bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of Flexible CO2 Capture Over an Investment Life Using a Dynamic Electric Grid Model
Authors: Fyffe John R. , Cohen Stuart M. , Webber Michael E. , Rochelle Gary T.
Published: January 2011

Global focus on greenhouse gas emissions has led the United State’s legislature to discuss various strategies to reduce carbon dioxide (CO2) emissions. With coal-fired plants responsible for roughly half of United States (U.S.) electricity generation and approximately 30% of the nation’s CO2 emissions, coal-fired plants will be largely affected by any future CO2 emission regulations. However, coal-based generation could continue to meet our electricity demands while complying with future CO2 emissions restrictions with the addition of carbon dioxide capture and sequestration (CCS) technology. Most studies of CCS systems have demonstrated a permanent energy requirement of 11–40% of a plant’s output when operating continuously at a 90% CO2 removal rate. This study, however, used a dynamic model of the Electric Reliability Council of Texas (ERCOT) electric grid to consider post-combustion CO2 capture systems that can operate flexibly. Post-combustion CO2 capture systems using chemical absorption and stripping are particularly suited for retrofitting existing plants and operating in a flexible manner. Flexible carbon capture allows plant operators to vary the energy used for CO2 capture and compression in order to regain this generation capacity when desirable. Thus, flexibility can be used to choose the CO2 capture rate that allows the most economical combination of operating costs, electricity price, and output levels. Furthermore, operating at lower CO2 capture energy requirement levels and increasing output capacity during peak demand periods could dramatically reduce the amount of replacement capacity needed to replace potential output lost when CO2 capture systems are in operation. This research uses an existing modeling framework of a dynamic hourly dispatch system to study the economic, environmental, and performance implications of flexible CO2 capture over an investment lifetime. The effects of CO2 prices, natural gas fuel prices, and replacement capacity costs were analyzed along with various operating strategies. The fuel mixture behavior and emissions effects are presented, showing that large emissions reductions can be achieved using the current ERCOT plant fleet with the addition of flexible CO2 capture. An annual system-level cash-flow analysis is used to determine a net present value (NPV) for a group of CO2 capture plants under a range of possible replacement capacity costs. If replacement capacity costs are accounted for, flexibility can improve the NPV of a CO2 capture investment by substantially lowering the associated capital costs to replace output lost to CO2 capture energy requirements.
Feasibility of Wind Power for Brackish Groundwater Desalination: A Case Study of the Energy-Water Nexus in Texas
Authors: Stillwell Ashlynn S. , Webber Michael E.
Published: January 2011

With dwindling water supplies and the impacts of climate change, many cities are turning to water sources previously considered unusable. One such source for inland cities is brackish groundwater. With prolonged drought throughout Texas, cities such as El Paso, Lubbock, and San Antonio are desalinating brackish groundwater to supplement existing water sources. Similar projects are under consideration elsewhere in Texas. While brackish groundwater contains fewer total dissolved solids than seawater, desalination of brackish groundwater is still an energy-intensive process. Brackish water desalination using reverse osmosis, the most common desalination membrane treatment process, consumes 20 to 40 times more energy than traditional surface water treatment using local water sources. This additional energy consumption leads to increased carbon emissions when using fossil fuel-generated electricity. As a result of concern over greenhouse gas emissions from additional energy consumption, some desalination plants are powered by wind-generated electricity. West Texas is a prime area for desalination of brackish groundwater using wind power, since both wind and brackish groundwater resources are abundant in the area. Most of the Texas Panhandle and Plains region has wind resource potential classified as Class 3 or higher. Additionally, brackish groundwater is found at depths less than 150 m in most of west Texas. This combination of wind and brackish groundwater resources presents opportunities for the production of alternative drinking water supplies without severe carbon emissions. Additionally, since membrane treatment is not required to operate continuously, desalination matches well with variable wind power. Implementing a brackish groundwater desalination project using wind-generated electricity requires economic feasibility, in addition to the geographic availability of the two resources. Using capital and operating cost data for wind turbines and desalination membranes, we conducted a thermoeconomic analysis for three parameters: 1) transmission and transport, 2) geographic proximity, and 3) aquifer volume. Our first parameter analyzes the cost effectiveness of tradeoffs between building infrastructure to transmit wind-generated electricity to the desalination facility versus pipelines to transport brackish groundwater to the wind turbines. Secondly, we estimate the maximum distance between the wind turbines and brackish groundwater at which desalination using wind power remains economically feasible. Finally, we estimate the minimum available brackish aquifer volume necessary to make such a project profitable. Our analysis illustrates a potential drinking water option for Texas (and other parts of the world with similar conditions) using renewable energy to treat previously unusable water. Harnessing these two resources in an economically efficient manner may help reduce future strain on the energy-water nexus.
Daily Exergy Assessment of LiBr-Water Absorption Chiller Used for Solar Cooling
Authors: Onan Cenk , O¨zkan Derya B.
Published: January 2011

