### Technical Support Document (TSD) for

New Source Performance Standard s for Carbon Pollution from
Electric Utility Generating Units (EGUs)

Docket ID No. EPA-HQ-OAR-2013-0495

Docket ID No. EPA-HQ-OAR-2013-0603



# Net-electric Sales Applicability Threshold for

Combustion Turbines as Related to
Integration of Intermittent Renewables

U.S. Environmental Protection Agency

Office of Air and Radiation
August 2015

### Page | 2 August 3, 2015 Purpose
The purpose of this TSD is to provide an analysis ass essing the claims made by respondents to the proposed

rule that reliable use of intermittent renewables causes percentage of electric sales relative to the potential
electric output of simple cycle turbines to increase.

Overall Relationship
This technical support document presents an analysis of the annual net generati on provided by solar and
wind electricity generators versus the annual net generation provided by simple cycle combustion turbines
for the years 2010 through 2014 based on EIA 1 

### Form 923 Data. In order to minimize the effect of
independent variables that may affect the percentage electric sales of combustion turbines but that are
unrelated to the expanding use of intermittent renewabl es, this analysis focused on the western United States,
the region of the U.S. that has seen the largest increase in output from renewable generating assets over the
study period. The analysis relies on the EIA net genera tor output data from the following states that provide
electricity to the Western Interconnection 2 

### :

Arizona California Colorado Idaho Montana New Mexico Wyoming

Nevada Oregon South Dakota Texas Utah Washington



### In addition to limiting the analysis to the states th at have seen the largest increases in output from
intermittent renewables, the following additional step s were also taken minimize the interference of
independent variables unrelated to incr easing output from intermittent renewables:

1. The output from simple cycle turbines serving comb ined heat and power functions were excluded
from the total output attributed to simple cycl e turbines because the reliability and availability
(to WECC system operators) of industrial combined heat and power output is largely driven by
independent factors specific to the associated indus trial process. These generators are identified in
the EIA Form 923 source data in column B (under the “Combined Heat & Power Plant” heading).

2. Consistent with the preceding rationale, output fro m simple cycle turbines with industrial NAICS
codes (e.g., NAICS codes beginning with “21”, “ 32”, and “33” were excluded from the total output
attributed to simple cycle turbines during the stud y period because independent factors specific to the
industrial process may limit the availability of th ese generating assets for balancing system load
during periods of rapid fluctuations in intermittent renewable output. Only generators identified with
NAICS codes beginning with “22” were included in the study because these assets are owned by
utility companies and strictly operated to mainta in reliable service to consumers regardless of
variations in the net output available from indus trial generators and in termittent renewables.

The general approach was to evaluate if a correla tion exists between increases in electrical output from
intermittent renewable generators (i.e., solar and wind only) and in creases in output from utility-owned
simple cycle combustion turbines. The data used in th e analysis are summarized in Tables 1.A. through 1.E.,

1 “Page 1 Generation and Fuel Data” available for 2010

‐ 2014 at http://www.eia.gov/electricity/data/eia923/

. 2 The Western Interconnection is comprised of the electricity generators and transmission systems that serve most of

the western regions of the United States. This interconnection is operated by the Western Electricity Coordinating

Council (WECC). https://www.wecc.biz/Pages/home.aspx. 

### WECC

### Page | 2 August 3, 2015 and the complete data set is include d in the docket with the filename
“EIA_2010_TO_2014_Renewables_vs_Simple_Cycles.xlsx.”Page|1August3,2015

### Page | 1 August 3, 2015 Discussion of Findings

As shown in Figure 1 , from 2010 - 2014 there was a strong correlation between increases in output from intermittent
renewables and increases in output from simple cycle turbines within the 13 western states. 3 Comparatively Figure 2

shows that there was a weaker
negative correlation for
conventional (non-combined
cycle) steam plants (e.g.,
nuclear and coal-fired EGUs);

these units have more limited
ramping 4 capabilities than
simple cycle turbines.
Additionally, Figure 3 shows

that there was a weaker
(compared to the simple cycle
correlation) positive
relationship between
increasing output from
renewables and output from
combined cycle power blocks

in the 13 interconnected

western states. Figure 1. Solar + Wind Output vs. Simple Cycle Output in 13 Interconnected Western States.

