Reserve MarginsBuilding Block vs Probabilistic
Matthew Elkins
Manager – Performance Analysis
Resource Adequacy
• Study of a single “Peak” hour
• How much is the appropriate margin?
Demand
0 150
Resource Availability
180
GW
Margin
~20%
Building Block - Inception
• Methodology created by WECC’s Reliability Assessment Work Group
• Do not reflect a criteria‐based margin‐determination process and do not reflect any BA‐ or Load‐Serving Entity (LSE)‐level requirements
• Not intended to supplant any requirements that may have been established through other processes (e.g., state regulatory authorities).
Building Block - Components
• Contingency Reserves – An amount of operating reserve sufficient to reduce Area Control Error to zero in 10 minutes following loss of generating capacity, which would result from the most severe single contingency. (Standard)
• Regulating Reserves – The amount of spinning reserves responsive to automatic generation control that is sufficient to provide the normal regulating margin. (Survey)
• Forced Outages – The capacity lost to forced outages for both the summer (July) and winter (December) is added by subregion and divided by the total capacity reported for each subregion. (GADS)
• Temperature Adders – The MW/°C coefficient is determined by WECC staff based on five years of daily peak demand regressed on daily maximum temperature for every weekday in the season. (WECC’s Analytical Team)
Resource Availability
180175
Building Block - Hypothetical Example
• Contingency Reserves
• Regulating Reserves
• Forced Outages
• Temperature Adders
Demand
0
GW
150
Margin
~20%
Reference
Margin
~16.7%
Building Block Application
Demand
Resource Availability
January December
With Building Block
Resource AvailabilityDemand
Resource Adequacy - Variability
• Study of a single “Peak” hour
• How much is the appropriate margin?
Demand
0 150
Resource Availability
180
GW
Supply Variability*Historical Data
Hydro
Wind
Supply Variability
100%Availability0%
JanuaryFebruaryMarchAprilMayJuneJulyAugustSeptemberOctoberNovemberDecemberJanuary
*Historical Data
*Theoretical
Solar
Probabilistic Application
Demand
Resource Availability
January December
With Building Block
Probabilistic Application –Convolution
Demand Resource Availability
0 150 180
GW
Probabilistic Application –Convolution
LOSS OF LOAD PROBABILITY (LOLP)
Transmission Benefits
Demand
Resource Availability
January December
WECC Footprint
• 329 Members
• 38 Balancing Authorities
• 1.8 million square miles
• 82.2 million people
Comparison
Questions
Matthew Elkins
Manager – Performance Analysis
801-819-7657
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