This study deals with the thermal modeling of U-tube evacuated solar collectors to investigate the heat transfer and performance characteristics. The U-tube evacuated solar collectors are integrated into solar-assisted new generation experimental organic Rankine cycle working with environmentally friendly supercritical CO2. For the modeling, one-dimensional heat transfer analysis is applied to the U-tube collectors for determining the heat transfer characteristics of the collectors as well as the CO2 exit temperature from the collectors for the steady heat transfer process. Additionally, heat loss coefficient and overall heat transfer coefficients are determined for the experimental U-tube collectors. The obtained results are also compared with the results of the experimental study.