Search

Welcome to this special section of the Journal of Micromechanics and Microengineering (JMM). This section, co-edited by myself and by Professor Jeffrey Lang of the Massachusetts Institute of Technology, contains expanded versions of selected papers presented at the Power MEMS meeting held in Atlanta, GA, USA, in December of 2012. Professor Lang and I had the privilege of co-chairing Power MEMS 2012, the 12th International Workshop on Micro and Nanotechnology for Power Generation and Energy Conversion Applications. The scope of the PowerMEMS series of workshops ranges from basic principles, to materials and fabrication, to devices and systems, to applications. The many applications of power MEMS (microelectromehcanical systems) range from MEMS-enabled energy harvesting, storage, conversion and conditioning, to integrated systems that manage these processes. Why is the power MEMS field growing in importance? Smaller-scale power and power supplies (microwatts to tens of watts) are gaining in prominence due to many factors, including the ubiquity of low power portable electronic equipment and the proliferation of wireless sensor nodes that require extraction of energy from their embedding environment in order to function. MEMS manufacturing methods can be utilized to improve the performance of traditional power supply elements, such as allowing batteries to charge faster or shrinking the physical size of passive elements in small-scale power supplies. MEMS technologies can be used to fabricate energy harvesters that extract energy from an embedding environment to power wireless sensor nodes, in-body medical implants and other devices, in which the harvesters are on the small scales that are appropriately matched to the overall size of these microsystems. MEMS can enable the manufacturing of energy storage elements from nontraditional materials by bringing appropriate structure and surface morphology to these materials as well as fabricating the electrical interfaces required for their operation and interconnection. Clearly, the marriage of MEMS technologies and energy conversion is a vital application space; and we are pleased to bring you some of the latest results from that space in this special section. Approximately 130 papers were presented at the Power MEMS 2012 conference. From these, the 20 papers you have before you were selected based on paper quality and topical balance. As you can see, papers representing many of the important areas of power MEMS are included: energy harvesters using multiple transduction schemes; MEMS-based fabrication of compact passive elements (inductors, supercapacitors, transformers); MEMS-enabled power diagnostics; MEMS-based batteries; and low power circuitry adapted to interfacing MEMS-based harvesters to overall systems. All of the papers you will read in this special section comprise substantial expansion from the proceedings articles and were reviewed through JMM's normal reviewing process. Both Professor Lang and I hope that you will share our enthusiasm for the field of power MEMS and that you will find this special section of JMM exciting, interesting and useful. Sincerely, Mark G Allen

This special section of Journal of Micromechanics and Microengineering features papers selected from the 11th International Workshop on Micro and Nanotechnology for Power Generation and Energy Conversion Applications (PowerMEMS 2011), held at Sejong Hotel in Seoul, Korea during 15–18 November 2011. Since the first PowerMEMS workshop held in Sendai, Japan in 2000, the workshop has developed as the premier forum for reporting research results in micro and nanotechnology for power generation, energy conversion, harvesting and processing applications, including in-depth technical issues on nanostructures and materials for small-scale high-density energy and thermal management. Potential PowerMEMS applications cover not only portable power devices for consumer electronics and remote sensors, but also micro engines, impulsive thrusters and fuel cells for systems ranging from the nanometer to the millimeter scale. The 2011 technical program consists of 1 plenary talk, 4 invited talks and 118 contributed presentations. The 48 oral and 70 poster presentations, selected by 27 Technical Program Committee Members from 131 submitted abstracts, have stimulated lively discussion maximizing the interaction between participants. Among them, this special section includes 9 papers covering micro-scale power generators, energy converters, harvesters, thrusters and thermal coolers. Finally, we are grateful to the members of the International Steering Committee, the Technical Program Committee, and the Local Organizing Committee for their efforts and contributions to PowerMEMS 2011. We also thank the two companies Samsung Electro-Mechanics and LG Elite for technical tour arrangements. Special thanks go to Dr Ian Forbes, the editorial staff of the Journal of Micromechanics and Microengineering, as well as to the staff of IOP Publishing for making this special section possible.

This special section of Journal of Micromechanics and Microengineering features papers selected from the 10th International Workshop on Micro and Nanotechnology for Power Generation and Energy Conversion Applications (PowerMEMS 2010). The workshop was organized in Leuven, Belgium from 30 November to 3 December 2010 by Katholieke Universiteit Leuven and the imec/Holst Centre. This was a special PowerMEMS Workshop, for several reasons. First of all, we celebrated the 10th anniversary of the workshop: the first PowerMEMS meeting was organized in Sendai, Japan in 2000. None of the organizers or participants of this first meeting could have predicted the impact of the workshop over the next decade. The second reason was that, for the first time, the conference organization spanned two countries: Belgium and the Netherlands. Thanks to the advances in information technology, teams from Katholieke Universiteit Leuven (Belgium) and the imec/Holst Centre in Eindhoven (the Netherlands) have been able to work together seamlessly as one team. The objective of the PowerMEMS Workshop is to stimulate innovation in micro and nanotechnology for power generation and energy conversion applications. Its scope ranges from integrated microelectromechanical systems (MEMS) for power generation, dissipation, harvesting, and management, to novel nanostructures and materials for energy-related applications. True to the objective of the PowerMEMSWorkshop, the 2010 technical program covered a broad range of energy related research, ranging from the nanometer to the millimeter scale, discussed in 5 invited and 52 oral presentations, and 112 posters. This special section includes 14 papers covering vibration energy harvesters, thermal applications and micro power systems. Finally, we wish to express sincere appreciation to the members of the International Steering Committee, the Technical Program Committee and last but not least the Local Organizing Committee. This special issue was edited in collaboration with the staff of IOP Publishing. PowerMEMS 2010 contents Harvesting energy from airflow with a michromachined piezoelectric harvester inside a Helmholtz resonator S P Matova, R Elfrink, R J M Vullers and R van Schaijk Analysis and characterization of triangular electrode structures for electrostatic energy harvestingDaniel Hoffmann, Bernd Folkmer and Yiannos Manoli A smart and self-sufficient frequency tunable vibration energy harvesterC Eichhorn, R Tchagsim, N Wilhelm and P Woias Power output enhancement of a vibration-driven electret generator for wireless sensor applicationsTatsuakira Masaki, Kenji Sakurai, Toru Yokoyama, Masayo Ikuta, Hiroshi Sameshima, Masashi Doi, Tomonori Seki and Masatoshi Oba Harvesting traffic-induced vibrations for structural health monitoring of bridgesT V Galchev, J McCullagh, R L Peterson and K Najafi Dispenser-printed planar thick-film thermoelectric energy generatorsA Chen, D Madan, P K Wright and J W Evans Silicon nanowire arrays as thermoelectric material for a power microgeneratorD Davila, A Tarancon, M Fernandez-Regulez, C Calaza, M Salleras, A San Paulo and L Fonseca A micro thermal switch with a stiffness-enhanced thermal isolation structureTakashiro Tsukamoto, Masayoshi Esashi and Shuji Tanaka A dielectric liquid contact thermal switch with electrowetting actuationA R McLanahan, C D Richards and R F Richards A self-regulating valve for single-phase liquid cooling of microelectronicsRadu Donose, Michael De Volder, Jan Peirs and Dominiek Reynaerts A MEMS-enabled 3D zinc–air microbattery with improved discharge characteristics based on a multilayer metallic substructureA Armutlulu, Y Fang, S H Kim, C H Ji, S A Bidstrup Allen and M G Allen Design, fabrication and testing of an air-breathing micro direct methanol fuel cell with compound anode flow fieldLuwen Wang, Yufeng Zhang, Youran Zhao, Zijiang An, Zhiping Zhou and Xiaowei Liu A shadow-mask evaporated pyroMEMS igniterD A de Koninck, D Briand and N F de Rooij Aerodynamic journal bearing with a flexible, damped support operating at 7.2 million DNTobias Waumans, Jan Peirs, Farid Al-Bender and Dominiek Reynaerts Thermoelectric energy harvester on the heated human machineVladimir Leonov

