Showing papers on "Energy conversion efficiency published in 1978"

Enhanced photoelectrochemical solar‐energy conversion by gallium arsenide surface modification

Abstract: In the n‐GaAs/Se=–Se=x–OH−/C liquid junction solar cell, modification of the semiconductor surface by incorporation of ruthenium increases both the fill factor and the open‐circuit voltage and improves the reproducibility of performance. The power conversion efficiency of the modified cell is 12% under ∼100 mW/cm2 sunlight. Surface metal atoms or ions are shown to alter GaAs cell behavior widely; Ru represents a case for which the effect on cell performance is both positive and persisting.

cw optical wave‐front conjugation by saturated absorption in atomic sodium vapor

Abstract: Reconstructed images have been obtained by direct wave‐front conjugation in atomic sodium vapor using a cw tunable dye laser. With a pump power of only 15 mW a conversion efficiency of 0.2% has been observed.

Solar power system

Abstract: A system for generating electrical power from sunlight, comprising a focussing diffraction grating or other focussing, spectrally dispersive means and a photocell array. The diffraction grating focuses sunlight into a spectrally dispersed band. The photocell array is composed of cells with different spectral sensitivities, located in positions in the dispersed band corresponding to the cell spectral sensitivities so that the net conversion efficiency of sunlight to electricity exceeds the conversion efficiency attainable with nondispersive collectors and single material photocells. Alternate embodiments of the invention provide sun tracking means, reflective or transmissive diffraction gratings, flat or curved diffraction grating surfaces, on- or off-axis focus, and optical coatings on the photocell surfaces.

Fluorescent solar energy collectors: Operating conditions with diffuse light

Abstract: The fluorescent energy conversion principle using several sheets of transparent material doped with fluorescent molecules to concentrate radiation is extended to include diffuse radiation. Two cases are treated here: diffuse radiation only and a composite spectrum consisting of 40% direct and 60% diffuse radiation simulating the average illumination of a flat exposure in central Europe. In both cases photovoltaic conversion efficiency is significantly higher than with the AM1 spectrum. This is due to the blue shift and narrow shape of the diffuse spectral distributions. With realistic boundary conditions the theoretical conversion efficiency is 1.56 times higher than for the AM1 case. The highest theoretical conversion efficiency is now 38%.

Regenerative energy transfer system

Abstract: A method and apparatus uses energy in an energy output system having a main power source, an energy transmission system and a mechanical output. A first portion of energy generated with the main power source is used to drive the mechanical output under operating conditions. The unused second portion of the energy is diverted to an energy storing means. The second portion of energy is then stored and regenerated on demand. The energy may be used directly to augment the energy requirements in the energy output system during peak periods. In a specific embodiment, a compressed air system is used for storing the energy not used in driving a mechanical output connected to the power source by an energy transmission assembly. The energy transmission in the energy output system is a hydraulic fluid transmission system. A hydraulic fluid diverting mechanism is used to maintain the flow of hydraulic fluid to the mechanical output and to the compressed air energy storage system.

Photoacoustic determination of photovoltaic energy conversion efficiency

Abstract: Photoacoustic (i.e., photocalorimetric) measurements on photovoltaic devices can directly yield their energy conversion efficiency. This is illustrated for a Si solar cell, for which case excellent agreement is found with normal electrical measurements. In addition, the photoacoustic spectra under load and at open‐circuit conditions are reported and compared with the cell’s spectral response. Together, such measurements can provide information on the wavelength dependence of the cell performance as well.

Simplified fabrication of GaAs homojunction solar cells with increased conversion efficiencies

Abstract: Conversion efficiencies as high as 20% of AM1 have been obtained for single‐crystal GaAs shallow‐homojunction solar cells without Ga1−xAlxAs layers. These cells, which are fabricated by a simplified technique that does not require any vacuum processing steps, utilize an n+/p/p+ structure with an antireflection coating prepared by anodic oxidation of the n+ layer.

Second‐harmonic generation in Ti‐diffused LiNbO3 optical waveguides with 25% conversion efficiency

Abstract: Using a tunable optical parametric oscillator, phase‐matched second‐harmonic generation was realized in high‐quality Ti‐diffused LiNbO3 optical waveguides near the 1.08‐μ fundamental wavelength. At 45 W peak power in 17‐mm‐long waveguides an efficiency for TM0→TE1 conversion up to 25% was achieved. This value is three orders of magnitude larger than previously published results.

Cascade solar cells

Abstract: A monolithic cascade cell for converting incident radiation, particularly solar radiation, into electrical energy at a high efficiency with at least three layers of semi-conductive Group III-IV material. The top layer is doped into p and n regions with a homojunction therebetween and has a bandgap such that photons above a predetermined energy interact with the semi-conductive material to produce a potential across the homojunction and current flow and photons below that energy pass through the first layer to a second similar layer having a lower bandgap so that some of the radiation passing through the first layer produces a potential across a homojunction in the second layer to improve the overall energy conversion efficiency of the cell. The first and second layers are separated by at least a third layer of a Group III-V material, similarly doped into p and n regions with a tunnel junction formed therebetween to provide a low voltage electrical connection between the first and second layers. In one embodiment, the first and second layers are connected in series to be additive so that current flow takes place between contacts associated with the first and second layers. In another embodiment, the first and second layers are connected in opposition with a third terminal connected to the third layer which, in this case, need not be a tunnel junction. Alternatively, the two layers may be light producing devices such as light emitting diodes (LEDs), emitting light at different wavelengths, or photodiodes, detecting light of different wavelengths, or one layer can be a light producing device such as an LED while the other layer is a light receiving device such as a photodiode, again operating at different wavelengths.

