The emerging field of energy transitions: Progress, challenges, and opportunities

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Original research article

The emerging field of energy transitions: Progress, challenges, and opportunities Kathleen Araújo ∗ Harvard Kennedy School of Government, Belfer Center for Science and International Affairs, 79 John F. Kennedy Street, Mailbox 117, Cambridge, MA 02138, USA1

a r t i c l e

i n f o

Article history: Received 23 January 2014 Received in revised form 4 March 2014 Accepted 5 March 2014 Keywords: Energy transition Energy system change Policy and governance Learning Path dependence Path creation Multi-level perspective Techno-economic paradigm Globalization Urbanization Population

a b s t r a c t Energy transitions are an unmistakable part of today’s public discourse. Whether shaped by fuel price fluctuation, environmental and security concerns, aspects of technology change, or goals to improve energy access, attention regularly turns to ways in which to improve energy pathways. Yet what is understood about energy system change is still emerging. This article explores the evolving field of energy transitions with an aim to connect and enlarge the scholarship. Definitions and examples of energy transitions are discussed, together with core ideas on trade-offs, urgency, and innovation. Global developments in energy and related mega-trends are then reviewed to highlight areas of analytical significance. Key information sources and suppliers are examined next. The article concludes with ideas about opportunities for further research. © 2014 Elsevier Ltd. All rights reserved.

1. Introduction Changing the way we utilize energy is a recurring theme in today’s public discussions. One need only look to policies that prioritize greener economies, evolutions in unconventional oil and gas, or post-Fukushima adjustments in nuclear energy utilization to see elements of change underway. Despite frequent focus, no universally accepted definition of ‘energy transition’ exists. A review of energy transition writing shows that varied meanings have been in use since the early 1900s for topics, including quantum electrodynamics and industrial adaptation (Fig. 1). Writing on the subject in the 1930s, for instance, considered change in energy states that occurs with molecular dissociation [2]. Coverage in the 1970s centered on fuel substitution and resource limitations [3]. More recent writing highlights ways to transform economies in order to reduce carbon emissions [4]. The contemporary focus also emphasizes how developments in technology,

∗ Tel.: +1 617 495 1314. E-mail address: Kathleen [email protected] 1 http://belfercenter.ksg.harvard.edu/experts/2696/kathleen araujo.html.

information and practices can alter the way that energy is utilized [5]. To bridge these nuances in meaning, a more cross-cutting definition is used here – namely, a shift in the nature or pattern of how energy is utilized within a system.2 This definition recognizes the change associated with fuel type, access, sourcing, delivery, reliability, or end use as well as with the overall orientation of the system. Change can occur at any level – from local systems to the global one – and is relevant for societal practices and preferences, infrastructure, as well as oversight [6]. Prominent examples of energy transitions are evident today. Change in the Danish energy system, for instance, reflects a rise in the overall annual share of wind power in the electricity mix from under 1% in 1980 to 33% in 2013 [7]. Similar growth occurred in the Danes’ use of combined heat and power (CHP or cogeneration), rising from 18% to 75% in total thermal production between 1980 and 2012, and from 39% to 73% in district heating [8]. These changes have enabled the Danish energy system to become increasingly

2 An energy system is a constellation of energy inputs and outputs, involving suppliers, distributors, and end users along with institutions of regulation, conversion and trade. Energy system change and energy transitions or shifts are used interchangeably in this article.

http://dx.doi.org/10.1016/j.erss.2014.03.002 2214-6296/© 2014 Elsevier Ltd. All rights reserved.

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With this context in mind, I begin by examining some prevailing ideas relating to energy system change. I then evaluate key patterns of analytical significance in energy transitions and related megatrends. This is followed, next, by a discussion of key resources, actors and theory. I conclude with some ideas about opportunities for further research.

