Refined Prototype Design & Construction
Annotated pictures shown in Figure 6 show the refined prototype design. The development and construction of the refined prototype design fulfills goal 2 of the Project Goals. In addition to the deletion of the toroidal balloon and the movement of the reflective surface to the equator under a transparent-upper-surface substantially spherical balloon, the refined prototype design also features a new pointing control system with stepper motor controlled toothed belts for elevation and azimuth control, as illustrated. The reflective surface is mounted to the base balloon through a lightweight aluminum ring, and can be focused by applying differential pressure between the upper and lower hemispheres of the balloon. For the prototype, a mylar membrane was used for the reflective surface, and optical vinyl with heat-seamed joints was used for the transparent upper surface. These prototype material and construction selections were made based on exigencies of cost and availability, and with the recognition that better solutions could be found for production applications
Aerodynamic loads from winds and gusts are relatively low due to low drag coefficient of the spherical shape.
No unsymmetrical aerodynamic loads regardless of heliostat orientation or wind direction.
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Mirror can readily be focused using differential pressure. Inflated domes protect mirror from exposure to weather.
The combination of low loads, direct load paths, and the inherent efficiency of inflated structures result in a lightweight, low-cost design.
A video description of the prototype is also included in on the CD-ROM. The prototype was transported and shown at the Solar2002 National Solar Energy Conference held in Reno, Nevada, in June 2002. The prototype has also been featured in the August edition of the Journal of Solar Energy Engineering published by the American Society of Mechanical Engineers, with the photographic illustration shown in Figure 8.
summary, the refined design concept offers the following advantages:
Simple drive system using only two motors, and having low torque requirements.
Inertia and moments).
November 24, 2002