Many studies have concluded that the current global economy can transition from fossil fuels to be powered entirely by renewable energy. While supporting such transition, we critique analysis purporting to conclusively demonstrate feasibility. Deep uncertainties remain about whether renewables can maintain, let alone grow, the range and scale of energy services presently provided by fossil fuels. The more optimistic renewable energy studies rely upon assumptions that may be theoretically or technically plausible, but which remain highly uncertain when real-world practicalities are accounted for. This places investigation of energy-society futures squarely in the domain of post-normal science, implying the need for greater ‘knowledge humility’ when framing and interpreting the findings from quantitative modelling exercises conducted to investigate energy futures. Greater appreciation for the limits of what we can know via such techniques reveals ‘energy descent’ as a plausible post-carbon scenario. Given the fundamental dependence of all economic activity on availability of energy in appropriate forms at sufficient rates, profound changes to dominant modes of production and consumption may be required, a view marginalised when more techno-optimistic futures are assumed. Viewing this situation through the lens of ‘post-normal times’ opens avenues for response that can better support societies in navigating viable futures.
Energy descent as a post-carbon transition scenario: how
‘knowledge humility’ reshapes energy futures for post-normal times
Joshua Floyd1, Samuel Alexander1, Manfred Lenzen2, Patrick Moriarty3, Graham Palmer4,
Sangeetha Chandra-Shekeran1, Barney Foran5, and Lorenz Keyßer6
1 Melbourne Sustainable Society Institute, University of Melbourne, Australia
2 School of Physics, Faculty of Science, University of Sydney, Australia
3 Department of Design, Monash University, Australia
4 Mechanical and Aerospace Engineering, Monash University, Australia
5 Institute of Land, Water, and Society, Charles Sturt University, Australia
6 Department of Environmental Systems Science, Institute for Environmental Decisions, ETH Zurich,
Cite as: Floyd, J., Alexander, S., Lenzen, M., Moriarty, P., Palmer, G., Chandra-Shekeran, S., Foran, B,
Keyßer, L. (2020). Energy descent as a post-carbon transition scenario: how ‘knowledge humility’ reshapes
energy futures for post-normal times. Futures. doi: https://doi.org/10.1016/j.futures.2020.102565.
Abstract: Many studies have concluded that the current global economy can transition from fossil fuels to be
powered entirely by renewable energy. While supporting such transition, we critique analysis purporting to
conclusively demonstrate feasibility. Deep uncertainties remain about whether renewables can maintain, let
alone grow, the range and scale of energy services presently provided by fossil fuels. The more optimistic
renewable energy studies rely upon assumptions that may be theoretically or technically plausible, but which
remain highly uncertain when real-world practicalities are accounted for. This places investigation of energy-
society futures squarely in the domain of post-normal science, implying the need for greater ‘knowledge
humility’ when framing and interpreting the findings from quantitative modelling exercises conducted to
investigate energy futures. Greater appreciation for the limits of what we can know via such techniques reveals
‘energy descent’ as a plausible post-carbon scenario. Given the fundamental dependence of all economic
activity on availability of energy in appropriate forms at sufficient rates, profound changes to dominant modes
of production and consumption may be required, a view marginalised when more techno-optimistic futures are
assumed. Viewing this situation through the lens of ‘post-normal times’ opens avenues for response that can
better support societies in navigating viable futures.
Keywords: energy descent, energy-society futures, energy transition, post-normal science, quantitative
modelling, knowledge humility
1. Introduction
Transcending fossil fuels by initiating a swift decarbonisation of the global economy is one of
the defining challenges of the 21st century. The most prominent factor necessitating this shift is
climate change (and its related impacts), driven primarily by greenhouse gas (GHG) emissions
for which fossil fuel combustion is the leading source (IPCC, 2018). Alongside this driver, the
geological inevitability of fossil fuel depletion, with its potential to disrupt economies due to the
increasing costs of maintaining anticipated energy supply rates, is relevant on a similar
timeframe (Mohr et al., 2015; Wang et al., 2017).
In light of the transition imperative’s urgency and the high-stakes implications for
sociopolitical stability, the extent to which alternative energy sources can reprise the physical
economic roles of incumbent primary sources demands close and thorough investigation
(Moriarty & Honnery, 2016, 2019). Will alternatives specifically renewables and/or nuclear
energy be able to replace, in an economically and energetically affordable (let alone equitable)
way, the fossil energy sources of today’s complex and globalised industrial civilization? Might a
transition to post-carbon energy systems (‘a post-carbon transition’) imply fundamental
discontinuities or step changes beyond present cultural, social and political-economic
arrangements, rather than incremental techno-economic adjustments along a relatively smooth
Today, more than thirty years after the IPCC was established, fossil energy sources still make
up 84% of global commercial primary energy supply, and global emissions continue to rise (BP,
2019), suggesting that transcending fossil fuels may be harder and more problematic than some
optimistic studies suggest (see, e.g., Jacobson et al., 2011, 2017a). Assessing the theoretical
performance of systems comprising alternative energy technologies in the abstract, via
quantitative modelling exercises that consider historically unprecedented developments
unfolding decades into the future, cannot hope to address the full spectrum of questions relevant
to establishing the practically realizable potential for such systems (Lenzen et al., 2016). Given
the rate and scale of economic change required to minimise climate risks (i.e. net-zero emissions
by 2050 or sooner), in navigating the terrain ahead we should expect that knowledge systems and
practices established to deal with past and even current change processes will at best provide
partial guidance, and at worst be misguiding.
In light of this, we believe that there is much insight to be gained by locating the investigation
of energy-society futures squarely within the domain of post-normal science (Friedrichs, 2011).
That is, we are dealing with situations that accord fully with Funtowicz & Ravetz’s (1993)
original characterization of ‘post-normality’ in terms of uncertain facts, disputed values, high
stakes, and urgent decisions. At the same time, the arguments we present in this paper are not
limited to such framing. Even if energy-society futures are considered from a viewpoint of
normal science and policy formulation, the case we make has direct relevance.
This paper assumes that transitioning to 100% renewable energy supply is an urgent and
appropriate goal for humankind. However, informed by and consistent with the cautions from the
post-normal perspective (Saltelli, 2019; Saltelli & Funtowicz, 2014; Ravetz, 1998; Funtowicz &
Ravetz, 1993), we present a critical and somewhat sobering assessment of the potential for
quantitative analytical approaches to provide conclusive answers about whether renewable
energy conversions can meet in full the demands for work, heat transfer, lighting and data
manipulation made by today’s globalised and growth-orientated world economy (Alexander &
Floyd, 2018). Reflecting an implicit positivist orientation, the findings of model-based energy
and sustainability transition studies are frequently presented as if they relate directly to a ‘real
world’ that a model is purported to represent, rather than relating to a ‘model world’ (McDowall
& Geels, 2017; Ramirez et al. 2019). Even where correspondence between findings and ‘model
world’ rather than ‘real world’ is strictly observed by study authors, such correspondence is often
neglected in third party interpretation and reporting. This gives rise to what we see as a
dangerously misleading optimism. While the post-normal framing directly challenges the
grounds for such optimism, we emphasise once more that the case we set out is relevant even
under the presumption of normalcy.
In this paper we show that energy transition modelling exercises are necessarily based on
myriad complex and often controversial assumptions that necessitate the interpretation of their
findings strictly in relation to the model as an abstract representation of a real world as
understood by the modeler. Any conclusions drawn from such studies should be presented and
applied with due acknowledgement of the deep uncertainties and limitations inherent therein.
When the range of uncertainties and controversies is given due weight, we argue that a position
of ‘knowledge humility’ is called for when assessing and developing scenarios and policies for a
post-carbon transition (Amara, 1975; Sardar, 2010; Fazey et al., 2018; Jasanoff, 2018; McDowall
& Geels, 2017; Ramirez et al., 2019; Sovacool & Brown, 2015). A disposition of knowledge
humility entails reflexivity with respect to the epistemological foundations and commitments that
inform transition-oriented decision making and action. Here the response to the dilemma of
uncertainty and ignorance is not to deny it or seek to eliminate it, but to learn to live with it
through reflexive governance (Voß, Bauknecht, & Kemp, 2006).
Our review of the evidence and arguments suggests it is highly plausible that the transition to
post-carbon energy sources and technologies implies reducing demand for energy services, per-
capita and perhaps overall, below the levels of energy services enabled by existing fossil fuel-
dominated global energy supply. While this statement is subject to the same circumspection that
we argue should apply to contrary findings, we contend that such futures, which are presently
marginalized (Laugs & Moll, 2017), should be elevated from a peripheral concern to one that
actively shapes the ways in which actors engage in energy transition praxis. The case for this is
sufficiently plausible that in the energy-intensive developed regions of the world, a post-carbon
transition should include policy making and planning for what can be called ‘energy descent’
(see Odum and Odum, 2008; Holmgren, 2012); or, to use the terminology previously introduced
to Futures by Friedrichs (2011), ‘peak energy’ (i.e. futures characterised by significantly reduced
energy supply). This would mean planning for and managing major supply reductions in coming
decades, not just ‘greening’ existing supply (Moriarty & Honnery, 2008, 2012a). This has
profound implications for the basic social and political-economic formations that underpin our
current modes of production and consumption.
