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Resource Adequacy: How did we get here (and where are we
going)?
Michael Milligan, Consultant
NARUC/NASEO Training, May 6, 2021
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2Michael Milligan, Consultant | milligangridsolutions.com
Outline
• Historical reliability assessments: LOLE• Impact of renewables• Emerging interest in portfolio effects• What about transmission, and long‐term weather?
• Gap between model capability and decision‐making
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3Michael Milligan, Consultant | milligangridsolutions.com
Reference: The North American Grid
Source: NERC
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Resource Adequacy
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5Michael Milligan, Consultant | milligangridsolutions.com
Resource Adequacy (RA) is a counting problem
• Have we built enough stuff to supply demand at some future date(s)?o RTO, utility IRP, region
• “How adequate” can be turned upside down into “How often do we have a problem?”
• How many problems?• How long did they last?• How large was the energy deficit?
• How large was the capacity deficit?
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6Michael Milligan, Consultant | milligangridsolutions.com
What should be counted?
• Do we want to count only resources (RA)?
• Do we want to include resources plus transmission (system adequacy)?
• Do we want to consider external support from power pool participation or other neighbors who might have the capacity/energy to help during an emergency?
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7Michael Milligan, Consultant | milligangridsolutions.com
…and what is “acceptable” RA target?
• How many loss‐of‐load events per period?
• How long of a LOL event is too long?
• How much demand/energy is “ok” to not supply?
• Policy questions
• Trade‐off between reliability and cost. Reliability is not free
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8Michael Milligan, Consultant | milligangridsolutions.com
Traditional Approach to RA• Often measured based on installed capacity, peak load, and a
planning reserve• A fixed planning reserve margin (PRM), often in a range of 12‐15%
above forecasted peak demand, was (and is still, unfortunately) common
o 10,000 MW peak, 11,500 Installed capacity is a 15% PRM.• However, this isn’t a true reliability measure; the following
questions are not answered:o How often does it fail?o How long are failures?o Or…how successful are we in keeping the lights on?
• And – it does not work with high levels of renewables
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9Michael Milligan, Consultant | milligangridsolutions.com
Resource Adequacy: From PRM to LOLP
• How adequate is adequate enough?
• Quantify the number of times system will be inadequate – often measured as hours/year or days/year (1d/10y ≈ 99.97%)
• Probability that demand will exceed supply: Loss of load probability (LOLP)
0
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All Sizes 001‐099 100‐199 200‐299 300‐399 400‐599 600‐799 800‐999
Forced Outage Rate (EFO
Rd)
Unit Size (MW)
Forced Outage Rates for Oil Fired Generating Units
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001‐099 100‐199 200‐299 300‐399 400‐599 600‐799 800‐999Fo
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Forced Outage Rates for Gas Fired Generating Units
Forced outage rates source: NERC
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All Sizes 001‐099 100‐199 200‐299 300‐399 400‐599 600‐799 800‐999 1000 Plus
Forced Outage Rate (EFO
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Forced Outage Rates for Coal Fired Generating Units
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10Michael Milligan, Consultant | milligangridsolutions.com
Resource Adequacy: From PRM to LOLP• How adequate is adequate
enough?• Quantify the number of times
system will be inadequate – often measured as hours/year or days/year (1d/10y ≈ 99.97%)
• Probability that demand will exceed supply: Loss of load probability (LOLP)
• The “Loss of load” part of this term should be changed to “probability of emergency import” in interconnected systems
0
5
10
15
20
25
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All Sizes 001‐099 100‐199 200‐299 300‐399 400‐599 600‐799 800‐999
Forced Outage Rate (EFO
Rd)
Unit Size (MW)
Forced Outage Rates for Oil Fired Generating Units
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001‐099 100‐199 200‐299 300‐399 400‐599 600‐799 800‐999Fo
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Forced Outage Rates for Gas Fired Generating Units
Forced outage rates source: NERC
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All Sizes 001‐099 100‐199 200‐299 300‐399 400‐599 600‐799 800‐999 1000 Plus
Forced Outage Rate (EFO
Rd)
Capacity (MW)
Forced Outage Rates for Coal Fired Generating Units
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11Michael Milligan, Consultant | milligangridsolutions.com
First assessments using LOLP
• Computation capability limited
• Select the peak hour from each weekday
• Exclude holidays (~6) falling on weekdays
• 5 x 52 – 6 = 254 peak demand values used for an annual assessment (about 3% of the year)
11
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12Michael Milligan, Consultant | milligangridsolutions.com
LOLP development
• Calabrese et al introduced convolution method in 1947 that is still common
• Calabrese (1950): 1 day in 50 years ”should be satisfactory”
• Remember – one data point per non‐holiday weekday!
