Abstract Flat-plate solar thermal collectors are the most common devices used for the conversion of solar energy into heat. Water-based fluids are frequently adopted as heat carriers for this technology, although their efficiency is limited by certain thermodynamic and heat storage constraints. Latent heat, which can be obtained from microencapsulated Phase Change Slurry (mPCS) – that is a mixtures of microencapsulated Phase Change Materials (mPCM), water and surfactants – is an innovative approach that can be used to overcome some of the aforementioned limitations. The viscosity of these fluids is similar to that of water, and, as a result, they can be pumped easily. Some of the thermo-physical and rheological properties and the material behaviour of flat-plate solar thermal collectors with an mPCS as the heat carrier fluid are analysed in the present work. Solar thermal systems filled with an mPCS are proposed and a prototypal system is presented. The possible advantages and drawbacks of this technology are also discussed.