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Showing papers in "Journal of Solar Energy Engineering-transactions of The Asme in 2010"


Journal ArticleDOI
TL;DR: The Solid Particle Receiver (SPR) as mentioned in this paper is a direct absorption central receiver, which was built and evaluated on-sun at power levels up to 2.5 MW at Sandia National Laboratories in New Mexico.
Abstract: A prototype direct absorption central receiver, called the solid particle receiver (SPR), was built and evaluated on-sun at power levels up to 2.5 MW th at Sandia National Laboratories in Albuquerque, NM. The SPR consists of a 6 m tall cavity through which spherical sintered bauxite particles are dropped and directly heated with concentrated solar energy. In principle, the particles can be efficiently heated to a temperature in excess of 900°C, well beyond the stability limit of existing nitrate salt formulations. The heated particles may then be stored in a way analogous to nitrate salt systems, enabling a dispatchable thermal input to power or fuel production cycles. The focus of this current effort was to provide an experimental basis for the validation of computational models that have been created to support improved designs and further development of the solid particle receiver. In this paper we present information on the design and construction of the solid particle receiver and discuss the development of a computational fluid dynamics model of the prototype. We also present experimental data and model comparisons for on-sun testing of the receiver over a range of input power levels from 1.58―2.51 MW th . Model validation is performed using a number of metrics including particle velocity, exit temperature, and receiver efficiency. In most cases, the difference between the model predictions and data is less than 10%.

164 citations


Journal ArticleDOI
TL;DR: In this paper, a dynamic wake meandering (DWM) model has been developed on this background, and the basic physical mechanisms in the wake-i.e., the velocity deficit, the meandering of the deficit, and added turbulence-were modeled as simply as possible in order to make fast computations.
Abstract: As the major part of new wind turbines are installed in clusters or wind farms, there is a strong need for reliable and accurate tools for predicting the increased loadings due to wake operation and the associated reduced power production. The dynamic wake meandering (DWM) model has been developed on this background, and the basic physical mechanisms in the wake-i.e., the velocity deficit, the meandering of the deficit, and the added turbulence—are modeled as simply as possible in order to make fast computations. In the present paper, the DWM model is presented in a version suitable for full integration in an aeroelastic model. Calibration and validation of the different parts of the model is carried out by comparisons with actuator disk and actuator line (ACL) computations as well as with inflow measurements on a full-scale 2 MW turbine. It is shown that the load generating part of the increased turbulence in the wake is due almost exclusively to meandering of the velocity deficit, which causes "apparent" turbulence when measuring the flow in a fixed point in the wake. Added turbulence, originating mainly from breakdown of tip vortices and from the shear of the velocity deficit, has only a minor contribution to the total turbulence and with a small length scale in the range of 10-25% of the ambient turbulence length scale. Comparisons of the calibrated DWM model with ACL results for different downstream positions and ambient turbulence levels show good correlation for both wake deficits and turbulence levels. Finally added turbulence characteristics are compared with correlation results from literature.

128 citations


Journal ArticleDOI
TL;DR: Progress is demonstrated in addressing significant technological barriers including development of frequency-dependent modeling of double-feedpoint square spiral nantenna elements, selection of materials with proper THz properties, and development of novel manufacturing methods that could potentially enable economical large-scale manufacturing.
Abstract: The research described in this paper explores a new and efficient approach for producing electricity from the abundant energy of the sun, using nanoantenna (nantenna) electromagnetic collectors (NECs). NEC devices target midinfrared wavelengths, where conventional photovoltaic (PV) solar cells are inefficient and where there is an abundance of solar energy. The initial concept of designing NECs was based on scaling of radio frequency antenna theory to the infrared and visible regions. This approach initially proved unsuccessful because the optical behavior of materials in the terahertz (THz) region was overlooked and, in addition, economical nanofabrication methods were not previously available to produce the optical antenna elements. This paper demonstrates progress in addressing significant technological barriers including: (1) development of frequency-dependent modeling of double-feedpoint square spiral nantenna elements, (2) selection of materials with proper THz properties, and (3) development of novel manufacturing methods that could potentially enable economical large-scale manufacturing. We have shown that nantennas can collect infrared energy and induce THz currents and we have also developed cost-effective proof-of-concept fabrication techniques for the large-scale manufacture of simple square-loop nantenna arrays. Future work is planned to embed rectifiers into the double-feedpoint antenna structures. This work represents an important first step toward the ultimate realization of a low-cost device that will collect as well as convert this radiation into electricity. This could lead to a broadband, high conversion efficiency low-cost solution to complement conventional PV devices.

