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SAHs are classified based on their design and operational characteristics.PCMs absorb and store excess heat during peak sunlight hours and release it when sunlight is unavailable, thereby ensuring a more stable and continuous heat supply.Research has shown that adding roughness elements, such as ribs or baffles, disrupts the laminar sublayer, increasing turbulence and enhancing convective heat transfer (Kumar et al., 2012) [12].Studies suggest that integrating PCMs with SAHs can extend heat retention for several hours, making them suitable for applications requiring sustained thermal energy (Tyagi et al., 2012) [13].Active systems utilize external power sources, such as fans, to enhance airflow and heat transfer, whereas passive systems rely on natural convection for air circulation.Studies indicate that double-pass configurations achieve higher thermal performance compared to single-pass systems due to increased residence time and better heat absorption (Alam & Kim, 2017) [11].The primary classifications include active, passive, and hybrid systems, each with distinct advantages and limitations.

SAHs are classified based on their design and operational characteristics. The primary classifications include active, passive, and hybrid systems, each with distinct advantages and limitations. Active systems utilize external power sources, such as fans, to enhance airflow and heat transfer, whereas passive systems rely on natural convection for air circulation. Hybrid systems combine elements of both to optimize performance.
Another important classification is based on the number of air passes single-pass or double-pass. In a single-pass SAH, air flows over or under the absorber plate in a single direction. In contrast, double-pass systems allow air to pass through two channels, significantly improving heat transfer efficiency. Studies indicate that double-pass configurations achieve higher thermal performance compared to single-pass systems due to increased residence time and better heat absorption (Alam & Kim, 2017) [11].
One of the most effective strategies for improving SAH performance is the use of artificial roughness on the absorber plate. Research has shown that adding roughness elements, such as ribs or baffles, disrupts the laminar sublayer, increasing turbulence and enhancing convective heat transfer (Kumar et al., 2012) [12]. However, this comes at the cost of increased pressure drop and energy consumption for airflow, necessitating a balance between heat transfer enhancement and system efficiency.
Another widely studied approach is the incorporation of phase change materials (PCMs) to address the issue of solar intermittency. PCMs absorb and store excess heat during peak sunlight hours and release it when sunlight is unavailable, thereby ensuring a more stable and continuous heat supply. Studies suggest that integrating PCMs with SAHs can extend heat retention for several hours, making them suitable for applications requiring sustained thermal energy (Tyagi et al., 2012) [13].