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Technical Support Document (TSD)

for the final Transport Rule

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

Revised Capacity Factors Analysis for New Units

U.S. Environmental Protection Agency

Office of Air and Radiation

June 2011
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Capacity Factors Analysis for New Units

This Technical Support Document (TSD) provides updated information that 

supports the EPA’s determination of default capacity factors for new units to be adopted 

by the Transport Rule. Section V.D.4 in the preamble of the Transport Rule proposal

described proposed assurance provisions that require the use of default capacity factors

for new units without allowance allocations. In the TSD entitled “Capacity Factors 

Analysis for New Units (June 2010)” EPA documented how the proposed default 

capacity factors were determined for coal-fired boilers and combustion turbines. This 

TSD describes how EPA determined the final default capacity factors for those same unit 

types of units and other types of units using updated information now available. The 

TSD is organized as follows:

1. Introduction

2. Determination of default capacity factors

1. Introduction

Section VII.E of the preamble of the final Transport Rule describes EPA’s 

assurance provisions. As described in the preamble, if the assurance provisions in a state 

are triggered, then EPA applies additional criteria to determine which source owners and 

operators in the state are subject to an allowance surrender requirement. In particular, the 

owners and operators of a group of sources having a common designated representative 

and having total emissions exceeding the common designated representative’s share of 

the state budget must surrender allowances. The common designated representative’s 

share of the state budget includes the total allocations of the units in the group. In the 

event that such a unit is a new unit receiving no allocation for the control period 

involved, EPA uses a surrogate allocation value that is calculated using a representative 

capacity factor.

A new unit’s surrogate allocation number is calculated by multiplying the unit’s 

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

the default capacity factor for the unit type, and the number of days in the control period 

involved and divided by 2,000/lb/ton.
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The default capacity factors for new units – which are presented in preamble 

section VII.E – are shown below in Table 1. This TSD describes how EPA determined 

these default capacity factors.

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-fired Steam Boiler 85 92

IGCC (coal gasification) 74 73

Oil-fired Steam Boiler 30 39

Natural Gas-fired Steam Boiler 44 47

Simple cycle combustion turbine 24 32

Combined cycle combustion turbine 66 71

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, EPA calculated both annual and ozone season capacity

factor for each unit between the years 2008 and 20101. For this analysis, we removed any 

partial years from the data sets. In general, EPA focused this analysis on units that 

commenced commercial operation after the year 2000.

2

 However, as discussed in section 

VII.D.2 of the preamble, some units commencing operation in 2000 or earlier (such as 

older units that are not initially but later become subject to the Transport Rule trading 

 

1 EPA also calculated capacity factors for 2000-2007 and 2000-2010 and selected the use of the capacity 

factors from 2008 through 2010 because this time period is thought to be more representative of present 

conditions. Note that, in the June 2010 analysis performed for the proposed rule, the capacity factors were 

calculated from all data from 2000 through 2009 for coal and from 2004 through 2009 for combustion 

turbines. In this final analysis EPA has chosen to rely on the more representative, recent data. 

2 Note that the analysis done for the proposed rule utilized data from units commencing operation 

beginning in year 1999 or later. 
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program) can be treated as new units and may need surrogate allocation values. For the

unit types of IGCC and oil-fired boiler, no recently constructed units exist. Therefore, 

EPA used data from 2008 through 2010 from all existing units of those unit types to 

derive appropriate capacity factors to be applied to any such new units.

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 is reported to EPA. From these annual capacity factors EPA

then determined the 95th percentile values of capacity factors for each unit type. 

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

calculations, except based on the potential load during the 3,672 hours of the ozoneseason control period, rather than 8,760 hours.

As described in the original TSD analysis, EPA chose the 95th percentile annual 

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

annual and ozone season trading programs. EPA believes that this approach will take 

into account a reasonable range of operating conditions for new units.
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Figure 1

* Unit types for which existing units (units that commenced operation before 2000) were used.
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Figure 2

* Unit types for which existing units (units that commenced operation before 2000) were used.