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

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.

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 2010.  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.  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 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 ozone-season 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.

Figure 1

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

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

 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. 

 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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