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2. Ideas about energy transitions

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Fig. 1. Publications covering ‘energy transitions’. Source: Based on ‘energy transition’ in titles, abstracts, or keywords of scholarly publications [1] A more, narrow search of the social sciences and humanities revealed a similar, albeit smaller-scaled, trend. The search could also be varied for related terms like ‘energy system change’, ‘energy transformations’, etc.

decentralized and efficient3 [9]. Somewhat different in nature is Germany’s nuclear phase-out, following the Fukushima Daichi accident in 2011. This shift entailed the shutdown of 8 out of 17 nuclear reactors, with the remaining nuclear fleet scheduled for closure by 2022 [10]. If the German power supply is considered between 2010 and 2012, the total decreased by 3% [11] as its share from renewable energy rose from 10% to 12% [12].4 Contrary to some expectations, Germany’s net exports in electricity also grew by 5586 GWh in the period between 2010 and 2012 [11,13].5 Yet another example of an energy transition can be seen with what is occurring in the United States. In this instance, the application of hydraulic fracturing and horizontal drilling technology to unconventional gas and oil in recent years has contributed to a notable rise in output. Between 2002 and 2012, natural gas and oil production grew by 27% and 13%, respectively [14]. In line with these changes, the United States has reduced its oil imports by 30% and is on the cusp of becoming a net exporter of natural gas [15]. While the above examples offer interesting views of contemporary energy system change, they do not entirely explain how the shifts are accomplished or what implications the transition may have. That is where social science plays an instrumental role. The launch of the Energy Research & Social Science journal provides a forum to more fully explore such areas. In this article, I draw upon previous analyses of energy systems and technology change [16,17], surveys of data and literature, as well as discussions with energy researchers,6 to explore elements in the emergent field of energy transitions. The resultant overview identifies a number of areas where researchers, particularly those in the social sciences and humanities, might strengthen the scholarship. Other articles in this special issue consider related themes, including Sovacool’s content analysis of energy publications and proposed research agenda [18]; Brown and Pasqualetti’s discussion of geographic contributions to energy-society studies [19]; Fri and Savitz’s writing on ways that the social sciences can support the management of an energy transition [20]; and Jones and Hirsh’s exploration of how history enhances energy research and policy [21], among others.

3 Danish CHP plants can scale heat or power output, based on demand. Since they also have heat storage, surpluses can be set aside for later use. Note: The shift in self-sufficiency and clean energy is another area of significance in energy transitions research. 4 The domestic power supply (production with net imports) declined 3% from 613,941 GWh to 597,059 GWh [11]. The trend toward renewables continued in 2013 to 11.8% [12]. 5 Imports grew by 3307 GWh, while exports increased by 8893 GWh. [11] 6 This essay is not intended to be a comprehensive review.

To understand the nature of energy transitions studies, it’s useful to first identify prominent ideas in the energy and policy communities. 2.1. Urgency In today’s discussions, an often-articulated perspective emphasizes how current conditions (unlike those in previous periods) present an imperative to alter society’s energy utilization [20,22–24]. This view is shaped by pressures relating to sustainability, access, security and/or reliability of energy. It’s worth noting that pressures to alter energy pathways have existed in the past, particularly during periods of war and global oil shocks. Societal responses to the oil shocks of the 1970s and early 1980s, for example, included country-level initiatives that strengthened domestic energy self-sufficiency through conservation, efficiency and/or scaling of domestic sourcing and industries [16,17,25]. What differs today is arguably a heightened awareness relating to the scope of energy challenges, their cross-border impacts, and efforts (depending on the challenge) that may be needed. It is, here, where social science has potentially its most significant role. Natural science and technological solutions can be brilliant, and yet remain untapped within a lab or field project. Understanding how knowledge, perceptions and practices are shaped and influence; what finance and markets can and cannot do; and how a society’s ‘social contract’ enables or detracts from problem-solving are areas where scholarship can contributen. 2.2. Tradeoffs The International Energy Agency estimates that roughly $38 trillion is needed in global investment to meet energy demand by 2035 [26]. Questions naturally arise about who pays (i.e. consumers, tax payers, industry, etc.), who decides, and how this is settled. One can also ask whether strategic interests such as jobs, science and technology leadership, relevant timelines, flexible response, and responsible stewardship are prioritized. Similarly, what is required for underlying infrastructure (i.e. land use and siting, displacement, and acceptance)? Are short-term objectives guiding choices and/or are longer-term aspects also seriously weighed? If more significantly altered pathways are considered, such questions are amplified by institutional considerations of how to navigate new directions. Whichever path is taken, costs entail more than finance. There are political, environmental, security and other societal effects that are not monetized. Understanding the tradeoffs and how to effectively address them is a fundamental concern for decision-makers, and a pivotal area for scholarly investigation. 2.3. Innovation Game-changing breakthroughs in how energy is sourced, delivered and utilized – such as what historically occurred with the combustion engine or controlled nuclear fission – are often pointed to as being critical for a new energy transition. In this line of thinking, there is no shortage of writing on the concept of accelerating innovation [27,28]. However, care is needed in how innovation