The uncertainty attending energy-society futures, and the knowledge humility it demands,
supports the case for adopting an anticipatory stance that is open to energy descent. Energy is a
critical factor in economic production, but appreciation for the significance of this is weak within
orthodox economics (Keen & Ayres, 2019). Reduced overall availability of energy services
implies economic degrowth, or downsizing of economies in terms of physical production (Sakai
et al., 2018). This view diverges from mainstream green growth aspirations that involve
‘decoupling’ GDP from physical production, and physical production from energy and other
resource use, enabled by technological efficiency gains and greater emphasis on services
(Hatfield-Dodds et al., 2015). Evidence continues to mount that decoupling is incapable of
meeting green growth expectations (Hickel & Kallis, 2019; Parrique et al., 2019; Bithas &
Kalimeris, 2018). Furthermore, empirical studies cast doubt on the intuitively appealing idea that
orienting economies towards services and ICT-mediated activity will reduce their energy
intensity (Fix, 2019; Palmer, 2017a; Parrique et al., 2019). On the other hand, the case for
reduced economic growth allowing much more rapid decarbonisation is strongly supported
(Foran, 2011; Victor, 2012; Le Quéré et al., 2018).
Before beginning our assessment of renewable energy’s physical and economic prospects, a
brief note on nuclear power is required to delimit the scope of the present analysis. We
appreciate that nuclear energy will play an important role in global energy systems for many
decades ahead. Whether its share of total final energy supply increases modestly (Froggart,
2015), or perhaps even declines as old plants are decommissioned faster than new plants are
brought on-line, nuclear energy’s persistence contributes only marginally to the question of
energy descent plausibility and does not fundamentally alter our conclusions. We justify this on
the pragmatic ground that, regardless of their relative techno-economic and environmental
merits, considered globally, renewable energy sources seem to have achieved a large advantage
over nuclear energy in terms of social and political support.
Given the extent to which renewable energy dominates visions of post-carbon futures, and the
associated weight of research effort that it receives, it seems reasonable to focus attention on this
prospectively dominant share of total supply. Nonetheless, the broad arguments that we make
about the relationship between quantitative modelling and knowledge pertaining to plausible
futures apply also to visions of alternative futures in which the relative contributions of nuclear
and renewable sources are reversed. On this basis, the primary focus in this paper is the question
of whether existing energy service expectations in the developed industrial economies can be
satisfied primarily and as close as possible to ‘entirely’ – via renewable sources.
2. Making sense of model-based feasibility assessments: a map is not the territory
Many distinct forms of social organization reliant entirely on renewable energy flows have
persisted over prolonged periods throughout human history (Smil, 2017). But renewable energy
(hereafter ‘RE’) feasibility research overwhelmingly has a narrower focus. In essence, it asks
whether currently commercial and close-to-market RE conversion technologies (especially wind
turbines and solar PV) can support industrial, growth-oriented societies and economies
functionally equivalent to those in place today.
In response to this research question two polarised perspectives dominate, holding that current
renewable technologies absolutely can or absolutely cannot provide the scope and scale of
energy services currently provided by fossil fuels (see e.g. Hansen et al., (2019) for a survey of
perspectives; for a sense of the long history of polarisation in relation to energy futures, see
Thompson, 1984). There is a broad middle-ground, though, who support the transition to
renewable energy to whatever extent is possible, and who at the same time regard the nature of
future energy systems and, often, the forms of economy and society that they enable as open
questions. The following critical inquiry seeks to deepen the understanding of an area that is
presently, and will remain for some time at the very least, subject to major uncertainties.
When findings from any conceptual modelling exercise are claimed to prove feasibility (or
non-feasibility) of transition to 100% RE, careful critical interpretation is obviously required.
Many such studies have been conducted to date (see Elliston et al., 2014; Jacobson et al., 2018;
Lenzen et al., 2016; Wiseman et al., 2013) and, when they are published by government
organisations or in prestigious scientific journals, accepting the conclusions at face value has
social legitimacy. As Loftus et al. (2015) and Heuberger & MacDowell (2018) argue, media
outlets may report on the findings of such studies without critical insight and necessary nuance.
Indeed, given the complexity of the issues under consideration, it can require considerable
expertise to interpret the findings of such studies.
Decision makers relying on such studies may be inclined to assume that the peer-review
process provides sufficient assurance of authority (Pfenninger, 2017) and that the latest
modelling exercise demonstrates a transition to 100% RE faces no insurmountable technical,
economic or practical barriers and, moreover, that the engineering challenges confronting such
an undertaking are all resolvable. Perhaps the most pervasive assumption is that of economic
growth (Stern 2013). The large-scale models used for the climate mitigation scenarios
summarised by the IPCC simply assume a baseline economic growth forecast. Compounded over
the 21st century, the annual growth projections result in a three to eight-fold increase in global
per-capita income by 2100 regardless of biophysical constraints (Palmer 2018).
But such models and the findings derived from them cannot be validated against real-world
outcomes, because those outcomes relate to situations decades in the future (Ravetz, 1998;
DeCarolis et al., 2012; Heuberger & MacDowell, 2018; Nelder & Koomey, 2016). This is not to
say that such forward-looking models cannot be valid. High quality energy-economy models are
routinely based on 20-50 years of actual past performance data and must replicate historical
behaviour accurately to be considered robust (see for instance, Turner et al., 2011; Roberts et al.,
2018). It is also possible to have high degrees of confidence in relation to overall mass and
energy balances, given the very well established physical and engineering principles on which
energy conversion processes are based. If the underlying energy-economy structural
relationships that have prevailed in the past are accurately represented in a model, and if these do
in fact remain sufficiently unaffected by the transition process that the model seeks to
investigate, then model-based findings can provide plausible forward views.
However, establishing whether or not the evolution of real-world behaviour will remain
within the performance envelope bounded by the model structure is not a question that can be
answered from within the model environment itself. All models are conceived and implemented
within superordinate, encompassing and exogenous contexts that are necessarily external to the
model itself. These contexts are by definition fixed for the purpose of the modelling exercise
the model cannot respond to or influence them. There is a boundary beyond which the model
cannot ‘see’, because those aspects of the real world are not endogenized. In the real world
though, these superordinate contexts are always subject to potential change, possibly under the
influence of changes originating from processes that are included in the model itself. Futures-
oriented model-making necessarily and unavoidably entails judgements by the modellers about
what is and is not relevant, which means that all such models are subject to a degree of
irreducible uncertainty (Voros, 2007; Saltelli & Funtowicz, 2014).
Furthermore (and this is more philosophically mundane but of great practical significance),
modelling outcomes are a function of the assumptions on which models are constructed, and
different assumptions can lead to disparate and conflicting conclusions (see, e.g., Jacobson, et al.,
2017a; Clack et al., 2017; Heard et al., 2017; Brown et al., 2018; Diesendorf & Elliston, 2018).
As such, any model-derived knowledge is relative to a model’s limited context and assumptions,
and not the actual situation within which the envisaged change process would need to be realised
in practice (Grunwald, 2011). What is assumed to be relevant for a particular model is a function,
in part, of the modeller’s worldview, and worldviews give rise to perspectives that are
unavoidably partial (Checkland & Poulter, 2006; Hodges & Dewar, 1992; McDowall & Geels,
2017; Valentine et al., 2017).
The real world always holds unforeseen complexities and obstacles in store, and it is very
difficult to ‘out-smart’ it when grappling with a situation of the size and complexity entailed by
rapid global transformation of humanity’s tightly coupled economy-energy systems (Jefferson,
2014; Cherp et al, 2018). In this respect, the management of ‘energy systems’ and their
transitions is better understood not as a technological or even techno-economic challenge, but as
a complex of interacting challenges that are essentially socio-technical in character (Büscher,
Schippl, & Sumpf, 2019). Each of the myriad social dimensions involved in energy transition
processes has potential to feedback upon other dimensions. There is simply no ‘technological
world’ that can be said to stand alone from its social contexts for analytical purposes.
If a single key assumption in a feasibility study turns out to be flawed, the entire conclusion
can be called into question (Saltelli & Funtowicz, 2014). The socio-technical character of energy
transition amplifies this basic vulnerability, due to the diversity of interactions across the
multiple dimensions of the social world that are implicated in the associated change processes. If
many or all of the assumptions are dubious, then the uncertainty or implausibility of the
conclusions compounds (Keepin, 1984). When serious critics examine high-profile models that
claim to prove feasibility for transition to 100% RE over territories ranging from regional to
global scale, they typically find that these exercises are informed by many uncertainties and
contestable assumptions (Clack et al., 2017; Heard et al., 2017; Capellán-Pérez et al., 2017),
even if they do not remain unanswered (Jacobson et al., 2017b; Brown et al., 2018; Diesendorf &
Elliston, 2018). It follows that ‘real-world’ inferences extrapolated from such research should be
viewed as speculative at best and dangerously misleading at worst.
Modelling exercises of this nature certainly play an important role in the scoping process for
any large-scale engineering initiative. But transition of energy systems globally away from fossil
fuels represents an engineering undertaking of utterly unprecedented scale (Smil, 2010).
