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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

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)


Normal Conditions


Normal conditions

Regulation Reserve(AGC, load frequency control)

Following Reserve(Flex reserve, load following, balancing reserve)

Contingency Conditions


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


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


Regulation Reserve in North America


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


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


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


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


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


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


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!


Next Steps…

Questions?

[email protected]

[email protected]


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