Showing papers on "Electricity generation published in 2005"

Energy scavenging for mobile and wireless electronics

Abstract: Energy harvesting has grown from long-established concepts into devices for powering ubiquitously deployed sensor networks and mobile electronics. Systems can scavenge power from human activity or derive limited energy from ambient heat, light, radio, or vibrations. Ongoing power management developments enable battery-powered electronics to live longer. Such advances include dynamic optimization of voltage and clock rate, hybrid analog-digital designs, and clever wake-up procedures that keep the electronics mostly inactive. Exploiting renewable energy resources in the device's environment, however, offers a power source limited by the device's physical survival rather than an adjunct energy store. Energy harvesting's true legacy dates to the water wheel and windmill, and credible approaches that scavenge energy from waste heat or vibration have been around for many decades. Nonetheless, the field has encountered renewed interest as low-power electronics, wireless standards, and miniaturization conspire to populate the world with sensor networks and mobile devices. This article presents a whirlwind survey through energy harvesting, spanning historic and current developments.

Comparison of piezoelectric energy harvesting devices for recharging batteries

Abstract: Piezoelectric materials can be used as a means of transforming ambient vibrations into electrical energy that can then be stored and used to power other devices. With the recent surge of microscale devices, piezoelectric power generation can provide a convenient alternative to traditional power sources used to operate certain types of sensors/actuators, telemetry, and MEMS devices. However, the energy produced by these materials is in many cases far too small to directly power an electrical device. Therefore, much of the research into power harvesting has focused on methods of accumulating the energy until a sufficient amount is present, allowing the intended electronics to be powered. In a recent study by Sodano et al. (2004a) the ability to take the energy generated through the vibration of a piezoelectric material was shown to be capable of recharging a discharged nickel metal hydride battery. In the present study, three types of piezoelectric devices are investigated and experimentally tested to deter...

Organic-Based Photovoltaics: Toward Low-Cost Power Generation

Abstract: Harvesting energy directly from sunlight using photovoltaic technology is a way to address growing global energy needs with a renewable resource while minimizing detrimental effects on the environment by reducing atmospheric emissions. This issue of MRS Bulletin on “Organic-Based Photovoltaics” looks at a new generation of solar cells that have the potential to be produced inexpensively. Recent advances in solar power conversion efficiencies have propelled organic-based photovoltaics out of the realm of strictly fundamental research at the university level and into the industrial laboratory setting. Fabricated from organic materials—polymers and molecules—these devices are potentially easier to manufacture than current technologies based on silicon or other materials. In this introductory article, we describe the motivation for pursuing research in this field and provide an overview of the various technical approaches that have been developed to date. We conclude by discussing the challenges that need to be overcome in order for organic photovoltaics to realize their potential as an economically viable path to harvesting energy from sunlight.

Generating Electricity While Walking with Loads

Abstract: We have developed the suspended-load backpack, which converts mechanical energy from the vertical movement of carried loads (weighing 20 to 38 kilograms) to electricity during normal walking [generating up to 7.4 watts, or a 300-fold increase over previous shoe devices (20 milliwatts)]. Unexpectedly, little extra metabolic energy (as compared to that expended carrying a rigid backpack) is required during electricity generation. This is probably due to a compensatory change in gait or loading regime, which reduces the metabolic power required for walking. This electricity generation can help give field scientists, explorers, and disaster-relief workers freedom from the heavy weight of replacement batteries and thereby extend their ability to operate in remote areas.

Energy management strategies for vehicular electric power systems

Abstract: In the near future, a significant increase in electric power consumption in vehicles is expected. To limit the associated increase in fuel consumption and exhaust emissions, smart strategies for the generation, storage/retrieval, distribution, and consumption of electric power will be used. Inspired by the research on energy management for hybrid electric vehicles (HEVs), this paper presents an extensive study on controlling the vehicular electric power system to reduce the fuel use and emissions, by generating and storing electrical energy only at the most suitable moments. For this purpose, both off-line optimization methods using knowledge of the driving pattern and on-line implementable ones are developed and tested in a simulation environment. Results show a reduction in fuel use of 2%, even without a prediction of the driving cycle being used. Simultaneously, even larger reductions of the emissions are obtained. The strategies can also be applied to a mild HEV with an integrated starter alternator (ISA), without modifications, or to other types of HEVs with slight changes in the formulation.

