Overcoming Power Limitations of Electric Heating in a Solar Salt Thermal Storage by Microwave Heating

Roberto Grena, Mattia Cagnoli (), Roberto Zanino and Michela Lanchi
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Roberto Grena: ENEA, C.R. Casaccia, Via Anguillarese 301, 00123 Roma, Italy
Mattia Cagnoli: ENEA, C.R. Casaccia, Via Anguillarese 301, 00123 Roma, Italy
Roberto Zanino: Dipartimento Energia, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy
Michela Lanchi: ENEA, C.R. Casaccia, Via Anguillarese 301, 00123 Roma, Italy

Energies, 2025, vol. 18, issue 8, 1-21

Abstract: The expected increase in energy production from VRE (Variable Renewable Energy) requires a significant increase in energy storage capacity, with thermal storage potentially offering a key contribution. However, heat transfer mechanisms can limit the maximum power instantaneously transferable to the storage medium, posing a significant operational challenge. An analysis is presented here of the power limitations that arise when molten salt thermal storage adopting Solar Salt (NaNO 3 /KNO 3 , 60/40%wt) is heated by electrical resistances (Joule heating), and a possible alternative—the volumetric heating of the salt mass by microwaves—is discussed. Results show that microwave heating is an interesting path to overcome the power limitations of Joule heating. A first, theoretical analysis indicates a potential increase of more than 10 times in the maximum power transferable per unit area. Thermal-fluid-dynamic and electromagnetic models have been developed to numerically test the performance of a one-tank thermocline system endowed with a microwave heater. The proposed heating system showed limitations in terms of the maximum power that can be transferred to the salt because of the high temperatures established in the boundary layer. Finally, it performs in a comparable way with respect to an (ideal) heating system based on the Joule effect. However, many design improvements can still be adopted to enhance the performance of the proposed technology, likely overcoming the performance reachable using Joule heating systems.

Keywords: thermal energy storage; electrical heating; microwave; solar salt; CFD (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2025
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