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3 Global Primary Energy (EJ)

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Biomass

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Hydro

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New Renewables

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New Renewables Figs. 2 and 3. Global Primary Energy by unit amount (EJ) and relative shares. Note: Other reported totals for 2008 include: 478.91 EJ [31]; and 514.10 EJ [11]; 514.89 EJ [32]. For a discussion of variations in energy data, see Section 5. Source: Adapted from [30]. Note: ‘New’ renewables include technologies like solar photovoltaic energy, geothermal power, and wind power. They do not include energy derived from traditional water or wind mills, wind-powered sea travel, solar water heating, etc. The chart also does not reflect animal and human power.

is conceived, as discoveries do not happen on demand. Additionally, translation and scaling of innovation can encompass more than simply the commercialization of a patent. The adoption of a novel idea into widespread practice, for example, can be driven by factors which originate outside of a market. Distinctions are also important when considering the rapid diffusion of an energy innovation versus that of an energy transition. While overlap may exist between these phenomena, underlying socio-technical conditions can also radically differ. Here, work by specialists in the history of science; science, technology and society (STS); anthropologists, political scientists, and policy can enlarge the theory and empirical insights on underlying determinants of change. 3. Observing energy transitions When examining the field of energy transitions, scale, structure and quality of change are common points of analysis [29]. The growth in the scale of different fuel types, for instance, is shown in Fig. 2 with global primary energy increasing by nearly a factor of 20 from 28 Exajoules (EJ) in 1850 to 533 EJ in 2008. Fig. 3 shows the same evolution, but in terms of the relative structure of the global fuel mix. In this case, the diversification of fuels is readily apparent with the shift from a heavy reliance on biomass, like fuel wood, in the mid-1800s to a more varied combination of inputs in the 1900s, including nuclear generation that was not commercially available in the 1800s.7 A more specific comparison of relative fuel shares in the global energy mix for 1971 and 2011 (Fig. 4) shows a decrease in the dominance of oil as growth occurred in the shares of natural gas, coal/peat, nuclear power, and some renewables. In terms of quality, energy systems can be evaluated with any number of characteristics, including density, portability, environmental or health effects, efficiency, sustainability and reliability. Energy density relates to the amount of energy contained within a unit of mass or volume. The historical shift from biomass to fossil fuels and nuclear power (embodied in uranium, for instance) constitutes a major change toward higher energy densities. Energy

7 A metric to illustrate aspects of these shifts is the ratio of renewables to fossil fuels changing from 16:1 to 0.2:1 for the period [30].

portability, or the ability to move energy with ease, has increased with the growth in use of fossil fuels and electricity. Such portability is not entirely intrinsic to the fuel type, since concerted investment in infrastructure is required, including that for pipelines, tankers, liquefaction plants and/or power grid networks. Other qualitative attributes relating to environmental and health effects may focus on kinds of resource and material inputs, releases (i.e. emissions or waste), as well as impacts on land and biodiversity, with marked differences in local and global character. Fig. 5 shows one environmental attribute, CO2 emissions from fossil fuels since the early 1970s. Here, OECD countries (traditional emitters) are shown as being surpassed by Non-OECD countries in 2004. Considered in terms of single country contributors, the United States has dominated recent history for its output of CO2 emissions from energy consumption. In 2006, the US was surpassed by China. (Note: Some variation may exist in the reported year of this shift, depending on the form of CO2 accounting that is used.). When evaluating energy trends by countries more fully, the way in which countries are characterized and gauged is subject to debate, and ripe for social science evaluation. Short-hand classifications of OECD versus Non-OECD countries, industrialized versus industrializing, and developed versus developing characterizations are frequently employed, but not fully accepted. ‘Developed and developing’, for instance, can have a highly subjective meaning with little relevance for energy. 4. Energy-related mega-trends Trends in population, urbanization, and globalization are significant for energy in terms of interdependencies and co-evolutionary developments. 4.1. Population The relationship between energy use and population is positively correlated, with substantial relevance for energy transitions analysis. Since 1800, the world’s population has increased by a factor of more than 7, from under 1 billion to 7.2 billion in 2012 [33,34]. This growth coincides with more than 20-fold increase in energy use [16,30]. Projections suggest that the world may reach 9.6 billion by mid-century with the greatest growth occurring in

