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Papers by Joseph O'Gallagher

Research paper thumbnail of Fundamentals and techniques of nonimaging optics: Progress report, May 1988--January 1989

Topics covered by the progress report are: flowline approach to nonimaging concentration; radianc... more Topics covered by the progress report are: flowline approach to nonimaging concentration; radiance and radiometry; and applications of nonimaging optics.

Research paper thumbnail of Design and test of non-evacuated solar collectors with compound parabolic concentrators

Solar Energy, 1980

CPC's and reviews measured performance d a t a and c r i t i c a l d e s i g n c o n s i d e r a ... more CPC's and reviews measured performance d a t a and c r i t i c a l d e s i g n c o n s i d e r a t i o n s. Concentrations i n t h e upper p o r t i o n s of t h e p r a c t i c a l range (e.g. 6X) can p r o v i d e good e f f i c i e n c y (40% t o 50%) i n t h e 100°C-160°C temperature range

Research paper thumbnail of The radial variation of solar flare proton anisotropies observed in deep space on Pioneers 10 and 11

Geophysical Research Letters, 1976

Research paper thumbnail of Implications of the cosmic-ray radial intensity gradients observed during minimum solar modulation

Canadian Journal of Physics, 1968

Research paper thumbnail of Applications of maximally concentrating optics for solar energy collection

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

Research paper thumbnail of Performance Benefits From Nonimaging Secondary Concentrators in Point Focus Dish Solar Thermal Applications

Advances In Solar Energy Technology, 1988

Research paper thumbnail of Design and Comparative Analysis of High Concentration Secondary Elements for Photovoltaic Applications

Clean and Safe Energy Forever, 1990

Research paper thumbnail of Maximally Concentrating Optics for Solar Electricity Generation

Intersol Eighty Five, 1986

Research paper thumbnail of Fundamentals and Techniques of Nonimaging

Research paper thumbnail of Nonimaging Concentrators (Optics)

Encyclopedia of Physical Science and Technology, 2003

Research paper thumbnail of Cosmic-Ray Radial Density Gradient and its Rigidity Dependence Observed at Solar Minimum on Mariner IV

The Astrophysical Journal, 1967

Research paper thumbnail of Stationary nonimaging concentrator as a second stage element in tracking systems

Solar Energy, 1983

An increase in the concentration in line focus solar concentrators is shown to be available using... more An increase in the concentration in line focus solar concentrators is shown to be available using an evacuated compound parabolic concentrator (CPC) tube as a second stage element. The absorber is integrated into an evacuated tube with a transparent upper section and a reflective lower section, with a selective coating on the absorber surface. The overall concentration is calculated in

Research paper thumbnail of Approximations to the CPC—a comment on recent papers by Canning and by Shapiro

Solar Energy, 1978

The purpose of this note is to clarify the issues involved in approximating the compound paraboli... more The purpose of this note is to clarify the issues involved in approximating the compound parabolic concentrator: (CPC) [I-3] or other "ideal" concentrators (e.g. asymmetric ideal concentrators [4]) by non-ideal reflector shapes. Errors in recent articles by Canning[5] (see Gurnee[6]) and Shapiro show that some misconceptions persist.

Research paper thumbnail of Test of a “trumpet” secondary concentrator with a paraboloidal dish primary

Solar Energy, 1986

ABSTRACT

Research paper thumbnail of Thermal and optical performance test results for compound parabolic concentrators (CPCs)

Solar Energy, 1990

The primary objective of the present study was to evaluate the performance characteristics (therm... more The primary objective of the present study was to evaluate the performance characteristics (thermal and optical) of a properly truncated CPC that could be used in two-stage solar thermal power generation systems. The CPCs selected for testing were the 5:1 cones with a 25° acceptance angle and an untruncated concentration ratio of 5.6X. Experiments were carried out at the Advanced

Research paper thumbnail of Performance model for two-stage optical concentrators for solar thermal applications

