Showing papers on "Energy conversion efficiency published in 1975"

Efficient CuInSe2/CdS solar cells

Abstract: We report the preparation of a CuInSe2/CdS heterojunction solar cell having a solar power conversion efficiency of 12% measured on a clear day in New Jersey (∼92‐mW/cm2 solar intensity).

A new concept for solar energy thermal conversion

Abstract: A material has been developed which allows a new approach to be made to the conversion of solar energy to heat. It consists of a dense array of metal whiskers grown with spacings of a few wavelengths of visible light. The material selected has low emissivity, and achieves significant optical absorption by trapping the light by a geometric maze effect. We have deomonstrated that absorption of normal incidence light is greater than 98% from 0.5 to 40‐μm wavelengths, and hemispherical emissivity at 550 °C can be made less than 0.26. Since surfaces can be made of a single refractory element, such as W, high‐temperature solar conversion (550 °C) should be maintained with good surface stability.

Electrochemical aspects of solar energy conversion

Abstract: Current research and development work in solar energy utilization is very briefly reviewed. Attention is drawn to the possible use of photoelectrochemical effects to convert solar energy directly to electric power or synthetic fuel. Photoelectrochemical cells that have been proposed for this purpose are classified into three types, and a detailed description of their mode of action is given. The solar spectrum at the earth's surface and terrestrial receipts of solar energy are discussed. The factors that limit the power conversion efficiency of photoelectrochemical cells are described, and a brief reference is made to the thermodynamics of photoelectric transducers. Some work that, although not directly related to solar energy conversion, is of possible relevance, is summarized: the topics covered are the photosensitization of processes at semiconductor electrodes, pigment films on metal electrodes, and the primary processes of energy and charge transfer in natural and artificial photosynthetic membranes.

p−InP/n−CdS solar cells and photovoltaic detectors

Abstract: We have prepared p−InP/n−CdS heterodiode photovoltaic detectors with a uniform quantum efficiency of ∼70% for wavelengths between 550 and 910 nm. On a cloudy day in New Jersey, (53 mW/cm2) solar power conversion efficiencies of 12.5% have been measured on cells provided with antireflection coatings.

Solar energy converter with waste heat engine

Abstract: A solar energy converter uses gallium arsenide photovoltaic cells to convert light to direct current. Optical concentrators reduce the needed area of cells. Gallium arsenide retains high conversion efficiency up to several hundred degrees, so the waste heat may be used to produce mechanical power in a Rankine cycle engine.

GaAs concentrator solar cell

Abstract: For terrestrial applications, the figure of merit for photovoltaic solar energy conversion devices is watts output per dollar of cost. AlGaAs/GaAs heterojunction cells have a very favorable watts per dollar figure of merit when used at high values of sunlight concentration. An experimental 1/2−in.−diam cell was operated in air mass 1.4 sunlight with an output power density of 4.52 W/cm2 at an effective concentration of 312 suns with a power conversion efficiency of 17.5%. The same cell was operated at 200 °C with an output power density of 3.45 W/cm2 at a 14% efficiency. The efficiency of the cell was 23% with a fill factor of 0.85 at a lower concentration ratio which is obtainable using simple concentrator schemes.

Direct thermal-electric conversion for geothermal energy recovery

Abstract: Direct conversion systems for in situ conversion of geothermal energy into electricity are described in which thermoelectric generators and/or thermionic convertors directly convert the earth's thermal energy into electrical energy. The choice of a thermoelectric or thermionic system is dictated by the temperature domain of the particular geothermal formation. The basic unit of the described system includes at least two coaxially-intersecting heat pipes, extending between a high temperature geological strata and a low temperature geological strata. Thermal-electric energy conversion devices are positioned within an annulus between the intersecting heat pipes.

Radiated microwave power transmission system efficiency measurements

Abstract: The measured and calculated results from determining the operating efficiencies of a laboratory version of a system for transporting electric power from one point to another via a wireless free space radiated microwave beam are reported. The system's overall end-to-end efficiency as well as intermediated conversion efficiencies were measured. The maximum achieved end-to-end dc-to-ac system efficiency was 54.18% with a probable error of + or - 0.94%. The dc-to-RF conversion efficiency was measured to be 68.87% + or - 1.0% and the RF-to-dc conversion efficiency was 78.67 + or - 1.1%. Under these conditions a dc power of 495.62 + or - 3.57 W was received with a free space transmitter antenna receiver antenna separation of 170.2 cm (67 in).

Third harmonic generation in phase‐matched alkali metal vapors

Abstract: We report improvements in conversion efficiency for third harmonic generation in sodium and rubidium vapor. 30‐psec pulses of radiation at 1.064 μm have been converted to 0.3547 μm with an energy conversion efficiency of 10%. Factors limiting conversion efficiency are discussed.