Comparison of Figures 1, 2 and 3 confirms that a uniquely-strong positive correlation exists between increasing output

from intermittent renewables
and output from simple cycle

turbines. The correlation
equation suggests that for
approximately every 11
megawatt hours of additional
carbon-free electrical output
capacity that was added in the

13 interconnected western

states from 2010 to 2014, about
1 additional megawatt hour of
simple cycle operations was
necessary to ensure reliable

transitions from nondispatchable to dispatchable

generators. Figure 2. Solar + Wind Output vs. Steam Plant Output in 13 Interconnected Western States

3 This analysis does not attempt to account for the impact of increased electric demand.

4 The term “ramping capabilities” refers to a generating unit’s ability to rapidly increase or decrease output in situations where the system operator

must rapidly replace a sudden loss of output such as when clouds associated with a thunderstorm suddenly decrease the output from a large bank

of photovoltaic cells or when the wind suddenly stops blowing.

### Page | 2 August 3, 2015 Figures 4 and 5 provide a comparison of the percentage electric sales of utility owned simple cycle turbines

within the 13 western, interconnected states to the percentage electric sales of utility owned combined cycle

turbines within the 13 states.

Figure 4. Percentage of Electric Sales of Simple Cycle Combustion Turbines Serving in the 13 Western States. 0.0% 5.0% 10.0% 15.0% 20.0% 25.0% 30.0%

0 20 40 60 80 100 120 

## SIMPLE CYCLE CAPACITY FACTORS

IN 13 INTERCONNECTED WESTERN STATES

SC CAP. FACTORS, 2010

SC CAP. FACTORS, 2011

SC CAP. FACTORS, 2012

SC CAP. FACTORS, 2013

SC CAP. FACTORS, 2014 

### Figure 3. Wind + Solar Output vs. Combined Cycle Output in 13 Western

### Page | 3 August 3, 2015 Figure 5. Capacity Factors of Combined Cycle Combustion Turbines Serving in the 13 Western States.



### Figures 4 and 5 demonstrate that the percentage of electric sales of combined cycle turbines and simple cycle turbines can have significant overlap.

Figure 4 demonstrates that even in states with significa nt intermittent renewable capacity, simple cycle operating profiles are consistent with the national sta tistic that simple cycle units continue to operate primarily as peaking units.

Impact on Percentage Electric Sales

While the overall generation data s uggests a positive relationship between the absolute amount of electricity generated by simple cycle turbines and intermittent rene wable generation, the percentage electric sales for individual simple cycle units is the relevant threshold fo r this final rule. For the preamble discussion, we used

EIA data from 2008 to 2014 and indi vidual generation data the EPA’s Clean Air Markets Division to determine the impact on individual units. As discussed in the preamble to this final rule, we reviewed the historical generation from simple cycle generation in states with increasing and significant amounts of generation (e.g., California and Tex as) to determine the relationship between simple cycle turbines and generation from intermittent renewable generation (i.e ., wind and solar). To date, increased generation from renewable generation has had minimal impact on the way the existing simple cycle fleet operates. These units continue to be used primarily to satisfy peri ods of peak electric demand. The primary relationship appears to be the addition of large capacity of new si mple cycle units to provide firm backup power. These units would be subject to the 111(b) requirements . However, these units are operating well below the percentage electric sales threshold for base load units in this final rule. See the preamble for a detailed

discussion.

Base Load Percentage Electric Sales Threshold

The rationale for the sliding scale percentage electric sales threshold is described in detail in the preamble to this final rule. The following is a brief discussion on why the EPA concluded that a single value percentage electric threshold below one-third electric sales is not appropriate at this time. For example, 88 percent of existing simple cycle units did not have annual electri c sales that exceeded 10 percent of their potential electric output between 2005 and 2014. However, we have concluded that implementing a limitation this low could constrain further expansion of renewables. Specifically, commenters from the utility sector 0.0% 10.0% 20.0% 30.0% 40.0% 50.0% 60.0% 70.0% 80.0% 90.0% 100.0%