PowerMatcher: multiagent control in the electricity infrastructure

Abstract: Different driving forces push the electricity production towards decentralization. As a result, the current electricity infrastructure is expected to evolve into a network of networks, in which all system parts communicate with each other and influence each other. Multi-agent systems and electronic markets form an appropriate technology needed for control and coordination tasks in the future electricity network. We present the PowerMatcher, a market-based control concept for supply and demand matching (SDM) in electricity networks. In a presented simulation study is shown that the simultaneousness of electricity production and consumption can be raised substantially using this concept. Further, we present a field test with medium-sized electricity producing and consuming installations controlled via this concept, currently in preparation.

A hybrid power system using alternative energy facilities in isolated island

Abstract: A hybrid power system uses many wind turbine generators in isolated small islands. The output power of wind turbine generators is mostly fluctuating and has an effect on system frequency. In order to solve this problem, we propose a new power system using renewable energy in small, isolated islands. The system can supply high-quality power using an aqua electrolyzer, fuel cell, renewable energy, and diesel generator. The generated hydrogen by an aqua electrolyzer is used as fuel for a fuel cell. The simulation results are given to demonstrate the availability of the proposed system in this paper.

Design of Commercial Solar Updraft Tower Systems—Utilization of Solar Induced Convective Flows for Power Generation

Abstract: A solar updraft tower power plant-sometimes also called solar chimney, or just solar tower-is a solar thermal power plant utilizing a combination of solar air collector and central updraft tube to generate a solar induced convective flow which drives pressure staged turbines to generate electricity The paper presents theory, practical experience, and economy of solar updraft towers: First a simplified theory of the solar tower is described Then results from designing, building and operating a small scale prototype in Spain are presented Eventually technical issues and basic economic data for future commercial solar tower systems like the one being planned for Australia are discussed

Synchronization methods for three phase distributed power generation systems - An overview and evaluation

Abstract: Nowadays, it is a general trend to increase the electricity production using distributed power generation systems (DPGS) based on renewable energy resources such as wind, sun or hydrogen. Jf these systems are not properly controlled, their connection to the utility network can generate problems on the grid side. Therefore, considerations about power generation, safe running and grid synchronization must be done before connecting these systems to the utility network. This paper is mainly dealing with the grid synchronization issues of distributed systems. An overview of the synchronization methods as well as their major characteristics is given. New solutions to optimize the synchronization methods when running on distorted grid conditions are discussed. Simulation and experimental results are used to evaluate the behavior of the synchronization methods under different kind of grid disturbances such as voltage dips, harmonics and notches.

Sensitivity Analysis and Energy Harvesting for a Self-Powered Piezoelectric Sensor

Abstract: Sensors play a crucial role in structural systems with concern over reliability/ failure issues. The development of wireless monitoring systems has been of great interest because wireless transmission has been proven as a convenient means to transmit signals while minimizing the use of many long wires. However, the wireless transmission systems need sufficient power to function properly. Conventionally, batteries are used as the power sources for the remote sensing systems. However, due to their limited lifetime, replacement of batteries has to be carried out periodically, which is inconvenient. In recent years, piezoelectric materials have been developed as sensing and actuating devices mostly, and power generators in some cases. In this article, a self-powered piezoelectric sensor is studied, in which one piece of piezoelectric element is simultaneously used as a sensor and a power generator under vibration environment. Concurrent design with piezoelectric materials in sensor and power generator is inte...