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13Michael Milligan, Consultant | milligangridsolutions.com
Terms
• Probability: between 0, 1 inclusively• P(heads) = 0.5• Expected value = probability x number of trials (or similar)
• Expected number of heads after 100 coin tosses = 100 x 0.5 = 50
• Power systemo LOLP = loss of load probability (0.0‐1.0)o LOLE = loss of load expectation (days/year, hours/year, etc.)
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14Michael Milligan, Consultant | milligangridsolutions.com
LOLE development: 1 day/10 years • 1 day/10 years is a “nice round
number” for a reliability target• Is it from Marsh? • We don’t know where it came
from• Corresponding LOLP = 1/3650 =
0.0002734
LOLP: probability, 0 <= LOLP <= 1LOLE: expected value = P x TimeLOLH: hours of LOL eventsLOLEv: # of events of LOLEEUE: Expected unserved energy
0 1 2 3 4 5 6 7 8 9 10 Years
One event
Remember, one data point per non‐holiday weekday.
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15Michael Milligan, Consultant | milligangridsolutions.com
Renewables are complicating risk assessment• Traditional
o Most LOL risk during/near system peak
o Focus on daily LOLP; ignore hourly data
• With renewableso Shifting risk periodso More interest in hourly viewo More interest in energy metrics
• Fortunately, methods and computational tools exist that can help
See ESIG: Redefining Resource Adequacy: https://www.esig.energy/resources/redefining‐resource‐adequacy‐for‐modern‐power‐systems‐derek‐stenclik‐december‐2020/
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16Michael Milligan, Consultant | milligangridsolutions.com
Effective load‐carrying capability (ELCC)
• Rooted in base‐load evaluations from the 1950’s forward
• Easily adapted to renewables
• Part of a framework of reliability assessments 0.06
0.07
0.08
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0.1
0.11
0.12
8 8.5 9 9.5 10 10.5 11
Loss of Loa
d Expe
ctation (days/year)
Load (GW)
Original Reliability Curve
Target Reliability Level
1
2
4
3
Each generator added to the system helps increase the load that can be supplied at all reliability levels.
Added generators
Gi+1Gi Gi+2Gn‐2
400MW
Larger graph is on next slide
• ELCC calculation assumes no other changes to power system
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17Michael Milligan, Consultant | milligangridsolutions.com
Graphical depiction of ELCC
0.06
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Loss of Loa
d Expe
ctation (days/year)
Load (GW)
Original Reliability Curve
Target Reliability Level
1
2
4
3
Each generator added to the system helps increase the load that can be supplied at all reliability levels.
Added generators
Gi+1Gi Gi+2Gn‐2
400MW
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18Michael Milligan, Consultant | milligangridsolutions.com
Recipe for ELCC
• Reliability model, or production simulation model
• Inputs:o Hourly demand, wind, solar, hydro datao Resource data including forced outage rateso Multiple years of time‐sync’d data
• Outputo Each model run provides LOLE outputo Iteratively re‐run model until LOLE target is achieved with, and without, renewable resource (multiple model runs)
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19Michael Milligan, Consultant | milligangridsolutions.com
Enter: Renewables (wind example)
16x103
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0
MW
13401320130012801260124012201200Hours
Load Net Load Wind
Steeper ramps Lower turn-down
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20Michael Milligan, Consultant | milligangridsolutions.com
Enter: Renewables (wind example)
16x103
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0
MW
13401320130012801260124012201200Hours
Load Net Load Wind
Steeper ramps Lower turn-down
Partial capacity contribution
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21Michael Milligan, Consultant | milligangridsolutions.com
Example Wind/Solar Capacity Value
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0
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AZ‐NM‐NV Basin CA‐North CA‐South RMPA Interconnect
Solar P
V Ca
pacity Value
as % of R
ated
Cap
acity
ELCC of Solar
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AZ‐NM‐NV Basin CA‐North CA‐South RMPA Alberta NWPP BC
Wind Ca
pacity Value
as %
of R
ated
Cap
acity
ELCC of Wind
Adapted from Milligan, Michael; Bethany Frew; Ibanez, Eduardo; Kiviluoma, Juha; Holttinen, Hannele; Söder, Lennart, Capacity Value Assessments for Wind Power: An IEA Task 25 Collaboration. Wiley Wires. 2016.
