Comprehensive analysis of key design parameters affecting the efficiency of flat plate solar thermal collectors

Abstract

This study investigates key parameters affecting solar thermal collector efficiency through both simulation and experimental validation. A TRNSYS model was used and validated against experimental data from two solar thermal collectors tested under various conditions, showing strong agreement between predicted and measured values, with a maximum deviation of approximately 4 %. The investigation systematically analyzes key design parameters: flow rate, inlet water temperature, ambient temperature, pipe diameter, absorptance, emissivity, plate-to-glass gap, and insulation materials and thickness. The results indicate that the best performance occurs at flow rates between 175 and 225 kg/h, with a peak efficiency of 81.2 % at 175 kg/h, and ambient temperatures of 30–34 °C, achieving an efficiency of 84.1 % at 34 °C. The absorptance ratio exhibits a linear relationship with collector efficiency, increasing from 48.4 % at 0.60 absorptance to 81.2 % at 0.95 absorptance, while emissivity negatively affects efficiency, showing an 8.3 % reduction when increased from 0.05 to 0.40, but its impact is less significant than the positive effect of absorptance. Furthermore, simulations of various insulation materials with thermal conductivity coefficients ranging from 0.015 to 0.050 W/m·K demonstrated higher efficiencies at greater thicknesses; however, improvements beyond 45 mm were minimal. Finally, a plate-to-glass gap of 13 mm achieved maximum efficiency among tested gaps.