Energy Research Community Research Articles

Recent Advances in Self‐Powered Tribo‐/Piezoelectric Energy Harvesters: All‐In‐One Package for Future Smart Technologies

AbstractElectric devices has become a necessity in modern smart societies. The energy research community is continually exploring new solutions that can be employed as potential and reliable alternatives to satisfy future energy requirements in this context. Triboelectric/piezoelectric nanogenerators (TNGs/PNGs) are considered promising renewable energy harvesting technologies. TNGs/PNGs are gaining considerable research attention because of their advantages such as ease of fabrication, cost effectiveness, flexibility, lightweightness, long‐term‐durability, and excellent output performance. The TNGs/PNGs have enormous potential in harvesting energy from water waves (blue energy), airflow (wind energy), sound frequency (acoustic energy), vibrations/mechanical motions (such as body motions activities/sleeping), and in vivo body motions. These technologies are thus an “all‐in‐one package,” which is a unique selling point. The advantage of this technology is that all sources are natural and abundant. This paper provides a review of the potential use of PNGs/TNGs and includes a description of the rise of nanogenerators, their underlying mechanisms, different materials used, various models, possible applications, and future prospects. Stored energy can be used to develop smart/informative technologies (as ultrasensitive sensors) and self‐powered biomedical science. Owing to their considerable effects, these harvesting technologies are expected to dominate the future smart world.

An adaptation of the super-Gaussian wake model for yawed wind turbines

The wake of a yawed wind turbine tends to be deflected and does not follow the incoming wind direction. This phenomenon, often referred to as “wake deflection”, has recently received a lot of attention from the wind energy research community: it is possible to dynamically optimize a wind farm power production by yawing some turbines to deflect their wakes, thus minimizing wake losses over the whole wind farm. In the present work, an analytical model for estimating the deflection of a yawed wind turbine wake is proposed. This new model is based on a super-Gaussian shape assumption for the velocity profile, enabling the estimation of the wake deflection in both near and far wake regions. First, the super-Gaussian model will be briefly introduced. Then, the new wake deflection model will be presented, as well as an updated version of the well known Jimenez model. This revised model allows a proper comparison with the proposed super-Gaussian model, since it is based on a similar definition of the wake width. Finally, results will be compared with experimental data from the literature.

Data fusion strategies for energy efficiency in buildings: Overview, challenges and novel orientations

Recently, tremendous interest has been devoted to develop data fusion strategies for energy efficiency in buildings, where various kinds of information can be processed. However, applying the appropriate data fusion strategy to design an efficient energy efficiency system is not straightforward; it requires a priori knowledge of existing fusion strategies, their applications and their properties. To this regard, seeking to provide the energy research community with a better understanding of data fusion strategies in building energy saving systems, their principles, advantages, and potential applications, this paper proposes an extensive survey of existing data fusion mechanisms deployed to reduce excessive consumption and promote sustainability. We investigate their conceptualizations, advantages, challenges and drawbacks, as well as performing a taxonomy of existing data fusion strategies and other contributing factors. Following, a comprehensive comparison of the state-of-the-art data fusion based energy efficiency frameworks is conducted using various parameters, including data fusion level, data fusion techniques, behavioral change influencer, behavioral change incentive, recorded data, platform architecture, IoT technology and application scenario. Moreover, a novel method for electrical appliance identification is proposed based on the fusion of 2D local texture descriptors, where 1D power signals are transformed into 2D space and treated as images. The empirical evaluation, conducted on three real datasets, shows promising performance, in which up to 99.68% accuracy and 99.52% F1 score have been attained. In addition, various open research challenges and future orientations to improve data fusion based energy efficiency ecosystems are explored.