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Fig. 4. Recent shifts in Global Primary Energy by shares of fuels. Source: Ref. [11].

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Fig. 5. CO2 from fossil fuels (Mt of CO2 ). Source: [11]. The Reference Approach, used here, is based on a country’s energy inventory and is calculated in such a way to include fugitive emissions from energy transformation (e.g. from oil refineries).

the least developed countries – namely Bangladesh, Ethiopia, the Democratic Republic of the Congo, the United Republic of Tanzania and Uganda, are projected to be among the twenty most populous nations in the world [33,34]. Such trends can have significant energy implications and related societal pressures, as the high population growth centers are the same regions where pronounced energy access challenges exist today [35]. To put population trends into a slightly different energy context, energy per capita on a global basis has more than tripled between 1850 and 2000 [30,32]. While the world average has changed incrementally in recent years, a number of country distinctions are worth emphasizing (Fig. 7). The United States continues to far exceed the world average for energy use per capita. Increases in areas like the Russian Federation, China and Brazil are also noticeable. Underlying drivers and international pressures associated with these differences will continue to be an area of necessary research for the social sciences.

Africa and India (Fig. 6). By the middle of the 21st century, five of

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Figs. 6 and 7. Population indicators. Source: Fig. 6 – [33]. The 2050 estimate is based on medium case assumptions. Fig. 7 – Ref. [11].

4.2. Urbanization

development choices remains a priority for urban planners, regulators, utilities, and community members.

Urbanization is another area that presents opportunities and challenges for energy (and, by extension, energy transitions research), as underlying choices in power delivery and transportation, infrastructure, land use, and industry affect energy utilization. In 1800, roughly 2% of the world population lived in urban centers [36]. Today, more than half the world population does so [32,33]. In fact, mega-cities of 10+ million residents are on the rise (Fig. 8). As two thirds of current energy consumption occurs in cities [35], such shifts have significance for energy markets, efficiency potential, as well as environmental and health impacts. Energy demand centers, for instance, are now much more concentrated, so losses from the long-range distribution of electricity may be minimized [37]. With these conditions, urbanization can lessen the areas of land use impacts. However, environmental impacts may also intensify in certain areas as air and water pollution is typically more concentrated around urban centers. Here, there is potential for mitigation at the source point. Understanding the strategic options of

2025

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Fig. 8. Number of mega-cities with 10+ million inhabitants in recent years. Source: [33].

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4.3. Globalization Globalization – the intensification of cross-border flows of people, information, and trade – is yet another mega-trend with relevance for energy system change. Within this phenomenon, countless sub-developments matter for energy transition analysis. One area of particular importance is the substantial rise in crossborder energy trading (Table 1). If one considers the global supply of natural gas, for example, one finds that 31% of natural gas consumed in 2011 was imported compared to 5% in 1971. To place this in context, the amount of natural gas imports worldwide grew by more than a factor of 17 during the period. This shift reflects a greater degree of systemic complexity, when more borders are involved. Daniel Yergin and Michael Levi have written extensively about the complex dynamics of global energy. In particular, they have pointed to the increasingly integrated world economy and level of interconnectivity among countries that factor in energy demand [38]. Such inter-relatedness can be seen with the disruptive shifts in the global economy and geopolitics that are associated with unconventional gas and oil. Views differ on whether this higher degree of integration constitutes an improvement, as it provides opportunities to rapidly respond to new conditions, like risk, in a distributed manner. However, it also brings issues from distant geographies into close proximity. For analysts of energy transitions, globalization presents opportunity for more sophisticated focus on: changing models of energy self-sufficiency in international markets, the systemic interaction of global environmental and security concerns with long-term energy planning, the enlarged influence of IGOs and international finance institutions in regional energy investment, and the ways that shifting travel modalities alter cross-border energy tracking.

