bluuebunny/crossref_metadata_2025 huggingface dataset:
An Intraocular Camera for Retinal Prostheses
Authors: Nasiatka Patrick J. , Hauer Michelle C. , Stiles Noelle R. B. , Lue Jaw-Chyng , Takahashi Satsuki , Agrawal Rajat , Weiland James D. , Humayun Mark S. , Tanguay Armand R.
Published: February 2009

Blindness due to degenerative retinal diseases such as Retinitis Pigmentosa (RP) and Age-Related Macular Degeneration (AMD) afflict millions of people worldwide. Recent advances in retinal implants that bypass damaged photoreceptor cells and electrically stimulate the remaining healthy retinal neurons show promise for restoring functional vision to the blind [1]. Current intraocular retinal prostheses driven by an external camera mounted on the subject’s head require slow and unnatural head movements. To allow for normal foveation and expanded depth of field, a novel intraocular camera (IOC) has been designed to work in conjunction with an epiretinal microstimulator array, as shown schematically in Fig. 1.
Energy Performance of European Buildings
Authors: Balaras Constantinos A. , Dascalaki Elena G. , Gaglia Athina G. , Droutsa Kaliopi , Kontoyiannidis Simon
Published: February 2009

The existing buildings stock in European countries accounts for over 40% of final energy consumption in the European Union (EU) member states. Consequently, an increase of building energy performance can constitute an important instrument in the efforts to alleviate the EU energy import dependency and comply with the Kyoto Protocol to reduce carbon dioxide emissions. This is also in accordance to the European Directive on the Energy Performance of Buildings (EPBD), which is currently under implementation in all EU member states. This paper presents an overview of EPBD and ongoing national activities, and focus on building energy performance assessment methodologies, in line with the EPBD. These methods and software can be used to perform building energy audits and assess buildings in a uniform way, perform demand and savings calculations, provide owners with specific advice for measures that can improve energy performance, and issue an Energy Performance Certificate (EPC) for existing buildings. Another ongoing European project is developing a common database structure and an evaluation scheme, which is being used to collect, process and evaluate data from 12 European countries. The results will constitute a good basis for the implementation of harmonized monitoring systems in the building sector on regional and national level.
A Comparison of Predicted to Measured Photovoltaic Module Performance
Authors: Fanney A. Hunter , Dougherty Brian P. , Davis Mark W.
Published: February 2009

Computer simulation models to accurately predict the electrical performance of photovoltaic modules are essential. Without such models, potential purchasers of photovoltaic systems have insufficient information to judge the relative merits and cost effectiveness of photovoltaic systems. The purpose of this paper is to compare the predictions of a simulation model, developed by Sandia National Laboratories, to measurements from photovoltaic modules installed in a vertical wall fac¸ade in Gaithersburg, MD. The photovoltaic modules were fabricated using monocrystalline, polycrystalline, tandem-junction amorphous, and copper-indium diselenide cells. Polycrystalline modules were constructed using three different glazing materials — 6 mm low-iron glass, 2 mm ethylene-tetrafluoroethylene copolymer (ETFE), and 2 mm polyvinylidene fluoride (PVDF). In order to only assess the simulation model’s ability to predict photovoltaic module performance, measured solar radiation data in the plane of the modules is initially used. Additional comparisons are made using horizontal radiation measurements. The ability of the model to accurately predict the temperature of the photovoltaic cells is investigated by comparing predicted energy production using measured versus predicted photovoltaic cell temperatures. The model was able to predict the measured annual energy production of the photovoltaic modules, with the exception of the tandem-junction amorphous modules, to within 6% using vertical irradiance measurements. The model overpredicted the annual energy production by approximately 14% for the tandem-junction amorphous panels. Using measured horizontal irradiance as input to the simulation model, the agreement between measured and predicted annual energy predictions varied between 1% and 8%, again with the exception of the tandem-junction amorphous silicon modules. The large difference between measured and predicted results for the tandem-junction modules is attributed to performance degradation. Power measurements of the tandem-junction amorphous modules at standard reporting conditions prior to and after exposure revealed a 12% decline. Supplying post-exposure module parameters to the model resulting in energy predictions within 5% of measured values.
Performance Characterization of a Wind Turbine Simulator for Grid Connected and Islanded Wind Turbine Operation
Authors: Zimmerle Dan , Pacific Oliver , Howard Nathan
Published: February 2009

To better understand the effect of significant wind power production on distributed electrical networks, a Wind Turbine Simulator (WTS) was incorporated into the Grid Simulation Laboratory (GSL) at Colorado State University. This paper discusses the development of the engine controls, gain tuning and response matching to field measurements of wind turbines. Response was characterized while connected to the transmission grid, similar to the field information, using a series of transient events gleaned from field information. Transients caused by breaker events, which emulate connecting or disconnecting the individual wind turbines, were also considered. While overall correlation between commanded and actual power output was strong, several limitations were identified and are described.
The Use of Ejector Refrigeration Systems for Turbine Inlet Air Cooling: A Thermodynamic and CFD Study
Authors: Al-Ansary Hany A.
Published: February 2009