This special section of the Journal of Micromechanics and Microengineering presents papers selected from the 9th International Workshop on Micro and Nanotechnology for Power Generation and Energy Conversion Applications (PowerMEMS 2009), which was held in Washington DC, USA from 1?4 December 2009. Since it was first held in Sendai, Japan in 2000, the PowerMEMS workshop has focused on small-scale systems that process, convert, or generate macroscopically significant amounts of power, typically with high power density or high energy density. In the workshop's early years, much of the research presented was on small-scale fueled systems, such as micro heat engines and micro fuel cells. The past nine years have seen a dramatic expansion in the range of technologies that are brought to bear on the challenge of high-power, small-scale systems, as well as an increase in the applications for such technologies. At this year's workshop, 158 contributed papers were presented, along with invited and plenary presentations. The papers focused on applications from micro heat engines and fuel cells, to energy harvesting and its enabling electronics, to thermal management and propulsion. Also presented were the technologies that enable these applications, such as the structuring of microscale, nanoscale and biological systems for power applications, as well as combustion and catalysis at small scales. This special section includes a selection of 12 expanded papers representing energy harvesting, chemical and fueled systems, and elastic energy storage at small scales. We would like to express our appreciation to the members of the International Steering Committee, the Technical Program Committee, the Local Organizing Committee, and to the workshop's financial supporters. We are grateful to the referees for their contributions to the review process. Finally, we would like to thank Dr Ian Forbes, the editorial staff of the Journal of Micromechanics and Microengineering, and the staff of IOP Publishing for making this special section possible.

This special issue of the Journal of Micromechanics and Microengineering features papers selected from The 8th International Workshop on Micro and Nanotechnology for Power Generation and Energy Conversion Applications (PowerMEMS 2008) with the 2nd Symposium on Micro Environmental Machine Systems (μMEMS 2008). The workshop was held in Sendai, Japan on 9–12 November 2008 by Tohoku University. This is the second time that the PowerMEMS workshop has been held in Sendai, following the first workshop in 2000. Power MEMS is one of the newest categories of MEMS, which encompasses microdevices and microsystems for power generation, energy conversion and propulsion. The first concept of Power MEMS was born in the late 1990's from a MEMS-based gas turbine project at Massachusetts Institute of Technology. After that, the research and development of Power MEMS have been promoted by the strong need for compact power sources with high energy and/or power density. Since its inception, Power MEMS has expanded to include not only various MEMS-based power generators but also small energy machines and microdevices for macro power generators. Previously, the main topics of the PowerMEMS workshop were miniaturized gas turbines and micro fuel cells, but recently, energy harvesting has been the hottest topic. In 2008, energy harvesting had a 41% share in the 118 accepted regular papers. This special issue includes 19 papers on various topics. Finally, I would like to express my sincere appreciation to the members of the International Steering Committee, the Technical Program Committee, the Local Organizing Committee and financial supporters. This special issue was edited in collaboration with the staff of IOP Publishing.

Integrated energy supply and emerging new energy is a sign of transformation of energy system for environmental protection. This paper firstly models the key components of source side in integrated energy system. On the one hand, this paper models integrated energy supply and energy conversion devices involving multiple energy systems, on the other hand, it models new energy which is rapidly growing, so that all of these energy supply methods can serve the coordinated dispatch of integrated energy system. Then this paper focuses on CHP with heat storage which is a typical energy supply method involving both integrated energy supply and energy conversion. Through case study, we find that the heat storage system can bring friendly interaction between heat and power system, enhance the flexibility of integrated energy system, and decouple complex integrated energy system, so as to improve the social economic welfare.

Tailings pond is used to store the tailings discharged from the mine after separation and mining. As a potential hazard source with high potential energy, the tailings mortar with high potential energy after dam break is transformed into high-speed dynamic energy sand flow to impact the downstream area through energy conversion. In this paper, through the establishment of a three-dimensional model of a tailings pond, the FLOW-3D software is used for numerical simulation, and the influence of correlation coefficient on the discharge speed of tailings mortar after dam break is analyzed, and the relevant migration law is obtained. The test in this paper can provide a reference for the corresponding disaster and protection engineering research.

This paper proposes a vertical axis power generation device based on tidal energy for sensor used for information collection, the energy supply bottlenecks solving, and the sensor working efficiency improvement. The underwater operation test of the prototype system is carried out for finding the relation between the output power and the blade deflection angle and the blade speed ratio. This paper discusses how to improve the efficiency of energy conversion by modifying the parameters of prototype, which can provide a reliable guidance method for the next practical application. Experimental results show that the device can meet the energy demand of sensor networks.