Solar Energy, 1988

A performance model has been developed for evaluating benefits associated with the addition of a ... more A performance model has been developed for evaluating benefits associated with the addition of a nonimaging secondary concentrator to a conventional paraboloidal solar dish. The model uses a Monte Carlo ray-trace procedure to determine the focal plane distribution as a function of optical parameters and, by evaluating the trade-off between thermal losses and optical gain, calculates the corresponding optimized concentration and thermal efficiency as a function of temperature, both with and without the secondary. These comparative optimizations, carried out over a wide range of design parameters, show that the efficiency of a two-stage concentrator is always greater than that of a single stage if all other design parameters are the same. For example, for a reference design corresponding to a dish with a focal length to diameter ratio of 0.6 and a characteristic slope error of 5 milliradians operated at a receiver temperature of 1000°C, the optimized efficiency with a secondary is 0.07 compared to 0.59 for the primary alone. At fixed focal ratio, the relative performance advantage with a secondary increases, if either the temperature or the primary slope error or both, are increased, whereas it decreases if they are decreased. However, the advantage remains significant at temperatures above 400°C, even in the high performance limit of slope errors <2 milliradians.

Research paper thumbnail of A dynamic model for the time evolution of the modulated cosmic ray spectrum

Journal of Geophysical Research, 1976

Research paper thumbnail of Development of compound parabolic concentrators for solar energy

International Journal of Ambient Energy, 1983

The compound parabolic concentrator (CPC) is not a specific collector, but a family of collectors... more The compound parabolic concentrator (CPC) is not a specific collector, but a family of collectors based on a general design principle for maximizing the geometric concentration, C, for radiation within a given acceptance half angle ±θc. This maximum limit exceeds by a factor of 2 to 4 that attainable by systems using focusing optics. The wide acceptance angles permitted using these techniques have several unique advantages for solar concentrators including the elimination of the diurnal tracking requirement at intermediate concentrations (up to ~10x), collection of circumsolar and some diffuse radiation and relaxed tolerances. Because of these advantages, CPC type concentrators have applications in solar energy wherever concentration is desired, e.g., for a wide variety of both thermal and photovoltaic uses. The basic principles of nonimaging optical design are reviewed. Selected configurations for both non-evacuated and evacuated thermal collector applications are discussed with particular emphasis on the most recent advances. The use of CPC type elements as secondary concentrators is illustrated in the context of higher concentration photovoltaic applications.

Research paper thumbnail of Design and test of an optimized secondary concentrator with potential cost benefits for solar energy conversion

Energy, 1987

Point-focus solar thermal concentrators usually employ only one concentrating mirror, a large-are... more Point-focus solar thermal concentrators usually employ only one concentrating mirror, a large-area paraboloidal dish or similar configuration with approximately the same optical properties. Substantial improvements can be achieved with recently developed two-stage configurations employing a non-imaging Compound Parabolic Concentrator (CPC)-type secondary. Such compound systems have the capability of achieving typically a four-fold increase over the concentration attainable by a single-stage primary of given optical quality. Recent efforts have been to design the secondary to relax the optical quality requirements for the large-area primary as much as possible, thereby potentially reducing system cost considerably. These new designs favor longer focal ratios than those characteristic of typical single-stage configurations. Two features of these designs make the approach particularly promising. First, the long focal length two-stage design always provides a fundamental increase in the tolerance for optical errors. Second, many primary fabrication and design techniques which seek to approximate a paraboloid become much better approximations in the long focal length limit. A conceptual design which illustrates these features and which could achieve a geometrical concentration of 215 x with a CPC secondary and a primary comprising only 60 flat mirror facets is described. To carry out an operational test a secondary concentrator suitable for use with a variety of long focal length primaries was designed and several different test models were fabricated. A series of optical and thermal performance measurements was carried out at the Advanced Components Test Facility (ACTF) operated by the Georgia Tech Research Institute. The results have established that thermal control can be readily achieved with simple passive means for moderate concentration and power ranges. Preliminary analysis yields values of approximately 90 f 3% for the optical efficiency of the CPC secondaries with silver reflecting surfaces.

