Optically Transparent Thermally Insulating Silica Aerogels for Solar Thermal Insulation

A. Alperen Günay, Hannah Kim, Naveen Nagarajan, Mateusz Lopez, Rajath Kantharaj, Albraa Alsaati, Amy Marconnet, Andrej Lenert, Nenad Miljkovic

Research output: Contribution to journalArticlepeer-review

Abstract

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. Most techniques utilize a vacuum gap between the solar absorber and the surroundings to eliminate conduction and convection losses, in combination with surface coatings to minimize reradiation losses. Here, we present an alternative approach that operates at atmospheric pressure with simple, black, absorbing surfaces. 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. To demonstrate their heat-trapping properties, we fabricated tetramethyl orthosilicate-based silica aerogels. 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 minimize unwanted solar absorption by O-H groups, we functionalized the aerogel to be hydrophobic, resulting in a solar-averaged transmission of 88%. 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.

Original languageEnglish (US)
Pages (from-to)12603-12611
Number of pages9
JournalACS Applied Materials and Interfaces
Volume10
Issue number15
DOIs
StatePublished - Apr 18 2018

ASJC Scopus subject areas

  • Materials Science(all)

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