Browsing by Subject "Solar collectors"
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Item A cloud shading direct solar radiation model(Texas Tech University, 1985-12) Smalley, David JThe Crosbyton Solar Power Project (CSPP) was initiated to study the feasibility of using hemispheric bowl solar collectors for power generation. A non-spectral direct solar radiation (DSR) model was developed to aid in determining whether there exists a preferred spacing of these solar collectors based solely on meteorological considerations. The DSR model is applicable to the Northern Hemisphere and, with a few adjustments, to the Southern Hemisphere. The DSR model considers the reduction of direct insolation through the atmosphere due to Rayleigh scattering, uniformly mixed gases, ozone, precipitable water, and aerosols. It incorporates geographical information along with temperature, dew point, barometric pressure, and visibility data, updated every 15 minutes. This clear sky DSR model was verified against actual direct insolation data. Propagating cloud field algorithms were added to this model to yield the cloud shading DSR model. A variety of cloud patterns typically observed in the West Texas area were chosen to be modelled. Specified parameters are speed and direction of propagation, cloud base height, size, and transmissivity- Six solar collector array patterns were tested. Each array consisted of four 100-foot radius collectors, spaced differently in each array. For a given cloud pattern, a cloud shading DSR model run was made for each collector array. The model output includes, for each collector, the amount of time shaded and the average direct insolation for the day, and, for the array, the percentage of time any number of collectors were simultaneously shaded. The majority of model runs were for 60% cloud coverage. Additional runs for 15% coverage led to extrapolation of results for all non-clear and non-overcast sky conditions. It was concluded that the closest possible spacing of the collectors, in any pattern, was desirable. This coincided with engineering considerations. The use of the clear sky DSR model in an early warning network is discussed.Item A solar adsorption cooling system: an analytical and experimental study(Texas Tech University, 1977-08) Thongprasert, ManitNot availableItem A theoretical analysis of solar collector/storage panels(Texas Tech University, 1977-12) Fender, David AllenA theoretical model for the evaluation of the transient performance of combination solar energy collection and heat storage panels is derived and analyzed. Beginning with the MIT II House (1947) and including several houses built in the 1960's by the CRNS Solar Energy Laboratory in Odeillo, France, published experimental studies of CS systems have shown considerable variance in determined operating effectiveness. Economic advantages have led to commercial exploitation of these systems, although design criteria are absent from the literature. Use is made of an analytical method for determining fully developed natural convection in a vertical, symmetrically heated channel derived by Ostrach (1952), further developed by Bodoia and Osterle (1962), and modified and empirically verified for simple, uniform, asymmetrically heated boundary conditions by Aung (1972). This method is then further expanded for use with numerically implicit boundary conditions involving glazing wall heat conduction. A simulation program is used to establish CS panel operating characteristics and design criteria for performance optimization. Results indicate that solar thermal efficiencies of up to approximately five percent are obtainable during mild weather with useful heat being recoverable up to about 50 percent of the time, depending on ambient temperature, selected design criteria, and incident solar energy. In cooler weather, excessive heat loss out of the cover glazing prevents any useful heat gain from being obtained.Item Comparison of analog design verification system data to receiver heat transfer code outputs for the Crosbyton Solar Power Project(Texas Tech University, 1989-05) Walter, Joseph L.The Fixed Mirror Distributed Focus concept for the collection of solar energy is unique in that a linear boiler (receiver) tracks the sun while the spherical mirrored collector remains stationary. The experimental Fixed Mirror Distributed Focus system at Crosbyton, Texas, has been in operation since 1981 with several operational schemes designed and constructed. Several analytical models were developed that can be adapted to evaluate the different configurations. The predicted output of the system requires the integration of these individual models. This report compares the results of integrating these models to predict the output from the Crosbyton Solar Bowl Facility to what was actual measured.Item Design and analysis of a distributed control system for a multi-bowl solar power plant(Texas Tech University, 1985-05) Bryans, Mark AdrianThe Cnosbyton Solar Power Project has proposed a design for a solar-fossil hybrid electric power plant. The proposed plant will utilize ten hemispherical solar collections and a fossil boiler to produce 5 MWe on a steady basis. Before the final design for this plant can be made, detailed operational procedures must be defined. This study investigates the development of a control algorithm for the multi-bowl plant by the use of a computer simulation. The first objective was to develop a one bowl simulation model. The one bowl model simulates the exit temperature given the solar insolation, the temperature setpoint, and the pressure setpoint. The one bowl simulation model was tested with data from July 5, 1980. The rms error between the simulated exit temperature and the