Abstract The present numerical study comprises thermal performance investigation of double glazed single pass solar air heater exhibiting wavy finned absorber plate integrated with and without PCM. The main objective of the present research work is to design sustained solar air heating systems that can efficiently perform during sunshine, off sunshine and nocturnal hours. In this direction, Design-I (wavy fined solar air heater without PCM) and Design-II (wavy fined solar air heater with PCM) are investigated to obtain the best values of the geometrical and flow parameters. In the present work, first, investigation is carried out to obtain optimum values of geometrical and flow parameters for Design-I, work is then extended to investigate the Design-II exhibiting wavy absorber plate and PCM. MATLAB codes are developed to carry out numerical investigations under transient conditions using an implicit scheme to study the effect of geometrical parameters i.e. amplitude ( 0.005 ≤ α ≤ 0.015 m ) , wavelength ( 0.03 ≤ λ ≤ 0.1 m ) and number of fins ( 5 ≤ n ≤ 25 ) , and flow parameter i.e. mass flow rate ( 0.005 ≤ m ˙ ≤ 0.0128 kg / s ) . The maximum outlet air temperature for Design-I corresponds to optimum values of geometrical parameters obtained at a mass flow rate of 0.005 kg/s, 0.0075 kg/s and 0.01 kg/s is 85.44 C, 73.34 C and 64.9 C, respectively. However, the maximum thermohydraulic efficiency is predicted to be about 47% at the mass flow rate of 0.01 kg/s. Results of Design-II revealed 10 hours thermal backup after sunset at the mass flow rate of 0.0128 kg/s. In addition, investigation for Design-II is extended to present a cold weather condition of an average ambient air temperature of 15oC and an off sunshine hour situation to present possible thermal backup of Design-II. The results of this investigation delineated that using wavy fins on the top and PCM on the bottom side of absorber plate can efficiently provide appreciable instant and high thermal efficiency and thermal energy backup during sunshine, off sunshine and nocturnal hours.