Design and techno-economic analysis of a molten-salt driven energy conversion system for sustainable process heat supply

Abstract

Storing off-peak cheap electricity from wind/solar farms for high-temperature heat storage in different mediums and using that for steam or high-temperature heat supply is a promising concept. A major issue for implementing high-temperature molten salt-based process heating systems is designing an appropriate heat exchanger system that can minimize the technical and operational risks and maximize the economic benefits. This study focuses on designing an optimal energy conversion unit based on this approach and conducts a techno-economic analysis of the developed system for a case study in Denmark to prove its proficiency. The system comprises a kettle boiler heat exchanger compatible with a high-temperature Sodium Hydroxide (NaOH) salt, and the case study is a cardboard factory demanding saturated steam at 10 bar, placed in the sustainable industrial business park GreenLab Skive. The results for the developed energy storage/conversion system with the given specifications and the salt are compared to an optimal design of the system when a conventional molten salt (solar salt mixture) is used. The results prove that the cost-effectiveness of the concept, in general, will be much dependent on the cost of charging electricity, and the system will only be promising if cheap off-grid electricity could be used during the whole charging process. It was found that the system with the benchmark salt NaOH for medium temperature use of ∼180 °C will be able to offer an LCOH of 67 €/MWh at an average cost of charging electricity of 63.6 €/MWh. The solar salt-cased energy conversion unit is less attractive economically but yet promising economically at cheap electricity charging rates.