The three products are formed as result of sewage sludge pyrolysis: solid residue, liquid fraction and non-condensable gases. The major product is the pyrolysis liquid (53 wt%). Pyrolysis liquid produced from sewage sludge is studied in present time yet. It has a relatively high calorific value, but it is stratified into fractions, contains a large amount of water and has an acid reaction of the medium, which complicates the process of its energy use. Therefore many researches of pyrolysis process is conducted to avoid producing of liquid fraction and obtain more gas fraction. This paper falls into this studies. To avoid pyrolysis liquid thermal cracking of it is used. The temperature in cracking zone is 1000 °C. The medium for cracking is charcoal and ceramics. In this paper it is presented the mass balances of pyrolysis and pyrolysis with cracking of sewage sludge, comparison of specific volume, degree of energy conversion, composition of gases mixtures obtained.

Photovoltaics (PV) cell is a common energy harvester that had been used to harvest solar energy and convert it into electrical energy. However, the vast energy from the spectrum of sunlight is not fully harvested. Therefore, thermoelectric (TE) module that harvest electrical energy from heat is being proposed in this paper. Generally, the part of the sunlight spectrum that induce heat is in the spectrum band of infrared (IR). For the experimental set-up in this paper, infrared (IR) light bulb was being used to simulate the IR spectrum band of the sunlight. In order to maximize the heat energy collection, a convex lens was being used to converge the IR light and therefore focused the heat on an aluminium sheet and heat sink which was placed on top of the hot side of the TE module. The distance between convex lens and IR light bulb is varying in between 10cm and 55cm and the reading was taken at an interval of 5cm. Firstly, the temperature of the IR light and converged IR light were recorded and plotted in graph. The graph showed that the temperature of the converged IR light bulb is higher than the IR light bulb. Lastly, the voltage and power output of the TE module with different heat source was compared. The output voltage and power of the TE module increased inverse proportional to the distance between IR light bulb and TE module.

An active material system may be generalized as an electro-mechanical network because of the incorporation of actuators (electrically driven) and sensors (that convert mechanical energy into electrical energy). An investigation of the coupled electrical and mechanical aspects of an active material system will help reveal some of its most important characteristics, in particular regarding energy conversion and consumption issues. The research performed in the area of the electro-mechanical impedance (EMI) modeling of active material systems is herein summarized. In this paper, a generic EMI model to describe the electro-mechanical network behavior (time domain and frequency domain) of active material systems will be discussed. The focus of the discussion will be on the methodology and basic components of the EMI modeling technique and its application to assist in the design of efficient active control structures. This paper will first introduce the basic concept of the EMI modeling and its general utility in the area of active material systems. The methodology of the EMI modeling technique will be illustrated using an example of PZT actuator-driven mechanical systems. The basic components of the EMI modeling, including the electro-mechanics of induced strain actuators, the dynamic analysis of active material systems, and the electrical power consumption and requirements, will be discussed. Finally, some applications of the EMI modeling approach, including the determination of the optimal actuator locations, modal analysis using collocated PZT actuator - sensors, and the prediction of radiated acoustic power, will be presented.

In this paper, a vibration-based MEMS electromagnetic energy harvester (EM-EH) device with two-degree-of-freedom (2DOF) configuration has been presented, modeled and characterized. The proposed 2DOF system comprises a primary subsystem for power generation, and an accessory subsystem for frequency tuning. A lumped parametric 2DOF model is built and examined in respect of energy harvesting capabilities. By controlling the mass ratio and frequency ratio, the first two resonances of primary mass can be tuned close to each other while maintaining comparable magnitudes. The 2DOF configuration is expected to be more adaptive and efficient than the conventional 1DOF structure, which could only operate near its sole resonance. The 2DOF EM-EH chip is fabricated on silicon-on-insulator (SOI) wafer through double-sided deep reactive-ion etching (DRIE). Induction coil is only patterned on the primary mass for energy conversion. With current prototype at an acceleration of 0.12 g, two resonances of 326 and 391 Hz with output voltages of 3.6 and 6.5 mV are obtained respectively, providing good validation for the modeling results. This paper offers new insights of implementing a multimodal MEMS EM-EH device.

The paper presents the computer simulation of the improved prediction model in Part 1 and compared with the classical density model. The prediction model in Part 1 is improved by incorporating the effect of fluid dynamic viscosity when there are salinity and temperature differences between two fluids, for better prediction of kinetic power output. The viscosity prediction model takes account of the water head losing causing by frictional effect and viscous dissipation which in turns provides an analytical predicted outcome. Computer simulations are presented in this paper to assess the system as the parameters of system are varied using the Viscosity Model.

This special issue of Journal of Micromechanics and Microengineering contains a selection of papers from the Fifth International Workshop on Micro and Nanotechnology for Power Generation and Energy Conversion Applications (PowerMEMS 2005). The meeting was held on 28–30 November 2005 in Tokyo, Japan, and was supported by the 21COE Program 'Mechanical Systems Innovation' at the University of Tokyo. Power MEMS is one of the newest categories of MEMS, encompassing microdevices and microsystems for power generation, energy conversion and propulsion. The series of PowerMEMS workshops started in 2000 in Sendai, Japan and then moved to Tsukuba, Makuhari, Kyoto and Tokyo. At the 2005 meeting there were four invited, 25 oral and 26 poster presentations from 14 different countries. From the 55 papers in the proceedings, 18 papers have been selected for this special issue. The papers were chosen on the basis of their quality, scientific impact and relevance to the scope of the journal. The authors of the selected papers were invited to expand their manuscripts beyond the workshop page limitation and to revise the papers to meet the criteria of archival journal publication. All papers have been subjected to the journal's standard peer review process. The papers included herein are ordered according to four areas: energy harvesting, micro combustors and fuel processors, micro fuel cells, and micro engines and generators. It is my pleasure to present these selected papers from PowerMEMS 2005, and I hope that this special issue provides a valuable overview of the latest research in micro and nanotechnology for power generation and energy conversion.

