Assessment of liquid metal technology status and research paths for their use as efficient heat transfer fluids in solar central receiver systems

• Liquid metals are proposed as advanced heat transfer fluids.
• Relative advantages and limitations of liquid metals are analyzed.
• Three main candidate liquid metals are identified: Na, PbBi and Sn.
• The state of liquid metal technology is evaluated as generally advanced.
• Research and development needs for practical implementation are outlined.

Concentrated solar power, and in particular central receiver systems, can play a major role as a renewable energy source with the inherent possibility of including a thermal energy storage subsystem for improving the plant dispatchability. Next-generation systems, in an effort for increasing the overall efficiency and reducing specific costs, will require higher operating temperatures and larger heat flux densities. In that context, liquid metals as advanced heat transfer fluids can face those challenges and largely contribute to the economics of future systems. Liquid metals have been proposed in recent publications from a thermodynamic perspective. The present article focuses in a complementary way on the current state of liquid metal technology.Based on the main requirements and previous experiences, three main candidate liquid metals are considered: sodium (Na), lead–bismuth eutectic alloy (LBE or PbBi) and molten tin (Sn), each of them with relative advantages and limitations. The state-of-the-art is reviewed, indicating that the readiness of liquid metal technology is quite advanced, mainly for the two first candidates. Recommended research and development activities are outlined, mainly in two directions: compatibility with structural materials at high temperature and indirect thermal storage solutions. Overall, provided that some challenges can be overcome, significant advantages can be obtained from the use of liquid metals as heat transfer fluids in central receivers systems.