Cooling turbine inlet air is a proven method of increasing turbine power output, especially during peak summer demand. It is estimated that turbine power output can increase by as much as 0.7% for every 1°C drop in inlet air temperature. Two inlet air cooling systems are widely used: evaporative cooling systems and chiller systems. Evaporative cooling is economical and uncomplicated, but its efficiency can significantly drop if the relative humidity is high. There is also a potential for excessive wear of compressor blades if water droplets are carried into the compressor section. On the other hand, chiller systems have the advantage of being independent of humidity and do not have the potential to cause damage to compressor blades. However, chiller systems consume power and cause a larger pressure drop than evaporative coolers. In this work, the possibility of using an ejector refrigeration system to cool turbine inlet air is explored. These systems are low-maintenance, fluid-driven, heat-operated devices that can use part of the turbine exhaust flow as the heat source for running the cycle. These systems require only pump power to feed liquid refrigerant to the vapor generator, making the power consumption potentially lower than conventional chiller systems. Using thermodynamic analysis, this paper compares the performance of ejector refrigeration systems with that of chiller systems based primarily on their power consumption. Performance characteristics for the ejector system are obtained through a CFD model that uses a real-gas model for R-134a. Published data on the performance of a commercial gas turbine is also considered. The power consumption of ejector refrigeration systems is found to be significantly smaller than that of vapor compression systems, with savings ranging from 19% to 80%. Power consumption is also found to be small compared to the boost in turbine power that is obtained. The percentage of waste heat needed to operate the ejector refrigeration system is found to be generally less than 25%.
Solar Absorption Cooling and Heating System in the Intelligent Workplace
Authors: Qu Ming , Archer David H. , Yin Hongxi , Masson Sophie
Published: February 2009

A solar thermal driven absorption cooling and heating system has been installed in Carnegie Mellon University’s Robert L. Preger intelligent Workplace, the IW. The purpose of this solar installation is to investigate the technical and economic aspects of using high temperature solar thermal receivers driving a two stage absorption chiller to cool and heat a building space. The solar system consists primarily of 52 m2 of single-axis tracking parabolic trough solar collectors (PTSC), and a 16 kW double effect absorption chiller driven by either a fluid heated in solar receivers or by natural gas fuel. The receivers convert solar radiation to thermal energy in a heated fluid; the chiller then uses this energy in summer to generate chilled water. In winter, the thermal energy is directly used for heating. A performance analysis was carried out to estimate the conversion efficiency of the PTSC based on mass and energy balances and heat transfer computations programmed in Engineering Equation Solver (EES). The performance of the overall solar cooling and heating for the IW has been programmed in TRNSYS modeling system. This solar energy system has been estimated to provide 38–50% of the cooling and 9–30% of heating energy depending upon orientation, insulation and storage capacity for 245 m2 of space in the IW. Experimental data are now being collected and will be used for validating the solar collector model. The solar system model will be used in interpreting the data yet to be obtained on the system performance. The primary purpose of this research program is the development of systems which reduce the energy requirements for the operation of buildings by a factor of two or greater, and the provision of techniques and tools for the design and evaluation of such systems.
Southern Nevada Renewable Resource Assessment
Authors: Gray Allison , Sahm Aaron , Newmarker Marc , Hurt Rick , Boehm Robert , Hale Mary Jane , Andreas Afshin , Gotseff Peter , Stoffel Thomas
Published: February 2009

University of Nevada, Las Vegas Renewable Energy Center (UNLV-REC) currently monitors three meteorological stations in southern Nevada under the direction of the National Renewable Energy Laboratory (NREL) and is funded by the Nevada Southwest Energy Partnership (NSWEP). The three station locations are Eldorado Valley, UNLV-REC Solar Site, and Nevada Power Company Clark Station. The installation dates for each of the locations were October of 2004 for Eldorado Valley station, August of 2003 for the UNLV-REC Solar Site, and March of 2006 for the Nevada Power Clark Station. Publicly available data from each site have been archived since installation completion. This paper discusses the installation of the equipment for each site and images of the setup. The data that is being collected between the sites is also compared. Data comparisons between the sites include net monthly solar energy; monthly peak direct normal irradiance (DNI), average daily wind speed, monthly wind roses, and average monthly dry bulb temperatures. The recently measured data is also compared to resource maps developed by NREL and to TMY data. With these meteorological resources, microclimatic variations can be studied for the area and used as a renewable energy resource for renewable installations in southern Nevada.
Field Testing and Performance of an Amonix Multi-Junction Cell Module at the University of Nevada Las Vegas
Authors: Stone Kenneth W. , Gordon Robert , Dutra David , Gray Allison , Hurt Rick , Boehm Robert , Hale Mary Jane , Eddy Fannie Pose
Published: February 2009

