Integrating renewable energy in the NEM: Technical issues

Transcription

1 Integrating renewable energy in the NEM: Technical issues Renewable energy and the National Electricity Market: Issues & Challenges CEEM, 23 November 2005

2 Outline Wind energy as intermittent generation Intermittent generation- definition & issues Trends in wind farm installations in Australia Network-related issues: Connection & security issues Power variability issues Forecasting, ancillary services & power system security 2

3 Energy service delivery in the stationary energy sector Energy service companies focus on end-use options, eg: efficiency, CHP, solar Primary energy forms e.g: coal, gas, nuclear, renewable The electricity supply industry generation transmission distribution Equipment providers The natural gas supply industry treatment transmission distribution end-use equipment delivering energy services eg: light, heat, motive power energy losses & external impacts 3

4 Key issues for the electricity industry Part of the stationary energy sector: In competition with other energy vectors to deliver end-use energy services Significant externalities: Environmental (eg climate change) Social (eg essential good ) Characteristics of electrical energy: A high quality, secondary energy form: Expensive to make but easy to use Flows at the speed of light from generators through the network to end-use equipment: Can be difficult to maintain continuous energy flow 4

5 Specific properties of electrical energy: No cost-effective storage of AC electricity Instantaneous transmission & distribution Energy flows according to network laws: From all generators to all consumers Implications: Supply & demand balance physically at all times: A flow industry that benefits from active demand-side participation Electrical continuum - power station to end-use Cannot assign energy from a particular power station to a particular consumer: pool rather than bilateral physical trade Wholesale & retail trading activities not easily separated 5

6 An electricity trading framework large generators Interchange to other wholesale market regions Primary energy markets transmission network Wholesale Market region risks to end-use energy service delivery Retail Market 1 most consumers embedded generators distribution network Retail Market 2 distribution network distribution network large consumer Retail Market 3 Small consumers, embedded generators & storage should be supported by energy service advisers Wholesale & retail market designs should be compatible Both should include network models 6

7 Australian wind resource (Estimate of background wind (m/s) AGO) 7

8 Comparing AusWEA prediction ( & readily acceptable (RA) wind capacity for Australia ( Qld NSW Vic SA Tas WA Aus Inst MW Approved MW Total MW RA MW (?)

9 Wind penetration in SA & Eleswhere 9

10 Physical context for wind - power system integration (photo courtesy AusWEA) Independently owned wind farms Shared, distributed, time-varying, non-storable wind energy flux Shared electricity network & Power stations of other types End-use equipment providing energy services 10

11 Key issues for wind energy integration Physical complexity: Shared, non-storable, time-varying wind energy flux Shared, non-storable, time-varying electrical energy flow Commercial complexity: Electricity industry infused with short- to long-term risks that are difficult to commercialise (correctly allocate to industry participants) Institutional complexity: Shared issues in wind farm approvals, grid connection & management of power system security High wind energy penetration tests design adequacy of electricity industry restructuring 11

12 Illustration of complexity: managing supplydemand balance in the electricity industry Generator input power Thermal power stations Hydro generators + _ Load electrical power plus network losses Industrial Commercial Wind farms Residential Frequency is a measure of supply-demand balance: always varying due to fluctuations in the power flows associated with particular devices Wind energy is only one of many fluctuating power flows 12

13 Demand forecast errors South Australia,2004 Q4 (NECA, 04Q4 Stats, 2005) 13

14 Timeline for electricity trading in NEM (requires locational detail & active demand-side participation) Financial instrument (derivative) trading & spot market projections Commercial issues (decentralised) Physical issues (centralised) time forward-looking ancillary service (AS) acquisition markets & security assessment Spot market for period t uncertainty increases looking forward spot period t Spot market for period t+1 ancillary service actuation markets for period t spot period t+1 ancillary service actuation markets for period t+1 14