121 citations


Journal ArticleDOI
TL;DR: In this article, a high temperature biomass gasification has been performed in a prototype concentrated solar reactor, where the effects of temperature, gas flow rate, and feed type were conducted at the high flux solar furnace at the National Renewable Energy Laboratory, Golden, CO.
Abstract: High temperature biomass gasification has been performed in a prototype concentrated solar reactor. Gasification of biomass at high temperatures has many advantages compared with historical methods of producing fuels. Enhancements in overall conversion, product composition ratios, and tar reduction are achievable at temperatures greater than 1000°C. Furthermore, the utilization of concentrated solar energy to drive these reactions eliminates the need to consume a portion of the product stream for heating and some of the solar energy is stored as chemical energy in the product stream. Experiments to determine the effects of temperature, gas flow rate, and feed type were conducted at the high flux solar furnace at the National Renewable Energy Laboratory, Golden, CO. These experiments were conducted in a reflective cavity multitube prototype reactor. Biomass type was found to be the only significant factor within a 95% confidence interval. Biomass conversion as high as 68% was achieved on sun. Construction and design considerations of the prototype reactor are discussed as well as initial performance results.

102 citations


Journal ArticleDOI
TL;DR: In this paper, an analytical model of the heat transfer in a parametric 360 deg cylindrical and tubular central receiver was developed to examine the receiver's efficiency characteristics, which are based on different irradiation levels relative to the receivers's design point, are, then, used to interpolate the receivers thermal efficiency in an hourly based annual calculation of one typical year that is defined by hourly based real measurements of the direct normal irradiance and the ambient temperature.
Abstract: For clean and efficient electric power generation, the combination of solar power towers (SPTs) with ultrasupercritical steam cycle power plants could be the next development step. The methodology of the European concentrated solar thermal roadmap study was used to predict the annual performance and the cost reduction potential of this option applying tubular receivers with various appropriate high temperature heat transfer media (HTM). For the assessment, an analytical model of the heat transfer in a parametric 360 deg cylindrical and tubular central receiver was developed to examine the receiver's efficiency characteristics. The receiver's efficiency characteristics, which are based on different irradiation levels relative to the receiver's design point, are, then, used to interpolate the receiver's thermal efficiency in an hourly based annual calculation of one typical year that is defined by hourly based real measurements of the direct normal irradiance and the ambient temperature. Applying appropriate cost assumptions from literature, the levelized electricity costs (LEC) were estimated for each considered SPT concept and compared with the reference case, which is a scale-up of the state of the art molten salt concept. The power level of all compared concepts and the reference case is 50 MW el . The sensitivity of the specific cost assumptions for the LEC was evaluated for each concept variation. No detailed evaluation was done for the thermal storage but comparable costs were assumed for all cases. The results indicate a significant cost reduction potential of up to 15% LEC reduction in the liquid metal HTM processes. Due to annual performance based parametric studies of the number of receiver panels and storage capacity the results also indicate the optimal values of these parameters con cerning minimal LEC.

82 citations


Journal ArticleDOI
TL;DR: In this article, a thermofluid dynamic model for parabolic trough collectors was developed and used for carrying out systematic calculations on different design options, based on detailed energy balances, and it was applied to evaluate collector thermal performances with different working fluids: oil, molten salt, or water/steam.
Abstract: This paper describes the development and use of a thermofluidynamic model for parabolic trough collectors, specifically suited for carrying out systematic calculations on different design options. The model is based on detailed energy balances, and it has been applied to evaluate collector thermal performances with different working fluids: oil, molten salt, or water/steam. For each heat transfer fluid technology, four parameters have been analyzed: collector length, absorber tube diameter, working temperature, and pressure. The influence of these factors has been studied from the point of view of heat loss, pressure drop, energy and exergy efficiencies. Exergy is considered the suitable magnitude to guide any optimization process in this field, because it accounts for all relevant energy gains and losses, characterized by their corresponding temperature and pressure. Preliminary conclusions point out that direct steam generation is more efficient than oil and molten salt systems.

79 citations


Journal ArticleDOI
TL;DR: In this article, the interaction between the three subsystems of a parabolic trough power plant with direct steam generation (DSG) is analyzed, and boundary conditions arising from the thermal storage system are identified.
Abstract: For the future market potential of parabolic trough power plants with direct steam generation (DSG), it is beneficial to integrate a thermal storage system. Heat storage media based on phase change materials offer heat transfer at constant temperatures needed for the evaporation process. Different options for a plant layout are presented and discussed. The interactions between the three subsystems—solar field, power block, and thermal storage—are analyzed, and boundary conditions arising from the thermal storage system are identified. Compared with a system without storage the number of operating points increases significantly since different combinations of storage charge and discharge operations go along with a varying power output of the solar field. It is shown that the large number of theoretical operating points can be reduced to a subset with practical relevance. Depending on the live steam parameters a reheat is necessary within the power block. Compared with parabolic trough fields with a single phase heat transfer medium such as oil, a special heat exchanger configuration is needed for a DSG plant. Different alternatives based on available technologies are presented and evaluated.

