Eco-friendly and low-cost nanofluid for direct absorption solar collectors

Abstract

Nanofluids are promising receivers for solar collectors with volumetric absorption. These solar collectors are 1.2…1.4 times more efficient than conventional technology. However, most of the considered nanofluids are expensive and toxic. This work demonstrates how to treat instant coffee to produce inexpensive and environmentally friendly nanofluids for solar collectors. Our nanofluid contains particles with an average size below 100 nm. The nanofluid extinction coefficient is up to 300 1/m when 2% wt. of coffee is used. The toxicity of the nanofluid is of the same order as for the conventional coolants.