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Solar energy is one of the most promising resources to help reduce fossil fuel consumption and mitigate greenhouse gas emissions to power a sustainable future. Devices presently in use to convert solar energy into thermal energy mostly rely on the indirect absorption of sunlight, where the efficiency is generally limited as a result of major convective heat losses into the surrounding environment. A promising alternative is the direct absorption of sunlight, where a fluid can serve as both solar energy absorber and heat carrier. The advantage of the technique is based on reduced convective and radiative heat losses, since temperature peak shifts from the absorbent surface (indirect absorption) to the bulk region of the carrier fluid (direct absorption). In a recent study, Matteo Alberghini and co-workers at the Departments of Energy, Applied Science and Technology, and the National Institute of Optics in Italy, investigated a sustainable, stable and inexpensive colloid based on coffee solutions to implement direct solar absorption. Results of their work are now published on Scientific Reports.
In the work proposed by Alberghini et al. the colloid consisted of distilled water, Arabica coffee, glycerol and copper sulphate to optimize the properties and biocompatibility of the fluid. The scientists analyzed the photothermal performance of the proposed fluid for direct solar absorption and compared its performance with traditional flat-plate collectors. They showed that the collectors could be precisely tailored and realized with 3-D printing for the experimental tests.
Nanocolloids - Drawbacks - Properties - Absorption - Result
Existing carbon-based nanocolloids have presented drawbacks, despite promising thermo-physical properties suited for direct solar absorption, as a result of cytotoxicity and harmful impacts on the environment. In pioneering experimental work, researchers have therefore used a black fluid containing India ink in water (3.0 g/l) for direct solar thermal energy absorbance. They observed an encouraging performance, which lead to the use of nanocolloids also known...
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