Performance Analysis and Applicability of Molten Salt Thermal Energy Storage in Different Solar Power Plant Technologies

Abstract

Introduction:
Molten-salt thermal energy storage (TES) enables concentrated solar power (CSP) plants to store high-temperature heat efficiently and deliver dispatchable solar power. Because molten salts operate reliably between roughly 290-565 °C, their suitability varies across solar technologies with different temperature requirements, making a comparative assessment essential.

Objectives:
This study evaluates how molten-salt TES performs across solar power plant types and identifies the operational and economic conditions under which molten salts provide clear advantages.

Methods:
Thermophysical data, heat-loss modeling, degradation behavior, and system-level performance analyses from commercial CSP plants were reviewed. These results were compared to operational requirements in trough CSP, tower CSP, PV systems, and low-temperature solar thermal applications.

Results:
Findings show that molten-salt TES enables trough CSP plants to maintain full-load operation for 6-12 hours after sunset and can increase annual capacity factors from 25% to higher than 50% when storage is adequately sized. In tower CSP systems, direct molten-salt receivers achieve operating temperatures near 565 °C, supporting higher turbine efficiency and improving round-trip thermal performance. Long-duration tank studies indicate cooling rates of only around 1 °C/day, with monthly losses remaining below 30-35 K under proper insulation, confirming the feasibility of multi-day or seasonal storage. By contrast, PV modules operate at only 25-70 °C, far below the 290 °C freezing point of Solar Salt, making molten-salt TES technically impractical in PV-based systems.

Conclusions:
Molten-salt TES is a robust and efficient storage approach for high-temperature solar thermal technologies, particularly tower CSP, where it enhances dispatchability and overall system efficiency. Its application to PV and low-temperature solar thermal systems is limited by fundamental temperature incompatibilities, though opportunities remain in hybrid and high-temperature renewable-energy systems.