The dominant energy sources used by human societies and the transitions from one energy source to another have fundamental implications for societal development. A future energy transition is pending but it remains unclear what its socioeconomic corollaries will be.

The history of the dominant energy sources used by human societies and their implications for societal development are traced in this review. “Passive solar energy utilization” in the hunting and gathering mode requires mobility of societies following the biomass that is their sole energy input. Fertility is constrained both by the available nutrition and by the need to migrate: population density is low. The agrarian mode relies on “active solar energy utilization”. Solar energy is harnessed through cultivated crops providing energy to humans. This mode requires a sedentary way of life and allows for much higher population density; progress in raising yields is achieved by additional labor-inputs and drives population growth. The industrial mode relies largely on fossil energy carriers supplying human societies with an amount of energy never accessible before, and with new materials. It relieves human societies of their dependence on land, fosters urban growth, and decreases fertility. At the same time, the industrial mode is based on a dominant energy source that will not be available indefinitely and that is associated with severe impacts on the environment. A future energy transition seems unavoidable and historical evidence suggests that it will be associated with fundamental socioeconomic change.

The significant advances in high-power lasers with the attainment of tens of kilowatts of optical power, high repetition rates (>MHz), reduction in size, lower cost per photon (<1$/watt), and high optical power conversion efficiency (>30%) are driving the use of lasers for material processing for renewable energy materials.

The significant advances in high-power lasers with the attainment of tens of kilowatts of optical power, high repetition rates (>MHz), reduction in size, lower cost per photon (<1$/watt), and high optical power conversion efficiency (>30%) are driving the use of lasers for material processing with very high throughput. The use of renewable energy is also increasing as an alternative power source. This review examines the various aspects of laser processing for renewable energy materials and provides an overview of fundamentals of laser material interactions, advances in high-power lasers, and specific examples of laser processing of materials for photovoltaics, solar thermal energy, thermophotovoltaics, thermoelectrics, and thin films. High-power lasers have been adapted for solar cell manufacturing applications, and new processes such as laser doping, laser transfer of metal contacts, laser annealing, etc. are being advanced further for industrial applications. The future of laser processing for renewable energy materials looks very bright with further advances expected in high-power lasers, beam delivery systems, and decreasing cost with very high reliability. Lasers can provide noncontact localized energy deposition with the potential for all low-temperature processing of materials and a very low thermal budget.

The direct methanol fuel cell (DMFC) enables the direct conversion of the chemical energy stored in liquid methanol fuel to electrical energy, with water and carbon dioxide as by-products. Compared to the more well-known hydrogen fueled polymer electrolyte membrane fuel cells (H2-PEMFCs), DMFCs present several intriguing advantages as well as a number of challenges.

This review examines the technological, environmental, and policy aspects of direct methanol fuel cells (DMFCs). The DMFC enables the direct conversion of the chemical energy stored in liquid methanol fuel to electrical energy, with water and carbon dioxide as byproducts. Compared to the more well-known hydrogen fueled PEMFCs, DMFCs present several intriguing advantages as well as a number of challenges. Factors impeding DMFC commercialization include the typically lower efficiency and power density, as well as the higher cost of DMFCs compared to H2-based fuel cells. Because of these issues, it is likely that DMFC technology will first be commercialized for small portable power applications (e.g., the displacement of batteries in consumer electronic applications), where the shorter product lifetimes (∼1–2 yrs for a battery versus 8–15 yrs for a car) and the much higher price points (∼$10/W for a laptop battery vs. ∼$0.05/W for a vehicle engine) provide a more attractive entry point. While such applications are not likely to significantly impact the global energy sustainability picture, they provide an important initial market for fuel cell technology. As such, in this review, we provide an overview of recent research and the challenges to the development of DMFCs for both the portable (shorter-term) and transport (longer-term) sectors.

This paper reviews recent developments in the production and use of unconventional natural gas in the United States with a focus on water and greenhouse gas emission implications. If unconventional natural gas in the U.S. is produced responsibly, transported and distributed with little leakage, and incorporated into integrated energy systems that are designed for future resiliency, it could play a significant role in realizing a more sustainable energy future; however, the increased use of natural gas as a substitute for more carbon intensive fuels will alone not substantially alter world carbon dioxide concentration projections.