Conceptual modelling is only the first step in figuring out what might be possible in practice, and
what efforts might be involved in realising such a vision. Its utility lies in its ability to interact
with, and inform, practical implementation steps, including the design, construction, operational
management and maintenance activities of engineers, experience that can then provide feedback
to improve subsequent modelling efforts, in a process of continuous action learning. The actual
engineering practice of building plant and infrastructure, and then operating it over extended
periods, is, however, absolutely essential to this learning. It is in the strictest sense ‘learning by
doing’. Knowing and doing are inseparable here: certainty can only be claimed with respect to
what has been done and shown to be effective in practice. Even then, the application of
knowledge developed in one context to another demands that a great deal of care be taken in
understanding the equivalence of those contexts.
In light of the socio-technical character of energy transition, the need for an action learning
orientation extends beyond the engineering domain into transition governance more broadly. The
uncertainties faced call for governance that is reflexive with respect to the knowledge
foundations informing decisions and actions. We should expect the knowledge that informs
governance to be informed in turn by the decisions and actions taken, in a process of continuous
and open-ended learning (Grunwald, 2004).
The preliminary message here is that the status of claims based on conceptual modelling
exercises alone that is, where these relate to initiatives that have never before been attempted
and for which there is no equivalent precedent are best treated with a healthy dose of critical
scepticism. This reveals as problematic any truth claims made by studies purporting to
demonstrate the feasibility of a 100% RE transition. The interests of sound public policy and
decision making require that this message be taken seriously. Notably in the financial sector,
where uncertainty with respect to future developments entails significant and immediate
monetary costs, this is not a controversial matter (Anthony & Coram, 2019). In important
respects, success in the realm of finance reflects skill in assessing the robustness of knowledge
about possible futures. Taking a leaf out of the financiers’ book may serve other investigators of
energy-society futures well.
3. Fully replacing fossil fuels with renewable energy: challenges to definitive feasibility
The analysis below presents a range of feasibility issues that we maintain cannot be answered by
analytical and quantitative modelling methods with the confidence they are often assumed to
provide (DeCarolis et al., 2012; Loftus et al., 2015). When these feasibility issues are considered
in aggregate, uncertainty is compounded about the viability of RE sources and conversion
technologies to fully or directly replace the magnitude and nature of energy services provided by
fossil fuels. Viewed as a whole, the post-normal character of energy-society futures within the
context of transition away from fossil fuels is, we contend, readily apparent.
The case we make recognizes that in a world powered entirely by RE, the primary energy
required to provide final energy services of the magnitude used in the non-energy economic
sectors today will almost certainly reduce significantly.
Most final energy services today are
provided via thermal conversions which necessarily make only a portion of the primary energy in
fuels available as work, dispersing the balance as waste heat. It is therefore likely that current
global primary energy use significantly overstates the scale of the supply task for scenarios
where electricity from non-thermal energy conversions (including wind, PV and hydro) is the
principal energy carrier.
Current global final energy use is a better guide to future primary energy requirements. In a
future fully-electrified world, the portion of this comprising transport fuels could also be
expected to reduce significantly, due to the current reliance on thermal conversions for transport
work. On the other hand, if transport remains significantly reliant on alternative liquid and
gaseous fuels, and hence on thermal energy conversions, the difference may be smaller. A
further unknown relates to the potential cost reductions for energy services resulting from the
higher efficiency of electrical energy conversions, with consequential possibility of rebound
effects driving primary energy consumption up again, e.g. electric vehicles being used more
frequently than their internal combustion engine counterparts (Parrique et al., 2019, Hickel &
Kallis, 2019). This illustrates the deep uncertainties that energy transition presents.
A basic limitation encountered in applying prospective analytical techniques (Voros, 2006) to
an issue such as global shift in the means by which energy is distributed is that implementing the
proposed changes would fundamentally alter important contextual assumptions that the analysis
itself relies upon (Voros, 2007; Scher & Koomey, 2011; Hodges & Dewar, 1992). A particularly
important aspect of systemic feedback challenge relates to the question of how the global energy
sector’s own demand for energy services might change in the transition to a fully electrified or
100% RE-powered world (Palmer & Floyd, 2017; Palmer, 2017b; King & van den Bergh, 2018).
As we discuss below, there is reason to expect that the scale of the energy services required for
energy supply will increase significantly (Bardi & Sgouridis, 2017).
We acknowledge that the issues discussed below are complex and that space does not permit
comprehensive treatment. Nevertheless, by reviewing a broad range of diverse challenges and
limitations of RE it is hoped more energy transition advocates come to recognize that replacing
fossil fuels with RE may be harder than some optimistic modelling studies suggest, from which
we hope increased knowledge humility flows.
3.1. ‘Theoretical potential’ is not ‘practically realisable potential’
In stating this, we adopt the International Energy Agency’s convention, based on the UN’s ‘International
Recommendations for Energy Statistics’, of defining ‘primary energy’ at the point where ‘the energy source
becomes a “marketable product”’; see Millard & Quadrelli, 2017; see also Palmer & Floyd, 2017 for discussion of
the distinction between the ‘energy harvested’ and ‘energy harvestable’ concepts for defining primary energy, both
of which are employed in life-cycle assessment.
The scale of solar energy’s theoretical potential is vast (Moriarty & Honnery, 2012b). However,
this metric diverts attention from a more important question: what is the practically realisable
potential of solar energy, after accounting for the full range of factors affecting its conversion to
energy forms useful to human societies (de Castro et al., 2013)?
In considering the potential for RE, there is a series of unavoidable ‘discounts’ applied to the
earth energy flows that act as the primary sources from which human use is derived (Moriarty &
Honnery, 2016). The naturally occurring energy flows that are accessible must then be converted
via techniques for which the useful outputs entail inherent reductions relative to the inputs. This
technical potential is governed by fundamental physical relations that are not subject to human
influence, and is also mediated by practical technology-specific constraints.
The wider array of renewable energy sources without doubt holds promising potential
(Jacobson et al., 2017a). But the proportion of RE’s theoretical potential that can be realised in
practice, once the broad spectrum of geographical, technical, engineering, environmental,
economic and socio-political factors is taken into account, is far less certain though certainly
orders of magnitude less than theoretical potential in absolute scale (Moriarty & Honnery, 2016).
The practically realisable potential for RE is ultimately dependent on engineered systems. But
engineers design systems within limits that pay little heed to abstract ideas about theoretical
maxima. Engineers work with, but ultimately within, the performance characteristics, properties
and availability of materials; the bounds of manufacturing techniques; the bounds of established
transport, handling, and logistics infrastructures and institutions; the bounds of operability,
maintainability and control; and so on.
Beyond this, the practical challenges of engineering systems for capturing, converting and
distributing energy must be tackled within complex and encompassing socio-political contexts.
This raises a raft of further questions. Will politicians be prepared to drive a renewables
transition? Will vested interests (continue to) get in the way? Will cultural values adapt to
accommodate higher energy prices and the behavior changes those prices prompt or require?
Will rural communities object to wind farms on aesthetic grounds? Will environmental groups
object to large-scale RE projects that threaten biodiversity? There are myriad socio-political,
economic and engineering reasons why the practically realisable potential of renewables will
remain a fraction only of even conservative estimates for the technical potential (Heuberger &
MacDowell, 2018).
The foundational point, then, is that policy-making and planning processes should not treat
the best-case scenarios for technical potential, let alone the much larger theoretical potential, as
models for plausible futures since these almost certainly will not be realised (see, e.g. de Castro
& Capellán-Perez, 2018; Jefferson, 2014; Gans et al., 2012; Miller et al., 2011).
3.2. Variability, base-load, dispatchability and cost
When considering the prospects for transition to renewably powered economies, the variable
electricity supply provided by PV and wind (variable renewable energy, or VRE) looms large as
the principal challenge that must be confronted (Rai et al., 2019). This contributes to what is
sometimes referred to as the ‘base-load problem’.
We recognize here that increasing VRE penetration implies a shift away from the past base-
load dominated operating regime, and that old assumptions about this will not hold in the future.
Nonetheless, there are significant techno-economic and related path dependencies to which the
transition process is subject by virtue of the historical fact of base-load and the ways in which it
has helped shape the present situation. Current demand patterns have typically developed to suit
the supply-side characteristics of thermal generation systems biased towards continuous, steady-
state operation. Such base-load oriented demand patterns are subject to significant structural
‘lock-in’, due to the myriad social and economic habits and expectations that the availability of
base-load power has given rise to (Yakubovich et al, 2005). As such, there is a basic structural
requirement, in the short term at the very least, that replacements for conventional steam-turbine
thermal power generation provide, in the aggregate, equivalent dispatchability characteristics.
Grids highly reliant on generation sources that, by their very nature, cannot be considered as
having the dispatchability characteristics of fossil fuel-powered generators therefore face what
can be characterised in common parlance as the ‘base-load problem’.
