Preliminary Production Design
Goal 7 of the Project Goals has been accomplished with the development of a preliminary design for a production heliostat, which applies the technology demonstrated by the prototype. The preliminary production design is illustrated in Figures 10a and 10b, using four views. Note that the production design is fundamentally the same as the prototype design, with a few design refinements and a general scale-up in size. The size selected for this embodiment of a production design features a reflector diameter of 13.5 feet, as large as feasible to permit transport on flatbed trailers using the road system. The reflector is proposed to be made of 7 mil highly-reflective Mylar, with a reflective area of 143.1 sq.ft. or 13.30 sq.m. The reflective membrane is mounted on a .125” guage 2”x2” aluminum L-bend ring, and can be deflected into a desired concave- upward focusing configuration using differential pressure between the upper and lower inflated hemispheres. Alternate production designs are clearly possible at much larger scale for mega- scale solar thermal powerplants - however these alternate designs may not be road or rail transportable, or possibly may be road or rail transportable in sub-modules which then have to be assembled in-situ at the powerplant site.
The upper transparent hemisphere is proposed to be constructed of 15 mil Tefzel, thermoformed into the desired hemispherical shape out of a single sheet of material. The lower hemisphere is constructed of 20 mil vinyl or other plastic sheet, to reduce cost relative to the Tefzel. The upper and lower hemispheres are both fastened to the L-bend ring and thus to the reflective membrane. The L-bend ring is fitted with sphere-side pivot bearings, which connect it to curved support members, as illustrated. The curved support members are mounted on a base turntable structure, and are also stabilized by brace members. The lower inflated hemisphere also rests on a ring of sphere support bearing posts, which are also mounted on the turntable. The combination of the braced curved support members and the bearing posts will provide a lightweight, low-cost method of supporting the inflated sphere while holding it precisely and stably in a desired position. The turntable is fitted with a turntable edge ring, which in turn is engaged and held in position by a plurality of anchor legs secured in the ground surface. This preliminary design illustrates the use of four anchor legs, but based on performance and cost trade studies, a final design may use somewhere between three and six anchor legs.
Precise pointing control of the heliostat reflective surface is accomplished through the use of a turntable-mounted elevation control motor and winch for elevation control, and an azimuth control motor engaging a toothed surface on the turntable edge ring, for azimuth control.
November 24, 2002