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Resource Adequacy and Reliability in the IPM Projections for the MATS Rule

This document describes resource adequacy and reliability results in the IPM 2015 projections 

for the base case and MATS rule policy cases. As used here, the term Resource Adequacy

means the provision of adequate generating resources to meet projected load and generating 

reserve requirements in each region, while Reliability includes the ability to deliver the 

resources to the loads so the overall power grid remains stable. IPM is specifically designed to 

ensure generation resource adequacy, either by using existing resources or through the 

construction of new resources. IPM addresses reliable delivery of generation resources only for 

the delivery of electricity between regions, by setting limits to the ability to transfer power 

between regions using the bulk power transmission system. Within each model region, IPM 

assumes that adequate transmission capacity exists to deliver any resources located in, or 

transferred to, the region.

Summary of Changes in Operational Capacity

Total operational capacity is lower in the policy scenario, primarily as a result of increases in 

coal retirement. Since most regions are projected to have excess capacity above their target 

reserve margins, most of these retirements are absorbed by a reduction in excess reserves. 

Operational capacity1changes from the base case in 2015 are summarized below:

Table 1. Operational Capacity Summary in 2015

Base case operational capacity (MW) 1,025,477

 Minus Changes in Policy Case:

 (-) Coal retirements -4,677

 (-) Coal capacity derated -697

 (+)New Capacity Additions 0

 (+)Lower non-coal retirements +386

 Net Change in Policy Case -4,988

Equals Policy Case Operational Capacity 1,020,4892

Since the model must maintain adequate reserves in each region, the reduced operational 

capacity of 4,988 MW in the policy case is taken largely from excess reserves that are not 

needed. In order to maintain resource adequacy in each region where coal resources retire, 

the model relies on this excess reserve reduction, on lower retirements of non-coal capacity 

and on greater new capacity additions. In some regions there may be fewer retirements under 

 

1

Operational capacity is any existing, new or retrofitted capacity in the lower 48 states that is not retired. 

2

Numbers in this table may not sum due to independent rounding.
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the policy case than under the base case, as a result of shifts in the regions where the model 

determines that retaining such capacity remains economic. As the table shows, the reduction 

in capacity (excess reserves) is the largest source of change, followed by lower non-coal 

retirements. There was no change in aggregate new capacity additions between the base and 

policy case projections. Each of these policy case changes is discussed further below.

Reduction in Excess Reserves

IPM uses a target reserve margin in each region as the basis for determining how much capacity 

to keep operational in order to preserve resource adequacy. IPM retires capacity if it is no 

longer needed to provide energy for load or to provide capacity to meet reserve margin during 

the planning horizon of the projections. Since current regional reserves are generally higher 

than the target reserve margin for the region, IPM may retire reserve capacity in 2015 if it is not 

economic to maintain relative to alternatives such as building new capacity or transferring 

capacity from another region. As a result, many of the coal plants that are projected to retire in 

2015 will not need to be replaced for resource adequacy until later years when demand 

increases and reserves approach the target reserve margin. 

Reserve margin targets are generally based on the NERC 2010 10 Year Assessments for the 

region, except in cases where there are more stringent state requirements or other exceptions. 

In one region, ERCOT, the system planners recently raised their target reserve from the 12.5% 

used in IPM to 13.75%, subsequent to the most recent NERC assessment. However, IPM’s 

projected margin for ERCOT under MATS in 2015 remains above this revised 13.75% target, 

even when taking into account only the capacity reported by ERCOT as being available.

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Table 1 above shows that operational capacity is reduced by less than one percent nationwide 

in 2015 under the policy. This reduction will have little overall impact, since the weighted 

average reserve margin at the national level are projected to be approximately 25% in the base 

case, compared to a default NERC level of 15%. Moreover, coal retirements are distributed 

throughout the power grid, so there will be only small impacts at the regional level. For 

example, in the RFC NERC reliability region, containing the coal-fired generating areas in 

Pennsylvania, West Virginia and the Midwest, there was a decrease less than 2% in policy case 

 

3

ERCOT recently revised its projection of available capacity for 2015 to be 78,144 MW in 2015 (Report on the 

Capacity, Demand, and Reserves in the ERCOT Region, June 9, 2011, Revision 2), which is lower than the total 

capacity of units in ERCOT as tracked by EPA’s NEEDS database (the source for determining IPM-projected reserve 

margins as presented in table A2). However, even ERCOT’s revised projection of available capacity in 2015 is more 

than adequate to meet IPM’s 2015 peak summer demand for ERCOT of 65,810 MW, yielding a reserve margin of 

18.7% under those revised capacity assumptions. 
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and a remaining overall reserve margin of over 20%.4 These excess regional reserves above the 

target margin can be shared among subregions to ensure adequate reserve margins within a 

larger reliability region. IPM permits these transfers of reserves, but limits their level to ensure 

the reliability of the bulk power system (see discussion below.) 

