Large Wind Integration Challenges for Operations / System Reliability

1. Large Wind Integration Challenges for Operations / System Reliability By : Steve Enyeart, BPA With contributions from: Bart McManus, BPA Roy Ellis, BPA Dmitry Kosterev 2/12/08 Photo courtesy of PPM Energy

2. NW Wind Integration Action Plan Summary • NW added ~900 MW of wind in 2007, >2200 MW Total now • Total Wind in the NW Forecast 3500 - 3800 MW by end of 2009 • Northwest Wind Integration Forum formed to Address … • Transmission System Expansion and Funding • Wind Integration Costs and Cost Shifts from Load to Wind Generation • Operating Issues including Regulation and Balance of Hour • A Regional Wind Forecasting System • ACE Diversity Interchange and other Control Area sharing ideas to increase flexibility for Wind Integration • Severe Wind Ramps Impact on Reliability

3. Impact of State RPS Requirements • Montana, Washington, and Oregon have implemented Renewable Portfolio Stds • According to the estimates from the NW Power Council: • Oregon ~15% by 2015 - 650 aMW, 25% by 2025 • Washington ~7.5% by 2015 – 672 aMW, 15% by 2020 • Wind is the primary Renewable Resource at this time • Assume 1400 aMW @ 30% equals 4700 MW peak capacity. This and export of 2000 MW would be ~7, 000 MW by 2015. • BPA has provided interconnection for 3500 MW at various locations and Rock Creek, John Day 500 kV interconnects (1200 MW each). • Other NW Utilities have connected over 800 MW with plans for more.

5. Wind Gen. within BPA Control Area (BAA) • BPA integrated 650 MW in 2007, total ~1400 MW, may be 3000+ MW by late 2009 • Queue requests exceed 10,000 MW under study (due in part to BPA transmission location relative to wind resources) • Present 1400 MW, ~15% of 9000 MW Peak BPA Load, higher than any BAA in US. • BPA Addressing: • Intra-hour increases in total Balancing* requirements • Impact of severe wind ramps on Balancing Capacity • Cost/Cost Shift of add’l Balancing Capacity • Need for Voltage Support, Dynamic VAr * Balancing = within 1 Minute Regulation (AGC response) + Load Following for balance of hour schedule – see next slide

6. Within Hour Balancing – Definitions • Regulation – minute-minute difference between generation and load (AGC). • Following is defined as the change in the general trend over a specific time interval 5, 10, 15 or even 60 minutes. Within-Hour Balancing = Load Following + Regulation = + Within Hour Balancing defined as the with-in hour generation adjustments for variances of Load / variable (wind) Generation – New Requirement for Wind Generation

8. Wind Balancing Analysis As previous slide demonstrates, Wind Generation is quite variable, impacting BAA Balancing and total AGC Capacity Requirements. The next slide shows the balancing required for a recent large wind ramp. Not nearly as extreme as the previous slide would have implied. The 2nd slide shows the balancing required for simulated period for total wind of 2700 MW. Note the peak Balancing required.

9. Regulation versus Following (Wind Example)

10. 2700 MW Simulated Balancing Capacity Requirements 2nd 3 week Period Simulation

11. Wind Balancing Analysis (Cont.) The next slide shows the problems with scheduled vs actual (even with hourly adjustments) Note that scheduled trails actual and misses peaks and valleys. This increases Within-Hour Balancing reserves requirements. Better forecasts would reduce this problem. The 2nd slide is Frequency Distribution Analysis for total Balancing Capacity requirements assuming 5000 MW.

12. Schedule Vs. Actual – 12/27 – 12/29 2007 <= Actual Note: - Wind acts more like load - generation seldom matches schedule, and - Good hourly schedule will still increase Balancing Capacity requirements.

13. Example: Frequency Distribution of Wind Generation Variation

14. Wind Within-Hour Balancing Analysis • The next slide BPA estimates the increase in Balancing Capacity required for up to 2880 MW.* • Cumulative Frequency Distribution method used to calculate increase in Balancing Capacity, assuming 97.5% of Regulation and 95% Balance of Hour events are covered. • The “Tail” events from the previous slide indicate that some wind ramps could exceed Balancing Capacity. Options include: • Increase Balancing Capacity – More cost to all wind farms • Wind Ramp Controls to limit severe ramps • Other BA tools like shared ACE *Analysis includes using locations of proposed wind sites in BPA queue to provide simulation of locational diversity.