Waste heat regenerating system

Abstract: The invention described herein pertains to a combination hydraulic thermodynamic prime mover, for the conversion of thermal energy from low-temperature heat sources, such as solar heat, geothermal steam of poor quality and waste heat of all kinds, into useful mechanical or electrical power, employing a new and novel technique of low temperature-pressure energy conversion.

Low‐threshold cw LiNdP4O12 laser

Abstract: We have studied cw room‐temperature lasing behavior of LiNdP4O12. A threshold of 360‐μW optical excitation power at 0.582‐μm wavelength was measured, with 18% power conversion efficiency to 1.048‐μm radiation at 1‐mW output. The crystal structure is found to be monoclinic (C2/c) rather than orthorhombic as previously reported.

Modeling and Computer Simulation of a Microwave-to-DC Energy Conversion Element

Abstract: A microwave-to-dc energv conversion element consisting of a dipole antenna, a low-pass filter, a Schottky-barrier diode, and a dc filter has been modeled using a distributed transmission-line modeling technique that includes skin-effect losses. Computer simulation has shown 80-percent conversion efficiency and has indicated that the diode generates significant power at higher harmonics due to a resonance effect.

Enhancement of Schottky solar cell efficiency above its semiempirical limit

Abstract: Geometries are described for increasing the efficiency of Schottky solar cells above the theoretical limits recently calculated. The ultimate conversion efficiencies for the new cells are the same as for p‐n junction devices. With present technology, improvements of over 50% above the old limits are possible.

High-efficiency graded band-gap Al/x/Ga/1-x/As-GaAs solar cell

Abstract: A detailed theoretical analysis of an n-on-p graded band-gap Al(x)Ga(1-x)As-GaAs solar cell yields a maximum air mass zero power conversion efficiency of 17% compared to 9% for a similar GaAs cell. The analysis includes surface and bulk minority carrier recombination, junction recombination current, spectrally varying surface reflection, and series resistance loss. The maximum efficiency is determined for a surface recombination velocity of 10,000 cm/sec and hole and electron diffusion lengths of 2.1 and 7.6 microns, respectively. The improved efficiency is primarily due to a built-in electric field, caused by the band-gap gradation, accelerating photogenerated holes toward the p-n junction. This field reduces the surface and bulk recombination of the holes, and thereby enhances their collection.

Thick semiconductor films for photothermal solar energy conversion

Abstract: Efficient and economical photothermal conversion of solar energy requires the use of spectrally selective surfaces for collection and retention of incident solar flux. This spectral selectivity can be obtained from an absorber–reflector tandem by overcoating an opaque metal film having high infrared reflectance with a thick film (1–5μm) of semiconductor having an appropriate band gap. The practical implementation of this design using films of silver and silicon on a variety of substrate materials is described. Chemical vapor deposition (CVD) is used for depositing the absorber and the antireflection layers. The spectral reflectance of coated samples has been measured at temperatures up to 500 °C and gives α/e values in the range of 12–15, with a solar absorptance of 75%. The solar absorptance increases with temperature, while the thermal emittance typically increases by 2%–4% at 500 °C. Both the film adhesion and the spectral reflectance have remained stable after over 2000 cycles to 450 °C.

Optically pumped infrared V-V transfer lasers

Abstract: Laser action in OCS, CO2, N2O, C2H2, and CS2 has been obtained by resonant vibrational‐to‐vibrational (V‐V) energy transfer from CO gas excited by a frequency‐doubled CO2 TEA laser. Output energies up to 0.5 mJ, energy conversion efficiencies as high as 7%, and thresholds as low as 0.1 mJ have been observed.

Scaling of the helium‐nitrogen charge transfer laser

Abstract: The scaling to high powers of the nitrogen ion laser pumped by charge transfer from He+2 is reported. Intense emission has been found from three laser lines at 3914, 4278, and 4709 A upon discharge of a fast‐pulsed electron beam gun, APEX‐1, into several atmospheres of a mixture of helium and nitrogen. Excitation current densities were 1.4 kA/cm2 at 1 MV over a 1×10‐cm transverse geometry. The efficiency of the 4278‐A laser emission was found to be proportional to the total pressure raised to the 1.2 power. Outputs of 36 mJ have been obtained from the 16‐cm3 working volume at 30‐atm pressure and a peak efficiency of 1.6% relative to the energy lost by the electron beam in this radiating volume has been achieved.

