Concentrated Solar Power Could Become More Attractive with this Innovation

A Purdue University-led team has developed a new composite ceramic material that can be used to harvest electricity from the Sun’s heat for generating energy on demand, paving the way for generating cheaper solar power on cloudy days and at nighttime. The innovation is an important step for putting solar heat-to-electricity generation in direct cost competition with fossil fuels, according to the team. 

“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.

Solar power doesn’t only generate electricity via panels on farms or on rooftops. Another option is concentrated power plants that run on heat energy. 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. This serves as the thermal energy storage or TES, from where heat is then transferred to a “working” fluid, supercritical carbon dioxide, that expands and works to spin a turbine for generating electricity. Large CSP projects today come with a specific guarantee of storage for 5-7 hours after sundown. 

To make solar-powered electricity cheaper, the turbine engine would need to generate even more electricity for the same amount of heat, which means the engine needs to run hotter. The issue is with 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.

Inspired by the temperature resilient materials that had been previously developed for different applications, the team consisting of scientists from Georgia Institute of Technology, the University of Wisconsin-Madison and Oak Ridge National Laboratory along with Purdue set out to tackle the issue with the material of heat exchangers in concentrated solar plants. 

Two materials showed promise together as a composite: The ceramic zirconium carbide, and the metal tungsten. Materials that could handle high heat and pressure under extreme applications. Purdue researchers created plates of the ceramic-metal composite. The plates host customizable channels for tailoring the exchange of heat, based on simulations of the channels conducted at Georgia Tech by Devesh Ranjan’s team.

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 claims that the scaled-up manufacturing of the heat exchangers could be conducted at comparable or lower cost than for stainless steel or nickel alloy-based ones.“Ultimately, with continued development, this technology would allow for large-scale penetration of renewable solar energy into the electricity grid,” Sandhage said. “This would mean dramatic reductions in man-made carbon dioxide emissions from electricity production.”

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. 

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