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Optical performance of the TBC-2 solar collector before and after the 1993 mirror lustering

Description: In 1993, the mirror facets of one of Sandia`s point-focusing solar collectors, the Test Bed Concentrator {number_sign}2 (TBC-2), were reconditioned. The concentrator`s optical performance was evaluated before and after this operation. This report summarizes and compares the results of these tests. The tests demonstrated that the concentrator`s total power and peak flux were increased while the overall flux distribution in the focal plane remained qualitatively the same.
Date: February 1, 1995
Creator: Houser, R. & Strachan, J.
Partner: UNT Libraries Government Documents Department

Heat loss from an open cavity

Description: Cavity type receivers are used extensively in concentrating solar thermal energy collecting systems. The Solar Total Energy Project (STEP) in Shenandoah, Georgia is a large scale field test for the collection of solar thermal energy. The STEP experiment consists of a large field array of solar collectors used to supplement the process steam, cooling and other electrical power requirements of an adjacent knitwear manufacturing facility. The purpose of the tests, conducted for this study, was to isolate and quantify the radiative, conductive, and convective components of total heat loss, and to determine the effects of operating temperature, receiver angle, and aperture size on cavity heat loss. An analytical model for radiative heat loss was developed and compared with two other methods used to determine radiative heat loss. A proposed convective heat loss correlation, including effects of aperture size, receiver operating temperature, and receiver angle is presented. The resulting data is a source to evaluate the STEP measurements.
Date: December 1, 1995
Creator: McDonald, C.G.
Partner: UNT Libraries Government Documents Department

Solar-Electric Dish Stirling System Development

Description: Electrical power generated with the heat from the sun, called solar thermal power, is produced with three types of concentrating solar systems - trough or line-focus systems; power towers in which a centrally-located thermal receiver is illuminated with a large field of sun-tracking heliostats; and dish/engine systems. A special case of the third type of system, a dish/Stirling system, is the subject of this paper. A dish/Stirling system comprises a parabolic dish concentrator, a thermal receiver, and a Stirling engine/generator located at the focus of the dish. Several different dish/Stirling systems have been built and operated during the past 15 years. One system claims the world record for net conversion of solar energy to electric power of 29.4%; and two different company`s systems have accumulated thousands of hours of on-sun operation. Due to de-regulation and intense competition in global energy markets as well as the immaturity of the technology, dish/Stirling systems have not yet found their way into the marketplace. This situation is changing as solar technologies become more mature and manufacturers identify high-value niche markets for their products. In this paper, I review the history of dish/Stirling system development with an emphasis on technical and other issues that directly impact the Stirling engine. I also try to provide some insight to the opportunities and barriers confronting the application of dish/Stirling in power generation markets.
Date: December 31, 1997
Creator: Mancini, T.R.
Partner: UNT Libraries Government Documents Department

Concentrating Solar Power Program overview

Description: Over the last decade, the US solar thermal industry has established a track record in the power industry by building and operating utility-scale power plants with a combined rated capacity of 354 megawatts (MW). The technology used in these power plants is based on years of research and development (R and D), much of it sponsored by the US Department of Energy (DOE). DOE`s Concentrating Solar Power (CSP) Program is collaborating with its partners in the private sector to develop two new solar technologies -- power towers and dish/engines -- to meet the huge commercial potential for solar power.
Date: April 1, 1998
Partner: UNT Libraries Government Documents Department

The lustering of TBC-2

Description: Two test bed concentrators (TBCs) were designed to provide high-performance test beds for advanced solar receivers and converters. However, the second-surface silvered-glass mirror facets on the TBCs, which were originally manufactured by the Jet Propulsion Laboratory, have experienced severe silver corrosion. To restore reflectance, TBC-2 was refurbished with a lustering technique developed at Sandia National Laboratories. In the lustering technique, second-surface silvered thin-glass mirrors were applied over the corroded facets, thereby increasing the dish reflectivity and raising the available power of TBC-2 from approximately 70 to 78 kW{sub t}. Degradation of the original optical accuracy of the TBC facets was determined to be minimal. Lustering was chosen over facet replacement because of the lower cost, the anticipated improvement in corrosion resistance, and the shorter project duration. This report includes background information, details of the lustering process, and test results from TBC-2 characterization, both before and after lustering.
Date: May 1, 1995
Creator: Diver, R.B.; Jones, S.; Robb, S. & Mahoney, A.R.
Partner: UNT Libraries Government Documents Department