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Table 1 Energy imports. Global imports by fuel type

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2011

Growth factor 1971–2011

% Fuel that is consumed 1971–2011

Electricity Coal Gas Crude oil, NGL and feedstock

0.3 EJ 5.4 EJ 2.0 EJ 52.1 EJ

2.3 EJ 29.2 EJ 36.2 EJ 96.3 EJ

8.9 5.9 17.5 1.8

2% → 4% (final energy) 9% → 18% (TPES) 5% → 31% (TPES) 50% → 54% (TPES)

Source: Ref. [11].

5. Resources and suppliers of energy information In recent decades, energy analysis and the field of energy transitions have evolved with the diversification and growth of information sources and suppliers of content.8 5.1. Key suppliers During the global oil shocks of the 1970s, individuals interested in energy transitions would have been hard-pressed to locate information on the subject. Many energy ministries had yet to be created, and in-depth writing or reporting on energy was limited. Contributions of early pioneers, like Putnam [39] and Darmstadter et al. [40], provided some of the first, detailed historical accounts and synthesized data from the League of Nations and United Nations [41]. Such work has been extended by theoretical contributions, discussed in Section 6, like that of physicist Marchetti and energy economist Nakicenovic [42]; physicist Goldemberg [43]; natural scientist Smil [44]; and technical scientist/planner Grubler [27,29,32,41,45]. Interestingly, many of the prominent, early thought leaders in the field of energy transitions have been natural scientists and economists. Today’s analysts and scholars are able turn to a diverse range of sources for industry and policy-relevant writing. Intergovernmental organizations (IGOs) such as the United Nations; the Organization of Petroleum Export Countries; the International Atomic Energy Agency; and International Energy Agency (IEA), are joined by new players, like the International Renewable Energy Agency (IRENA), as producers of key energy reporting and policy-relevant writing [46–51]. Energy industry actors, like the International Geothermal Association and BP, also contribute, complemented by a host of regional and international financial institutions, non-governmental organizations/think tanks and consultancies [31,52–58]. 5.2. Types of energy information When evaluating energy systems, data sets can vary based on definitions, fuel inclusion, and estimations, among factors. Energy systems, for instance, can be assessed in terms of primary or final energy. Primary energy is essentially raw or unrefined energy as it is found in natural form. Examples include: the chemical energy of fossil fuels and biomass; the kinetic potential of river water, the electromagnetic potential of solar radiation, as well as the energy that is released in a controlled fission reaction with uranium [30]. By contrast, final energy is the converted or refined form of energy that is utilized in end use, as with gasoline and electricity. Another distinction in energy data involves commercial versus non-commercial forms. Commercial energy is generally

8 This article focuses mostly on global and national data. Related information at the regional and local levels provides another valuable level of analysis. Varying socio-political influences and discontinuities of information across local, regional and national entities present interesting areas for further study.

