Cost Benefit Methodology for Optimal Design of Offshore Transmission Systems

Transcription

1 DTI Centre for Distributed Generation and Sustainable Electrical Energy Cost Benefit Methodology for Optimal Design of Offshore Transmission Systems Predrag Djapic and Goran Strbac Annex 25: Grid Integration of Offshore Wind Monday 18 th June 2007, DTI London

2 Content Scope Methodology Key results Application to Round II Impact on the regulatory regime design Reports: (1)Cost Benefit Methodology for Optimal Design of Offshore Transmission Systems (2) Grid Integration Options for Offshore Wind Farms

3 Scope Onshore system (Transmission or Distribution) Shoreline Offshore Transmission System Wind Generator Onshore TO / DNO Onshore Grid Entry Point or User System Entry Point Offshore TO Offshore Grid Entry Point Generator Ratings: 1500MW Distance: up to 100km Voltage level: 132kV and above

4 Examples of direct configurations Windfarm electrical system Windfarm electrical system 33 kv 33 kv 220 kv Shoreline Onshore network Onshore network 220kV

5 Example of shared AC connection 33 kv 33 kv 33 kv 400 kv 400 kv Onshore transmission network

6 Example of shared DC connection 33 kv 33 kv 33 kv 400 kv AC DC AC DC AC DC 275 or 400 kv 400 kv DC AC DC AC DC AC

7 Scope of cost-benefit analysis Offshore networks Switchgear reliability, installation cost, platform cost, ratings, maintenance requirements Cable reliability, installation cost, maintenance requirements, ratings Transmission mode (AC vs DC) Compensation requirements Losses Windfarms Wind resource characteristics Typical turbine ratings, availability, cost Windfarm size Windfarm distances from shore Future value of energy and ROCs Impact on onshore system operation Additional reserve costs

8 Concept of cost-benefit analysis Cost Total Cost Cost of curtailed wind energy and losses Optimal network Investment &Maintenance Costs Network Capacity and Redundancy

9 Wind characteristics 45 Frequency (%) Non-diverse wind source Diverse wind source Normalized Wind Output

10 Curtailment and loss factors Constrained Energy (p.u.) Load factor: 0.4 Non-diversified profile Diversified profile Power (p.u.) Profile Load factor (%) Loss factor (%) Non-diversified Diversified 40 23

11 Key results Offshore platform (AC or HVDC) Flexibility is of high value Offshore platform capacity should be about 95% of the maximum export capacity of the wind farm connected. For wind farms with a capacity of 120MW or greater, following an outage (planned or unplanned) of any offshore platform transformer, there should be, at a minimum, 50% of the installed platform transformer capacity remaining. Offshore cable network Optimal capacity installed can be lower than the maximum export capacity of the wind farm connected (X factor)

12 Design of cable networks Wind farm profile X factor (%) Condition - Increase in Cable length (km) Non-diversified wind profile Cable rating >95 Number of cables >91 >88 >86 >84 Diversified wind profile Cable rating >90 Number of cables >85 >82 >79 >77

13 Robustness of design (cable network) Length (km) Fixed value MTTR (months) Energy cost ( /MWh) MTTR case Energy cost case Energy cost ( /MWh) MTTR (months)

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15 33k Robin RiggV Walney Ormonde 1x132kV West Duddon 3x220kV Shell Flats 2x132kV Barrow 1x220kV Hillhouse Rhyl Flats Gwynt Y Mor 2x220k V 1x132k V Burbo Bank North Hoyle 2x33kV Rh yl 1x132k V New substation

16 Teeside 33kV Redcar 33kv New 2 x275 line 2 x132kv Westermost Rough Garton 2 x132kv Inner Dowsing 33kV or 132kV Skegness Lynn 2 x220kv Humber Gateway 2 x220kv Lincs Triton Knoll Docking Shoal 4 x220kv Race Bank 2 x220kv Sall Dugeon East Sheringham Shoal Cromer 33kV Earlham 33kV Caister Scroby Sands

17 Bramford 3x132kV Clacton-on-Sea Greater Gabbard 1X132kV Gunfleet Sands Gunfleet Sands II London Array 3x220kV Kentish flats 1x33kv Herne Bay 2x132kV Thanet Richborough Power Station

18 Impact on the regulatory regime design (compensation scheme) On shore: Generators that obtain Firm Access Rights by purchasing TEC (at TNUoScharges) TEC provides compensation for constrained off generation Offshore: different regime proposed No fundamental difference in approach to design Network design based on long term average value of wind energy curtailed (large number of farms operated over long period of time) Impact of technology limitations: large wind farms supplied with multiple cables (600MW wind farm = 8% curtailment after a loss of a single cable) Risk to individual small projects potentially higher Different treatment will be inconsistent with the standards developed Cost of constraints All Round II projects: 10.8m and 13.1m per annum (post BETTA constraint costs 100m)

19 DTI Centre for Distributed Generation and Sustainable Electrical Energy Cost Benefit Methodology for Optimal Design of Offshore Transmission Systems Predrag Djapic and Goran Strbac Annex 25: Grid Integration of Offshore Wind Monday 18 th June 2007, DTI London