A theoretical model has been developed for analysis and optimization of the solar system using phase change material (PCM). The later consists of a solar air heating collector coupled with a cylindrical storage tank which contains spherical capsules filled with a PCM. Energy and exergy analyses are carried out to understand the behavior of the system using single PCM or multiple PCMs. Numerical results show that the performance of the latent thermal storage system can be ameliored by the judicious choice of the melting temperature of the PCM. (c) 2007 Elsevier B.V. All rights reserved.