Abstract
The wide-spread adoption of solar thermal absorbers is currently hampered by their low absorption efficiencies and their high capital cost. As a result, a number of initiatives, including direct absorption solar collectors (DASC), are currently underway to improve the absorber efficiencies. In this regard, this study focused on application of hybrid nanofluids containing reduced graphene oxides decorated with silver nanoparticles in volumetric solar absorbers. Their superior solar absorptance and thermal conductivity is based on the plasmonic effect of the nanoparticles and high thermal conductivity of graphene nanosheets, respectively. Several parameters such as mass concentration of graphene nanosheets and Ag decoration contents were studied that could affect the thermal and optical properties of the nanofluids. The results indicated that the prepared nanofluids can be employed for direct absorption solar collectors over a short period of solar irradiation time, even at a low illumination intensity of one sun. A collector efficiency of 77% is achievable at low concentration of 40 ppm owing to the enhanced light absorption of graphene at the excitation wavelength. These findings therefore suggest that this solution can contribute to the final goal of utilizing nanofluids for efficient solar thermal energy harvesting.
Highlights
A vast use of photovoltaic, concentrated solar power and solar thermal technologies is anticipated to play a decisive role in the future energy landscape, considering that the conversion of solar energy becomes more efficient and cost-effective [1]
The S1 nanofluids with lower Ag content show a higher photothermal capability due to the lower scattering effects resulting in a higher absorption. These findings indicate the potential of these nanofluids with Ag decorated rGO nanosheets for better photo-thermal conversion performances of the direct absorption solar collectors (DASC) collectors
To summarize,this study demonstrated a versatile and efficient approach to prepare stable plasmonic graphene nanofluids for volumetric solar thermal energy harvesting
Summary
A vast use of photovoltaic, concentrated solar power and solar thermal technologies is anticipated to play a decisive role in the future energy landscape, considering that the conversion of solar energy becomes more efficient and cost-effective [1]. Nanofluids that contain nanoparticles which efficiently absorb solar radiation promise to overcome these difficulties in photo-thermal solar energy conversion Their superior optical and thermo-physical properties, including thermal conductivity, play a key role to enhance solar energy absorption and conversion [7]. There are many studies that have investigated solar energy trapping and conversion of Ag or graphene based nanofluids separately [43], while there are no studies focusing on photothermal effects of Ag decorated graphene nanofluids for low-temperature DASCs. This study aims to overcome the issues reviewed above and perform a well-controlled experiment for hybrid plasmonic nanofluids that can be used for volumetric solar collectors. This work advances the understanding of plasmonic graphene based nanofluids, which promises to be a low-cost option with potential application for DASCs systems
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