Solar radiation is a clean and renewable source of energy, which can be employed in various forms. In contrast to electricity, the use of solar energy in the form of heat is simple and straightforward. Solar air collectors (SAC), which convert solar radiation into heat and transfer it to the air, represent a way how to use solar energy for space heating in buildings. In the paper, the operation and optimal design of a solar air collector integrating a phase change material (PCM) for thermal energy storage is computationally investigated. A computer model of a front and back pass solar air collector with a PCM-based absorber was developed and validated against experimental data. The energy balance approach coupled with the control volume method was implemented for solving conduction heat transfer inside the PCM, and the effective heat capacity method was used for phase change modelling. The developed model was consequently coupled with the self-adaptive differential evolution optimization method. The cost function was defined as the root mean square error between the outlet SAC temperature and the set temperature. Using PCM parameters and its width as variables, the optimal set of parameters was determined. The optimal temperature of phase change was equal to 64.8 °C, PCM thickness 0.08 m and material parameter c 1 = 69,997 J/kg?K.