Globally, more than 740 million people live on islands which are often seen as ideal environments for the development of renewable energy systems. Hereby, they play the role to demonstrate technical solutions as well as political transition pathways of energy systems to reduce greenhouse gas emissions. The growing number of articles on 100% renewable energy systems on islands is analyzed with a focus on technical solutions for transition pathways. Since the first “100% renewable energy systems on islands”-article in a scientific journal in 2004, 97 articles handling 100% renewable energy systems on small islands were published and are reviewed in this article. In addition, a review on 100% renewable energy systems on bigger island states is added. Results underline that solar PV as well as wind are the main technologies regarding 100% RES on islands. Not only for the use of biomass but for all RES area limitation on islands needs to be taken more seriously, based on full energy system studies and respective area demand. Furthermore, it is shown that there is still not the same common sense in the design approach including and starting at the energy needs as well as on multi-sectoral approach. The consideration of maritime transport, aviation, cooling demands, and water systems beyond seawater desalination is only poorly considered in existing studies. Future research should also focus on developing pathways to transform the existing conventional infrastructure stepwise into a fully renewable system regarding also the interconnections with the mainland and neighboring islands.

The concept of Positive Energy Districts (PEDs), introduced in the Strategic Energy Technology Plan, is one of the fundamental approaches for a successful, clean and sustainable urbanization by 2025. According to the European Commission, a PED is a set of buildings where the community controls the energy flows and aims at a net positive energy balance over a year by utilizing renewable energy sources. There are a plethora of concepts similar to PEDs, such as Positive Energy Community, Net Zero Energy Neighborhood, Plus Energy Districts, that create a need to establish a structure that can facilitate the definition, development, and precise identification of PEDs. Thus, this paper aims to fill this research gap by comparing these and other related concepts through a critical literature review based on three pillars composing the triangle of sustainability: economic, social and environmental. By doing this, the paper aims to determine the connections between these similar concepts, homogenize the use of terms and avoid the issue of repetitions, which can help draw lessons learnt from other energy-savings concepts. This study shows how PEDs and Nearly Zero Energy Communities have similar bases, aims and omissions. They diverge in a few key concepts, which can become learning points for PEDs.

More than 30 years have passed since Curitiba, Brazil, and Jaime Lerner, the three-time mayor of the city, first became famous for the innovations that were implemented there, many environmental in focus. The most famous of these was the creation of a highly used and efficient public transportation system based on buses. Many have sought to emulate elements of the innovation put in place in that city. In recent years, however, both the country and the city have been beset by political scandals, economic malaise, and social problems, which have adversely affected many of these innovations. As a result, some question whether Curitiba remains relevant today as a model for the rest of the world. This perspective will examine the legacy of Lerner and Curitiba. Focusing on the public transportation system, it will make the case that the innovative principles underlying the original design of the public transportation system remain as relevant today for Curitiba and cities globally as they were then. These principles are design of an efficient and hierarchical public transportation system that takes its users from their first mile of commute to their last mile; construction of an urban infrastructure that supports and enhances use of public transportation; establishment of an effective public–private partnership where the private sector owns, operates and upgrades the vehicles while the public sector plans and oversees the system; and creation of a metropolitan governance strategy when the needs for public transportation go beyond city borders.

Unique features of vanadium redox flow battery (VRFB), such as easy scalability and long durability, qualifies it as one of the prominent renewable energy storage technologies. Attracted by its features, scientific and commercial community around the globe have now begun to test prototypes/demonstrations of VRFB for a wide array of applications that deal at a scale of kW-MW. A few scientific groups have discussed the design and performance of kW-scale (up to 10 kW) VRFB in literature. It is interesting to note that the discussed designs have been developed with a diverse approach and have achieved different results. In this review, we critically examine and discuss those contributions at kW-scale VRFB by analyzing the materials associated with their design, understanding the development of the flow engineering aspects in order to tackle the pressure and shunt current losses and the overall electrochemical performance. Till date, kW-scale VRFB system has achieved an energy efficiency of ~80% at current densities of 100 mA⋅cm−2. Though the choice for majority of VRFB components is fixed, the right choice for its separator/membrane still needs to be standardized. With these aspects in picture, this review article will help to lay a background for researchers and engineers to know the present state-of-art and engineering issues at kW-scale VRFB, which is a building block for scaling up.

