Techno-economic comparison of different thermal energy storage technologies for medium-scale CSP plants

This paper is focused on the ongoing studies at the Ottana Solar Facility, a new experimental power plant located in Sardinia (Italy). The Ottana solar facility includes a 630 kWe CSP plant and a 400 kWe CPV plant. With reference to the CSP section, a solar field based on Fresnel technology with a net collecting area of about 8600 m2 is used to heat up a Heat Transfer Fluid (HTF) trough solar energy. A Turboden 6HR Special ORC unit is used for the thermal to electrical energy conversion by means of a regenerative Rankine cycle operated by an organic fluid. The system is also equipped with a two-tank direct Thermal Energy Storage (TES) system with a storage capacity of about 15 MWht. However, other possible configurations of the TES section are currently under investigation. In this regard, asingle-tank packed-bed TES system based on encapsulated phase-change materials (PCM) is proposed in this study as an alternative to the two-tank direct TES system currently in operation. A techno-economic analysis has been therefore carried out to compare the two TES configurations. A mathematical model has been developed under MATLAB environment for assessing the expected yearly performance of the plant. Finally, a preliminary economic analysis based on the calculation of the levelized cost of storage has been conducted. The results show that a decrease in the overall energy production occurs with the use of the single-tank TES system due to a general decrease of the HTF temperature feeding the ORC unit, as a consequent of the indirect heat exchange. On the other hand, the lower investment costs arising from the lower volume of oil and the use of a sole tank make the proposed TES alternative more attractive from an economic point of view.