Thermal performance of parabolic trough integrated with thermal energy storage using carbon dioxide, molten salt, and oil

Abstract

Finding clean and affordable energy sources is the focus of extensive research efforts globally. A primary approach to achieving that is through improving the performance and economic competitiveness of renewable energy systems. Parabolic trough collector (PTC) solar plants are mature renewable solutions to reduce current dependence on fossil fuels. However, in these plants, heat is transferred within the subsystems using a heat transfer fluid (HTF) that is primarily molten salt or synthetic oil. These HTF options play an important role in the thermal and economic performance of the solar power plant. In this paper, supercritical carbon dioxide (s-CO2) is investigated as an economical alternative to the costly molten salt and Therminol-PV1. Therefore, comparative heat transfer, energy, and exergy analyses are conducted for a PTC plant with s-CO2, Therminol-VP1, and molten salt as an HTF. A heat transfer model is developed for the PTC in one- and two-dimensions to accurately evaluate heat losses. In addition, the energy and exergy concepts are used to compare the thermal performance of these HTFs. In contrast to previous studies that were limited to PTC, we considered the integration of thermal energy storage (TES) with both Therminol-PV1 and molten salt as a storage medium for a full-day operating cycle. The PTC performance while using these HTFs under various operating and design conditions is examined, including variation in wind velocity, beam radiation, and pressurized s-CO2 operation. The results show that the considered HTFs are achieving comparable energy and exergy efficiencies within the PTC. Furthermore, the Therminol-PV1 has an advantage of compact storage volume compared with molten salt, about one-third; nevertheless, the latter exhibits higher TES energy and exergy efficiencies. This comparative analysis reveals that the s-CO2 can replace synthetic oil and molten salt in the PTC loop.