On either side of these values exists another estimate that is different by approximately a factor of two. Shaner and Wilson (Ref. 8) reviewed many different one-piece dish fabrication techniques. The more interesting approaches use pressed glass (>1 ft diameter), hydro-drawn aluminum (1.5 ft to 6 ft diameter), and spinformed aluminum (6 ft to 22 ft diameter). Surface materials were considered such as vapor deposited aluminum and silver for the pressed glass. The aluminum was to be buffed and anodized. Their cost estimates included fabrication, materials, labor, profit, shipping and field installation. The net results were a locus of minimum cost design which were in the range of $5.36/ft2 to $5.92/ft2 for aperture sizes from 1 ft to 22 ft diameter. As size increased, the fabrication technique selected changed in order to maintain costs in the above range. Production was based on 180 x 10^6 ft2 annually from 5 plants based on 250 working days per year. A correction factor of 1.12 was used to convert 1972 dollars to 1974 dollars. Surface contour error of 0.1 degree was felt to be possible, and tracking of 0.1 degree was assumed. These results are impressive and are about half the other estimates. The main difference is that this, is for 1 piece fabrication with full advantage taken of mass fabrication techniques. In fact, the results show that production is so developed that material costs are somewhat more than half the total costs. At sizes greater than approximately 12 ft diameter, shipping problems would increase for one- piece fabrication. At small sizes, the costs of tracking and external plumbing would increase. For both these reasons, the $5-6/ft2 estimates are felt to be optimistic. The other cost estimate is based on a Burns and Roe study (Ref. 9) in which they predicted approximately $24/ft2 . Included in this estimate were the reflector, supports, absorber, foundation, motors, tracking mechanism, shipping and installation.
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