Twenty Years’ Experience with a Novel Geometry ICPC Evacuated Solar Collector

Abstract

A novel geometry ICPC evacuated tube solar collector was developed at the University of Chicago and Colorado State University in 1993. Individual evacuated tubes of this novel geometry ICPC were experimentally fabricated and tested at Colorado State University in 1994-96 and at the University of Chicago in 1996-97. In 1998 two 14 tube modules were tested on Sandia National Laboratory's two-axis tracking (AZTRAK) platform in Albuquerque New Mexico by Sandia National Laboratory and the University of Chicago. A 336 tube 100 m2 array of this collector has been in continuous operation at a demonstration project in Sacramento California since 1998. From 1998 to the present performance of the Sacramento demonstration array and single and double effect cooling systems has been monitored and evaluated by the California State University at Sacramento and Colorado State University. Optical ray tracing modelling, thermal performance modelling and collector reliability studies have been conducted by Colorado State University during the 1998 to 2013 period.Performance approaching the theoretical predictions was achieved for the individual ICPC evacuated tubes experimentally fabricated by Colorado State University and the University of Chicago. While operating in the range of 120 to 160C, daily solar collection efficiencies of nearly 0.50 and instantaneous solar collection efficiencies of about 0.60 were achieved. Daily cooling COPs of 1.1 were achieved while operating the double effect chiller with energy supplied from the ICPC solar collectors. A ray tracing simulation incorporating ray transmittance and translation, the gap between the glass tube and fin, reflectivity of the reflective surface, absorptivity of the fin and blocking and displacement of the rays by adjacent tubes has been developed. Animation of individual rays and associated summary graphics and an optical and thermal performance model of the collector have also been developed. Performance of the novel ICPC solar collector at various specified angles along the transverse and longitudinal evacuated tube directions was experimentally measured on the Sandia National Laboratory's two-axis tracking (AZTRAK) platform. Data from the Sandia tests was used to validate the ray tracing simulation performance. Data from the initial operation of the Sacramento array were used to further validate the ray tracing simulation and thermal modelling. The primacy of the two identified collector reliability failure modes was established. Details of the various testing and research activities and results are presented. Animations of the ray tracing are also included in the oral presentation.