  Inconsistent calculation of grid emission factors (EF) can result in widely
divergent corporate greenhouse gas (GHG) emissions reports. We dissect this
issue through a comprehensive literature review, identifying nine key aspects -
each with two to six methodological choices - that substantially influence the
reported EF. These choices lead to relative effect variations ranging from 1.2%
to 69%. Using Germany's 2019-2022 data as a case study, our method yields
results that largely align with prior studies, yet reveal relative effects from
0.4% to 34.6%. This study is the first to methodically unpack the key
determinants of grid EF, quantify their impacts, and offer clear guidelines for
their application in corporate GHG accounting. Our findings hold implications
for practitioners, data publishers, researchers, and guideline-making
organizations. By openly sharing our data and calculations, we invite
replication, scrutiny, and further research.
