CONNECTION OF OFFSHORE WIND ONSHORE -- Some Food for Thought to Aid the Discussion at the Post-Conference Workshop

Transcription

1 Deeper Water Offshore Wind Conference by GIC CONNECTION OF OFFSHORE WIND ONSHORE -- Some Food for Thought to Aid the Discussion at the Post-Conference Workshop Dr Chuan Zhang The Crown Estate, UK London, 8 th March 2012

2 CONTENTS 0. A brief introduction to The Crown Estate 1. Overview of connecting ashore 2. Connection btw generator and collection station voltage, configuration and power quality Connection A brief introduction btw offshore to The and Crown onshore Estate 4. Transmission cables and cable corridors 5. Offshore grid regulation and coordination 6. Summary (not Conclusions)

3 A BRIEF INTRODUCTION TO TCE Urban Estate Marine Estate Rural Estate Windsor Estate (park only) Property, land and seabed owner, established broadly in its current form 250 years ago; Not part of the Government, not a regulator; but is a public body operating under The Crown Estate Act 1961; Net revenue surplus paid to the Government ( 230.9m, FY2010/11) with a portfolio capital value of 7.3bn; Investment of 120m in offshore energy development.

4 THE MARINE ESTATE OF THE CROWN ESTATE Owns and manages 22,000km of coastline ~50% UK foreshore almost all seabed out to 12nm Out to 200nm 88 million hectares of seabed Energy rights (not fossil fuels) Mineral rights UK 12 nm Limit UK Continental Shelf

5 CONTENTS 0. A brief introduction to The Crown Estate 1. Overview of connecting ashore 2. Connection btw generator and collection station voltage, configuration and power quality Connection A brief introduction btw offshore to The and Crown onshore Estate 4. Transmission cables and cable corridors 5. Offshore grid regulation and coordination 6. Summary (not Conclusions)

6 OVERVIEW OF CONNECTION ASHORE Large Wind farms Array Cable Offshore Substation Transmission Cable Onshore Substation Main AC network An Offshore Driven AC Transmission System Source of the pictures: ABB & ODIS 6

7 OVERVIEW OF CONNECTION ASHORE Distant Wind farms Offshore AC platform Offshore Converter DC cable transmission Onshore Converter Main AC network An Offshore Driven HVDC Transmission System Source of the pictures: ABB 7

8 SCOPE OF THE DISCUSSION Array configuration Likely the default and common way Potential alternative ways (not to be ruled out lightly) Transmission from offshore to shore Cables and cable corridors Regulation & coordination in offshore grid development C Zhang 8

9 CONTENTS 0. A brief introduction to The Crown Estate 1. Overview of connecting ashore 2. Connection btw generator and collection station voltage, configuration and power quality Connection A brief introduction btw offshore to The and Crown onshore Estate 4. Transmission cables and cable corridors 5. Offshore grid regulation and coordination 6. Summary (not Conclusions)

10 POPULAR PRACTICE Voltage at generator terminals: Most turbines: <1kV e.g. Bard 5MW, 690V Siemens 3.6MW, 750~690V Repower 5MW, 950V Vestas 3MW, 1kV Larger turbines: >1kV e.g. Areva 5MW, 3.3kV Vestas 7MW, 3.3kV Repower 6MW, 6.6kV Power quality on leaving turbine: Standard quality (exc some reactive power compensation) Array configuration: Turbine transformer to step up to 33kV (or 66kV potentially); String by string (radial or looped) 10

11 POSSIBLE ALTERNATIVE WAYS? Voltage at generator terminals: At 11kV~22kV Power quality on leaving turbine: Not fully cleaned Clean-up onshore Array configuration: No turbine transformer Group step transformers to step up from 11kV (or 17.5 or 22kV) to 132kV No main offshore step-up transformer Can be in starburst or circular layout etc 11

12 CONTENTS 0. A brief introduction to The Crown Estate 1. Overview of connecting ashore 2. Connection btw generator and collection station voltage, configuration and power quality Connection A brief introduction btw offshore to The and Crown onshore Estate 4. Transmission cables and cable corridors 5. Offshore grid regulation and coordination 6. Summary (not Conclusions)

13 POSSIBLE WAYS OF TRANSMISSION connection offshore wind transmission systems Source: Qin, N; You, S; Xu, Z, Offshore Wind Farm Connection with Low Frequency AC Transmission Technology 2009, IEEE 13

14 LOW FREQUENCE TRANSMISSION Power capacity of AC and DC transmission corridors, utilising cables Source: Breuer, W; Christl, N, Grid Access Solutions Interconnecting Large Bulk Power On / Offshore Wind Park Installations to the Power Grid, GWREF 2006, October 23-27, Beijing, China. 14

