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Wind power intermittency makes it imperative to conduct transient modeling to highlight and address the challenges related to longer-term dynamics prior to demonstration projects. This paper presents the transient modeling and simulation of offshore wind energy integrated with a "green hydrogen" and "green ammonia" synthesis system. Since the transmission of electricity produced from far offshore sites to onshore points is challenging and submarine power cables are a significant cost, a fully off-grid offshore location is proposed for green ammonia production (power-to-ammonia) in contrast to previous studies that have examined grid-tied approaches. This approach can utilize the massive unexploited potential of remote offshore locations where wind velocities and capacity factors are comparatively higher, with produced green ammonia transported to onshore demand points via pipelines or ships. The offshore wind energy can directly be converted into ammonia using water and air as input materials, starting with the generated wind power used in the water electrolysis system to split water into hydrogen and oxygen. Nitrogen is separated by an air separation unit and mixed with the hydrogen to produce ammonia through an all-electric ammonia synthesis system. The transient analysis results include ammonia production at each hour of the year and an integrated hydrogen storage system to buffer production for nominally steady ammonia ouput throughout the year. An economic analysis is also conducted that reveals offshore wind and electrolysis as the leading cost drivers. • Transient modeling of an offshore wind energy based green ammonia production system. • A fully off-grid offshore location is hypothesized for green ammonia production (power-to-ammonia). • Utilization of the massive unexploited potential of remote offshore locations. • The economic analysis also predicted that the offshore wind farm and electrolyser dominate the overall costs with 45% and 29% respectively. • A hydrogen storage system of 80,000 kg capacity was found to be required to help meet a steady green ammonia demand of 554 kg/h. [ABSTRACT FROM AUTHOR]

This work assesses the role of biomass and municipal solid waste in isolated energy systems. For this, La Réunion, a French overseas territory in the Indian Ocean with a population of about 850,000, serves as a case study. Methodically, the study assesses technical biomass-based potentials based on an island-wide digital landscape model, detailed information on land use, soil, and climate, and a dynamic yield simulation tool, while technical waste-based energy potentials are calculated from local data. In total, 9 crops, 11 waste streams, and forested areas are considered. The potential contribution of biomass and waste to the energy system is studied in three scenarios. In all, unsustainable outcomes are avoided by valorizing only crop residues and applying sustainable harvesting rates to forests. Depending on the scenario, biomass or waste based energy could cover between 19% and 22% of 2019 electricity demand compared to an actual value of 6% (2019). Furthermore, prioritizing the production of secondary energy carriers allows to meet 8% of 2019 energy demand in the transport sector. These results are in good accordance with previous studies and scenarios on Réunion's energy transition. Given its bottom-up approach based on standard geoinformatic data, the proposed method is in principle transferable to other isolated regions, also in developing countries. A first, high-level assessment of four comparable island (states) shows that in three cases similar contributions of biomass and waste as in Réunion can be expected. As a next step, the purely technical assessment shall be complemented by economic considerations. • Method: Application of an innovative bottom-up and spatially resolved biomass potential analysis with local waste potentials. • Result: Exploitation of local energy resource potentials in biomass and waste can cover up to 49% of local electricity demand. • Transfer: The method can be applied to other isolated regions or developing countries. [ABSTRACT FROM AUTHOR]

Highlights • Near-wall vertical cable fire experiment was conducted in an analogue nuclear compartment. • Wall confinement and source-ceiling height variation effect was considered. • A new correlation for heat release rate of near-wall vertical cable fire was established. Abstract Nuclear power plant will be significant energy system for sustainable cities. The safety risk of the cable fire is an important issue for managing and operating a nuclear power plant. A simple and useful method to estimate the fire scale is urgently needed for safety management. In this work, experiment was conducted in a typical underground compartment of nuclear power plant, which primarily focused on safety monitoring and management of the vertically arranged cable. The burning characteristic of the cable was firstly measured by cone calorimeter. Then, full-scale experiment was conducted, in which the real-time heat release rate was recorded through mass variation and the real-time temperature beneath the ceiling was simultaneously measured by the thermocouples. A modified model to predict the real-time heat release rate of the vertical cable fire base on measured temperature beneath the ceiling was established and was then validated through the experimental result. It's shown that the predicted heat release rate could well match with that measured in the experiment. The results of this work may provide guidance for the cable fire risk assessment and safety monitoring, and may also provide reference for underground nuclear power plant design and safety management. [ABSTRACT FROM AUTHOR]

