Research Papers

Methodology to Assess Potential Glint and Glare Hazards From Concentrating Solar Power Plants: Analytical Models and Experimental Validation

[+] Author and Article Information
Clifford K. Ho, Cheryl M. Ghanbari, Richard B. Diver

Concentrating Solar Technologies Department, Sandia National Laboratories, P.O. Box 5800, Albuquerque, NM 87185-1127ckho@sandia.gov

The ratio of spectrally weighted solar illuminance to solar irradiance at the earth's surface yields a conversion factor of ̃100 lumens/W.

The effective spot size assumes that the reflected sun image is circular. In reality, the shape of the reflected sun image as viewed by an observer will become elongated along the linear (long) axis of the collector with increasing distance.

J. Sol. Energy Eng 133(3), 031021 (Aug 05, 2011) (9 pages) doi:10.1115/1.4004349 History: Received November 03, 2010; Accepted May 25, 2011; Published August 05, 2011; Online August 05, 2011

With a growing number of concentrating solar power systems being designed and developed, the potential impact of glint and glare from concentrating solar collectors and receivers is receiving increased attention as a potential hazard or as a distraction for motorists, pilots, and pedestrians. This paper provides analytical methods to evaluate the irradiance originating from specularly and diffusely reflecting sources as a function of distance and characteristics of the source. Sample problems are provided for both specular and diffuse sources, and validation of the models is performed via testing. In addition, a summary of safety metrics is compiled from the literature to evaluate the potential hazards of calculated irradiances from glint and glare for short-term exposures. Previous safety metrics have focused on prevention of permanent eye damage (e.g., retinal burn). New metrics used in this paper account for temporary after-image, which can occur at irradiance values several orders of magnitude lower than the irradiance values required for irreversible eye damage.

Copyright © 2011 by American Society of Mechanical Engineers
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Figure 1

Image projected onto the retina of the eye

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Figure 2

Potential impacts of retinal irradiance as a function of subtended source angle. Data for irreversible eye damage are from Refs. [1,10-11] for 0.15 s exposure (typical blink response time). Data for temporary after-image are from Refs. [12-14].

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Figure 3

Illustration of specular versus diffuse reflections

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Figure 5

Specular irradiance at the cornea as a function of distance from point-focus and line-focus mirrors with different focal lengths, b, for a solar irradiance of 0.1 W/cm2

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Figure 6

Illustration of parameters used for diffuse-reflection calculations (e.g., viewing an external cylindrical receiver on top of a tower)

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Figure 7

Irradiance at the cornea as a function of distance from a diffuse source with different reflectivities

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Figure 4

Geometry of specular solar reflections from a focused mirror where b is the focal length, Rh is the radius of the mirror, β is the beam divergence angle, and Rx is the radius of the beam cross section at distance, x, from the mirror (adapted from Ref. [1])

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Figure 8

Predicted and measured normalized irradiance as a function of distance caused by specular reflections from the Mod 2-2 10 kW parabolic dish

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Figure 9

Predicted and measured normalized irradiance as a function of distance caused by diffuse reflections from the NSTTF central receiver tower



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