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Thermocline vs. two‐tank direct thermal storage system for concentrating solar power plants: A comparative techno‐economic assessment
Author(s) -
Cascetta Mario,
Petrollese Mario,
Oyekale Joseph,
Cau Giorgio
Publication year - 2021
Publication title -
international journal of energy research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.808
H-Index - 95
eISSN - 1099-114X
pISSN - 0363-907X
DOI - 10.1002/er.7005
Subject(s) - organic rankine cycle , thermal energy storage , concentrated solar power , working fluid , storage tank , solar energy , engineering , solar power , environmental science , process engineering , rankine cycle , energy storage , degree rankine , waste management , nuclear engineering , mechanical engineering , waste heat , power (physics) , electrical engineering , thermodynamics , heat exchanger , physics
Summary This paper concerns the ongoing studies on a Concentrated Solar Power (CSP) plant in operation in Ottana (Italy), comprising a 629 kW organic Rankine cycle (ORC) unit fed by a linear Fresnel solar field. Hexamethyldisiloxane (MM) and “Therminol SP‐I” are used respectively as ORC working fluid and heat transfer fluid in the solar receivers. A two‐tank direct Thermal Energy Storage (TES) system is currently integrated in the CSP plant, serving as a direct interface between solar field and ORC. With the view of improving the solar facility, two alternative TES configurations were proposed in this study: a one‐tank packed‐bed TES system using silica as solid storage media and another similar one including encapsulated phase‐change material (molten salt). Comprehensive mathematical models were developed for simulating daily behaviour as well as for assessing yearly performance of the various TES technologies. Furthermore, a preliminary economic analysis was carried out. Results showed poorer response of the one‐tank TES system to large fluctuations in the ORC inlet fluid temperature, leading to reduction in the mean ORC efficiency (18.2% as against 19.7% obtained with the two‐tank TES). Conversely, higher energy storage density and lower thermal losses were obtained adopting the one‐tank TES, resulting in about 5% more annual solar energy yield. Invariably, equivalent annual ORC energy production of 0.92 GWh/year was obtained for the three TES configurations. Additionally, adopting a one‐tank TES system meant that the purchase costs of a second tank and its storage medium (thermal oil) could be saved, resulting in investment costs about 45% lower and, ultimately, levelized cost of storage about 48% lower than what obtains in the two‐tank TES system.