On low-frequency electric power generation with PZT ceramics

Abstract: Piezoelectric materials have long been used as sensors and actuators, however their use as electrical generators is less established. A piezoelectric power generator has great potential for some remote applications such as in vivo sensors, embedded MEMS devices, and distributed networking. Such materials are capable of converting mechanical energy into electrical energy, but developing piezoelectric generators is challenging because of their poor source characteristics (high voltage, low current, high impedance) and relatively low power output. In the past these challenges have limited the development and application of piezoelectric generators, but the recent advent of extremely low power electrical and mechanical devices (e.g., MEMS) make such generators attractive. This paper presents a theoretical analysis of piezoelectric power generation that is verified with simulation and experimental results. Several important considerations in designing such generators are explored, including parameter identification, load matching, form factors, efficiency, longevity, energy conversion and energy storage. Finally, an application of this analysis is presented where electrical energy is generated inside a prototype Total Knee Replacement (TKR) implant.

Generation and Storage of Electricity from Power Harvesting Devices

Abstract: The concept of capturing the normally lost energy surrounding a system and converting it into electrical energy that can be used to extend the lifetime of that system's power supply or possibly provide an endless supply of energy to an electronic device has captivated many researchers and has brought forth a growing amount of attention to power harvesting. One of the most common methods of obtaining the energy surrounding a system is to use piezoelectric materials. Piezoelectric materials have a crystalline structure that provides a unique ability to convert an applied electrical potential into a mechanical strain or vice versa, or convert an applied strain into an electrical current. The latter of these two properties allows the material to function as a power harvesting medium. In most cases the piezoelectric material is strained through the ambient vibration around the structure, thus allowing a frequently unused energy source to be utilized for the purpose of powering small electronic systems. However, the amount of energy generated by these piezoelectric materials is far smaller than that needed by most electronic devices. For this reason, the methods of accumulating and storing the energy generated, until sufficient power has been captured, is the key to developing completely self-powered systems. This article quantifies the amount of energy generated by a piezoelectric plate and investigates two methods of accumulating the energy thus produced. The first method uses a capacitor, which in early research has been the most common method of storing the energy generated and the second utilizes rechargeable nickel metal hydride batteries. The advantages of each method are discussed and the rechargeable battery is found to have more desirable qualities for power harvesting than the capacitor. Additionally, this manuscript represents, for the first time, the fact that the power output by a piezoelectric material is capable of recharging a discharged battery. Through the excitation of a piezoelectric plate, it is demonstrated that a 40 mAh battery can be charged in less than half an hour at resonance and in only a few hours with a random signal similar to that of a typical vibrating piece of machinery.

An overview of current and future sustainable gas turbine technologies

Abstract: In this work an overview of current and future sustainable gas turbine technologies is presented. In particular, the various gas turbine technologies are described and compared. Emphasis has been given to the various advance cycles involving heat recovery from the gas turbine exhaust, such as, the gas to gas recuperation cycle, the combined cycle, the chemical recuperation cycle, the Cheng cycle, the humid air turbine cycle, etc. The thermodynamic characteristics of the various cycles are considered in order to establish their relative importance to future power generation markets. The combined cycle technology is now well established and offers superior to any of the competing gas turbine based systems, which are likely to be available in the medium term for large-scale power generation applications. In small-scale generation, less than 50 MWe, it is more cost effective to install a less complex power plant, due to the adverse effect of the economics of scale. Combined cycle plants in this power output range normally have higher specific investment costs and lower electrical efficiencies but also offer robust and reliable performance. Mixed air steam turbines (MAST) technologies are among the possible ways to improve the performance of gas turbine based power plants at feasible costs (e.g. peak load gas turbine plants).