77 citations


Journal ArticleDOI
TL;DR: In this paper, three approaches for ranking the impact importance of measurable turbine parameters on the vibrations of the drive train and the tower are discussed, including the predictor importance analysis, the global sensitivity analysis, and the correlation coefficient analysis.
Abstract: Vibrations of a wind turbine have a negative impact on its performance. Mitigating this undesirable impact requires knowledge of the relationship between the vibrations and other wind turbine parameters that could be potentially modified. Three approaches for ranking the impact importance of measurable turbine parameters on the vibrations of the drive train and the tower are discussed. They include the predictor importance analysis, the global sensitivity analysis, and the correlation coefficient analysis versed in data mining and statistics. To decouple the impact of wind speed on the vibrations of the drive train and the tower, the analysis is performed on data sets with narrow speed ranges. Wavelet analysis is applied to filter noisy accelerometer data. To exclude the impact malfunctions on the vibration analysis, the data are analyzed in a frequency domain. Data-mining algorithms are used to build models with turbine parameters of interest as inputs, and the vibrations of drive train and tower as outputs. The performance of each model is thoroughly evaluated based on metrics widely used in the wind industry. The neural network algorithm outperforms other classifiers and is considered to be the most promising approach to study wind turbine vibrations.

70 citations


Journal ArticleDOI
TL;DR: In this paper, a windowed solar reactor prototype designed for beam-down optics was constructed at a laboratory scale and demonstrated for CO2 gasification of coal coke using concentrated visible light from a sun-simulator as the source of energy.
Abstract: Solar thermochemical processes, such as solar gasification of coal, require the development of a high temperature solar reactor operating at temperatures above 1000°C. Direct solar energy absorption by reacting coal particles provides efficient heat transfer directly to the reaction site. In this work, a windowed reactor prototype designed for the beam-down optics was constructed at a laboratory scale and demonstrated for CO2 gasification of coal coke using concentrated visible light from a sun-simulator as the source of energy. Peak conversion of light energy to chemical fuel (CO) of 14% was obtained by irradiating a fluidized bed of 500–710 μm coal coke size fraction with a power input of about 1 kW and a CO2 flow-rate of 6.5 dm3 min−1 at normal conditions.

61 citations


Journal ArticleDOI
TL;DR: In this article, a comparison of an AndaSol-I type solar thermal power plant with the original two-tank molten salt storage and with a "hypothetical" concrete storage shows an advantage of the concrete storage technology concerning environmental impacts.
Abstract: For parabolic trough power plants using synthetic oil as the heat transfer medium, the application of solid media sensible heat storage is an attractive option in terms of investment and maintenance costs. One important aspect in storage development is the storage integration into the power plant. A modular operation concept for thermal storage systems was previously suggested by DLR, showing an increase in storage capacity of more than 100 %. However, in these investigations, the additional costs needed to implement this storage concept into the power plant, like for extra piping, valves, pumps and control had not been considered. These aspects are discussed in this paper, showing a decrease of levelized energy costs with modular storage integration of 2 to 3 %. In a Life Cycle Assessment (LCA) a comparison of an AndaSol-I type solar thermal power plant [1] with the original two-tank molten salt storage and with a "hypothetical" concrete storage shows an advantage of the concrete storage technology concerning environmental impacts. The environmental impacts of the “hypothetical” concrete based AndaSol-I decrease by 7 %, considering 1 kWh of solar electricity delivered to the grid. Regarding only the production of the power plant, the emissions decrease by 9.5 %.