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22Michael Milligan, Consultant | milligangridsolutions.com
Wind/Solar Capacity Value Depends on…
• Penetration rates ofo Windo Solar
• Storage and mode of operation• Maintenance schedules• Demand patterns/levels• Forced outage rates of other units
• Imports/exports• Hydro generation patterns• Inter‐annual variation
22
Andrew Mills, LBNL
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23Michael Milligan, Consultant | milligangridsolutions.com
Storage and demand response examples
23
E3, https://irp.nspower.ca/files/key‐documents/presentations/20190807‐02_‐E3‐Capacity‐Study‐Overview.pdf
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24Michael Milligan, Consultant | milligangridsolutions.com
Emerging interest in portfolio effects
Adapted from Mills and Wiser (2012), An Evaluation of Solar Valuation Methods Used in Utility Planning and Procurement Processes. https://eta‐publications.lbl.gov/sites/default/files/lbnl‐5933e.pdf
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25Michael Milligan, Consultant | milligangridsolutions.com
Emerging interest in portfolio effects
First‐in contribution
Last‐in contribution
Portfolio contribution – area under curve
Adapted from Mills and Wiser (2012), An Evaluation of Solar Valuation Methods Used in Utility Planning and Procurement Processes. https://eta‐publications.lbl.gov/sites/default/files/lbnl‐5933e.pdf
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26Michael Milligan, Consultant | milligangridsolutions.com
Emerging interest in portfolio effects
E3, https://irp.nspower.ca/files/key‐documents/presentations/20190807‐02_‐E3‐Capacity‐Study‐Overview.pdf
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27Michael Milligan, Consultant | milligangridsolutions.com
Wind and Storage Example
27
E3, https://irp.nspower.ca/files/key‐documents/presentations/20190807‐02_‐E3‐Capacity‐Study‐Overview.pdf
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28Michael Milligan, Consultant | milligangridsolutions.com
How does weather affect RE? Climate.gov
Milligan, M. R.; Artig, R. (1999). Choosing Wind Power Plant Locations and Sizes Based on Electric Reliability Measures Using Multiple‐Year Wind Speed Measurements. Prepared for the U.S. Association for Energy Economics Annual Conference, 29 August—1 September 1999, Orlando, Florida; 11 pp.; NREL Report No. CP‐500‐26724. Available at http://www.nrel.gov/docs/fy99osti/26724.pdf
0%
5%
10%
15%
20%
25%
30%
35%
40%
45%
2002 2003 2004EL
CC
% o
f Rat
ed C
apac
ity
Wind (Northern Cal)Wind (San Gorgonio)Wind (Tehachapi)
05
10152025
2003 2004 2005
Year
Perc
ent o
f Win
d Ra
ted
Capa
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15%20%25%
California RPS Integration Study
Minnesota Wind Integration Study
Adapted from Shiu, H.; Milligan, M. Kirby, B.; Jackson, K. (2006). California Renewables Portfolio Standard Renewable Generation Integration Cost Report. Prepared for the California Energy Commission, May.
Zavadil, King, et al. 2006 Minnesota Wind Integration Study. https://mn.gov/puc/assets/000664_tcm14‐4689.pdf
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29Michael Milligan, Consultant | milligangridsolutions.com
What is appropriate reliability/RA target?
• 1 day/10 years legacy target, no real justification, focuses on daily evento No information about the event length, depth, capacity
• Are 10 “small” events the same as 1 “large” event?
• Should we focus on hours lost, capacity lost, energy lost?