Data analysis and collection techniques now allow for detailed inventory-building of urban rooftops for the purposes of identifying solar energy potential within geographically defined boundaries, including those of cities. The complexity and inherent diversity of a city's building stock has propelled the introduction of many so-called “solar city” assessment methods that, with varying levels of accuracy, scalability, and ease of use, seek to characterize the citywide solar photovoltaic (PV) resource potential. A review of the landscape of available methods supports a fundamental distinction across two classes of methods. First, “solar city” assessment methods can principally rely on inference to identify and characterize rooftop solar potential. Such inferential methods can establish estimates of citywide solar potential without needing direct insight into rooftop conditions or morphology, Second, measurement-based methods estimate rooftop solar opportunities based on the direct measurement of rooftop conditions, often conducted through remote sensing. Comparative performance testing of several inferential- and measurement-based methods using case study analysis underscores the importance of measurement-based methods. In particular, measurement-based methods are likely better positioned to support the needs of policy-makers and investors interested in transforming a city or metropolitan area into a sustainable city whose buildings serve as the host of a new solar PV-powered distributed electricity service system.

The outbreak of COVID-19 pandemic has caused changes worldwide in a dimension that has not been seen since the Second World War. This pandemic and the measures taken to moderate the negative consequences have affected almost all aspects of our life. Transport has been one of the most affected sectors. In general, the global car market is very sensitive to macroeconomic conditions. This applies especially to electric vehicles, which are still very dependent on financial support measures. A combination of travel restrictions, unemployment, and low oil prices could have significant impact on electric vehicles. This paper provides an overview of the development of electric vehicles and corresponding policies covering the period before and during the COVID crisis. Policy framework and the future development of the annual gross domestic product per capita have a significant impact on diffusion of battery electric vehicles. However, since the crisis is still ongoing, the full impact of the COVID crisis on mobility is still to be seen but the findings so far show rather favorable signs for electric mobility.

This article expounds on the challenges of sustainable global energy development to conventional econometrics in energy research. It introduces energy big data's “4V” characteristics, that is, volume, variety, velocity, and veracity. Further, the article presents a series of challenges the “4V” feature brings to conventional econometrics research on energy issues. Then, by reviewing the existing literature, the article proposes the improvement and promotion of conventional econometrics in the three directions of data exploration and variable generation, prediction, and causal inference of machine learning in big data. Finally, the article concludes that the discipline of econometrics will never go out of fashion. Although big data and machine learning will increasingly challenge the conventional econometrics research paradigm, econometrics will be reborn in the way of “phoenix nirvana”.

Electrification of heating, particularly with highly-efficient heat pumps, is increasingly viewed as essential for reaching the targets of the Paris Climate Agreement. China has promoted replacement of dirty coal heating in rural areas. More recently China has also begun promoting distributed solar photovoltaic (PV) energy as a rural development strategy, particularly with the launch of the Whole County PV pilot program in 2021. While several studies have examined the economics of heat pump adoption, with or without solar PV, the Whole County PV program has not been specifically studied. Further, many prior studies utilize monthly average solar production or temperature ranges. This study examines the economics of heat pumps in participating counties in the Whole County PV program, employing hourly data for both PV output and ambient temperature in participating counties. The analysis shows that pairing residential heat pumps with PV in counties in Shandong, Henan, and Jiangsu would result in short economic payback periods versus gas or resistance heat, while also increasing self-consumption of PV. The results suggest that expanding the Whole County PV program to incorporate energy efficiency and heating/cooling measures represents an economically attractive way to accelerate the rural energy transition and improve rural livelihoods. Such a policy would help accelerate the low-carbon energy transition, reduce air pollutant emissions, and help address oversupply of midday PV output in local areas. Barriers to the approach include involvement of different government ministries, the cost of upgrading building insulation, the design of building codes, and the structure of electricity tariffs.

The twenty-first century is confronted with the consequences of enormous amounts of global emerging plastic waste resulting from an excessive use of plastic, which has been imparting several negative impacts on the environment and human health. Moreover, some novel variants have also been reported in some coastal environments, so far, as a result of mixing of plastic waste with various other matrices. As a result, the problem of various forms of plastic waste within the marine ecosystem has emerged as a major concern in recent years. The current review is focused on the detrimental implications of various emerging and novel plastic variants, with an emphasis on coastal and marine environments. This review highlights the fate and transportation patterns of plastic waste, along with the contemporary examples of its implications on marine biota. Additionally, this work also examines the impacts of marine plastic waste on the environment. The review further highlights the importance of circular economy of plastic waste for sustainability. Then in the end, the growing anxieties about the impacts of plastic waste on coastal as well as marine environment, along with the strategies for reducing its impacts on ecological sustainability are discussed.

