1. Operating Reserves and Variable Generation
Erik Ela, Michael Milligan
January 28, 2012
WECC Webinar

2. National Renewable Energy Laboratory Innovation for Our Energy Future
Outline
Overview: Operating Reserve categories
Operating Reserves in Practice
WECC
Other areas (North America and Europe)
Operating Reserve Methods with High VG
FESTIV and Plexos models
Proposal for NREL/WECC study
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3. 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?
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4. 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)
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Normal Conditions
Normal
conditions
Regulation Reserve
(AGC, load frequency control)
Following Reserve
(Flex reserve, load following, balancing reserve)
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6. Contingency Conditions
Disturbance
Primary Reserve (frequency responsive reserve)
Frequency (Hz) 60
Secondary Reserve (spinning and non-spinning reserve)
Secondary Freq. Control
Bring back to a secure state
Tertiary Reserve (supplemental reserve)
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New Condition
ERCOT event: February 26, 2008
1600 MW in 3.5 hours
Mention forecasting the ramp is important in terms of requirements
Potential for a “Ramping Reserve”
More significant and rare than Following Reserve
Much slower than Contingency Reserve
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8. 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

9. Typical Methods in WECC
Secondary(Spinning) reserve: Max { 3% load + 3% generation , Largest Contingency }
50% synchronized, all deployable within 10 minutes
Primary (FRR) reserve: no requirement yet, Part of new BAL003
Regulation Reserve: To meet CPS1 and CPS2
No explicit requirement
Typically percent of load
Reliability based control will likely affect requirements
Following reserve: no explicit requirement
CAISO flexible ramping product proposal
Ramping Reserve: no explicit requirement
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10. 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.
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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
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Future methods with consideration of high penetration of Variable Generation
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13. 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.

14. 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.

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

16. Simulation Tools

17. 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

18. FESTIV 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

19. FESTIV
The model focuses on short-term reliability impacts (i.e. 1 day-1week)
It can be used to compare inputs (e.g. VG penetrations) as well as scheduling strategies (e.g. dispatch frequency)
Metrics:
Extreme imbalances - CPS violations (with configurable L10 and CPS interval)
Total imbalances - Absolute ACE Energy (AACEE)
Variability of imbalances - sACE
Similar metrics can be made for line flow, voltage, etc.
e.g. Absolute Line Flow Exceedance in Energy (ALFEE)

20. FESTIV Flow Diagram Data Flow Process Flow
Unit status and unit start-up for all units with start time > tRTCSTART
Run DASCUC
tRTC interval? no
Data Flow
yes
Unit status and unit start-up for all units
Run RTSCUC
Process Flow
t = t+tAGC
tRTD interval? no
yes
Run RTSCED
Dispatch schedules and reserve schedules for all units
AGC schedule, realized generation for all units, production cost, and ACE
Run AGC

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Metric and Outputs
ACE with Regulating Reserve
ACE without Regulating Reserve
Case
CPS2 score
AACEE(MWh)
sACE (MW)
Costs ($)
Case 6: Imperfect real-time forecasts at 5-minute intervals ,regulation reserves = 1.5% of load
27 violations
96.3%
3027
46.6
$13.237M
Case 7: Imperfect real-time forecasts at 5-minute intervals, with WWSIS2 regulation reserves
19 violations
97.4%
3610
43.5
$13.313M
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22. Coal, nuclear commitment
PLEXOS
SCUC and dispatch model with sub-hourly resolution (down to 5 min) Evaluate effectiveness of following (flex) reserves
Contingency, flex, and regulation reserve requirements
DA wind, solar forecasts
DA unit commitment
Coal, nuclear commitment
Contingency and regulation reserve requirements
Flex deployed
4-HA wind, solar forecasts
4-HA unit commitment
+ Gas CC commitment
Actual wind, solar generation
RT dispatch

23. Project Proposal in collaboration with WECC
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24. National Renewable Energy Laboratory Innovation for Our Energy Future
Project Proposal
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
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25. Reserve Requirement Methods
The following methods have already been in discussion with the WECC VGS:
Current WECC requirements
ERCOT
BPA
NREL Western Wind and Solar Integration Study
NREL Eastern Wind Integration and Transmission Study
PNNL’s method
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26. Example: WWSIS-2
Total requirement
Components

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Approach
FESTIV can show the benefits and tradeoffs of different regulation reserve methods using cost and ACE metrics
Plexos model can show the benefits and tradeoffs of different following (Flex) reserve methods using cost metrics
Wind and solar will have different impacts
Project to be proposed to the OC
Suggest Bi-monthly meeting with interested members of OC/VGS for review and guidance
Stakeholder participation is key!
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28. National Renewable Energy Laboratory Innovation for Our Energy Future
Next Steps… Questions?
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