Marginal Emissions Factors for the US Electricity System Kyle Siler-Evans Department of Engineering & Public Policy Carnegie Mellon University

Research Question 1 Avoided Energy (MWh) Avoided Emissions (kg) ? -CO 2, NO x, SO 2 Energy efficiency is widely seen as the low-hanging fruit for CO 2 reductions

Data Continuous Emissions Monitoring System (CEMS) – Hourly, generator level CO 2, SO 2, and NO x emissions data – Includes fossil-fuel generators larger than 25MW 2

Method & Example Analysis ΔG = G h – G h+1 (MWh) ΔE = E h – E h+1 (kg) 3 Marginal CO 2 Factor MRO region (Midwest)

Method & Example Analysis 4 Marginal Fuels: MRO Region (Midwest)

Results: Marginal Fuels 5

6

Results: Marginal Fuels in SPP 7

Results: Marginal CO 2 Factors 8 +30%

Results: Marginal SO 2 Factors 9 20 ×

Results: Influence of dispatch order 10 System Demand (GW) MRO (Midwest)

Results: Influence of dispatch order 11 System Demand (GW) TRE (Texas)

Results: Influence of dispatch order 12 System Demand (GW) FRCC (Florida)

13 SERC (South) Results: Temporal Trends

14 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. 15

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 CO 2, 12 times more SO 2, and 3 times more NO x emissions 16

Summary & Conclusions Average emissions rates may grossly misestimate the emissions benefit of an intervention. Temporal differences are modest in terms of marginal CO 2 rates, but more pronounced when considering NO x and SO 2. 17

Thank You Questions? 18