A study of the effect of in situ doping on the crystallinity of LPCVD polysilicon

Results are presented for the degree of crystallinity, determined by Raman spectroscopy, of in situ B-doped LPCVD polysilicon as a function of deposition temperature. The results are compared with those reported in the literature for P-doped polysilicon and it is found that for B doping full crystallinity of the layer is achieved at a significantly lower deposition temperature than is required for P doping. An attempt to understand this effect is made in terms of a quantitative model which allows an estimation of values for silicon self-diffusivity and which is in accord with the experimental observations.     

Formation of silicon nitride films by remote plasma-enhanced chemical vapour deposition

In this paper we describe the growth of silicon nitride from nitrogen and silane for the first time by capacitively coupled remote PECVD. We report on the effect of process parameters on the composition and properties of the deposited films and we show that by adjustment of these parameters it is possible to produce high-quality material which could be of interest for electronic applications. Of particular note is that the growth rate is about one order of magnitude higher than any previously reported for nitride growth with remote PECVD using molecular nitrogen as the nitrogen source. We also discuss the mechanism of growth and propose that electron excitation of nitrogen and silane occurs in the gas phase, producing SiH_x species which are adsorbed on the growing surface. The nitrogen is then incorporated into the layer by heterogeneous reaction.     

Supreme Court Precedents Tested Again by NY Zero-Emission Regs

Recently in these pages—in fact, quite recently—we conducted an extensive review of new US Supreme Court landmarks that unequivocally established the paramountcy of federal law regulating the interstate energy markets. This noble triad is composed of Oneok, Inc. v. Learjet, Inc., establishing that federal law is supreme over state promulgations regulating the natural gas industry, followed by FERC v. Electric Power Supply Association, which likewise declared that the interstate wholesale market in electricity is subject solely to national regulation, to the exclusion of state law, and, finally, Hughes v. Talen Energy Marketing, LLC, where, consistent with its earlier precedents, a unanimous Supreme Court voided a state-aid program to certain energy producers as an unlawful intrusion into a domain constitutionally mandated as one susceptible only to federal oversight.     

A novel approach for the modeling of advanced photovoltaic devices using the SILVACO/ATLAS virtual wafer fabrication tools

In this paper a new method for developing a realistic model of any type of solar cell is presented. Taking into account the high cost of research and experimentation involved with the development of advanced cells, we present here this novel methodology. In our opinion, the introduction of this modeling technique to the photovoltaic community will prove to be of great importance in aiding in the design and development of advanced solar cells. Two models of a single GaAs and an InGaP/GaAs/Ge multi-junction solar cell are prepared and are fully simulated. The major stages of the process are explained and the simulation results are compared to published experimental data to demonstrate the accurate results produced by the model utilizing this technique. The flexibility of the proposed methodology is illustrated and example results are shown throughout the whole process, demonstrating some of the different parameters effects on the model performance.     

Parametric sensitivity study of operating and design variables in wellbore heat exchangers

A numerical study was conducted to evaluate the potential for using Wellbore Heat Exchangers (WBHX) to extract heat for use in electricity generation. Variables studied included operational parameters such as wellbore geometries, working fluid properties, circulation rates, and regional properties including basal heat flux and formation rock type. Energy extraction is strongly affected by fluid residence time, heat transfer contact area, and formation thermal properties. Water appears to be the most appropriate working fluid. The effects of tubing properties and casing lengths are of second-order.On the basis of a sensitivity study, a Best Case model was simulated, and results compared against the geothermal fluid requirements of existing power generation plants that use low-temperature geothermal fluids. Even assuming ideal work conversion to electricity, a WBHX cannot supply sufficient energy to generate 200 kWe at the onset of pseudo-steady-state (PSS) conditions. Using realistic conversion efficiencies it is unlikely that the system would be able to generate 50 kWe at the onset of PSS.     

Durability of polymeric glazing materials for solar applications

The economic viability of solar collector systems for domestic hot water (DHW) generation is strongly linked to the cost of such systems. Installation and hardware costs must be reduced by 50% to allow significant market penetration. An attractive approach to cost reduction is to replace glass and metal parts with less expensive, lighter weight polymeric components. Weight reduction decreases the cost of shipping, handling, and installation. The use of polymeric materials also allows the benefits and cost savings associated with well established manufacturing processes, along with savings associated with improved fastening, reduced part count, and overall assembly refinements. A key challenge is to maintain adequate system performance and assure requisite durability for extended lifetimes. Results of preliminary and ongoing screening tests for a large number of candidate polymeric glazing materials are presented. Based on these results, two specific glazings with moderate and poor weathering stability are selected to demonstrate how a service lifetime methodology can be applied to accurately predict the optical performance of these materials during in-service use. A summary is given for data obtained by outdoor exposure and indoor testing of polyvinyl chloride (PVC) and high temperature modified polycarbonate copolymer (coPC) materials, and an initial risk analysis is given for the two materials. Screening tests and analyses for service lifetime prediction are discussed. A methodology that provides a way to derive correlations between degradation experienced by materials exposed to controlled accelerated laboratory exposure conditions and materials exposed to in-service conditions is given, and a validation is presented for the methodology based upon durability test results for PVC and coPC.     

