EuroSun2008-5

Reflectivity Measurement

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The device shown in Fig. 15 consists of a laser and detector mounted on a support structure that can be positioned to measure reflectance of mirror surface samples from the ICPC. Using this device, a map of reflector performance for the ICPC array has been generated.

Fig. 18. Third Level Reflectance Degradation. Fig. 19. Fourth Level Reflectance Degradation.

Four levels of reflectance degradation are identified for the Sacramento site. At level 1 degradation, shown in Fig. 16, the reflector still performs well with just a minor change in the reflector appearance. In level 2 degradation, shown in Fig. 17, there is some whitening of the reflector. In level 3 degradation, shown in Fig.18, there is a substantial amount of degradation of
the reflector. In level 4 degradation, shown in Fig. 19, most of reflector is gone and you can easily see through it.

At the site, all 336 tubes were categorized, one-by-one, by their reflectivity levels, existence of a glass crack, surface temperature, water leakage, and fin orientation. Each tube was divided into ten sections along its length. Degradation levels were identified and marked for each of the ten sections. Fig. 20 shows a color mapping of tube degradation information for a portion of the array.

Подпись:

Подпись: 3. Conclusions A detailed ray trace analysis for characterizing the optical performance of ICPC evacuated tubes has been described and its results illustrated. As a consequence of the ray tracing, it was found that reflectivity degradation will play a significant role in the reduction of array efficiency. The nature of reflectivity degradation depends on the type of failure, such as water leakage from the heat transport tube or cracks in the cover glass. Overall performance is also degraded by the loss of vacuum in the tube. An analysis of the performance consequences of reflector degradation and loss of vacuum degradation will be incorporated into the reliability study.

Reflector samples representative of the four different degradation levels were taken from the Sacramento site for measurements in the laser laboratory at Colorado State University, as in Fig. 21. The samples for the four levels of degradation and undegraded reflector samples were measured for their reflectivity by the laser and detector device. Using this device, a map of reflector performance for the ICPC array is being generated. The reflectance results are shown in Table 1 for each level of degradation.

References

[1] Garrison, J. D., Optimization of Fixed Solar Thermal Collectors, Solar Energy, v23, 1979

[2] Snail, J. J., O’Gallagher and R. Winston, A Stationary Evacuated Collector with Integrated Concentrator, Solar Energy, v33, 1983

[3] Подпись: Fig. 21: Laser and Sensor Assembly in the Colorado State University Laser Laboratory. Winston, R, O’Gallagher, J., Mahoney, A. R., Dudley, V. E. and Hoffman, R., “Initial Performance Measurements from a Low Concentration Version of an Integrated Compound Parabolic Concentrator (ICPC)”, Proceedings of the 1999 ASES Annual Conference, Albuquerque NM, June, 1998 [5] [6]

O’Gallagher, Tom Henkel and Jim Bergquam, “Performance of the Sacramento Demonstration ICPC Collector and Double Effect Chiller in 2000 and 2001”, Solar Energy, vol. 76, pages 175-180, January 2004.

[6] Duff, William, Jirachote Daosukho, Klaus Vanoli, Roland Winston, Joseph O’Gallagher, Tom Henkel and Jim Bergquam, “Comparisons of the Performance of Three Different Types of Evacuated Tubular Solar

Collectors”, American Solar Energy

Table 1: Measurement of Reflectivity S°ciety 2006 Denvei;

Colorado, July 2006.

[7] Подпись: Degradation Level Percent Reflectivity Good 93.48 1st 79.66 2nd 38.46 3rd 22.93 4th 1.24 Duff, William S. and Jirachote Daosukho, “A Performance and Reliability Study of a Novel ICPC Solar Collector Installation”, American Solar Energy Society 2007 Congress, Cleveland, Ohio, July 2007.

EuroSun2008-5

Automatic Control System

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The application of the regulations minimal solar collector area

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Measured sequences used for validation purposes

The comparison of experimental and calculated instantaneous power results, obtained after the different approaches presented in the previous section, is based on instantaneous efficiency measurements for a CPC collector (C …

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