This paper investigates the technical feasibility of innovative solar collectors. The proposed collectors have a phase change material (PCM) integrated into them as the storage mechanism. The PCM-integrated solar collector eliminates the need of conventional storage tanks, thus reducing cost and space. The present work uses a paraffin-graphite composite as the PCM to increase the conductivity of the PCM matrix. The paraffin's melting point is around 89 degrees C, which is appropriate for use in single-effect absorption systems. The mathematical model that describes the thermal process in the PCM is presented and differs from the analysis of conventional flat plate solar collectors making use of the lumped capacitance method which neglects spatial variations. The proposed model is calibrated favorably with a more detailed mathematical model that uses finite differences and considers temporal and spatial variations. Results for the collectors' thermal performance are presented along with the effects of the composition of the PCM. The results for the PCM integrated collector proposed here, are very encouraging. Therefore, there is an indication that conventional storage tanks may be replaced for the PCM integrated in the solar collector.