The use of primary energy factors and CO2 intensities -- reviewing the state of play in academic literature

Reaching the 2030 targets for the EU primary energy use (PE) and CO2eq emissions (CE) requires an accurate assessment of how different technologies perform on these two fronts. In this regard, the focus in academia is increasingly shifting from traditional technologies to electricity consuming alternatives. Calculating and comparing their performance with respect to traditional technologies requires conversion factors (CFs) like a primary energy factor and a CO2eq intensity. These reflect the PE and CE associated with each unit of electricity consumed. Previous work has shown that the calculation and use of CFs is a contentious and multifaceted issue. However, this has mostly remained a theoretical discussion. A stock-taking of how CFs are actually calculated and used in academic literature has so far been missing, impeding insight into what the contemporary trends and challenges are. Therefore, we structurally review 65 publications across six methodological aspects. We find that 72% of the publications consider only a single country, 86% apply a purely retrospective perspective, 54% apply a yearly temporal resolution, 65% apply a purely operational (instead of a life-cycle) perspective, 91% make use of average (rather than marginal) CFs, and 75% ignore electricity imports from surrounding countries. We conclude that there is a strong need in the literature for a publicly available, transparently calculated dataset of CFs, which avoids the shortcomings found in the literature. This would enable more accurate and transparent PE and CE calculations, and support the development of new building energy performance assessment methods and smart grid algorithms.