actual exit temperature was 6.2% of the temperature setpoint. The one bowl model was then incorporated into a multi-bowl model. For an N-bowl system there is one master controller and N-1 slave controllers. The master controller consists of the one bowl model, the economic model, and the master communication software. The economic model is used to determine the appropriate temperature and pressure setpoints for each bowl based on economic and environmental conditions. The slave controllers each consist of the one bowl model integrated with the appropriate slave communication software. A three bowl system was simulated, but the results can be extrapolated to a system with any number of bowls. Three computers were used, instead of one, so that the simulation could be executed in parallel. The multi-bowl simulation showed that a distributed control system would be ideal for the proposed power plant. Also, the simulation showed that this type of control strategy is flexible and can be easily expanded on modified.Item Development and use of a duststorm simulation chamber to evaluate solar concentrator degradation as characterized by loss in reflectivity(Texas Tech University, 1980-12) Collier, Elwin GreggNot availableItem Development of an improved, accelerated test for the effect of blowing dust on the service-life of solar collectors(Texas Tech University, 1985-12) Cooper, Austin MNot availableItem Engineering analysis of site-dependent factors affecting the Crosbyton solar power project(Texas Tech University, 1973-12) Barriger, Mark ThomasNot availableItem Feasibility of photovoltaic cells on a fixed mirror distributed focus solar bowl(Texas Tech University, 1986-08) Calico, Steve EugeneThe object of the Crosbyton Solar Power Project was to design a solar-fossil hybrid power plant to provide electrical power to Crosbyton, Texas. To meet this objective a test facility was built south of town. The power is produced by focusing sunlight to convert water to steam then using the steam to turn a generator to produce electricity. In times of inclement weather, darkness, or breakdown, electricity is provided by conventional fossil fuels. With the advances in photovoltaic cell efficiency and decreases in cost of manufacturing, direct conversion from solar energy to electrical energy could be possible. The purpose of this study is to determine the technical feasibility of solar cells on a fixed mirror distributed focus solar bowl, such as at the test facility at Crosbyton. Most of the research effort was devoted to the design of the receiver. The cells are mounted on the movable receiver, which tracks the sun during the day. The receiver with attached photovoltaic cells is the critical design element in this solar-electric concept. Its shape and size impact the solar concentration on the cells and the cooling requirements. Once the receiver was designed the essential support equipment needed was studied. These support systems provide for the cooling of the cells and conditioning the direct current electrical output from the solar array to be compatible with the load requirements. No estimate of the cost of construction and operation of such a solar system was made. Such an estimate would be needed to determine the overall feasibility of such a system. However, the simplicity of the receiver designed here and the projections of low cost commercially available solar cells indicate that the feasibility of direct energy conversion by solar cells on a distributed focus receiver may become practical in the near future.Item Forced convection mass transfer from a cylindrical cavity(Texas Tech University, 1981-08) Chang, Chin-tsunOverall convection mass transfer coefficients from the interior of a cylindrical cavity have been determined. By analogy, the present mass transfer experiements model the heat transfer at a heated isothermal downward-facing 'cavity type' solar receiver. The overall mass transfer coefficients over ranges of variables including free stream velocity, aperture opening (d), cavity diameter (D) and depth (L), and inclination angle (0). A total of 145 experimental data were analyzed using a stepwise multiple regression method to obtain a correlation equation. This equation predicts the Sherwood number as a function of four nondimensional parameters - Re, L/D, d/D and 0. This relation is inteded to provide a means of calculating the dependence of the cavity convection heat loss on wind speed and direction and the overall geometry of the cavity. The thin-film naphthalene mass transfer technique provides a rapid and economical method to find the convection heat transfer coefficients in a variety of situations.Item Nonlinear thermoelastic stress analysis of spherically curved solar panels(Texas Tech University, 1985-05) Vungutur, Krishna V S RSpherically curved glass panels are used to concentrate solar energy onto a line focus in fixed mirror distributed focus type solar collectors. These solar panels consist of thin flat glass plates bent to form a spherical surface, glued onto a paper honeycomb backing, and covered with steel plate at the back and with plastic strips on the sides. Stresses are produced in the glass plates as they are formed into spherical surfaces. In addition, when the solar receiver is not in focus relative to the bowl and the sun, a mirror hot spot condition is developed, resulting in large thermally induced stresses within glass plates. The curved glass panel is modeled as a plate on elastic foundation in order to represent the behavior of the plate in relation to other panel components. Since lateral deflections of these plates are large compared to their thickness, nonlinear von Karman plate equations are used in the analysis, A computer model has