Mid-Continent Area Power Pool

1. Mid-Continent Area Power Pool Wind Integration Studies Edward P. Weber August 16, 2007

2. OVERVIEW • Study Background • MN Wind Development • Dakotas Wind Development • Key Issues • Operation Impacts • Reliability Impacts • Wind Modeling Challenges • Wind Impacts on Transmission Lines • Potential Use of New Technology • Summary • References

3. Study Background • MN Wind Development • In May of 2005 the MN Legislature adopted a requirement for a Wind Integration Study of the impacts on reliability and costs associated with increasing wind capacity to 20% of MN retail electric energy sales by 2020. • That’s approximately 4,500 MW more wind generation than exists today • Dakotas Wind Development • Western to perform a “transmission study on the placement of 500 MW of wind energy in North Dakota and South Dakota” • The Dakotas lead the nation in potential wind resources • New WAPA study underway to consider wind-hydro integration

4. Wind Power Resource • 152 proxy tower (wind plant) locations • Modeled results include wind speed, air density, power density, energy production • Temporal and geographic variations are characterized • Benefits shown for geographic diversity & for a sophisticated method of forecasting wind power production

6. Key Issues • Reliable power system operation requires precise balance between load and generation. • Capacity value of power plants depends on their contribution to system reliability. • Output of wind plants cannot be controlled and scheduled with a high degree of accuracy. • Wind generation is becoming large enough to have measurable impact on system operations and planning.

7. Operation Impacts • Regulation: Does wind plants affect or increase the area control error (ACE)? • Load following: What happens if wind plant output decreases in the morning when the load is increasing? • Scheduling: How can committed units be scheduled for the day if wind plant output is not predicted? What happens if the wind forecast is inaccurate? • Committing generating units: Over several days, how should wind plant production be factored into planning what generation units need to be available?

8. Reliability Impacts • Reliability analysis • Loss of Load Probability (GE MARS and NEA Marelli) • Wind generators capacity contribution is based on its influence on overall system reliability • Effective Load Carrying Capability (ELCC), a common reliability measure, is evaluated to determine wind generation reliability impacts • The system’s hourly loads and generation are modeled with and without the wind generators while maintaining a fixed reliability level (one day in ten years) • Results show the ELCC values of approx 12% at 4600 MW • Significant inter-annual variability exists, more years of data would increase confidence

9. Wind Modeling Challenges • Capturing seasonal, diurnal characteristics of wind generation in a “snapshot” model • Insuring that wind and load patterns correlated • “wind doesn’t blow on hot humid days” • “wind blows at night and in spring” • Difficult to capture in a statistical model • Can be addressed by treating wind generation as load modifier • Availability of dynamic wind models • How do we model various control modes (power factor versus voltage control) • Improve wind model representation

10. ND/SD FPLE Projects: 80 MW

12. Wind Impact on Transmission • Wind Needs Transmission Lines • To deliver output from generation to market • Windiest areas are sparsely populated; little load • Most wind energy is off-peak • Off-peak, output has to travel further to serve load • To “hide” output fluctuations in a large system • Area Control Error (“ACE”) • Avoid need for higher spinning reserves

13. Wind Impact on Transmission • Fluctuations in generation output cause voltage fluctuations that must be considered • Turbine MW output: proportional to cube of wind speed • Line & transformer loadings: proportional to generator output (MW) • Line & transformer reactive power consumptions: proportional to the square of current • Result: Transmission system reactive consumption is proportional to sixth power of wind speed !! • Example: if wind speed doubles, reactive power requirement increases by factor of 64.

14. Wind Impact on Transmission Lines • Reactive power supply must be fast enough to keep up with wind generation output fluctuations, (including trip out of wind farm). • FERC reactive power standard is of modest magnitude (.95 pf) and does not require dynamic response. • Prudent developers provide better reactive output capability (.90 pf), and dynamic response • Concentration of wind farms means that future years’ largest single generation contingency could be trip of several wind farms due to a single fault.

15. Potential Use of New Technologies • Study technology-based solutions that can increase the use of existing transmission lines • Technologies studied include: • Static Var compensation • Series compensation • Phase-shifting • Dynamic line ratings • Reconductoring with new conductor

16. Summary • High voltages (345 & 765 kV) required to • achieve reasonable efficiency; • achieve good dynamic stability & voltage stability performance; • To achieve adequate voltage control, we’ll need more • Shunt capacitors • Series capacitors • Static VAR Systems (SVS or SVC) • Additional reactive capability from wind generators (.90 pf rather than .95 pf) would help significantly .90 pf was achievable and proven in 2000. We should be able to do better (lower pf) today.

17. References • 2006 Minnesota Wind Integration Study by MN PUC • Dakotas Wind Transmission Study by Western Area Power Administration • Transmission Needs for “20% Renewables” Penetration of the Minnesota Electric Energy Market by Excel Engineering

18. QUESTIONS ?