15 LOW FREQUENCE TRANSMISSION Swedish traction power supply network Source: 15

16 LOW FREQUENCE GENERATION 25Hz Adams Power Station generators at Niagara Falls in the 1920s Source: 16

17 TRANSFORMER AT CONVERTER STATION dc dc Vac dc Purpose of the transformer in converter station: Change the voltage levels to match the need on AC and DC sides. Act as an electrical isolation or decoupling btw AC and DC sides. One Indicative relationship of the (max) voltage of AC and DC sides may be that (for a VSC converter) when Vac=400kV, Vdc would be 320kV (if there is no voltage step-up or down by the converter transformer). dc 17

18 CONTENTS 0. A brief introduction to The Crown Estate 1. Overview of connecting ashore 2. Connection btw generator and collection station voltage, configuration and power quality Connection A brief introduction btw offshore to The and Crown onshore Estate 4. Transmission cables and cable corridors 5. Offshore grid regulation and coordination 6. Summary (not Conclusions)

19 UK offshore activity plan Seabed and foreshore cables (power / telecomm) and pipelines are already crowded.

20 PRACTICE IN CABLE CORRIDOR ROUTEING Conflict check : One of the industry practice in routeing subsea infrastructure may be to begin with a straight line between the points to be connected and to deviate where necessary to avoid constraints and exclusions. Exclusions are areas to be avoided including areas of activities, obstacles and existing structures. Then survey work along the preferred route Then planning and consenting process progressed to point of route selection on shore (inc. land agreements) 20

21 WHAT IS A CABLE CORRIDOR? Onshore substation Each Designated Area is a 30m wide strip of seabed between the shore and the offshore substation, to accommodate a single power cable. Offshore Wind Farm Landing points Dredging Restriction Zone which means the area extending to 235m either side of the Designated Area. Offshore substation A cable corridor could comprise upto: N x 30m (N is the number of circuits/cables) + 2 x 235m 21

22 THINGS CAN GET COMPLICATED 22

23 HOT TOPICS ON CABLE AND CORRIDORS Definition of a cable corridor In place (as shown in preceding slides) Separation distance btw cables and turbines To be place shortly by Subsea Cables UK The Crown Estate has also got work done (see next slide) Separation distance btw cables Work is under way by The Crown Estate in coordination with Subsea Cables UK UK SQSS review will also take this into account Cable supply chain The Crown Estate has also got work done and will share the results Installation guidance Work is under way by a Europe-wide group 23

24 PROXIMITY BTW CABLES AND TURBINES 24

25 CONTENTS 0. A brief introduction to The Crown Estate 1. Overview of connecting ashore 2. Connection btw generator and collection station voltage, configuration and power quality Connection A brief introduction btw offshore to The and Crown onshore Estate 4. Transmission cables and cable corridors 5. Offshore grid regulation and coordination 6. Summary (not Conclusions)

26 ISSUES ON REGULATION & COORDINATION Immediate Issues: Oversizing and coordinated development Transmission charging on offshore schemes Standardisation Technology nurturization Longer term issues: Single purposed interconnector vs wind power pick-up Wind driven vs trade driven Do it alone vs do it together Smart grid/electric vehicle/energy storage to mitigate the variability (intermittency) of wind in addition to improving forecast 26

27 LARGER LINKS HVDC, 150km offshore A is 500MW; B is 500MW HVDC, 150km offshore A is 500MW; B is 500MW 510m 510m 1020m (capex) 720m (capex) Saving: 300m or 30% (But partial redundancy is lost) All numbers are hypothetical and for illustration only 27

28 HUB CONNECTION Source: OffshoreGrid.eu 28

29 HUB ONLY WORKS IN SOME CASES 2GW 250MW 200MW 300MW 500MW 450MW 300MW 2GW 2GW 29

30 ANY NEED FOR INTERCONNECTION? 2GW 2GW This link will increase the cost of offshore network BUT may be helpful for resilience reason or for replacing onshore reinforcement 2GW 2GW 30

31 COORDINATION OF CAPACITY RATING Coordination of the Capacity Rating btw Transmission Module and Generation Modules If there is a possibility to be of use to a second generation projects, a transmission module built for the first generation project should be oversized for the benefit of lower cost overall. Coordination of the Capacity Rating btw Generation Capacity and Export Capacity It may be possible to make the installed capacity of an offshore wind farm higher than the capacity of its individual export substation/cables to make full use of the transmission rating potential and life potential, thus reducing overall cost. 12-Mar-12 31

