Sunlight can do lots of useful things. It can make plants grow. It can allow solar panels to make electricity. And it can be used to heat stuff up to extremely high temperatures. That last one is what makes concentrated solar power possible. According to a report in Science Daily, “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.”
The critical elements in that process are the heat exchangers used to transfer the heat stored in the molten salt to the carbon dioxide working fluid. If the whole process could be made to operate at even higher temperatures, CSP systems could make more electricity from a given amount of sunlight.
“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,” says Kenneth Sandhage, a professor of materials engineering at Purdue University.
At the present time, those heat exchangers are made of stainless steel or nickel based alloys, but they get too soft at the desired higher temperatures and at the elevated pressure of supercritical carbon dioxide. Professor Sandhage has been collaborating with researchers at the Georgia Institute of Technology, the University of Wisconsin – Madison, and Oak Ridge National Laboratory to develop new materials that can be used in heat exchangers that operate at those higher temperatures. The results of their research have been published recently in the journal Nature.
The scientists looked at the materials used to make nozzles for solid fuel rocket engines and created new heat exchangers made from zirconium carbide and tungsten that can withstand the high temperature, high pressure supercritical carbon dioxide needed for generating electricity more efficiently. 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.
“Ultimately, with continued development, this technology would allow for large scale penetration of renewable solar energy into the electricity grid,” Sandhage says. “This would mean dramatic reductions in human-made carbon dioxide emissions from electricity production.” What a delicious irony that carbon dioxide — the molecule responsible for most global warming — could be used to help reduce carbon emissions from the energy generation sector. Check out the video below for more on this breakthrough research.