The diurnal thermal performance of a Solar Air Heater (SAH) integrated with Phase Change Material (PCM) based thermal battery is numerically studied. A control volume based advection-diffusion model is coupled with Discrete Ordinate Model (DOM) for considering the effects of solar radiation. Enthalpy-porosity technique is employed to consider various phases of the PCM (solid, liquid and mushy zone). At first, the model is validated with the available experimental result of outlet air temperature for a solar air heater. Thereafter, solar air heaters with and without thermal battery are compared to evaluate the effect of PCM on the thermal performance of the SAH. The local and global heat transfer, the phase change characteristics and their effect on the charging/discharging operation are described. Various numerical simulations are performed to propose optimized operational and design parameters. The integration of the thermal battery enables the SAH to work as diurnal (both day and night) which was not possible with the conventional SAH. The operating time of SAH integrated with thermal battery increases notably by 6 h. To evaluate the enactment of the system, thermal performance indicators are discussed. (C) 2019 Elsevier Ltd. All rights reserved.