This paper discusses the installation, operation, and performance of a high concentration photovoltaic single-plate, multi-junction module developed by Amonix and installed at the Center for Energy Research at the University of Nevada, Las Vegas (UNLV). The paper discusses the objectives and goals of this project and describes the principal of the Fresnel optics, the module, and how it was attached to the Amonix 25-kW unit located at the UNLV Center for Energy Research. Also described are how the module is connected to a load and the measurements taken. Data is presented in the paper showing the module has produced power for over 2200 hours at a power efficiency of 26% to 28.6%. Data is also presented showing the next generation single-plate, multi-junction module achieving an efficiency of nearly 30%.
Reactive Fe-YSZ Coated Foam Devices for Solar Two-Step Water Splitting
Authors: Kodama Tatsuya , Hasegawa Tomoki , Nagasaki Ayumi , Gokon Nobuyuki
Published: February 2009

A thermochemical two-step water splitting cycle using a redox system of iron-based oxides or ferrites is one of the promising processes for converting solar energy into clean hydrogen in sunbelt regions. An iron-containing YSZ (Yttrium-Stabilized Zirconia) or Fe-YSZ is a promising working redox material for the two-step water splitting cycle. The Fe2+ YSZ is formed by a high-temperature reaction between YSZ, and Fe3O4 supported on the YSZ at 1400°C in an inert atmosphere. The Fe2+-YSZ reacts with steam and generate hydrogen at 1000–1100°C, to form Fe3+-YSZ that is re-activated by a thermal reduction in a separate step at temperatures above 1400°C under an inert atmosphere. In the present work, a ceramic foam coated with the Fe-YSZ particles is examined as the thermochemical water splitting device for use in a solardirectly-irradiated receiver/reactor system. The Fe-YSZ particles were coated on an Mg-partially-stabilized zirconia foam disk and the foam device was tested on the two-step water splitting cycle being performed alternately at temperatures between 1100 and 1400°C. The foam device was irradiated by concentrated visible light from a sun-simulator at the peak flux density of 1000 kW/m2 and the average flux density of 470 kW/m2 in a N2 gas stream, and then, was reacted with steam at 1100°C while heating by an infrared furnace. Hydrogen successfully continued to be produced in the repeated cycles.
Influence of Natural Primary Thermal-Source Temperatures on Power Consumption in Air-Conditioning Plants
Authors: Cerri Giovanni , Gazzino Marco , Botta Fabio , Salvini Coriolano
Published: February 2009

This paper is focused on exploring the potential of connecting air-conditioning plants to primary thermal sources qualified by temperatures. Several connection layouts between plant components and thermal sources are investigated. Traditional systems including chillers and heat pumps, as well as systems based on chillers equipped with partial or total heat recovery devices are considered. The influence of primary thermal-source temperatures on overall design performance of such systems is deeply investigated and results focusing on power consumption and energy savings, as well as on reduction of CO2 emissions produced by the source of mechanical work, will be presented and widely discussed.
Preparation of Mixed Iron Oxides for Solar Hydrogen Production by Means of the Pechini Technique
Authors: Marcos Mari´a J. , Herna´ndez Teresa , Sa´nchez Miguel , Quejido Alberto J. , Romero Manuel
Published: February 2009

A process of synthesis of mixed iron oxides for their application to solar hydrogen production is reported. To analyze the suitability of the selected technique, different compositions in the compound MnxNi1−xFe2O4−5 were prepared by varying the Ni/Mn ratio between 0 and 3. The main objective was to identify the optimal amount of dopants for hydrogen production in such a magnetite. The powders were obtained from a solution of Ni, Mn and Fe nitrates by a polymeric method based on the Pechini process and were characterized by XRD and SEM. The characterization results indicated that the magnetite is fully developed at 1200°C by a multi-step solid state reaction between the mixed oxides produced after the resin heating (α- Fe2O3 and nickel-iron spinel). The particles have a polygonal morphology and are softly agglomerate. Their grain size vary with de manganese content and is about 1 micron for 0.25Mn in the mixed ferrite composition and 10 micron in the mixed ferrite without nickel. The activation endothermic step eventually resulting in an oxygen-deficient ferrite was carried out within a thermogravimetric balance. The TGA/DTA mixed magnetite analysis carried out with nitrogen as inert carrier gas showed a weight loss that can be attributed to the partial reduction of the magnetite. The weight losses and the activation temperature increases when the Ni/Mn ratio decreases, being 0.5% at 700°C and 2.57% at 900°C for Ni/Mn ratio 3 and 0 respectively. A series of experimental tests will follow at laboratory test facility with indirect and direct illumination, in order to select the most adequate operation conditions and to quantify the maximum cycle efficiency for a solarized process.
Development of an Alternative Energy System For Use as an Active Learning Platform
Authors: Mindek Richard B. , Rickis Aaron F. , Dini Said
Published: February 2009

