• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 349
  • 70
  • 58
  • 40
  • 28
  • 19
  • 17
  • 15
  • 8
  • 6
  • 5
  • 5
  • 3
  • 1
  • 1
  • Tagged with
  • 792
  • 792
  • 205
  • 181
  • 157
  • 130
  • 118
  • 117
  • 99
  • 95
  • 83
  • 77
  • 74
  • 74
  • 73
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Real time computer controls for energy transfer involving superconductive magnetic energy storage

Ho, Ying-Wai. January 1984 (has links)
Thesis (M.S.)--University of Wisconsin--Madison, 1984. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 132-133).
2

Flywheel energy storage : a conceptucal study

Östergård, Rickard January 2011 (has links)
This master thesis was provided by ABB Cooperate Research in Västerås. This study has two major purposes: (1) to identify the characteristics of a flywheel energy storage system (FESS), (2) take the first steps in the development of a simulation model of a FESS. For the first part of this master thesis a literature reviews was conducted with focus on energy storage technologies in general and FESS in particular. The model was developed in the simulation environment PSCAD/EMTDC; with the main purpose to provide working model for future studies of the electrical dynamics of a flywheel energy storage system. The main conclusion of the literature review was that FESS is a promising energy storage solution; up to multiple megawatt scale. However, few large scale installations have so far been built and it is not a mature technology. Therefore further research and development is needed in multiple areas, including high strength composite materials, magnetic bearings and electrical machines. The model was implemented with the necessary control system and tested in a simulation case showing the operational characteristics.
3

Development and Evaluation of a CFD Model to Simulate Thermal Performance of Phase Change Material (PCM) Based Energy Storage Systems

Hassan, Hafiz Muhammad Adeel January 2014 (has links)
Waste heat can be recovered and used in different processes to increase energy efficiency and reduce CO2 emissions. It has become an attractive area of research for scientists and several techniques are being investigated and practiced to recover, store and use waste heat. Thermal Energy Storage is one of the modern techniques that is used to store and use waste heat. Energy can be stored in both sensible and latent forms of heat. Latent heat storage is the most efficient way of storing thermal energy as it provides higher storage density and lower temperature differential between storing and releasing heat. The materials that are used for latent energy storage are termed as Phase Change Materials (PCMs). This thesis work investigates the feasibility of a latent heat storage and heat exchanger performance based on phase change material to recover heat at elevated temperatures. The heat transfer study is done by using state of the art commercial CFD tool. Different model geometries of the Thermal Storage equipped with Shell and tube heat exchanger were built with different pipe configurations. The 1st type of model is a set of three 2D models built in COMSOL Multiphysics. These models constitute a cross section of a small portion of heat exchanger having four 10 mm outer diameter pipes immersed in PCM. Fins were mounted on the pipes to enhance the area for heat transfer and hence the heat transfer rate in modified models. Simulations were carried out for melting and solidification of PCM with these 2D models. After analyzing the results, a 3D model of the small block was created to get more realistic results and analyze the effect of pipe diameter on melting and solidification of PCM. The results of 2D models show the effect of fins on heat transfer rates. The model with eight fins on each pipe shows the best results as compared to other two models. The melting and solidification rates are nearly half for eight fin model as compared to the model without fins. The four fin model shows moderate results but better than the model without fins. The comparison of the results for different diameter pipes in 3D model shows that heat transfer rate increases for increasing diameters of the pipe with same flow rate in the case of melting.
4

Solution grown silicon and germanium nanostructures : characterization and application as lithium ion battery anode materials