Time
EUE
MW dropped
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Transmission can increase reliability, enhance markets, and reduce need to build resources
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31Michael Milligan, Consultant | milligangridsolutions.com
Transmission can play a critical role• Increasing transmission links and associated operational coordination can reduce the need for installed capacity
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Scenario 1 Scenario 2 Scenario 3 Scenario 4
Wind ELCC
as %
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ated
Cap
acity
ELCC of Wind + Transmission for 3 Years
Generation w/transmission
Adapted from Eastern Wind Integration and Transmission Study https://www.nrel.gov/docs/fy11osti/47078.pdf
0
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40
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60
Reference High Wind High Mix High Solar
ELCC
of Tr
ansm
ission (M
W)
Benefit of Aggregation
Interconnection Subregion
ELCC
of T
ransmission
(GW)
Ibanez and Milligan (2012), “Impact of Transmission on Resource Adequacy in Systems with Wind and Solar Power.” IEEE Power and Energy Society General Meeting, Summer 2012. San Diego, and “A Reliability‐Based Assessment of Transmission Impacts in Systems with Wind Energy”. Available at www.nrel.gov/publications
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What do we need to do?
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33Michael Milligan, Consultant | milligangridsolutions.com
What do we need to do?
• Integrate resource, transmission, distribution planning
• Focus on “energy‐first” planning• Think more about long‐term weather impacts – on demand and resources (wind, solar, hydro)
• Re‐think metrics• Incorporate DR, storage• Close the gap between technical modeling capability and decision‐making
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34Michael Milligan, Consultant | milligangridsolutions.com
Integrate transmission & resource planningExample:MISO/NREL Study Process (EWITS, 2010)
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35Michael Milligan, Consultant | milligangridsolutions.com
https://www.hawaiianelectric.com/documents/clean_energy_hawaii/integrated_grid_planning/20180301_IGP_final_report.pdf
Integrate G, T, D planning (HI example)
HECO Integrated Grid Planning
35
Incorporate market input
Integrated T&D solutions
Utility solutions vs aggregated DER vs tariffs
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36Michael Milligan, Consultant | milligangridsolutions.com
Transmission planning challenges
• Most are well‐known…• Design and build for the short‐term, or the long‐term?• Renewable energy siting in advance?
o Example: ERCOT’s Competive Renewable Energy Zones (CREZ)
Donohoo, P. 2011. Integrating Dynamics and Generator Location Uncertainty for Robust Electric Transmission Planning. INFORMS Annual Meeting. Charlotte, North Carolina, USA.
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37Michael Milligan, Consultant | milligangridsolutions.com
Energy‐first planning
• Who is in charge?• ”energy‐first”* planning
o Focus on clean energy firsto Then “fill in” to achieve RA (energy adequacy?)
• Fill in witho Storageo DR/dispatchable demando Quick‐start thermalo Other
• Move away from “peak only” and focus on energy adequacy
Renewables & DR
Other
*First coined by Dave Olsen, CAISO
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38Michael Milligan, Consultant | milligangridsolutions.com
Weather, weather, weather
Resource Adequacy/Capacity
Value Determination
Transmission Planning
Operations & Markets
It’s the meteorology stupid!
Forecastability
Variability• Seasonal• Diurnal• Ramping
Uncertainty• Climate scales• Weather scales
Correlations:• Wind↔Solar ↔ Load ↔ Hydro
ClimateChange
Resource Diversity• In time• In space
Extreme Events• Impacts• Scale• Longevity• Connections
Justin Sharp
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39Michael Milligan, Consultant | milligangridsolutions.com
Long‐term weather; need more robust planning
• As a species, humans often don’t have the capability to incorporate uncertainty and volatility into planning
• Planning is usually done based on “average” or “representative” weather
You’re so above average!
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40Michael Milligan, Consultant | milligangridsolutions.com
Long‐term weather; need more robust planning
• As a species, humans often don’t have the capability to incorporate uncertainty and volatility into planning
• Planning is usually done based on “average” or “representative” weather
You’re so above average! That’s cold!
