Abstract:In this study, the efficiencies of flat-plate and U-tube solar collectors were investigated experimentally when an Al 2 O 3 nanofluid was used as a working fluid and compared to those of solar collectors using water. The energy savings and CO 2 and SO 2 generated were calculated and compared to those of solar collectors using water. In addition, based on the experimental results, an economic analysis of the use of solar collectors in various countries was performed. As the concentration of the Al 2 O 3 nanofluid increased, the performance of the solar collector improved. The highest efficiency for the solar collectors was shown at the concentration of 1.0 vol % with the nanoparticle size of 20 nm. The maximum efficiencies of the flat-plate and U-tube solar collectors using a 1.0 vol %-Al 2 O 3 nanofluid with 20-nm nanoparticles was 74.9% and 72.4%, respectively, when the heat loss parameter was zero. The efficiencies of the flat-plate and U-tube solar collectors using Al 2 O 3 nanofluid were 14.8% and 10.7% higher, respectively, than those using water. When 50 EA (each) flat-plate solar collectors were operated for one year using an Al 2 O 3 nanofluid, the coal use, generated CO 2 , and generated SO 2 were 189.99 kg, 556.69 kg, and 2.03 kg less than those of solar collectors using water, respectively. In addition, the largest electricity cost reduction was in Germany.