In today’s society in which energy costs are high, the use of renewable energy sources has gained importance in cooling and heating systems. In recent years, solar cooling, which is a type of renewable energy source, is increasing rapidly in use in Europe. A solar assisted absorption cooling system was designed for acclimatizing villas in Mardin, Turkey, and the performance of the system under different temperatures was analyzed using Matlab. The cooling load of the villas was calculated assuming a cooling season of May 15 to September 15. The cooling capacity was calculated to be 106 kW. Changes in the coefficient of performance, the capacity of the hot water driven absorption cooling system and the exergy destruction values of the system according to our country’s meteorological data were calculated using Matlab. The amounts of inlet and outlet exergy were calculated separately for each component. Calculations were performed for two dead state temperatures: 25 °C and the environmental temperature, which is a more realistic approach. Therefore, the effect of varying the dead state temperature on the results was determined. It is observed that the greatest source of exergy destruction in the system was the solar collectors and the second greatest source of exergy destruction was the generator. The hourly distributions of exergy destruction values are given in a table. The effects of environmental temperature and solar insulation were stated for the optimization of energy and exergy in the combined system, which are planned to be established.
Numerical Modeling of Turbulent Natural Convection in a Concentrating Photovoltaic System
Authors: Ahsan K. M. Nazmul , Boehm Robert F. , Chen Yitung , Nie Jianhu
Published: January 2011

A Concentrating Photovoltaic (CPV) system arranged in an asymmetrically heated inclined parallel plate configuration is numerically simulated to investigate the turbulent natural convection inside the system. The flow is induced by the thermal buoyancy force. A low-Reynolds-number k-ε model with modified near wall functions from the Yang-Shih turbulence model has been adapted to numerically solve transport equations for k and ε. The model predictions are validated with available numerical and experimental data given in the literature. The comparison with the published data indicates a good agreement. The calculations are performed for asymmetric heating and assuming the fixed value for CPV cell temperature. The aspect ratio (L/W) and Rayleigh number are kept constant at 36.75 and 2.49×108 respectively. The current study is focused on evaluating the impact of variation of channel inclination and Nusselt number on the thermal profile inside the CPV system.
A Scalable, Economical, Uninterrupted Solar Thermal Power System
Authors: Bartlett Brent R. , D’Orsi Nicholas C. , Hobson Chip , McGeoch Bruce , Whitaker Edward , Torrey David A.
Published: January 2011

Recent years have seen a surge of interest in renewable energy sources. Most renewable energy sources are intermittent in their production of power. One solution is to store the energy and draw from that stored energy in a controlled fashion. Recent advances have been made in solar thermal storage that would allow a solar thermal power system to operate year round and around the clock at nearly constant levels of electrical power production. This paper outlines how this can be accomplished.
Preliminary Analysis of a 100-kWth Mini-Tower Solar Field With an Integrated Optical Waveguide Receiver for Solar Chemistry
Authors: Gonzalez Aurelio , Gonzalez-Aguilar Jose , Romero Manuel
Published: January 2011

Solar-driven thermochemical hydrogen production, CO2 abatement technologies and production of solar fuels and chemicals in general, are candidates in the near future to be scaled-up at solar thermal concentrating facilities in the framework of demonstration projects. Chemical demonstrators undoubtedly will be more demanding in terms of temperature and solar flux than current applications oriented to electricity production. Some of the more promising H2 production technologies are already in the position to scaling reactors up to the 1-MWth level. Demonstration scale useful to develop new solar chemistry processes usually considers input thermal powers between 100 kWth and 1,000 kWth. In this range, the best option is making use of mini-towers with heliostat fields. Then, the challenge is to efficiently introduce high fluxes (above 2,000 kW/m2) with a small field of heliostats in solar chemical reactors (usually requiring high temperatures, above 1,000 °C, and high pressures). In order to overcome it, some authors have proposed the use of light waveguides collecting systems for directing concentrated solar light towards a reactor cavity (1, 2, and 3). This solution makes possible the use of a large variety of reactor geometries and to guarantee the reactor tightness even working at high pressures. However it becomes the critical component of the plant design since it largely governs the facility efficiency and configuration due to its optical properties. This work presents the design of a 100-kWth demonstration plant placed in Mo´stoles, Spain (40° 20′ N, 3° 52′ W) with the concepts mentioned above, in which the light waveguide system is formed by a set of units that are composed by a secondary concentrator and a bundle of optical fibers. This study has paid special attention to optical performances of the facility by analyzing the coupling between solar heliostats field layout and the solar receiver composed by light waveguides. In addition, the paper provides information on sizing, efficiencies and expected investment cost based on light waveguides specifications.
Human Power Generation in Fitness Facilities
Authors: Haji Maha N. , Lau Kimberly , Agogino Alice M.
Published: January 2011

