Molten salt possesses notable advantages including high operational temperatures, exceptional thermal stability, high specific heat capacity, strong convective heat transfer coefficient, low viscosity, and low vapor pressure, making it an excellent heat transfer and thermal storage medium. Having gained extensive application in concentrated solar power (CSP) generation, it has laid a solid foundation for expansion into other fields.
Within the CSP sector, molten salt is widely adopted. Among the first batch of 20 CSP demonstration projects in China, 18 utilize molten salt for thermal storage and power generation. Furthermore, out of 92 newly registered and planned CSP stations, 86 have adopted molten salt thermal storage technology.
Both the molten salt thermal storage system and steam generation system have demonstrated maturity, stability, and reliability through practical application in CSP plants. Beyond CSP, molten salt thermal storage technology is now being implemented in steam heating storage and supply, as well as valley electricity-based heating applications.
Molten salt exhibits several distinct properties compared to aqueous solutions:
(1) As an ionic melt typically composed of cations and anions, it demonstrates good electrical conductivity—approximately one order of magnitude higher than electrolyte solutions.
(2) It offers a wide operational temperature range. Conventional molten salts operate between 300°C and 1000°C, while newly developed low-melting-point mixed molten salts have expanded this range to 60–1000°C.
(3) Low saturated vapor pressure ensures operational safety for high-temperature molten salt equipment.
(4) High heat capacity.
(5) Strong dissolving capacity for various substances.
(6) Low viscosity.
(7) Good chemical stability.
(8) Readily available raw materials at low cost. Compared to common high-temperature heat transfer and storage media like thermal oil and liquid metal, most molten salts are inexpensive and easily accessible.
These superior characteristics have led to the widespread use of molten salt as a thermal medium in energy storage applications.
Roles of Molten Salt Thermal Storage:
1. Participating in Flexibility Retrofits of Thermal Power Units
Integrating the "energy storage" attribute of molten salt into the "instant generation and consumption" nature of thermal power units weakens the rigid coupling between the "boiler and turbine," achieving thermal-electrical decoupling. This enhances operational flexibility and further improves deep peak-shaving capability.
2. Industrial Steam Supply Using Off-Peak Electricity for Molten Salt Storage
Utilizing low-cost off-peak electricity during nighttime hours to heat and store thermal energy in molten salt. During daytime demand periods, high-temperature molten salt is extracted and passed through a molten salt-water heat exchanger to produce steam for industrial use.
3. Centralized Heating Using Off-Peak Electricity for Molten Salt Storage ("Coal-to-Electricity" Conversion)
This system transforms the coal-fired boiler equipment of centralized heating systems into molten salt storage electric heating systems. It uses off-peak electricity at night to heat molten salt for storage. During the day, a salt-water heat exchanger heats the circulating water to the required temperature for space heating.
4. Heating Using Curtailed Wind and Solar Power to Heat Molten Salt
With the rapid development of wind and photovoltaic power, installed capacity increases annually. However, integration challenges have become increasingly prominent, and the curtailment of wind and solar power results in significant energy waste and economic loss. Utilizing this curtailed electricity to directly heat molten salt for thermal storage and heating holds substantial market potential.
5. Industrial Waste Heat Utilization
Industrial processes generate substantial intermittent waste heat, such as high-temperature flue gas waste heat, combustible exhaust gas waste heat, and waste heat from condensate and wastewater. This waste heat can be stored using molten salt thermal storage systems and converted into a stable heat source for continuous heating or hot water supply, achieving energy conservation and consumption reduction.
