Common breakfast beverage bolsters direct solar absorption
S. Himmelstein | March 25, 2019A promising alternative to the indirect absorption of solar radiation, which is limited by the high surface temperature of the absorber as well as convective heat losses with the surrounding environment, is direct absorption technology. Using a fluid as both the energy absorber and heat carrier reduces heat losses, as demonstrated by researchers from Politecnico di Torino and the National Institute of Optics, Italy, with a colloid based on coffee solutions.
Such nanofluids applied to allow direct solar absorption are characterized by a suspended phase that can confer enhanced photo-thermal properties to the base of the fluid. Convective and radiative heat losses are reduced as temperature peak shifts from the absorbent surface to the bulk region of the carrier fluid.Colloids with different G30 concentration, right to left: pure G30 fluid (56.17 g/l of suspended particles); G30w10 fluid (10% dilution); G30w1 fluid (1% dilution in water); pure water. Source: Scientific Reports
The colloid tested consisted of distilled water, Arabica coffee, glycerol and copper sulfate 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. The researchers also evaluated different concentrations of glycerol, added to lower the freezing point and allow technology deployment in cold climates.
An intense optical coefficient determined for the solution containing glycerol 30% weight/volume (G30) was attributed to the coffee content. This fluid also had the highest stored energy, which gradually decreased with the increased dilution of water.
The photothermal performance of the coffee-based colloids was compared to a selective absorber with specifically designed solar collectors. Optical losses were observed to depend on optical properties of the flowing fluids and the material composition of the collectors. The efficiency of the coffee colloid collector was maintained by striking a balance between heat absorption and reflection for optimal thermal performance. The system described in Scientific Reports was demonstrated to perform similarly to traditional indirect absorption techniques.
Solar energy applications for biocompatible, environmentally sustainable and inexpensive colloids could include solar-driven evaporation, seawater desalination and domestic water heating.
Being as this could drive up the price of my precious coffee, did they try any other sources of Maillard reaction products, such as wood, paper waste, grasses, or even plastics, possibly?