As energy usage across the world continues to rise, there is a strong need to develop new methods for energy conservation and power generation, particularly approaches that have less environmental impacts. Although human power is not ideal in terms of life cycle costs [1], there are promising application areas for human power in emerging regions where electric power is either not available or not affordable [2]. There is also untapped potential for harnessing human power at most fitness facilities. This paper focuses on the feasibility of capturing this energy at fitness facilities, particularly the Recreational Sports Facility (RSF) at University of California, Berkeley, which averages over 2,800 patrons per day. In particular, we estimated that patrons using 28 elliptical machines would supply approximately 10,000 kWh into the electric grid over a year. This amounts to only 0.7% of the RSF’s total energy needs, but is valuable nonetheless. An additional benefit in human power generation is its positive social impact. A survey of the RSF users has evinced remarkable enthusiasm for implementing energy generation technology into the facility, both as a power generation tool and as an educational resource. This paper will also address the social benefits of human power generation technology in the gym.
Renewable Hydrogen From the Zn/ZnO Solar Thermochemical Cycle: A Cost and Policy Analysis
Authors: Haltiwanger Julia F. , Davidson Jane H. , Wilson Elizabeth J.
Published: January 2011

Flexible energy carriers are a crucial element of our energy portfolio. In a future in which a significant fraction of our energy comes from renewable sources, renewably produced fuels will be vital. The zinc/zinc-oxide thermochemical redox cycle is one approach for producing hydrogen using solar energy. This paper explores the level of carbon taxation necessary to make the cycle competitive with hydrogen production via methane reforming. In addition, the time frame for economic viability is assessed through the use of experience curves under minimal input, mid-range, and aggressive incentive policy scenarios. Prior work projects that hydrogen produced by the zinc/zinc-oxide cycle will cost between $5.02 and $14.75/kg, compared to $2.40 to $3.60/kg for steam methane reforming. Overcoming this cost difference would require a carbon tax of $119 to $987/tCO2, which is significantly higher than is likely to be implemented in most countries. For the technology to become cost competitive, incentive policies that lead to early implementation of solar hydrogen plants will be necessary to allow the experience effect to draw down the price. Under such policies, a learning curve analysis suggests that hydrogen produced via the Zn/ZnO cycle could become economically viable between 2032 and 2069, depending on how aggressively the policies encourage the emerging technology. Thus, the Zn/ZnO cycle has the potential to be economically viable by mid-century if incentive policies—such as direct financial support, purchase guarantees, low interest rate loans, and tax breaks—are used to support initial projects.
Waste Heat Use Through Microfabrication and Micro System Development
Authors: Hemphill H. , Maharjan S. , Fang J. , Weiss L.
Published: January 2011

To effectively harvest waste heat from larger devices, a MEMS-based boiler is fabricated to boil working fluids for use in a low temperature steam system. The boiler is designed and fabricated to collect waste heat and drive working fluid phase change through novel microstructures. This boiled working fluid can then be made available for expansion by other MEMS-based components like piezoelectric membranes or cantilevers. Two different boiler designs are studied and compared in these experiments. Both designs rely on capillary channels to pump working fluid from surrounding reservoirs out across heated boiling surfaces. First, a baseline silicon device is fabricated using standard RIE techniques to produce silicon capillary channels. Channel widths of 300 and 100 μm are studied with maximum aspect ratios of 1:1. Improved aspect ratio capillary channels are investigated through the use of SU-8 polymer structures. The maximum aspect ratios of the SU-8 based channels are 20:1 with channel widths down to 10 μm. SU-8 based boilers deliver improved performance compared to their silicon counterparts. The maximum mass transfer rate was 4.49 mg/s for SU-8 channels with 20:1 aspect ratios. By contrast, the maximum mass transfer rate was 3.18 mg/s for silicon capillary channels with 1:1 aspect ratios. Working fluids like 3M™ HFE 7200 are used in these experiments.
A Free and Open Source Monte Carlo Ray Tracing Program for Concentrating Solar Energy Research
Authors: Petrasch Jo¨rg
Published: January 2011

A free and open source Monte Carlo ray-tracing program for concentrating solar energy research and development is presented. The program uses non energy partitioning Monte Carlo methods to model radiative exchange between arbitrarily arranged surfaces. Surface models include concentrating geometries, such as spherical, parabolic, and elliptical concentrators as well as compound parabolic concentrators. The program’s modular design allows implementation of additional surface and source models. The program has been thoroughly tested and experimentally validated. It has been used to model several concentrating devices including PSI’s high flux solar furnace and ETH’s high flux solar simulator. Furthermore, it has been used to design PSI’s high flux solar simulator and UFL’s high flux solar simulator. The code is particularly suited to provide radiative boundary conditions for numerical models of high temperature solar receivers and solar thermochemical reactors.
Integrated Biomass Gasification Small-Scale Combined Cycle Distributed Generation Plant With Microturbine and ORC
Authors: Kalina Jacek
Published: January 2011