Electrical and photovoltaic characteristics of indium-tin oxide/silicon heterojunctions

Abstract: Measurements on indium-tin-oxide/Si heterojunctions indicate that the conduction band discontinuity at the interface, ΔEc, is on the order of 0.45 eV for ITO with 9 mole-% SnO2. This value is inappropriate for use of ITO/Si heterojunction cells for photovoltaic energy conversion. It is too large for ITO/p-Si cells and too small for ITO/n-Si devices. For either type of device the resultant built-in voltage is inadequate for high efficiency solar cells. The maximum solar conversion efficiencies obtained are on the order of 0.3%. These results are in disagreement with previous work on ITO/Si heterojunctions.

A 15% efficient silicon MIS solar cell

Abstract: Substantial improvements in energy conversion efficiency are reported for silicon MIS solar cells fabricated on both single‐crystalline and semicrystalline substrates. Based on active area, AM1 efficiencies of 15.1% and 12.6%, respectively, have been obtained for 3.1‐cm2 cells at 26 °C.

Compact thermal energy reservoirs

Abstract: Light weight, compact and efficient thermal energy reservoirs are described in which thin layers of a heat storage material, such as an inorganic salt having a high latent heat of fusion, are heated or cooled by an intermittent primary energy source, such as solar or off-peak electric power. The stored energy is utilized during periods when the primary energy source is not available. The heat storage material is contained in flat fluid tight packages, such as a heat sealed polyethylene film bag, which can readily be removed and replaced through removable panels or doors in the insulated reservoir enclosure.

Method for forming p-n junctions and solar-cells by laser-beam processing

Abstract: This invention is an improved method for preparing p-n junction devices, such as diodes and solar cells High-quality junctions are prepared by effecting laser-diffusion of a selected dopant into silicon by means of laser pulses having a wavelength of from about 03 to 11 μm, an energy area density of from about 10 to 20 J/cm 2 , and a duration of from about 20 to 60 nanoseconds Initially, the dopant is deposited on the silicon as a superficial layer, preferably one having a thickness in the range of from about 50 to 100 A Depending on the application, the values for the above-mentioned pulse parameters are selected to produce melting of the silicon to depths in the range from about 1000 A to 1 μm The invention has been used to produce solar cells having a one-sun conversion efficiency of 106%, these cells having no antireflective coating or back-surface fields

Organometallic‐sourced VPE AlGaAs/GaAs concentrator solar cells having conversion efficiencies of 19%

Abstract: AlGaAs/GaAs heterojunction solar cells having conversion efficiencies greater than 19% have been produced on large‐area substrates (13 cm2) using the organometallic‐sourced VPE process. At 1 sun (simulated AM2) these devices have open‐circuit voltages of 1.01 V and short‐circuit currents of 20.9 mA/cm2. In sunlight at a flux concentration of 933 suns at AM2.1, a conversion efficiency of 19% and a fill factor of 0.757 was measured.

Efficiency of Drude mirror-type selective transparent filters for solar thermal conversion.

Abstract: The efficiency of the solar collector consisting of a selective absorber and a selective transparent filter is derived for comparing and evaluating the collectors. The efficiency of Drude mirror type selective transparent filters is calculated in cases of a blackbody absorber and the Al2O3–Mo–Al2O3–Mo highly selective absorber. As Drude mirrors, Sn-doped In2O3 films were formed on Pyrex glass plates by rf sputtering, and the dependence of the efficiencies on the operating conditions of the collector, including solar concentration and temperature of the absorber, is discussed.

Thermodynamic and kinetic limitations on the conversion of solar energy into storable chemical free‐energy

Abstract: — Energy-storing reactions in a system after light excitation transform the system into a thermo-dynamically metastable state. The effects of the microreversible back-reaction on the net yield of the storage process and on the stability of the products are discussed. It is shown that the inevitable losses of photon energy in the conversion process may be estimated and considered as roughly independent of the threshold frequency of the system. The best attainable conversion efficiency as a function of the threshold absorption wavelength may then be estimated. Rough calculations show an ultimate efficiency of about 20% with the optimum threshold wavelength in the range 600–800 nm. Photochemical production of fuel, like hydrogen from water, requires that more than one photon of the solar spectrum is used per product molecule formed. The low photon density of sunlight leads to troublesome stability requirements on the intermediates in the reaction mechanism. Some features of consecutive two-photon mechanisms in organized systems and homogenous solutions are discussed.

Performance limits of a Josephson‐junction mixer

Abstract: We present the results of extensive analog‐computer simulations of a Josephson junction used as a mixer with an external local oscillator. The resistively shunted junction model was used throughout, and the effects of intrinsic junction noise were included. When the source impedance is much greater than the junction resistance R, our simulations permit predictions of conversion efficiency, noise temperature, and saturation level to be made for a wide range of experimental parameters. The possibility of harmonic mixing has also been considered. With a source resistance comparable to R (i.e., conventional ’’matching’’) the behavior of the system is too complicated to permit such general predictions of performance. From the results of simulations for a particular set of parameters, it appears that the best noise temperature will usually be achieved for a source impedance somewhat greater than R. An upper limit for the mixer‐noise temperature is ∼40T over a broad range of junction parameters, where T is the effective temperature of the junction. The conversion efficiency under these circumstances should be comparable to what is potentially available from Schottky‐diode mixers. Our simulations show that with stronger microwave coupling it is possible to obtain conversion gain—i.e., a conversion efficiency exceeding unity. This, however, will probably be at the expense of a higher mixer‐noise temperature. Saturation can be important even for source temperatures ∼300 K. To avoid saturation it is necessary either to restrict the coupling bandwith or use an array of junctions.