• Experimentally characterize the initial presence of lithium in shale rocks and brines. • Experimentally analyze the release mechanism of lithium from solid to fluid. • Numerically model the release, transport, and accumulation of lithium in shale brines. • Evaluate the lithium concentration in shale brines. • Contribute to the diversification and enhancement of sources of lithium supply. In order to mitigate climate change, diversifying the sources of lithium supply is crucial for the decarbonization of energy sector through enhanced renewable electricity generation and electrified transportation. Shale brines have been recently found to be containing significant amount of lithium, but relevant subsurface phenomena regarding its origin, fate, and transport are unknown. Here we present a suite of geochemical experiments to elucidate the initial presence of lithium in shale rocks and its release mechanism from solid phase into fluid, and numerical modeling to estimate the resources of lithium in shale brines by addressing its fate and transport. We find that the majority of lithium is inorganically bound as an interlayer cation of clay in shale rock, while a sparingly small portion is organically bound. Hydrothermal reaction experiments for leaching lithium reveal that calcium ion in fluid has strongest impact on lithium to be released into fluid, while sodium ion has minimal impact. From the numerical modeling combined with the experimental findings, average concentration of lithium in shale brines mimicking Marcellus Shale system is estimated to be about 135 ppm under calcium ion dominancy in pore fluid, which shows excellent match with actually measured values from produced Marcellus Shale brines. This study provides the understanding of fundamental phenomena addressing release, transport, and accumulation of lithium in geologic system, and hence contributes to the enhancement of sources of lithium supply for energy decarbonization. [ABSTRACT FROM AUTHOR]

Highlights • Power-to-gas can provide energy storage for renewable energy storage. • PtG can play different roles in different energy systems. • PtG can support the transition of energy system toward sustainability. • PtG can be an important source of renewable gases such as hydrogen, methane or SNG. Abstract This paper presents an overview of power-to-gas opportunities. Power-to-gas technology is gaining more and more popularity. It can provide large and long-term storage for increasing share of renewable sources in the energy system. In this paper, we would like to review the role of the power-to-gas system in different energy system architectures. Authors have analyzed the literature in the context of the problems, which could be solved by power-to-gas technology. Additionally, different assessment such as techno-economic, Life Cycle Assessment and Multi-criteria decision analysis for power-to-gas were revised. [ABSTRACT FROM AUTHOR]

Abstract Article shows how system dynamics modelling (SDM) approach could be used in modelling the energy transition towards low carbon energy system. SDM can be used to combine the techno-economic and socio-technical analysis. The study considers flexibility issues related to integration of renewable energy sources. Simplified model structure is made to illustrate how flexibility as well as other socio-technical aspects might be modelled. Results of the model correspond to the behavior anticipated from the model structure. Namely, model imitates effects of technological disruption which rises the limits of intermittent power production from renewable sources which can be integrated into power system. The limits are increased stepwise, as a share of intermittent power production reaches certain threshold value, resulting in sequence of S-shaped growth. This study presents flexibility increase of a power system conceptually and more detailed study should uncover leverage points which could stimulate this increase and thus, transition to sustainable energy system. [ABSTRACT FROM AUTHOR]

Sustainable and clean multi-energy systems have been hybrid coordinated in microgrid (MG) to fulfill regional multi-energy users economically, but shortages and surpluses still exist. The growth of win-win energy sharing between MGs attracts attention to smart information center (SIC) concept in MGs' community, which facilitates sustainable solutions across three key objectives: lower carbon emission, sufficient utilization, and long-term cooperation. This paper designs a two-stage decision framework for day-ahead operations of SIC, where the first stage minimizes the total cost (i.e. operational cost and carbon emission cost) by the proposed multi-energy intra-scheduling and inter-sharing model (MIIM) and the second stage implements the smart cost-saving redistribution model (SCRM) to stimulate MGs in long-term joining of energy sharing. The extended alternating direction multipliers method algorithm (E-ADMM) is developed to protect the privacy of MGs' data while approximating the optimal solution of MIIM. The case study proves that a) demand response and energy sharing in MIIM result in cost savings of 2.01% for carbon emissions and 7.25% for total operations; b) renewable energy has been fully utilized and the total multi-energy loss has been avoided nearly 92.22% in MIIM; c) the asymmetric Nash bargaining approach fits the SCRM with incentive cooperation, whereby those who contribute more gain a higher share; d) the optimal gap of E-ADMM is less than 0.2% by iterated insensitive decision result from each MG, which computes in polynomial time when the scale of MG increases; e) the two-stage framework performs better with more heterogeneity of MGs. Furthermore, we provide valuable insights for guidance and models with worldwide generalization potential. [ABSTRACT FROM AUTHOR]

