Optically Transparent Thermally Insulating Silica Aerogels for Solar Thermal Insulation.Rooftop solar thermal collectors have the potential to meet residential heating demands if deployed efficiently at low solar irradiance (i.e., 1 sun).  The efficiency of solar thermal collectors depends on their ability to absorb incoming solar energy and minimize thermal losses.  Silica based aerogels coated on black surfaces have the potential to act as simple and inexpensive solar thermal collectors because of their high transmission to solar radiation and low transmission to thermal radiation.  A hydrophilic aerogel with a thickness of 1 cm exhibited a solar-averaged transmission of 76% and thermally averaged transmission of ≈1% (at 100 °C).  To provide a deeper understanding of the link between aerogel properties and overall efficiency, we developed a coupled radiative-conductive heat transfer model and used it to predict solar thermal performance.  Instantaneous solar thermal efficiencies approaching 55% at 1 sun and 80 °C were predicted.  This study sheds light on the applicability of silica aerogels on black coatings for solar thermal collectors and offers design priorities for next-generation solar thermal aerogels.
THERM