es7b03047_si_001.pdf (2.85 MB)
Marginal Emissions Factors for Electricity Generation in the Midcontinent ISO
journal contribution
posted on 2017-11-20, 00:00 authored by Maninder
P. S. Thind, Elizabeth J. Wilson, Inês L. Azevedo, Julian D. MarshallEnvironmental consequences of electricity
generation are often
determined using average emission factors. However, as different interventions
are incrementally pursued in electricity systems, the resulting marginal
change in emissions may differ from what one would predict based on
system-average conditions. Here, we estimate average emission factors
and marginal emission factors for CO2, SO2,
and NOx from fossil and nonfossil generators
in the Midcontinent Independent System Operator (MISO) region during
years 2007–2016. We analyze multiple spatial scales (all MISO;
each of the 11 MISO states; each utility; each generator) and use
MISO data to characterize differences between the two emission factors
(average; marginal). We also explore temporal trends in emissions
factors by hour, day, month, and year, as well as the differences
that arise from including only fossil generators versus total generation.
We find, for example, that marginal emission factors are generally
higher during late-night and early morning compared to afternoons.
Overall, in MISO, average emission factors are generally higher than
marginal estimates (typical difference: ∼20%). This means that
the true environmental benefit of an energy efficiency program may
be ∼20% smaller than anticipated if one were to use average
emissions factors. Our analysis can usefully be extended to other
regions to support effective near-term technical, policy and investment
decisions based on marginal rather than only average emission factors.