This article provides a comprehensive review about passive flow control devices (PFCDs) implemented in lift-type vertical axis wind turbine (LVAWT), focusing on the underlying flow physics mechanisms and to what extents they can improve the LVAWT performance. In addition, some novel concepts that can be potentially implemented in future are also presented. Based on literature review, it is observed that PFCDs can enhance the power generation of LVAWT up to 172.73% compared with a clean LVAWT. However, this significant improvement still needs to be evaluated carefully by considering the economic feasibility aspect, because PCFDs can increase the design complexity, weight penalty and manufacturing cost of LVAWT. Furthermore, it is essential to design and evaluate the effectiveness of PFCDs using a full VAWT configuration by considering the blade rotating effects and blade-to-blade interactions. Finally, evaluation of PFCDs needs to be performed at all ranges of tip speed ratios (TSRs) operation conditions, as there are clear evidences on the correlation between LVAWT performance and different range of TSRs.

The continuous increase in global surface temperature, which has been triggered by the increase in atmospheric CO2 concentration from anthropogenic activity, results in damage not only in the short term but also in the long term. This damage, called the social cost of carbon (SCC), has been widely estimated using integrated assessment models (IAMs). A large range of estimated SCC values have been observed because of uncertainties in IAMs' parameters. This study provides a comprehensive review of these uncertainties after dividing IAM modules into four categories: climate sensitivity, damage function, discount rate, and regional–sectoral validation. The review was conducted by comparing key ideas considered by various IAMs: socioeconomic conditions in relation to projected CO2 emissions, estimation of the atmospheric concentration of CO2, estimation of total radiative forcing, parameters of the temperature function, parameters of the damage function, and discount rate value. In addition, this study presents an alternative approach to capture the uncertainties embedded in the SCC estimation, using a machine learning approach. This enables a probabilistic evaluation of a specific level of SCC and improves our comprehension of the implication of the calculated SCC using IAMs. This alternative approach provides a basis for further study of SCC.

Small Island States present features, such as compact road networks, low commuter distances, and often large tourism service sectors, that could make the adoption of electric vehicles for transportation which is an attractive way to reduce their costly dependence on imported fossil fuel and their greenhouse gas emissions. Through the transition theory lens, we review the national policy measures and broad clean transportation targets that small island countries are implementing to encourage electric mobility deployment. From information compiled for 18 small island countries, we find a growing trend in electric vehicle and infrastructure development incentives among broader clean transportation transformation policies and nationally determined contribution targets; and large country-to-country variations in enabling conditions to smoothen EV transition. Small island countries are not uniform but instead are very dispersed across the transition S-curve. The review, therefore, finds that the mobility transition requires island-specific approaches and solutions that will accentuate critical policy and management elements for fostering transitions.