The dispatchability problems that arise for grid systems dependent on variable primary energy
sources are more general, though, than the requirement to meet base-load demand. For instance,
winter peaking grids, where demand is highest during winter evenings when the sun is not
shining, present a particular challenge (Palzer & Henning, 2014; van der Wiel et al., 2019;
Trainer, 2013). A proposed response to this issue is to distribute renewable electricity generation
capacity sufficiently widely and then transmit that electricity to where it is needed. For example,
Europe could import electricity from the Sahara, as the Desertec project envisioned (Samus et
al., 2013). The strategy of geographically diversifying across regions or national borders is
important for utilising variable renewables. At the same time, greater dependence on long
distance, undersea and trans-national electricity flows opens the way to novel security risks and
governance challenges, increasing the divergence between envisaged future energy systems and
historical experience (Ralph & Hancock 2019). Further, this strategy requires replicating
generation and transmission capacity across multiple regions. For instance, Lenzen et al. (2016)
found that meeting 2016 electricity demand in Australia from RE sources would require
increasing supply infrastructure by a factor of approximately 5, with levelised cost of electricity
around 0.15-0.20 AU$/kWh. Exploiting opportunities to shift demand load out of peak periods
can reduce the cost, but for those options studied to date the reductions implied are only 0.055
AU$/kWh (Ali, Lenzen & Huang, 2018) and 0.028 AU$/kWh (Ali, Lenzen & Tyedmer, 2019)
respectively. During periods of favourable weather conditions, supply will exceed immediate
demand, and so grid operation and market dynamics can be expected to depart significantly from
historical behaviour. Grid operators and market participants can also be expected to adapt to
these new conditions, for instance via novel load shifting regimes and related demand
management techniques. Exactly how these might unfold though, and what their second-order
economic, political and social consequences might be, are open questions that will ultimately
only be resolved through building and operating actual systems.
The challenge presented by RE variability can also be addressed via integration of storage
technologies into electricity supply systems (Blakers et al., 2018). We note in this respect that the
very promising cost declines for wind and PV electricity reflect the cost of supplying that
electricity at the margins of existing grid systems. Here, the ability of grid systems to meet
demand is underwritten by dispatchable capacity mainly reliant on fossil fuels. If the
intermediate storage required to make intermittent RE sources similarly dispatchable is included
(i.e. pumped hydro storage (PHS), batteries, hydrogen and similar) then the economics may
change dramatically. The economics of grid-connected PV (or wind) when integrated with fossil
fuel dispatchable capacity may be very different from PV (or wind) with sufficient storage to
meet demand whenever it occurs (Jenkins & Thernstrom 2017).
Future energy systems will involve the coordination of a wide diversity and increased number
of VRE sources on shorter time intervals than the past (Rai et al., 2019). Intermediate energy
storage is one part only of this picture, and subject to local conditions will be complemented by
stock-based supply in the form of dispatchable thermal generation powered by bio-fuels. The
challenge, however, is largely defined by the required buffering or storage scale. Even if
significant weather anomalies occur only infrequently, it is these statistical outliers that
determine the performance criteria for which supply systems must be designed. Perspectives on
the quantity of storage required currently rely on quantitative modelling that cannot yet be
calibrated against large-scale field performance. Findings are dependent on starting assumptions,
and these can diverge very significantly (Palmer 2017b; Palmer & Floyd, 2020). One study for
RE electricity supply in Australia reported a PHS requirement of 450 GWh or 19 hours average
demand (Blakers et al., 2017; see also Trainer, 2019a). At the other extreme, a study for
Germany covering electricity and heating found that 45 days full load storage via synthetic gas
would be required (Palzer & Henning, 2014). A study for 100% RE electricity in Texas found a
requirement of approximately 14 days storage capacity (Preston, 2015).
Distributed storage will take on an important role for supporting network stability, but this
relates primarily to short term buffering rather than multi-day or multi-week storage. The
practical benefits for grid management currently being realised as a consequence of battery
technology and manufacturing developments relate to a class of problems quite distinct from the
far larger challenge of long-term energy storage at a systemic scale. Furthermore, large scale
consumer-side battery storage will have safety, maintenance and disposal implications that are
yet to play out. The rapid reduction in price for lithium ion batteries is clearly improving the
economics of electricity buffering, in both grid-connected and off-grid situations. But the current
deployment rate is remarkable relative to the small existing installed base, rather than in relation
to the macro-level physical economics of a global transition in all energy supply. The global
market for lithium-ion batteries in 2018, for all uses, was 210 GWh, with roughly 1,000 GWh of
installed capacity (Austrade 2018). For comparison, the current capacity of the European gas
network is 1,131,000 GWh (GIE, 2018).
Concentrated solar power (CSP) offers a further option that can help address the challenges
associated with variable irradiance, when coupled with molten salt thermal storage and/or via
hybridization by coupling with auxiliary boilers fired with conventional fuels or biomass
(Lenzen et al. 2016). The economics of CSP also continue to improve (Mir-Artigues et al.,
2019). Recent analysis of field data indicates, however, that actual performance of CSP plants is
significantly below design and theoretical expectations (de Castro & Capellán-Pérez, 2018;
Yousefzadeh & Lenzen, 2019). This illustrates how the anticipatory problem faced in closing the
gap between theoretical and practically realizable RE potential is not ameliorated even by
focusing on commercially available technology options.
A further challenge in this respect, especially when considering feasibility questions at global
scale, is that local context has a major bearing on the prospects for different renewable sources
and conversion technologies in different regions (Heuberger & MacDowell, 2018). For example,
most of Norway’s electricity comes from hydroelectricity, a vastly different situation to the
world considered as a whole. Iceland’s hydro and geothermal resources make its situation
similarly unique. The prospects for PV electricity are far more favourable in Australia than in the
UK, Canada or Japan, which is a function not only of local irradiance, but of implications of
local irradiance for the relationship between supply and demand power densities (Smil, 2015).
From a global and systemic perspective, this supports the plausibility that powering societies
with 100% RE will be costlier and more difficult than typically assumed, and in turn provides
grounds for preparing and planning for reduced energy supply (by managing demand) rather than
merely trying to ‘green’ existing, or even growing, supply.
There are important nuances here. The economic arrangements that currently prevail globally
entail what could be viewed as enormous waste. For instance, Australians spend AU$24 billion
annually (AU$1300 per capita) on gambling. Diverting expenditure from gambling and other
activities detrimental to health towards zero-carbon energy supply represents a compellingly
straightforward net societal benefit. It seems likely that the financial cost of RE transition,
viewed from a more technocratic perspective in isolation, will be affordable. The question that
we pose here though is what the systemic socio-economic consequences might be of the
fundamental restructuring this implies, given the actual political contexts within which such
change would need to occur. For instance, historical evidence suggests a significant correlation
between expenditure on energy as a proportion of GDP and economic recession (Hall &
Klitgaard, 2011). This appears to be a function of marginal changes in cost share, rather than a
question of affordability in the conventional sense of expenditure exceeding income.
Regardless of this though, reducing overall demand must make the cost of transition lower,
and therefore the scale of the financing task must become comparatively smaller. Here again,
energy descent provides avenues to mitigate obstacles. That said, we would anticipate major
shifts in the means by which financing is achieved under energy descent conditions, especially if
this entails more general economic degrowth not just ‘no growth’ stabilization (see e.g., Jackson
& Victor, 2015). So, this financing question (which cannot be addressed herein) should not
necessarily be viewed through the lens of the finance mechanisms currently employed for RE
3.3. Electricity is only a minor share of global final energy
The storage challenge gets comparatively easier as electricity demand reduces, and becomes
more flexible through load shifting. On the other hand, it is significantly compounded when the
task expands from decarbonizing electricity via RE, to decarbonizing all global energy use.
Transport presents a particular conundrum. The key RE technologies of solar, wind and hydro
produce electricity but electricity comprises between 18% and 40% of global energy use,
depending on the stage of the transformation process and energy accounting methodology. As a
share of ‘World total final consumption by fuel’ reported by IEA (2018, p.16), electricity
comprised 18.8% in 2016, having risen from 9.4% in 1973. Measured in terms of primary energy
use, electricity production accounts for roughly 40% (Palmer & Floyd, 2017).
There is currently a clear trend towards greater electrification of final energy use. As noted
earlier though, the extent to which electrification can reduce primary energy demand for
transport is highly uncertain. Heavy haulage presents a formidable challenge (Friedemann,
2016). For many transport tasks in this and the aviation spheres, electrification will require
energy intensive electricity-to-synfuel processes.
There are many industrial processes that rely on fossilized carbon and hydrocarbons either as
fuels, chemical reactants or both, and for which electrification is not a practical option. Examples
include ammonia production (for fertilizers), and iron ore reduction. The task of satisfying
electricity demand from predominantly intermittent renewable sources is difficult and expensive
even when this is a minor share of the global final energy supply task (Trainer, 2018). The
magnitude of the challenge amplifies if all or almost all energy demand is to be met with
electricity from a similar mix of sources.
Solving this liquid fuel problem appears to be the greatest challenge to creating post-carbon
societies in the present mould (Sims et al. 2014, section 8.3). The realisation of a long-touted
'hydrogen economy', whether in parallel with the current petroleum system or replacing it,
certainly seems to have significant potential for mitigating the scale of this liquid fuel problem,
nonetheless the challenges to this remain formidable (Palmer & Floyd, 2020; Staffell et al.,
3.4. Biofuels?
If the transition to a post-carbon civilisation hinges primarily on addressing the liquid fuels
challenge, and if electrification alone is unable to decarbonize a growing and diversifying fleet of
transport vehicles, then could biofuels offer a solution (Robertson et al., 2017)? Considered
globally, the primary obstacle to scaling up biofuels is the land and resources (or, in the case of
algal biofuels, impacts on marine environment) needed to do so (Mediavilla et al., 2013). Global
population is approaching eight billion people, many of whom today live in conditions of
material deprivation (Hickel, 2017), trending to exceed eleven billion by the end of the century.
