Due to the advantages offered by latent heat thermal storages, phase change materials (PCM) are used in numerous applications including building air conditioning systems. In this work, the development is reported of an approximate analytical model for the solidification process in a shell and tube finned thermal storage. A comparative study is presented for solidification of the PCM in cylindrical shell and rectangular storages having the same volume and heat transfer surface area. The PCM solidification rate in the cylindrical shell storage is found to exceed that for the rectangular storage. The effects are investigated of heat thermal fluid (HTF) inlet temperature and flow rate on thermal storage performance.