32 OUTSTANDING ISSUES ON CHARGING Immediate outstanding issues: Local treatment not resolved. This leads to Over-recovery from offshore generators and unexpected subsidies to onshore generation. If resolved, this could lead to a reduction of annual opex of offshore wind by 5% of wind farm annual revenue. TNUoS charges recover offshore transmission costs over 20 years, not 50 as onshore, artificially inflating charges. Suitability for future: The charging would not work for integrated offshore transmission. Forthcoming integration of electricity networks in the EU. 32

33 NEED FOR HIGH LEVEL STANDARDISATION Geographical Areas Number of Designs Ratings (MW) Voltage (kv) Operational Dates GENERATION MODULES (Offshore Substations or Collector Stations) UK 12 90~368MW 132~150kV Scandinavia and Benelux 9 110~400MW 132~220kV Germany 6 60~400MW 110~150kV Other countries 0 n/a n/a n/a In total: 27 different Power Module designs used in 32 Generation Blocks (Offshore Substations) Based on a review of all offshore transmission schemes for wind power in the world at above 100kV. 33

34 NEED FOR HIGH LEVEL STANDARDISATION Geographical Areas Number of Designs Ratings (MW) Voltage (kv) Operational Dates TRANSMISSION MODULES (Export Circuits fm Offshore to Onshore) UK 12 90~184MW 132~150kV Scandinavia and Benelux 9 120~400MW 132~220kV Germany 7 60~400MW 110~150kV (AC) 150~320kV (DC) Other countries n/a n/a n/a In total: 28 different designs (export circuits, including 4 HVDC schemes) used in 41 actual Transmission Modules. Based on a review of all offshore transmission schemes for wind power in the world at above 100kV. 34

35 NEED FOR HIGH LEVEL STANDARDISATION It is possible to have a win-win case if the industry can work towards a less divergent and more harmonised design approach. Key Features: a set of 3-4 standardised generation modules, and a set of 3~4 transmission modules Key Benefits: 1. economies of scale and capex reduction; 2. safer in operation and better operational performance; 3. better availability of spares; 4. better skill sets / training around standardised designs; 5. less pressure on supply chains; 6. better inter-operability and connectivity if needed. 12-Mar-12 35

36 ISSUES ON REGULATION & COORDINATION Immediate Issues: Oversizing and coordinated development Transmission charging on offshore schemes Standardisation (TCE has proposed a potential enabling action) Technology nurturization (TCE has made a proposal) Longer term issues: Single purposed interconnector vs wind power pick-up Wind driven vs trade driven Do it alone vs do it together Smart grid/electric vehicle/energy storage to mitigate the variability (intermittency) of wind in addition to improving forecast 36

37 MULTI-PURPOSED INTERCONNECTORS Source: OffshoreGrid.eu

38 MULTI-PURPOSED INTERCONNECTORS 1. The two options give different and incomparable operational capabilities. 2. The choice btw the two options needs a much wider deliberation beyond transmission of wind power as it may be purely trade driven. Source: OffshoreGrid.eu

39 CONTENTS 0. A brief introduction to The Crown Estate 1. Overview of connecting ashore 2. Connection btw generator and collection station voltage, configuration and power quality Connection A brief introduction btw offshore to The and Crown onshore Estate 4. Transmission cables and cable corridors 5. Offshore grid regulation and coordination 6. Summary (not Conclusions)

40 KEY POINTS WE HAVE DISCUSSED Array configuration Transmission from offshore to shore Cables and cable corridors Likely the default and common way ~1kV at gen terminal; 33kV (or 66kV) after turbine transformer; Array (string by string) at 33kV; Step up to 132kV (150kV) or 220kV at main offshore substation; Power quality clear-up at turbine. <50km ish, 50Hz AC >50km ish, HVDC (all HVDC converter stations will have a transformer) Individual development with improved corridor definition and installation Potential alternative ways (not to be ruled out lightly) 11~22kV at gen/turbine terminal; Small array at 11~22kV then step to 132kV or 220kV locally; Although there will be more local substations, there will be no need for a main step-up transformer (and possibly ac substation) Possibility to negate converter transformer; Possible to go for a low frequency AC rather than DC in some projects. Proximity btw power circuits Strategic corridors/ potentially collective surveying etc Regulation & coordination in offshore grid development Single project approach; Do it alone approach. C Zhang 40 Anticipatory consenting & investment Standardisation in design; Use of larger transmission modules Multi-purpose interconnectors Energy storage/smart grid