The objective of this work is to evaluate thermodynamic and economic performance of a small-scale combined cycle plant with microturbine and ORC. The primary source of fuel for the plant is wood. The biomass is converted into a gaseous fuel by means of gasification in a downdraft fixed bed reactor. Size of the plant is limited to 350 kg/h of wet biomass input into the gasifier. Two alternative configurations of the bottoming ORC cycle are taken into account: single stage cycle and cascade cycle. In the first case R123 and n-pentane are analyzed as potential working fluids. In the cascade cycle toluene and n-pentane are selected for top and bottom cycle respectively. Electricity generation efficiency of the proposed small-scale plant is at the level of 23%, that is comparable with direct combustion based systems of much higher electric output. An initial economic evaluation of a sample project gives an outlook on economic effectiveness, that nowadays is strongly dependent on stimulation measures for “green” electricity generation.
Revamping, Energy Efficiency and Exergy Analysis of an Existing Upstream Gas Treatment Facility
Authors: Margarone Michele , Magi Stefano , Gorla Giuseppe , Biffi Stefano , Siboni Paolo , Valenti Gianluca , Romano Matteo C. , Giuffrida Antonio , Negri Emanuele , Macchi Ennio
Published: January 2011

Surface oil and gas treatment facilities in service for decades are likely to be oversized due to the natural depletion of their reservoirs. Despite these plants might have been designed modularly, meaning they comprise multiple identical units serving the same task, such units operate often in conditions far from the design point and inefficiently. This work analyzes the revamping options of an existing upstream gas facility, which is chosen because representative of a wide set of plants. A flexible numerical model, implemented in the HYSYS environment and dynamically linked to an Excel spreadsheet, includes the performance maps of all turbo machineries and the main characteristics of the investigated modifications in order to run simulation for many gas input conditions and to predict the performance over a year of operation and for different possible future scenarios. The first objective is to assess economically the considered options, which shall be applied only if yielding short return times of the investment since the reservoir is mature. Moreover, all options are appreciated adopting a figure of merit, here defined, that compares the overall energy consumption to that calculated with state-of-the-art technologies. In addition, an exergy and an environmental analyses are executed.
Assessment of a Syngas-Diesel Dual Fuelled Compression Ignition Engine
Authors: Sahoo Bibhuti B. , Sahoo Niranjan , Saha Ujjwal K.
Published: January 2011

Synthesis gas (Syngas), a mixture of hydrogen and carbon monoxide, can be manufactured from natural gas, coal, petroleum, biomass, and even from organic wastes. It can substitute fossil diesel as an alternative gaseous fuel in compression ignition engines under dual fuel operation route. Experiments were conducted in a single cylinder, constant speed and direct injection diesel engine fuelled with syngas-diesel in dual fuel mode. The engine is designed to develop a power output of 5.2 kW at its rated speed of 1500 rpm under variable loads with inducted syngas fuel having H2 to CO ratio of 1:1 by volume. Diesel fuel as a pilot was injected into the engine in the conventional manner. The diesel engine was run at varying loads of 20, 40, 60, 80 and 100%. The performance of dual fuel engine is assessed by parameters such as thermal efficiency, exhaust gas temperature, diesel replacement rate, gas flow rate, peak cylinder pressure, exhaust O2 and emissions like NOx, CO and HC. Dual fuel operation showed a decrease in brake thermal efficiency from 16.1% to a maximum of 20.92% at 80% load. The maximum diesel substitution by syngas was found 58.77% at minimum exhaust O2 availability condition of 80% engine load. The NOx level was reduced from 144 ppm to 103 ppm for syngas-diesel mode at the best efficiency point. Due to poor combustion efficiency of dual fuel operation, there were increases in CO and HC emissions throughout the range of engine test loads. The decrease in peak pressure causes the exhaust gas temperature to rise at all loads of dual fuel operation. The present investigation provides some useful indications of using syngas fuel in a diesel engine under dual fuel operation.
Main Street Net-Zero Energy Buildings: The Zero Energy Method in Concept and Practice
Authors: Torcellini Paul , Pless Shanti , Lobato Chad , Hootman Tom
Published: January 2011

Until recently, large-scale, cost-effective net-zero energy buildings (NZEBs) were thought to lie decades in the future. However, ongoing work at the National Renewable Energy Laboratory (NREL) indicates that NZEB status is both achievable and repeatable today. This paper presents a definition framework for classifying NZEBs and a real-life example that demonstrates how a large-scale office building can cost-effectively achieve net-zero energy. The vision of NZEBs is compelling. In theory, these highly energy-efficient buildings will produce, during a typical year, enough renewable energy to offset the energy they consume from the grid. The NREL NZEB definition framework classifies NZEBs according to the criteria being used to judge net-zero status and the way renewable energy is supplied to achieve that status. We use the new U.S. Department of Energy/NREL 220,000-ft2 Research Support Facilities (RSF) building to illustrate why a clear picture of NZEB definitions is important and how the framework provides a methodology for creating a cost-effective NZEB. The RSF, scheduled to open in June 2010, includes contractual commitments to deliver a Leadership in Energy Efficiency and Design (LEED) Platinum Rating, an energy use intensity of 25 kBtu/ft2 (half that of a typical LEED Platinum office building), and net-zero energy status. We will discuss the analysis method and cost tradeoffs that were performed throughout the design and build phases to meet these commitments and maintain construction costs at $259/ft2. We will discuss ways to achieve large-scale, replicable NZEB performance. Many passive and renewable energy strategies are utilized, including full daylighting, high-performance lighting, natural ventilation through operable windows, thermal mass, transpired solar collectors, radiant heating and cooling, and workstation configurations allow for maximum daylighting. This paper was prepared by the client and design teams, including Paul Torcellini, PhD, PE, Commercial Building Research Group Manager with NREL; Shanti Pless and Chad Lobato, Building Energy Efficiency Research Engineers with NREL; David Okada, PE, LEED AP, Associate with Stantec; and Tom Hootman, AIA, LEED AP, Director of Sustainability with RNL.
Experimentally Derived Arrhenius Coefficients for the Reaction Modeling of Fast Pyrolysis
Authors: Mayor J. Rhett , Williams Alexander
Published: January 2011

