Adapting thermochromic ionogel for the use of solar thermal collectors

Abstract

Overheating of solar thermal collectors during stagnation is a problem that limits the widespread use of thermal collectors. The aim of this project was to adapt a new class of polyurethane based ionogels developed as optically ideal switching materials for solar thermal collectors, its function being to remain transparent in the solar spectrum range until the switching temperature and subsequently turning opaque with high reflectance after this temperature. The change in optical transmittance will reduce the efficiency of solar thermal collection and thus prevent overheating. Glass beads and glass fiber were used to form composites in an attempt to reduce the percentage of ionic liquids without comprising optical properties. UV-Vis spectroscopy was used to estimate the switching temperature by measuring reflectance at temperatures between 25°C and 100°C. Switching temperature was found out to be in the range of 70-80°C. The best reflectance switch was found to be from 0.07 to 0.28. Additional studies are needed to further improve the maximum reflectance of the gels, to test in outdoor settings and on the absorber and explore the possible composites.