A demonstration system that employs solar and wind energy to power a fuel cell was recently developed as part of a senior capstone design project. This system demonstrates the essential components of a completely renewable hydrogen recovery system. Using the renewable energy produced from a 80-watt photovoltaic solar panel and a 60-watt wind turbine, an electrolyzer, rated at 65 cm3 per minute, disassociates water into its components of hydrogen and oxygen. The hydrogen and oxygen are then recombined into water by the fuel cell, which produces electricity and releases heat in the process. The electricity is used to power a cooling fan installed in the system. The entire system, which is mounted on a mobile cabinet for easy transportability, and to facilitate outdoor testing, includes a control box to regulate the voltage and current into the electrolyzer, as well as a variable resistance box to test and demonstrate the energy efficiencies of the solar panel, wind turbine, electrolyzer, and fuel cell. It was recently incorporated as part of three separate active learning laboratories within a graduate course on alternative and renewable energy. The laboratories allow students to discover the theoretical and practical application of solar energy, wind energy, and fuel cells. This paper describes the development, operation and capability of the alternative energy demonstration system, as well as its utilization in developing the graduate laboratories. Plans for implementing the system in the undergraduate engineering curriculum are also discussed.
Terminal Box Minimum Airflow Optimization of Single Duct Air Handling Units
Authors: Cho YoungHum , Wang Gang , Liu Mingsheng
Published: February 2009

Terminal boxes control space conditions in variable air volume (VAV) air-handling unit (AHU) systems. Terminal boxes either modulate airflow with a control damper or adjust discharge air temperature with a reheat coil. Terminal boxes will have a significant amount of simultaneous heating and cooling and AHUs will consume more fan power if the minimum airflow is higher than required. On the other hand, conditioned space will have indoor air quality (IAQ) problems with less air circulation if the minimum airflow is less than required. The objective of this study is to optimize the minimum airflow ratio to improve thermal environment and save energy consumption. In this study, the problem of current fixed minimum airflow ratio of terminal box is analyzed and variable minimum airflow ratio as an alternative is suggested. The results of this study show that variable minimum airflow ratio can stably maintain the set room air temperature and reduce energy consumption for varying heating loads compared to the conventional fixed minimum airflow ratio.
Fabrication of Porous Calcium Oxide Film for UT-3 Thermochemical Hydrogen Production Cycle
Authors: Lee Man Su , Goswami D. Yogi , Kothurkar Nikhil , Stefanakos Elias K.
Published: February 2009

UT-3 thermochemical hydrogen production cycle has been studied, both theoretically and experimentally, and is one of the very few cycles studied on a pilot plant scale. The maximum operating temperature in this cycle is relatively lower than the temperatures in other cycles. Another advantage of this cycle is that it is comprised of four gas-solid reactions which simplify product separation. Although the cycle has several such advantages, one of the significant issues is the development of solid reactants that are chemically reactive and physically stable in cyclic operations between oxide and bromide forms, which have considerably different molar volumes. Acceleration of reaction rate as well as longer cyclic life time and durability of the solid reactant are important keys for the practicability of the cycle. Additionally, a simpler preparation step of the reactant is preferable. Therefore, in order to increase the surface area of the calcium oxide reactant and maintain reactivity as well as structure in cyclic transformations, porous calcium oxide films have been examined as candidates. The calcium oxide precursor was prepared by sol-gel chemistry following a metal alkoxide process and the film was fabricated by a dip coating procedure. The characterization of the calcium oxide film such as the structural changes in the film and compositional conversions due to the bromination reaction has been performed using SEM and EDS. Based on a preliminary experimental analysis as well as the advantages of a film type reactant, one can conclude that the calcium oxide film may be a feasible alternative to a pellet-type reactant.
Development of Standardized Domestic Hot Water Event Schedules for Residential Buildings
Authors: Hendron Robert , Burch Jay
Published: February 2009

The Building America Research Benchmark is a standard house definition created as a point of reference for tracking progress toward multi-year energy savings targets. As part of its development, the National Renewable Energy Laboratory (NREL) has established a set of domestic hot water events to be used in conjunction with sub-hourly analysis of advanced hot water systems. In certain applications (including analysis of recirculation loops, distribution losses, tankless gas water heaters, and solar hot water systems with load-side heat exchangers) energy use can be strongly affected by event flow rate, duration, frequency, clustering, and time of occurrence. High-level constraints on mains temperature and average daily hot water use, along with detailed event characteristics derived from past research and a software tool developed by Kassel University in Germany, were used to generate hot water events over one year for houses of different sizes in various locations. The events were established in 6-min increments for showers, baths, sinks, clothes washers, and dishwashers. Flow rates and times of occurrence varied randomly based on specified probability distributions. The final event schedules reflected the same daily variability as an actual household, thereby providing more realism to energy simulations involving advanced water heating systems.
Optimal Pump Speed Control in a Chilled Water System
Authors: Zheng Bin , Liu Mingsheng
Published: February 2009