60 citations


Journal ArticleDOI
TL;DR: In this paper, the benefits of the direct steam generation in parabolic trough collectors were investigated and compared with a reference system using synthetic oil as heat transfer fluid, and the main result of the investigation is that the benefit of the DSG process depends on the project site and can reach an 11 % reduction in the levelized electricity cost.
Abstract: The direct steam generation (DSG) in parabolic trough collectors is a promising option to improve the mature parabolic trough solar thermal power plant technology of the solar energy generating systems (SEGS) ; in California. According to previous studies (Langenkamp, 1998, "Revised LEC Projections and Discussion of Different DSG Benefits, " Technical Report No. DISS-SC-QA-02, Almeria, Spain; Price, et al., 2002, "Advances in Parabolic Trough Solar Power Technology, " ASME J. Sol. Energy Eng., 124(2), pp. 109-125; Zarza, E., 2002, "DISS Phase II Final Report, " Technical Report EU Contract No. JOR3-CT98-0277, Almeria, Spain], the cost reduction in the DSG process compared with the SEGS technology is expected to be 8-25%. All these studies were more or less preliminary since they lacked detailed information on the design of collector fields, absorber tubes required for steam temperatures higher than 400°C, and power blocks adapted to the specific needs of the direct steam generation. Power blocks and collector fields were designed for four different capacities (5 MW el , 10 MW el , 50 MW el , and 100 MW el ) and different live steam parameters. The live steam temperature was varied between saturation temperature and 500°C and live steam pressures of 40 bars, 64 bars, and 100 bars were investigated. To assess the different cases, detailed yield analyses of the overall system were performed using hourly data for the direct normal irradiation and the ambient temperature for typical years. Based on these results, the levelized costs of electricity were determined for all cases and compared with a reference system using synthetic oil as heat transfer fluid. This paper focuses on two main project findings. First, the 50 MW el DSG system parameter comparisons are presented. Second, the detailed comparison between a DSG and a SEGS-like 100 MW el system is given. The main result of the investigation is that the benefit of the DSG process depends on the project site and can reach an 11 % reduction in the levelized electricity cost.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the extreme load reduction potential of smart rotor control devices, namely trailing edge flaps, in the operation of a 5 MW wind turbine, using simple step functions in the wind to approximate gusts and investigate the performance of two load reduction methods: individual flap control and individual pitch control.
Abstract: Reducing the loads experienced by wind turbine rotor blades can lower the cost of energy of wind turbines. "Smart rotor control" concepts have emerged as a solution to reduce fatigue loads on wind turbines. In this approach, aerodynamic load control devices are distributed along the span of the blade, and through a combination of sensing, control, and actuation, these devices dynamically control the blade loads. While smart rotor control approaches are primarily focused on fatigue load reductions, extreme loads on the blades may also be critical in determining the lifetime of components, and the ability to reduce these loads as well would be a welcome property of any smart rotor control approach. This research investigates the extreme load reduction potential of smart rotor control devices, namely trailing edge flaps, in the operation of a 5 MW wind turbine. The controller utilized in these simulations is designed explicitly for fatigue load reductions; nevertheless its effectiveness during extreme loads is assessed. Simple step functions in the wind are used to approximate gusts and investigate the performance of two load reduction methods: individual flap control and individual pitch control. Both local and global gusts are simulated. The results yield important insight into the control approach that is utilized, and also into the differences between using individual pitch control and trailing edge flaps for extreme load reductions. Finally, the limitation of the assumption of quasisteady aerodynamic behavior is assessed.

Journal ArticleDOI
TL;DR: In this article, the authors developed a code based on a modified implementation of the variational-asymptotic beam sectional (VABS) technique proposed by Hodges VABS, allowing accurate modeling of the 3D structure of the blade as a 1D finite-element problem.
Abstract: An important aspect in wind-turbine technology nowadays is to reduce the uncertainties related to blade dynamics by the improvement of the quality of numerical simulations of the fluid-structure interaction process A fundamental step in that direction is the implementation of structural models capable of capturing the complex features of innovative prototype blades, so that they can be tested at realistic full-scale conditions with a reasonable computational cost To this end, we developed a code based on a modified implementation of the variational-asymptotic beam sectional (VABS) technique proposed by Hodges VABS has the capacity of reducing the geometrical complexity of the blade section into a stiffness matrix for an equivalent beam, allowing accurate modeling of the 3D structure of the blade as a 1D finite-element problem In this paper, we report some recent results we have obtained by applying our code to full-scale composite laminate wind-turbine blades, analyzing the fundamental vibrational modes and the stress load in normal operational conditions

Journal ArticleDOI
TL;DR: In this paper, a powder was easily prepared from Bi 2 O 3 and V 2 O 5 in an aqueous nitric acid solution at room temperature, in which the molar ratio of Bi 2 o 3 to V 2 o 5 was 1:1.
Abstract: BiV0 4 powder was easily prepared from Bi 2 O 3 and V 2 O 5 in an aqueous nitric acid solution at room temperature. The obtained crystal structure depended on the molar ratio of Bi 2 O 3 to V 2 O 5 , which is the concentration and volume of an aqueous nitric acid solution. BiV0 4 with monoclinic scheelite structure formed using starting materials, in which the molar ratio of Bi 2 O 3 to V 2 O 5 was 1:1. When the molar ratio was 4:3, BiVO 4 with tetragonal zircon structure was obtained. Although BiVO 4 with monoclinic scheelite structure was platelike particles reflecting the crystal structure, the thickness of the particle increased with an increase in the concentration of an aqueous nitric acid solution. The obtained BiVO 4 with monoclinic scheelite structure showed good photocatalytic performances for O 2 evolution and methylene blue degradation under visible-light irradiation.

