The energy produced by thermal solar plants does not have to be limited solely to hours of sunlight. It is possible to conceive a storage system and it is possible to extend the production of heat beyond the hours of full sunshine. The main aim of this paper is to propose and test the validity and effectiveness of the proposed fuzzy multi-criteria method (TOPSIS fuzzy) to compare different heat transfer fluids (HTF) in order to investigate the feasibility of utilizing a molten salt. The thermal processes involved in CSP will not analyzed. The use of molten salt offers the potential to reduce electricity production cost and to increase the energy performance in an eco-compatible way. Salt is less expensive and more environmentally benign than currently used HTFs but unfortunately the high freezing point leads to significant O&M challenges and requires an innovative freeze protection system.