15 Dispatch, Pre-dispatch, PASA, SOO & ANTS (source: NEMMCO) SOO & ANTS (10 yr) Medium Term PASA (2 yr, daily peak) Short Term PASA (7 days, 30 min res, 2hr update) Pre-dispatch, re-bid & final dispatch schedule 0 day 1 day 2 week 1 month 1 year 1 year 2 ST & MT Projected Assessment of System Adequacy support reserve assessment & participant operating decisions. ST PASA projects region demand & reserve for 7 30 min resolution, updated every 2 hours. MT PASA projects region daily peak demand & reserve for 2 yrs, updated weekly. Statement of Opportunities (SOO) & Annual National Transmission Statement (ANTS) are intended to inform generation, demand & network investment decisions (10 year horizon, issued annually) 15

16 Managing variability in supply or demand Time period <4 sec < 5 min 5-10 min min 1-2 days Issue Voltage & frequency perturbations moderated by system inertia & passive damping Ancillary services Central dispatch & spot pricing process Commitment of fast-start plant Commitment of slow-start plant 16

17 Predicted 1% probability change in output for 1000 MW wind in SA ( 17

18 Simulated 6-day dispatch of gen n in SA with 1000 MW of wind ( 18

19 NEMMCO concerns about wind energy (NEMMCO, 2003) Frequency control in normal operation: Frequency regulating service costs ~5 $/MWH Security control - largest single contingency Will wind farms ride-through disturbances? Adequacy of wind farm dynamic models Interconnection flow fluctuations: Exceeding flow limit may cause high spot price Forecast errors due to wind resource uncertainty: Five minute dispatch forecast (spot price) Pre-dispatch & longer term (PASA & SOO) forecasts 19

20 Western Power s proposed wind penalty charge (c/kwh) (Western Power, 2002) 20

21 Wind energy as intermittent generation Renewable energy fluxes are time-varying: Solar, wind, hydro (tidal), biomass, geothermal, wave Wind & solar are non-storable: Can be described as intermittent 21

22 Intermittent generation (NER) National Electricity Rules (NER) definition of intermittent generation: A generating unit whose output is not readily predictable, including, without limitation, solar generators, wave turbine generators, wind turbine generators and hydro generators without any material storage capability Issues identified by NEMMCO: Forecasting & reserves; frequency control ancillary services (FCAS); voltage control; management of network flows; modelling & security assessment 22

23 Network issues for wind farms #1 Networks are shared, centrally planned resources: Must limit network disturbances caused by wind farms Wind farms must survive disturbances from the network Renewable resources are often distributed differently from fossil fuel resources: Weak network conditions likely to be more common in Australia & New Zealand than Europe or North America Network must be built to carry peak flows: Want good estimates of aggregation & seasonal effects Benefits of staged development of wind resources: Network savings; reduced voltage & frequency impacts 23

24 Network issues for wind farms #2 Wind turbine starting & stopping transients: Severity can be alleviated by soft-start & high wind-speed power-management Some wind turbine designs: May cause voltage distortions: Harmonics &/or transients May have poor power factor, eg: Uncompensated induction generator May not ride-through system disturbances Temporary voltage or frequency excursions 24

25 Wind turbine type comparison (Slootweg & Kling, 2003, 25

26 Size of wind turbines used by Western Power ( 26

27 Wind turbine starting transients for Esperance 2 MW wind farm 9 x 225 kw turbines with squirrel cage IG Magnetisation inrush current may cause a voltage dip - starts should be spaced out (Rosser, 1995) 27

28 Network connection issues & examples Approximate ability of a transmission line to accept a wind farm: 66kV 30MVA 132kV 100MVA 330kV 200MVA Constraints may be determined by several factors: Thermal, voltage, fault clearance, quality of supply Thermal ratings depend on line temperature & wind speed Relevant wind farm rating is its maximum output, not the sum of turbine rated powers: Coincident output of the connected wind turbines 28

29 Conclusions Intermittent generation: Brings new challenges for electricity industry restructuring (technical, market design, regulation) Separate category only appropriate for small penetrations Wind energy: The first significant form of intermittent generation Network connection issues: Often distributed differently to traditional resources Forecasting & system security issues Regional, rather than project specific 29