Numerical simulation of lithium‐ion battery performance considering electrode microstructure

A spatially resolved three‐dimensional microscale model of a lithium‐ion battery half‐cell is developed and applied to periodic electrode microstructures made up of spherical particles following a bidisperse particle size distribution. The geometries of the periodic unit cells are derived from discrete element simulations using periodic boundary conditions. Three different particle arrangements, which consist of two layered structures and one mixed particle array, as well as three different compression rates, are considered. In the study, the cathode is assumed to consist of LiMn₂O₄ as active material. Layered particle arrangements comprising the particle fraction of the smaller particle size in the region close to the separator are found to be beneficial especially for high‐rate applications. According to the simulation results, the high‐rate capability is reduced upon compression of the electrode microstructures. Copyright © 2015 John Wiley & Sons, Ltd.     

Wind turbine response to parameter variation of analytic inflow vortices

As larger wind turbines are placed on taller towers, rotors frequently operate in atmospheric conditions that support organized, coherent turbulent structures. It is hypothesized that these structures have a detrimental impact on the blade fatigue life experienced by the wind turbine. These structures are extremely difficult to identify with sophisticated anemometry such as ultrasonic anemometers. This study was performed to identify the vortex characteristics that contribute to high‐amplitude cyclic blade loads, assuming that these vortices exist under certain atmospheric conditions. This study does not attempt to demonstrate the existence of these coherent turbulent structures. In order to ascertain the idealized worst‐case scenario for vortical inflow structures impinging on a wind turbine rotor, we created a simple, analytic vortex model. The Rankine vortex model assumes that the vortex core undergoes solid body rotation to avoid a singularity at the vortex centre and is surrounded by a two‐dimensional potential flow field. Using the wind turbine as a sensor and the FAST wind turbine dynamics code with limited degrees of freedom, we determined the aerodynamic loads imparted to the wind turbine by the vortex structure. We varied the size, strength, rotational direction, plane of rotation, and location of the vortex over a wide range of operating parameters. We identified the vortex conformation with the most significant effect on the blade root bending moment cyclic amplitude. Vortices with radii on the scale of the rotor diameter or smaller caused blade root bending moment cyclic amplitudes that contribute to high damage density. The rotational orientation, clockwise or counter‐clockwise, produces little difference in the bending moment response. Vortices in the XZ plane produce bending moment amplitudes significantly greater than vortices in the YZ plane. Published in 2005 by John Wiley & Sons, Ltd.     

Making enduring choices: Uncertainty and public policy

This paper provides an experimental test of the theory of investment under uncertainty and applies the theory to a group of policy decisions. Investment under uncertainty describes a class of problems, characterized by uncertainty that resolves itself over time, sunk costs that cannot be fully recovered, and the ability of the decision maker to wait without loss of strategic advantage. It also implies a “bad news principle,” under which decision makers are motivated by expected costs, but not expected benefits. The theory is illustrated as a two-period model for which the decision maker can either invest in the first period (and receive a known current return plus an uncertain future return) or defer until the second period when uncertainty is resolved. By foregoing current period benefits a “cost” that is sometimes referred to as an option value is incurred. Parameter values are specified and an experimental test, the results of which closely track the predictions of the theory, is described. Three cases, the structuring of contingent valuation questionnaires, the operalization of the precautionary principle in risk analysis, and the development of public policy to stimulate private investments (as for energy-saving products), are used to illustrate potential public policy applications.     

Green energy market development in Germany: effective public policy and emerging customer demand

This paper reviews the development of renewable energy in Germany from 1973 to 2003. It investigates the relative importance of energy policy and green power marketing in shaping the renewable energy market. More than a decade of consistent policy support for renewables under the feed-in law (StrEG) and its successor (EEG) has been an important driver for increasing renewable electricity generation to date, putting the country in a better position than most of its peers when it comes to achieving European Union targets for renewable energy. Green power marketing driven by customer demand, on the other hand, is growing, but has had limited measurable impact so far. We discuss potential intangible benefits of green power marketing and scenarios for future market development. The paper concludes with lessons that can be learned from the German case for policy design and market development in other countries.