Dr Raugei's 'Net energy analysis must not compare apples and oranges' published in Nature

Monday, 28 January 2019

nature energy

Anyone with an interest in renewable energy may do well to have a read of a new paper by Brookes’ own Dr Marco Raugei.

The new paper entitled ‘Net energy analysis must not compare apples and oranges’ has been published today (Monday 28 January) with Nature Energy. It delves into Net Energy Analysis (NEA); one of the ways we measure ‘return on investment’ of different energy sources.

NEA is a scientific discipline borne out of an ‘energy theory of value’. In layman’s terms, it is concerned with how much energy it takes to extract (from nature) and ‘return’ (to human societies) a unit of usable energy. Hence its principal metric is the ‘Energy Return on Investment’ (EROI), which is increasingly mentioned in discussions about the energy-economy nexus, both within and beyond the scientific arena.

Dr. Raugei has been deeply involved in the ongoing debate about net energy and EROI for over a decade, with his publications on the matter including a few widely-cited scientific rebuttals. He has also expanded on the subject as an invited speaker at a number of related conferences and events (including the Net Energy Analysis Workshop at Stanford University in 2015, the International Society for Bio-Physical Economics Conference in 2017, and the EROI Workshop hosted by the UK Government Dept. of BEIS in 2017).

A key point of contention has often been the relative net energy performance of conventional vs. renewable energy resources and supply chains. This debate leads on to a big question for the future: what effect will a projected increased reliance on renewable energies have on how much energy we have to support our societies in the future? Over the years, Dr. Raugei has witnessed with increasing concern the growing polarization of opinion on these matters, and realised that this is often rooted in inconsistent, and hence inherently flawed and potentially misleading, comparisons.

This new paper aims to set the record straight, by identifying the fundamental reasons for such lack of consistency, and proposing a way forward towards better applications of Net Energy Analysis. A key part of the paper looks at supply chains: different supply chains may lead to energy carriers that are not functionally equivalent. These carriers are also used in different applications, with an associated wide range of unavoidable thermodynamic losses. The paper also argues that combining carriers to arrive at estimates of ‘average’ EROI values is often fraught with methodological issues. A common notion in energy discourse is the idea of a ‘minimum’ EROI that would be necessary for a society to survive in future. But these minimums may only be deemed valid within the restricted confines of a specific type of energy carrier, and for a well-defined context in terms of the mix of technologies and applications in which that same energy carrier is used.

Dr. Raugei added: “The concept of EROI is deceptively simple at face value, but in truth the devil is in the details. For far too long, the debate has focused on the wrong end of the stick, as it were. The crux of the matter is not what is the energy ‘return’ of a resource at point of extraction, but rather, what is the net energy delivered to the end user, also considering the mix of technologies and applications in which it is going to be used. In light of the impending challenges of climate change and energy security, and of a complex and rapidly shifting landscape of many competing energy technologies, we must no longer rely on simplistic comparisons and postulated ‘minimum’ EROI thresholds. Instead, we must work hard to develop new rigorous, detailed and consistently-bounded scenario analyses.”

About the author

Dr. Marco Raugei is Senior Research Fellow and Associate Lecturer in the School of Engineering, Computing and Mathematics of Oxford Brookes University, as well as Visiting Scientist at the Center for Life Cycle Analysis of Columbia University in the City of New York (USA).

His main research interests and the core of his research activity to date have been in (i) the theoretical improvement of existing approaches for environmental sustainability assessment, taking into account a wide range of viewpoints and methods, and (ii) their application to energy systems and the development of strategic energy supply scenarios. To date, he is the author of 47 scientific papers published in peer-reviewed international journals, as well as almost 100 other scientific documents published in conference proceedings, reports, scientific books and encyclopaedias