bluuebunny/crossref_metadata_2025_split huggingface dataset:
Grid‐support photovoltaics: Evaluation of criteria and methods to assess empirically the local and system benefits to electric utilities
Authors: Shugar Daniel S. , Hoff Thomas E. 
Published: July 2007

AbstractIn 1988, researchers at the Pacific Gas and Electric Company (PG&E) formulated the hypothesis that strategically sited photovoltaics (PV) could provide substantial local benefits to a utility's electrical transmission and distribution (T&D) system. Initial modelling of simulated data confirmed this hypothesis. These results indicated a need for empirical testing through operation of a commercial‐scale grid‐support PV plant within an appropriate utility T&D system. Towards this end, a comprehensive research plan was formulated to characterize and evaluate local and system benefits. Local benefits to be evaluated are: extended distribution transformer life, increased distribution planning area capacity, extended load tap changer life and maintenance intervals, reduced electrical line losses, improved system voltage, improved distribution system reliability and increased transmission system capacity. System benefits to be evaluated are: reduced system energy production costs, reduced requirements for additional generation capacity, reduced minimum load operation costs and reduced environmental impacts of fossil energy generation.A 500 kW PV plant serving PG&E's Kerman Substation near Fresno, California, was selected and built as part of the Photovoltaics for Utility Scale Applications project. the plant began operating in April 1993, 6 months after construction was initiated, and evaluation of the benefits was initiated. Confirmation of the original hypothesis‐that strategically sited PV generation provides substantial benefits to selected T&D systems‐will demonstrate that PG&E and other utilities may be able to serve customers in a more cost‐effective and environmentally sensitive manner. In the process, utilities could provide new markets for PV and other modular generation technologies.
Decreased emitter sheet resistivity loss in high‐eficiency silicon solar cells
Authors: Aberle Armin G. , Wenham Stuart R. , Green Martin A. , Heiser Gernot 
Published: July 2007

AbstractState‐of‐the‐art two‐dimensional (2D) numerical semiconductor device simulation tools are applied to bifacially contacted silicon solar cells of practical dimensions in order to investigate the 2D effects arising from ohmic voltage drops in cell emitters due to finite front metal grid line spacings. the 2D simulations show that for typical front finger spacings of high‐efficiency silicon solar cells the minority carrier flow in the base deviates strongly from the purely linear flow assumed by one‐dimensional (1D) theory. Compared to conventional 1D theory, this 2D effect results in reduced emitter sheet resistivity losses, an increased optimum front finger spacing and a reduced impact of finger spacing on cell efficiency. the 2D effects are of particular importance for concentrator solar cells.The 2D simulations presented in this work considerably improve the general understanding of internal device physics of high‐efficiency silicon solar cells and reveal the limits of 1D models for the simulation of these devices.
Attaining a 30‐year photovoltaic system lifetime: The BOS issues
Authors: Durand Steven J. 
Published: July 2007

AbstractFailures of power conditioning systems and balance of system (BOS) components have been responsible for the majority of system downtime in virtually all of the USA's large grid‐tied photovoltaic (PV) power plants. For these and future PV power plants, therefore, improvements in component reliability must be made before the design goal of a 30‐year system liftime can be attained. Advances in technology can increase reliability and still reduce costs of PV modules and power conditioning systems.However, since BOS components come generally from mature technologies, increased reliability must be attained through the purchase of higher quality components.
Cost‐benefit analysis of high‐eficiency cast polycrystalline silicon solar cell sequences
Authors: Narayanan S. , Wohlgemuth J. 
Published: July 2007

