1. Operating Reserves Task Force
Erik Ela and Michael Milligan, NREL
July 18, 2012
MIC Meeting

2. Proposal to WECC OC
The VGS is proposing the creation of a task force to analyze the benefits and tradeoffs of different operating reserve calculation methods
The task force would fall under the OC reporting structure, with VGS SMEs prepared to participate
The task force would use tools and expertise from NREL

3. Task Force Objectives
Step 1: Review of current and proposed methods for reserve requirements (continuation of VGS initiative)
Step 2: Use requirements in simulation models and compare ACE and cost metrics among all methods
Step 3: Look through data results to see what influences needs
Step 4: Determine if new reserve requirement method is appropriate for recommendation

4. FESTIV Flexible Energy Scheduling Tool for Integration of VG
SCUC, SCED, and AGC sub-models
Models at high resolution
Typically AGC, the highest resolution is at 2-6 seconds
Models multiple time frames with communication between sub-models
Multiple chances of forecast error and forecast correction
Interval length, interval update frequency, process time and optimization horizon configurable
Flexible operating structures
All modeling timing parameters, how reserves are used, AGC mode of operation, etc.
Deployment of operating reserves modeled
Definitions defined by user
Reserves are held in one sub-model and used in another
Can measure effectiveness of operating reserves in terms of both costs and reliability

5. Operating Reserves and VG
“Operating Reserves and Variable Generation”
Erik Ela, Michael Milligan, and Brendan Kirby
August 2011:
What are the operating reserves standards and policies in practice?
What types of operating reserve methods are being proposed in research?
How does variable generation change the need?

6. Definitions (for this presentation)
Operating Reserves: Capacity above or below that which is scheduled and used to maintain the active power balance of the system during operations
Upward and downward response at all time scales
For multitude of reasons:
Maintain frequency at nominal level (60 Hz in U.S.)
Reduce Area Control Error (ACE) to zero
Assist neighboring balancing authority
Reduce over flow of transmission lines and transformers
Manage Voltage (mostly done with reactive power)
Etc.
Reactive Power Reserves: Reactive Power capacity to facilitate voltage control (not discussed here)
Planning Reserves: Long term capacity to ensure system adequacy (not discussed here)

7. Operating Reserve Categorization
Non-event
Event
Regulating Reserve
Following Reserve
Contingency Reserve
Ramping Reserve
Automatic
Within optimal dispatch
Manual
Part of optimal dispatch
Instantaneous
Non-Instantaneous
primary
secondary
tertiary
secondary
tertiary
Stabilize Frequency
Replace primary and secondary
Replace secondary
Return Frequency to nominal and/or ACE to zero
Correct the current ACE
Correct the anticipated ACE
Return Frequency to nominal and/or ACE to zero

8. Regulation Reserve in North America
Region
Requirement Definition
PJM
Based on 1% of the peak load during peak hours and 1% of the valley peak during off-peak hours.
NYISO
Set requirement based on weekday/weekend, hour of day, and season.
ERCOT
Based on 98.8th percentile of regulation reserve utilized in previous 30 days and same month of previous year and adjusted by installed wind penetrations (described further below)
CAISO
Use a requirement floor of 350-MW up and down regulating reserves which can be adjusted based on load forecast, must-run instructions, previous CPS performance, and interchange and generation schedule changes.
MISO
Requirement made once a day based on conditions and before the day-ahead market closes.
ISO-NE
Based on month, hour of day, weekday/sat/sun.

9. Future methods with consideration of high
penetration of Variable Generation

10. Wind Integration Study Summaries
NYISO/NYSERDA 2005 (10% capacity):
No additional contingency reserves.
Regulating reserves require slight increase based on keeping 3 sigma of variability.
Minnesota 2006 (25% energy):
Regulating reserves based on geometric addition of load and wind variability, with wind variability based on 100 MW wind farms. Used 5 sigma.
Load following reserve based on 2 sigma of five minute changes in net load.
Operating reserve margin (comb. of load following and ramping reserve) based on hourly forecast errors and was a dynamic requirement based on the hourly forecast.

11. Wind Integration Study Summaries
California ISO 2007 (20% capacity):
Detailed observation of CAISO scheduling time lines including ED initiation, completion, and basepoint interval.
Used “swinging door” algorithm to calculate regulating reserves and load following reserves which quantifies needs of capacity, ramp rate, and ramp duration.
Study showed that persistence forecast errors can impact regulating reserves.
All Island Grid Study 2008 (multiple scenarios):
Spinning Reserve based on largest contingency and additional contribution from wind.
Replacement reserve (can be provided by offline units with startup times less than 60 minutes) was calculated by tool that looked at probabilistic distributions of wind and load forecasts. This was based on how the thousands of scenarios for wind and load were reduced to the 5 or 6 used in the simulation that the 90th percentile should be met.

12. EWITS Methods Reserve demand as a function of
Predicted operating levels (wind, load)

13. Questions? Next Steps… Questions? Erik.Ela@nrel.gov

14. European comparison N America (NERC) Europe (ENTSOE)
Regulating Reserve
NERC does not provide for explicit quantitative requirements. Reserve is only used for normal conditions. NERC enforces compliance with Control Performance Standards CPS1 and CPS2. It. The CPS drive the requirements for each BA which are mostly based on time of day and season.
Secondary reserve requirement is explicitly based on statistical equation and mostly comes from load variability. However, secondary reserve is used for both contingencies and normal variations. There are no compliance measures.
Following Reserve
No requirements
Contingency Reserve (Primary)
No requirement. In discussions. Only a frequency bias requirement as part of ACE equation of 1% peak load.
Primary Control (3000 MW) split between TSOs based on load share. Full Response at 200 mHz. 20 mHz maximum insensitivity.
Contingency Reserve (Secondary)
Disturbance Control Standard DCS must recover from contingency in 15 minutes. Enough to recover largest contingency. Many regions require at least 50% to be online/spinning.
Similar requirement to DCS. Return ACE to zero within 15 minutes. Split between primary secondary and tertiary. Sum of secondary and tertiary should be at least as large as largest contingency
Contingency Reserve (Tertiary)
No quantifiable requirement but contingency reserve must be replaced within 105 minutes following contingency.
No requirement
Ramping Reserve