Calculations of the continuous-wave lasing range and light-output power for double-heterostructure lasers

Abstract: Procedures for calculating the range of currents and heat-sink temperatures in which continuous-wave (CW) operation is possible and the light-output power levels within this range are presented for double-heterostructure (DH) lasers with an oxide-insulated stripe geometry. A one-dimensional heat-flow model has been assumed within the device followed by two-dimensional heat flow into the heat sink. It is shown that a laser with stripe dimensions (13 μm \times 400\mu m) and typical thicknesses can achieve CW operation at heat-sink temperatures up to about 431 K. At 300 K, the theoretical power output is in the 40-50-mW range for J = 2J_{th} . The effects of varying thicknesses and the aluminum content in the GaAlAs confining layer are considered. The limitations of the calculation are discussed as well as its applicability to other stripe-geometry devices.

Solar‐energy materials preparation techniques

Abstract: The application of materials to the thermal control of structures, photothermal/electrical conversion, and photovoltaic conversion are reviewed. Applications include solar and infrared reflectors, optical filters, transparent conductors, bulk semiconductor materials, semiconductor films, and selective solar absorbers. The use of thin films in many conservation and photothermal applications is presently economical, but the economics of photothermal/electrical and photovoltaic conversion is still being investigated. The means of obtaining selective solar absorbers which have a high solar absorptance and low ir emittance are discussed, and specific data on an electrodeposited black‐chrome selective absorber is presented. It is shown that solar–electric generating plants must be constructed at a cost of about $50/m2 to be competitive with other electrical generating plants, and that a meaningful impact on the electrical energy economy will require a fabrication rate of greater than 1.8 × 108 m2 (50 square miles) per year. Present high‐volume deposition capabilities are reviewed, and it is shown that for some types of deposition, namely electrodeposition, e‐beam vacuum evaporation, and possibly sputter deposition, facilities exist which approach the desired volumes.

Effect of transferred‐electron velocity modulation in high‐efficiency GaAs IMPATT diodes

Abstract: Numerical calculations, supplemented by detailed physical interpretation, show that the high (greater than 30%) output efficiencies, experimentally obtained with GaAs non‐punch‐through IMPATT devices, are only possible due to the specific features (related to the transferred‐electron effect) of the electron velocity versus electric field dependence in this material. Comparison is made with experimental results. Based on this new understanding, suggestions are made for further improvement of IMPATT performance.

Gunn-diode oscillator at 95 GHz

Abstract: The results of Gunn-diode-oscillator development at 90 to 94 GHz are reported, along with a discussion of the devices and circuit used. The best performance obtained was 25 mW output power (at 30°C heatsink temperature) with a d.c.-to-r.f. conversion efficiency of 0.6% at an operating frequency of 93.7 GHz.

Conversion of radiation frequency in four-wave parametric resonance processes based on stimulated Raman scattering

Abstract: A theoretical analysis is made of the interaction between fields whose frequencies satisfy the relationship ωp–ωs=ωg±ωa≈ω21 , where ωp, ωs, ωg and ωa are the frequencies of the pump, Stokes, generated, and auxiliary fields; ω21 tne frequency of a transition between two levels in the investigated susbstance. The conditions are established for the maximum efficiency of the conversion of the fields ωp and ωa into the field ωg. It is shown that the optimal conversion conditions are obtained for a certain ratio of the pump and auxiliary field powers when the phases of the interacting waves are locked. Numerical estimates are obtained of the conversion efficiency and interaction length when the active substance is potassium vapor or compressed hydrogen.

Theoretical and experimental photovoltaic energy conversion in an organic film system

Abstract: A theoretical model in which charge separation takes place at an electrode energy barrier has been extended to estimate the photvoltaic energy conversion efficiency as a function of film thickness and energy barrier for an organic film system based on the (1 : 1) PVK‐TNF charge‐transfer complex. The model predicts that the theoretical efficiency will be determined by space‐charge‐limited conduction for films of thickness greater than 0.1 μ. The efficiency is proportional to the inverse cube of the film thickness in this film thickness range. In the case of ultrathin films (<0.1 μ), the model predicts that the efficiency will be determined by the photocarrier generation efficiency and can approach 1%. Experimental photovoltaic energy conversion efficiencies for films of thickness 5–25 μ are in agreement with the general features predicted by the model.

Semiconductor-electrolyte photovoltaic cell energy conversion efficiency

Abstract: Photocurrent and differential capacitance were measured as a function of terminal potential with CdS‐ and GaAs‐electrolyte photovoltaic cells to determine the open‐circuit voltage Voc and the power conversion efficiency ηp. Voc was found to be 1.2 V for both cells. With monochromatic excitation, ηp=32% for the CdS cell, and ηp=21% for the GaAs cell. For both cells the quantum efficiency was larger than unity at short wavelengths indicating that current doubling is occurring at the interface. For the GaAs cell, current flow is mostly due to the diffusion of minority carriers from the bulk to the space‐charge layer under illumination.