Predicting absorbed power of a wave energy converter in a nonlinear mixed sea

In this paper the power performances of a point absorber wave energy converter (WEC) operating in a nonlinear multi-directional mixed sea have been rigorously investigated. The absorbed power of the WEC Power Take Off (PTO) system has been calculated by incorporating a second order irregular wave model into a nonlinear dynamic filter. This is a new methodology that is uniquely proposed to the ocean wave energy research community. The predicted results of the WEC power performances have been rigorously analyzed and systematically compared, and the advantages of using our proposed new methodology under extreme wave states have been convincingly substantiated. The research findings in this paper highlight that it is important to employ a nonlinear wave theory under extreme wave states for studying the power performances of wave energy converters, but that linear wave theory gives good results under normal wave states.

Toward Greener Gaming: Estimating National Energy Use and Energy Efficiency Potential

Rising computing power, improved graphics quality, higher-resolution displays, and streaming delivery have rendered computer gaming an increasingly energy-intensive activity. However, the role of gaming-related energy use, and how it varies across platforms, has not been substantively examined by the energy or gaming research communities. We measured the energy consumption of 26 gaming systems representing the spectrum of technology, price, and performance. Among the findings, energy use varied widely by hardware, but equally widely depending on which of 37 game titles or 11 benchmarks were run. Cloud-gaming energy use in datacenters and networks is markedly higher than that for local gaming. Virtual-reality gaming can use significantly more or less energy than gaming with conventional displays, depending on hardware and software choices. In aggregate, we find that gaming represents $5 billion per year in energy expenditures across the United States or 34 TWh/year (2.4% of residential electricity nationally), with 24 MT/year of associated carbon-dioxide emissions equivalent to that of 85 million refrigerators or over 5 million cars. Targeted hardware and software strategies can reduce the gaming energy use by approximately half, while maintaining or improving metrics of user experience. In addition to system designers, gamers and game developers can play a significant role in managing the energy required for gaming.

Efficient electrocatalytic oxygen evolution by Fe3C nanosheets perpendicularly grown on 3D Ni foams

The development of efficient and earth-abundant catalyst for the oxygen evolution reaction (OER) is an important challenge for the renewable energy research community. Here, we report a facile method to design a nanosheet-like structure of Fe3C, perpendicularly grown on Ni foam (NF) as a catalyst for OER by hydrothermal reaction and annealing treatment at a low temperature. The synthesized Fe3C has good conductivity, small charge transfer resistance (Rct), high active site density, and excellent stability, which make it highly efficient OER catalyst. Fe3C/NF has a low overpotential of 262 mV at a current density of 10 mA cm−2 and a small Tafel slope of 49 mV dec−1. Remarkably, Fe3C/NF also has good electrochemical stability, which helps maintain its activity in 1.0 M KOH solution for at least 100 h. Therefore, the simple method to prepare perpendicularly grown Fe3C on a NF substrate can enhance the OER properties, which make Fe3C/NF a promising material for replacing noble metal-based catalysts for OER applications.

A Decision-making Model for Corrective Maintenance of Offshore Wind Turbines Considering Uncertainties

Maintenance optimization has received special attention among the wind energy research community over the past two decades. This is mainly because of the high degree of uncertainties involved in the execution of operation and maintenance (O&M) activities throughout the lifecycle of wind farms. The increasing complexity in offshore maintenance execution demands applied research and brings forth a need to develop problem-specific maintenance decision-making models. In this paper, a mathematical model is proposed to assist wind farm stakeholders in making critical resource- related decisions for corrective maintenance at offshore wind farms (OWFs), considering uncertainties in turbine failure information.

Flexibility capital and flexibility justice in smart energy systems

Flexibility has increasing value across sectors of the economy, including energy. The ability to be flexible is affected by a wide variety of sociotechnical factors and determines what we term ‘flexibility capital’. Levels of flexibility capital vary in populations, both absolutely and in the extent to which they are primarily derived from technological or social means, which has implications for the (dis)comfort and (in)convenience involved in economising flexibility capital. Furthermore, we argue that freedom of choice over whether and how to economise flexibility capital can be limited by factors such as financial resources, among others. In constrained systems (such as energy networks), the level of service enjoyed by the more affluent may not simply be higher than those who are less affluent, but may be directly enabled by reductions in the latter’s comfort and/or convenience which may not feel fully voluntary. There is a real risk that such injustices could be locked into energy infrastructure and market design and governance for the long term as has already happened in labour markets. We introduce the concept of ‘flexibility justice’ as a frame for these issues of fairness. While the concepts we offer in the paper emerge from longstanding engagements with energy research contexts and they relate directly to the issues currently being debated in the energy research and policy communities, we contend that they can be related to a much broader range of issues in 21st century economies.