Journal ArticleDOI
TL;DR: In this article, the authors provide an overview of the chemical literature dealing with the thermal decomposition of diphenyl oxide and biphenyl, the two constituents of Therminol VP-1.
Abstract: Solar parabolic trough systems for electricity production are receiving renewed attention, and new solar plants are under construction to help meet the growing demands of the power market in the Western United States. The growing solar trough industry will rely on operating experience it has gained over the last two decades. Recently, researchers found that trough plants that use organic heat transfer fluids (HTF) such as Therminol VP-1 are experiencing significant heat losses in the receiver tubes. The cause has been traced back to the accumulation of excess hydrogen gas in the vacuum annulus that surrounds the steel receiver tube, thus compromising the thermal insulation of the receiver. The hydrogen gas is formed during the thermal decomposition of the organic HTF that circulates inside the receiver loop, and the installation of hydrogen getters inside the annulus has proven to be insufficient for controlling the hydrogen build-up over the lifetime of the receivers. This paper will provide an overview of the chemical literature dealing with the thermal decomposition of diphenyl oxide and biphenyl, the two constituents of Therminol VP-1.

Journal ArticleDOI
TL;DR: In this article, a solar water heater using supercritical carbon dioxide as working fluid is proposed and experimentally studied, and the obtained results show that natural convective flow is well induced, and a flow of 1900 Reynolds number can be achieved even in winter, when the lowest level of solar radiation condition occurs.
Abstract: In this paper, a solar water heater using supercritical carbon dioxide as working fluid is proposed and experimentally studied. For supercritical carbon dioxide, a small change in temperature or pressure can result in large change in density, especially in the state close to the critical point. Thus, natural convective flow of the supercritical carbon dioxide can be easily induced by solar heating or water cooling. Such convective flow absorbs and transports heat to water in solar collector tubes. Motivated by the above idea, an experimental setup was designed, and a solar water heater was tested. The obtained results show that natural convective flow is well induced, and a flow of 1900 Reynolds number can be achieved even in winter, when the lowest level of solar radiation condition occurs. Furthermore, the measured collector and heat recovery efficiencies are 66.0% and 65.0%, respectively. More details of its mechanism are to be studied, and a complete performance analysis is needed.

Journal ArticleDOI
TL;DR: In this paper, the sandwich concept has been demonstrated successfully for three different storage units ranging from 2 kW to 100 kW at melting temperatures of 145°C and 225°C, respectively.
Abstract: Solar thermal systems using absorber evaporating steam directly require isothermal energy storage. The application of latent heat storage systems is an option to fulfill this demand. This concept has been demonstrated mainly for low temperature heating and refrigeration applications, the experience for the power level and temperature range characteristic of solar process heat and solar thermal power plants is limited. Cost effective implementation of the latent heat storage concept demands low cost phase change materials (PCMs). These PCMs usually show low thermal conductivity limiting the power density during the charging/discharging process. This paper describes various approaches, which have been investigated to overcome these limitations. Based on fundamental PCM-research and laboratory-scale experiments, the sandwich concept has been identified to show the highest potential. The sandwich concept has been demonstrated successfully for three different storage units ranging from 2 kW to 100 kW at melting temperatures of 145°C and 225°C.

Journal ArticleDOI
TL;DR: In this article, a three-part storage system is proposed where a phase change material (PCM) storage is deployed for the two-phase evaporation, while concrete storage will be used for storing sensible heat.
Abstract: For future parabolic trough plants direct steam generation in the absorber pipes is a promising option for reducing the costs of solar thermal power generation. These new solar thermal power plants require innovative storage concepts, where the two-phase heat transfer fluid poses a major challenge. A three-part storage system is proposed where a phase change material (PCM) storage will be deployed for the two-phase evaporation, while concrete storage will be used for storing sensible heat, i.e., for preheating of water and superheating of steam. A pinch analysis helps to recognize interface constraints imposed by the solar field and the power block and describes a way to dimension the latent and sensible components. Laboratory test results of a PCM test module with ∼140 kg NaNO 3 , applying the sandwich concept for enhancement of heat transfer, are presented, proving the expected capacity and power density. The concrete storage material for sensible heat was improved to allow the operation up to 500°C for direct steam generation. A storage system with a total storage capacity of ∼1 MWh is described, combining a PCM module and a concrete module, which will be tested in 2009 under real steam conditions around 100 bars.

