POWER May 2011 - 67

THE FUTURE OF COAL
includes both expense and replacement
capital. All data is subjected to a rigorous
validation process to ensure data quality
and comparability.
The database results are based on two important
assumptions. First, all calculations
are generation-weighted values (MWh, for
example), not nameplate-weighted (MW).
Also, plant efficiency over a defined period
is based on the quotient of net generation
converted (in Btu) and total fuel
consumed ,using the higher heating value
(HHV) of the fuel, as is the convention
in the U.S. Some countries use the lower
heating value of the fuel to calculate plant
thermal efficiency, which results in a higher
value than when using the HHV. (See
" Plant Efficiency: Begin with the Right
Definitions, " February 2010.)
We begin our evaluation of cost and performance
data for the existing PC fleet by
first segmenting the large number of subcritical
plants in the fleet into two groups
based on nameplate capacity. Later in this
article, we will use these data groupings,
plus the existing supercritical data, as a
starting point for predicting future cost and
performance trends. The three plant data
groupings used in this analysis are small
subcritical PC units less than 500 MW, large
subcritical PC units equal to or greater than
500 MW, and supercritical PC units equal to
or greater than 500 MW.
As shown in Table 1, both the large subcritical
and large supercritical units enjoy
a significant NFOM cost advantage over
small subcritical units, due primarily to the
size advantages and higher capacity factors
the larger plants enjoy. NFOM costs for supercritical
units are on average about $0.90/
MWh, or 12.8%, higher than for large subcritical
units.
Availability factors are also higher for
both sizes of subcritical units than for
supercritical units; large subcritical units
boast the highest availability numbers.
Availability for supercritical units is more
than 2% lower than for large subcritical
units. It is not unusual for small subcritical
units to run with lower availabilities than
large subcritical ones, as asset owners tend
to direct a larger portion of their financial
resources to the more-efficient, highercapacity-factor
units. Though supercritical
units tend to have slightly higher planned
outage factors than large subcritical units,
the major difference in availability is the
higher forced outage rates experienced by
supercritical units.
The major advantage of supercritical
units is their higher cycle efficiencies.
Table 1 also shows that supercritical unit
efficiency is nearly 1.5% higher than that
of large subcritical units and more than
2% higher than that of small subcritical
units. Because the efficiency calculations
used by the database are based on operating
efficiency rather than performance
test efficiency, the impact of start-ups and
shutdowns, load following, and the like,
are automatically factored into the data,
which will appear as lower-than-expected
design or baseload-type operation.
The impact of the general economic malaise
over the past three years and increased
reliance on gas-fired generation appears
as a downward trend in capacity factor.
These effects also compound to produce a
net drop in average coal-fired plant operating
efficiency over the same period (Figure
2). The net drop in average efficiency
is greatest for supercritical units (-0.7%),
followed by large subcritical units (-0.2%)
and small subcritical units (-0.4%). This
suggests that it may be more difficult for
supercritical units to adapt to running at
lower capacity factors than for subcritical
units. This is an important point: The main
advantage supercritical units have is their
higher cycle efficiencies that more than
balance out higher NFOM costs and lower
operating availability compared with large
subcritical units.
Rising Capital Construction Costs
Capital costs for coal-fired generation are rising
sharply. A review of recently completed
projects employing both subcritical and suTable
1. Comparison of existing coal-fired technology performance
metrics, using five-year average data (2005-2009). Plant efficiency is calculated
using net generation divided by actual fuel consumed, thereby including the effects of plant
cycling and load following. Source: Navigant
Technology
Small subcritical (<500 MW)
Large subcritical (≥500 MW)
Supercritical (≥500 MW)
Number
of units
308
75
76
Total nameplate
capacity (MW)
58,552
46,590
60,118
NFOM
($/MWh) EAF (%)
11.1
7.0
7.9
85.5
86.4
84.1
Plant thermal
efficiency % (HHV)
32.5
33.3
34.7
Notes: EAF = equivalent availability factor, HHV = higher heating value, NFOM= non-fuel operation and maintenance.
May 2011 | POWER
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percritical technology is shown in Table 2.
Despite a small sample size, the data in
Table 2 provides a relative indication of recent
capital construction costs for both types
of units. For new-build units, the capital
cost estimates provided in November 2010
by the EIA (based on estimates developed
for it by external consultant R.W. Beck) are
useful for showing the level to which costs
are escalating, especially compared with
alternatives such as gas-fired generation.
Table 3 shows the EIA cost estimates for
both single-unit and dual-unit advanced PC
units, with and without carbon capture and
sequestration (CCS), as well as an advanced
natural gas combined-cycle (NGCC) unit
for comparison.
2. Existing coal-fired fleet performance
trends, 2005-2009. Source:
Navigant
Small subcritical
Supercritical
16
14
12
10
8
6
4
2
0.0
2005 2006 2007 2008 2009
Non-fuel operation and maintenance trends
89
88
87
86
85
84
83
2005 2006 2007 2008 2009
Availability trends
36.0
35.5
35.0
34.5
34.0
33.5
33.0
32.5
32.0
2005 2006 2007 2008 2009
Efficiency trends
67
Large subcritical
Efficiency (HHV), %
Equivalent availability factor (%)
NFOM ($/MWh)

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POWER May 2011

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