The search for fossil fuel alternatives has been one of increasing interest in recent years and one method which shows evidence of feasibility on a large scale is the production of bio-oil through the pyrolysis of biomass. In order to mathematically characterize biomass pyrolysis reactions for the purpose of process modeling, reaction descriptors in the form of Arrhenius coefficients are frequently utilized. Due to the complexity and inhomogeneity of biomass molecular structures, strictly analytically derived Arrhenius coefficients are not capable of predicting pyrolysis behaviors and outcomes. Typically thermogravimetric analysis (TGA) is employed as a method of extracting mass conversion data as a function of temperature from which bulk reaction descriptors following the form of Arrhenius reaction coefficients are derived. The preceding time and temperature history, however, will have a significant impact on the biomass conversion processes at each subsequent data point. This renders derived process predictors from TGA incapable of approximating fast pyrolysis reactions which have a markedly different time and temperature history than is seen utilizing TGA methods. Experimentally derived reaction descriptors of the Arrhenius form for the fast pyrolysis of biomass have been investigated utilizing a novel isothermal fast pyrolysis reactor. Multiple reaction durations and reaction temperatures for Pinus Taeda were tested resulting in measurements of biomass conversion. Reaction coefficients derived from the data are compared to coefficients derived utilizing TGA data and their predictions for mass conversion are contrasted.
Effect of Solids Removal From Dairy Manure Feedstock on Biogas Production in Anaerobic Digesters
Authors: Zemke Peter E. , Wood Byard D. , Rohleder Christopher R.
Published: January 2011

Many modern anaerobic digesters in developed countries consist of a digestion process in which solids are reduced to biogas, followed by mechanical separation that removes the majority of the remaining solids from the effluent. Experience has shown that such systems are often plagued with plugging due to excessive solids in the digester influent. Moreover, the mechanical separation equipment is prematurely degraded due to the elevated temperatures and corrosive compounds in the digester effluent. Reversing the order of separation and digestion offers a proven method of eliminating these problems, but at the expense of lower biogas production. The work presented in this paper quantifies this difference in biogas production by comparing the biogas yields of dairy wastewater feedstocks with and without prior mechanical solids separation through a 0.75-mm screen. Laboratory-scale batch digesters were operated up to 40 days at 35–40 °C and monitored for mass of volatile solids consumed and biogas production. Although the initially separated influent contained only half as much volatile solids, the ultimate biogas yield was only 25% less than that obtained with non-separated influent, demonstrating some tradeoff between higher energy production and system reliability.
Adaptive Geometry Wind Turbine Blades for Increasing Performance
Authors: Albanese Leonardo C. , Gandhi Farhan , Stewart Susan W.
Published: January 2011

With wind turbines working to capture energy at different wind speeds rotor morphing could potentially increase energy capture over wind speeds up to the rated speed. This study examines what the optimal geometry might look like at different wind speeds, how it might differ from one speed to another, and how much increase in power and annual energy production could be realized with the optimal geometry at each wind speed. Using a blade-element theory based analysis and conducting simulations on the 1.5 MW WindPACT turbine and the 5MW NREL concept turbine, variations in blade twist and collective pitch, chord, radius, and airfoil characteristics were considered. The results indicate that there are negligible benefits to changing blade collective pitch, twist, chord, and airfoil characteristics. Only radius increase has a dominant effect, with 20% increase in radius resulting in power increase of over 45% at 8 and 10 m/s and much higher percentage increases at lower speeds, for both turbines. The increase in annual energy production is in the range of 20%. However, a larger radius increases rotor thrust.
Electrodeposition and Characterization of Very Thin Film II-VI Compounds for Novel Superlattice Solar Cells
Authors: Jain Sukriti , Singh Pritpal
Published: January 2011

Thin films of lead telluride (PbTe) and zinc telluride (ZnTe) have been electrodeposited on indium tin oxide (ITO)-coated glass substrates. Uniform dense films of ∼ 100 nm have been obtained for both materials. The electrochemical deposition procedures for fabricating these films are described. The as-deposited films have been characterized by scanning electron microscopy, energy dispersive spectroscopy, and optical absorption spectrophotometry. Multi layer structures, up to 3 layers, of ZnTe/PbTe films, have been fabricated.
A Parametric Study of the Impact of Various Error Contributions on the Flux Distribution of a Solar Dish Concentrator
Authors: Andraka Charles E. , Yellowhair Julius , Iverson Brian D.
Published: January 2011