Journal ArticleDOI
TL;DR: In this paper, the guidelines for the design of dc-dc converters for distributed maximum power point tracking (DMPPT) applications are presented and discussed, and the power stage of such a converter is a challenging task because of the very high efficiency requirements and of the continuous changes of the operating point depending on the sun irradiation conditions.
Abstract: Distributed maximum power point tracking (DMPPT) is one of the most promising solutions to overcome the drawbacks associated with mismatching phenomena in photovoltaic (PV) applications. DMPPT is based on the adoption of a dc/dc converter dedicated to each PV module. The design of the power stage of such a converter is a challenging task because of the very high efficiency requirements and of the continuous changes of the operating point during the day, depending on the sun irradiation conditions. In this paper the guidelines for the design of dc-dc converters for DMPPT applications are presented and discussed.

Journal ArticleDOI
TL;DR: In this article, a combination of a compound parabolic concentrator (CPC) and a thermoelectric module (TEM) was used to generate electricity from the sun using a small appliance.
Abstract: Generating electricity from the sun using a combination of a compound parabolic concentrator (CPC) and a thermoelectric module (TEM) has been studied. The system was modeled, analyzed, and tested. The model equations and the methodology used for the demonstration are presented and experimentally validated. The experimental setup comprised a manually fabricated CPC placed on a commercially available TEM. The results showed that the combination can generate and sustain enough power for a small appliance. It was also shown that there is enough dissipated heat from the system, which could be harnessed for additional uses. The cost is still high, about $35/Wp, but if credit is given for the thermal energy the initial cost goes down.

Journal ArticleDOI
TL;DR: In this paper, the optical characteristics of the planar concentrator that is specially designed to be incorporated in concentrator photovoltaic systems were explored. But, the design and construction of miniature prototype of non-imaging planar concentrate was presented in the previous paper.
Abstract: The design and construction of miniature prototype of nonimaging planar concentrator, which is capable of producing much more uniform spatial irradiance and reasonably high concentration ratio, were presented in the previous paper. In this paper, we further explore the optical characteristics of the new concentrator that is specially designed to be incorporated in concentrator photovoltaic systems. For this study, we have carried out a comprehensive analysis via numerical simulation based on all the important design parameters, i.e., array of facet mirrors, f/D ratio, receiver size, and the effect of suntracking error, which lead to the overall optical performance of the new concentrator.


Journal ArticleDOI
TL;DR: In this paper, the authors presented advances toward near-optimal building thermal mass control derived from full factorial analyses of the important parameters influencing the passive thermal storage process for a range of buildings and climate/utility rate structure combinations.
Abstract: Using a simulation and optimization environment, this paper presents advances toward near-optimal building thermal mass control derived from full factorial analyses of the important parameters influencing the passive thermal storage process for a range of buildings and climate/utility rate structure combinations. Guidelines for the application of, and expected savings from, building thermal mass control strategies that can be easily implemented and result in a significant reduction in building operating costs and peak electrical demand are sought. In response to the actual utility rates imposed in the investigated cities, fundamental insights and control simplifications are derived from those buildings deemed suitable candidates. The near-optimal strategies are derived from the optimal control trajectory, consisting of four variables, and then tested for effectiveness and validated with respect to uncertainty regarding building parameters and climate variations. Due to the overriding impact of the utility rate structure on both savings and control strategy, combined with the overwhelming diversity of utility rates offered to commercial building customers, this study cannot offer universally valid control guidelines. Nevertheless, a significant number of cases, i.e., combinations of buildings, weather, and utility rate structure, have been investigated, which offer both insights and recommendations for simplified control strategies. These guidelines represent a good starting point for experimentation with building thermal mass control for a substantial range of building types, equipments, climates, and utility rates.

Journal ArticleDOI
TL;DR: Using fluorescence microscopy, the inkjet deposition dynamics of monodispersed polystyrene particles in the size range of 0.02-1.1 μm have been studied on glass, Ar plasma cleaned glass, and PDMS coated glass substrates.
Abstract: Using fluorescence microscopy, the inkjet deposition dynamics of monodispersed polystyrene particles in the size range of 0.02–1.1 μm have been studied on glass, Ar plasma cleaned glass, and PDMS coated glass substrates. The results show that the substrate properties play an important role in determining the final dried patterns formed by the colloidal particles. Our observations also reveal that particle size and contact angle formed by the solvent in the dispersion determine how close to the contact line the particles can be deposited. It is found that smaller particles can move closer to the deposited contact line than particles with bigger sizes. This study can serve as a realistic experimental model system for a number of fundamental queries on how the final deposition microstructure depends on the ink formulation and substrate properties. The knowledge obtained here can be explored further to optimize process parameters for the fabrication of hybrid solar cells with improved morphology and device properties.

