• Energy Research

A high energy return on energy investment (EROI) of an energy production process is crucial to its long-term viability. The EROI of conventional thermal electricity from fossil fuels has been viewed as being much higher than those of renewable energy life-cycles, and specifically of photovoltaics (PVs). We show that this is largely a misconception fostered by the use of outdated data and, often, a lack of consistency among calculation methods. We hereby present a thorough review of the methodology, discuss methodological variations and present updated EROI values for a range of modern PV systems, in comparison to conventional fossil-fuel based electricity life-cycles.

The thermodynamic efficiency and the environmental sustainability of selected processes that deliver gaseous energy carriers (natural gas, syngas from coal gasification, and hydrogen from steam reforming of natural gas and alkaline electrolysis) is explored by means of a multi-criteria, multi-scale approach based on four methods: material flow accounting, energy analysis, exergy analysis, and emergy synthesis. The average energy and exergy conversion efficiencies of syngas (76% and 75%, respectively) are found to be higher than those for hydrogen (64% and 55%). However, coal-to-syngas conversion generates a significant amount of solid waste, which should be dealt with carefully. In addition, the material intensity is much higher for syngas (e.g. abiotic MI=768 g/g) than for natural gas and hydrogen (21 and 39 g/g, respectively), indicating a higher load on the environment. On the other hand, the emergy intensity (transformity) for syngas (5.25×104 seJ/J) is shown to be lower than for hydrogen (9.66×104 seJ/J), indicating a lower demand for global environmental support. Therefore, material intensities and transformities offer two complementary pieces of information: transformities account for the “memory” of the environmental resources that were used up in the past for the production of the inputs, whereas MIs are strictly calculated within the time frame of the life cycle of the investigated process. The higher transformity values calculated for pure hydrogen suggest careful and appropriate use of such an energy vector.

AbstractThere appears to be growing polarization in a large swath of the recent scientific literature on the renewable energy transition, where two opposed “camps” may be identified, i.e. that of the “systemic pessimists”, who champion the broad concepts of carrying capacity and the limits to growth, but often harbour what appears to be pre-conceived scepticism towards renewable energies, and that of the “technological optimists”, who instead typically focus more narrowly on the immediate goal of phasing out fossil fuels, and see great potential for renewable energies to achieve that, but often fail to address other issues of ultimate planetary limits. It is argued here that this is a false dichotomy that is damaging to the reputation of both “camps”, and which risks devaluing and trivializing the most important question of all, namely how to achieve long-term sustainability. This paper calls for the rekindling of a more constructive debate that starts from the recognition that both sets of core arguments (respectively, those centred on the limits to growth and those pointing to the viability of renewable energies) are often simultaneously true, and which moves the goalposts further, to establish to which extent a more sustainable future is indeed possible, and which systemic changes (including, but not limited to, phasing out fossil fuels) will be required to achieve it.

Most existing life cycle assessment models of waste management have so far underplayed the importance of the waste collection phase, addressing it only in a simplified fashion, either by requesting the total amount of fuel used as a direct user input or by calculating it based on a set of input parameters and fixed diesel consumption factors. However, if the main purpose of the study is to improve the efficiency of the collection system itself, a more detailed analysis of the collection phase is required, avoiding oversimplified and potentially misleading conclusions. The new LCA collection model presented here relies on a large number of parameters (number and type of containers, collection frequency, distances for the various legs of transport, etc.) and allows the detailed predictive analysis of alternative collection scenarios. The results of applying this newly developed model to a number of experimental case studies in Portugal are analyzed, discussed, and compared to those produced by a selection of pre-existing, more simplified models such as ORWARE and MSW-DST. The new model is confirmed as being the most accurate and, importantly, as the only one capable of predicting the consequences of a range of possible changes in the collection parameters.

A recent paper by Ferroni and Hopkirk (2016) asserts that the ERoEI (also referred to as EROI) of photovoltaic (PV) systems is so low that they actually act as net energy sinks, rather than delivering energy to society. Such claim, if accurate, would call into question many energy investment decisions. In the same paper, a comparison is also drawn between PV and nuclear electricity. We have carefully analysed this paper, and found methodological inconsistencies and calculation errors that, in combination, render its conclusions not scientifically sound. Ferroni and Hopkirk adopt ‘extended’ boundaries for their analysis of PV without acknowledging that such choice of boundaries makes their results incompatible with those for all other technologies that have been analysed using more conventional boundaries, including nuclear energy with which the authors engage in multiple inconsistent comparisons. In addition, they use out-dated information, make invalid assumptions on PV specifications and other key parameters, and conduct calculation errors, including double counting. We herein provide revised EROI calculations for PV electricity in Switzerland, adopting both conventional and ‘extended’ system boundaries, to contrast with their results, which points to an order-of-magnitude underestimate of the EROI of PV in Switzerland by Ferroni and Hopkirk.

This paper exposes the many flaws in the article “Through the Eye of a Needle: An Eco-heterodox Perspective on the Renewable Energy Transition, authored by Siebert and Rees and recently published in Energies as a Review. Our intention in submitting this critique is to expose and rectify the original article’s non-scientific approach to the review process that includes selective (and hence biased) screening of the literature focusing on the challenges related to renewable energies, without discussing any of the well-documented solutions. In so doing, we also provide a rigorous refutation of several statements made by a Seibert–Rees paper, which often appear to be unsubstantiated personal opinions and not based on a balanced review of the available literature.