Flat-plate solar water heaters are commonly used because of easy to use and acceptable performance relative to their cost. However, the novelty of this work lies in studying numerical simulations using computational fluid dynamics for the integration of helical half-fins into a phase-change material placed welded on the tube surface of solar water heater to immersed in the phase change material. The method of finite-volume are used to analysis of the phase-change materials transition time from liquid to molten state. Calculations for both (Ra ≈ 2.3 × 10³) and (Ste ≈ 0.19) revealed the true behavior of transfer latent heat when melting of the phase-change material. Numerical analysis showed of 9.33 % increase in the average liquid content in the helical half-fin model from 2:00 PM to 8:00 PM, indicating that the paraffin melting rate is faster in this model compared to the paraffin-only model. In addition, the temperatures of the water exiting the three samples at midnight were 300.37 K, 302.043 K, and 304.36 K, respectively. These results confirm the improvement in the performance to the solar water heater happened due to integration to both of paraffin wax and spiral fins, which that accelerates the melting process, and thus improves thermal energy storage