Traditionally, chilled water pump speed is modulated to maintain the water loop differential pressure set point and the control valve at the air handling unit (AHU) is modulated to maintain the supply air temperature. This paper introduces a new VFD pump speed control algorithm, optimal pump head control strategy. The algorithm focuses on minimizing the water loop differential pressure in order to reduce the overall pump energy consumption. The new algorithm is implemented in a real chilled water system. The pump power consumption is compared between the traditional algorithm and new algorithm. The implementing result demonstrates that the new algorithm results in improved pump efficiency, reduced pump head and pump speed and remarkable energy savings.
Dry Methane Reforming in a Directly Irradiated Solar Particle Reactor Without a Metal Catalyst
Authors: Klein Hanna Helena , Karni Jacob , Rubin Rachamim
Published: February 2009

Methane reforming with carbon dioxide in a directly irradiated particle receiver seeded with carbon black is presented in this study. Carbon particles were entrained in the reacting gases and acted as heat transfer and reaction surface. The reactions were not catalyzed by a metal catalyst. The molar ratio between the entrained carbon particles and the working gases (Ar, CO2 and CH4) was 4–7 mmol carbon/mol gas. The temperature of the reforming experiments varied from 900°C to 1450°C with CO2/CH4 ratios of 2–6. Experimental results show that methane reacts at lower temperatures than expected for its thermal decomposition; this indicates that the decomposing reaction is enhanced by the presence of the carbon black particles. At 1170°C 90% of the methane reacted in the receiver during a residence time of 0.3 s. The reaction between carbon dioxide and carbon black is faster than is documented in the literature, but the reaction rate does not seem to change if only carbon dioxide and carbon black are present in the receiver, compared to experiments where methane is also part of the gas mixture. The experimental results indicate that a high solar flux, i.e., about 2500 kW/m2 or higher, significantly accelerates the reaction rate of methane decomposition. Total or partial blockage of the solar radiation reduced the yield by about 50%, compared to tests when the receiver was exposed to the full solar radiation flux, at the same operating temperature.
Numerical Analysis of the Heat Transfer in Passive Solar Composite Wall Collectors System With Porous Absorber
Authors: Chen Wei
Published: February 2009

In this paper, heat transfer and flow in the composite solar wall with porous absorber has been studied. The unsteady numerical simulation is employed to analyze the performance of the flow and temperature field in the composite solar wall. The excess heat is stored within the porous absorber during solar radiation and there is stratification in the porous layer. So, the porous absorber works as thermal insulator in a degree when no solar shining is available. The heating characteristic of two types of the composite solar wall with porous absorber has been conducted. The influence of particle size, porosity and porous absorber arrange in the solar composite wall on the heating room temperature is significant. The results show that all these factors should be taken into account for a better design of a heating system.
Parabolic Trough Receiver Thermal Testing
Authors: Burkholder Frank , Brandemuehl Michael , Price Henry , Netter Judy , Kutscher Chuck , Wolfrum Ed
Published: February 2009

NREL has fabricated a parabolic trough receiver thermal loss test stand to quantify parabolic receiver off-sun steadystate heat loss. At an operating temperature of 400°C, measurements on Solel UVAC2 and Schott PTR70 receivers suggest off-sun thermal losses of approximately 370 W/m receiver length. For comparison, a receiver from the field with hydrogen in its annulus loses approximately 1000 W/m receiver length. The UVAC2 heat loss results agree within measurement uncertainty to previously published data, while the PTR70 results are somewhat higher than previously published data. The sensitivity of several receiver performance parameters is considered and it is concluded that differences in indoor and outdoor testing cannot account for the difference in PTR70 thermal loss results.
Experimental Investigation of the SO2 Abatement Capacity of South African Calcium-Based Materials
Authors: Siagi Zachary O. , Mbarawa Makame
Published: February 2009

One of the most important steps in the wet limestone-gypsum flue gas desulphurization (WFGD) process is CaCO3 dissolution, which provides the dissolved alkalinity necessary for SO2 absorption. Accurately evaluating the CaCO3 dissolution rate is important in the design and efficient operation of WFGD plants. In the present work, the dissolution of limestone from different sources in South Africa has been studied in a pH-stat apparatus under conditions similar to those encountered in wet FGD processes. The influence of various parameters such as the reaction temperature (30 ≤ T ≤ 70°C), CaCO3 particle size (25 ≤ dp ≤ 63μm), solution acidity (4 ≤ pH ≤ 6), and chemical composition were studied in order to determine the kinetics of CaCO3 dissolution. The results obtained indicate that the dissolution rate increased with a decrease in particle size and an increase in temperature. The dissolution curves were evaluated in order to test the shrinking core model for fluid–solid systems. The analysis indicated that the dissolution of CaCO3 was controlled by chemical reaction, i.e. 1 − (1 − X)1/3 = kt.
Numerical Simulation of Air Distribution in a Residential Building With Capillary Plane HVAC Terminal System
Authors: Bing Wei , Lu Jiang , Li Li , Wang Zhiwei
Published: February 2009

