Non-inverting heliostat study

ABSTRACT:
Implications of employing a non-inverting he1iostat design with a lower capital cost relative to an inverting design are considered from three standpoints: (1) effects of dust buildup, corresponding cleaning frequencies, and resultant cleaning costs; (2) effects of hail impact; and t3)

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reflected beam safety issues. It is concluded that elimination of the inverting stow hardware and addition of reflector area in the slot required for inverting the reflector provides a direct subsystem cost savings. Since the non-inverting heliostat must be stowed face-up during high winds, reflectance degradation rates due to dust buildup are increased. The economic optimum cleaning frequency and allowed loss of reflectance due to dust buildup are determined so as to minimize the total system cost, and it is found that an overall cost savings of 12- 13 percent results if the inverting capability is eliminated. Hail impact damage and probability of occurrence for the United States are determined within the accuracy of available data. Analysis indicates that the commercial heliostat laminate glass design considered will survive 1-1/2 inch hailstones and is suitable for installation over most of the U.S. with low to negligible risk from hail damage. Reflected beam safety hazards are analyzed for the non-inverting design relative to the inverting design. No compelling reason is found to require an inverting stow capability, and therefore, a non-inverting stow heliostat is concluded to be a viable, cost-effective option.

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