[en] Using thermal energy balance, this paper analyzes and investigates the thermal performance of a U-tube solar collector whose temperature thermal energy is high due to solar radiation. A working fluid of 20% PG (propylene glycol)–water is used. Solar collector efficiency was calculated and energy savings predicted for various nanofluids, such as MWCNT, Al_2O_3, CuO, SiO_2, and TiO_2. As a result, thermal conductivity increased as the concentration of nanofluid increased. Solar collector efficiency increased in the following order from greatest to least: MWCNT, CuO, Al_2O_3, TiO_2, and SiO_2 nanofluids. When the thermal loss value ((T_i−T_a)/G) was equal to 0, the solar collector using 0.2vol% MWCNT nanofluid showed the greatest efficiency (62.8%, a 10.5% improvement compared to 20% PG–water). By dispersing nanoparticles in the working fluid, the coal usage could be further reduced by approximately 39.5–131.3 kg per year when 50 solar collectors are used. Therefore, CO_2 generation could be reduced by 103.8–345.3 kg and SO_2 generation by 0.4–1.1 kg per year, compared to solar collectors using a base working fluid of 20% PG–water. These findings contribute to knowledge of solar energy technology, which has the potential to reduce electricity and energy consumption world-wide. - Highlights: • Thermal performance of an U-tube type solar collector was analyzed theoretically. • MWCNT, Al_2O_3, CuO, SiO_2, and TiO_2 nanofluid with 20% PG-water were applied. • Solar collector using 0.2vol%-MWCNT nanofluid showed the highest efficiency. • By using nanofluids, the coal usage can be further reduced by 131.3–39.5 kg for one year when the 50 solar collectors are used.