Dennis J. Flood

Solar radiation on Mars

Detailed information on solar radiation characteristics on Mars are necessary for effective design of future planned solar energy systems operating on the surface of Mars. Presented here is a procedure and solar radiation related data from which the diurnally, hourly and daily variation of the global, direct beam and diffuse insolation on Mars are calculated. The radiation data are based on measured optical depth of the Martian atmosphere derived from images taken of the sun with a special diode on the Viking cameras; and computation based on multiple wavelength and multiple scattering of the solar radiation.

SOLAR CELL TEMPERATURE ON MARS

Missions to the Martian surface will require electric power. Of the several possibilities, photovoltaic power system can offer many advantages. Photovoltaic cell performance increases with decreasing temperatures. The present paper deals with the calculation of the operating temperature of a e exible photovoltaic array needed for the determination of the electric output power from the array. The diurnal temperature variation was determined based on the solution of the heat-balance equation considering radiation, free and forced convection, and conduction. The photovoltaic array was divided into three layers (cover glass, solar cells, and substrate ), for which three differential equations were obtained and solved. The solution takes into account the special atmospheric condition prevailing on Mars, considering the diurnal variation of the ambient and surface temperatures, diurnal variation of direct beam, diffuse and albedo irradiances, variation of wind speed, and variation of various Mars atmospheric parameters with temperature.

Design modeling of high-efficiency p/sup +/-n indium phosphide solar cells

A parametric study of p/sup +/-n indium phosphide solar cells has been conducted using the PC-1D computer program. The effect of base doping on cell efficiency has been studied, and it is found that cell efficiency is a maximum for impurity concentrations around 10/sup 17/ cm/sup -3/. The variation of minority-carrier diffusion length as a function of base doping has been included. Using realistic values of electronic and material parameters, cell efficiencies in excess of 24% AM0 (25 degrees C) are predicted. >

SOLAR RADIATION ON MARS : TRACKING PHOTOVOLTAIC ARRAY

A photovoltaic power source for surface-based operation on Mars can offer many advantages. Detailed information on solar radiation characteristics on Mars and the insolation on various types of collector surfaces are necessary for effective design of future planned photovoltaic systems. In this article we have presented analytical expressions for solar radiation calculation and solar radiation data for single axis (of various types) and two axis tracking surfaces and compared the insulation to horizontal and inclined surfaces. For clear skies (low atmospheric dust load) tracking surfaces resulted in higher insolation than stationary surfaces, whereas for highly dusty atmospheres, the difference is small. The insolation on the different types of stationary and tracking surfaces depend on latitude, season and optical depth of the atmosphere, and the duration of system operation. These insolations have to be compared for each mission.

Lattice-matched and strained InGaAs solar cells for thermophotovoltaic use

Lattice‐matched and strained indium gallium arsenide solar cells can be used effectively and efficiently for thermophotovoltaic applications. A 0.75 eV bandgap InGaAs solar cell is well matched to a 2000 K blackbody source with a emission peak around 1.5 μm. A 0.60 eV bandgap InGaAs cell is well suited to a Ho‐YAG selective emitter and a blackbody at 1500 K which have emission peak around 2.0 μm. Modeling results predict that the cell efficiencies in excess of 30% are possible for the 1500 K Ho‐YAG selective emitter (with strained InGaAs) and for the 2000 K blackbody (with lattice‐matched InGaAs) sources.

Electrolyte for electrochemical C-V profiling of InP- and GaAs-based structures

Abstract A new electrolyte (UNIEL) based on HF, NH3F2, C9H14CIN, CH3COOH and o-H3PO4 has been developed for accurate EC-V net majority carrier concentration profiling of InP- and GaAs-based III–V semiconductors. The new electrolyte was tested with good results on heterostructures containing p- and n-type InP, GaAs, InGaAs and InGaAsP layers.

Comparison of n/sup +/p and p/sup +/n structures in indium phosphide solar cells

The expected performances of n/sup +/p and p/sup +/n indium phosphide solar cells are compared. PC-1D, a quasi-one-dimensional computer program based on solving semiconductor transport equations by a finite-element method, was used to model n/sup +/p and p/sup +/n indium phosphide solar cell structures. The calculations show that the n/sup +/p structure offers a better short-circuit current, but that the p/sup +/n structure offers improved open-circuit voltage and overall gain in cell efficiency. The radiation resistance of p/sup +/n InP cells is compared to that of n/sup +/p cells. It is shown that the conflicting results obtained in experiments indicate the need for a systematic reevaluation of the comparative radiation resistance of the two InP cell configurations.<<ETX>>

Photovoltaic power system operation in the Mars environment

Variation of solar insolation (global, direct and diffuse) at the Viking Lander locations is described. The radiation data are based on measured optical depth of the Martian atmosphere derived from images taken of the Sun, through the atmosphere, with a special diode on the Viking cameras and on computations based on multiple wavelength and multiple scattering of the solar radiation. The data are used to estimate photovoltaic system power, area and mass for a surface power system using regenerative fuel cells for storage and night-time operation.<<ETX>>

Advanced space solar cells

This paper will present a brief overview of the status of research and development of advanced space solar cells from a variety of materials. Most of the investigations at present are focused on binary, ternary and quaternary III–V semiconducting compounds such as InP, GaInAs and GaInP2. Growth techniques used for producing laboratory cells include liquid-phase epitaxy (LPE), organometallic vapor phase epitaxy (OMVPE), molecular beam epitaxy (MBE) or any of a number of variations of these techniques, such as atomic layer epitaxy (ALE), etc. Gallium arsenide is at present the only commercially available III–V compound solar cell. Compound III–V multiple bandgap cells are now under development in a jointly sponsored NASA/Air Force manufacturing technology demonstration program. In general, the decision to use a particular cell technology in space is determined by several factors, emphasis on any particular one depending on the mission environment: some are related to the properties of the photovoltaic material itself, such as efficiency and resistance to radiation damage, and some are related to details of the cell structure and associated materials, such as survivability under repeated thermal cycling and resistance to atomic oxygen erosion. The impact of these requirements on cell material selection and structural design is briefly discussed. This paper was produced under the auspices of the US Government and is therefore not subject to copyright in the USA

Modeling of low‐bandgap solar cells for thermophotovoltaic applications

Low‐bandgap solar cells can be used effectively and efficiently for thermophotovoltaic applications. A 0.75 eV bandgap InGaAs solar cell is an ideal device for the Er‐YAG selective emitter with a emission peak around 1.5 μm. Modeling results predict that the InGaAs cell efficiencies of nearly 30% are possible for the Er‐YAG selective emitter source at 1500 K.