This special issue of the Journal of Micromechanics and Microengineering features papers selected from the Fourth International Workshop on Micro and Nanotechnology for Power Generation and Energy Conversion Applications (PowerMEMS 2004). The workshop was held in Kyoto, Japan, on 28–30 November 2004, by The Ritsumeikan Research Institute of Micro System Technology in cooperation with The Global Emerging Technology Institute, The Institute of Electrical Engineers of Japan, The Sensors and Micromachines Society, The Micromachine Center and The Kyoto Nanotech Cluster. Power MEMS is one of the newest categories of MEMS, which encompasses microdevices and microsystems for power generation, energy conversion and propulsion. The first concept of power MEMS was proposed in the late 1990s by Epstein's group at the Massachusetts Institute of Technology, where they continue to study MEMS-based gas turbine generators. Since then, the research and development of power MEMS have been promoted by the need for compact power sources with high energy and power density. Since its inception, power MEMS has expanded to include not only various MEMS-based power generators but also small energy machines and microdevices for macro power generators. At the last workshop, various devices and systems, such as portable fuel cells and their peripherals, micro and small turbo machinery, energy harvesting microdevices, and microthrusters, were presented. Their power levels vary from ten nanowatts to hundreds of watts, spanning ten orders of magnitude. The first PowerMEMS workshop was held in 2000 in Sendai, Japan, and consisted of only seven invited presentations. The workshop has grown since then, and in 2004 there were 5 invited, 20 oral and 29 poster presentations. From the 54 papers in the proceedings, 12 papers have been selected for this special issue. I would like to express my appreciation to the members of the Organizing Committee and Technical Program Committee. This special issue was edited in collaboration with Professor Toshiyuki Toriyama (Ritsumeikan University), Co-chair of the Technical Program Committee, and the Institute of Physics Publishing staff.

This special issue is based on the symposium on Non-thermal Plasma Assisted Fuel Conversion for Green Chemistry, a part of the 240th ACS National Meeting & Exposition held in Boston, MA, USA, 22–26 August 2010. Historically, the Division of Fuel Chemistry of the American Chemical Society (ACS) has featured three plasma-related symposia since 2000, and has launched special issues in Catalysis Today on three occasions: 'Catalyst Preparation using Plasma Technologies', Fall Meeting, Washington DC, USA, 2000. Special issue in Catalysis Today 72 (3–4) with 12 peer-reviewed articles. 'Plasma Technology and Catalysis', Spring Meeting, New Orleans, LA, USA, 2003. Special issue in Catalysis Today 89 (1–2) with more than 30 peer-reviewed articles. 'Utilization of Greenhouse Gases II' (partly focused on plasma-related technologies), Spring Meeting, Anaheim, CA, USA, 2004. Special issue in Catalysis Today 98 (4) with 25 peer-reviewed articles. This time, selected presentations are published in this Journal of Physics D: Applied Physics special issue. An industrial material and energy conversion technology platform is established on thermochemical processes including various catalytic reactions. Existing industry-scale technology is already well established; nevertheless, further improvement in energy efficiency and material saving has been continuously demanded. Drastic reduction of CO2 emission is also drawing keen attention with increasing recognition of energy and environmental issues. Green chemistry is a rapidly growing research field, and frequently highlights renewable bioenergy, bioprocesses, solar photocatalysis of water splitting, and regeneration of CO2 into useful chemicals. We would also like to emphasize 'plasma catalysis' of hydrocarbon resources as an important part of the innovative next-generation green technologies. The peculiarity of non-thermal plasma is that it can generate reactive species almost independently of reaction temperature. Plasma-generated reactive species are used to initiate chemical reactions at unexpectedly lower temperatures than conventional thermochemical reactions, leading to non-equilibrium product distribution or creating unconventional reaction pathways. When non-thermal plasma is combined with catalysts, a synergistic effect is frequently observed. Such unique properties of non-thermal plasma are expected to contribute excellent control over process parameters that meet the need for energy saving, environment protection, and material preservation. This special issue consists of eleven peer-reviewed papers including two invited publications. Professors Alexander Fridman and Alexander Rabinovich from Drexel University, and Dr Gutsol from the Chevron Energy Technology Company present a critical review of various industry-oriented practical plasma fuel conversion processes. Professor Richard Mallinson from University of Oklahoma describes his recent project on E85 (85%-ethanol/15%-gasoline) upgrading using non-thermal plasma and catalyst hybrid reactor, and highlights the synergistic effect on fuel conversion processes. Other papers focus on plasma/catalyst hybrid reactions for methane dry (CO2) reforming, plasma synthesis of carbon suboxide polymer from CO, the gas-to-liquid (GTL) process using a non-thermal plasma-combined micro-chemical reactor, and molecular beam characterization of plasma-generated reactive species. Much research regarding plasma catalysis is ongoing worldwide, but there is plenty of room for further development of plasma fuel processing, which could eventually provide a viable and flexible solution in future energy and material use. Finally, we would like to thank all symposium participants for their active discussion. We appreciate the sponsorship of the Division of Fuel Chemistry of the American Chemical Society. We express special thanks to the program chair of the Fuel Chemistry Division, Professor Chang-jun Liu at Tianjin University, for his dedication to the success of the symposium. We particularly express our appreciation to the Editorial Board of Journal of Physics D: Applied Physics for publication of the special issue.

Electronic and photonic information technology and renewable energy alternatives, such as solar energy, fuel cells and batteries, have now reached an advanced stage in their development. Cost-effective improvements to current technological approaches have made great progress, but certain challenges remain. As feature sizes of the latest generations of electronic devices are approaching atomic dimensions, circuit speeds are now being limited by interconnect bottlenecks. This has prompted innovations such as the introduction of new materials into microelectronics manufacturing at an unprecedented rate and alternative technologies to silicon CMOS architectures. Despite the environmental impact of conventional fossil fuel consumption, the low cost of these energy sources has been a long-standing economic barrier to the development of alternative and more efficient renewable energy sources, fuel cells and batteries. In the face of mounting environmental concerns, interest in such alternative energy sources has grown. It is now widely accepted that nanotechnology offers potential solutions for securing future progress in information and energy technologies. The Canadian Semiconductor Technology Conference (CSTC) forum was established 25 years ago in Ottawa as an important symbol of the intrinsic strength of the Canadian semiconductor research and development community, and the Canadian semiconductor industry as a whole. In 2007, the 13th CSTC was held in Montreal, moving for the first time outside the national capital region. The first three meetings in the series of 'Nano and Giga Challenges in Electronics and Photonics'— NGCM2002 in Moscow, NGCM2004 in Krakow, and NGC2007 in Phoenix— were focused on interdisciplinary research from the fundamentals of materials science to the development of new system architectures. In 2009 NGC2009 and the 14th Canadian Semiconductor Technology Conference (CSTC2009) were held as a joint event, hosted by McMaster University (10–14 August, Hamilton, Ontario, Canada) and the scope was expanded to include renewable energy research and development. This special issue of Nanotechnology is devoted to a better understanding of the function and design of semiconductor devices that are relevant to information technology (both electronics and photonics based) and renewable energy applications. The papers contained in this special issue are selected from the NGC/CSTC2009 symposium. Among them is a report by Ray LaPierre from McMaster University and colleagues at the University of Waterloo in Canada on the ability to manipulate single spins in nanowire quantum bits. The paper also reports the development of a testbed of a few qubits for general quantum information processing tasks [1]. Lower cost and greater energy conversion efficiency compared with thin film devices have led to a high level of activity in nanowire research related to photovoltaic applications. This special issue also contains results from an impedance spectroscopy study of core–shell GaAs nanowires to throw light on the transport and recombination mechanisms relevant to solar cell research [2]. Information technology research and renewable energy sources are research areas of enormous public interest. This special issue addresses both theoretical and experimental achievements and provides a stimulating outlook for technological developments in these highly topical fields of research. References [1] Caram J, Sandoval C, Tirado M, Comedi D, Czaban J, Thompson D A and LaPierre R R 2101 Nanotechnology 21 134007 [2] Baugh J, Fung J S and LaPierre RR 2010 Nanotechnology 21 134018