Research paper thumbnail of Fundamentals and techniques of nonimaging optics: Progress report, May 1988--January 1989

Topics covered by the progress report are: flowline approach to nonimaging concentration; radianc... more Topics covered by the progress report are: flowline approach to nonimaging concentration; radiance and radiometry; and applications of nonimaging optics.

Research paper thumbnail of Design and test of non-evacuated solar collectors with compound parabolic concentrators

Solar Energy, 1980

CPC's and reviews measured performance d a t a and c r i t i c a l d e s i g n c o n s i d e r a ... more CPC's and reviews measured performance d a t a and c r i t i c a l d e s i g n c o n s i d e r a t i o n s. Concentrations i n t h e upper p o r t i o n s of t h e p r a c t i c a l range (e.g. 6X) can p r o v i d e good e f f i c i e n c y (40% t o 50%) i n t h e 100°C-160°C temperature range

Research paper thumbnail of The radial variation of solar flare proton anisotropies observed in deep space on Pioneers 10 and 11

Geophysical Research Letters, 1976

Research paper thumbnail of Implications of the cosmic-ray radial intensity gradients observed during minimum solar modulation

Canadian Journal of Physics, 1968

Research paper thumbnail of Applications of maximally concentrating optics for solar energy collection

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

Research paper thumbnail of Performance Benefits From Nonimaging Secondary Concentrators in Point Focus Dish Solar Thermal Applications

Advances In Solar Energy Technology, 1988

Research paper thumbnail of Design and Comparative Analysis of High Concentration Secondary Elements for Photovoltaic Applications

Clean and Safe Energy Forever, 1990

Research paper thumbnail of Maximally Concentrating Optics for Solar Electricity Generation

Intersol Eighty Five, 1986

Research paper thumbnail of Fundamentals and Techniques of Nonimaging

Research paper thumbnail of Nonimaging Concentrators (Optics)

Encyclopedia of Physical Science and Technology, 2003

Research paper thumbnail of Cosmic-Ray Radial Density Gradient and its Rigidity Dependence Observed at Solar Minimum on Mariner IV

The Astrophysical Journal, 1967

Research paper thumbnail of Stationary nonimaging concentrator as a second stage element in tracking systems

Solar Energy, 1983

An increase in the concentration in line focus solar concentrators is shown to be available using... more An increase in the concentration in line focus solar concentrators is shown to be available using an evacuated compound parabolic concentrator (CPC) tube as a second stage element. The absorber is integrated into an evacuated tube with a transparent upper section and a reflective lower section, with a selective coating on the absorber surface. The overall concentration is calculated in

Research paper thumbnail of Approximations to the CPC—a comment on recent papers by Canning and by Shapiro

Solar Energy, 1978

The purpose of this note is to clarify the issues involved in approximating the compound paraboli... more The purpose of this note is to clarify the issues involved in approximating the compound parabolic concentrator: (CPC) [I-3] or other "ideal" concentrators (e.g. asymmetric ideal concentrators [4]) by non-ideal reflector shapes. Errors in recent articles by Canning[5] (see Gurnee[6]) and Shapiro show that some misconceptions persist.

Research paper thumbnail of Test of a “trumpet” secondary concentrator with a paraboloidal dish primary

Solar Energy, 1986

ABSTRACT

Research paper thumbnail of Thermal and optical performance test results for compound parabolic concentrators (CPCs)

Solar Energy, 1990

The primary objective of the present study was to evaluate the performance characteristics (therm... more The primary objective of the present study was to evaluate the performance characteristics (thermal and optical) of a properly truncated CPC that could be used in two-stage solar thermal power generation systems. The CPCs selected for testing were the 5:1 cones with a 25° acceptance angle and an untruncated concentration ratio of 5.6X. Experiments were carried out at the Advanced

Research paper thumbnail of Performance model for two-stage optical concentrators for solar thermal applications

