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

melkins@wecc.biz

801-819-7657