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Concentrated solar power gets a superior composite for heat exchangers


Solar power accounts for less than 2 percent of total U.S. electricity. However, it could make up more than that if the cost of electricity generation and energy storage, for cloudy days and nighttimes, were cheaper. A Purdue University-led team developed a new material and manufacturing process that would make the use of solar and heat-power more efficient in generating electricity.

“Storing solar energy as heat can already be cheaper than storing energy via batteries, so the next step is reducing the cost of generating electricity from the sun's heat with the added benefit of zero greenhouse gas emissions,” said Kenneth Sandhage, Purdue’s Reilly Professor of Materials Engineering.

Concentrated solar power plants convert solar energy into electricity by using mirrors or lenses to concentrate a lot of light onto a small area, which generates heat that is transferred to a molten salt. Heat from the molten salt is then transferred to a working fluid - supercritical carbon dioxide - that expands and works to spin a turbine for generating electricity.

In order for solar-powered electricity to be cheaper, the turbine engine needs to be more efficient, which means the engine needs to run hotter. The heat exchangers, which transfer heat from the hot molten salt to the working fluid, are currently made of stainless steel or nickel-based alloys, that get too soft at the desired, higher temperatures and at the elevated pressure of supercritical carbon dioxide.

Sandhage worked with Asegun Henry, from Massachusetts Institute of Technology, to conceive a composite for more robust heat exchangers. Two materials showed promise together as a composite: The ceramic zirconium carbide, and the metal tungsten. The researchers created plates of the ceramic-metal composite.

The plates host customisable channels for tailoring the exchange of heat, based on simulations of the channels conducted by Devesh Ranjan's team, at Georgia Tech.

Mechanical tests by Edgar Lara-Curzio’s team at Oak Ridge National Laboratory and corrosion tests by Mark Anderson’s team at Wisconsin-Madison helped show that this new composite material could be tailored to successfully withstand the higher temperature, high-pressure supercritical carbon dioxide needed for generating electricity more efficiently than today’s heat exchangers.

An economic analysis by Georgia Tech and Purdue researchers also showed that the scaled-up manufacturing of these heat exchangers could be conducted at comparable or lower cost than for stainless steel or nickel alloy-based ones.

The research, done at Purdue in collaboration with Georgia Institute of Technology, University of Wisconsin-Madison and Oak Ridge National Laboratory, was published in the journal Nature.

A patent application has been filed for this advancement. The work is supported by the U.S. Department of Energy, which has also recently awarded additional funding for further development and scaling up the technology.