Direct flow ETC
4. 
Conclusion
Side-by-side tests of seven differently designed evacuated tubular collectors were carried out in an outdoor test facility. The observations from the measurements show that the direct flow ETC and the all-glass ETC have relatively high thermal performance m2 transparent area. The all-glass ETC with solar collector fluid in the tubes and the double-glass ETC with heat pipe perform relatively better in summer than in the rest of the year. This behaviour is insignificantly influenced by the mean collector fluid temperature. The heat pipe ETC with flat fin performs better than the ETC with curved fin in most of the test period and the superiority will increase in winter periods and in periods with high mean solar collector fluid temperature.
[1] Z. Q. Yin, “Development of Evacuated Tubular Collectors in China”, Proceedings of the Solar Thermal Industry Forum, Munich, April 22, 2008.
[2] W. B. Koldehoff, “The Solar Thermal Market-Today and Tomorrow”. Proceedings of the Solar Thermal Industry Forum, Munich, April 22, 2008.
[3] Z. He, H. Ge, F. Jiang, W. Li. A Comparison of Optical Performance between Evacuated Collector Tubes with Flat and Semicylindrical Absorbers. Solar Energy, 60 (2), 1997, PP. 109-117.
[4] J. Fan, J. Dragsted, S. Furbo. Side-by-side Tests of Differently Designed Evacuated Tubular Collectors. Proceedings of the 2007 Solar World Congress, pp. 634-637, Beijing, China, 2007.