Journal ArticleDOI
TL;DR: In this article, robust solar cells and submodules with a novel protection layer of metal circuit and tightly sealing package were developed to prevent water intrusion, and the resulting cell employing noble construction and ionic liquid electrolyte showed an extremely high stability to pass several endurance tests standardized in JIS for the photovoltaic submodule.
Abstract: It was investigated that the intrusion of water into the electrolyte was the most critical reason for the low stability of a dye-sensitized solar cell. To prevent the water intrusion, robust solar cells and submodules with a novel protection layer of metal circuit and tightly sealing package was developed. The excellent stability of the cell with ionic liquid electrolyte at high temperature conditions was also reveled. The resulting cell employing noble construction and ionic liquid electrolyte showed an extremely high stability to pass several endurance tests standardized in JIS for the stability of the photovoltaic submodule.

Journal ArticleDOI
TL;DR: In this paper, a high-temperature lab-scale solar reactor prototype was designed, constructed and operated, allowing continuous ZnO thermal dissociation under controlled atmosphere at reduced pressure.
Abstract: A high-temperature lab-scale solar reactor prototype was designed, constructed and operated, allowing continuous ZnO thermal dissociation under controlled atmosphere at reduced pressure. It is based on a cavity-type rotating receiver absorbing solar radiation and composed of standard refractory materials. The reactant oxide powder is injected continuously inside the cavity and the produced particles (Zn) are recovered in a downstream ceramic filter. Dilution/quenching of the product gases with a neutral gas yields Zn nanoparticles by condensation. The solar thermal dissociation of ZnO was experimentally achieved, the reaction yields were quantified, and a first concept of solar reactor was qualified. The maximum yield of particles recovery in the filter was 21% and the dissociation yield was up to 87% (Zn weight content in the final powder) for a 5 NL/min neutral gas flow-rate (typical dilution ratio of 300).

Journal ArticleDOI
TL;DR: In this article, a cylindrical cavity-receiver containing a tubular absorber that uses air as the heat transfer fluid is proposed for a novel solar trough concentrator design, and a numerical heat transfer model is developed to determine the receiver's absorption efficiency and pumping power requirement.
Abstract: A cylindrical cavity-receiver containing a tubular absorber that uses air as the heat transfer fluid is proposed for a novel solar trough concentrator design. A numerical heat transfer model is developed to determine the receiver’s absorption efficiency and pumping power requirement. The 2D steady-state energy conservation equation coupling radiation, convection, and conduction heat transfer is formulated and solved numerically by finite volume techniques. The Monte Carlo ray-tracing and radiosity methods are applied to establish the solar radiation distribution and radiative exchange within the receiver. Simulations were conducted for a 50 m-long and 9.5 m-wide collector section with 120°C air inlet temperature, and air mass flows in the range 0.1‐1.2 kg/s. Outlet air temperatures ranged from 260°C to 601°C, and corresponding absorption efficiencies varied between 60% and 18%. Main heat losses integrated over the receiver length were due to reflection and spillage at the receiver’s windowed aperture, amounting to 13% and 9% of the solar power input, respectively. The pressure drop along the 50 m module was in the range 0.23‐11.84 mbars, resulting in isentropic pumping power requirements of 6.4510 4 0.395% of the solar power input. DOI: 10.1115/1.4001675 Cavity-receivers are typically used in point-focusing solar concentrating systems e.g., dishes and towers to efficiently capture incoming radiation through multiple internal reflections, while providing sufficient heat transfer area for heat removal by a heat transfer medium or by chemical reactions. In contrast, tubular receivers are typically used in line-focusing solar concentrator systems e.g., parabolic troughs to efficiently absorb incident solar radiation through the application of selective coatings and vacuum insulations. However, when the heat transfer fluid HTF has low volumetric heat capacity and thermal conductivity, as is usually the case for gases, cavity-receivers are an interesting alternative to conventional tube receivers, as they offer the potential for larger heat transfer area and flow cross section without significantly affecting the reradiation losses from the absorber. Cylindrical cavity-receivers have been previously analyzed for an annular flow cross section 1 and for a cavity containing a single absorber tube or an array of absorber tubes 2‐4. Air is used as the HTF in the present case. The advantages are fourfold: 1 Performance loss and operating temperature constraints due to chemical instability of the HTF are avoided; 2 operating pressure can be close to ambient, eliminating the need for sophisticated sealing; 3 a packed-bed thermal storage can be incorporated to the system and heated directly by air, eliminating the need for a heat exchanger between HTF and thermal storage medium; and 4 costs for the heat transfer fluid are removed. Further, by employing conventional materials of construction and avoiding selective absorber coatings, vacuum insulation, or getters, significantly lower fabrication costs per unit receiver length are expected than those for existing receivers. On the other hand, the disadvantages of air-receivers are associated with the larger mass flow rates and surface area needed due to the lower volumetric heat capacity and thermal conductivity of air as compared with those of thermo-oils, molten salts, sodium, or other heat transfer fluids proposed. These drawbacks translate into higher pressure drops and concomitant energy penalties. In this paper, a numerical heat transfer model of an air-based cylindrical cavityreceiver is developed and applied to investigate the influence of air mass flow rate on outlet air temperature, receiver’s absorption efficiency, pumping power requirements, and thermal losses.