AbstractThe incorporation of eficiency enhancement techniques and the use of high‐eficiency process sequences have led to the fabrication of polycrystalline silicon solar cells with efficiencies nearing 18% in the laboratory by various investigators. In this paper a number of cell process sequences used to fabricate high‐efficiency polycrystalline silicon solar cells are reviewed. A cost‐benefit analysis of the efficiency enhancement techniques was performed using the Interim Price Estimation Guidelines 2 model, developed by the Jet Propulsion Laboratory, Pasadena, USA. the figure of merit used to compare the sequences was that the cost of additional power, generated by the efficiency enhancement technique, should be less than the selling price of the product. Techniques like oxide passivation and emitter etch‐back, and sequences like the buried‐contact process, were found to be cost effective.
A Ga0.51In0.49P/GaAs‐based photovoltaic converter for two‐directional optical power and data transmission
Authors: Vänttinen K. , Lammasniemi J. , Rakennus K. , Asonen H. , Jurva R. , Karioja P. 
Published: July 2007

AbstractA GaAs‐based photovoltaic converter for optical‐to‐electrical power conversion and for data transmission was developed. the device structure is based on a modified GaAs solar cell structure having a lattice‐matched Ga0.51In0.49P window layer. the converter consists of an array of series‐connected photovoltaic cells. the input optical laser power is transmitted via a single optical multimode fibre and distributed homogeneously to the separate cells. One of the cells has separate connections for acting as a light‐emitting diode for data transmission in the opposite direction. the conversion eficiency of the individual cells was measured to be 49%, and the array conversion efficiency was 41%.
Analysis and control of mismatch power loss in photovoltaic arrays
Authors: Roche David , Outhred Hugh , Kaye R. John 
Published: July 2007

AbstractConnecting photovoltaic cells to form an array can cause problems when the characteristics of the cells are not matched. This problem, known as mismatch, can reduce the power output of the array and lead to cell degradation through localized heating of individual cells. Such problems can arise simply through the shading of a single cell. In this paper, which has a substantial tutorial content, three methods of reducing the effects of mismatch are investigated and compared; the use of integral bypass diodes (IBDs), series/paralleled circuit designs and reduced cell shunt resistance.Experiments were performed on arrays incorporating cells with IBDs and their tolerance to shading was tested and compared to arrays with other cell designs. the potential benefits and costs of using IBDs are then assessed and conclusions drawn about the relative effectiveness of this strategy. the circuit design strategy known as series/paralleling is described and analysed and its effect on minimizing mismatch power loss is evaluated. Also, an expression for the optimum cell shunt resistance in a general shaded array is derived and the technique of reducing cell shunt resistance to minimize mismatch effects is assessed.
Photovoltaics in grid‐connected buildings: Energy flow and economic aspects
Authors: Caamaño E. , Lorenzo E. 
Published: July 2007

AbstractTwo main subjects must be considered in the analysis of a photovoltaic grid‐connected building. the first concerns the various energy flows, such as the hourly photovoltaic generation and the electricity consumption of the building, that determine the global energy balance, i.e. the extent to which the system will be able to supply the building's electricity consumption. This paper provides a simple method to estimate this behaviour. Secondly we must consider the long‐term cost of the system, a key aspect that depends on the economic scenario and can be made attractive given the appropriate policies (some examples are mentioned).
Bandgap engineering of amorphous semiconductors for solar cell applications
Authors: Bernhard N. , Bauer G. H. , Bloss W. H. 
Published: July 2007

AbstractDifferent bandgap engineering approaches are discussed with respect to their application in thin‐film solar cells based on hydrogenated amorphous silicon (a‐Si: H) and its alloys with Ge or C. After a survey of the different approaches reported so far in the literature, the main emphasis will lie on the application of a‐Si: H/a‐Si1‐xCx:H multilayers for use in the p‐doped window layer, or a graded bandgap a‐Si1‐xCx:Hintrinsic layer with varying Ge content x. But also the possibility of using an a‐Si: H/a‐Si1‐xCx:H multilayer as the i‐layer will be addressed. Intrinsic films of both multilayers and graded bandgap material have been deposited in different series, varying electronic well and barrier widths in the first case, and the amount, form or local position of a change of the bandgap in the second case. Physical properties of both classes of materials have been investigated thoroughly. the results are discussed with respect to an application in amorphous thin‐film solar cells, also taking into account results from the literature about the implementation of these heterostructures in devices. Conclusions for the future perspectives of these approaches are drawn.
Experimental extraction of light confinement parameters for textured silicon wafers
Authors: Tobias I. , Rodriguez J. M. , Luque A. 
Published: July 2007