Although there are substantial existing regional variations in reserve margin, IPM adjusts 

regional capacities in 2015 to meet the specific target reserve margin in each region, through 

reduction in non-coal retirements, construction of new generating capacity and transfers of 

capacity among regions to meet the specific reserve margin in each region. Each of these 

adjustments in the 2015 projections is described below.

Reduction in Non-coal Retirements

Reducing non-coal retirements relative to these retirements in the base case is the second 

largest adjustment needed to balance the loss of coal capacity. Overall combined cycle, 

combustion turbine and nuclear retirements are 386 MW lower in the policy case compared to 

the base case. Lower nuclear retirement of 440 MW in the policy case occurred because this 

capacity became economic to maintain under policy in order to offset retirements of coal. The 

increased nuclear capacity under the policy was offset by increased retirement of 54 MW of

gas-fired capacity, for a net reduction of 386 MW. The distribution of these retirements across

IPM regions is shown in the Appendix.

Reserve Transfers

In cases where it is economic to transfer reserves from a neighboring region rather that supply 

reserves from within a region, IPM will transfer reserves, subject to summer and winter limits 

that are designed to ensure that these reserves can be transferred reliably. The transfer of 

reserves can occur, for example, if a region must retire a large amount of coal capacity that was 

used in the base case to meet reserve requirements. There are only a few significant shifts

between the base and policy cases in reserve transfers, and most of these occur in neighboring 

IPM regions. For example, there is a net increase in transfer of summer reserves out of MACW

(an increase of 1,729 MW) and a net decrease in transfer of summer reserves out of RFCP (a 

decrease of 1,345 MW). Reserve transfers by IPM region are provided in the appendix.

 

4

See map of IPM regions and Table of target and projected reserve margins in the Appendix. The IPM regions 

comprising the RFC NERC regions are MACE, MACS, MACW, RFCO, RFCP,MECS and COMD. 
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Appendix: Tables by IPM Region

A1. Projected Operational Capacity in 2015

A2. Summary of Target and Projected Reserve Margins in 2015

A3. Policy Case Retired Capacity Incremental to Base Case in 2015

A4. Capacity Transfers Region in Base and Policy Scenarios in 2015

Map of IPM Regions
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A1. Projected Operational Capacity in 2015(MW)

All Generation Sources Coal Only

Region Base Policy Change Base Policy Change

AZNM 35,829 34,974 -855 9,603 8,749 -854

CA-N 41,285 41,285 0 217 217 0

CA-S 32,676 32,675 -1 213 212 -1

COMD 25,232 25,240 8 4,227 4,235 8

DSNY 9,747 9,742 -5 369 364 -5

ENTG 40,298 40,108 -190 8,397 8,360 -37

ERCT 89,845 89,837 -8 18,409 18,149 -260

FRCC 55,632 55,616 -16 9,173 9,157 -16

GWAY 31,829 31,914 85 19,320 19,437 117

LILC 5,487 5,423 -64

MACE 30,626 30,626 0 2,759 2,759 0

MACS 12,111 12,003 -108 5,109 5,001 -108

MACW 30,852 30,939 87 10,882 10,969 87

MECS 27,607 27,585 -22 10,820 10,798 -22

MRO 50,038 49,962 -76 20,801 20,725 -76

NENG 33,106 33,103 -3 2,699 2,608 -91

NWPE 19,726 19,468 -258 12,263 12,005 -258

NYC 9,333 9,333 0

PNW 49,147 47,741 -1,406 1,990 584 -1,406

RFCO 48,174 47,450 -724 29,966 29,242 -724

RFCP 44,413 44,241 -172 32,305 32,144 -172

RMPA 18,374 18,573 199 7,529 7,728 199

SNV 9,196 8,490 -706 2,555 1,849 -706

SOU 62,845 62,550 -295 24,583 24,288 -295

SPPN 17,228 17,230 2 7,905 7,961 56

SPPS 40,168 40,188 20 12,023 12,133 110

TVA 37,065 36,851 -214 12,228 12,014 -214

TVAK 12,998 12,994 -4 9,445 9,441 -4

UPNY 15,776 15,724 -52 2,328 2,276 -52

VACA 48,680 48,347 -333 18,428 18,095 -333

VAPW 22,251 22,241 -10 4,325 4,315 -10

WUMS 17,903 18,036 133 8,229 7,922 -307

Total 1,025,477 1,020,489 -4,988 0 309,100 303,737 -5,374
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A2. Summary of Target and Projected Reserve Margins in 2015

