Available information defining the state of the art of encapsulation materials and processes for terrestrial photovoltaic devices and related applications were collected and analyzed. Based on criteria of properties, processability, availability, and cost, candidate materials were identified which have potential for use in encapsulation systems for low-cost, long-life terrestrial photovoltaic arrays manufactured by automated, high-volume processes. The criteria for consideration of the encapsulation systems were based on the goals for arrays with a lifetime of over 20 years high reliability, an efficiency greater than 10 percent, a total array price less than $500/kW, and a production capacity of 5 x 10/sup 5/ kW/yr. (WDM)

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Review of world experience and properties of materials for encapsulation of terrestrial photovoltaic arrays. Final report

Various solar cell interconnector designs are analyzed for fatigue failures under extended temperature cycling. Test results are presented for several configurations. The stresses and failures of the solder joint between interconnector and silicon cell are discussed in light of test results, new long-term cycling data showing much greater incipient failures than previously expected based on extrapolation. Data are also presented for solder creep strength at elevated temperatures. A comparison between soldered and welded joints shows that both approaches have their weaknesses. The bonding method of cells to substrate must be integrated with the interconnector design to obtain optimum performance, mechanically as well as electrically.

Solar Cell Interconnector Design

Purpose of this work was the selection of materials and manufacturing processes able to withstand the high temperature conditions typical of interplanetary space missions towards the Sun (e.g. Mercury). There are only few experiences reported on this subject by the scientific community. The limited time (18 months) and funding available for this study imposes a developing approach using as much as possible existing technologies. This goal is achieved by means of an optimisation work performed on the already available space solar cells and photovoltaic assembly (PVA). The studies were developed in two different paths: experiments have been carded out through tests at CIC and coupon level; analyses based on a mathematical modelling of PVA concepts to confirm the experimental data. The above led to a "high temperature and insolation" PVA baseline technology selection that is now under testing. This campaign includes tests at CIC level (single and triple-junction GaAs calls) and at coupon level (Carbon and Aluminium substrate skins) and it will be completed within the end of year 2002.

Development activities of GaAs space solar cells and photovoltaic assemblies for high temperature applications

This final report summarizes the results of a study to assess the feasibility of a 10, 000 watt solar array panel which has a minimum power-to-mass ratio of 110 watt/kg. The application of this ultralightweight solar array to three possible missions was investigated. With the interplanetary mission as a baseline, the constraining requirements for a geosynchronous mission and for a manned space station mission are presented. A review of existing lightweight solar array system concepts revealed that changes in the system approach are necessary to achieve the specified 110 watt/kg goal. A comprehensive review of existing component technology is presented in the areas of thin solar cells, solar cell covers, welded interconnectors, substrates and deployable booms. Advances in the stateof-the-art of solar cell and deployable boom technology were investigated. System level trade studies required to select the optimum boom bending stiffness, system aspect ratio, bus voltage level, and solar cell circuit arrangement are reported. Design analysis tasks included the thermal analysis of the solar cell blanket, thermal stress analysis of the solar cell interconnectors/substrate, and the thermostructural loading of the deployed boom. A new "V" stiffened solar array concept was conceived and analyzed. This solar array geometry results in increased system stiffness with no increase in total system weight (or reduced weight with the same deployed frequency requirement). A subscale model of this "V" stiffened geometry was fabricated along with a similar model of the conventional planar blanket geometry. These models provide a graphical illustration of the stiffening effect of the "V" geometry.

Feasibility study of a 110 watt per kilogram lightweight solar array system. Final report

Solar cell array fabrication for operation at 173- 383 K, discussing honeycomb sandwich substrate using epoxy-novolac-fiberglass facings and Al core

C. A. Lewis

Papers

Engineering study of elevated temperature solar cell panel fabrication techniques