Validation of Optical Modeling of Parabolic Trough Collectors by Flux Measurement

2007 ◽  
Author(s):  
Bjo¨rn Schiricke ◽  
Robert Pitz-Paal ◽  
Eckhard Lu¨pfert ◽  
Andreas Neumann ◽  
Klaus Pottler ◽  
...  
Keyword(s):  
Density Distribution ◽  
Flux Density ◽  
Ray Tracing ◽  
Fiber Optics ◽  
Flux Measurement ◽  
Measured Temperature ◽  
Parabolic Trough ◽  
Optical Efficiency ◽  
Good Spatial Resolution ◽  
Flux Density Distribution

In order to optimize the solar field output of parabolic trough collectors (PTC) it is essential to study the influence of collector and absorber geometry on the optical performance. The optical ray-tracing model of PTC conceived for this purpose uses photogrammetrically measured concentrator geometry in commercial Monte Carlo ray tracing software. The model has been validated with measurements of a scanning flux measurement system, measuring the solar flux density distribution close to the focal line of the PTC. The tool uses fiber optics and a CCD-camera to scan the focal area of a PTC module. Since it is able to quantitatively detect spilled light with good spatial resolution it provides an evaluation of the optical efficiency of the PTC. For comparison of ray tracing predictions with measurements, both flux maps and collector geometry have been measured under identical conditions on the Eurotrough prototype collector at PSA. The validation of the model is provided by three methods: the comparison of measured intercept factors with corresponding simulations; comparison of measured flux density distributions with corresponding ray tracing predictions; and comparison of thermographically measured temperature distribution on the absorber surface with flux density distribution predicted for this surface. Examples of sensitivity studies performed with the validated model are shown.

Experimental Verification of Optical Modeling of Parabolic Trough Collectors by Flux Measurement

2009 ◽  
Vol 131 (1) ◽  
Author(s):  
Björn Schiricke ◽  
Robert Pitz-Paal ◽  
Eckhard Lüpfert ◽  
Klaus Pottler ◽  
Markus Pfänder ◽  
...  
Keyword(s):  
Density Distribution ◽  
Flux Density ◽  
Ray Tracing ◽  
Fiber Optics ◽  
Flux Measurement ◽  
Measured Temperature ◽  
Parabolic Trough ◽  
Optical Efficiency ◽  
Good Spatial Resolution ◽  
Flux Density Distribution

In order to optimize the solar field output of parabolic trough collectors (PTCs), it is essential to study the influence of collector and absorber geometry on the optical performance. The optical ray-tracing model of PTC conceived for this purpose uses photogrammetrically measured concentrator geometry in commercial Monte Carlo ray-tracing software. The model has been verified with measurements of a scanning flux measurement system, measuring the solar flux density distribution close to the focal line of the PTC. The tool uses fiber optics and a charged coupled device camera to scan the focal area of a PTC module. Since it is able to quantitatively detect spilled light with good spatial resolution, it provides an evaluation of the optical efficiency of the PTC. For comparison of ray-tracing predictions with measurements, both flux maps and collector geometry have been measured under identical conditions on the Eurotrough prototype collector at the Plataforma Solar de Almería. The verification of the model is provided by three methods: the comparison of measured intercept factors with corresponding simulations, comparison of measured flux density distributions with corresponding ray-tracing predictions, and comparison of thermographically measured temperature distribution on the absorber surface with flux density distribution predicted for this surface. Examples of sensitivity studies performed with the validated model are shown.

Flux Density Distribution in the Focal Region of a Solar Concentrator System

1991 ◽  
Vol 113 (2) ◽  
pp. 112-116 ◽  
Author(s):  
M. Schubnell ◽  
J. Keller ◽  
A. Imhof
Keyword(s):  
Density Distribution ◽  
Flux Density ◽  
Ray Tracing ◽  
Radiation Flux ◽  
Focal Length ◽  
Solar Furnace ◽  
Focal Region ◽  
The Sun ◽  
Parabolic Dish ◽  
Flux Density Distribution

In high temperature solar energy applications highly concentrating optical systems, such as, e.g., parabolic dishes, achieve typical radiation flux densities >2 MW/m2. In order to investigate thermo and photochemical reactions at temperatures >1500 K and radiation flux densities >2 MW/m2 a solar furnace was built at Paul Scherrer Institute (PSI). This furnace is a two-stage concentrator. The first stage is a prefocusing glass heliostat with a focal length of 100 m. The second stage is a highly concentrating parabolic dish with a focal length of 1.93 m. To design experiments to be carried out in the focal region of the parabolic dish, the radiation flux as well as its density distribution have to be known. This distribution is usually measured by radiometric methods. However, these methods are generally rather troublesome because of the high temperatures involved. In this paper we present a simple method to estimate the characteristic features of the radiation flux density distribution in the focal region of a concentrator system. It is well known from solar eclipses that the mean angular diameter of the moon is almost equal to that of the sun (9.1 mrad versus 9.3 mrad). Hence, the lunar disk is well suited to be used as a light source to investigate the flux distribution in a solar furnace. Compared to the sun the flux density is reduced by 4·105 and the flux density distribution can be inspected on a sheet of paper located in the plane of interest, e.g., the focal plane. This distribution was photographed and analyzed by means of an image processing system. The density distribution was also simulated using a Monte Carlo ray tracing program. Based on this comparison, and on further ray tracing computations, we show that the peak flux density decreases from 8.9 MW/m2 in December to values below 4 MW/m2 in June and the net radiation flux from 25 kW to 15 kW, respectively.

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