Development of a 75-kW heat-pipe receiver for solar heat-engines

Description: A program is now underway to develop commercial power conversion systems that use parabolic dish mirrors in conjunction with Stirling engines to convert solar energy to electric power. In early prototypes, the solar concentrator focused light directly on the heater tubes of the Stirling engine. Liquid-metal heat-pipes are now being developed to transfer energy from the focus of the solar concentrator to the heater tubes of the engine. The dome-shaped heat-pipe receivers are approximately one-half meters in diameter and up to 77-kW of concentrated solar energy is delivered to the absorber surface. Over the past several years, Sandia National Laboratories, through the sponsorship of the Department of Energy, has conducted a major program to explore receiver designs and identify suitable wick materials. A high-flux bench-scale system has been developed to test candidate wick designs, and full-scale systems have been tested on an 11-meter test-bed solar concentrator. Procedures have also been developed in this program to measure the properties of wick materials, and an extensive data-base on wick materials for high temperature heat pipes has been developed. This paper provides an overview of the receiver development program and results from some of the many heat-pipe tests.
Date: May 1, 1995
Creator: Adkins, D.R.; Andraka, C.E. & Moss, T.A.
Partner: UNT Libraries Government Documents Department

National Solar Thermal Test Facility

Description: This is a brief report about a Sandia National Laboratory facility which can provide high-thermal flux for simulation of nuclear thermal flash, measurements of the effects of aerodynamic heating on radar transmission, etc
Date: December 1989
Creator: Cameron, C. P.
Partner: UNT Libraries Government Documents Department

An investigation of corrosion in liquid-metal heat pipes

Description: Research is underway to develop a 75-kW heat pipe to transfer solar energy from the focus of a parabolic dish concentrator to the heater tubes of a Stirling engine. The high flux levels and high total power level encountered in this application have made it necessary to use a high-performance wick structure with fibers on the order of 4 to 8 microns in diameter. This fine wick structure is highly susceptible to corrosion damage and plugging, as dissolved contaminants plate out on the evaporator surface. Normal operation of the heat pipe also tends to concentrate contaminants in localized areas of the evaporator surface where heat fluxes are the highest. Sandia National Laboratories is conducting a systematic study to identify procedures that reduce corrosion and contamination problems in liquid-metal heat pipes. A series of heat pipes are being tested to explore different options for cleaning heat-pipe systems. Models are being developed to help understand the overall importance of operating parameters on the life of heat-pipe systems. In this paper, the authors present their efforts to reduce corrosion damage.
Date: August 1, 1998
Creator: Adkins, D.R.; Rawlinson, K.S.; Andraka, C.E.; Showalter, S.K.; Moreno, J.B.; Moss, T.A. et al.
Partner: UNT Libraries Government Documents Department

Dish/Stirling systems: Overview of an emerging commercial solar thermal electric technology

Description: Dish/Stirling is a solar thermal electric technology which couples parabolic, point-focusing solar collectors and heat engines which employ the Stirling thermodynamic cycle. Since the late 1970s, the development of Dish/Stirling systems intended for commercial use has been in progress in Germany, Japan, and the US. In the next several years it is expected that one or more commercial systems will enter the market place. This paper provides a general overview of this emerging technology, including: a description of the fundamental principles of operation of Dish/Stirling systems; a presentation of the major components of the systems (concentrator, receiver, engine/alternator, and controls); an overview of the actual systems under development around the world, with a discussion of some of the technical issues and challenges facing the Dish/Stirling developers. A brief discussion is also presented of potential applications for small Dish/Stirling systems in northern Mexico.
Date: November 1, 1995
Creator: Strachan, J.W.; Diver, R.B. & Estrada, C.
Partner: UNT Libraries Government Documents Department

Concentrating Solar Power strategic plan summary

Description: A strategic plan for Concentrating Solar Power (CSP) -- A Bright Path to the Future -- was completed and released by the US Department of Energy`s Office of Solar Thermal, Biomass Power, and Hydrogen Technologies in December 1996. This strategic plan document will help bring CSP (formerly solar thermal electric) technologies to the marketplace over the course of the next 20 years (1996--2015) -- taking us from the current pre-competitive status closer to full commercialization. The plan, developed in concert with stakeholders, is a living document and will undergo periodic reevaluation as well as revision to reflect changes in the market environment, the progress of the technologies, and the development of new concepts and ideas.
Date: May 1, 1998
Partner: UNT Libraries Government Documents Department