Solar Energy, 1988

A performance model has been developed for evaluating benefits associated with the addition of a ... more A performance model has been developed for evaluating benefits associated with the addition of a nonimaging secondary concentrator to a conventional paraboloidal solar dish. The model uses a Monte Carlo ray-trace procedure to determine the focal plane distribution as a function of optical parameters and, by evaluating the trade-off between thermal losses and optical gain, calculates the corresponding optimized concentration and thermal efficiency as a function of temperature, both with and without the secondary. These comparative optimizations, carried out over a wide range of design parameters, show that the efficiency of a two-stage concentrator is always greater than that of a single stage if all other design parameters are the same. For example, for a reference design corresponding to a dish with a focal length to diameter ratio of 0.6 and a characteristic slope error of 5 milliradians operated at a receiver temperature of 1000°C, the optimized efficiency with a secondary is 0.07 compared to 0.59 for the primary alone. At fixed focal ratio, the relative performance advantage with a secondary increases, if either the temperature or the primary slope error or both, are increased, whereas it decreases if they are decreased. However, the advantage remains significant at temperatures above 400°C, even in the high performance limit of slope errors <2 milliradians.

Research paper thumbnail of A dynamic model for the time evolution of the modulated cosmic ray spectrum

Journal of Geophysical Research, 1976

Research paper thumbnail of Development of compound parabolic concentrators for solar energy

International Journal of Ambient Energy, 1983

The compound parabolic concentrator (CPC) is not a specific collector, but a family of collectors... more The compound parabolic concentrator (CPC) is not a specific collector, but a family of collectors based on a general design principle for maximizing the geometric concentration, C, for radiation within a given acceptance half angle ±θc. This maximum limit exceeds by a factor of 2 to 4 that attainable by systems using focusing optics. The wide acceptance angles permitted using these techniques have several unique advantages for solar concentrators including the elimination of the diurnal tracking requirement at intermediate concentrations (up to ~10x), collection of circumsolar and some diffuse radiation and relaxed tolerances. Because of these advantages, CPC type concentrators have applications in solar energy wherever concentration is desired, e.g., for a wide variety of both thermal and photovoltaic uses. The basic principles of nonimaging optical design are reviewed. Selected configurations for both non-evacuated and evacuated thermal collector applications are discussed with particular emphasis on the most recent advances. The use of CPC type elements as secondary concentrators is illustrated in the context of higher concentration photovoltaic applications.

Research paper thumbnail of Design and test of an optimized secondary concentrator with potential cost benefits for solar energy conversion

Energy, 1987

Point-focus solar thermal concentrators usually employ only one concentrating mirror, a large-are... more Point-focus solar thermal concentrators usually employ only one concentrating mirror, a large-area paraboloidal dish or similar configuration with approximately the same optical properties. Substantial improvements can be achieved with recently developed two-stage configurations employing a non-imaging Compound Parabolic Concentrator (CPC)-type secondary. Such compound systems have the capability of achieving typically a four-fold increase over the concentration attainable by a single-stage primary of given optical quality. Recent efforts have been to design the secondary to relax the optical quality requirements for the large-area primary as much as possible, thereby potentially reducing system cost considerably. These new designs favor longer focal ratios than those characteristic of typical single-stage configurations. Two features of these designs make the approach particularly promising. First, the long focal length two-stage design always provides a fundamental increase in the tolerance for optical errors. Second, many primary fabrication and design techniques which seek to approximate a paraboloid become much better approximations in the long focal length limit. A conceptual design which illustrates these features and which could achieve a geometrical concentration of 215 x with a CPC secondary and a primary comprising only 60 flat mirror facets is described. To carry out an operational test a secondary concentrator suitable for use with a variety of long focal length primaries was designed and several different test models were fabricated. A series of optical and thermal performance measurements was carried out at the Advanced Components Test Facility (ACTF) operated by the Georgia Tech Research Institute. The results have established that thermal control can be readily achieved with simple passive means for moderate concentration and power ranges. Preliminary analysis yields values of approximately 90 f 3% for the optical efficiency of the CPC secondaries with silver reflecting surfaces.