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

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 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? National Renewable Energy Laboratory Innovation for Our Energy Future

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) National Renewable Energy Laboratory Innovation for Our Energy Future

National Renewable Energy Laboratory Innovation for Our Energy Future Normal Conditions Normal conditions Regulation Reserve (AGC, load frequency control) Following Reserve (Flex reserve, load following, balancing reserve) National Renewable Energy Laboratory Innovation for Our Energy Future

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) National Renewable Energy Laboratory Innovation for Our Energy Future

National Renewable Energy Laboratory Innovation for Our Energy Future 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 National Renewable Energy Laboratory Innovation for Our Energy Future

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

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 National Renewable Energy Laboratory Innovation for Our Energy Future

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. National Renewable Energy Laboratory Innovation for Our Energy Future

National Renewable Energy Laboratory Innovation for Our Energy Future 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 National Renewable Energy Laboratory Innovation for Our Energy Future

National Renewable Energy Laboratory Innovation for Our Energy Future Future methods with consideration of high penetration of Variable Generation National Renewable Energy Laboratory Innovation for Our Energy Future

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.

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 of Predicted 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 - sACE 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 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

National Renewable Energy Laboratory Innovation for Our Energy Future 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 National Renewable Energy Laboratory Innovation for Our Energy Future

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

Project Proposal in collaboration with WECC National Renewable Energy Laboratory Innovation for Our Energy Future

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 National Renewable Energy Laboratory Innovation for Our Energy Future

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 National Renewable Energy Laboratory Innovation for Our Energy Future

Example: WWSIS-2 Total requirement Components

National Renewable Energy Laboratory Innovation for Our Energy Future 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! National Renewable Energy Laboratory Innovation for Our Energy Future

National Renewable Energy Laboratory Innovation for Our Energy Future Next Steps… Questions? Erik.Ela@nrel.gov Michael.Milligan@nrel.gov National Renewable Energy Laboratory Innovation for Our Energy Future