understood as the kind that is monetized and traded within a market [30]. Non-commercial energy, collected by end-users outside of markets, is often excluded from global calculations. The exclusion of non-commercial energy in reporting can be significant as it often represents sizeable shares of an industrializing country’s current consumption and all countries’ historical totals. Beyond data sets, technology roadmaps are increasingly used, such as those generated by the IEA [59]. This form of planning tool generally evaluates prospective energy trajectories by integrating resource assessments with modeled scenarios.9 The annual World Energy Outlook is a widely recognized reference which draws upon this approach, in conjunction with in-depth discussion of issues and developments [49]. Another type of reference material that is relevant for energy transitions research is produced by large teams of specialists. The World Energy Assessment [37], the Global Energy Assessment [30], and the MIT Future of energy technology series [60] are all examples of such authoritative writing which focuses on the boundaries of the knowledge frontier. With these references, the mode of report development matters, if, for instance, consensus is required. In such cases, key points may be diluted to secure buy-in. However, unanimity may bolster the legitimacy of the findings. The diversity of disciplinary, regional, and technology representation on expert panels also matters, as variation in methods, experience, and expertise can substantially alter how biases and knowledge gaps are handled. 5.3. Challenges As energy data and information providers have become increasingly diverse, discretion is needed to ensure that information limits and compatibilities are reasonably understood. Specific to data collection, the United Nations, International Energy Agency, and World Energy Council rely on surveys of country authorities or industry members to accurately convey national energy information. While this is arguably an efficient approach, it is subject to different respondent interpretations, varying degrees of rigor with data collection and estimation, and sometimes the politics of reporting [61]. Reporting on energy reserves and resources, for example, often involves different sets of assumptions and political objectives which can alter technology and economic feasibilities, and, in turn, translate to widely ranging totals. Social scientists and experts in the humanities can improve such resources with better harmonization of cross-cultural information and analytical approaches that are attuned to regionally idiosyncratic nuances. Another consideration for energy transitions research is the accounting method that is employed when developing primary energy data. With combustible fuels, namely fossil fuels and biomass, the selection of high or low heat values in calculations

9 Scenario modeling employs backcasting, a method used in resource management and strategic planning that works backwards from a desired target to identify actions or paths to attain the objective.

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can produce a spread of 5–6% for solid and liquid fuels and 10% for gas [30]. Variances for non-combustibles, by contrast, can be much wider [30]. Methods of conversion frame these kinds of differences and generally encompass substitution, direct equivalents or hybridized approaches. Basic gaps in data also exist. Global and country level information is fairly comprehensive from the 1970s to recent years with less detail available on a historical basis for industrializing countries. Estimates of non-commercial energy (when they do exist) generally focus on biomass, like fuel wood and waste, but exclude other forms of non-commercial energy, such as that derived from traditional water wheels and wind mills, windpropelled sea travel, and solar water heating. Here, historians and sociologists, as well as scholars of international development are well-suited to apply disciplinary tools, methods, and insights to improve and extend existing estimates. The need for more differentiated data is another challenge in energy transitions analysis. Renewable energy information is often bundled as one technology in such a way that discrete energy trajectories are obscured, including those associated with geothermal heat and power, solar thermal heat and power, wind power, biofuels, ocean power, etc. Whether by design or an indirect consequence, this unevenness in reporting creates a resource bias for researchers that favors more data-rich topics, like historically commercialized energy. Simplified reporting also misses nuanced technology options, like efficiency, storage, and systems approaches. Recent efforts by organizations, including the IEA, IRENA and REN21 are making some inroads. In terms of data on energy research and development funding, country level data has mostly reflected Organization of Economic Cooperation and Development (OECD) governmental support. Relatively recent efforts have also begun to report on research, development and demonstration expenditures at a more global level, including large industrializing countries and private sector investment [27,62]. Nonetheless, much remains to be studied, including that associated with state-owned enterprises and non-OECD national laboratories. Similar to basic data gaps noted above, historians, sociologists, and perhaps industry-focused scholars may be able to extend estimates, when access to concrete information is limited. At a more theoretical level, the way that energy information is created and reported can be mapped more fully to identify underlying influences in knowledge development–a subject which experts on institutions and STS have natural strengths.

6. Theorizing energy transitions The multi-disciplinary nature of energy transitions is wellsuited for theoretical inquiry which considers how and why transitions occur; what enables ‘successful’ models vs. ‘unsuccessful’ ones; and whether certain attributes, like historical familiarity or technology conduciveness are critical determinants for energy system change. The following conceptual framings reflect some of the more central ideas of current relevance for the field of energy transitions.