A long-term strategic plan for development of solar thermal electric technology

Description: Solar thermal electric (STE) technologies--parabolic troughs, power towers, and dish/engine systems--can convert sunlight into electricity efficiently and with minimum effect on the environment. These technologies currently range from developmental to early commercial stages of maturity. This paper summarizes the results of a recent strategic planning effort conducted by the US Department of Energy (DOE) to develop a long-term strategy for the development of STE technologies (DOE, 1996). The planning team led by DOE included representatives from the solar thermal industry, domestic utilities, state energy offices, and Sun-Lab (the cooperative Sandia National Laboratories/National Renewable Energy Laboratory partnership that supports the STE Program) as well as project developers. The plan was aimed at identifying specific activities necessary to achieve the DOE vision of 20 gigawatts of installed STE capacity by the year 2020. The planning team developed five strategies that both build on the strengths of, and opportunities for, STE technology and address weaknesses and threats. These strategies are to support future commercial opportunities for STE technologies; demonstrate improved performance and reliability of STE components and systems; reduce STE energy costs; develop advanced STE systems and applications; and address nontechnical barriers and champion STE power. The details of each of these strategies are discussed.
Date: June 1997
Creator: Williams, T. A.; Burch, G. D.; Chavez, J. M.; Mancini, T. R. & Tyner, C. E.
Partner: UNT Libraries Government Documents Department

Solar dish/engine systems

Description: Solar dish/engine systems convert the energy from the sun into electricity at a very high efficiency. Using a mirror array formed into the shape of a dish, the solar dish focuses the sun's rays onto a receiver. The receiver transmits the energy to an engine that generates electric power. Because of the high concentration ratios achievable with parabolic dishes and the small size of the receiver, solar dishes are efficient at collecting solar energy at very high temperatures. Tests of prototype systems and components at locations throughout the US have demonstrated net solar to electric conversion efficiencies as high as 30%. This is significantly higher than any other solar technology.
Date: April 1, 1998
Partner: UNT Libraries Government Documents Department

Performance and cost benefits associated with nonimaging secondary concentrators used in point-focus dish solar thermal applications

Description: Using nonimaging secondary concentrators in point-focus applications may permit the development of more cost-effective concentrator systems by either improving performance or reducing costs. Secondaries may also increase design flexibility. The major objective of this study was to develop as complete an understanding as possible of the quantitative performance and cost effects associated with deploying nonimaging secondary concentrators at the focal zone of point-focus solar thermal concentrators. A performance model was developed that uses a Monte Carlo ray-trace procedure to determine the focal plane distribution of a paraboloidal primary as a function of optical parameters. It then calculates the corresponding optimized concentration and thermal efficiency as a function of temperature with and without the secondary. To examine the potential cost benefits associated with secondaries, a preliminary model for the rational optimization of performance versus cost trade-offs was developed. This model suggests a possible 10% to 20% reduction in the cost of delivered energy when secondaries are used. This is a lower limit, and the benefits may even be greater if using a secondary permits the development of inexpensive primary technologies for which the performance would not otherwise be viable. 20 refs., 15 figs., 3 tabs.
Date: September 1, 1987
Creator: O'Gallagher, J. & Winston, R.
Partner: UNT Libraries Government Documents Department

Comparison of predicted optical performance with measured results for dish concentrators

Description: Several optical design tools have been developed at the National Renewable Energy Laboratory (NREL) during the past two years. These have been used extensively both in-house and by industry to analyze dish concentrator systems and to optimize performance of such designs. The first program, OPTDSH, models single-element dish concentrators. The second code, ODMF, allows multifacet dish arrays to be modeled. The accuracy of performance simulations by these programs has been established by comparing predicted results with measured on-sun data. ODMF evolved from NREL's High-Flux Solar Furnace (HFSF) design tool, SOLFUR, and in fact is a special case of SOLFUR in which the primary facet array is on sun.'' Consequently, confirmation of the accuracy of SOLFUR would verify the results from ODMF as well. Furthermore, because OPTDSH can be viewed as a single-facet case of ODMF, determination of the precision of SOLFUR/ODMF would also substantiate OPTDSH. Thus, the approach to verifying the correctness of all three codes was to compare flux patterns as predicted by SOLFUR with those actually measured at NREL's HFSF. Measured vs. calculated data have been compared on the basis of flux distribution (in terms of contour plots) and peak flux for both single-facet and multiple-facet cases. Agreement in measured vs. predicted peak flux values has been obtained within the uncertainty associated with the measurement/calibration process. Excellent agreement has also been demonstrated by comparing contour maps of measured vs. computed flux levels. 7 refs.
Date: April 1, 1991
Creator: Jorgensen, G.
Partner: UNT Libraries Government Documents Department