Journal ArticleDOI
TL;DR: A method for applying probabilistic models to concentrating solar-thermal power plants is described and two examples, a simple cost model and a more detailed performance model of a hypothetical 100-MW e power tower, are provided to illustrate the methods.
Abstract: A method for applying probabilistic models to concentrating solar-thermal power plants is described in this paper. The benefits of using probabilistic models include quantification of uncertainties inherent in the system and characterization of their impact on system performance and economics. Sensitivity studies using stepwise regression analysis can identify and rank the most important parameters and processes as a means to prioritize future research and activities. The probabilistic method begins with the identification of uncertain variables and the assignment of appropriate distributions for those variables. Those parameters are then sampled using a stratified method (Latin hypercube sampling) to ensure complete and representative sampling from each distribution. Models of performance, reliability, and cost are then simulated multiple times using the sampled set of parameters. The results yield a cumulative distribution function that can be used to quantify the probability of exceeding (or being less than) a particular value. Two examples, a simple cost model and a more detailed performance model of a hypothetical 100-MW e power tower, are provided to illustrate the methods.

Journal ArticleDOI
TL;DR: In this paper, an existing trailing edge noise model is validated by comparing with airfoil surface pressure fluctuations and far field sound pressure levels measured in three different experiments, and the model reproduces the main tendencies observed in the measurements with respect to varying flow conditions.
Abstract: The aim of this article is twofold. First, an existing trailing edge noise model is validated by comparing with airfoil surface pressure fluctuations and far field sound pressure levels measured in three different experiments. The agreement is satisfactory in one case but poor in two other cases. Nevertheless, the model reproduces the main tendencies observed in the measurements with respect to varying flow conditions. Second, the model is implemented into an airfoil design code that is originally used for aerodynamic optimization. An existing wind turbine airfoil is optimized in order to reduce its noise emission, trying at the same time to preserve some of its aerodynamic and geometric characteristics. The new designs are characterized by less cambered airfoils and flatter suction sides. The resulting noise reductions seem to be mainly achieved by a reduction in the turbulent kinetic energy across the boundary layer near the trailing edge and to a lesser extent by a smaller boundary layer displacement thickness.

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TL;DR: In this paper, a novel solar-hybrid gas turbine combined cycle was proposed, which integrates methanol-fueled chemical-looping combustion and solar thermal energy at around 200°C, and it was investigated with the aid of the energy-utilization diagram.
Abstract: A novel solar-hybrid gas turbine combined cycle was proposed. The cycle integrates methanol-fueled chemical-looping combustion and solar thermal energy at around 200°C, and it was investigated with the aid of the energy-utilization diagram (EUD). Solar thermal energy, at approximately 150°C―300°C, is utilized to drive the reduction in Fe 2 O 3 with methanol in the reduction reactor, and is converted into chemical energy associated with the solid fuel FeO. Then it is released as high-temperature thermal energy during the oxidation of FeO in the oxidation reactor to generate electricity through the combined cycle. As a result, the exergy efficiency of the proposed solar thermal cycle may reach 58.4% at a turbine inlet temperature of 1400°C, and the net solar-to-electric efficiency would be expected to be 22.3%. The promising results obtained here indicate that this solar-hybrid combined cycle not only offers a new approach for highly efficient use of middle-and-low temperature solar thermal energy to generate electricity, but also provides the possibility of simultaneously utilizing renewable energy and alternative fuel for CO 2 capture with low energy penalty.