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framework is used by a variety of authorities, including the European Commission and UNIDO [63]. When applying the IS lens, scoping may be done at the technological, regional, sectoral, national or global level with the choice depending largely on the case(s) and unit of analysis. The notion of national systems of innovation (NIS), for instance, is useful for cross-country studies of energy system change [64–66] that encompass interactions of national drivers which spur systemic feedbacks and adaptations [67]. In contrast to NIS is the notion of the technological innovation system (TIS) which considers the development, diffusion and use of a specific technology, such as geothermal energy, that may be a sub-system of a sector (i.e. electricity) or bridge several sectors (power, heat, and tourism) [68]. At the global IS level, work now focuses on cross-border elements, like transnational institutions, that can advance innovation in ways where countries may be limited [69]. Broadly speaking, the strength of IS theory is in its fairly coherent conceptualization of complex ecosystems which allows for in-depth analysis of interdependencies and comparisons across related cases. This theoretical area has the potential to be extended with directions, like socio-political investigation of power dynamics. 6.2. Techno-economic paradigms and socio-technical multi-level perspectives Drawing upon ideas about long wave cycles of business development and innovation [70], the concept of techno-economic paradigms (TEP) provides another theoretical lens with which to examine energy transitions. Highlighting ties between innovation, economic development, technology and institutional change, TEP postulates that new research rationales and norms can develop over the course of five or six decades to explain technological revolutions. As seen with work on low carbon energy today, a new paradigm guides the upgrading and modernization of existing industries to harmonize or synergize with newer industries [71–73]. A related school of thought includes the sociotechnical systems multi-level perspective (MLP). MLP expands on transition ideas found in policy, demographics, ecology, sociology and evolutionary economics, adding normative aims related to sustainable development [74,75]. MLP’s framework views transitions as occurring in situations such as those where external pressures destabilize a prevailing regime to allow for breakthroughs in niches [74,76–78]. Here, disruptive technologies co-evolve with shifts in markets, regulations, infrastructure, user practices, industrial networks, cultural meaning and scientific understanding [79]. In recent years, the disparate lines of TEP and STS MLP theory have become more closely aligned, with writing, such as that of Freeman and Louc¸ã [72], which introduced a layered, subsystem model for TEP. Both sets of theory are useful for conceptualizing coevolving trends amidst larger system change. Their framing is more complex than IS and positions energy transitions within broader developments. While this kind of framing is used by authorities, like the Dutch government, some experts note that its level of focus can miss insights specific to an energy system [41].

6.1. Innovation systems

6.3. Path dependence and creation

Innovation systems theory (IS) is an approach which has been used increasingly to explain technological shifts, like that to low carbon energy or to distributed generation. With IS, elements of a system are highlighted for their roles in how innovation is actively or passively enabled. IS goes beyond technical componentry and processes to include actors, institutions, and networks [63]. This

Another set of ideas of relevance to energy transition research centers on how inertia and enablement shape courses of action. Path dependence refers to inertia of prior choices constraining future pathways, based on self-reinforcing limits like sunk investment costs; increasing returns; inter-relatedness of technologies; and network effects [80]. Sometimes called ‘lock-in’, this idea explains

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why new energy technology, may not be adopted even if it is superior and/or economically feasible [81]. In contrast to the impedance of path dependence is the notion of path creation which highlights the agency of entrepreneurs who at least in part define the flow of events [82]. Writing, such as that by Garud and Karnoe’s provides a useful foundation for additional research on agents of change in the context of energy system change. 6.4. Learning Learning is yet another integral concept that relates to energy transitions. While learning generally implies improvement, based on novel or accrued knowledge, it can be operationalized in a variety of ways, including experience curves and adaptive capacity. Experience curves provide a quantitative means to assess cost improvements. Such curves are developed from double log functions to evaluate change in costs for every doubling of output [83]. A variant to this approach is one which considers economies of scale in installed or investment cost curves for similar energy projects over time [84]. Both forms allow the opportunity to contrast changes in energy costs by technology or region, however their simplification limits their use in explaining the rationale for change. A somewhat different theoretical tie between energy transitions and learning may be found in ideas on adaptiveness, openness, and innovative capacities. Adaptiveness and openness of complex energy systems generally refer to the resilience and capacity of a system to interact with external influences [85]. Smil has, for example, comparatively analyzed national energy transitions, arguing that agility can be a compelling factor in countries’ ability to adapt [86]. A similar idea is the notion of national innovative capacities (NICs), which indicates that a country’s enabling environment (i.e. factors that shape its innovative propensity) are key for competitive performance [87]. 6.5. Time scales, and early vs. late adoption Time scales, forms of adoption, and diffusion rates also have obvious significance for energy system change. Marchetti and Nakicenovic provided an early basis for theory-building around time constants for energy shifts, based on logistic modeling of energy systems transitions [42]. Using equations to evaluate global energy technology substitution, they found that periods of 80–130 years were needed for a shift from 1 to 50%, or 10–90% of the market share. A different study of 14 historical energy transitions by Fouquet at sectoral and service levels [88] found that the time to move from technological innovation to niche market utilization to market dominance took at least 40 years. Subtle differences between these studies, including their scoping, timelines and methods for evaluation present promising areas for further exploratory work. The sequencing of adopters is another critical area of relevant theory. Grubler and Wilson have highlighted how first adopters reach a higher market saturation level, while later adopters scale more quickly, but less extensively [89]. An important insight is that early adopters may well become entrenched in the lock-in of their existing technology choice, as with fossil fuels. Meanwhile, late adopters may have less sunk costs and be more nimble in adopting a subsequent option. Goldemberg approached this idea somewhat differently by articulating how late adopters benefit from the opportunity to sidestep early issues in order to advance directly to newer, more superior technologies [90]. 6.6. Policy and governance Because energy is fundamental to society’s day-to-day dealings, government can be expected to take an active interest in