Development of a solar thermal receiver for high temperature applications

Description: A thermal receiver for point focus collectors is being constructed. Its design, which is based upon experience with a commercial receiver, employs the advantages of that receiver and improves some of its features. The new receiver uses as a buffer between the cavity surface and the heat transfer fluid a thermal mass, which with a very small temperature drop penalty smooths the flux distribution to eliminate hot spots. Maximum operating temperature range was extended from 620/sup 0/C to 870/sup 0/C and receiver efficiency was improved. The design of the receiver enables significant spillage flux at the receiver to be used. Thus, lower quality optics can be employed in applications not requiring very high temperatures. Design and construction features of the receiver are presented and the testing program is described.
Date: November 1, 1979
Creator: Bohn, M. & Bessler, G.
Partner: UNT Libraries Government Documents Department

Sun{diamond}Lab test facilities

Description: This country's efforts to successfully develop and commercialize concentrating solar power (CSP) technologies depend on specialized research and testing capabilities. To Support this effort, the US Department of Energy's Concentrating Solar Power Program maintains two major test facilities: the National Solar Thermal Test Facility at Sandia National Laboratories in Albuquerque, New Mexico, and the High Flux Solar Furnace at the National Renewable Energy Laboratory in Golden, Colorado. These test facilities combine to be instrumental in the development of parabolic dishes, troughs, and solar power towers.
Date: April 1, 1998
Partner: UNT Libraries Government Documents Department

Solar thermal bowl concepts and economic comparisons for electricity generation

Description: This study is aimed at providing a relative comparison of the thermodynamic and economic performance in electric applications for fixed mirror distributed focus (FMDF) solar thermal concepts which have been studied and developed in the DOE solar thermal program. Following the completion of earlier systems comparison studies in the late 1970's there have been a number of years of progress in solar thermal technology. This progress includes developing new solar components, improving component and system design details, constructing working systems, and collecting operating data on the systems. This study povides an update of the expected performance and cost of the major components, and an overall system energy cost for the FMDDF concepts evaluated. The projections in this study are for the late 1990's and are based on the potential capabilities that might be achieved with further technology development.
Date: April 1, 1988
Creator: Williams, T.A.; Dirks, J.A.; Brown, D.R.; Antoniak, Z.I.; Allemann, R.T.; Coomes, E.P. et al.
Partner: UNT Libraries Government Documents Department

Parabolic concentrating collector: a tutorial

Description: A tutorial overview of point-focusing parabolic collectors is presented. Optical and thermal characteristics of such collectors are discussed. Data representing typical achievable collector efficiencies are presented and the importance of balancing collector cost with concentrator quality is argued through the development of a figure of merit for the collector. The impact of receiver temperature on performance is assessed and the general observation made that temperatures much in excess of 1500 to 2000/sup 0/F can actually result in decreased performance. Various types of two-axis tracking collectors are described, including the standard parabolic deep dish, Cassegrainian and Fresnel, as well as two forms of fixed mirrors with articulating receivers. The present DOE program to develop these devices is briefly discussed, as are present and projected costs for these collectors. Pricing information is presented for the only known commercial design available on the open market.
Date: February 15, 1979
Creator: Truscello, V.C.
Partner: UNT Libraries Government Documents Department

Application of field-modulated generator systems to dispersed solar thermal electric generation

Description: A Parabolic Dish-Electric Transport concept for dispersed solar thermal generation is considered. In this concept the power generated by 15 kWe Solar Generation Units is electrically collected in a large plant. Various approaches are possible for the conversion of mechanical shaft output of the heat engines to electricity. This study focuses on the Application of Field Modulated Generation System (FMGS) for that purpose. Initially the state-of-the-art of FMGS is presented, and the application of FMGS to dispersed solar thermal electric generation is investigated. This is followed by the definition of the control and monitoring requirements for solar generation system. Then comparison is made between FMGS approach and other options. Finally, the technology developmental needs are identified.
Date: August 15, 1979
Creator: Ramakumar, R. & Bahrami, K.
Partner: UNT Libraries Government Documents Department