AbstractA procedure for extracting the internal reflectivities and the mean tilt angle of light rays inside silicon wafers from reflectance measurements is presented. the procedure, based on a simple model of light confinement, is applied to silicon wafers textured with random pyramids. the results obtained are shown to be in good agreement with ray‐tracing calculations and theoretical estimates.Se presenta un método para extraer, a partir de medidas de reflectancia, los valores de las reflectividades internas y del ángulo medio de inclinación de los rayos de luz en el interior de células solares. Este método está basado en un modelo sencillo del confinamiento interno de la luz y se aplica aqui a obleas de silicio con textura piramidal aleatoria. Los resultados obtenidos están de acuerdo con los calculados mediante trazado de rayos y con las estimaciones teóricas.
Performance analysis of photovoltaic pumping systems using switched reluctance motor drives
Authors: Metwally Hamid M. B. , Anis Wagdy R. 
Published: July 2007

AbstractA photovoltaic (PV) pumping system using a switched reluctance motor (SRM) is investigated in this work. the motor is supplied by a DC voltage through a simple switching circuit. This drive circuit is much simpler than the normal DC/AC inverter required to supply an induction motor. the efficiency of the SRM is considerably higher than that of equivalent DC or induction motors. In addition, because of its simple construction, the SRM is cheaper than these conventional drives. These advantages give the proposed system higher efficiency and lower cost compared with other systems.In this paper, which has a substantial tutorial content, a design example is studied in detail to explore the advantages of PV pumping systems based on the new drive. Study of the performance of the proposed system showed that the operating efficiency of the motor is about 85% during most of its working time. the matching efficiency between the PV array and the proposed system approaches 95%. the major part of the losses takes place in the pump and the riser pipes; this loss represents one‐third of the total available energy.
Phytochemical study of Solanum lycocarpum (St. Hil) unripe fruit and its effects on rat gestation
Authors: Schwarz Aline , Pinto Ernani , Haraguchi Mitsue , Oliveira Cláudio Alvarenga de , Bernardi Maria Martha , Spinosa Helenice de Souza 
Published: July 2007

AbstractSolanum lycocarpum, St. Hil (Solanaceae) is a common native shrub in the Brazilian cerrado. The fruits are used in folk medicine as a hypoglycaemic agent in the management of diabetes, obesity and to decrease cholesterol levels. In this study the glycoalkaloids, solamargine and solasonine, were isolated from unripe fruits of S. lycocarpum. To evaluate the effects of the fruits on gestation, pregnant rats (n = 25) were fed from day 6 to 22 with chow containing 10% of dried and ground unripe fruits. The control group (n = 21) received regular chow. During and after the treatment period the dams showed reduced body weight and slower body weight gain, even with no change in food and water intake, evidencing mild maternal toxicity. Gestation was not significantly impaired, although experimental fetuses presented reduced body length at birth. Also, 20% of the treated dams showed one or two dead pups at birth. On day 22 of gestation and on post‐natal day 1, the levels of metabolites of the sex hormones oestradiol, progesterone and testosterone were measured in faeces by radioimmunoassay. On post‐natal day 1, tissue portions from the dams were collected for histopathological evaluation. No alterations were detected in either study. The results suggest that S. lycocarpum fruit did not impair gestation, however, it did promote mild maternal toxicity and mild fetotoxic effects if ingested as a food source during the gestation period. This study has implications for pregnant women, who employ phytotherapeutic formulations under the impression that they are harmless. Copyright © 2007 John Wiley & Sons, Ltd.
Efficient MPC optimization using Pontryagin's minimum principle
Authors: Cannon Mark , Liao Weiheng , Kouvaritakis Basil 
Published: July 2007