Graphitic Carbon Nitride and Titanium Dioxide Modified with 1 D and 2 D Carbon Structures for Photocatalysis.

Enhancing the photocatalytic performance of graphitic carbon nitride (g-C3 N4 , GCN) and titanium dioxide (TiO2 ) has played a key role in the energy and environmental protection research community. Therefore, it is necessary to explore the synergy of both materials with carbon nanostructures for photocatalysis. Among the variety of carbon materials, graphene flakes and nanotubes, as nanoadditives to improve electron charge transfer and the optical absorption behavior in the visible-light region, have been widely explored. Thus, flake-like (2 D) and tubular (1 D) carbon structures in composition with GCN and/or TiO2 are reviewed, as are their photocatalytic response. Current trends clearly indicate that this type of molecular hybrids can be efficiently exploited in this field. This Minireview covers state-of-the-art research over the period of 2015 to 2018.

Office occupants as active actors in assessing and informing comfort: a context-embedded comfort assessment in indoor environmental quality investigations

ABSTRACTThe energy and building research community acknowledges the importance of including occupants' wellbeing in the evaluation of building energy performance. Particularly in office buildings, occupants' comfort assessment is not yet a common practice, partially due to the shortcomings of the comfort assessment activities. Contextual factors such as the organizational culture, occupants' personality traits and emotional states, and the building and research measurement infrastructures do interact with occupants' motivation to report and influence their actual reporting behaviour. By means of an in situ mixed method approach combining real-world research and user-centric methods, this study investigates the impact of a reporting-based comfort assessment. Two buildings, representing different organizational cultures, were selected to study the influence of reporting behaviour on comfort assessment. The buildings were equipped with innovative indoor climate monitoring and in situ comfort reporting infrastructure and 2-week field studies were conducted in both buildings. By discussing results from these studies, this paper contributes to the development of building research methodologies of indoor climate and comfort assessment by providing practical experience in embedding comfort reporting behaviour in the analysis of comfort assessment. A contextual typology of reporting behaviour is introduced and its implications regarding the reliability and validity of comfort reporting techniques are discussed.

Optimal distribution width for ALM in LES for (NEW) MEXICO experiment

The Actuator Line Method exists for more than a decade and has become a well established choice for simulating wind rotors in computational fluid dynamics. Numerous implementations exist and are used in the wind energy research community. A crucial parameter of this method is the distribution width used to distribute the blade forces in the domain in order to attain numerical stability but also to apply the force term over a length which makes physically sense. In this work the implementation is verified with results from the (NEW) MEXICO experiment and the optimal distribution width is found by setting the global torque as target variable.

Wind tunnel experiments of a pair of interacting vertical-axis wind turbines

Vertical-axis wind turbines (VAWTs) have received a renewed interest in the wind energy research community, mainly for off-shore applications. One advantage is that installing a pair of counterrotating VAWTs on the same floating platform would result in thrust reduction and potential cancellation of the mooring yaw moment. In addition, such configurations could benefit from increased power output and reduced wake losses.In this article, we report on wind tunnel experiments to study the mechanical power output of a reference VAWT scale model, tested individually and in a closely-spaced pair of VAWTs. The power output of the individual VAWT configuration is compared with a pair of VAWTs spaced 1.3 diameters apart for two counterrotating directions. A net power increase in the power coefficient for the paired configuration of up to 17.0% compared with two individual rotors has been observed.

Fabrication of Cu2 O-based Materials for Lithium-Ion Batteries.

