Assessing wind power impacts on the flexibility of a power system

1. Mark O’Malley, Michael Milligan, Hannele Holttinen Assessing wind power impacts on the flexibility of a power system

2. Flowchart of a Wind Integration study • Reserverequirements • Flexibility assessment • Production cost simulations: • Unit commitment and Economic Dispatch

3. Inputs • Important input data: • Wind power (hourly or faster) • Load (synchronized with wind) • Generation data including • Ramp rate • Minimum run levels • Min up-time, down-time • Heat rate • Other relevant constraints • Dispatch time step • Commitment time step; whether rolling, lock-down time, etc. • Inputs from other boxes in the flow chart

4. Additional Wind Induced Reserve • Contingency reserve has basic (N-1) rules – wind rarely (if ever) influences • Operating reserves for normal operation (load variability and forecast errors) do not have set rules (e.g. U.S. Vs. European reserve categories !) • this is the part that wind will influence

5. Reserve requirements

6. Estimating Reserve Requirements • Manymethodsusedto estimateincreasedue to windpower • Drawbackof deterministicmethodsaddingupextremecasesfromload / contingencyevent / wind is thatwillover-estimate • Simplestatisticalmethodcombiningwind and loadvariability and forecasterrors exceedencebetterthan n timesσ as windnotnormallydistributed. • Risk/reliabilitybasedmoreadvancedmethodsalsorecommended. • Dynamic reserve is recommended. • Forecast errors day-ahead will bring high reserve requirements – needed for Unit Commitment but operationally we can update

7. Increasing demand for Reserve

8. Recommendations for Reserves • Method: • not just adding up extreme events but combining with risk/reliability levels. • dynamic not static • Timing is important - horizon etc. • Beware • Definitions are different

9. Flowchart of a Wind Integration study • Reserverequirements • Flexibility assessment • Production cost simulations: • Unit commitment and Economic Dispatch

10. WHAT IS FLEXIBILITY? “Flexibility is the ability of a system to deploy its resources to respond to changes in net load, where net load is the remaining system demand not served by variable generation”

11. Flexibility in a power system Installed • Operational (short-term) • Constrained by previous unit commitment • What can be dispatched or accessed via markets? • Operational (Mid-Term) • Constrained by existing (planned and built) sources of flexibility • Unit commitment problem to ensure sufficient committed generation for flexibility requirements • Planning (long-run) • Necessary but not sufficient for real-time flexibility provision • Needs an assessment of long-term flexibility requirements Committed Dispatched Internal resources External resources

12. Production Cost Simulation Meibom, P., Barth, R., Hasche, B., Brand, H., Weber, C. and O´Malley, M.J., “Stochastic optimisation model to study the operational impacts of high wind penetrations in Ireland”, IEEE Transactions on Power Systems, Vol. 26, pp. 1367 - 1379, 2011.

13. Ramp ERCOT – 18/19th April 2009 Wind Power Output (MW) +3,039 MW in 1 hour Source: http://www.nerc.com/docs/pc/ivgtf/IVGTF_Task_1_4_Final.pdf

14. Sources of Flexibility Need to modelled Facilitators Sources Sink Physical Planning • Conventional Generation • Electricity Storage • Interconnection • Demand Side • Variable Generation • Load • Outages • Solar • Wind etc.. • Transmission Networks • Fuel Storage Institutional Operations • Forecasting • Gate Closure • Grid Codes • Market Resolution • Balancing Area Size • Unit Commitment Markets Economic • Ancillary Services Reparation • Cycling Costs

15. Transmission playing its part Note the sag on the line

16. Available Flexibility The purpose of this graph is to demonstrate the variable flexibility that exists in the market place to accommodate wind. http://www.aeso.ca/gridoperations/14246.html

17. Quantifying Flexibility

18. The FAST Method Step 1: Identify flexible resources Step 2: are they available? Step 3: what are the needs? Step 4: Compare need & resource Optimise resource /deploy additional

19. FlexibilityMetrics Lannoye, Flynn & O’Malley, Evaluating Power System Flexibility, IEEE Trans. Power Systems, in press, 2012.

20. Effects of Cycling

21. Production Cost Simulation Comparison methods e.g. varying output or block output ?. Meibom, P., Barth, R., Hasche, B., Brand, H., Weber, C. and O´Malley, M.J., “Stochastic optimisation model to study the operational impacts of high wind penetrations in Ireland”, IEEE Transactions on Power Systems, Vol. 26, pp. 1367 - 1379, 2011.

22. Recommendations • Flexibility assessment • Dispatch and Unit Commitment models • Iterate between them or develp a new method of assessment • Key Messages • Representativeness of input data for wind power variability and uncertainty • capturing system characteristics and response through operational simulations and modelling; • examining actual costs independent of tariff design structure and

23. Mark O’Malley, Michael Milligan, Hannele Holttinen Assessing wind power impacts on the flexibility of a power system