This work-study deals with the economic planning of an island sustainable system that consists of a wind turbine, battery, combined heat and power system, and thermal storage to meet electrical and thermal loads at the same time. The approach attempts to find minimum capital cost, repair and maintenance cost, and operating cost, as well as minimize the pollution of these elements. It is also constrained by the operation-planning model of the mentioned resources and storage, provided that a wind turbine and combined heat and power system have priority in electrical load supply, a combined system of heat and power has priority in thermal load supply, and batteries and storage devices have the task of filling the gap between supply and demand profiles. Uncertainty parameters of the scheme include electrical and thermal load and power output of the wind system. The scheme adopts the unscented transformation method to provide proper modeling of the mentioned uncertainties. Moreover, the essence of the problem is integer nonlinear programming, which uses the combined gray wolf optimization and honey bee mating optimization algorithm to achieve the desired solution. Simultaneous supply of electrical and thermal loads, modeling of uncertainties, and adoption of a combined solver in the proposed scheme are among the contributions. Finally, by implementing this scheme on data from the city of Espoo, Finland, the numerical results indicate a reduction of 10%–11% in the planning cost of the proposed scheme compared to a design that only supplies electricity. • Planning an island sustainable system with WT, CHP, and storages in the Espoo, Finland. • Simultaneous supply of electrical and thermal energy. • Modeling uncertainties of wind speed and load in accordance with the UT method. • Using UT for a reliable solution to power fluctuations in load and WT relative to predictions. • Optimal solution obtained by GWO-HBMO with minimal standard deviation and fast convergence. [ABSTRACT FROM AUTHOR]

Coal is the most abundant fossil energy, however, coal industry is threatened by its environmental problems caused by the traditional way of utilization. In recent years, China has developed a series of clean coal technologies to transform black-dirty coal into clean fuels and chemicals. Shenhua Group, the largest coal company in China is leading the commercialization of modern clean-coal technologies for value-added chemicals and clean transportation fuels, in which CO 2 is captured in the process and ready for carbon capture, utilization and storage (CCUS). Industrial plants for coal based methanol production and conversion are flourishing in last decade. With the development of renewable H 2 , methanol production could be realized by CO 2 hydrogenation to transform into “Methanol Economy”, the sustainable energy development system. This paper will focus on the overview of research and development of methanol-based coal conversion technologies in China, such as methanol synthesis, methanol to olefins (MTO), chemicals (formaldehyde, acetic acid, aromatics, ethanol, ethylene glycol, etc.), gasoline (MTG), dimethyl ether (DME), polyoxymethylene dimethyl ethers (DMM n ), methyl tert -butyl ether (MTBE), direct combustion (DMFC), and as energy carrier. Commercial and successfully demonstrated units in China on both the synthesis of methanol and its utilization are discussed in detail. [ABSTRACT FROM AUTHOR]

Deployment of efficient, integrated energy systems can make a substantial contribution to reduction in greenhouse gas emissions. Such systems are suitable for the provision of distributed energy supply in remote areas, and offer the advantages of compactness and operational flexibility. Also, the simultaneous production of multiple products provides the opportunity for Process Integration, thus leading to improved fuel efficiency and reduced carbon emissions. Process Systems Engineering methods can be applied for the synthesis of such sustainable energy systems. For example, process graph (or P-graph) models have previously been developed for synthesizing single-period polygeneration systems based on the Process Network Synthesis framework. In this work, a P-graph model for multi-period optimization of sustainable energy systems is developed. The model is able to synthesize flexible systems that can cope with changes in the availability of raw material supply and variations in product demand. In addition, the P-graph model is also capable of generating near-optimal solutions, which provide insights that may be significant to decision-makers, such as structural features that are common to a range of good solutions. Two case studies are presented to demonstrate the approach developed in this work. [ABSTRACT FROM AUTHOR]