Dish concentrators can produce highly concentrated flux for the operation of an engine, a chemical process, or other energy converter. The high concentration allows a small aperture to control thermal losses, and permits high temperature processes at the focal point. A variety of optical errors can influence the flux pattern both at the aperture and at the absorber surface. Impacts of these errors can be lost energy (intercept losses), aperture compromise (increased size to accommodate flux), high peak fluxes (leading to part failure or life reduction), and improperly positioned flux also leading to component failure. Optical errors can include small scale facet errors (“waviness”), facet shape errors, alignment (facet pointing) errors, structural deflections, and tracking errors. The errors may be random in nature, or may be systematic. The various sources of errors are often combined in a “root-mean-squared” process to present a single number as an “error budget”. However, this approach ignores the fact that various errors can influence the performance in different ways, and can mislead the designer, leading to component damage in a system or poor system performance. In this paper, we model a hypothetical radial gore dish system using Sandia’s CIRCE2 optical code. We evaluate the peak flux and incident power through the aperture and onto various parts of the receiver cavity. We explore the impact of different error sources on the character of the flux pattern, and demonstrate the limitations of lumping all of the errors into a single error budget.
Cost and Performance Analysis of a Solar Thermal Cooling Project
Authors: Dickinson Joel K. , Hess Robert O. , Seaton Jeff , van Lambalgen Henny , Burnham Andrea L.
Published: January 2011

This paper presents the findings of a field study and performance analysis of a solar thermal cooling system located in Phoenix, Arizona. This system is compared to conventional air conditioning equipment, as well as conventional air conditioning equipment powered by solar electric (photovoltaics). The design of the solar cooling system, which incorporates solar-generated hot water and a single-stage absorption chiller, is discussed. Capital and maintenance cost estimates, including auxiliary electric load and water, are also provided. Operational problems are reviewed together with the design modifications that were required to resolve these issues. Performance of the system and the individual components was determined based on field data collected. Using this data the solar cooler energy savings over conventional air conditioning equipment was determined (Figure 1).
Radial Inflow Turbine Assessment for Small-Scale Concentrated Solar Rankine Combined Heat and Power Technology
Authors: Sunter Deborah A. , Carey Van P. , Norwood Zack
Published: January 2011

Recent studies suggest that small scale (5–10kW) distributed solar Rankine combined heat and power could be a viable renewable energy strategy for displacing fossil fuel use in residential buildings, small commercial buildings, or developing rural communities. One of the primary obstacles of scaling down solar Rankine technology to this level is finding an appropriate expander design. This paper considers the radial-inflow turbine for such an application. Although well-tested methodologies exist for design analysis of radial inflow turbines, existing analysis tools are generally focused on machines using a combustion gases in a Brayton cycle. Use of Rankine cycle working fluids under conditions optimal for small scale Rankine solar systems result in turbine operating conditions that can be dramatically different from those in combustion-based Brayton cycle power systems. This investigation explored how analysis tools developed by NASA and others for conventional Brayton cycle power systems can be adapted to analyze and design radial inflow expanders for small scale Rankine solar combined heat and power systems. Using a 1D model derived from analysis methodologies used by NASA for conventional aerospace gas turbine power applications, the effect of reduced power output on performance is explored. Since the model contains several non-dimensional variables, a variety of geometries are surveyed, and performance sensitivity to various geometric parameters is observed. The interplay between radial inflow turbine performance and cycle efficiency for the system is examined in detail. Several fluids are compared to access how critical temperature and the shape of the saturation dome affect thermodynamic performance of the cycle and efficiency of the turbine. Conclusions regarding optimal fluids and geometric parameters for the radial-inflow turbine are discussed.
Analysis of Potential for Mitigation of Building-Integrated PV Array Shading Losses Through Use of Distributed Power Converters
Authors: MacAlpine Sara M. , Brandemuehl Michael J. , Erickson Robert W.
Published: January 2011

Partial shading of building-integrated photovoltaic (BIPV) arrays is very common, as they are limited by building geometry and most often installed in crowded urban or suburban environments. Power losses in shaded BIPV systems tend to be disproportionately large, due in large part to mismatches in operating conditions between panels. Maximum power point tracking at a modular level, which can be achieved through the use of module integrated dc-dc converters (MICs), may be used to mitigate some of these losses. This paper investigates the potential power gain provided by MICs for several representative partially shaded BIPV array scenarios. A flexible, comprehensive simulation model for BIPV systems is developed, which allows for variations in insolation and temperature at the PV cell level, while accurately modeling MICs and their effect on array performance. Shadows from nearby objects are mapped onto the modeled BIPV arrays and simulated on an annual, hourly basis, with varying array configuration as well as object size and placement. Results of these simulations show that the impact of MICs on system power output varies depending on factors such as radiation availability, time shaded throughout the year, shadow size and distribution on the array, and inverter design. Annual power gains of 3–30% are realized for a moderately shaded system with MICs when compared to conventional approaches. Further opportunities for increased energy capture in a BIPV system with MICs are identified and discussed.
Thermal Performance of a Natural Ventilation System
Authors: Jime´nez M. J. , Guzma´n J. D. , Heras M. R. , Arce J. , Xama´n J. P. , Alvarez G.
Published: January 2011