Nowadays the capillary plane HVAC terminal system as an advanced terminal air conditioning system is being widely used. It has many advantages such as thermal comfort, energy conservation and saving indoor space etc. In this paper, with the example of a typical residential room where the capillary plane HVAC terminal system is installed, the indoor thermal environment is simulated and the influence of different capillary mat placement modes is analyzed, three operating modes in summer and winter are simulated by using the method of CFD, and the corresponding temperature fields are presented. Based on the simulation results, the temperature fields are appraised from the view of thermal comfort. These will be good references to the design and application of the capillary plane HVAC terminal system.
Improving the Efficiency of the Advanced Injection Low Pilot Ignited Natural Gas Engine Using Organic Rankine Cycles
Authors: Srinivasan K. K. , Mago P. J. , Zdaniuk G. J. , Chamra L. M. , Midkiff K. C.
Published: February 2009

Intense energy security debates amidst the ever increasing demand for energy in the country have provided sufficient impetus to investigate alternative and sustainable energy sources to the current fossil fuel driven economy. This paper presents the Advanced injection Low Pilot Ignition Natural Gas (ALPING) engine as a viable, efficient and low emissions alternative to conventional diesel engines, and discusses further efficiency improvements to the base ALPING engine using Organic Rankine Cycles (ORC) as bottoming cycles. The ALPING engine uses very small diesel pilots, injected early in the compression stroke to compression-ignite a premixed natural gas–air mixture. It is believed that the advanced injection of the higher cetane diesel fuel leads to longer incylinder residence times for the diesel droplets, thereby resulting in distributed ignition at multiple spatial locations, followed by lean combustion of the higher octane natural gas fuel via localized flame propagation. The multiple ignition centers result in faster combustion rates and higher fuel conversion efficiencies. The lean combustion of natural gas leads to reduction in local temperatures and oxides of nitrogen (NOx) emissions, since NOx emissions scale with local temperatures. In addition, the lean combustion of natural gas is expected to produce very little particulate matter (PM) emissions (not measured). Representative baseline ALPING (60° BTDC pilot injection timing) (without the ORC) half load (1700 rev/min, 21 kW) operation efficiencies reported in this study are about 35 percent while the corresponding NOx emissions is about 0.02 g/kWh, which is much lower than EPA 2007 tier 4 heavy duty diesel engine statutes of 0.2 g/kWh. Furthermore, the possibility of improving fuel conversion efficiency at half load operation with Organic Rankine Cycles using “dry fluids” are discussed. Dry organic fluids, due to their lower critical points, make excellent choices for bottoming Rankine cycles. Moreover, previous studies indicate that “dry fluids” are more preferable compared to wet fluids because the need to superheat the fluid to extract work from the turbine is eliminated. It is estimated that ORC–turbocompounding results in fuel conversion efficiency improvements of the order of 10 percent while maintaining the essential low NOx characteristics of ALPING combustion.
Solar Dish Field System Model for Spacing Optimization
Authors: Igo John , Andraka Charles E.
Published: February 2009

Dish Stirling power generation systems have been identified by DOE, Sandia National Laboratories, and Stirling Energy Systems (SES) as having the capability of delivering utility-scale renewable energy to the nation’s electrical grid. SES has proposed large plants, 20,000 units or more (0.5 GW rated power) in one place, in order to rapidly ramp up production automation. With the large capital investment needed in such a plant it becomes critical to optimize the system at the field level, as well as at the individual unit level. In this new software model, we provide a tool that predicts the annual and monthly energy performance of a field of dishes, in particular taking into account the impact of dish-to-dish shading on the energy and revenue streams. The Excel-based model goes beyond prior models in that it incorporates the true dish shape (flexible to accommodate many dish designs), multiple-row shading, and a revenue stream model that incorporates time-of-day and time-of-year pricing. This last feature is critical to understanding key shading tradeoffs on a financial basis. The model uses TMY or 15-minute meteorological data for the selected location. It can incorporate local ground slope across the plant, as well as stagger between the rows of dish systems. It also incorporates field-edge effects, which can be significant on smaller plants. It also incorporates factors for measured degraded performance due to shading. This tool provides one aspect of the decision process for fielding many systems, and must be combined with land costs, copper layout and costs, and O&M predictions (driving distance issues) in order to optimize the loss of power due to shading against the added expense of a larger spatial array. Considering only the energy and revenue stream, the model indicates that a rectangular, unstaggered field layout maximizes field performance. We also found that recognizing and accounting for true performance degradation due to shading significantly impacts plant production, compared with prior modeling attempts.
Novel Parabolic Trough Collectors Driving a Small-Scale Organic Rankine Cycle System
Authors: Kohlenbach P. , McEvoy S. , Stein W. , Burton A. , Wong K. , Lovegrove K. , Burgess G. , Joe W. , Coventry J.
Published: February 2009