Piezoelectric energy harvesting techniques have experienced increasing research effort during the last few years. Possible applications including wireless, fully autonomous electronic devices, such as sensors, have attracted great interest. The key aspect of harvesting techniques is the amount of converted and stored energy, because the energy source and the conversion rate is limited. In particular, switching techniques offer many parameters that can be optimized. It is therefore crucial to examine the influence of these parameters in a precise manner. This paper addresses an accurate analytical modeling approach, facilitating the calculation of standard-DC and parallel SSHI-DC energy harvesting circuits. In particular the influence of the frequency ratio between the excitation and the electrical resonance of the switching LR-branch, and the voltage gaps across the rectifier diodes are studied in detail. Additionally a comparison with the SSDI damping network is performed. The relationship between energy harvesting and damping is indicated in this paper.

The analytical model presented in this paper describes the energy conversion mechanism of a piezoelectric beam (bimorph) under small-deflection static and vibrating conditions. The model provides an improved approach to design and analyze the performance of piezoelectric actuators and energy harvesters (sensors). Conventional models assume a linear voltage distribution over the piezoelectric beam thickness, which is shown here to be invalid. The proposed modeling method improves accuracy by using a quadratic voltage distribution. The equivalent capacitance of a beam shows a 40% discrepancy between a conventional model and the proposed model for PZT5A material. This inaccuracy level is not negligible, especially when the design of micro-power electrical energy harvesting is concerned. The method solves simultaneously the solid mechanics and Maxwell's equations with the constitutive equations for piezoelectric materials. The paper also proposes a phasor-based procedure for measuring the damping of a piezoelectric beam. An experimental setup is developed to verify the validity of the model. The experimental results confirm the accuracy of the improved model and also reveal limitations in using models for small deflections.

The UK Energy Research Centre (UKERC) in it's submission to the DTI's 2006 Energy Review reminded us that the ''UK has abundant wind, wave and tidal resources available; its mild climate lends itself to bio-energy production, and solar radiation levels are sufficient to sustain a viable solar industry''. These technologies are at different stages of development but they all draw on basic and applied Science and Engineering. The paper will briefly review the renewable energy technologies and their potential for contributing to a sustainable energy supply. Three research topics will be highlighted that bridge the gap between the physics underpinning the energy conversion, and the engineering aspects of development and deployment; all three are highly relevant to the Government's programme on micro-generation. Two are these are taken from field of thin film photovoltaics (PV), one related to novel device development and the other to a measurement technique for assessing the manufacturing quality of PV modules and their performance. The third topic concerns the development of small building integrated wind turbines and examines the complex flow associated with such applications. The paper will conclude by listing key research challenges that are central to the search for efficient and cost-effective renewable energy generation.

With the rapid development of my country's new energy field, higher requirements have been put forward for the wind-photovoltaic-hydrogen coupled absorption and capacity configuration of the power system. Therefore, the physical nature and regular characteristics of energy conversion, storage, and coupling between wind-photovoltaic-hydrogen multi-differential energy sources are different. This article first starts from the perspective of power/energy supply and demand balance, and comprehensively considers system output, conversion efficiency, energy loss and other factors to establish a wind-photovoltaic-hydrogen coupling system analysis model. Then, according to the relationship between power and time, the system's model operation domain is comprehensively analyzed. Finally, combined with the actual measured data of wind power and load in a certain area, using simulation software, the system's operating domain and spatial flexibility are analyzed, and the validity of the system model constructed in this paper is verified.

In recent years, a novel electro-hydraulic integrated self-powered brake system for aircraft has been proposed. A modular “self-powered device” is installed near the wheel to recover the rotational kinetic energy when the wheel lands and convert it into hydraulic energy for braking. The energy conversion device is the compact high-power-weight ratio energy harvesting mechanism, which needs to be designed in the extremely narrow internal space of the wheel. At the same time to ensure high reliability, high strength, high power weight ratio, difficult, and wheel brake disc internal temperature reaches 600 °C above, this to the design of the can take institutions are challenges. In this paper, the high strength compact high power-weight ratio energy conversion device as the research goal, through new principles, new structure, new materials, new technology, new methods and other means of the energy taking mechanism design and development, and finally achieve the strength, stiffness, reliability, life of the energy conversion device to meet the requirements of the system.

Flywheel energy storage system (FESS) has significant advantages such as high power density, high efficiency, short charging time, fast response speed, long service life, maintenance free, and no geographical environment restrictions. Motor is the energy conversion core of FESS and plays a significant role on system performance. In this paper, the design features of the motor for FESS are analyzed first. Then, a permanent magnet synchronous motor (PMSM) with a rated speed of 12000 rpm and a rated power of 250 kW is designed. Thirdly, aiming at the key problem of difficult heat dissipation of rotor, an improved rotor structure with “1” rotor permanent magnets layered and divided where placed in tangential and radial directions is proposed, which can reduce eddy current loss by 22.8%. Finally, based on Ansys FEM software, electromagnetic characteristics of the designed motor at no-load and full-load conditions are simulated and analyzed. The results show that the designed electromagnetic scheme meets the expected performance requirements and has guiding significance for prototype.