0 10 20 30 40 50 60 70 80 

## COMBINED CYCLE CAPACITY FACTORS

IN 13 INTERCONNECTED WESTERN STATES

CC CAP. FACTORS, 2010

CC CAP. FACTORS, 2011

CC CAP. FACTORS, 2012

CC CAP. FACTORS, 2013

CC CAP. FACTORS, 2014

### Page | 4 August 3, 2015 consistently objected to the proposed one-third electric sales threshold, so few, if any, of these commenters would consider a 10 percent threshold sufficiently flexib le for new non-base load units. In addition, our cost

models show that it would not be cost-effective to in stall a NGCC combustion turbine that would operate at a capacity factor near 10 percent.

The EPA also considered a percentage electric sal es threshold of 25 percent for non-base load units. Nationally, ninety-eight per cent of existing simple cycle turbines did not exceed this level of sales between 2005 and 2014. In addition, at this level of electric sales, our cost models indicate that it would be cost

effective to install an NGCC combustion turbine. This le vel is further supported by the permit restriction for the CPV Sentinel facility in Desert Hot Springs, Californi a. This facility consists of eight high-efficiency intercooled simple cycle turbines intended to support wi nd generation in California. Each unit at this facility is restricted to 2,803 hours of operation annually. 5 

### Assuming an average duty cycle of 90 percent, this is equivalent to an annual percentage electric sal es restriction of approximately 29 percent.

Similar to the 10 percent threshold, however, the EPA acknowledges that a 29 percentage electric sales threshold to distinguish non-base load and base load units is not appropriate for multiple reasons. First, many commenters stated that existing simple cycle turbines are currently permitted to ope rate 2,920 hours or more annually to respond to variable annual demands a nd to provide capacity reserve (and the associated payments). Commenters stated that, due to the changi ng nature of the grid (e.g., increased generation from intermittent renewable generation), these needs will incr ease in the future. The cited permit from California is only for a single location, and a 29 percent electric sa les constraint may not be representative of units in

other areas.

In the proposal, the EPA estimated the number of exis ting simple cycle turbines that would have exceeded the proposed one-third percentage el ectric sales threshold by determining if operated over 2,920 hours in any given year. However, this method overestimated the number of simple cycle turbines that would have exceeded the threshold in two ways. First, it did not a ccount for hours in which simple cycle turbines were operating at part load. The typical duty cycle (i.e., aver age capacity factor while operating) of simple cycle turbines is approximately 70 percent. Therefore, simp le cycle turbines can operate in excess of 2,920 hours and still not sell one-third of their potential electric output to the grid. Historically, simple cycle turbines sell approximately 3 percent of their potential electric output, and only 10 of the 1,939 existing simple cycle turbines have individual years where the percentage of electric sales exceeded one-third of their potential electric output. Second, we proposed to calculate the percentage electric sales criterion on a 3-year rolling average basis. Using a 3-year rolling average, only tw o existing simple cycle turbines historically sold enough electricity to exceed the proposed one-third percen tage electric sales threshold. While this threshold appears to sufficient flexibility, as descr ibed in the preamble to this final rule the EPA has concluded that due to the changing nature of the electric grid it is prudent at this time to offer greater flexibility.

Conclusion

The final rule acknowledges the relationship between the use of flexible generating technologies (e.g., simple cycle turbines and fast-start combined cycle units) a nd expanded integration of intermittent renewables by providing a subcategory for non-base load combustion turb ines. Non-base load turbines supply no more than their design efficiency times their potential electric output as net-electric sales on both a 12-operating month and 3 year rolling average basis. We refer to “desi gn efficiency times the unit’s potential electric output” as “the sliding applicability scale.” The EPA has determined that this form of the applicability threshold is appropriate because it encourages capital investments in the most efficient fast-start technologies and accounts for the requirements necessary for integrating intermittent renewables.

5 http://docketpublic.energy.ca.gov/PublicDocu ments/Regulatory/Non %20Active%20AFC's/07

‐ AFC

‐ 3%20Sentinel/2010/DECEMBER/TN%2059190%2012

‐ 8

‐ 10%20Final%20Commission%20Decision.pdf