Trends and Opportunities in Direct Absorption Solar Thermal Collectors

Abstract

Efficient conversion of sunlight into useful heat or work is of increasing global interest. Solartothermal energy conversion, as opposed to solartoelectricity, is enabled by solar thermal collectors that convert sunlight into heat at some useful temperature. We review here recent developments in solar thermal energy conversion. Our emphasis is on “directabsorptionâ€‌ solar thermal collectors, in which incident sunlight is absorbed directly by a working fluid. This contrasts with conventional solar thermal collectors where the sunlight strikes and is absorbed by a solid receiver, which then transfers heat to the working fluid. Both liquidbased and gasbased directabsorption collectors are described, although liquidbased systems are emphasized. We propose that if “directabsorptionâ€‌ technologies could be developed further, it would open up a number of emerging opportunities, including applications exploiting thermochemical and photocatalytic reactions and direct absorption of a binary fluid for absorption refrigeration.