16. Wind Ramps • Wind Ramps are large unscheduled changes in the output of a wind farm or the aggregate of all wind farms in a Control Area. • As seen above Wind increases Balancing Capacity Requirements. • BPA now Concerned for Reliability Impacts (CPS2 Violations). • Late fall 2007 BPA experienced increase in within-hour Balancing due to wind. CPS2 Violations are also increasing. • Wind Ramp Controls now considered necessary and may be implemented in some form in the next year.

17. Improved AGC Response Improving the AGC response to deviations of the load-generation balance due to wind generation is one option to reducing overall wind integration costs. BPA Proposal: Modify AGC Algorithm (Feed – Forward AGC) Present AGC = Actual Load – Scheduled Generation (includes Wind schedules) New AGC = Load Forecaster* – Scheduled Generation – Forecasted Wind Generation Goal is to anticipate AGC response, reduce overshoot, cycling of units (wear and tear) and minimize generation on stand-by. * Load Forecaster module to also be included in FF AGC.

18. Wind Forecast Module for FF AGC • Develop 5 minute within-hour wind generation forecasts enhanced with weather and regional monitoring of wind generation. • Uses Data (MW, wind speed, direction, unit status) from WTG’s in Wind Farm, from all wind farms in BAA • Other goals: • Provide output to adjust FCRPS generation schedules (mid-hour adjustment), reducing AGC units on stand-by or set aside for AGC. • Provide mechanism to automate Wind Ramp Limits control if Balancing reserves below minimum capability (next 10 – 30 minutes). • Pilot Project underway with 3-Tier to provide ‘Forecasts’ • Target Mid 2009 to have Pilot FF AGC implemented

19. BPA Wind Integration Rate • Traditionally Loads have paid for regulation and load following as generation deviations were rare – not so for wind. • BPA held Public workshops to develop a new Wind Integration Rate for within-hour balancing. (Public review still underway). • Rate to be applied to Wind Generation • Rate to be effective for a one-year period, FY 2009 • Rate will be based on installed capacity during rate period • Assumes 2240 MW up to 2880 MW in BPA Control Area • Estimates up to $23M needed for FY09 rate period

20. Wind Farm Dynamic Voltage Performance • Early WTG designs were mostly induction machines (used switched caps for PF correction) • Voltage control was limited to switched Caps on 34.5kV bus • Integration of large amounts of wind generation requires dynamic reactive control capabilities • Need to match Synchronous Machines performance to maintain system performance and line loadings. • Next slide compares effect of 2700 MW of wind on grid without Dynamic VAr support to synchronous generation response

21. Dynamic Simulations - Malin 500-kV bus voltage Baseline 2700 MW of Wind with No Voltage Control replaced 2700 MW of hydro + thermal

22. Wind Farm Voltage Controller Requirements • Voltage control of wind farms required to provide primary voltage support for system events. Options include: • High side Voltage Control (may be overly sensitive) • Low side Voltage Control (may be too insensitive for system response) • Line Drop reactive compensated Voltage Control (Qdroop) • Line Drop adjustable up to15% (mid-line subgrid applications), for 7.5% typical applications allows for fine tuning of VC. • Next slide demonstrates Line Drop options

23. Voltage Control Types POI Voltage High Side Voltage Control VC with 7.5 % Reactive Droop VC with 15% Reactive Droop ~ Low Side Voltage Control Power Factor / VAR Control POI Reactive Power

24. Wind Farm Dynamic Performance Summary • For Large Wind Generation BPA Requires - Controllable Dynamic VAr devices required (either WTG or DVAr devices) • Voltage control mode required (no PF control) to provide primary voltage support for system events • Type of voltage control depends on application, but Line Drop compensation preferred for flexibility of Application. • Smaller Wind farms or those in mid-line or remote areas will still need to be evaluated on case-by-case basis.

25. Summary Wind Integration for BPA • BPA continues to study a lot of wind interconnection requests (presently >9000 MW in study queue) • Total ~1400 MW now interconnected and operating, may be 3000+ MW by late 2009. Operation Challenges to be Addressed: • Regulation/Balance of Hour AGC/reserve requirements are increasing and are being addressed with new rate • FF AGC should reduce impact and cost of Wind in BAA • Wind ramp controls may be needed for Reliability • Dynamic VAr for Voltage control needed to maintain system capacity and reliability

26. Questions?