Heliostat dust buildup and cleaning studies

by Albuquerque Sandia Laboratories, NM

Other authorsRaymond S. Berg
Technical Report, 1978

Barcode

CSP Unique ID 190707372

Status

Electronic Resource

Call number

**Click on MARC view for more information on this report.**

Publication

SAND Report: SAND78-0510, March 1978.

Language

Library's review

ABSTRACT:
Dirt accumulation on solar energy optical surfaces such as heliostats can cause losses of over 25% after relatively short outdoor exposure. The optical loss is due to absorption and scattering by particulates that collect on the surface. Particulates impinge on the surface through complex
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fluid mechanical interactions between the dust-laden airstream and the heliostat structure and reflector surface. dominated by surface energetics. Initial particle adhesion is However, condensed water vapor at the particle-surface interface provides a vehicle for soluble components of the surface and dirt to establish very strong chemical and physical bonds between the dirt particle and the surface. Cleaning effectiveness depends on the technique used, the environmental conditions, and the amount of time the mirror has been exposed. Several continuous and periodic cleaning techniques have shown promise. Continuous cleaning using electrostatic repulsion has been tested in laboratory experiments and was shown to reduce dust accumulation. These experiments were performed in a low velocity (0-25 m/s) atmospheric wind tunnel fitted with a dust injector capable of injecting 104 times as many-optically important particles as are present in the normal aerosol. Periodic cleaning using high pressure sprays of up to 10,000 psi have been used to clean dirt from outdoor test samples. Tap water sprays at pressures above 500 psi seem to be equally effective and recover about 95% of the reflectance loss from dirt buildup. Several common detergents have been examined. Detergents with low pressure sprays generally must be used on short intervals, less than two weeks, or they lose their effectiveness. Measurements on accumulated dirt show that a limited number of measurements are required to characterize the optical loss of a dirty mirror. Weighted reflectivity measurements at 500 nm can be used. The dirt buildup is a very complex function of time and environmental conditions.
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