The paper discusses the comparison of the performance of steam generators in large and small receivers, using a Fresnel lens concentrator. The goal is to get the best value from the efficiency of a steam generator between large and small receivers, with the following task details: a) design a conical cavity receiver that has the most efficient geometric concentration ratio; b) compare the thermal efficiency of conical cavity receivers that have different geometric concentration ratios; c) analyze the potential of the steam energy from the conical cavity receiver produced by the PMMA Fresnel lens concentrator based on the amount of average radiation directly at the study site. The study uses an experimental field research method, which is conducted outdoors. This research was conducted in the energy conversion laboratory, Universitas Brawijaya (Latitude: 7.9553° S and Longitude: 112.6145° W), in September 2019. The PMMA Fresnel lens is used for the solar thermal concentrators. The two receivers with a conical cavity that were compared were made of copper with a volume of 2 litres and 0.25 litres, respectively. They are coated with a glass wool insulator with a thickness of 10 mm. Direct Normal Irradiance (I b ) is measured by a solar power meter. The cup anemometer is used to measure wind speed (v w ) around the receiver. Digi-Sense 12 Channel Scanning Benchtop Thermometer connected to the laptop is used to measure temperature. The positions of the four K-type thermocouples are as follows: 1) ambient temperature (T a ); 2) focal point temperature (T f ); 3) receiver wall temperature (T r ); 4) steam/water temperature (T w ). A pressure gauge to measure the pressure of the steam that goes to the measuring cup was used. After saturation pressure (P sat ) has been reached, it will be known from the condensation process through the copper coil, which functions as a condenser. From the results of the study, the large receivers have specifications CR g =8 and a volume of 2 litres of water. Whereas, the small receiver is CR g =30 and 0.25 L. The large receivers can produce steam latent heat energy Q s =1.37 MJ per cycle with useful efficiency (utilization efficiency) η Th =31.81 %. Whereas the small receiver can produce steam energy, Q s =579.17 kJ per cycle with useful efficiency, η Th =33.31 %. Hence, from the two types of conical cavity receivers, small receivers have that higher effectiveness than large ones can be recommended