been prepared to assist in the nonlinear analysis of stresses using finite difference method. The model has flexibility to analyze a variety of rectangular plate geometries subjected to thermal and other applied loads.Item Optical analysis of spherical segment solar collectors(Texas Tech University, 1977-05) Brock, Billy C.A powerful new approach for the calculation of optical flux distributions and power concentration ratios is described. This theory can be applied to mirrors of any shape, illuminated by a source of arbitrary angular extent provided appropriate structure relations can be determined. The method is not restricted to single reflections, but is valid for light which reflects from the mirror any number of times. The work focuses on spherical mirror segments with conical receivers. The result is an extremely accurate expression for the optical power concentration. The method is also applicable for point source illumination.Item Optical power concentrations on aligned and misaligned receivers in solar gridiron power systems(Texas Tech University, 1978-08) Leung, HipsumA powerful strategy, the ROSA approach, has been developed for calculation of optical power concentrations produced by solar collectors. The ROSA method is yery general and can be applied to concentrators and receivers of any geometrical shape. In addition, the method can be used for light from a source of finite extent undergoing any number of multiple reflections on the collector mirror. The work presented here is applied to optical concentrations on a conical receiver suspended in a spherical segment collector as appropriate for a Solar Gridiron Power System. Optical power concentrations on both aligned and misaligned receivers are described for various solar inclinations. A simplified approach for calculating azimuthally averaged power concentrations on a perfectly aligned receiver is also presented.Item Performance analysis of a solar gridiron design verification system(Texas Tech University, 1981-05) Watson, Karan LeaNot availableItem Reflection characteristics at large incident angles with reference to solar bowl(Texas Tech University, 1988-05) Trahan, Markham RayA computer code was developed for the Crosbyton Solar Power Project to calculate the optical concentration along the receiver of the Crosbyton Solar Bowl. The predicted values have been in agreement with the observed data during the middle period of the solar day. However, optical flux distributions along the receiver in the mornings and afternoons have been found to be approximately 8 percent below what was predicted for the system. The purpose for this investigation is to identify the cause(s) for this discrepancy. To account for these discrepancies, a set of simple experiments were performed in the lab using the same kind of mirrors which are mounted on the solar bowl. The data analysis and calculations show that a significant quantity of this discrepancy is due to the focusing defect caused by two properties of back surface reflecting mirrors. They are surface defects introduced during the manufacturing process, and internal reflections between the glass/air interface and the back reflecting surface. These properties have significant effect at large incidence angles.Item Simulation and Analysis of the Process Control for a Solar Gridiron Power System(Texas Tech University, 1981-12) Jiwani, Enayet AlyNot Available.Item Simulation of the Crosbyton receiver(Texas Tech University, 1986-12) Subramanyam, SavithriA thermal-fluid model was developed to describe the collector/ receiver for a fixed-mirror distributed-focus (FMDF) spherical arc reflector. The performance of the system is predicted using a mechanistic model solving an enthalpy balance with the appropriate heat-transfer and pressure-drop correlations. The model includes a rigorous package for predicting the thermodynamic and transport properties for the water/steam system. The steady-state model predicts the exit conditions of the steam, and the radiation and convection losses from the receiver for a given set of Inlet conditions. A correlation based on dimensionless numbers predicts the overall efficiency of the receiver, the exit enthalpy, and the pressure drop for a given heat-flux profile. These predictions compare favorably with the rigorous model results over the ranges tested. The model also predicts the transient response of the collector/ receiver system to disturbances in the input variables. The results of the transient analysis provide insight to the type of control system required to handle start-up, shut-down, intermittent cloudy periods, and failure modes. Thermlnol 55 and molten salt were also used as transport fluids in the case studies. The feasibility of a new type of receiver called the "gun-barrel” design was explored.Item Simulation of the Receiver in a Fixed-Mirror Distributed Focus Solar Power System(Texas Tech University, 1981-08) Shankar, HariharanNot Available.Item Solar concentrator wind loadings(Texas Tech University, 1996-12) Wagner, Geoffrey L.The objective of this project was to determine the maximum wind loadings on a notched parabohc solar concentrator. To accomplish this objective, a test program was conducted using the Texas Tech tow tank. The results from testing a one-tenth scale model were put into nondimensional force and moment coefficients. The maximum coefficients are as follows: hft,0.92; drag, 1.42; side force, 1.05; yaw moment, -0.23; roll moment, 0.72; and pitch moment, 1.28. These results shovdd be used as a starting estimate for the beginning stages of the structural design of the solar concentrator support structure.Item Solar reflectivity and absorptivity studies(Texas Tech University, 1978-05) Chin, ShaulongNot available