Chockla, Aaron Michael 13 November 2013 (has links)
Solution-grown silicon and germanium nanowires were produced using various solvents and nanocrystalline seed materials. Silicon nanowires grown using monophenylsilane as the silicon source and gold catalyst seeds were made into a freestanding, lightweight, mechanically robust fabric and tested as a negative electrode material in lithium ion batteries. Annealing the fabric under reducing atmosphere converts the intrinsic poly(phenylsilane) shell into a highly conductive carbonaceous coating, improving Li storage behavior. Reduced graphite oxide (graphene) was studied as a freestanding support for gold-seeded germanium and silicon nanowires, the latter grown using trisilane. Graphene improves capacity retention for germanium nanowires but shows little improvement for silicon. Slurry-cast films of nanowires were also tested as negative electrodes in lithium ion batteries using a variety of electrolyte solvent / binder combinations. Gold is detrimental to performance of silicon nanowires grown using trisilane. Removing gold through a simple wet etching procedure dramatically improves capacity retention. Silicon nanowires were also synthesized using in-situ formed tin seeds. Tin-seeded nanowires are easier to produce and outperform gold-seeded wires in lithium ion batteries. Germanium nanowires perform exceptionally well under high current loads when cycled using electrolyte solutions that contain fluoroethylene carbonate and show promise for high- power applications. Controlled synthesis of solution-grown germanium nanorods is demonstrated using nanocrystalline bismuth seeds. The addition of poly(vinylpyrrolidinone) / hexadecene copolymer leads to branched nanorods. Absorbance spectra were calculated using the discrete dipole approximation to compare against spectra obtained experimentally. The absorbance spectra and electric field internal to the nanorods depend highly on nanorod orientation. The presence of bismuth or gold at the tip of the nanorods also significantly alters the spectra and electric fields. Ligand and surface chemistry of solution grown indium phosphide nanowires is also examined. Octylphosphonic acid and hexadecylamine are both essential for the growth of single crystalline indium phosphide nanowires. Potential solution synthesis routes to indium (III) oxide nanowires and indium phosphide nanowires with twinning superlattice structure are presented. Various phosphoric acid derivatives were tested in place of octylphosphonic acid and the efficacy of each is discussed. / text
5

Battery energy storage for intermittent renewable electricity production : A review and demonstration of energy storage applications permitting higher penetration of renewables / Batterienergilager för intermittent förnyelsebar elproduktion : Litteraturöversikt och demonstrering av användingsområden för att möjliggöra en högre andel förnyelsebar energikällor

Görtz, Steffen January 2015 (has links)
Driven by resource politics and climate change, the transition from conventional fossil fuel based and centralized energy generation to distributed renewables is increasing rapidly. Wind and solar power generation offer carbon dioxide neutral electricity but also present some integration difficulties for energy system operators and planners due to intermittent power output. A promising way of dealing with the intermittency from renewables is energy storage. The method of storing energy in the electricity grid, especially by the means of electrochemical storage, has gained a lot of attention over the last years in the energy sector. While most utilities and energy market stakeholders have the basic understanding of energy storage, a more profound knowledge of grid storage applications is often lacking. This thesis aims to highlight and explain possible energy storage applications with focus on renewables integration. Battery energy storage can allow higher amounts of renewable electricity generation to be integrated by smoothening power output, time shifting generated energy to follow demand and increase hosting capacities through peak shaving. Power quality related issues due to intermittency can be mitigated by controlling the storage’s charging patterns to respond to grid variables. For optimal utilization and maximum storage value, several applications should be within the operational repertoire of the storage unit. Other applications including arbitrage, grid investment deferral and load following are discussed. Several battery technologies which have been developed and tested for such applications including lead acid, sodium sulfate and lithium-ion are presented. The most promising battery energy storage technology is lithium-ion with exceptional storage characteristics and most importantly a favorable near term price development. Two case studies on two of Umeå Energy’s low voltage networks simulating high penetrations of solar generation have been carried out to demonstrate mitigation of overvoltage and peak shaving with battery energy storage systems. The simulations show that energy storage systems can successfully be used to aid the integration of renewables in the electricity grid. Present capital costs are still too high for energy storage to be feasible but falling pricing and a developing market is foreseen to lower the hurdles.  The main obstacle for energy storage at grid scale besides high capital costs are, in principle, non-existing legal frameworks regulating the ownership of energy storage systems and system technology standardization. Further discussions on the matter in combination with testing and pilot projects are needed to gain national and international experience with battery energy storage for the successful high share integration of renewables. / Sinande naturresurser och växthuseffekten driver på övergången från centraliserad kraftproduktion baserad på fossila bränslen till distribuerad förnyelsebar energiproduktion i rask takt. Vind- och solkraft levererar koldioxidneutral el men ställer samtidigt balansansvariga och elnätsplanerare inför en rad problem på grund av periodiskt återkommande och tidvis ostabil effektgenerering. Energilager presenteras som en lovande lösning på problemen orsakade av förnyelsebara energikällor Att lagra energi i elnätet, i synnerhet med batterier, har fått en hel del uppmärksamhet de senaste åren i energibranschen. De flesta elnätsbolag och intressenter på energimarknaden har en grundläggande förståelse kring energilagring i elnätet men saknar ofta mer djupgående kunskap. Detta examensarbete syftar att belysa och förklara användningsområden och potentialer för energilagring med fokus på integreringen av förnyelsebara energikällor. Teorin beskriver hur batterilager kan användas för tillåta integreringen av en hög andel förnyelsebar elproduktion. Några tillämpningar är; effektutjämning, lagring av producerad energi för senare bruk samt ökad nätkapacitet genom att kapa toppar. Problem relaterade till försämrad elkvalité orsakad av varierande kraftproduktion visas kunna pareras med hjälp av programmerbara energilagringssystem som läser av storheter på elnätet såsom spänning och frekvens. För att utnyttja energilagret optimalt och komma åt dess maximala värde bör flera användningsområden kombineras. Därför diskuteras även andra användningsområden såsom arbitrage, lagringskapacitet för att skjuta upp eller undvika förstärkning av elnätet och lastföljning. Ett flertal batteriteknologier aktuella för de diskuterade användningsområdena såsom bly-, natriumsulfat- och litium-jonbatterier presenteras. Den mest lovande teknologin är litium-jon tack vare dess utmärkta egenskaper och framförallt mycket gynnsamma förväntade prisutveckling. Två fallstudier av två av Umeå Energi´s nätområden med hög simulerad andel solenergiproduktion har utförts för att demonstrera utnyttjandet av energilager för reglering av överspänning och kapning av toppar. Simuleringarna visar att energilagringssystem med framgång kan underlätta integreringen av förnyelsebara energikällor. Dagens kapitalkostnader är fortfarande för höga för att energilagring ska vara ekonomiskt försvarbart men fallande priser och en växande marknad väntas verka till teknikens fördel. Det visar sig att regelverk gällande ägandeskapet och standardiseringen av energilager är i det närmaste obefintliga vilket utgör ytterligare hinder för tekniken. Fortsatta diskussioner gällande dessa punkter i kombinationen med test- och pilotanläggningar för att införskaffa erfarenhet av energilagring i elnätet krävs.
6

