An experimental study of a hemi-spherical solar collector under Egyptian climate

Traditional flat plate collectors have shown, under many investigations, low system operating efficiency, which prompted the idea of designing new solar collectors operating with higher efficiency. Such designs include spherical, hemi-spherical, cylindrical, or rhombic solar collectors. The current study experimentally investigates the performance of a stationary newly designed hemi-spherical solar collector in comparison with a flat plate solar collector with the same surface area and weather conditions. This target has been achieved through designing and manufacturing a hemi-spherical collector, followed by analyzing its performance under normal operating conditions of Egyptian climate. The Hemi-spherical solar collector showed a maximum efficiency of 69% compared to 42% for the flat plate solar collector. Additionally, the hemi-spherical collector resulted in an optical efficiency of 75% compared to 54% for the flat plate collector. Also, the flat plate collector achieved an average efficiency of 31%, compared to an average efficiency of 48.5% for the hemi-spherical collector. The hemi-spherical collector showed a more constant hourly efficiency distribution which makes the spherical solar collector a more reliable source of heating throughout the day, unlike the flat plate collector, where efficiency only peaks during midday, and drops significantly during the early morning and late afternoon