how energy is sourced, accepted and utilized. The way that this is done plays out often with lines diverging around market-based versus regulatory approaches. This widely used form of classification can obscure a range of approaches that include direct deployment by government employees, information or educationled change, leadership by example, and bottom-up or societal-led change, among possibilities [16,91]. An important strand of policy writing centers on the relative performance of specific tools to attain defined objectives [92–94]. This work contributes to broad understanding of options. Yet it’s worth underscoring that policy tools which effectively contribute to or enable an energy transition in one culture can dramatically differ from those in another. Evaluating policy tools without consideration of institutions, mechanisms or societal orientation will limit the applicability of findings [85,95]. Research on societal orientations, the interactions of plural governance around energy, and the multi-polarity of global actors and stresses are promising areas that are gaining intellectual ground under the banner of energy governance [17,96–98]. 7. Areas for future work and conclusion After examining points raised in this article, one can see that a substantial agenda exists for energy transitions research – one where social science and humanities can add importantly. To begin, scholarly writing can be enhanced with greater comparative depth on shifts in practices, perceptions, knowledge, and financing relating to energy. In addition, data could be extended with more complete and systematic estimates of historical energy activity, particularly with respect to Non-OECD countries. Potential also exists for more comprehensive work on the sociopolitical and socio-technical conduciveness of differing energy technologies as they relate to decentralized versus centralized pathways, and adoption-acceptance factors. While important, foundational research exists on time constants of change and learning, the significance of timing and readiness, convergence of co-evolutions, and instrumentality of focusing events are also promising areas. The agency of actors could be explored by more fully evaluating types of change agents in relation to different kinds of energy transitions. Similarly, the role of spillovers, unintended consequences, and dual purpose technology present additional lines of inquiry for comparative energy transition cases. Systems change theory that is now en vogue also leaves the door open for alternative conceptual models which more squarely consider industrial and societal readiness in relation to energy shifts. Empirical insight on the differences between deliberate and emergent energy pathways could be also amplified with greater attention to modalities of change – namely, deployment, encouragement, monitoring, and organic emergence. This article set out to highlight areas of progress, challenge, and opportunity for the field of energy transitions. Continued complexities in energy pathways and the timeless nature of transitions research underscore a genuine and ongoing need for innovative scholarship. References [1] Scopus database, January 1, 2014. Scopus covers peer-reviewed journal articles and other publications from the life sciences (4300+ titles), health sciences (6800+ titles), physical sciences (7200+ titles), and social sciences and humanities (5300+ titles). It is one of two premium periodical databases. The coverage and functionality of Scopus made it a reasonable choice. Web of Science/Knowledge would be another reasonable option. [2] Semenoff N, Shecter A. Transition of kinetic into vibrational energy by collisions with particles. Nature 1930;126(3177):436–7. [3] Robinson C. The energy market and energy planning. Long Range Planning 1976;9(6):30–8;

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