The effect of heat pipe thermosiphon in reducing the operating temperature of a photovoltaic panel has been analyzed theoretically and experimentally in this paper. Copper heat pipe thermosiphon with acetone as a working fluid was used. The theoretical study involved a heat balance analysis of the panel with cylindrical heat pipe with surface contact with the panel bottom. The experimental study involved recording temperature variations, with and without a heat pipe, which had very good agreement with the theoretical results of 2.61%. Additionally, the optimum quantity of acetone was 50 mL, with a maximum reduction in panel temperature of 10 °C.