Benefit of Distributed Generation: A Line Loss Reduction Analysis

Abstract: The impending deregulated environment facing the electric utilities in the twenty first century is both a challenge and an opportunity for a variety of technologies and operating scenarios. The need to provide acceptable power quality and reliability will create a very favorable climate for the entry of distributed resources and innovative operating practices. Of all the different parts of an electric power system, customers identify closely with the distribution subsystem due to its proximity and visibility on a daily basis. Several recent developments have encouraged the entry of power generation and energy storage at the distribution level. Distributed resources (DR) is a term that encompasses both distributed generation (DG) and distributed energy storage (DS). A distributed utility will use both distributed resources and load management to achieve its goal. In addition, several compact distributed generation technologies are fast becoming economically viable. Integration of DG into an existing utility can result in several benefits. These benefits include line loss reduction, reduced environmental impacts, peak shaving, increased overall energy efficiency, relieved transmission and distribution congestion, voltage support, and deferred investments to upgrade existing generation, transmission, and distribution systems. Benefits are not limited to utility. Customers also benefit from DG in term of better quality of supply at lower cost. Among the many benefits of distributed generation is a reduced line loss. The purpose of this paper is to quantify this benefit for the simple case of a radial distribution feeder with concentrated load and distributed generator. With the introduction of DG, line loss reduction can be expected. The analysis is presented for varying locations of the distributed generator along the feeder and for varying output capacities. The results are presented in graphical form in terms of clearly-defined normalized parameters

Multiphysics simulation of wave energy to electric energy conversion by permanent magnet linear generator

Abstract: The possibility to use three-phase permanent magnet linear generators to convert sea wave energy into electric energy is investigated by multiphysics simulations. The results show a possibility, which needs to be further verified by experimental tests, for a future step toward a sustainable electric power production from ocean waves by using direct conversion. The results suggest that wave energy can have an impact on tomorrow's new sustainable electricity production, not only for large units, but also for units ranging down to 10 kW. This gives wave power a larger economical potential than previously estimated. The study demonstrates the feasibility of computer simulations to give a broad, and in several aspects a detailed, understanding of the energy conversion. The simulation results also give a useful starting point for future experimental work.

Minimization of imbalance cost trading wind power on the short term power market

Abstract: Present power markets are designed for trading conventional generation. For wind generation to participate in short-term energy market lengthy (up to 36 hours) wind power production forecasts are required. Although wind speed forecasting techniques are constantly improving, wind speed forecasts are never perfect and resulting wind power forecast errors imply imbalance costs for wind farm owners. This paper presents a method for minimization of imbalance costs. Stochastic programming is used to generate optimal wind power production bids for short term power market. Wind power forecast error is represented as stochastic parameter. The imbalance costs resulting from this strategy are then compared to the case when wind power production bids on short term power market are based only on wind speed forecast.

Hybrid generation with alternative fuel sources

Abstract: A generating facility is provided for generating electricity from both solar and non-solar energy sources. The solar generating portion of the facility includes capability to directly generate electricity from solar insolation, or to store the solar energy in a tangible medium, including stored heat, or solar generating fuel. The generating facility is configured to generate electricity simultaneously from both solar and non-solar sources, as well a solely from immediate solar insolation and from solar energy stored in a tangible medium. Additionally, the solar generating capacity may be segregated; such that separate spectra of solar insolation are used to capture heat for steam turbine based electrical generation, capture light energy for photovoltaic based electrical generation, and to grow biomass to generate a solar fuel.

Axial-flux permanent magnet machines for micropower generation

Abstract: This paper reports on the design, fabrication, and testing of an axial-flux permanent magnet electromagnetic generator. The generator comprises a polymer rotor with embedded permanent magnets sandwiched between two silicon stators with electroplated planar coils. Finite element simulations have been carried out using ANSYS to determine the effects on performance of design parameters such as the number of layers in the stator coils, and the rotor-stator gap. The effect of including soft magnetic pole pieces on the stators has also been studied. A prototype device with a diameter of 7.5 mm has been tested, and shown to deliver an output power of 1.1 mW per stator at a rotation speed of 30 000 rpm. The generator has been integrated with a microfabricated axial-flow microturbine to produce a compact power conversion device for power generation and flow sensing applications.