The recent publication of the Sixth Assessment Report on Climate Change (AR6) by the Intergovernmental Panel on Climate Change (IPCC) (IPCC, 2021) reveals an increasingly difficult challenge: the nature and rate of change in the world's climate due to human activity is occurring at a pace faster than the best science and research is organized to report. Successive IPCC reports, for example, document changes that often are out of date by the time it takes the Panel to organize an assessment. There is growing concern in the research community that what we know today about the climate system is destined to understate our actual challenges and risks (Beck & Mahony, 2018; Hayhoe & Kopp, 2016; Xu et al., 2018). This raises serious problems with policy designs that rely on known current costs and benefits, which will almost certainly be wrong tomorrow. And, even more concerning, policy designs built on the knowns of social and economic valuation imply that climate change is an incremental process. From the available evidence, this assumption is clearly no longer valid. Policy designs need to immediately move away from approaches meant to balance incremental social and economic costs and benefits and face the reality of “compounding extremes” (a concept introduced in the latest IPCC report). Updated estimates in the 2021 report re-confirm facts described in previous assessments, but the damage and risks of escalating change are far worse than previously identified. For instance, AR6 once more underscores the “established fact” that climate change is due to human activity, but it then documents a “substantial increase” in global warming relative to previous reports and indicates that the required reduction in human-induced greenhouse gas releases is much deeper than we thought just a few years ago. AR6 now assesses our challenge as compounding, with “increased intensities, durations, and/or spatial extents unprecedented in the observational record” now accelerating (IPCC, 2021, p. SPM-35). These compounding processes appear to create “climate surprises” with potentially dramatic consequences and almost no time to mitigate, much less adapt to, them.1 The implication for policy is profound. Policy analysis and policy-making have all too often been far behind in conceiving, much less actually addressing the latest realities of climate change. In effect, policy analysis and policy-making have become a reactive process of following climate change rather than leading social transformation. The Paris Climate Agreement is an example of how this process plays out: the Parties to the Agreement widely understood that the ambitions and concessions made by nation-states at the international negotiation table are insufficient to address assessment targets based on physical changes recorded by science that is 5 years or older (e.g., Roelfsema et al., 2020). Promises of “ramping-up” ambition under the Paris Agreement architecture signal the incremental character of climate policy-making—a process found to be lacking even when considering multiple collective improvement scenarios (Geiges et al., 2020). This troubling condition of policy failure is directly traceable to how policy research thinks about the problem. Commonly practiced “business-as-usual” (BAU) benchmarking and search processes to find least-cost options can only deliver out-of-date and mostly wrong characterizations of costs and benefits when the underlying process of climate change has advanced several iterations beyond BAU.2 Policy research suffers from a deeply misguided understanding of its task as it scours the rear-view mirror of past change in hopes of finding the future. The flaw of incremental climate policy-making and the research that informs it is now obvious: using the cost of mitigation and adaptation as the ranking principle to guide decisions is a formula for doing nothing or very little. Positioning the cost of change as the primary guidepost for public action delivers policy hesitancy—a condition that is bound to be increasingly wrong in a rapidly transforming climate system of “compounding extremes” (IPCC, 2021). A climate system of compounding extremes precludes an assumption that overshoot can be repaired by belated but “serious” climate policy interventions. As a case in point, rampant wildfires in California are associated with compounding conditions of drought, extreme precipitation, and more. Their currently known cost is astonishing—California's annual wildfire-related costs are upwards of $50 billion in 2018 (Figure 1; see also AghaKouchak et al., 2020)—but it can hardly provide a usable benchmark when the damage and the mechanics creating it were heretofore inconceivable or dramatically understated. FIGURE 1Open in figure viewerPowerPoint Example of compounding climate extremes in California Recent findings in AR6 make clear that a rapid and far-reaching social transformation unprecedented in terms of scale is required (see also IPCC, 2018). Levels of technological and social change sufficient to overcome decades of policy hesitancy are urgently needed. A lesson from policy analysis failure is that BAU benchmarking and “lowest cost” design are useless today. The climate system, and therefore, societies and economies, are increasingly susceptible to dramatic decline and catastrophe than our benchmarks and lowest-cost metrics presume. Put bluntly, we can no longer be guided by a policy regime that depends on prior experience with previous circumstances that no longer apply.

Since the early beginnings of the electricity system, storage has been of high relevance for balancing supply and demand. Through expanded electricity production by variable renewable technologies such as wind and photovoltaics, the discussion about new options for storage technologies is emerging. In addition, the electricity markets were subject to remarkable alterations. Some developments which describe these changes are increasing electricity generation from variable renewables and the continuing decentralization. These developments have led, among other required transformations, to demands for additional capacities of storage technologies. However, their economics will play a crucial role in their effective market penetration in the following years. The core objective of this work is to conduct a review on the relevance of storage options for electricity and its costs, economics, welfare effects, and on issues of electricity market design. In addition, based on expected Technological Learning prospects for future economics are derived. The major result is that the perspectives of electricity storage systems from an economic viewpoint are highly dependent on the storage's operation time, the nature of the overall system, availability of other flexibility options, and sector coupling. All market-based storage technologies have to prove their performance in the large electricity markets or if applied decentralized, the (battery) systems compete with the electricity prices at the final customers level when the battery costs are also taken into consideration. Yet, new storage capacities should only be added when it is clear that electricity generation from variable renewables will also be expanded in a way that excess generation is expected.

The concept of technological learning is a method to anticipate the future development of the costs of technologies. It has been discussed since the 1930s as a tool for determining manufacturing cost reductions, starting in an airplane manufacturing plant, by means of learning curves and has been widely used since the 2000s in energy models to endogenize technological change. In this paper, the theoretical concept of technological learning based on energy technologies is analyzed based on examples from the literature. The main low-carbon power generation technologies, photovoltaics, concentrated solar power, wind and nuclear energy were analyzed, showing different cost trends. Additionally, the impact of policy support on technological learning was discussed in concrete examples of bioethanol and heat pumps. We find that the homogeneity and the modularity of a technology are essential for high learning rates. A good proof is the manufacturing cost development of photovoltaics in recent decades, where a rather stable learning rate of 20% has been identified. On the contrary, nuclear power did not evolve into a homogeneous technology due to required environmental adaptations caused by accidents and the lack of standardization and application of new engineering approaches. In that case, the overall price further increased. Finally, another important condition is stable legal and regulatory conditions regarding the implementation.

