In this study, a U-pipe evacuated tube solar collector was tested in a solar simulator under indoor conditions and an efficiency curve was formed. The pressure drop of the solar collector was determined for different mass flow rates. Beams that come from the simulator to the solar collector are provided with halogen lamps. Since beams from the lamps do not come parallel to the collector like solar beams, it would be misleading to use the absorber projection area in the calculation of efficiency. As a more realistic approach, a method that calculates the angular absorber area of beams was developed. While collector efficiency that depends on the collector absorber projection area varies between 116% and 80%, collector efficiency that depends on the field of the angular absorber has changed between 56% and 38%. These results obtained from the experimental study reveal the importance of determining the collector's area to be used in the solar simulator for the efficiency calculation of evacuated tube solar collector tests. The effect of fluid flow on collector efficiency and pressure drop is also investigated. As the fluid flow in the collector increases, the pressure drop also increases and a relatively increase in the efficiency is observed.