This paper reviews recent developments in the production and use of unconventional natural gas in the United States with a focus on environmental impacts. Specifically, we focus on water management and greenhouse gas emission implications. If unconventional natural gas in the United States is produced responsibly, transported and distributed with little leakage, and incorporated into integrated energy systems that are designed for future resiliency, it could play a significant role in realizing a more sustainable energy future. The cutting-edge of industry water management practices gives a picture of how this transition is unfolding, although much opportunity remains to minimize water use and related environmental impacts. The role of natural gas to mitigate climate forcing is less clear. While natural gas has low CO2 emissions upon direct use, methane leakage and long term climate effects lead to the conclusion that increased use of natural gas as a substitute for more carbon intensive fuels will not substantially alter world carbon dioxide concentration projections, and that other zero or low carbon energy sources will be needed to limit GHG concentrations. We conclude with some possible avenues for further work.

Over the last decade, our understanding regarding the nature and drivers of criticality risk has matured significantly. We review modeling efforts to date, specific to evaluation of future material availability, and identify research gaps.

Many advanced energy technologies are fundamentally “materials-dependent”; they are enabled directly by, or designed around, a particular material or materials. Society's acute dependence on materials has increased in recent years as these technologies tap into an ever broader range of the periodic table and, therefore, into a broader set of underdeveloped and complex supply chains. Ultimately, concern around the supply of materials strategic to energy and security interests has led to the development of a range of systems used to assess criticality—the confluence of vulnerability and risk. Concerning the assessment of criticality risk, this review accomplishes two primary goals. First, through a review of several broad assessments of criticality metrics, we identify those metrics that incorporate assessment of future production and consumption. We review the methods that have been applied to project production and consumption along two axes, one around degree of detail or granularity pursued by the model and the second around the degree to which market function is modeled endogenously. Regarding the second, material projection methods can be broadly classified as (a) those which project material flows only and (b) those which use market modeling to explicitly simulate (endogenously) the associated economic behavior and its implication on material flows.

New research results in several areas that can help to facilitate the large-scale integration of variable renewable power sources into the electric power system are reviewed.

Increasing the market share of variable renewable electric power generation in the United States from the present 4% is eminently feasible, and can be facilitated by recent research. The amplitude of variability of wind and solar power is much less at high frequencies than at low frequencies, so that slow-ramping generators such as combined-cycle natural gas and coal can compensate for most of the variability. The interannual variability of wind power is beginning to be understood, as are the biases in its day-ahead forecasts. Geographic aggregation of wind and solar power has been proposed as a method to smooth their variability; for wind power, it has been shown that there is little smoothing at timescales where the magnitude of variability is strongest. It has also been shown that the point of diminishing returns is reached after a relatively few wind plants have been interconnected. While good prospects for lower cost electric storage for grid applications exist, the profitability of storage for integration of renewable power is likely to remain a difficult issue. New extremely efficient, low pollution, and fast-ramping natural gas plants have come on the market. It is now possible to predict the amount of additional capacity of this sort that must be procured by system operators to cover the uncertainty in wind forecasts.

The widening gap between the short battery life (<8 years) and patients' life expectancy (20 years) is a growing concern for long-term implantable devices and adds to outpatient costs. This gap coupled with significant advancements in circuit, device design, and lowered power consumption (<1 mW) has refueled the interest in implantable energy harvesters.

As the complexity of implantable devices is increasing, the size and power requirements of implantable devices have shrunk by more than double over the past few decades. However, the functionality or lifespan of the devices is often found to be limited due to shortage of power. With more than 50% of the device size being occupied by the battery alone, longevity of such implantable devices has garnered huge concern over the years. Fueled by the demand of additional biosensors coupled to such devices, implantable energy harvesters, capable of harvesting the body's chemical, thermal, or mechanical energy over a long period of time, have gained tremendous popularity. Among these technologies, implantable glucose fuel cells provide a promising method to generate a small yet continuous supply of power. Implantable fuel cells tap into the available free blood glucose to generate electricity. With the trend moving toward the use of semiconductor technologies for glucose-based fuel cells, fabrication of reliable and effective technology is within feasible limits. Realization of such implantable power sources can shift the burden from commonly used lithium-ion batteries by utilizing physiological resources. The present review focuses on recent developments on abiotic glucose fuel cell for bioenergy harvesting.

This review article evaluates the structure–property relations of inorganic clathrates and clathrate hydrates and their potential role in energy harvesting. There is potential cross-fertilization between the two research areas.