AbstractA method of solving the online optimization in model predictive control (MPC) of input‐constrained linear systems is described. Using Pontryagin's minimum principle, the matrix factorizations performed by general purpose quadratic programming (QP) solvers are replaced by recursions of state and co‐state variables over the MPC prediction horizon. This allows for the derivation of solvers with computational complexity per iteration that depends only linearly on the length of the prediction horizon. Parameterizing predicted input and state variables in terms of the terminal predicted state results in low computational complexity but can lead to numerical sensitivity in predictions. To avoid ill‐conditioning an alternative parameterization is derived using Riccati recursions. Comparisons are drawn with the multiparametric QP solution, and the computational savings are demonstrated over generic QP solvers. Copyright © 2007 John Wiley & Sons, Ltd.
Supplemental water releases for fisheries restoration in a Brazilian floodplain river: a conceptual model
Authors: Godinho Alexandre L. , Kynard Boyd , Martinez Carlos B. 
Published: July 2007

AbstractHighly productive floodplain rivers in Brazil and elsewhere provide livelihood and recreational fishing for millions of people around the world, but damming and controlled water discharge are a threat to these valuable ecosystems. Supplemental water releases (SWRs) at a dam are increasingly used for restoring fisheries productivity in many floodplain rivers. We proposed a conceptual model for a hypothetical water release to enhance fisheries using Três Marias Reservoir (TMR) on the São Francisco River (SFR), Brazil. The information needed by the model follows: (i) Biologically, what is the best release date? (ii) How much water will be released? (iii) What is the pattern of impoundment and how much impounded water will be released? (iv) What is the lost revenue to the power plant associated with SWR? (v) What is the relationship between river discharge and the area of floodplain that is flooded? (vi) What is the relationship between SWR and fisheries value? Ichthyoplankton studies in the SFR showed a clear positive relationship between fish density and water level (WL). While the relationship between WL and floodplain area flooded and recruitment is not known, we concluded the best date for release is when there is a natural flood, which naturally triggers fish spawning and the SWR will add to the natural flood and cover a greater floodplain area. The released volume will range from 0.302 km3 to 2.192 km3, depending on SWR duration. In most years from 1976 to 2003, TMR impounded enough water for SWR only in the second half of the fish‐spawning season (January–March). Lost revenue at TMR depended on release volume and ranged from US$ 0.493 million to US$ 3.452 million for the actual power rate. However, SWR could increase commercial fisheries income an estimated US$ 4.468 million. We forecast that SWR can bring fisheries benefits that surpass the lost revenue. Published in 2007 by John Wiley & Sons, Ltd.
Fluid therapy in acute large area burns: A system dynamics model
Authors: Bush James W. , Schneider Alan M. , Wachtel Thomas L. , Brimm John E. 
Published: July 2007

AbstractA preliminary mathematical model of fluid dynamics in acute large area burns at present incorporates plasma water, urine output, burn water loss, insensible losses via the nonburned skin, lungs, and GI tract, as well as inputs of maintenance water and therapeutic (Brooke formula) fluids. The model is an initial step in a longer‐term project to identify the pathogenetic mechanisms that control fluid shifts and to evaluate the effects of crystalloid (sodium ion), colloid (albumin), and other guidelines for fluid resuscitation. The model is initialized in homeodynamic equilibrium for a standard 70‐kg person and gives reasonable, realistic responses to a wide range of parameter variations (body sizes, burn wound loss factors), step functions (burn size, discontinuation of maintenance water), and rates of therapeutic fluid administration, given its present structure. The addition of burn and nonburn interstitial and intracellular spaces and their constituents (water, sodium, albumin, and potassium) will (1) permit validation against a wide range of clinical and experimental data, (2) suggest refinements of current resuscitation guidelines, (3) suggest more incisive research on pathogenetic mechanisms and treatment modalities, and (4) permit comparison of system dynamics with alternative modeling and simulation approaches.
The world hunger problem: Do we really understand it?
Authors: Saeed Khalid 
Published: July 2007