Projected Reserve Margins

IPM Region

Target Reserve 

Margin Base Case Policy Case

AZNM 13.6% 34.8% 29.4%

CA-N 14.6% 18.4% 18.4%

CA-S 14.8% 14.8% 14.8%

COMD 15.3% 21.3% 21.3%

DSNY 18.0% 18.0% 18.0%

ENTG 15.0% 37.2% 35.8%

ERCT 12.5% 24.8% 24.8%

FRCC 19.3% 22.2% 22.1%

GWAY 11.9% 61.0% 60.5%

LILC 18.0% 24.7% 18.0%

MACE 15.3% 15.3% 15.3%

MACS 15.3% 15.3% 15.3%

MACW 15.3% 53.4% 41.8%

MECS 15.3% 47.2% 47.0%

MRO 15.0% 15.0% 15.0%

NENG 15.0% 25.7% 25.3%

NWPE 12.0% 79.2% 76.4%

NYC 18.0% 18.0% 18.0%

PNW 20.0% 46.6% 41.6%

RFCO 15.4% 19.8% 15.4%

RFCP 15.3% 15.3% 15.3%

RMPA 12.3% 12.3% 12.3%

SNV 13.6% 13.6% 13.6%

SOU 15.0% 26.7% 26.2%

SPPN 13.6% 75.2% 74.4%

SPPS 13.6% 18.8% 18.9%

TVA 15.0% 15.0% 15.0%

TVAK 15.0% 37.2% 38.9%

UPNY 18.0% 21.4% 20.9%

VACA 15.0% 15.0% 15.0%

VAPW 15.3% 15.3% 15.3%

WUMS 15.0% 32.7% 33.3%
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A3. Policy Case Retired Capacity Incremental to the Base Case in 2015 

(MW) 

CC Coal CT Nuclear OG Steam Total

AZNM 0 1151 0 0 0 1151

ENTG 0 0 0 0 153 153

ERCT 0 236 0 0 -252 -16

GWAY 0 -167 0 0 32 -135

LILC 0 0 0 0 65 65

MACE 0 0 0 0 0 0

MACS 0 102 0 0 0 102

MACW 0 -102 0 0 0 -102

MECS 0 0 0 0 0 0

NENG 0 84 0 0 -88 -4

NWPE 0 232 0 0 0 232

PNW 0 1405 0 0 0 1405

RFCO 0 685 0 0 0 685

RFCP 0 81 0 0 0 81

RMPA 0 0 0 0 0 0

SOU 0 245 0 0 0 245

SPPN 3 -77 51 0 0 -23

SPPS 0 0 0 0 90 90

TVA 0 163 0 0 0 163

TVAK 0 0 0 0 0 0

UPNY 0 53 0 0 0 53

VACA 0 293 0 0 0 293

VAPW 0 0 0 0 0 0

WUMS 0 293 0 -440 0 -147

Total 3 4677 51 -440 0 4291
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A4. Net Capacity Transfers by IPM Region in Base and Policy Scenarios in 2015 (MW)

(Net outflows are positive; net inflows negative)

Base Case Policy Case Net Change in Policy Case

Region NetWinter NetSummer NetWinter NetSummer NetWinter NetSummer

AZNM 0 681 0 1,185 0 504

CA-N 0 3,515 0 3,515 0 0

CA-S 0 -11,014 0 -11,014 0 0

COMD 749 321 749 321 0 0

DSNY 447 2,502 447 2,498 0 -4

ENTG 0 768 0 987 0 219

ERCT 0 0 0 0 0 0

FRCC 0 0 0 0 0 0

GWAY 0 385 0 385 0 0

LILC 0 222 0 439 0 217

MACE 0 -4,205 0 -4,205 0 0

MACS -932 -2,908 -1,096 -3,072 -164 -164

MACW 2,893 5,573 1,119 7,302 -1,774 1,729

MECS 1,968 1,880 2,617 1,880 649 0

MRO 256 -3,085 256 -3,240 0 -155

NENG 1,803 0 1,803 0 0 0

NWPE 0 1,966 0 1,966 0 0

NYC -437 -2,670 -437 -2,670 0 0

PNW 0 2,945 0 2,945 0 0

RFCO 2,786 6,909 3,691 7,108 905 199

RFCP -5,367 -7,226 -6,712 -8,571 -1,345 -1,345

RMPA 0 -225 0 -27 0 198

SNV 0 2,505 0 1,798 0 -707

SOU 0 1,189 0 1,113 0 -76

SPPN 0 570 0 570 0 0

SPPS 0 0 0 0 0 0

TVA 0 -613 250 -827 250 -214

TVAK 0 166 166 0 166 -166

UPNY 2,325 1,259 2,325 1,259 0 0

VACA 0 679 416 345 416 -334

VAPW 0 -467 929 -477 929 -10

WUMS 0 256 0 256 0 0
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