U.S. Department of Energy - Energy Efficiency and Renewable Energy

SunShot Initiative

Deep Eutectic Salt Formulations Suitable as Advanced Heat Transfer Fluids

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Robotic high-throughput screening methods typically used in the pharmaceutical industry are being applied by Halotechnics to map out phase diagrams in order to define low melting point salt combinations for use as heat transfer fluids in CSP applications.

Halotechnics, under the Thermal Storage FOA, is conducting high-throughput, combinatorial research and development of salt formulations for use as highly efficient heat transfer fluids (HTFs).


This project involves investigating complex mixtures of inorganic salts to discover deep eutectic or low freezing point formulations. The desired properties are thermal stability as a liquid to about 500°C, a freezing point less than 80°C, vapor pressure less than 5 atmospheres to about 500°C, specific gravity in the range of 0.7–1.7 to about 500°C, heat capacity in the range of 2–5 J/g/K to about 500°C, viscosity of about 1 centipoise to about 500°C, and chemical compatibility with common stainless steels.


The research involves combinatorial screening of salt mixtures with four or more components. Candidate mixtures will exhibit reduced freezing point and higher thermal stability than in currently available HTFs. Halotechnics is looking for earth abundant salts, such as sulfates or chlorides, which can be used to replace solar salt.

At the end of this project, Halotechnics intends to have developed a salt mixture that eliminates the need for heat tracing along a parabolic trough system that is capable of operation at a temperature of at least 500°C.

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