The improvement of the performance of advanced batteries has played a key role in the energy research community since its inception. Therefore, it is necessary to explore high-performance materials for applications in advanced batteries. Among the variety of materials applied in batteries, much research has been dedicated to examine cuprous oxide materials as working electrodes in lithium cells to check their suitability as anodes for Li-ion cells and this has revealed great working capacities because of their specific characteristics (polymorphic forms, controllable structure, high cycling capacity, etc.). Thus, cuprous oxide and its composites will be fully introduced in this Review for their applications in advanced batteries. It is believed that, in the future, both the study and the impact of cuprous oxide and its composites will be much more profound and lasting.

Evaluating approaches for district-wide energy model calibration considering the Urban Heat Island effect

Over the past decade, the building energy research community has increasingly focused on urban-scale models. The shortcomings of analyzing isolated buildings in an urban context are well-known and far from negligible, mainly due to the inability to account for Urban Heat Island (UHI), shading from neighboring obstructions, and obstructed wind flow. The aim of this paper is to evaluate the impact of the urban context via urban-scale modelling and inverse parameter estimation (calibration) using metered building energy consumption. We describe an automated calibration process for modelling 56 buildings in a representative district in downtown Abu Dhabi (UAE), where a detailed energy audit was conducted with data from 2008 to 2010. Since the urban ambient air temperature could differ significantly from the reference rural air temperature used in most building simulations, the calibration procedure will also consider this UHI effect. Two main approaches of district-wide energy model calibration are proposed using a genetic algorithm and compared to a baseline case where UHI is not considered. The first approach estimates seven building-related parameters together with four microclimate-related variables (describing annual average and seasonal variation of the UHI effect on both air temperature and humidity). The second one uses the Urban Weather Generator (UWG) to pre-process the urban EPW file, thereby reducing the number of the parameters to be estimated. In addition, two approaches are investigated for the calculation of the ASHRAE Guideline 14 calibration error metrics (CvRMSE and NMBE). One approach is to look at the whole district as one aggregate building, while the other, introduced for the first time herein, consists in deriving the weighted-average of the error of each building. The main contribution of this study is to provide simultaneous calibration for multiple buildings in the same district—and subject to the same UHI intensity. Hence, the UHI intensity (urban-rural temperature/humidity differential) is estimated alongside other calibration parameters. For the weighted average approach, CvRMSE found is between 19.09% and 19.40%, while NMBE is between 16.24% and 16.39%. For the aggregated building, CvRMSE is between 2.71% and 4.04%, while NMBE is between 1.95% and 2.35%.

MDSplus yesterday, today and tomorrow

MDSplus is a data acquisition and analysis system used worldwide predominantly in the fusion research community. Development began 31 years ago by a collaboration of software developers who were charged with providing a data acquisition system for three new fusion experiments under construction: CMOD at MIT, ZTH at LANL and RFX at Padova, Italy. The design of MDSplus combined the functionality of MDS (MIT/Model Data System developed at MIT for the Alcator and Tara fusion experiments) with new features suggested by the developers from the other laboratories. The development of MDSplus used a RAD (rapid application development) approach before RAD became a mainstream methodology. MDSplus was implemented and ready for the initial operation of CMOD in 1991. Since that time, many other fusion facilities started using MDSplus for data acquisition and/or for exporting their data to other sites. Today MDSplus is still used around the world for fusion energy research, space exploration and other fields of science and technology. Work on MDSplus continues to enhance its capabilities, support more platforms, and improve its reliability. It is anticipated that MDSplus will continue to provide valuable tools for the fusion energy research community. This paper describes some of the history of the MDSplus software, the work that is currently underway, and the plans to enable MDSplus to continue to be available and supported long into the future.