This paper presents component performance results of a new parabolic trough collector array driving an organic Rankine cycle (ORC) power generation system. The system has been installed in the National Solar Energy Centre at CSIRO Energy Technology in Newcastle, NSW, Australia. It consists of four rows of 18 parabolic mirrors each in a 2×2 matrix with a total aperture area of approximately 132m2. The absorber tube is a laterally aligned, 40mm copper tube coated with a semi-selective paint and enclosed in a 50mm non-evacuated glass tube to reduce convection losses. The mirror modules, which are light-weight and robust, are made from thin low iron back silvered glass bonded to a sheet steel substrate. They are supported by a box truss on semi circular hoops running on rollers for single axis tracking. The mirror design has been chosen to allow low-cost manufacturing as well as simple commissioning and operation. The ORC unit is a FP6 unit sourced from Freepower Ltd. with a net power output of 6kWel at 180°C inlet temperature and a total heat input of 70 kWth. It uses a two-stage expansion process with hydrofluoroether as the working fluid. A wet cooling tower is used to dissipate the reject heat from the ORC. The two key components of the envisioned system are the trough reflector/receiver and the ORC unit. The optical performance of the mirror elements was investigated with regard to the flux mapping onto the receiver tube. The ORC unit has been tested separately using an electrical oil heater as the heat source. This paper presents results for irradiation capture and intensity over the receiver width of a single trough mirror module. The complete system including trough collectors and ORC has not been in transient operation yet, thus experimental steady-state results of the ORC unit are presented.
Modelling and Control of a Solar-Thermal Parabolic Trough DSG Superheater With Several Parallel Rows and Central Steam Separation
Authors: Koch Stephan , Eck Markus , Hirsch Tobias
Published: February 2009

In this paper, a solar-thermal parabolic trough power plant with direct steam generation (DSG) is investigated with respect to the controllability of the superheating section in a commercial-scale facility with several parallel collector rows. The plant is operated in recirculation mode which has been proven to provide a good live steam quality under changing operating conditions in single-row systems. In a multiple-row collector field, the separation of the remaining water at the end of the evaporator can be achieved by using one central or several distributed separators. Central separation, which will be investigated in this work, appears to be the superior concept. The article proposes a decentralized adaptive proportional-integral (PI) control approach together with a static output mapping for the control valves at the end of the superheating section. The section is fed by a single saturated steam mass flow which has to be distributed on the parallel superheater rows. Together with the individually controlled injection coolers in each row, the distribution control enables the solar field to provide the power block with a reliable steam temperature in the presence of significant local irradiance and input mass flow transients induced by varying solar intensity during the day and passing clouds.
Wind Induced Heat Transfer Coefficient From Flat Horizontal Surfaces Exposed to Solar Radiation
Authors: Mullick Subhash C. , Kumar Suresh , Chourasia Basant K.
Published: February 2009

Upward heat losses have strong effect on the performance of flat plate solar collectors under different operating conditions. Suitable equations for estimation of top heat loss coefficient have already been proposed [1,2]. The top heat loss coefficient is a function of wind induced convective heat transfer coefficient in a flat plate solar collector. It is, therefore, important to choose appropriate values of this convective heat transfer coefficient for correct estimation of the top heat loss coefficient. Researchers [3–6] have suggested different wind speed based correlations for estimation of the wind induced convective heat transfer coefficient. These correlations give different values of wind heat transfer coefficient thus resulting in variation in values of the top heat loss coefficient of a solar collector under same operating conditions. In present study, an attempt has been made to measure and study the wind induced convective heat transfer coefficient from exposed flat horizontal surfaces in real wind. For this purpose, three unglazed test plates of similar construction and different sizes were employed. Experiments were conducted on the three test plates over rooftop of a building in built environment. From experimental data of the test plate, of size 925mm × 865mm × 2mm, a correlation between wind heat transfer coefficient and wind speed has been obtained by linear regression. The obtained correlation has also been compared with work of other researchers [3–6]. Results obtained from experimental data of the three test plates provide some interesting information about wind induced convective heat transfer coefficient.
Numerical Simulation of Turbulent Biogas Combustion
Authors: Yan Beibei , Bai Xuesong , Chen Guanyi , Liu Changye
Published: February 2009

Operating parameters are considered important for the biogas combustion process and the resulted flame features. The paper investigated the influence of typical parameters through numerical simulation, which include the dimension of combustor, fuel and air mass flow, and secondary air supply. The results from the simulations show that the biogas combustion behaves, to some extent, similarly to the methane combustion, yet significant differences exist between their flames. The combustion process is fairly sensitive to the geometrical and operational parameters. Biogas flame temperature is even lower compared to the methane flame temperature because biogas contains CO2 resulting in low heating value, therefore it is not straightforward to obtain stable combustion. Preheated secondary air or reduced its mass flow may have to be used in this case.
Comparison and Optimization of Heliostat Canting Methods
Authors: Buck R. , Teufel E.
Published: February 2009