Food security is already a serious problem today and will only become more challenging with
population growth and climate destabilisation (Bowles, Alexander, and Hadjikakou, 2019).
Available arable land is finite. The more land and resources dedicated to biofuels, the less there
is for food production, or for biomass for materials such as lumber and pulp (Moriarty &
Honnery, 2018). There is also the risk that expanding biofuel production will drive yet more
deforestation (IPBES, 2019; IPCC, 2018).
A further limitation of biofuels is their typically low energy return on (energy) investment
(EROI) generally less than 5:1 and, for corn ethanol in the United States, close to 1:1 (Murphy
et al., 2011). In comparison, Murphy (2014) found the EROI for petroleum at point of
acquisition to be in the range 10-20:1. More recently, Brockway et al. (2019) have found
aggregate EROI for all final energy carriers from fossil fuels, at the point of entry to the
economy, to be 6:1.
While this closes the gap between conventional energy carriers and
biofuels, biofuels are clearly in the zone of minimum energetic viability (Murphy et al., 2011).
Moriarty & Honnery (2019) have considered the case of biodiesel replacing oil-based diesel in
the production and transport of bioenergy. If, say, the EROIs for conventional diesel and
biodiesel are 10.0 and 2.0 respectively, it is clear that the overall EROI for bioenergy will fall as
biodiesel replaces fossil fuel diesel.
With 2018 global biofuel production only 2% of annual world oil production (BP, 2019), the
prospects for significant scale-up seem remote. Biofuels are sure to play important niche roles in
post-carbon societies, but the overall scale of the contribution, at least on a global scale, is likely
to be very limited relative to liquid fuel use today. On the other hand, biofuels can clearly have
great technical and economic potential in particular contexts. Foran has studied the potential for
We also note in relation to Brockway et al.’s finding that Raugei (2019) cautions against practices of the type that
must be employed in arriving at an aggregate global EROI figure for all energy carriers. Aggregating energy carriers
implicitly treats them as interchangeable, or capable of substituting for one another. In some instances this may be
possible, but only with requisite changes to supply chains and end-use energy conversion devices. In other instances
though, substitution may not be practically possible, even via changes to physical plant and equipment.
bio-methanol use in Australia very extensively, finding much higher EROI values of around 8:1
for the entire fuel cycle (Foran, 2009, 2011).
Again, the questions that we raise with this paper relate to the contexts that lie beyond techno-
economic analysis, for instance the political implications of major shifts in land use, and the
potential for resource use (including land and water) problem shifting (Alexander, Rutherford, &
Floyd, 2018; Van den Bergh et al., 2015). Similar issues can be raised concerning bioenergy with
carbon capture and storage (BECCS), which features centrally as a negative emission technology
in IPCC climate mitigation scenarios (IPCC, 2018; Palmer, 2018; Minx et al., 2018).
3.5. Renewable technologies rely on fossil fuels
Currently the availability of RE interception and conversion technologies their manufacture,
deployment, operation, maintenance and end-of-life management is inextricably dependent on
the fossil fuels that it’s hoped they will replace. This has led some investigators to characterise
wind and solar electricity as fossil fuel ‘extenders’ rather than replacements (Tverberg, 2011).
By adding energy (with zero operational fuel input) at the margins of an electricity grid
system, RE generators reduce the average fuel input per unit of electricity delivered by the grid
system as a whole. But the renewable generators remain reliant on the existing grid to give value
to the electrical energy that they contribute (Palmer, 2014). Beyond this system operability issue,
the situation ramifies on taking into account the myriad ways that fossil fuels enable the supply
chains through which wind turbines and PV equipment come to be deployed in the first place.
For the foreseeable future the deployment of RE infrastructure will remain locked via
innumerable path dependencies to fossil-fuelled industrial production and distribution systems. It
is theoretically conceivable that in the future all the processes involved in RE supply system
production including mining, manufacture and transport can be powered by renewably
generated electricity. But this is subject to a wide range of engineering, economic and
institutional challenges. It will not be possible to anticipate many of the consequences of
confronting these.
This is no argument against as rapid a deployment of RE technology as humanity can
mobilise. Instead, it is a further argument for anticipating societies that require as little energy as
possible to flourish, rather than assuming that energy-intensive societies can simply transition to
RE technologies without difficulty or disruption.
3.6. Energy return on investment
The implications of energy return on investment (EROI) for RE transition feasibility is a vexed
and often highly contentious area of inquiry (Moriarty & Honnery, 2012b, 2016, 2019). The
EROI for an energy supply technology is highly context specific, and it is not possible to arrive
at definitive assessments of EROI for any one RE source that apply to all situations (Palmer &
Floyd, 2017). Nonetheless, some general observations can be made about EROI of wind and PV
electricity relative to incumbent energy sources, and how this relates to questions about the
forms that future societies may take.
Firstly, it is axiomatic that adding energy storage, increased transmission and distribution, and
redundant supply capacity to existing systems entails significant energy costs and hence reduces
EROI at the overall system level (Palmer & Floyd, 2017). Additionally, at higher grid
penetrations the EROI of RE decreases, since the most productive spaces get used first (Dupont
et al., 2018; Moriarty & Honnery, 2012b). This can be mitigated only to the extent that
technology change and efficiency improvements offset these increasing system-level energy
costs. Secondly, to the extent that RE systems remain dependent on a globally integrated
industrial economy dependent on fossil fuels (see subsection 3.5 above), then declining EROI of
fossil fuels will feed through into declining EROI of these systems.
Following from this, a question arises as to what declining EROI implies for the viability of
consumption- and growth-oriented industrial economies (Hall et al., 2014; Lambert et al., 2014).
As EROI declines, the proportion of total available energy services that must be directed towards
the overall economy’s energy supply sub-system increases. If overall supply of energy services
cannot expand fast enough to compensate, then this implies reducing energy service availability
for all other economic activity enabled by the energy sub-system. In such a situation, the strong
dependence of economic activity on sufficient energy services implies a contraction in the rest of
the physical economy (Ayres & Voudouris, 2014).
A situation such as this would be exacerbated in the transition phase to RE, as the energy
investment in transitioning supply systems to renewable sources represents an additional drain on
available energy services. The required energy investment rate is particularly sensitive to the rate
of transition (Honnery & Moriarty, 2011; Kessides & Wade, 2011; Neumeyer & Goldston, 2016;
Carbajales-Dale et al., 2014; Capellán-Pérez et al., 2019; Carbajales-Dale, 2019). Wind and PV
electricity supply systems require nearly all of their energy investment up front, before they
deliver useful outputs, increasing the sensitivity to transition rate. The higher the transition rate,
the greater the diversion of energy services from the rest of the economy to the energy sector.
Attention at this point often turns to the question of the minimum EROI required to support
societies functionally equivalent to today’s (Hall et al., 2009; Brandt, 2017; Capellán-Pérez et al.,
2019; Raugei, 2019). Brandt (2017), for instance, finds that below 5:1, energy available for
discretionary purposes declines rapidly. Views vary on precisely where this threshold might lie
for any given society. What can be stated clearly, however, is that in order to remain viable in
energetic terms, any social form ultimately requires that forms of energy services appropriate to
support its basic ‘economic metabolism’ be available when and where required at sufficient
rates. In principle, so long as the energy sector delivers more energy over its lifecycle than it
uses for that task (i.e. EROI > 1), then viability is dependent on having sufficient power
availability at any given instant in time. But EROI is specifically defined over the full lifecycle
of an asset. Even if a supply system comprises assets with EROI much greater than 1 over their
operating lives, the power return ratio (the rate of energy return over the rate at which energy is
used to provide the return) (King et al., 2015) for the system as a whole at a given instant in time
can be far lower, even less than one.
Ultimately, the viability of a society from an energy perspective depends on its ability to meet
the ongoing costs (financial, environmental, material and energetic) of providing sufficient
power at any given point in time. Energy-focused lifecycle assessment is clearly essential for
understanding the long-term prospects of any social form, and hence for assessing the feasibility
of transitions to 100% RE. But at the whole-of-society level for which such assessment must be
conducted, it is power return ratios that are most directly relevant (King et al., 2015).
Transition from fossil fuelled societies to societies powered by 100% RE, at least on the
multi-decadal timeframes that are typically discussed by proponents, will most likely constrain
the energy available to non-energy supply economic sectors (Capellán-Pérez et al., 2019). To
enable such transition, economies and the societies that they support will need to adapt
3.7. Power density
The spatial intensity of energy use is often overlooked in assessing the prospects for renewably
powered societies, but is critically important. This spatial intensity is most readily measured via
power density, typically the rate of energy use or supply per unit of horizontal land area occupied
by the systems involved (Smil, 2015).
