The present experimental study focuses on the passive thermal regulation of photovoltaic (PV) systems using heat pipe-based heat sinks. The design and selection of practical and efficient heat pipe based thermal regulation systems necessitate a comprehensive understanding of the effect of using different working fluids with different charging ratios. Thus, a fabricated heat pipe with an elliptical cross section area is attached to a silicon rubber heater to imitate the heat dissipation from PV cells in heat pipe-PV systems. This single heat pipe thermal system is designed and assembled to be used with other identical pipes as a heat sink to dissipate waste heat from a PV system with the purpose of efficiency enhancement. Several sets of experiments are performed indoors to inspect the effect of using two working fluids (Ethelene and pure water), four charging ratios (50, 60, 70, and 80%) and different heat loads to mimic the absorbed energy due the incident solar irradiance received by the solar cell. Results revealed that the heat pipe filled with Ethelene as the working fluid with a charging ratio of 70 % achieves a maximum reduction in the operating temperature of PV cells when compared to pure water and other charging ratios. The current findings can open doors for further research towards the development and commercialization of novel passive cooling technology for PV systems.