The functional localization of pumped storage station is analysed in this paper on the basis of summarize of the new situation and industrial advantages. It is a special power supply with the characteristics of peak shaving, valley filling, frequency modulation, phase modulation, emergency reserve and black start and so on. With the continuous acceleration of energy structural adjustments in China, the new energy power supply development rapidly, the demand for pumped storage station is increasingly urgent and its future growth is very broad.

In last few years, municipal waste generation and regulating are common problems forall over worldcountries. Conversions of waste to energy technologies arecreating manyend-products like electricity, thermal energy, fertilizer and biogas etc. Due to this, compression of solid waste has become compulsory to save the space in garbage carrying tuck, which is also known as hydraulic compactor machine. Hydraulic compactor machine is a garbage carrying compact truck after Compressing the garbage up to 50 to 60 percent more than the capacity of truck of municipal solid waste (MSW). Solid waste contains different component, high compressibilityfactor, and more water content. This study has been carried out with the municipal solid waste. The unpredictable compression mechanical characteristic varies with the simulation of solid waste compression process. The process shows the compression and shear characteristic analysisfor compressing garbage. Experimental analysis of the mechanical properties of solid waste, animportant test instrumentfor shear test and compression test was designed. Total fourteen tests on solid waste wereconducted as pe the designed test instrument and themodel parameters by analyzing testing data. At last, the defined characteristicstests were simulated ontested model and designed model factors werejustified. This paper gives us information for the mechanical behavior of garbage compression in hydraulic compactor for energy generation process.

Potential energy is wasted from vehicle vibration caused by road roughness. The suspension system absorbs vibration and dissipates energy in the form of heat. The dissipated energy can be recaptured into useful energy to enhance electric vehicles efficiency. This paper proposes a dual-mass unidirectional shock absorber with a piezoelectric harvester to assess the potential power that can be harvested from vibration. The regenerative suspension can be divided into two parts: transmission module and conversion module. The components of the transmission model are rack and pinion, bevel gears, planetary gearbox, shaft, and overrunning clutch that make the harvester rotates in one direction. The conventional electromagnetic model is replaced by a conversion model that consists of piezoelectric plates that are excited by magnetic forces induced by rectangular magnetic plates that are uniformly placed on an internal ring rotator and concentric external ring stator. A mathematical model is built to describe the process and calculate the power output resulting from the piezoelectric plates. The theoretical results illustrate a root mean square of output power of 16 W and 242 W can be achieved with a ring radius of 0.05 m with vehicle speed 120 km/h on good road condition and poor road condition, respectively.

Building an energy Internet ecosystem is an effective mode to expand new energy businesses, give digital energy to traditional energy enterprises and promote energy transformation and development. In this paper, by analyzing and expounding the concept, development situation, construction theory, practice summary, exploration path and other dimensions of the energy Internet ecosystem, putting forward counter-measures and Suggestions on the construction path and other aspects. Energy Internet ecological construction should take electric energy as the core, and establish the development factors of commercial ecology, so as to achieve "drainage + empowerment" of the energy Internet ecological system and support energy transformation and high-quality economic development in Henan province.

The control of energy conversion processes in an alternating current electric traction drive with asynchronous (induction) motors under asymmetric operating conditions are considered in the paper and the ways to improve their efficiency are proposed. It was stated that asymmetric modes create asymmetry of currents in the AM phases, which negatively affects both the electrical and mechanical parts of electric traction drives. The analysis of electromagnetic processes in the complex asymmetry of currents and voltage in the circuits of electric traction drives allows creating an adaptive algorithm for electric locomotives control which allows increasing electric power indices and the system reliability.

Most of the surface of the earth is occupied by oceans, and huge energy is stored in the oceans. Among marine energy sources, wave energy, tidal energy, tidal current energy, etc. are included. As a widely distributed, high energy density, pollution-free and environmentally friendly renewable energy source, ocean wave energy attaches great importance to ocean energy in most countries in the world. Compared with wind power and photoelectricity, the utilization of ocean energy with wider distribution and greater energy density is still lagging behind. Ocean wave energy power generation mainly refers to the use of corresponding technical equipment to convert the powerful kinetic energy of ocean waves into electrical energy. In view of the current tight supply of traditional energy, it can effectively relieve the problem, promote the development of marine resources and improve the environment. Therefore, this paper studies the wave power generation technology. First, the article analyzes the system principle of using wave energy to generate electricity, introduces several commonly used wave energy conversion devices, and then studies its power generation technology from the aspect of control strategy, so as to maximize the energy conversion power in the wave energy generation process. It will maximize the conversion of wave energy to electrical energy.

This work is devoted to the numerical analysis of the opportunity to obtain a steady generation of electromotive force (EMF) in a two-chamber gas cell exposed to concentrated solar/lamp radiation. For this purpose, we have carried out 2D simulations of the low-pressure photoplasma in the mixtures of sodium atom vapor and different noble gases and their pressures at different values of photoexcitation rate of resonance levels of Na. Herewith plasma chemistry and transfer of charges and radiation in the volume have been taken into account. It has been established that argon is a better candidate to be used as a buffer gas for photoplasma electric converter based on the obtained plasma parameters and commercial aspects. A parametric study has been carried out for the Na–Ar mixture to investigate the effect of increasing homogeneous photoexcitation rate in the small chamber on plasma parameters and obtained EMF. Another parametric study has been conducted to calculate the output current and electric power at a loaded chain. The results show that EMF could be obtained using the photovoltaic effect in photoplasma for the two-chamber cell. The present paper gives a key to the understanding of the effect of different processes (radiation, chemical, and electric) in the cell with these gas mixtures. The obtained results can be used in projecting a solar photoelectric converter based on a two-chamber device with a mixture of sodium and noble gases.

For the park level integrated energy system with renewable energy access, in order to optimize the operation cost of the park and solve the problem of renewable energy consumption, this paper proposes a day ahead optimized scheduling model of the park integrated energy system, which provides an effective solution for renewable energy consumption by considering the coordination of energy conversion and energy storage equipment to achieve multi-energy complementarity. Finally, an example is given to verify the validity and feasibility of the proposed model.

