<p>The performance of an evacuated tube solar collector in the presence of phase change materials (PCMs) in the collector, nanoparticles in the heat pipe, and special heat fins are experimentally investigated in this paper. In this paper, two evacuated tube solar collectors (ETC), without and with PCM called ETC-A and ETC-B, were considered, respectively. The effect of geometry, PCM addition, and evacuation on the performance have studied. Initially, the performance of both solar collectors without PCM was evaluated under similar conditions, and calibrations were applied. Then, the thermal performance of collectors (ETC) A and B was compared at five different flow rates of water passing through the condenser. It is worth noting that stearic acid was used as the phase change material in three volume fractions. Experiments started at 8:00 AM on various sunny days, and data were recorded every 5&#xa0;min in the north of Iran (Babol's climate). Measurement data included air temperature, inlet and outlet water temperatures at the condenser, heat pipe body temperature, PCM temperature, air temperature inside the collector, PCM volume fraction, and water flow rate. Objective functions considered were useful thermal, heat flux, thermal resistance, PCM heat, and thermal efficiency. The results indicate that PCM, nanofluid, and placing the collector under a vacuum have individually increased the thermal energy storage time. Collector B, with a 52% volume fraction and a flow rate of 20&#xa0;L h⁻¹, performed better, such that the thermal efficiency of Collector B (79.8%) compared to Collector A (37.3%) under these conditions increased by 53%. Adding nanoparticles enhanced the efficiency by 12.1%, the use of evacuated conditions (− 0.6&#xa0;bar) further increased the performance of collector A to 55.4%, with a difference in the efficiency of the two collectors under these conditions being 18.1%.</p> Graphical abstract <p></p>