Study and Characterization of a Spherical Solar Collector. I. Efficiency and Thermal Losses Coefficient

This paper studies and characterizes a solar collector with spherical geometry to produce hot water for sanitary and domestic applications and other facilities. The new geometry enlarges the solar collector surface and allows full sun tracking during the day without needing a solar tracking system. Although this geometry has been in use for some time, its market penetration is low due to the lack of perfect knowledge of solar collector behavior and the benefits compared with conventional solar collectors. The studies carried out in the lab for small domestic application has shown that this new geometry has better efficiency than flat plate collectors because its particular structure maintains water temperature inside the hot water tank for longer, which allows better production and longer use. The carried-out tests have shown an increase of up to 38% in the collector’s efficiency at high-range operation and 13% at the low range. This increase is enlarged to 40% and 15% when dealing with the compact system (collector-storage tank). Global losses coefficient is also lower, around 50%, than for a flat plate solar collector of an equivalent cross-section.