• Mathematical modeling of a deep-decarbonized energy system combining nuclear reactors, renewable resources, and energy storage systems. • Development of a novel research framework to assess the impact of resource uncertainty in a nuclear-renewable integrated energy system. • Evaluation and validation of research key findings using two recent nature-based optimization algorithms. Zero-carbon energy infrastructure design has become one of the most consequential pivotal toward sustainable development. This article introduces a novel approach to energy infrastructure innovation that incorporates carbon-free energy generation resources- renewables and Micro Nuclear Reactors (MNRs). The integrated Nuclear-Renewable Microgrid (NRM) has minimal greenhouse gas emissions and the utmost reliability. However, the planning and modeling of NRMs may face challenges due to the variability and uncertainty of renewable resources. Therefore, the study proposes a probabilistic energy modeling approach for NRMs, which provides an outstanding estimation for energy system planning in terms of economics and resiliency. Multiple load-generation scenarios have been formulated based on the probability distribution functions. A recent nature-based optimization technique, Slime Mould Algorithm (SMA), is employed to minimize the total annual cost of the probabilistic model with reliability constraints. The statistical analyses reveal that the probabilistic energy modeling method perfectly evaluates how energy generation resources should be mixed to fulfill energy demand in an optimal manner. The key findings also demonstrate observations on finance, system resiliency, and system components before the commencement of the project. The results are validated by another recent metaheuristic optimization algorithm called Aquila Optimizer (AO). [ABSTRACT FROM AUTHOR]

More variable renewable energy sources and energy efficiency measures create an additional flexibility gap and require a novel energy planning method for sustainable national energy systems. The firstly presented method uses only EnergyPLAN tool in order to decrease the flexibility gap in a national energy system. Generic Optimization program (GenOpt ® ) is an optimization program for the minimization of a cost function that is evaluated by an external simulation program, such as EnergyPLAN, which was used as the second method in this research. Successful strategies to decrease the flexibility gap are verified on the case of the Serbian national energy system using two methods for its structure design: (1) the iterative method, based on heuristics and manual procedure of using only EnergyPLAN, and (2) the optimization method, based on soft-linking of EnergyPLAN with GenOpt ® . The latter method, named EPOPT (EnergyPlan-genOPT), found the solution for the structure of the sustainable national energy system at the total cost of 8190 M€, while the iterative method was only able to find solutions at the cost in the range of 8251–8598 M€ by targeting only one sustainability goal. The advantages of the EPOPT method are its accuracy, user-friendliness and minimal costs, are valuable for planners. [ABSTRACT FROM AUTHOR]

The replacement of traditional process design approach by a more holistic approach is exigent in view of developing sustainable industrial systems and effectively reducing the energy and emission intensities in the process industries. Polygeneration systems are flexible and integrated multi-product systems that can potentially enhance energy efficiency, minimise financial risk and mitigate environmental impact. This paper presents a systematic conceptual process design and decision-making framework for facilitating multi-criteria analysis and selection of design options by considering three major criteria at process level—energy, environment and economy (3E). In this framework, three major steps are carried out: (i) defining system boundary, (ii) performance evaluation on the inner and outer system boundaries, (iii) 3E performance evaluation. 3E metric is proposed and it is derived from the relative economic worthiness associated with process energy intensity, greenhouse gas intensity and energy recovery which collectively indicates the techno-economic and environmental performances of a system with respect to the base case system. The methodology has been demonstrated through methanol and electricity production system with eight alternative configurations. Among the configurations under consideration, high offgas recycle for methanol production followed by electricity generation in series configuration has been found to carry the best 3E performance. [ABSTRACT FROM AUTHOR]

Hydrogen fuel cell vehicles (FCVs) are expected to have a significant impact in meeting both energy security and environmental concerns globally. Public and private support is however essential for successful transition to a sustainable energy system. Several studies have looked into the issues and considered the purchase behaviour of related Alternative Fuel Vehicles (AFCs) and more research momentum is seen towards hydrogen FCV. The article aims to critically review and identifies gaps of acceptance, preferences and attitudes of hydrogen FCV and examine whether attitudes, subjective norms (SNs) and perceived behaviour control (PBC) have significant associations with customer purchase intention (PI) and purchase behaviour of hydrogen FCV in Malaysia. This is a timely study to address useful policies for decarbonizing the transportation sector. [ABSTRACT FROM AUTHOR]

