple publications• Thesis will be first complete academic examination of electrical

systems for wave energy converters• Practical focussed research and developed methodologies, tools

and conclusions will be valuable to industry at current stage.