While the power densities achieved by incumbent supply systems typically exceed the power
densities at which energy is used in urban industrial societies, for RE this relationship between
power density of supply and use is reversed. In fact with power densities ranging from roughly 1
W/m2 (electricity out) for wind to a few tens of watts per square metre for PV (averaged over a
year), RE supply power density is orders of magnitude lower than peak usage rates for industrial
plants and high-rise buildings (often greater than 1000 W/m2), and lower even than average rates
over city centres (in the order of 500 W/m2) (Smil, 2015). Even energy use power densities
averaged over entire city areas (including low-density suburbs) can be several times higher than
maximum power densities for best-case PV supply. More recent estimates for supply-side power
densities of onshore wind and PV derived from large numbers of geographically diverse actual
installations are considerably lower even than Smil’s estimates above: 0.5 W/m2 and 5.4 W/m2
respectively (Miller & Keith, 2018).
Consequently, a transition to energy systems dominated by renewable sources will see a shift
from energy supply occupying much smaller areas than those over which it is used, to one in
which human settlements depend on hinterlands many times their size to capture and concentrate
the energy that they rely on (Smil, 2015). Without vast reductions in power density of energy
use, there is essentially no prospect that urban densification and local energy self-sufficiency will
coexist. Such self-sufficiency will be possible only where demand expectations are reduced, and
density of habitation is sufficiently low. Where local climate conditions are favourable, suburban
population densities probably represent the upper limit for household or neighbourhood energy
This presents a major challenge in light of the ongoing urban densification trajectory (Burger
et al, 2019). A shift to energy supply dominated by RE will also mean high reliance on utility-
scale systems, and an increased rather than decreased reliance on grid interconnectivity, though
with major changes in grid architecture. While this is clearly the direction that electricity grids
are heading in any case (Rai et al., 2019), widespread shift towards greater local energy self-
sufficiency would also require reversal in densification of settlements. This infers major
implications for settlement forms and governing institutions. Fundamental indeterminacy in
relation to the specifics of these forms and institutions, and the second-order consequences of
such changes, is therefore implied. Again, however, the disruptions entailed would be
significantly ameliorated by energy demand reductions realised through coordinated social
change processes (Trainer, 2019b).
3.8. Energy system transitions are slow and complicated
The experience of accelerating technological change, particularly in relation to computing and
information technology, but also in the renewable energy area itself, drives a widespread
perception that a transition to 100% RE can occur on a timeframe of a few decades (Jacobson et
al., 2017a). Some proponents even tout the plausibility of achieving this in a single decade (e.g.
Gore, 2008). Such hopes are strongly at odds with the record of historical energy transitions
(Grubler et al., 2016, Smil, 2010; Smil, 2014; Smil, 2016).
The concept of ‘energy transition’ can be defined in different ways, and can refer to energy
supply, end-use converters, and prime movers (Sovacool 2016). There are many context-specific
examples of rapid development in the historical record, including nuclear electricity in France,
flex-fuel vehicles in Brazil, and combined heat and power in Denmark. However, if a transition
is measured from the time an energy system or technology occupies a 1% global share, up until
reaching a significant share, such as 25%, the timeframe is of the order of many decades up to
longer than a century.
Furthermore, none have involved the scope and scale of change involved in shifting en
masse to renewable energy. This is because past transitions, even with the large-scale expansion
of coal use, have tended to involve expansion of total supply by adding new energy sources to
the existing base, rather than substituting incumbent sources with alternatives. For RE to replace
rather than just extend fossil fuels, fossil-fuelled supply capacity will need to be retired as RE
capacity is rolled out. This is a far more institutionally, infrastructurally and logistically complex
challenge than expanding existing capacity by adding RE at the margins of the fossil-fuelled
As we have noted, rapid transition can have significant implications for energy service
availability for the rest of the economy. Retiring existing assets in parallel exacerbates this.
3.9. Two meta-factors
In addition to the eight points just discussed, we highlight two ‘meta-factors’ that constrain the
potential for humanity to do via RE what it currently does via its incumbent energy systems.
Firstly, RE technology is dependent on a wide range of mineral resources for which a major
transition effort will have significant implications for overall demand (Jefferies, 2015). This can
be expected to drive environmental and resource use ‘problem shifting’, whereby addressing one
set of challenges leads to new problems in other areas (van den Bergh et al., 2015, Parrique et al.
2019). The increased engineering and economic effort to meet new demand implies major costs,
measurable in financial, environmental and resource terms.
The second ‘meta-factor’ enters the picture here. If such a transition is long, difficult and
expensive, then systems of human organisation and their environments will evolve together
accordingly in a manner that conserves their mutual adaptation. Whatever forms this takes will
very likely entail reduced availability of, and hence demand for, energy services and so energy
will be intercepted from the environment and converted to forms useful to human systems at
rates far lower than for incumbent sources.
4. Conclusion: a call for knowledge humility in response to post-normal times
Here we have attempted to set out a cumulative case (albeit in summary form) demonstrating
why quantitative analytical methods cannot definitively demonstrate that industrialised societies
functionally equivalent to those familiar today can be powered entirely (or almost so) via RE.
However, as we have argued throughout, unpacking this question of renewable energy’s capacity
to meet humanity’s demand for energy services depends also and significantly on the level of
that demand. Here we need to consider what is required, in terms of energy services, to live in
the ways that humans are content to live which is a highly vexed and contested issue.
The nature of the envisaged transition means that we are entering entirely unexplored territory,
and the pathways that we walk into existence are subject to inherent, irreducible uncertainty. It is
impossible to know up front just how these pathways will unfold, the full range of challenges
that will be encountered along the way, and where the novel responses to them will take us. As
such, there is very good reason to think that the situations that emerge will be very different from
the expectations created by any model constructed or plan conceived today. It seems prudent to
conclude that global-scale transition away from fossil fuels leads humanity into the post-normal
realm of ‘unthought future(s)’ (Sardar & Sweeney, 2016).
Here actors will do better to anticipate complex, uncertain and chaotic conditions as typical,
rather than extreme outliers. The perspectives on energy-society futures that are most influential
today typically remain grounded in Sardar and Sweeney’s (2016) ‘extended present’.
Unanticipated developments are treated as perturbations away from the historical conditions of
order and equilibrium stable conditions towards which systems can be expected to return via
the interventions of orthodox governance institutions. The analysis presented here implies that
this stance is no longer tenable. Uncertainty of the nature now faced demands new governance
approaches that embody learning and reflexivity as the basis for guiding action (Grunwald, 2004;
Voß, Bauknecht, & Kemp, 2006).
Consistent with such a conclusion, we believe that the situation we have outlined here infers
the need for a high degree of ‘knowledge humility’ in approaching energy transition questions.
The prospects for viable futures will be greatly assisted by acknowledging that even the best
available evidence today leaves many questions open and in need of continued inquiry. This case
for humility can only be emphasised further when one looks at the real world to see how slowly
the renewable energy transition has advanced in recent decades. The world knew enough about
fossil fuels and climate change in 1988 to establish the IPCC, but in the last thirty years, very
modest progress has been made on the post-carbon transition. Wind, solar and geothermal
together provided merely between 1.7% (IEA, 2018) and 4.1% (BP, 2019) of global primary
energy supply depending on energy accounting convention. A transition to 100% renewable
energy is likely going to be more difficult, slower and almost certainly more expensive than is
typically thought to be the case.
We believe that such an assessment holds regardless of whether the challenge is framed in
post-normal terms. Even if transition is viewed through the prism of normalcya matter of
incrementally applying established science and technological understanding with no major
further-order implications for wider social contextsthen a situation is still faced in which
relying upon a ‘normal’ change trajectory leads to extraordinary climate impacts. While
knowledge humility is a disposition suited especially well to post-normal times, it will also
support more judicious policy and action where prevailing conditions are perceived as normal.
The greater the demand for energy services, the lower the likelihood that RE can meet that
demand. As demand expectations decrease, the likelihood increases. The fundamental practical
point, with respect to energy-intensive societies, is that it would be better to organise and prepare
for reduced energy demand (i.e. energy descent), because the less energy we need, the more
readily any transition to 100% RE will be realised. This is so, even as the particular forms of the
societies and political-economies to which such transitions give expression become increasingly
difficult to envision where thinking is constrained by past experience where, as Ramirez et al.
(2019, p. 76) discuss, drawing on Kahneman and Klein’s (2009) work on expert judgement,
“those with the most experience will not necessarily make the wisest decisions”. And in light of
this, the distributive question of how to equitably share the RE that is available in any post-
carbon society only strengthens the case for preparing for energy descent futures.
Within these circumstances, humility becomes more than a precautionary support to better
quality policy and planning. Following Sardar (2010), alongside the virtues of modesty and
accountability, it forms part of an adaptive value set that may support human societies in
navigating as-yet unknown pathways to live well in the face of post-normal dilemmas.
This research did not receive any specific grant from funding agencies in the public,
commercial, or not-for-profit sectors.
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... Confidence in the possibility of completely replacing fossil fuels with energy production based on renewable sources is the central element on which the transition plans are being developed [4]. However, there are several reasons to be cautious and to point out the limitations of a strategy focused solely on "greening" energy production, without acting simultaneously on energy demand, may encounter [5]. Strategies focused exclusively on the energy-climate dimension often hide many other elements that need to be taken into account to achieve a transition that does not worsen ecological degradation, such as biodiversity loss [6]. ...
