Many organizations, including governments, utilities, and businesses, have
set ambitious targets to reduce carbon emissions as a part of their
sustainability goals. To achieve these targets, these organizations
increasingly use power purchase agreements (PPAs) to obtain renewable energy
credits, which they use to offset their ``brown'' energy consumption. However,
the details of these PPAs are often private and not shared with important
stakeholders, such as grid operators and carbon information services, who
monitor and report the grid's carbon emissions. This often results in incorrect
carbon accounting where the same renewable energy production could be factored
into grid carbon emission reports and also separately claimed by organizations
that own PPAs. Such ``double counting'' of renewable energy production could
lead to organizations with PPAs to understate their carbon emissions and
overstate their progress towards their sustainability goals. Further, we show
that commonly-used carbon reduction measures, such as load shifting, can have
the opposite effect of increasing emissions if such measures were to use
inaccurate carbon intensity signals. For instance, users may increase energy
consumption because the grid's carbon intensity appears low even though carbon
intensity may actually be high when renewable energy attributed to PPAs are
excluded. Unfortunately, there is currently no consensus on how to accurately
compute the grid's carbon intensity by properly accounting for PPAs. The goal
of our work is to shed quantitative light on the renewable energy attribution
problem and evaluate its impact of inaccurate accounting on carbon-aware
systems