In last years, the demand of flat-plates solar collectors is constantly increasing; for this reason, it is necessary to improve their performance under different operating conditions. In this paper, experimental tests of a two-phase flat-plate solar collector using acetone as a working fluid are analyzed. Advantages of Phase Change Systems (CPS) are the decrease of the risk of deformation or fissure due to freezing, as well as problems of fouling, scaling, corrosion and incrustations, increasing the lifetime of the systems. The thermal performance of the developed systems is evaluated based on the NMX-ES-004-NORMEX-2010 Mexican standard. Efficiency curves of thermal performance during the day and thermal losses at night, following the Mexican standard protocol, have been obtained. Results show that the thermal behavior of the system studied is a little bit lower than the conventional systems for the day tests. For the night tests, the results are better than the conventional systems in one of the PCS, obtaining lower losses of temperature. It is necessary to continue with this research in order to obtain a PCS competitive against conventional systems.