A sustainable energy system can be treated as a development of the distributed generation concept. It meets energy demands locally from renewable energy or/and high-efficiency polygeneration production technologies, and is characterized by energy and cost efficiency, reliability, and environmental-friendliness. Distributed energy systems typically use renewable energy resources to supply all energy demands, such as heat, cooling, and electric power in an integrated way. However, it seems that too much emphasis is placed on power and associated renewable energy-based power technologies for dealing with sustainability issues in public discussion and the research community. Often, equally important thermal energy (heat and cooling) and polygeneration are ignored. Polygeneration is an energy-efficient technology for generating simultaneously heat and power as well as other energy products in a single integrated process. Energy efficiency contributes significantly to CO 2 emission reduction. This paper discusses the role of polygeneration in a distributed energy system and the contributions of polygeneration to the development of sustainable energy systems. The paper also stresses that efficient decision support tools for sustainable polygeneration systems are important to achieve sustainability. First, the joint characteristic of a polygeneration plant that defines the dependency between different energy products is reviewed. Then, typical methods for dealing with polygeneration systems are reviewed. The review attempts to highlight the complexity of polygeneration systems and potential of polygeneration systems to adjust output of different energy products. Next, the challenges of sustainable polygeneration energy systems are discussed. Then some practices for operating polygeneration plants are discussed. [ABSTRACT FROM AUTHOR]

The city of Pécs in Hungary has developed an energy strategy to be implemented in the years to come which proposes structural changes in both the supply and demand sides. This paper offers a model based on the proposed system aimed at providing a basis for comparison for decision-makers. The model has been developed with the help of energy system analysis tool energyPRO, and covers the three basic sectors of heat, electricity and transport. It shows the energy system of Pécs in terms of hourly production and demand levels – and these values enable the model to analyse intermittent energy sources. The model is also validated – to ensure that it is satisfactory for the simulation of future energy systems. It analyses two scenarios – one where the city does not implement the changes proposed in the strategy, and one where it does. The paper compares the two scenarios based on sustainability, energy security and affordability. [ABSTRACT FROM AUTHOR]

Abstract: The transformation of existing energy systems into sustainable energy systems is a task which is related to several of the most urgent global problems, e.g. security of energy supply, shortage of resources, and climate change. Energy system modeling has played an important role in the computation of optimal possible future energy systems. In particular, technology oriented bottom-up energy system models have given insight into the required evolution of the energy technology mix. In face of the discussion about climate change, energy systems analysis has focused on the calculation of cost minimal energy futures subject to greenhouse gas mitigation paths, especially CO2 mitigation paths. IKARUS-LP is a model of the German energy system which has been used for optimization tasks of this type. As CO2 mitigation covers only one facet of sustainability, IKARUS-LP has been enhanced to optimize the German energy system for various sustainability targets specified by energy indicators for sustainable development. The resulting model is a fuzzy linear program, IKARUS-FLP. It computes an optimal compromise between the partly contradictory sustainability targets and system cost minimization. In this paper we introduce this model. Emphasis is given to the derivation of the crisp equivalent of the fuzzy problem. We show that a context-based semantics of fuzzy constraints is not adequate and found our semantics on the fuzzy extension principle. In a real-world case study for a time horizon until 2030 the mitigation path approach of IKARUS-LP and the sustainability optimization approach of IKARUS-FLP are compared. The results prove the feasibility of our new approach and its usefulness. [Copyright &y& Elsevier]

In a power grid with significant components of distributed generation and insufficient spinning reserve, the quality of delivered power may not meet the requirements of advanced manufacturing. A system design for power quality security which uses solid oxide fuel cell (SOFC) technology is described. Critical parameters for system performance are continuous supply voltage at the nominal voltage and frequency. The grid chosen for this study has significant voltage fluctuations and periodic voltage drops and surges, including total power loss. A supply of methane from a sewer sludge digester is scrubbed of CO2 and used for continuous standby operation, with excess stored to enable 8 h operation of an uninterruptible power supply (UPS). The system employs a modular, thermally coupled, SOFC architecture that includes steam reforming of the methane fuel, a rectifier, power controls, and control system. Continuous operation of a 125 kW tubular SOFC stack maintains operating temperature and steam for fuel reforming in a secondary SOFC stack, by exhausting through it before a gas turbine expands the exhaust to supply the plant air and fuel compression. Modelling of the energy balance of the system demonstrates the standby and full power operating modes. The system is sized at 250 kW to supply secure power for a manufacturing facility. [Copyright &y& Elsevier]