Prototype dish testing and analysis at Sandia National Laboratories

Description: During the past year, Sandia National Laboratories performed on-sun testing of several dish concentrator concepts. These tests were undertaken at the National Solar Thermal Test Facility (NSTTF). Two of the tests were performed in support of the DOE Concentrator Receiver Development Program. The first was on-sun testing of the single-element stretched-membrane dish; this 7-meter diameter dish uses a single preformed metal membrane with an aluminized polyester optical surface and shows potential for future dish-Stirling systems. The next involved two prototype facets from the Faceted Stretched-Membrane Dish Program. These facets, representing competitive design concepts, are closest to commercialization. Five 1-meter triangular facets were tested on-sun as part of the development program for a solar dynamic system on Space Station Freedom. While unique in character, all the tests utilized the Beam Characterization System (BCS) as the main measurement tool and all were analyzed using the Sandia-developed CIRCE2 computer code. The BCS is used to capture and digitize an image of the reflected concentrator beam that is incident on a target surface. The CIRCE2 program provides a computational tool, which when given the geometry of the concentrator and target as well as other design parameters will predict the flux distribution of the reflected beam. One of these parameters, slope error, is the variable that has a major effect in determining the quality of the reflected beam. The methodology used to combine these two tools to predict uniform slope errors for the dishes is discussed in this document. As the Concentrator Development Programs continue, Sandia will test and evaluate two prototype dish systems. The first, the faceted stretched-membrane dish, is expected to be tested in 1992, followed by the full-scale single-element stretched-membrane dish in 1993. These tests will use the tools and methodology discussed in this document. 14 refs., 10 figs., 5 tabs.
Date: January 1, 1991
Creator: Grossman, J.W.; Houser, R.M. & Erdman, W.W.
Partner: UNT Libraries Government Documents Department

Advanced Component Research Facility (ACRES)

Description: A detailed description of the SERI Advanced Component Research Facility (ACRES) is given. Background information explicates the facility's history, developed around the two Omnium-G parabolic dish concentrators. The Omnium-G concentrators and electrical power plant are described. The purpose and a detailed descripttion of ACRES is also given. Included is a description of the measurement capabilities, the controls, and each component of the facility.
Date: July 1, 1980
Creator: Bohn, M.
Partner: UNT Libraries Government Documents Department

Determination of accuracy of measurements by NREL's Scanning Hartmann Optical Test instrument

Description: NREL's Scanning Hartmann Optical Test (SHOT) instrument is routinely used to characterize the surface of candidate dish concentration elements for solar thermal applications. An approach was devised to quantify the accuracy of these measurements. Excellent reproducibility was exhibited and high confidence established. The SHOT instrument was designed to allow the surface figure of large optical test articles to be accurately specified. Such test articles are nominally parabolic with an f/D ratio (in which f=focal length and D=aperture diameter) in the range of 0.5--1.0. Recent modifications of SHOT have extended the characterization range out to about f/D=3.0. A series of experiments was designed to investigate and quantify the uncertainties associated with optical characterization performed by SHOT. This approach involved making a series of measurements with an arbitrary test article positioned at a number of locations transverse to the optical axis of SHOT. 3 refs.
Date: April 1, 1991
Creator: Jorgensen, G.; Wendelin, T. & Carasso, M.
Partner: UNT Libraries Government Documents Department

Secondary and compound concentrators for parabolic-dish solar-thermal power systems

Description: A secondary optical element may be added to a parabolic dish solar concentrator to increase the geometric concentration ratio attainable at a given intercept factor. This secondary may be a Fresnel lens or a mirror, such as a compound elliptic concentrator or a hyperbolic trumpet. At a fixed intercept factor, higher overall geometric concentration may be obtainable with a long focal length primary and a suitable secondary matched to it. Use of a secondary to increase the geometric concentration ratio is more likely to be worthwhile if the receiver temperature is high and if errors in the primary are large. Folding the optical path with a secondary may reduce cost by locating the receiver and power conversion equipment closer to the ground and by eliminating the heavy structure needed to support this equipment at the primary focus. Promising folded-path configurations include the Ritchey-Chretien and perhaps some three-element geometries. Folding the optical path may be most useful in systems that provide process heat.
Date: April 15, 1981
Creator: Jaffe, L.D. & Poon, P.T.
Partner: UNT Libraries Government Documents Department