Ocean energy is a kind of high-quality renewable energy. Therefore, it will not be exhausted and has attracted wide attention. China’s coastline is 18,000 kilometers long, so China has abundant ocean energy. In order to realize the utilization of wave energy, the research on wave energy power generation technology has never stopped. Wave energy generation refers to the use of wave motion to generate electricity, first converting wave energy into intermediate energy through a conversion device, and then converting intermediate energy into electrical energy. Combining with China’s actual situation, China’s research on wave energy devices mainly has three types: oscillating water column, pendulum, sink and float. Due to the huge difference in sea conditions and the characteristics of China’s offshore waves with short periods and relatively low energy density, wave energy conversion devices must be independently developed, and hydrodynamic behavior research is the basic work. In this paper, through the theoretical analysis and numerical calculation research methods, the hydrodynamic behavior characteristics of the wave energy conversion device are studied, and the simulation analysis is performed using the hydrodynamic software AQWA.

At present, with the rapid development of the world economy, the demand for energy and resources is increasing day by day. Resource scarcity and environmental deterioration have become important issues facing the world. The energy development mode based on traditional fossil energy cannot support the rapid economic development of our country, which makes the energy transformation of our country imperative. In this paper, the grey GM (1, 1) model and artificial neural network are combined to modify the prediction results of GM (1, 1) model. In order to make GM(1, 1) model have higher prediction accuracy in medium and long-term prediction, partial data GM(1, 1) model groups are respectively established by using partial data sequences of original data, and the nonlinear mapping relationship between fitting values and original data is calculated by establishing this partial GM(1, 1) model groups by using BP neural network. The calculation results show that the prediction method is reliable and has high prediction accuracy.

This paper presents accurate control parameters estimation of the hydraulic Power Take-Off (PTO) model for the wave energy conversion system to maximise energy production. In general, the performance of the hydraulic PTO system depends on the parameters setting of hydraulic PTO system components such as hydraulic motor displacement setting, pre-charge of the hydraulic accumulator, and et cetera. Conventionally, it requires to manually obtain the optimal parameters of a hydraulic PTO system by repeating the simulation process. However, this estimation method exposed to human error and would easily be resulting in a non-optimal selection of hydraulic PTO parameters for the wave energy conversion system. Therefore, an easy and accurate approach of using the GA optimisation method for determining hydraulic PTO parameters was introduced in the present study. This approach is simple and more accurate compared to the conventional optimisation method. The hydraulic PTO model was developed in SIEMENS/Amesim environment using available components in the library. The specifications of the actual hydraulic PTO system components from the manufacturer were used during the simulation set-up. The complete hydraulic PTO system was optimised using a special genetic algorithm (GA) optimisation tools in the SIEMENS/Amesim software. The simulation results showed that GA was effective to determine the optimal configuration parameters of hydraulic PTO system. From the results, the optimal configuration parameters of hydraulic PTO system were successfully reduced about 38%. Consequently, the maximum force applied to the WEC devices was reduced up to 34%. This force reduction is important since it will enable the WECS to be operated during a smaller wave condition.

This paper presents the research, technologies and testing equipment developed for the energy plasma conversion of municipal waste in order to enhance energy-efficiency in the civil engineering domain. The purpose of this work is the environmentally friendly improving the efficiency of waste conversion processes by using controlled plasma decomposition reactors developed by the authors, which generate syngas, electrical and thermal energy which can be used in civil engineering.

The paper discusses the principle of construction of automatic control systems for the energy conversion complex of a spacecraft with a digital control system. It is shown that the proposed digital control system is able to solve all the tasks assigned to it. The results are tested on an experimental model.

The paper presents the analysis of energy conversion processes in the dc electromechanical devices with variable inductances. With respect to the instantaneous power balance in the electromechanical system, the mechanical power transfer is considered for the operating cycle. The generalized structural model of the electromechanical converter with variable inductance is proposed. The model consists of three subsystems which are cascaded by instantaneous power transfer channels. The model is distinguished by the internal magnetic energy source in the magnetic subsystem with additional channels for magnetic power transfer. Energy conversion conditions influence the instantaneous power transfer channel operation. The magnetic energy restoring factor and its sign are the criterions of the energy conversion processes difference. The instantaneous power flux circulation accompanied by complicated electromagnetic energy conversion processes in dynamic modes is established by experiments.

Piezoelectric energy harvesting (PEH) systems convert ambient vibration energy into useful electricity. An interface circuit intervenes the electromechanical energy conversion; it has a significant effect on the electromechanical joint dynamics and harvested power. Among the existing interface circuits, the synchronized electric charge extraction (SECE) solution was known for its unique feature of load independence. However, the actual harvested power was usually shown to be lower than the previous theoretical predictions. The reason is that the energy dissipation in power conditioning, e.g. the diode dissipation in the rectifier and the switching dissipation in each energy extraction, have not received sufficient consideration. This paper revisits the joint dynamics and harvested power of PEH systems with a SECE interface circuit by using the energy flow analysis and impedance modeling. By qualitatively scrutinizing the energy cycle of SECE, the electrically induced dynamic characteristics are broken down into three components: the equivalent capacitance, dissipative resistance, and harvesting resistance, which have the same effects but different values, like those in other PEH interface circuits. The three components are equivalent to an additional stiffness, a dissipative damper, and a regenerative damper in the mechanical domain. The theoretical harvested power, which is estimated based on the impedance modeling, shows good agreement with the experimental results under different loading conditions and operating frequencies. Owing to its modular way of thinking, the impedance modeling technique once again shows its effectiveness and efficiency towards the analyses of joint dynamics and harvested power in PEH systems using different power conditioning interface circuits.

The lattice Boltzmann method (LBM) is a suitable tool for solving transport phenomena that occur in gas- and liquid phases at different length scales, especially when complex geometries such as porous media are involved. However, investigations about applications of LBM in the solid electrical conducting material have not been carried out yet. Since in fuel cells (FCs) the multifunctional layers play an important role during the energy conversion process, and such layers consist of porous material, the ohmic resistance of porous materials represents a crucial characteristic to be studied to predict the internal ohmic losses. The purpose of this paper is to show the feasibility of LBM to determine the ohmic resistance of electrical conducting materials whose dimensions are modified considering the cross-sectional area and length. Characteristics, limitations and recommendations of LBM applied to solid electrical conducting materials calculating the ohmic resistance are presented considering the coupling of the methodology with the Ohm’s Law. Additionally, the behavior of the ohmic resistance for a given porous material is presented. (Less)

Linear compressors have received more and more attention for their compact structure and high efficiency. They are highly sensitive to the working condition, thus the control system is essential to ensure linear compressors are able to operate reliably and efficiently. Operating in a resonant state would improve linear compressor efficiency, while the natural frequency is also sensitive to the operating condition. This paper proposes the analysis of energy transfer process during linear compressor operation. Compared with force analysis, energy analysis uses the electromechanical analogy to show the energy conversion from electrical energy into mechanical energy during linear compressor operation. The principle for the control to achieve high efficiency is proposed and verified in a refrigeration system. The result shows it is practical and reliable to applied energy analysis in the control of linear compressor to achieve highly efficient driving.

