In this paper, the energy storage behavior of the thermal energy storage unit (TESU) using phase change material (PCM) and copper fins under artificial solar radiation was analyzed experimentally. The experimental tests of the TESU were performed at three different fin numbers (n = 3, 5, and 7) and fin thickness (t = 1, 1.5, and 2 mm) under variable solar radiations (q = 800, 900, and 1000 W/m(2)). The stored thermal energy of each TESU was calculated and compared with solar energy coming from a solar lamp. The highest thermal energy storage efficiency was computed as 95.08% in Type-VIII (n = 7, t = 1 mm) TESU below 1000 W/m(2) solar flux. The thermal energy storage efficiency enhancement ratio (TESEER) was defined to understand the effects of n and t of the thermal energy storage efficiency of TESUs. The highest TESEER was calculated as 1.68 in Type-VIII (n = 7, t = 1 mm) TESU below 1000 W/m(2) solar radiation. In conclusion, the TESEER values were decreased with increasing fin thickness, whereas its values were usually increased with the increase number of fins.