Marginal Emissions Factors for the US Electricity System

Kyle Siler-EvansDepartment of Engineering & Public Policy

Carnegie Mellon University

Research Question

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Avoided Energy(MWh)

Avoided Emissions(kg)

?

-CO2, NOx, SO2

Energy efficiency is widely seen as the low-hanging fruit for CO2 reductions

Data• Continuous Emissions Monitoring System

(CEMS)– Hourly, generator level CO2, SO2, and NOx

emissions data– Includes fossil-fuel generators larger than 25MW

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Method & Example AnalysisΔG = Gh – Gh+1 (MWh)

ΔE = Eh – Eh+1 (kg)

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Marginal CO2 Factor MRO region (Midwest)

Method & Example Analysis

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Marginal Fuels: MRO Region (Midwest)

Results: Marginal Fuels

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Results: Marginal Fuels

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Results: Marginal Fuels in SPP

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Results: Marginal CO2 Factors

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+30%

Results: Marginal SO2 Factors

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20 ×

Results: Influence of dispatch order

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System Demand (GW) System Demand (GW)

MRO (Midwest)

Results: Influence of dispatch order

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System Demand (GW) System Demand (GW)

TRE (Texas)

Results: Influence of dispatch order

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System Demand (GW)System Demand (GW)

FRCC (Florida)

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SERC (South)

Results: Temporal Trends

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SERC (South)

Results: Temporal Trends

Summary & Conclusions

• Policies often focus on energy, while our goal is (or should be) on emissions.

• Marginal emissions factors give a consistent metric for calculating displaced emissions.

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Summary & Conclusions

• There are significant regional differences in the emissions benefits of avoiding 1 MWh of electricity.– Compared to WECC (West), an equivalent energy

efficiency measure in MRO (Midwest) is expected to avoid roughly 75% more CO2, 12 times more SO2, and 3 times more NOx emissions

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Summary & Conclusions

• Average emissions rates may grossly misestimate the emissions benefit of an intervention.

• Temporal differences are modest in terms of marginal CO2 rates, but more pronounced when considering NOx and SO2.

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Thank You

Questions?

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