New material harvests Sun's heat for cheaper electricity

Scientists have developed a material that can be used to harvest electricity from the Sun's heat, 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, researchers said.

 "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, a professor at Purdue University in the US. 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.

 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 problem is that 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. Researchers conceived a composite of ceramic zirconium carbide and the metal tungsten for more robust heat exchangers. 

They created plates of the ceramic-metal composite. The plates host customisable channels for tailoring the exchange of heat. Mechanical tests and corrosion tests showed that the 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 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. "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 human-made carbon dioxide emissions from electricity production," he said.