• Sustainable retrofit of energy systems under uncertainties is investigated. • A multi-objective stochastic optimization framework is formulated for the retrofit. • Uncertainties including energy demands and renewable energy loads are considered. • SROM sampling method is introduced to describe the uncertainty with less samples. • Uncertain optimization leads to a reliable retrofit with a 10% increase of TAC. We report a multi-objective stochastic mixed-integer non-linear programming (MINLP) framework for sustainable retrofit and capability expansion of traditional energy systems in petrochemical complexes. Multiple uncertainties including energy demands, solar radiation and wind speeds are considered in the optimization framework, these are characterized by historical data or normal distributions which are pre-defined with assumed mean values and standard variations. A stochastic reduced order model approach is introduced to describe the uncertainties by a small number of scenarios and their individual probabilities. The optimization framework further accounts for system configuration selection and sizing of the candidate energy conversion equipment, such as thermal storage units, gas turbines, boilers, steam turbines, as well as their operating capacities in each time period. A case study is investigated to demonstrate the performance of the proposed strategy and then the optimization results under three modes (deterministic, stochastic and semi-stochastic programs) are compared. [Display omitted] [ABSTRACT FROM AUTHOR]

Perovskite oxides show high electrocatalysis behavior for energy-related applications due to their reactivity, adjustable properties and impurity tolerance. It is very important to improve the slow kinetics and long-term stability of perovskite oxides. The ability of perovskite oxides to accommodate more metallic element inside the crystal structure without compromising the matrix gives a chance to engineer the catalytic properties for various energy applications. In the perovskite structure, the transition metal at the B-site can come out at the surface upon reduction forming catalytically active nanoparticles. This is known as exsolution. Generation of different kinds of metal or alloy nanoparticles on the perovskite surface gives the opportunity of tailoring electrochemical properties for outstanding performance. The exsolution process creates active interfaces which also helps to enhance the performance and stability. The advancements in this area will drive this process further for application in different sustainable energy technologies. A report combining all the advancements and applications of exsolution in recent years may be helpful to understand the process in a more detail way. In this review, a broad overview of the exsolution process of perovskite oxides, its sustainable electrochemical energy systems are discussed. • Exsolution of perovskite oxides and its energy-related applications are discussed. • Common features, mechanism & driving forces of exsolution are discussed in detail. • The article provides fundamental understanding of the process. • It gives knowledge to select suitable perovskite oxides for specific application. [ABSTRACT FROM AUTHOR]

• Spin dependent DFT calculations are executed for MgPr 2 X 4 (X = S, Se). • Structural investigation represent FM stability of MgPr 2 X 4 (X = S, Se). • The band structures analysis show their FM nature of MgPr 2 X 4 (X = S, Se). • The computed optical parameters indicate potential opto-electronic devices applications. • Electronic thermal coefficients are probed and suggested studied spinels as promising sustainable energy materials. In this paper, density functional theory (DFT) calculations are performed to investigate the spin-dependent mechanical, electronic, magnetic, optical, and thermal transport properties of rare-earth-based chalcogenides MgPr 2 X 4 (X = S, Se) spinels. The mechanical properties are obtained by employing the modified Perdew-Burke-Ernzerhof generalized gradient approximation (PBEsol GGA). Also, the modified Becke and Johnson (mBJ) potential is engaged in examining the electronic, magnetic, optical, and transport properties. Structural stability in the ferromagnetic (FM) phase is confirmed by calculating the energy difference between the FM and non-magnetic states. Besides, the formation energies are computed for thermodynamic stability. The strong hybridization near the Fermi level comes from chalcogenides 2p-states and f-states of rare-earth metals, which results in the total magnetic moments. The in-depth optical properties are evaluated in terms of dielectric constant and refraction. Lastly, electronic thermal coefficients, such as Seebeck coefficient, electrical and thermal conductivity, and power factor, are also probed and suggested studied spinels as promising sustainable energy materials. [ABSTRACT FROM AUTHOR]