While silicon is abundant and its processing well founded with a number of organisations, mainly with terrestrial solar array interests actively developing the high production methods, the picture for the gallium arsenide option is not so clear. The main problems concern the supply of gallium in the amounts required and the development of a lighter substrate. Due to its inherently better performance, the active array area needs to be only one half that for silicon, therefore, both the development and production technology is of strong interest. It should be noted that the production technology must also include cell covering, interconnects, testing and repair as well as the cells themselves. Given below are some of the technology areas which should be considered: Cell and Covers • Thin film cells (50 p.m) • Advances in back surface reflection and front surface cell texturing • Alternatives cell configuration including size • Improvements in nonsilicon cell materials, for example, cadmium sulphide, copper indium selenide • Development of ribbon type cells • Development of radiation resistant covers • Development of UV transparent adhesives • Mass production technology for all associated components. Interconnections • Improvements in reliability • Alternative interconnect methods • Thermal cycling effects during laser annealing of silicon cells • Mass production, test and repair methods. Blankets • Automatic fabrication methods • Production of large area thin (50 p.m) borosilicate glass • Materials development aimed at optimising thermal expansion, anticharging methods • Development of bonding systems • Repair techniques. Annealing Systems — silicon cells • Alternatives to lasers, electron beams • Optimum wavelength investigations for cell annealing • Annealing control systems • Annealing through cover glasses — to reduce cover heating • Investigate temperature/time requirements and characteristics • Effects of radiation fluence on the ability to anneal radiation damage. GaAlAs solar cells are expected to be self annealing. These comments have not addressed the technology requirements of the SPS power collection system, cabling and switchgear systems. It must be remembered that all the foregoing points arise from studies of the Reference Design and therefore reflect current technology thinking, and not the outcome of future developments. The technology planning should take account of this fact.
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