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41Michael Milligan, Consultant | milligangridsolutions.com
We need more work on metric comparison
0
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34
LOL Even
t/Normalize
EUE
Example Comparison of LOLH and EUE
LOLH EUE
Two LOL eventsLOLH = 6 hoursEUE = 84.2 GWh
Avg LOLH/event = 3 hoursAvg EUE/event = 42.1 GWh
LOLH = loss of load hours (hours of emergency import), number of hours of shortageEUE = expected unserved energy (emergency import energy)
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42Michael Milligan, Consultant | milligangridsolutions.com
Some potentially useful metrics
• Models (generally):o LOLH – counts hours with LOL events
o LOLE – loss of load expectation (i.e. expected value). Can be measured in days, hours, or …
o LOLEv – counts eventso LOLH/LOLEv – average length of LOL events
o EUE – expected unserved energy (MWh, GWh)
o EUE/LOLEv – average energy lost in LOL event
Break down the wall between modeling capabilities and policy‐making – and re‐work target reliability
• Policy (generally):o Planning reserve margin (% by which installed capacity exceeds peak demand)
o 0.1 d/year (sometimes)
o Single year of modeling
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43Michael Milligan, Consultant | milligangridsolutions.com
Example demand response for regulation
http://enbala.com/solutions.html
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44Michael Milligan, Consultant | milligangridsolutions.com
Animation
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45Michael Milligan, Consultant | milligangridsolutions.com
Close the gap between modeling and decision‐making
Multiple potential metrics that models can produce today.
PRM or 1d/10y –often not even calculated properly
ModelsDecision‐makers
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46Michael Milligan, Consultant | milligangridsolutions.com
Conclude• We already have much of what we
need…in our collective heads/models, but not in practice
• Best practices must evolve – and we need to re‐think reliability targets
• Need common framework for all resources
• We need to focus more on inter‐annual variability inherent in wind/solar/hydro and demand
• We need to pay more attention to dispatchable demand and storage, and continually improve on algorithms
• Integrate transmission and resource planning
• Connect the tracks!
Renewables & DR
Other
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47Michael Milligan, Consultant | milligangridsolutions.com
Questions?
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Appendix: Long‐term adequacy and resilience
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49Michael Milligan, Consultant | milligangridsolutions.com
Our planning processes are not robust
• As a species, humans don’t have the capability to incorporate uncertainty and volatility into planning
• Planning is usually done based on “average” or “representative” weather
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50Michael Milligan, Consultant | milligangridsolutions.com
Single‐mode failure and resilience• Less convolution; more Monte Carlo*• Get the fundamental probability
distributions correct (a hard problem)• Summer vs. winter forced outage rates
should be a dependent variable, not an independent variable
• Lack of fuel supply for multiple gas plants
• Create plausible load‐weather‐RE years (NREL’s forthcoming study on extreme weather)
• Explore the corners
* Convolution example: 100 coin tosses. P(head) = 0.5. Expected heads = 50.Monte Carlo: Computer “tosses” the coin 100 times. Actual number of heads will be “close” to 50. Also results in 100 “scenarios” of coin toss
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51Michael Milligan, Consultant | milligangridsolutions.com
Infrequent events• What is the risk of
o “major” heat storm every 20 yearso “major” polar vortex every 13 years
• And how do collect good data sets and assess resilience?
• How to account for impact of climate change on these variables?
0 10 20 30 40 50 60 70 80 90 100 Years
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52Michael Milligan, Consultant | milligangridsolutions.com
Multiple dimensions
Time
EUE
MW dropped
Small and Short
Large and shortLarge and Long
Small and Long
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53Michael Milligan, Consultant | milligangridsolutions.com
Issues in assessment• See NREL’s forthcoming report on extreme weather• Is event outside “normal” data sets?• How to define large‐scale threats; i.e. what happens and
where? What damage/outages?o Use extreme weather scenarios as inputso NERC/National Labs archive for power sector use
• Each region will have different risk profile, for example:o SERC: hurricaneso SPP/MISO: tornadoso ISO‐NE/MISO: cold weather, gas supply disruptiono CAISO: forest fires
• Normalize reliability score to scale 0‐10 based on metric of choice (LOLH, EUE, ??). 10= resilient, 0=failure
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54Michael Milligan, Consultant | milligangridsolutions.com
Example Resilience Diagram
0
1
2
3
4
5
6
7
8
9
10
Normal Ops
Cyber
Fuel
Flooding
Severe heat
Polar Vortex
Scoring: 10=reliability target met; 0 = severe outages
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55Michael Milligan, Consultant | milligangridsolutions.com
Resilience to different storm profiles
0
1
2
3
4
5
6
7
8
9
Polar Vortex 1
Polar Vortex 2
Polar Vortex 3
Polar Vortex 4
Polar Vortex 5
Polar Vortex 6
Resilience to Different Extreme Storm Profiles
Scoring: 10=reliability target met; 0 = severe outages
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56Michael Milligan, Consultant | milligangridsolutions.com
Questions?