In many important industries (oil and gas, process gases, chemical process engineering) multi-stage reciprocating compressors are used, especially for high pressure ratios. The gas is compressed in multiple consecutive stages and cooled after each stage in order to reduce the maximum process temperatures. The rejected heat is often dissipated to the environment and the usable part – the exergy – is lost.The aim of this paper is to show how the waste heat potential of reciprocating compressors can be used. For this purpose, the waste heat available per stage is quantified for different compression scenarios. Based on this, the processes for the waste heat recovery suitable for the temperature range of the discharge gas as heat source are presented – in particular the structure, working principle and characteristics of the waste heat recovery system. It is shown that the waste heat can be used flexibly for different purposes (heating, power generation, cold supply). The potential of the possible methods of waste heat recovery can be estimated with the aid of the given efficiencies of the respective energy conversion processes.

Strong shock wave (SW) can be generated during underwater electrical wire explosion as the exploding wire rapidly expands and pushes the surrounding water. In this paper, a coupled model that describes the behaviours of the circuit, the exploding wire, and the evolution of SW was established. Wide range equation of state (EOS) data and conductivity data were used, making the calculation from solid state possible. The calculated discharge current, voltage across the wire, and trajectories of the wire radius and SW front were generally in good agreement with the experimental results, manifesting the validity of the model. Evolution of SW peak pressure, the process of energy conversion, and the effect of the discharge period were studied using the model. Simulation results showed that the radial attenuation of SW peak pressure is largely dependent on wire diameter and energy deposition process, while the efficiency of converting the deposited electrical energy to the mechanical energy of SW is not as sensitive, varying from 40% to 50% tens of microsecond after the current starts. Fast discharge tends to generate SW with higher initial SW peak pressure, while slow discharge enables higher initial energy storage within the limit of insulation and generates SW with slower radial attenuation. The presented model and numerical results could serve as a reference for parameter selection in related applications.

Over the past years, many researchers have been excited with the advent of two-dimensional (2D) materials such as graphene and MoSalt;subagt;2alt;/subagt; because of their intriguing physical and chemical properties. Furthermore, they have great potential in various applications including nanoelectronics, flexible or stretchable devices, energy conversion or storage devices, sensors, nanocomposites, and others. In addition to their electrical, mechanical, optical, and thermal properties, interfacial properties of 2D materials such as adhesion energy have recently attracted attention from researchers since interfacial interactions of 2D materials with others are of great importance in obtaining mechanical integrity of nanomanufacturing processes and related devices. In this respect, this paper reviews the adhesion properties of 2D materials. Measurement methods and characteristics of adhesion behaviors were summarized and discussed mainly for graphene and MoSalt;subagt;2alt;/subagt;.

With the development of economy and the improvement of human living standards, the demand for energy will only continue to grow. As one of the main renewable energy sources, River energy has made great progress. The equipment of river kinetic energy generation is different from that of conventional large and medium-sized high dam hydropower stations because of the different energy conversion modes. If the technology and equipment of Gaoba Hydropower Station are mature, the river kinetic power station system and its series technology and equipment are still in the primary stage of development. Different water flow generation methods use different platform positioning systems. In order to collect unstable water flow energy, the water flow power generation device is required to convert the mechanical energy in the water flow energy into electricity that can be used by two-stage energy conversion. Based on the fluid mechanics analysis, this paper determines the factors related to the energy conversion efficiency of the primary conversion device and the relationship between the influencing factors. I hope that I can make some contribution to the development of renewable energy.

With the acceleration of industrialization, urbanization and the continuous upgrading of consumption structure, China's energy demand has grown rigidly. The coal-based energy structure has caused China's economic development to face severe environmental pressures. Energy conservation and emission reduction in the power industry has become an inevitable development trend. In order to strengthen energy consumption management and control in the thermal power industry, improve energy efficiency, and comprehensively implement energy efficiency benchmarking, this paper establishes thermal energy plant energy consumption index system according to the characteristics of thermal power plant energy consumption, and uses multi-attribute decision-making methods to evaluate the index system for China's thermal power generation and provide theoretical guidance for energy transformation, energy conservation and emission reduction.

Deutsche Physikalische Gesellschaft logo Institute of Physics logo PAPER • THE FOLLOWING ARTICLE ISOPEN ACCESS Thermodynamics of metabolic energy conversion under muscle load Christophe Goupil1, Henni Ouerdane2, Eric Herbert1, Clemence Goupil3 and Yves D'Angelo4 Published 28 February 2019 • © 2019 The Author(s). Published by IOP Publishing Ltd on behalf of the Institute of Physics and Deutsche Physikalische Gesellschaft New Journal of Physics, Volume 21, February 2019 DownloadArticle PDF DownloadArticle ePub Figures References Download PDFDownload ePub 900 Total downloads 11 citation on Dimensions.Article has an altmetric score of 1 Turn on MathJax Share this article Share this content via email Share on Facebook Share on Twitter Share on Google+ Share on Mendeley Article information Abstract The metabolic processes complexity is at the heart of energy conversion in living organisms and forms a huge obstacle to develop tractable thermodynamic metabolism models. By raising our analysis to a higher level of abstraction, we develop a compact—i.e. relying on a reduced set of parameters—thermodynamic model of metabolism, in order to analyse the chemical-to-mechanical energy conversion under muscle load, and give a thermodynamic ground to Hill's seminal muscular operational response model. Living organisms are viewed as dynamical systems experiencing a feedback loop in the sense that they can be considered as thermodynamic systems subjected to mixed boundary conditions, coupling both potentials and fluxes. Starting from a rigorous derivation of generalized thermoelastic and transport coefficients, leading to the definition of a metabolic figure of merit, we establish the expression of the chemical-mechanical coupling, and specify the nature of the dissipative mechanism and the so-called figure of merit. The particular nature of the boundary conditions of such a system reveals the presence of a feedback resistance, representing an active parameter, which is crucial for the proper interpretation of the muscle response under effort in the framework of Hill's model. We also develop an exergy analysis of the so-called maximum power principle, here understood as a particular configuration of an out-of-equilibrium system, with no supplemental extremal principle involved.