... This fact could be accentuated by the decrease in the ore grade of some key minerals for these technologies, as is the case of copper [23]. Likewise, there are other issues that feed this uncertainty, such as the current dependence of renewable technologies on fossil fuels, the difficulties in the electrification of many current energy uses, or the integration of variability in the grid [5]. For these reasons, Floyd et al. call for "knowledge humility" about what the real energy transition scenarios might be [5]. ...
... Likewise, there are other issues that feed this uncertainty, such as the current dependence of renewable technologies on fossil fuels, the difficulties in the electrification of many current energy uses, or the integration of variability in the grid [5]. For these reasons, Floyd et al. call for "knowledge humility" about what the real energy transition scenarios might be [5]. ...
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A global energy consumption reduction is essential to address the many dimensions of the current ecological crisis. In this paper we have compiled the reasons that justify the necessity to start this energy descent process in the countries of the global North, where the annual per capita final energy consumption was 118 GJ in 2017. Based on recent research, we approach the necessary redistribution of energy consumption at the global level and the elements that should be present in energy descent strategies. We establish an approximate threshold of minimum and maximum per capita final energy consumption, between 15.6 GJ and 31.0 GJ for the year 2050, which serves as a reference for evaluating scenarios. We continue with an analysis of two ecological transition scenarios for Spain between 2020 and 2030, Green New Deal and Degrowth. Based on a schematic calculation model defined in “Labor Scenarios in the Ecosocial Transition 2020–2030” report, we evaluate the variations in energy consumption for 86 sectors of economic activity. Results show an annual final energy consumption per capita in 2030 of 44.6 GJ and 36.8 GJ for each scenario. We conclude by analyzing the hypothetical main drivers of this sharp decline in energy consumption.
... Quantification, through the language of mathematics, can give a false sense of concreteness which often serves to reinforce perceptual uniformity and rigidity. Floyd et al. (2020) argue that energy system models built on principles of pluralism and epistemic humility are needed, and the proper interpretation of results requires transparency regarding the limitations of the chosen modelling approach [127]. ...
Actions that transform our energy system are the cornerstone of decarbonizing our economy but have been hindered by the ineffective interface between researchers and decision-makers in Canada. This paper begins by arguing for a more holistic perspective on energy system decarbonization modelling and exploring how insights can aid evidence-based decision making. We then respond with the development of a modelling platform that includes three core pillars: (1) a toolbox of models that together represent the integrated energy system, (2) a dataset containing the inputs required to populate those models, and (3) a visualization suite to analyze and communicate their outputs. The Spine Toolbox is leveraged to process these three components in an efficient workflow. Taken together, the platform promotes the usability of model results by fostering consistency, transparency, and timeliness. Furthermore, the epistemic limitations of energy systems modelling and implications for platform and model design, and engaging extended peer communities, are discussed. Our hope is that this platform can be a foundational resource that facilitates collaboration between energy system and decarbonization researchers, modelling teams and decision-makers, ultimately enabling the effective application of evidence-based policy.
... A well-conducted futures exercise has a transformative potential to contribute to the development of pluralistic and desirable future scenarios and pathways. Increasingly, future studies are used in developing low carbon transition or sustainability transition studies (Floyd et al., 2020;Poggi et al., 2020;Söderholm et al., 2011). These future studies are used at different spatial scales ranging from global systems to city or municipal wide systems (Eames et al., 2013;Poggi et al., 2020;World Energy Council, 2017), and increasingly, future studies also focus on specific sociotechnical systems such as energy (Lachman, 2011), food (Chaudhury et al., 2013;Mitter et al., 2020), transport (Tuominen et al., 2014;Vallet et al., 2020) and consumer goods (Kuzmina et al., 2019). ...
The beginning of the post-fossil fuel era is evident in trends such as fossil fuel divestment, cheaper alternative energy sources, and disruptive technologies that are enabling responsive and reliable alternative energy systems. In this global low-carbon transition, states (countries) that are dependent on hydrocarbon revenues confront an uncertain future, requiring urgent actions to reduce their economic and societal dependence on hydrocarbon revenues. It is well known that choices made will have significant impacts on wealth and prosperity. Unfortunately, desirable transition pathways remain unclear and the benefits ill-defined. Addressing this critical gap in knowledge, this paper frames the construct of a ‘low-carbon transition’ for hydrocarbon-dependent rentier states, presenting 16 decision-support scenarios across three key categories of industrial, economic and energy/ environmental futures. The study used backcasting methods in four creative-narrative scenario workshops focusing on Qatar, engaging with a diverse group of senior technology and policy professionals. The authors discuss the findings in relation to tensions, contradictions and dominant narratives about a low carbon future. The utility of these narratives is concluded by providing a systematic approach for public and private sector leaders to appreciate and plan for a low carbon transition in hydrocarbon-dependent rentier states. The findings provide a useful framing for the future and foresight practitioners working in a similar cultural context.
... In Floyd et al. (2020) (hereafter Floyd et al.) we address anticipatory challenges associated with the envisaged transition from fossil fuels to renewable energy (RE). In particular, we consider the question of whether RE can replace (and replace in a timely way, see Floyd et al. section 3.8) the full scope of current global energy services. ...
Floyd et al. (2020), ‘Energy descent as a post-carbon transition scenario: How ‘knowledge humility’ reshapes energy futures for post-normal times’, addresses anticipatory challenges associated with the envisaged transition from fossil fuels to renewable energy. We make the case that the epistemic nature of analytical techniques based on quantitative modelling is such that it cannot establish in any definitive sense the feasibility of providing present and future projected global energy services via renewable sources, and that as such energy transition governance and management approaches should be adopted that recognise and respond to this situation, including the plausibility of futures characterised by energy descent that it implies. A response from Mark Diesendorf mischaracterises our case in multiple ways, including to suggest that it is an argument against renewable energy. Further, the response fails to engage with the substance of our arguments for the plausibility of energy descent, and in multiple instances presents our arguments erroneously. We identify the specific failings of the response and show why its claim to have refuted our case is not supported. We discuss the broader implications of the epistemic stance on which the response is based for energy-society futures inquiry.
... Overall, critical realism can be described as having a humble epistemological position. This is akin to the position of 'knowledge humility' of post-normal science (Floyd et al., 2020). ...
Degrowth scholarship has enjoyed considerable momentum in recent times, resulting in a growing, diverse and vibrant field of research. Against this background, it becomes pertinent to reflect on the nature of degrowth science and on the philosophical assumptions underpinning it. Advocates of the degrowth perspective have so far largely abstained from engaging in such reflections and have yet to discuss degrowth in relation to established philosophy of science perspectives. The present paper puts degrowth in a discourse with critical realist philosophy of science to provide visions as to what degrowth as a science can see itself as and strive to become. A dialogue between the two perspectives that brings into focus ontology, epistemology and axiology is initiated. It is suggested that degrowth scholarship contains many elements that are consistent with critical realism, albeit arguably in a scattered manner. While degrowth aims to enact change in the real world, critical realism offers a deep account of the real world and proposes how knowledge of it can emerge and result in transformative practice. The paper proposes that degrowth scholarship can come to be practised in a more holistic manner and thus advance by engaging with critical realism.
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The ability of RE to fully supply all global energy needs, both now and in the future, is subject to considerable controversy. This chapter first examines the concept of Energy Return on Investment (EROI) as a crucial test for FF project feasibility, and so the technical potential of RE sources. It is found that inclusion of the full input costs of RE, including the energy costs of maintaining ecosystem functions, leads to large reductions in evaluated EROI, even though exact values are not available. In principle, a graph of EROI versus energy production can be drawn for an energy source, enabling technical potential to be determined. The chapter then reviews in turn the prospects for solar, wind, biomass, hydro, geothermal, and ocean energy, pointing out their benefits as well as their environmental disadvantages. Although bioenergy and hydro are the most important sources today, wind and solar energy have by far the greatest potential—and are the most rapidly growing. It is concluded that renewable energy may not be as green or abundant as often portrayed.
A recent article by Floyd et al. argues a case for energy descent by critiquing renewable energy scenario modelling and arguing there is uncertainty as to whether a transition from fossil fuels entirely to renewable energy is possible. This paper addresses the part of their case that’s within the framework of normal science. In it, Floyd et al. uncritically cites well-known, previously-refuted criticisms of renewable energy to argue that uncertainties exist. In reply, this paper argues that energy modelling has produced valuable real-world results, the uncertainties within the framework of normal science are solvable given the political will, the critical articles cited by Floyd et al. are flawed or irrelevant, and most of the issues have been solved in practice in jurisdictions where the majority of electricity is supplied by variable renewables. There are better arguments by others for energy descent and degrowth than critiquing renewable energy. In the absence of political will to support socio-technical transitions, we enter the domain of post-normal science, also discussed by Floyd et al., where the barriers to energy descent and degrowth may be much greater than barriers to 100% renewable energy.
