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NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.
Operating Reserves and Variable Generation
Erik Ela, Michael Milligan
January 28, 2012
WECC Webinar
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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National Renewable Energy Laboratory Innovation for Our Energy Future
Operating Reserves and VG
“Operating Reserves and Variable Generation”
Erik Ela, Michael Milligan, and Brendan Kirby
August 2011: http://www.nrel.gov/docs/fy11osti/51978.pdf
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?
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
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Normal conditions
Regulation Reserve(AGC, load frequency control)
Following Reserve(Flex reserve, load following, balancing reserve)
Contingency Conditions
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Disturbance
Fre
qu
en
cy (
Hz)
60
Primary Reserve (frequency responsive reserve)
Secondary Reserve (spinning and non-spinning reserve)
Secondary Freq. Control
Tertiary Reserve (supplemental reserve)
Bring back to a secure state
New Condition
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ERCOT event: February 26, 2008
Potential for a “Ramping Reserve”
1600 MW in 3.5 hours
•More significant and rare than Following Reserve•Much slower than Contingency Reserve
Operating Reserve
Regulating Reserve
Contingency Reserve
Following Reserve
primary
Ramping Reserve
Non-event Event
Correct the current ACE
ManualPart of optimal dispatch
Instantaneous Non-Instantaneous
secondary tertiary secondary tertiary
Stabilize Frequency
Return Frequency to nom
inal and/or ACE to zero
Replace primary and
secondary
Return Frequency to nominal
and/or ACE to zero
Replace secondary
AutomaticWithin optimal dispatch
Correct the anticipated ACE
Operating Reserve Categorization
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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Regulation Reserve in North America
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Region Requirement DefinitionPJM 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.
European comparison
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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 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 No requirements No requirements
Future methods with consideration of high penetration of Variable Generation
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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): • No additional contingency reserves.• 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.
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.
EWITS Methods
Reserve demand as a function ofPredicted operating levels (wind, load)
Simulation Tools
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
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
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 - ACE
• Similar metrics can be made for line flow, voltage, etc.• e.g. Absolute Line Flow Exceedance in Energy (ALFEE)
FESTIV Flow Diagram
Data Flow
Process Flow
Run DASCUC
Unit status and unit start-up for
all units with start time >
tRTCSTART
tRTC interval?
Run RTSCUCUnit status and unit start-up for
all units
tRTD interval?
Run RTSCEDDispatch
schedules and reserve
schedules for all units
Run AGC
AGC schedule, realized
generation for all units,
production cost, and ACE
t = t+tAGC
yes
no
yes
no
Metric and Outputs
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ACE without Regulating Reserve
ACE with Regulating Reserve
Case CPS2 score AACEE(MWh) ACE (MW) Costs ($)
Case 6: Imperfect real-time forecasts at 5-minute intervals ,regulation reserves = 1.5% of load
27 violations96.3%
3027 46.6 $13.237M
Case 7: Imperfect real-time forecasts at 5-minute intervals, with WWSIS2 regulation reserves
19 violations97.4%
3610 43.5 $13.313M
PLEXOS
SCUC and dispatch model with sub-hourly resolution (down to 5 min)
Evaluate effectiveness of following (flex) reserves
DA unit commitment
DA wind,solar
forecasts
4-HA unit commitment
RT dispatch
Contingency and regulation reserve requirementsFlex deployed
4-HA wind, solar
forecasts
Contingency, flex, and regulation reserve requirements
Actual wind,solar generation
Coal, nuclearcommitment
+ Gas CCcommitment
Project Proposal in collaboration with WECC
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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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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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Example: WWSIS-2
Total requirement Components
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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Next Steps…
Questions?
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