Guest–host clathrate compounds exhibit unique structural and physical properties, which lead to their versatile roles in energy applications. Prominent classes of clathrate compounds are gas hydrates and inorganic clathrates. That said, there is limited cross-fertilization between the clathrate hydrate and inorganic clathrate communities, with researchers in the respective fields being less informed on the other field. Yet the structures and unique guest–host interactions in both these compounds are common important features of these clathrates. Common features and procedures can inspire and inform development between the compound classes, which may be important to the technological advancements for the different clathrate materials, e.g., structure characterization techniques and guest–host dynamics in which the “guest” tends to be imprisoned in the host structure, until external forces are applied. Conversely, the diversity in chemical compositions of these two classes of materials leads to the different applications from methane capture and storage to converting waste heat to electricity (thermoelectrics). This article highlights the structural and physical similarities and differences of inorganic and methane clathrates. The most promising state-of-the-art applications of the clathrates are highlighted for harvesting energy from methane (clathrate) hydrate deposits under the ocean and for inorganic clathrates as promising thermoelectric materials.

Current issues with carbon emissions need to be understood in terms of natural geologic processes that move carbon on the Earth. Comparison of modern emissions with the norms and extremes of natural processes emphasizes the enormity of the current challenge, and also the reason there are uncertainties about the future effects. Reaching sustainable emissions in the future can be viewed as a need to systematically reduce the carbon intensity of energy production.

Achieving sustainable carbon emissions requires understanding of Earth's natural carbon cycles. Geologic processes move carbon in large quantities between Earth reservoirs, including in and out of the deeper reaches of the planet, and regulate Earth's surface temperature within a narrow range suitable for life for the past 3–4 billion years. There have been large changes in atmospheric CO2 in the geologic past; the largest to offset changes in the brightness of the Sun. Atmospheric CO2 has been much higher in the past, but not since humans evolved. Geologic processes act slowly, even during times in the geologic past regarded as examples of catastrophic climate change. In contrast, over the past 100 years, Earth's carbon cycles have undergone revolutionary change as a result of a greatly accelerated transfer of carbon from geologic storage to the atmosphere. Today, about 98% of the movement of carbon out of geologic reservoirs (coal-, oil-, and gas-bearing sedimentary rocks and limestone) into the atmosphere is due to human activities; the total carbon flux is 40–50 times the geologic flux. The extremely large modern carbon flux is unprecedented in Earth history. Returning to a sustainable carbon cycle requires systematic lowering of the carbon emission intensity of energy production over the next century.

This study argues that the climate changes resulting from the continued burning of fossil fuels at present rates will very likely initiate extinction of many terrestrial and marine species, beginning by mid-century. Under this scenario, interactions of climate change with other well-known extinction threats promise to trigger a loss of life that has not been seen since an asteroid-strike eliminated most dinosaurs 66 million years ago. Avoiding this will require a very rapid shift of both our stationary and transportation energy sectors to carbon-neutral systems.

Mass extinctions, which result in loss of at least an estimated 75% of known species over a geologically short time period, are very rare in the 540 million year history of complex life on Earth. Only five have been recognized, the most recent of which occurred 66 million years ago, ending the reign of dinosaurs and opening the door for domination of the planet eventually by humans, who have now accelerated biodiversity loss to the extent that a Sixth Mass Extinction is plausible. Accelerated extinction rates up to now primarily have been due to human-caused habitat destruction and overexploitation of economically valuable species. Climate change caused by burning of fossil fuels adds a new and critically problematic extinction driver because the pace and magnitude of change exceeds what many species have experienced in their evolutionary history, and rapid climate change multiplies the already-existing threats. Particularly at risk are regions that contain most of the world's species, such as rainforest and coral reef ecosystems. Avoiding severe losses that would commit many species to extinction by 2100 will require transforming global energy systems to carbon-neutral ones by 2050. Currently, the transformation is occurring too slowly to avoid worst-case extinction scenarios.

A variety of inherently robust energy storage technologies hold the promise to increase the range and decrease the cost of electric vehicles (EVs). These technologies help diversify approaches to EV energy storage, complementing current focus on high specific energy lithium-ion batteries.

