Technical Support Document (TSD) 

for the Transport Rule 

Docket ID No. EPA-HQ-OAR-2009-0491 

Capacity Factors Analysis for New Units 

U.S. Environmental Protection Agency 

Office of Air and Radiation 

July 2010 

1 
Capacity Factors Analysis for New Units 

This Technical Support Document (TSD) provides information that supports the 

EPA’s determination of default capacity factors for new units in the Transport Rule 

proposal. Section V.D.4 in the Transport Rule preamble describes the proposed remedy 

including the use of default capacity factors for new units. This TSD describes how EPA 

determined the proposed default capacity factors. The TSD is organized as follows: 

1. Introduction 

2. Determination of default capacity factors 

1. Introduction 

Section V.D.4 in the preamble of the Transport Rule describes EPA’s proposed 

remedy including the assurance provisions. As described in the preamble, if the 

assurance provisions in a state are triggered then EPA would apply additional criteria to 

determine which source owners in the state would be subject to an allowance surrender 

requirement. In the case where the assurance provisions are triggered in the year that a 

new unit first operates, in order to apply the additional criteria, EPA would determine a 

specific surrogate emissions number for the new unit. 

As discussed in the preamble, in calculating a new unit’s surrogate emissions 

number EPA would use a default capacity factor specific to the unit type: a new unit’s 

surrogate emissions number would be calculated by multiplying the unit’s allowable 

emissions rate (in lbs/MWe) by the unit’s maximum hourly load (in MWe/hr) and the 

default capacity factor for the unit type. 

The proposed default capacity factors for new units – which are provided in 

preamble section V.D.4.b – are shown below in Table 1. This TSD describes how EPA 

determined these default capacity factors. 

2 
Table 1. Default Capacity Factors for New Units 

for Transport Rule Trading Programs 

(Percentage) 

Unit Types Annual SO2 & NOX

Programs 

Ozone Season NOX

Program 

Coal Steam 84 89 

Simple cycle combustion turbine 15 22 

Combined cycle combustion turbine 66 72 

2. Determination of Default Capacity Factors 

EPA determined the default capacity factors for new units in Table 1 based on 

analysis of capacity factors using data reported to EPA by source owners and operators as 

part of EPA’s emissions trading programs. These programs require industry sources to 

report hourly emissions data each quarter. 

Using the reported data, for coal boilers EPA calculated an annual capacity factor 

for each unit for each full year of operation between the years 2000 and 2009. For 

combustion turbines, EPA calculated an annual capacity factor for each unit for each full 

year of operation between 2004 and 2009.1

 For this analysis, we removed any partial 

years from the data sets. 

To determine annual capacity factors, EPA calculated the capacity factor for units 

reporting in electrical load units (MW) by dividing the gross electrical output (MWhr) by 

the maximum hourly load times 8,760 hours (the number of hours in a year). For units 

reporting in steam units (KLBsteam), i.e., coal boilers only, we divided the total mass of 

steam produced by the maximum steam rate times 8,760 hours. The maximum hourly 

load or maximum steam rate are reported to EPA. 

From these annual capacity factors that EPA calculated, we then determined the 

50th, 67th, 75th, 90th, 95th, 99th, and 100th percentile values of capacity factors for each unit 

type. Table 2, below, shows these percentile values. 

 

1

 The year 2009 was the most recent full year of data available at the time EPA conducted the analysis. 

We looked at more years of coal data (2000 through 2009) because there were fewer new coal units to draw 

on compared to the number of recent combustion turbines (CT). We looked at fewer years of CT data 

because there were more data points available in the recent data and the more recent data was thought to 

better represent the present, given that CT operation is more variable. 

3 
To determine ozone season capacity factors, EPA performed the same 

calculations except based on the possible capacity that could be produced during the 

3,672 hours of the ozone season control period. Table 3 shows the 50th, 75th, 90th, 95th, 

and 100th percentile values of ozone season capacity factors for each unit type. 

From the values in Table 2, the EPA chose the 95th percentile annual capacity 

factors for use as default capacity factors for new units in the Transport Rule annual SO2

and NOX trading programs. Similarly, from the values in Table 3 we chose the 95th 

percentile ozone season capacity factors for use as the default capacity factors for new 

units in the Transport Rule ozone season NOX trading program. EPA believes that this 

approach would cover a range of operating conditions for new units. 

Table 2. Summary of Annual Capacity Factors 

Percentile Coal Steam 

Boiler 

Simple Cycle 

Combustion 

Turbine 

Combined 

Cycle 

Combustion 

Turbine 

50th 0.76 0.02 0.26 

67th 0.79 0.03 0.37 

75th 0.80 0.05 0.43 

90th 0.83 0.09 0.57 

95th 0.84 0.15 0.66 

99th 0.86 0.42 0.73 

100th 0.87 0.63 0.78 

Table 3. Summary of Ozone Season Capacity Factors

Percentile Coal Steam 

Boiler 

Simple Cycle 

Combustion 

Turbine 

Combined 

Cycle 

Combustion 

Turbine 

50th 0.77 0.03 0.35 

75th 0.82 0.08 0.51 

90th 0.87 0.15 0.65 

95th 0.89 0.22 0.72 

100th 0.92 0.93 0.92 

 

4 
Figures 1, 2, and 3, below, show the distribution of annual capacity factors for 

coal-fired units, simple cycle turbines, and combined cycle turbines, respectively, based 

on the annual data EPA analyzed (the data is summarized in Table 2). Figures 4, 5, and 6 

show the distribution of ozone season capacity factors for coal-fired units, simple cycle 

turbines, and combined cycle turbines, respectively, based on the ozone season data EPA 

analyzed (the data is summarized in Table 3). 

Figure 1. Distribution of Annual Capacity Factors for Coal-Steam Boilers 

Distribution of Annual Capacity Factors 

for Coal-Steam Boilers

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Percentile

Capacity Factor

5 
Figure 2. Distribution of Annual Capacity Factors for Simple Cycle Turbines

 Distribution of Annual Capacity Factors 

for Simple Cycle Turbines

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Percentile

Capacity Factor

6 
Figure 3. Distribution of Annual Capacity Factors for Combined Cycle Turbines

Distribution of Annual Capacity Factors 

for Combined Cycle Turbines

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Percentile

Capacity Factor

7 
Figure 4. Distribution of Ozone Season Capacity Factors for Coal-Steam Boilers 

Distribution of Ozone Season Capacity Factors 

for Coal-Steam Boilers

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Percentile

Capacity Factors

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Figure 5. Distribution of Ozone Season Capacity Factors for Simple Cycle 

Turbines

Distribution of Ozone Season Capacity Factors 

for Simple Cycle Turbines

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Percentile

Capacity Factors

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Figure 6. Distribution of Ozone Season Capacity Factors for Combined Cycle 

Turbines

Distribution of Ozone Season Capacity Factors 

for Combined Cycle Turbines

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Percentile

Capacity Factors

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