Natural ventilation in buildings using solar passive systems, such as solar chimneys, has emerged in the last years. Several theoretical and experimental studies in the literature show that their design parameters strongly depend on the ambient conditions, in which they are installed. In order to increase the knowledge of this kind of systems, this work presents the thermal behavior of a stand alone experimental solar chimney during one year. The dimensions of the solar chimney are 5.60 m high, 1.0 m width, and 0.52 m depth. The absorber plate is made of a common reinforced concrete wall of 4.5 m high, 1.0 m wide and 0.15 m depth. This system was designed by Marti´ J., and Heras M.R. in 2003 [1,2] and it is located in the Laboratorio de Ensayos Energe´ticos para Componentes de la Edificacio´n (LECE) in the Plataforma Solar of Almeri´a (PSA) in Spain. The entrance of this solar chimney was redesigned in 2007 by Arce et al. [3] and also the instrumentation of the system was increased and improved. During one year, the solar chimney was monitored and several experimental variables were measured. The results present the temperature profiles of the different measured elements of the solar chimney as well as the air mass flow rate through the solar chimney channel. It was observed that the effect of the outdoor wind added to the thermal effects plays an important role affecting the performance of the solar chimney studied.
Characterizing the Response of Commercial and Industrial Facilities to Dynamic Pricing Signals From the Utility
Authors: Mathieu Johanna L. , Gadgil Ashok J. , Callaway Duncan S. , Price Phillip N. , Kiliccote Sila
Published: January 2011

We describe a method to generate statistical models of electricity demand from Commercial and Industrial (C&I) facilities including their response to dynamic pricing signals. Models are built with historical electricity demand data. A facility model is the sum of a baseline demand model and a residual demand model; the latter quantifies deviations from the baseline model due to dynamic pricing signals from the utility. Three regression-based baseline computation methods were developed and analyzed. All methods performed similarly. To understand the diversity of facility responses to dynamic pricing signals, we have characterized the response of 44 C&I facilities participating in a Demand Response (DR) program using dynamic pricing in California (Pacific Gas & Electric’s Critical Peak Pricing Program). In most cases, facilities shed load during DR events but there is significant heterogeneity in facility responses. Modeling facility response to dynamic price signals is beneficial to the Independent System Operator for scheduling supply to meet demand, to the utility for improving dynamic pricing programs, and to the customer for minimizing energy costs.
Design and Analysis of an Integrated Solar Absorption Cooling and Heating System at Purdue University
Authors: Hang Yin , Qu Ming
Published: January 2011

As one of the most promising solutions to the reduction of fossil fuel consumption and greenhouse gas emissions, the use of solar energy for building space heating and cooling recently has again aroused researcher’s interest with the growing awareness of the global warming and other environmental problems. Compared to the relatively mature solar heating, solar cooling technology remains at the demonstration and testing stage due to its complicated system characteristics, both in concept and construction. Among many solar cooling technologies, solar absorption technology is the most suitable technology for the solar cooling. The major barriers to widespread deployment of the solar absorption cooling are its high first cost, the lack of guidelines of its design and operation, and the relative low system performance due to the lack of the system integration. The paper provides detailed information of an on-going solar heating and cooling research project conducted at Purdue University in West Lafayette, Indiana. The aim of the research is to develop a cost-effective and integrated solar heating and cooling system. The solar thermal system primarily includes a 45kW single effect absorption chiller, evacuated tube solar collectors (ET), and heat storage tanks. The system has been designed based upon scientific principles and engineering fundamentals. It has been analyzed and optimized to achieve the high cost-effectiveness and the high system efficiency through the system performance simulation in Transient Energy System Simulation (TRNSYS) program.
A Simulation of the Thermal Performance of a Small Solar Chimney Already Installed in a Building
Authors: Arce J. , Xama´n J. P. , Alvarez G. , Jime´nez M. J. , Enri´quez R. , Heras M. R.
Published: January 2011

In this paper we present the theoretical and experimental study of a small solar chimney. The dimensions of the solar Chimney channel are 1.95 m high, 1.70 m width and 0.24 m depth. The channel of the solar chimney has in its backside a metallic plate as a solar heat absorber, and it is attached to a concrete wall, which acts as a storage and thermal isolation. On the front part of the chimney there is a glass plate used to decrease the heat losses to the exterior. Because the metallic plate is heated, air circulates from the lower side to the top side of the chimney channel. For the theoretical study, the steady state energy balance equations were solved for each element of the solar chimney following the methodology proposed by Ong in 2003 [8]. A numerical code was developed and reduced to cases of literature in order to validate it (Ong and Chow in 2003 [12]). The results showed the temperature distributions of the glass, the air inside the channel and the metallic plate. Also, the air mass flow rate was determined. For an hourly Irradiance of 400 W/m2, the efficiency of the solar chimney decreased from 38 to 15% as the height of the chimney increased from 0.25 to 1.95 m.
Enhanced Thermal Properties of PCM Based Nanofluid for Solar Thermal Energy Storage
Authors: Shin Donghyun , Banerjee Debjyoti
Published: January 2011