The need for emission-free transportation and a decrease in reliance on imported oil has prompted the development of EVs. To reach mass adoption, a significant reduction in cost and an increase in range are needed. Using the cost per mile of range as the metric, we analyzed the various factors that contribute to the cost and weight of EV energy storage systems. Our analysis points to two primary approaches for minimizing cost. The first approach, of developing redox couples that offer higher specific energy than state-of-the-art lithium-ion batteries, dominates current research effort, and its challenges and potentials are briefly discussed. The second approach represents a new insight into the EV research landscape. Chemistries and architectures that are inherently more robust reduce the need for system protection and enables opportunities of using energy storage systems to simultaneously serve vehicle structural functions. This approach thus enables the use of low cost, lower specific energy chemistries without increasing vehicle weight. Examples of such systems include aqueous batteries, flow cells, and all solid-state batteries. Research progress in these technical areas is briefly reviewed. Potential research directions that can enable low-cost EVs using multifunctional energy storage technologies are described.

The author defines sustainability as the condition that must be developed globally for humanity to flourish until technology advances extraterrestrial travel that will allow migration to another planet once conditions here deteriorate. The emphasis is on anthropogenic climate change caused primarily by changes in the chemistry of the atmosphere due to dominant use of fossil fuels.

This review is focused on climate change. It is based on the understanding that anthropogenic climate change is caused primarily by changes in the chemistry of the atmosphere due to dominant use of fossil fuels. Stabilization of the climate requires energy transition from business as usual scenarios to a mixture of noncarbon based energy sources. The starting point for discussing this transition is the so-called Kaya–IPAT identity, which parametrizes the transition in terms impact (I) driven by population growth (P), increase in the standard of living (A), the required energy intensity, and the transition to different sources of energy (T), i.e., both “hard” and “soft” science parameters. Important issues that are not explicitly part of the identity are the differentiated requirements of developed and developing countries and the required duration of such transition. Such a transition inevitably involves winners and losers and is, thus prone to lead to political conflicts on local and global scale. Such a transition brings also opportunities for future growth. The review highlights some of the specific opportunities that such a transition brings to material science.

Materials diagnostic techniques are the principal tools used in the development of low-cost, high-performance electrodes for next-generation lithium-based energy storage technologies. This review highlights the importance of materials diagnostic techniques in unraveling the structure and the structural degradation mechanisms in high-voltage, high-capacity oxides that have the potential to be implemented in high-energy-density lithium-ion batteries for transportation that can use renewable energy and is less-polluting than today.

The rise in CO2 concentration in the earth’s atmosphere due to the use of petroleum products in vehicles and the dramatic increase in the cost of gasoline demand the replacement of current internal combustion engines in our vehicles with environmentally friendly, carbon free systems. Therefore, vehicles powered fully/partially by electricity are being introduced into today’s transportation fleet. As power requirements in all-electric vehicles become more demanding, lithium-ion battery (LiB) technology is now the potential candidate to provide higher energy density. Discovery of layered high-voltage lithium-manganese–rich (HV-LMR) oxides has provided a new direction toward developing high-energy-density LiBs because of their ability to deliver high capacity (∼250 mA h/g) and to be operated at high operating voltage (∼4.7 V). Unfortunately, practical use of HV-LMR electrodes is not viable because of structural changes in the host oxide during operation that can lead to fundamental and practical issues. This article provides the current understanding on the structure and structural degradation pathways in HV-LMR oxides, and manifests the importance of different materials diagnostic tools to unraveling the key mechanism(s). The fundamental insights reported, might become the tools to manipulate the chemical and/or structural aspects of HV-LMR oxides for low cost, high-energy-density LiB applications.

This review article deals with the current state-of-art research and developments in the field of elasto-caloric effect as applicable for solid-state refrigeration devices. Furthermore, the current challenges and future prospects in the field of elasto-caloric refrigeration technology have also been discussed.

Solid-state refrigeration is of interest since it has the potential to be a light-weight and environmentally-friendly alternative for small scale cooling. Much research is currently being undertaken to develop solid-state cooling technologies which is primarily achieved by utilizing the significant caloric effect exhibited by particular classes of materials. A variety of caloric effects exist including: electro-caloric, magneto-caloric, baro-caloric, and elasto-caloric. Among these, the elasto-caloric effect has shown potential within the field of mechanical refrigeration with shape-memory alloys being potential materials for producing significant levels of elasto-caloric cooling. This article explains the elasto-caloric effect in shape memory alloys, polymers, and ferroelectric materials. Technical parameters associated with the elasto-caloric performance of these materials are discussed. A discussion regarding existing functional shortcomings and future prospects in the field of mechanical refrigeration is covered. Aspects related to the long term environmental impact of solid-state cooling technology are also discussed. This study is aimed at promoting the understanding and commercial investigation of the elasto-caloric effect in the field of solid state refrigeration.