Offshore renewable energies have been identified as important clean sources of energy in line with sustainable development goals. However, their use can generate conflicts with other maritime activities, as well as the protection of biodiversity and the marine environment. This article analyses the influence of regulatory frameworks and ocean governance in the implementation of such devices, from a legal–political point of view. In this sense, it studies how the law of the sea addresses potential international conflicts between ocean energy installations and other activities (e.g., navigation) developed by other states. It also studies the importance of preventive legal tools—marine spatial planning, strategic environmental assessment, and environmental impact assessment—to anticipate and reduce clashes with other sea users as well as environmental damages that may be caused by these structures. Likewise, this research analyses different national consent procedures and legal–economic supporting schemes, to identify those that boost the implementation of such projects more quickly. Finally, the relevance of enhancing the involvement of affected coastal communities and local stakeholders in the decision-making processes, as well as in the socio-economic benefits of offshore renewable energy projects to increase their social acceptance, is also emphasized.

Water splitting (WS) driven by solar energy is considered as a promising strategy to produce renewable hydrogen from water with minimal environmental impact. Realization of large-scale hydrogen production by this approach requires cost-effective, efficient and stable materials to drive the WS reaction. Perovskite oxides have recently attracted widespread attention in WS applications due to their unique structural features, such as compositional and structural flexibility allowing them to achieve desired sunlight absorption capability, precise control of electrocatalytic and redox activity to drive the chemical reaction, tuneable bandgaps and band edges, and earth-abundance. However, perovskite oxides contain a large family of metal oxides and experimental exploration of novel perovskites without a priori knowledge of their properties could be costly and time-consuming. First-principles approaches such as density functional theory (DFT) are a useful and cost-effective alternative towards this end. In this review, DFT-based calculations for accurate prediction of the critical properties of ABO3 perovskite oxides relevant to WS processes are surveyed. Structural, electronic, optical, surface, and thermal properties are grouped according to their relevance to photocatalytic (PC), electrochemical (EC), photo-electrochemical (PEC), and solar thermal water splitting (STWS) processes. The challenges associated with the choice of exchange-correlation (XC) functional in DFT methods for precise prediction of these properties are discussed and specific XC functionals have been recommended where experimental comparisons are possible.

The noise emission of wind turbines and farms can be an important and limiting factor for future cost reductions and growth of wind energy. Closing scientific and technological gaps on wind turbine noise is thus directly supporting the further development of renewable energy while reducing adverse reactions toward wind farms. The present article is providing guidance on the most relevant research directions from an engineering perspective, namely: simulation methods, wind tunnel testing, and wind turbine design. Each topic is addressed separately and specific scientific challenges are identified. Future research directions that may improve our physical understanding of wind turbine noise, as well as facilitate the deployment of wind energy, are outlined. It is concluded that future scientific research on the topic of wind turbine noise should be conducted in a multidisciplinary context to maximize its impact. The suggested topics shall be seen as a collection of what is seen as the most relevant topics across research and product development but shall not be seen as exclusive or interlinked with specific development plans.

Anion exchange membrane (AEM)-based fuel cells as an alternative to proton exchange membrane fuel cells (PEMFCs) are attracting a lot of attention due to lower cost perceived due to use of non-platinum group metals as the catalysts. This review has focused on the advancements in the materials that have led to achievements in performances similar to that of PEMFC and the challenges that need to be overcome to bring the technology to commercialization. The improvements in the properties of the AEM, the advancements in the AEM, binders and understandings of the cationic species adsorption on the catalysts have led to improved performances >3 W cm−2. The review also highlights the importance of the stability issues of the membranes that has to be overcome for >5000 h of continuous operation for commercialization of the alkaline AEM fuel cell technology. The advancements in other operational parameters like water management, carbonation are also highlighted.

Evaporative cooling has a major role to play in fighting climate change and in achieving a low-carbon economy. As it helps to reduce energy demand for air conditioning, it is gaining attention in terms of improving energy efficiency in buildings. Evaporative cooling from wetted media can enhance water–air contact, thereby improving heat and mass transfer further and avoiding aerosols. Wetted media are commonly called evaporative cooling pads and are widely used in greenhouses, intensive livestock farming, and industrial facilities. However, a deep understanding of evaporative cooling pad performance can enhance their application to indoor occupied spaces such as residential or commercial cooling, or in hybrid air conditioning systems. Most studies analyze pad performance mainly in terms of pressure drop and saturation effectiveness. However, some studies propose alternative cooling efficiency parameters and others provide insights into key aspects such as power requirements and the coefficient of performance, water consumption, risk of water entrainment, material decay, and air quality, as well as the effect of water temperature and salinity, solar radiation, or wind speed. Existing results on these less studied performance issues are reviewed, and we identify the gaps in the literature in addition to highlighting the main challenges encountered, in an effort to guide future researchers in the field and enhance the application of direct evaporative cooling.