Ultrafast and large scale preparation of superior catalyst for oxygen evolution reaction

The development of efficient and earth abundant catalyst for the oxygen evolution reaction (OER) is a key challenge for the renewable energy research community. Here, we report a facile and ultrafast route to immobilize nickel-iron layered double hydroxide (NiFe-LDH) nanoparticles on nickel foam (NF) via soaking the direct electroless deposited prussian blue analogue (PBA) on NF in 1 M KOH. This NiFe-LDH/NF electrode can be prepared in a few seconds without further treatments. It has three-dimensional interpenetrating network originated from its PBA precursor which facilitate the diffusion and ad/desorption of the reactants and producing for OER. And further characterization of the Faradaic efficiency and forced convection tests show direct evidence to demonstrate the formation of free intermediate(s) in the OER process. This electrode (typically NiFe-LDH-20s/NF) exhibits outstanding electrocatalytic activity with low overpotential of ∼0.240 V at 10 mA cm−2, low Tafel slope of 38 mV dec−1, and great stability. This feasible strategy affords a new strategy for the large scale manufacture of low-cost, effective and robust OER electrodes.

Efficient Model Predictive Control Strategies for Resource Management in an Islanded Microgrid

The energy research community is continuously pursuing improvements in power system resiliency and reliability. Microgrids offer a unique opportunity for enhanced reliability and resiliency by utilizing localized generation and energy storage when grid power is unavailable or too expensive. Energy management is a critical aspect of these systems to ensure proper balancing of sources and ensuring power supply to critical loads with minimum cost, especially in an islanded microgrid. This paper presents a hierarchical real-time optimization with mathematical formulations to achieve optimal operation for an islanded microgrid. The optimization is implemented using simple numerically tractable model predictive control strategies and enables appropriate decisions in response to constantly changing conditions. The optimization method is extended for experimentation within the real-time simulation. Simulation results show that the proposed resource management algorithm shows near-optimal performance while effectively dealing with uncertainties in forecasting.

A comprehensive review of solar thermoelectric cooling systems

Summary The negative environmental impacts of burning fossil fuels have forced the energy research community seriously to consider renewable sources, such as naturally available solar energy. This paper provides an overview of solar thermoelectric (TE) cooling systems. Thus, this review presents the details referring to TE cooling parameters and formulations of the performance indicators and focuses on the development of TE cooling systems in recent decade with particular attention on advances in materials and modeling and design approaches. Additionally, the TE cooling applications have been also reviewed in aspects of electronic cooling, domestic refrigeration, air conditioning, and power generation. Finally, the possibility of solar TE cooling technologies application in “nearly zero” energy buildings is briefly discussed, and some future research directions are included. This research shows that TE cooling systems have advantages over conventional cooling devices, including compact in size, light in weight, high reliability, no mechanical moving parts, no working fluid, being powered by direct current, and easily switching between cooling and heating modes.

Comparison of OpenFOAM and EllipSys3D actuator line methods with (NEW) MEXICO results

The Actuator Line Method exists for more than a decade and has become a well established choice for simulating wind rotors in computational fluid dynamics. Numerous implementations exist and are used in the wind energy research community. These codes were verified by experimental data such as the MEXICO experiment. Often the verification against other codes were made on a very broad scale. Therefore this study attempts first a validation by comparing two different implementations, namely an adapted version of SOWFA/OpenFOAM and EllipSys3D and also a verification by comparing against experimental results from the MEXICO and NEW MEXICO experiments.

A survey of modelling methods for high-fidelity wind farm simulations using large eddy simulation.

Large eddy simulations (LES) of wind farms have the capability to provide valuable and detailed information about the dynamics of wind turbine wakes. For this reason, their use within the wind energy research community is on the rise, spurring the development of new models and methods. This review surveys the most common schemes available to model the rotor, atmospheric conditions and terrain effects within current state-of-the-art LES codes, of which an overview is provided. A summary of the experimental research data available for validation of LES codes within the context of single and multiple wake situations is also supplied. Some typical results for wind turbine and wind farm flows are presented to illustrate best practices for carrying out high-fidelity LES of wind farms under various atmospheric and terrain conditions.This article is part of the themed issue 'Wind energy in complex terrains'.