Heliostat canting (alignment of mirror facets) is known to have a major influence on the optical efficiency of heliostat fields and therefore on the power output of solar tower plants. In recent years several canting concepts were used, mainly on- and off-axis canting. Several new canting concepts, like stretched-parabolic or target aligned canting, were proposed in order to improve the performance of heliostats. As solar power plants become economically more attractive, knowledge about the influence of canting becomes more important. In this context, the influence of several factors on the canting method is discussed and optimal canting strategies are described. The considered factors comprise plant power level, heliostat position in the field, heliostat area, receiver dimension and site latitude. It is concluded that the target aligned tracking method is superior to all other variants in the majority of cases. As for the standard azimuth-elevation tracking methods, no one of these exhibits a clear advantage. It is only the on-axis method that performs worst in all cases.
Current and Future Economics of Parabolic Trough Technology
Authors: Price Henry , Mehos Mark , Kutscher Chuck , Blair Nate
Published: February 2009

Solar energy is the largest energy resource on the planet. Unfortunately, it is largely untapped at present, in part because sunlight is a very diffuse energy source. Concentrating solar power (CSP) systems use low cost reflectors to concentrate the sun’s energy to allow it to be used more effectively. Concentrating solar power systems are also well suited for large solar power plants that can be connected into the existing utility infrastructure. These two facts mean that CSP systems can be used to make a meaningful difference in energy supply in a relatively short period. CSP plants are best suited for the arid climates in the Southwestern United States, Northern Mexico, and many desert regions around the globe. A recent Western Governors’ Association siting study [1] found that the solar potential in the U.S. Southwest is at least 4 times the total U.S. electric demand even after eliminating urban areas, environmentally sensitive areas, and all regions with a ground slope greater than 1%.While it is currently not practical to power the whole county from the desert southwest, only a small portion of this area is needed to make a substantial contribution to future U.S. electric needs. Many of the best sites are near existing high-voltage transmission lines and close to major power load centers in the Southwest (Los Angeles, Las Vegas, and Phoenix). In addition, the power provided by CSP technologies has strong coincidence with peak electric demand, especially in the Southwest where peak demand corresponds in large part to air conditioning loads. Parabolic troughs currently represent the most cost-effective CSP technology for developing large utility-scale solar electric power systems. These systems are also one of the most mature solar technologies, with commercial utility-scale plants that have been operating for over 20 years. In addition, substantial improvements have been made to the technology in recent years including improved efficiency and the addition of thermal energy storage. The main issue for parabolic trough technology is that the cost of electricity is still higher than the cost of electricity from conventional natural gas-fired power plants. Although higher natural gas prices are helping to substantially reduce the difference between the cost of electricity from solar and natural gas plants, in the near-term increased incentives such as the 30% Investment Tax Credit (ITC) are needed to make CSP technology approach competitiveness with natural gas power on a financial basis. In the longer term, additional reductions in the cost of the technology will be necessary. This paper looks at the near-term potential for parabolic trough technology to compete with conventional fossil power resources in the firm, intermediate load power market and at the longer term potential to compete in the baseload power market. The paper will consider the potential impact of a reduced carbon emissions future.
Thin Glass CSP Mirrors: “From Reflection to Concentration”
Authors: English Jeffrey D.
Published: February 2009

The goal for Concentrated Solar Power (CSP) mirror is not just reflection, but the complete capture and utilization of the entire solar spectrum. Solar radiation is emitted over a range of wavelengths, analytically measured between 250–2500 nm, to ensure maximum captivation. An effective solar mirror, utilized for concentrating this energy must be capable of maintaining a high level of reflectance, under adverse environmental conditions for a prolonged duration in a CSP system. Thin (1-mm) flat low-iron, silvered glass mirrors have been utilized for CSP applications for many years, but obstacles with respect to quality and durability have had to be overcome. Developments have improved the reflectance from averages in the low 90% range to averages between ∼96%–97%. The reflectance durability standard for utilization of mirror for solar applications requires a minimal reflective loss of less than 5% over a 15 year period in the field. The ultimate goal is to expand the solar mirror’s field life to 20–30 years, the life of a CSP system. Overcoming harsh accelerated testing parameters continues to be the focus, as these tests attempt to correlate the lifetime to actual field applications. Test chambers with elevated temperatures and humidity conditions continue to be the most severe, and results continually show dramatic improvement. Focus was drawn on the loss of spectral reflectance, as degradation was occurring at a rapid rate specifically with the lower wave spectra. Drawing on the expertise and direction of the National Renewable Energy Laboratory (NREL), CSP thin-glass mirrors are emerging to be a viable choice for solar concentration. Thinglass mirrors offer a low-weight, highly reflective option, that resists harsh weather conditions, including water and humidity variances along with surface contamination. Mirror coating advancements have exceeded the physical and chemical resistance properties of standard “off the shelf” mirror coating products to precise, industry specific components. This study will review the obstacles and highlight the progress that has led to the success of the thin-glass mirror CSP market. A compilation of test results from NREL and other analytical, laboratories along with the collaboration of mirror manufacturing expertise from a vast knowledge base in the chemically plated mirror industry. It is the primary focus of the industry to continue to strive for a superior quality concentrating mirror while making it economically viable to the solar industry.