Nanofluids are synthesized by doping solvents with nano-particles at minute concentrations (typically less than 1 percentage by volume). Experimental studies have shown that nano-particles can dramatically enhance thermal conductivity of various liquid solvents. This is also associated with enhancement of other transport properties (e.g., viscosity, specific heat, diffusivity, etc.). Hence, nanofluids are attractive materials for solar thermal applications. The objective of this study is to investigate the optimum performance of various nanofluids for solar thermal storage applications. Dimensional analyses and similitude techniques will be used to theoretically estimate the enhancement of transport properties of various nanofluids to predict their efficacy for solar thermal storage applications.
A CFD Study on the Effect of Carbon Particle Seeding for the Improvement of Solar Reactor Performance
Authors: Ozalp Nesrin , Kanjirakat Anoop
Published: January 2011

With the increasing concern of CO2 emissions and climate change, efforts have grown to include solar technologies in chemical processes to manufacture products that can be used both as a commodity and as a fuel, such as hydrogen. This study focuses on a technique, referred to as “solar cracking” of natural gas for the co-production of hydrogen and carbon as byproduct with zero emission footprint via the following reaction: CH4→C(s)+2H2(g). However, some portion of the incoming solar energy absorbed by the cavity greatly exceeds the surface absorption of the inner walls because of multiple internal reflections. Studies have shown that by seeding the reactor with micron-sized carbon particles, methane conversion improves drastically due to the radiation absorbed by the carbon particles and additional nucleation sites formed by carbon particles for heterogeneous decomposition reaction. This can maintain more heat at the core and can reduce the carbon deposits on the reactor walls. Present study numerically tries to investigate the above fact by tracking carbon particles in a Lagrangian frame-work. Initially, the numerical model is validated qualitatively by comparing the particle deposition on reactor window with the experimental observations. Effect of particle loading, particle emissivity, injection point location, and effect of using different window screening gases on a flow and temperature distribution inside a confined tornado flow reactor are studied. It is observed that the methane conversion substantially increases by particle seeding. The results of this research can be used in thermo-chemical reactor design.
Regeneration Strategies of Air-Purification TSA Process for Cryogenic Air Distillation Plant
Authors: Zhang Peikun , Wang Li , Cheng Yuzhi , Li Zhengqiang , Gao Yuan , Wang Ding
Published: January 2011

Since the regeneration step in the Temperature Swing Adsorption (TSA) process requires time enough to heat and cool the bed, it is often the time-limiting step in the TSA cycle and it consumes a huge amount of energy for regeneration. Therefore, a valid management of the regeneration process can minimize the energy consumption of the TSA process which is involved with regeneration time, purge gas requirements, and heat load. Simulation software was developed for industrial scale bed of TSA. A new isotherm equation which performs well in predicting experiment data was extended to multi-component form and then used to interpret the adsorption equilibria of water vapor and carbon dioxide on adsorbents. Preliminary linear drive force mass transfer coefficients and the heat transfer coefficients were calculated by empirical equations and then refined by matching breakthrough curves obtained from industrial field process monitoring to theoretical curves. Under a wide range of regeneration conditions, the temperature effluence and breakthrough were drawn and studied. With the application of this simulation software, the performance and operation data of the TSA beds under various conditions can be obtained conveniently. This enables the manager to minimize their TSA’s heat consumption.
On the Environmental Sustainability of Solar Technologies in a Coastal City
Authors: Lebassi B. , Gonza´lez J. E. , Bornstein R. D.
Published: January 2011

In this study, a first order environmental impact study of a large scale deployment of solar energy installed technologies in complex coastal urban environment is conducted. The work is motivated by the positive prospects of building integrated solar technologies as a sustainable alternative to energy demands and reduction of green house gases. Large scale deployment of solar technologies in rooftops of densely populated cities may have the potential of modifying surface energy budgets resulting in cooling or heating of the urban environment. To investigate this case the meso-scale model, Regional Atmospheric Modeling System (RAMS) is used, with a horizontal grid resolution of 4 km on an innermost grid over South Coast Air Basin (SocAB) region of Southern California. The simulation took place in summer 2002 where strong urban heat islands (UHIs) were observed for the region. The urban landscape was modified to represent a percentage of the rooftops with optical properties corresponding to solar PV and thermal collectors. Results show that the large scale presence of solar technologies in rooftops of SoCAB may have a net positive thermal storage effect enhancing the existing UHI by up to 0.3°F. This additional heat is advected inland as the sea-breeze develops warming further inland areas. The net environmental effect of solar technologies when compared with solar energy production was not investigated in this study.