AbstractIn this section the System Dynamics Review presents problems having the potential to stimulate system dynamics research. Articles may address real‐world dynamic problems that could be approached fruitfully from the system dynamics perspective, or methodological problems affecting the field. A paper submitted to the Research Problems section should concisely motivate and define a problem and start a process of conceptualization or formulation that can open the way for further studies. Manuscripts not exceeding 2,000 words should be sent to George P. Richardson, Department of Mathematics and Computer Science, Wheaton College, Norton, MA 02766, U.S.A.
A mathematical model to analyze predation and competition problems in a sheep‐farming region
Authors: Swart Johan , Hearne John W. 
Published: July 2007

AbstractSheep farmers in the Cape Midlands region of South Africa frequently sustain stock losses through predation by caracal lynx. Further losses are incurred because of hyrax competing with the sheep for pasture. As hyrax constitute the principal food of lynx, culling either hyrax or lynx has complex feedback effects.A system dynamics model of this system comprising sheep, hyrax, lynx, pasture, and revenue sectors has been formulated. The model is used to simulate the system under different culling strategies.By comparing stock positions and farming revenue generated over a number of years under different culling strategies, an optimal culling policy is determined using an optimization procedure. A parameter sensitivity analysis reveals that the policy recommendations are relatively insensitive to parameter uncertainty.
The spread of '88 Shanghai type‐A hepatitis: A system dynamics model and analysis
Authors: Su Mao‐Kang , Chen Keh‐Hsun , Wang Huan‐Chen 
Published: July 2007

AbstractThis articie examines a general infectious disease model and proposes a new epidemic threshold and an epidemic scale forecasting formula. Then a system dynamics model of an eruptive Spread of type‐A hepatitis in Shanghai in 1988 is presented. Various problems are resolved: simulating the incubation period of type‐A hepatitis; fitting the simulation results to real data; analyzing the reason that the predicted second peak of the eruptive spread did not occur. Short‐and long‐term prospects for recurrence are considered, especially the mechanisms of periodic epidemics and eruptive spreads of type‐A hepatitis. The results of this study have import for the prevention and control of type‐A hepatitis and other infectious diseases.
Dyadic processes, tempestuous relationships, and system dynamics
Authors: Radzicki Michael J. 
Published: July 2007

AbstractNotes and Insights is a forum for discussion and debate about current issues in the philosophy and application of the system dynamics approach, and a marketplace for the exchange of information about currant research, policy issues, and teaching experiences. Manuscripts treating material particularly suited to presentation in short form (less than 2,000 words) should be sent to Erich Zahn, Betriebswirtschaft‐liches Institut, Abt. IV, Universität Stuttgart, Keplerstr. 17, D‐7000 Stuttgart 1, Germany.
Systems thinking: Critical thinking skills for the 1990s and beyond
Authors: Richmond Barry 
Published: July 2007

AbstractThe problems we face at all levels in the world today resist unilateral solutions. While the web of interdependencies tightens, our capacity for thinking in terms of dynamic interdependencies has not kept pace. As the gap between the nature of our problems and the ability to understand them grows, we face increasing perils on a multitude of fronts. Systems thinking and one of its subsets‐system dynamics‐are important for developing effective strategies to close this gap. Unfortunately, system dynamicists and systems thinkers have not effectively taught their framework, skills, and technologies to others. The door has not been opened wide enough to let others share our insights with respect to the workings of closed‐loop systems. To transfer this understanding on a broad scale, we need a clearer view of its nature and of the education system into which it must be transferred. This article casts some light on what we have to bestow and on the education system that is to receive our bounty. Its intended audience is both system thinkers and educators, and the hope is to help eradicate the distinction between the two.
Fuzzy system dynamics: An approach to vague and qualitative variables in simulation
Authors: Tessem Bjørnar , Davidsen Pål I. 
Published: July 2007

AbstractThe application of fuzzy numbers is suggested as an alternative to probabilistic methods for the management of uncertainty and vagueness in system dynamics models. Fuzzy numbers are particularly well suited for representing qualitative values and are used during simulation. To handle interaction among variables, we utilize global optimization methods. In nonlinear models, however, our implementation does not suffice. We illustrate the use of fuzzy numbers, qualitative values, and the problems of implementation by some simple examples.