Stepped phase change material cavities for enhanced thermal management of photovoltaic panels

The stepped phase change material (PCM) cavity was investigated as a geometry-based passive thermal-management strategy for concentrated photovoltaic (CPV) modules. A two dimensional transient CPV-PCM conjugate heat transfer model was developed using the enthalpy-porosity method and the Boussinesq approximation. Four cavity orientations, obtained by combining the step-facing direction with upwardly expanding or upwardly narrowing cavity profiles, and three step widths of 4, 6, and 8 mm were compared with a flat cavity under an identical PCM cross-sectional area. Grid and time-step independence tests were examined, and the numerical framework was validated against published CPV temperature and PCM melting data. The obtained results indicate that the illumination side stepped cavity with an upwardly expanding profile shows the strongest heat transfer enhancement. At a step width of 8 mm, the peak value of the maximum PCM velocity increases by 41.4%, the complete melting time decreases by 14.0%, the maximum reduction in average cell temperature reaches 12.83 °C, the heat storage power increases by 8.9%, and the electrical efficiency increases by up to 7.4% relative to the flat cavity. In contrast, the upwardly expanding cavity with steps facing away from the illuminated side provides better temperature uniformity and extends the temperature control duration by up to 36.1%. These results reveal a geometry-induced trade-off between intensified natural convection and cell temperature control performance and provide a numerical basis for the structural screening of compact CPV-PCM thermal-management systems.