The present article addresses the design, mathematical modeling and analysis of a high temperature solar thermal energy storage unit based on molten soda-lime silica glass. The 126 kW hth storage unit is aimed to be used as one of the main components of a novel solar power-generation system intended for a continuous operation. The proposed design for the unit, as well as the restrictions imposed by its intended operation inside the power generation system, are thoroughly discussed. The development of the mathematical model used to calculate the efficiency and performance of the thermal storage unit during the different stages of the work cycle as well as the assumptions and simplifications made are comprehensively explained. The results obtained through the model are exhaustively analyzed. Special attention is paid to the assessment of the behavior of the storage unit to guarantee that the functional requirements are met; the performance of the unit is not evaluated exclusively from an energy standpoint, but an in-depth exergy analysis is also presented. The overall performance of the TES unit is satisfactory; the unit is capable of supplying the required 4 kWth output throughout the 16-h discharge while it reaches its fully charged state during the subsequent 8-h recharge. The proposed designed for the TES unit exhibits a round trip exergy-efficiency of 59%. Published by Elsevier Ltd.