An early production SURS collector using University of Sydney licenced double cermet coating evacuated tubes was tested by ITW (ITW, 2001) in Stuttgart, and measured optical efficiency is shown in Fig. 5. The reflector used was an aluminium reflector with reflectance of approximately 0.91, and the similarity to the earlier SURS B calculated plot in Fig. 4 is evident when the lower mirror reflectance is taken into account. However, the peak efficiency curve is flattened to some extent, possibly due to inaccuracies in reflector formation. In spite of this, the collector performed at the top of the range for evacuated tube modules tested by ITW, with very high diffuse acceptance because of the projecting tubes. Fig. 6 shows the measured thermal performance under standard conditions.

Conclusions

A practical evacuated tube system using using a multi-absorber CPC reflector design has been developed to a commercial product for domestic solar water heating, and performs very well with high diffuse acceptance and will not be as sensitive to snow build up as a conventional CPC system. The SURS concentrator can also be developed to use thin glass reflectors because of the low reflector curvatures used.

References

Winston, R. (1974). Principles of solar concentrators of a novel design. Solar Energy 16, (2), 89.

Mills D. R. 1995. Two-stage collectors approaching maximal concentration. Solar Energy 54, no.1, pp. 41-47.

Institut fur Thermodynamik and Warmetechnik (ITW), 2001. Forschungs- und Testzentrum fur Solaranlagen (TZS), Pfaffenwaldring 6, D-70550 Stuttgart

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0.9 0.8 0.7 0.6 Ц 0.5 0.4 0.3 0.2 0.1 0

Fig.6. Measured efficiency at different temperatures from a production collector module. A sketch of the reflector system is also shown. Obtained courtesy of ITW.