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Memorandum 

To: Clean Power Plan Docket

Subject: Historical Fossil EGU Performance

Date: July 2015

The EPA performed an analysis of the historical performance of fossil EGUs to inform the mass goal 

methodology adopted in the Clean Power Plan. Specifically, the analysis is designed to better 

understand the interaction between increasing demand levels and the generation levels of existing fossil 

EGUs over time. This memorandum describes the methodology and findings of this analysis. An 

accompanying spreadsheet that provides the full results of this analysis, also titled ‘Historical Fossil EGU 

Performance,’ is available in the docket. 

Methodology 

This analysis relies on data collected from units in the Acid Rain Program1

 in the Air Markets Program 

Data (AMPD).2 AMPD tracks the fuel heat input (measured in MMBtu) of fossil EGUs subject to the Acid 

Rain Program and how, for these units, their fuel heat input changes over time. We first gather the set 

of existing fossil units that existed for each year from 1995 to 2014. Each year will have a distinct 

inventory of units associated with it. For example, 1995 will have a different set of fossil units operating 

than 2005 for a variety of reasons, including the addition of new sources and unit retirements. The 

distinct set of units identified in each year is held constant when evaluating future year performance to 

better reflect how affected EGUs are defined under the Clean Power Plan (i.e., new sources are 

unaffected). We sum, by fuel, the heat input at the same units for up to ten years into the future. The 

EPA selected ten years because of the time between the BSER data year of 2012 and the start of the 

interim compliance period of the Clean Power Plan in 2022. 

Once we have heat input data for the base year and each of the ten future years, we combine this with 

an average heat rate by fuel type from the base year to calculate the change in generation for these 

units at each future year.3 Converting from heat input to generation ensures that shifts between fuel 

types (e.g., from coal to gas) are not interpreted as a change in total generation.4

Results 

The average results for all data years are presented below in Table 1. The change in generation column 

represents the average change in generation when a constant set of fossil EGUs advances a certain 

amount of years into the future. For example, the -0.3% value after one year means that a constant set 

of fossil EGUs will, on average, generate 0.3% less than in the previous year. The -0.3% value is the

result of 19 data points, with a high of 4.9% (change from 2009 to 2010) to a low of -8.9% (change from 

 

1

 Relying on the Acid Rain Program provides the greatest amount of historical data. 

2

 http://ampd.epa.gov/ampd 

3

The EPA does not collect generation data for all units in all years of the dataset. However, complete heat input 

data is available for all units and all years. By using heat input for all units combined with a year specific fuel 

average heat rate for all units with heat input and generation we obtain a more complete estimate of generation.

4

 The product of this conversion is gross, rather than net, generation. This data is intended to reflect the relative 

changes in output over time; consequently, using gross or net generation would not materially impact the analysis. 
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2008 to 2009). The full results for all years are available in the ‘Historical Fossil EGU Performance’ 

spreadsheet, available in the docket. 

Table 1. Average Change in Generation by Year for Constant Set of Fossil EGUs 

Number of Years Change in Generation (%)

1 -0.3%

2 -1.6%

3 -3.2%

4 -5.0%

5 -6.8%

6 -9.4%

7 -11.3%

8 -13.2%

9 -15.7%

10 -18.7%

The data shows that, for a constant set of fossil EGUs, generation markedly declines over the average 

ten-year period even as overall demand for generation increases. This data can be compared to the 

affected EGU generation associated with the mass goal methodology, in which affected EGUs are able to 

expand utilization in direct proportion to the amount of building block 3 generation that is not required 

to achieve the source category-specific emission performance rates.5

 Table 2 displays national-level 

affected EGU generation associated with the mass goals over time, as well as the percent change in 

affected EGU generation from the adjusted 2012 baseline. 

Table 2. Change in Affected EGU Associated with Mass Goal Methodology 

Year 

Affected EGU Generation After 

Application of Building Block 3 

(MWh) 

Change in Generation from 

2012 Adjusted Baseline (%) 

2022 2,568,561,026 -5.4%

2023 2,535,502,287 -6.6%

2024 2,475,561,707 -8.8%

2025 2,423,036,768 -10.8%

2026 2,369,242,861 -12.8%

2027 2,309,483,921 -15.0%

2028 2,265,759,000 -16.6%

2029 2,221,796,369 -18.2%

2030 2,175,690,991 -19.9%

The values above are consistent with the historical data in Table 1 and serve to validate the 

reasonableness of the assumption that affected EGUs will increase generation in an amount equal to the

building block 3 generation not required by the goal-setting methodology. 

 

5

 Refer to the preamble section VII for a description of the mass goal methodology. 
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