Cathode materials for 5V lithium batteries

Kawai, Hiroo January 1999 (has links)
Complex spinel-structure oxides based on Li<sub>2</sub>MM'<sub>3</sub>O<sub>8</sub> and LiMM'O<sub>4</sub> have been systematically investigated on the basis of solid state chemistry and thermodynamics, and are found to constitute a novel family of cathode materials for 5 V lithium batteries. We have targeted lithium cathode materials that operate over 5 V, linked to large capacity and good cycling stability. The spinels prepared by solid state synthesis have been characterised using powder X-ray and neutron diffraction, impedance measurements, thermal analyses, magnetic measurements, XANES spectroscopy, Mossbauer spectroscopy and electrochemical measurements. In a single lithium cell, Li<sub>2</sub>CoMn<sub>3</sub>O<sub>8</sub> and LiCoMnO<sub>4</sub> are shown to be the first cathode materials to operate at discharge voltages over 5 V; Li<sub>2</sub>FeMn<sub>3</sub>O<sub>8</sub> operates at a discharge plateau commencing at 5 V and centred on 4.9 V, offering potentially great economic and environmental advantages as a lithium cathode. LiCoMnO<sub>4</sub> exhibits a discharge capacity of <I>ca</I>. 95 mAhg<sup>-1</sup> at a long plateau centred on 5.0 V in a cell, Li/LiPF<sub>6</sub>, propylene carbonate / LiCoMnO<sub>4</sub>, and therefore has superior energy density to LiMn<sub>2</sub>O<sub>4</sub>, the cathode material used in state-of-the-art cells. This renders LiCoMnO<sub>4</sub> potentially very attractive as a cathode material in practical 5 V lithium battery systems.
7

Studies on the sodium-sulphur battery

Gonsalves, Valerie Clare January 1988 (has links)
No description available.
8

Transport applications of flywheel energy storage

Jefferson, C. M. January 1984 (has links)
No description available.
9

Thermo-chemical energy storage system

Tahat, M. A. January 1994 (has links)
No description available.
10

An investigation of thermal energy storage and its applications to industrial systems

Manning, R. E. January 1985 (has links)
No description available.

Page generated in 0.0655 seconds