We study numerically the effect of the Prandtl number on the thermal heat storage, heat flux, and melting dynamics in phase change materials enclosed in square geometries inclined from 0° (bottom horizontal heating) to 180° (top horizontal heating) at increments of at least 5°. Chosen phase change materials are representative of very low, moderate, and high Prandtl numbers: gallium ( P r = 0 . 021 ), water ( P r = 13 . 5 ), and erythritol ( P r = 201 ). The Stefan number is fixed to 0.5, and the Rayleigh number to R a ∼ 1 0 8 . Water and erythritol exhibit a global bifurcation angle at θ c = 3 0 ∘ , separating the liquid phase dynamics from turbulent to laminar. Gallium exhibits stages of turbulent behavior up to 165°. The optimum tilt for harvested thermal energy corresponds to 95° for water and erythritol, and 100° for gallium. The maximum energy efficiency in harvesting thermal energy corresponds to small inclinations within the turbulent region, and 50° for water and erythritol, and the region about 45° for gallium. The maxima at 50° and 95° are very close to those values of the most frequent inclinations 45° and 90° investigated in the experimental literature. There is a power-law dependence between the Nusselt and Rayleigh number N u ∼ R a α for all the Prandtl numbers. Power-law exponents for water and erythritol exhibit a global upward trend with the inclination and undefined for gallium. • Simulations on erythritol (Pr=201), water (Pr=13.5), gallium (Pr=0.021) for Rã10̂8. • Power-law with inclination between Nusselt and Rayleigh numbers for all the Prandtl. • Similar melting time, energy storage and efficiency curves for all Prandtl. • Exists a critical inclination splitting laminar from turbulent flow for all Prandtl. • Optimal inclination for energy storage: 95° water and erythritol, 100° for gallium.