Scope of the ORC-PLUS Project is the extension of a solar thermal power plant, already realized in Morocco, by using Fresnel linear collectors technology as a solar field and an ORC system as a heat engine. Besides the additional collector loops, a 20 MWh Thermal Energy Storage (TES) system has been added to the plant for increasing the full load hours and allowing the electricity production in the evening when there are demand peaks. In the case under exam, two different thermal storage technologies have been considered. The first technological option consists of the possibility to utilize a storage system with two internal heat exchangers to charge and discharge the thermal storage system and a low melting ternary salt mixture to exploit the energy of its sensible heat. Since in the solar collectors a mineral oil is used as Heat Transfer Fluid (HTF), the second technological option aims to realize a thermal storage system where the HTF can also be used as Heat Storage Medium (HSM). This solution can be affordable because the oil vapor pressure is lower than the ambient pressure, and mineral oil is much cheaper than synthetic oils. In this second case, to further reduce the cost and to increase the density of the stored energy, a cheap solid filler material has been inserted in the storage tank to reduce the required amount of thermal oil. In the framework of the ORC-PLUS Project activities, three different TES prototypes have been designed and assembled (by CIC, ENEA and F-ISE), in a scale of 1/100 (200 kWh) respect to the pre-industrial TES system that is being to realize at Benguerir (Morocco). The main goal of the TES prototypes was to validate the feasibility of the proposed TES technologies concepts. In this paper, the preliminary results of the testing activities performed by ENEA on his TES prototypes, based on low melting molten salt thermocline, are presented.

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