Just transition aims to reconcile environmental and social concerns especially for fossil-fuel dependent areas. Yet even with broad support, we can expect ongoing shocks and events to shape the implementation of just transition agendas. In concept and practice, just transitions must directly account for and anticipate profound uncertainties regarding the social and ecological context in which such projects are planned and implemented, while breaking from growth dependence. This paper argues that the future of just transitions must center on essential care work to better ensure well-being without economic growth. The essay examines diverse perspectives on the meaning of just transition, articulating a more transformative approach under conditions of economic instability. The review demonstrates broadening understandings of just transitions, spanning from those more narrowly focused on immediate worker- and sectoral supports to those aiming for more fundamental and lasting transformations of economies and societies. Given the extreme social, economic, and ecological uncertainties of our time, the paper lastly proposes temporally overlapping agendas for policies, strategies, and institutions of just transition organized around post-growth care work. As inspired by the field of futures studies, the article contributes a set of criteria to help advance just transitions beyond fossil fuel and growth dependence.
Water electrolysis powered by solar photovoltaics (PV) is one of several promising green hydrogen production technologies. It is critical that the life cycle environmental impacts and net energy balance are...
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While the crisis of statistics has made it to the headlines, that of mathematical modelling hasn’t. Something can be learned comparing the two, and looking at other instances of production of numbers.Sociology of quantification and post-normal science can help.
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Parrique T., Barth J., Briens F., C. Kerschner, Kraus-Polk A., Kuokkanen A., Spangenberg J.H. 2019, 78 pp. Is it possible to enjoy both economic growth and environmental sustainability? This question is a matter of fierce political debate between green growth and post-growth advocates. Over the past decade, green growth clearly dominated policy making with policy agendas at the United Nations, European Union, and in numerous countries building on the assumption that decoupling environmental pressures from gross domestic product (GDP) could allow future economic growth without end. Considering what is at stake, a careful assessment to determine whether the scientific foundations behind this “decoupling hypothesis” are robust or not is needed. This report reviews the empirical and theoretical literature to assess the validity of this hypothesis. The conclusion is both overwhelmingly clear and sobering: not only is there no empirical evidence supporting the existence of a decoupling of economic growth from environmental pressures on anywhere near the scale needed to deal with environmental breakdown, but also, and perhaps more importantly, such decoupling appears unlikely to happen in the future. The validity of the green growth discourse relies on the assumption of an absolute, permanent, global, large and fast enough decoupling of economic growth from all critical environmental pressures. The literature reviewed clearly shows that there is no empirical evidence for such a decoupling currently happening. This is the case for materials, energy, water, greenhouse gases, land, water pollutants, and biodiversity loss for which decoupling is either only relative, and/or observed only temporarily, and/or only locally. In most cases, decoupling is relative. When absolute decoupling occurs, it is observed only during rather short periods of time, concerning only certain resources or forms of impact, for specific locations, and with very small rates of mitigation. There are at least seven reasons to be skeptical about the occurrence of sufficient decoupling in the future: Rising energy expenditures, Rebound effects, Problem shifting, The underestimated impact of services, The limited potential of recycling, Insufficient and inappropriate technological change, and Cost shifting. Each of them taken individually casts doubt on the possibility for sufficient decoupling and, thus, the feasibility of “green growth.” Considered all together, the hypothesis that decoupling will allow economic growth to continue without a rise in environmental pressures appears highly compromised, if not clearly unrealistic. This report highlights the need for a new conceptual toolbox to inform and support the design and evaluation of environmental policies. Policy-makers have to acknowledge the fact that addressing environmental breakdown may require a direct downscaling of economic production and consumption in the wealthiest countries. In other words, we advocate complementing efficiency-oriented policies with sufficiency policies, with a shift in priority and emphasis from the former to the latter even though both have a role to play. From this perspective, it appears urgent for policy-makers to pay more attention to and support the developing diversity of alternatives to green growth.
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Under many scenarios, fossil fuels are projected to remain the dominant energy source until at least 2050. However, harder-to-reach fossil fuels require more energy to extract and, hence, are coming at an increasing ‘energy cost’. Associated declines in fossil fuel energy-return-on-investment ratios at first appear of little concern, given that published estimates for oil, coal and gas are typically above 25:1. However, such ratios are measured at the primary energy stage and should instead be estimated at the final stage where energy enters the economy (for example, electricity and petrol). Here, we calculate global time series (1995–2011) energy-return-on-investment ratios for fossil fuels at both primary and final energy stages. We concur with common primary-stage estimates (~30:1), but find very low ratios at the final stage: around 6:1 and declining. This implies that fossil fuel energy-return-on-investment ratios may be much closer to those of renewables than previously expected and that they could decline precipitously in the near future.
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A number of official energy forecasts-including those compatible with the aspirational 1.5 °C Paris Accord global temperature rise limit-see both global primary and net energy use continuing to rise, even out to 2100. Various technologies, including greatly increased use of renewable and nuclear energy, negative emission technologies such as direct air capture, and geoengineering are proposed as approaches for meeting the 1.5 °C target. In contrast, we argue that meeting this target and avoiding significant increases in extreme weather events will require marked reductions in future energy demand. We argue that the combined fossil fuel and renewable net green energy production will fall in the coming decades, after subtraction of various energy costs essential for ecosystems maintenance, including those needed to stabilise climate. At best, nuclear energy will only fractionally increase its global energy share, because of its high capital costs and political opposition arising from accident risks, waste disposal and proliferation concerns. Geoengineering will not solve fossil fuel depletion, and has serious known-and perhaps unknown-risks. We conclude that global net energy produced in an ecologically sustainable manner will start falling in a decade or so, and suggest the need to account for this at a policy level by introduction of a green EROI-EROIg.
Fossil fuels comprise the accumulation of prehistoric biomass that was energised by sunlight, and formed by earth system dynamics. Fossil fuels can be conceptualized as stored energy stocks that can be readily converted to power flows, on demand. A transition from a reliance on stored energy stocks, to renewable energy flows, will require a replication of energy storage by technological devices and energy conversion methods. Most analyses of energy storage focus solely on the economic-technical properties of storage within incumbent energy systems. This book broadens the scope of the study of storage by placing it within a broader, historical, biophysical framework. The role and value of storage is examined from first principles, and framed within the contemporary context of electrical grids and markets. The energy-economic cost of electrical storage may be critical to the efficacy of high penetration renewable scenarios, and understanding the costs and benefits of storage is needed for a proper assessment of storage in energy transition studies. This book provides a starting point for engineers, scientists and energy analysts for exploring the role of storage in energy transition studies, and for gaining an appreciation of the biophysical constraints of storage.
Concentrating Solar Power (CSP) plants can make a significant contribution to renewable energy supply in many regions of the world. Several bottom-up engineering performance models for CSP plants have been developed. However, they require the capacity of the plant to be known. In whole-of-grid optimization models, the capacity of the plants is an optimization variable and therefore not known in advance. In this case, researchers have taken a simplified modelling approach that overestimated CSP performance, especially for low-DNI conditions. In this paper, we offer a novel density-based engineering modelling approach in which CSP performance is determined independently of the capacity of the power plant, and which can be used in whole-of-grid optimization models. We investigate a case study of the site of the new Aurora CSP project in Port Augusta, South Australia, to be one of the world's largest solar thermal power plants by 2020. Using a Geographical Information System (GIS)-grid representation of Australia, we compare CSP performance resulting from a simplified model with our new approach.
A novel methodology is developed to dynamically assess the energy and material investments required over time to achieve the transition from fossil fuels to renewable energy sources in the electricity sector. The obtained results indicate that a fast transition achieving a 100% renewable electric system globally by 2060 consistent with the Green Growth narrative could decrease the EROI of the energy system from current ~12:1 to ~3:1 by the mid-century, stabilizing thereafter at ~5:1. These EROI levels are well below the thresholds identified in the literature required to sustain industrial complex societies. Moreover, this transition could drive a substantial re-materialization of the economy, exacerbating risk availability in the future for some minerals. Hence, the results obtained put into question the consistence and viability of the Green Growth narrative.
The increasing penetration of variable renewable electricity generation in Australia’s National Electricity Market over the past decade has led to a sustained change in the shape of electricity demand. In particular, intra-day demand has become more volatile, with demand in some Australian regions increasingly resembling the widely-cited ‘duck curve’ or more appropriately the ‘emu curve’. The changes in demand have, in turn, economically driven out generators whose technical characteristics are ill-suited to supplying this demand profile: high capacity-factor, slow-start plant. In this article, we describe the changes to date in the profile of electricity demand, and draw on other studies to argue that these trends are likely to accelerate going forward based on projected future uptake of variable renewables. In combination with technological and policy developments, these trends imply that flexible plant, such as peaking gas, hydro, and dispatchable storage, are likely to be better suited to the changing profile of demand, in contrast to slow-start and relatively inflexible technologies such as coal and combined-cycle gas plants. These trends are based on the flexibility of different generation technologies and their interaction with emissions considerations
The CSP value chain comprises many activities ranging from the development, civil works, solar field, tower, receiver, control, piping/valves, steam generation, turbine, cooling system, electrical system, auxiliary system, assembling, and research [15]. As of today, Europe is still the technological leader in the CSP sector and, given that one of the priorities of the Energy Union is to “become world leader in renewables”, Europe is making efforts to preserve this status.
Blakers et al. claim that pumped hydro storage will enable a 100% renewable electricity supply for Australia. However aspects of their case are questionable and require clarification or confirmation. This study seeks to discuss these, not with the aim of settling questions but of pointing to issues that would require verification before the viability of the proposal could be regarded with confidence.