A Hot-as-Lava New Composite Could Revolutionize Solar Energy Affordability

A team led by Purdue University unveiled a new solar composite that could significantly improve concentrated solar power plants in both efficiency and cost, according to a new study published in Nature last week. This collaboration between Georgia Institute of Technology, University of Wisconsin-Madison, and Oak Ridge National Laboratory hopes to increase the current use of solar in the US, which remains at less than 2 percent of our electricity generation. But the team’s new material may revolutionize the concentrated solar power industry.

“I think we’re tantalizingly close,” Purdue professor Kenneth Sandhage tells Inverse.

The composite, made of [cer]amic zirconium carbide and [met]al tungsten, falls under a category of materials called “cermets,” known for their ability to withstand high temperatures and pressure. Popularized after World War II for their use in jet engines, the US Air Force (the ones who coined the term) “cermets” have become a go-to for airplanes and space rockets. And hip replacements.

The Purdue team took note of cermet’s qualities and found a new high-temperature environment to test it out: concentrated power plants.

Opposed to a typical photovoltaic solar farm with idle panels installed on farms or rooftops, concentrated solar power plants are basically the large-scale, well-intentioned version of burning ants under a magnifying glass. These plants use mirrors or lenses to concentrate energy from the sun. Instead of dead ants, we get heat transferred to molten salts. Plates made of stainless steel or nickel-based alloys are used to transfer the heat from salts to a fluid that expands to spin a turbine, which finally gives you electricity. Purdue used supercritical CO2 as the fluid in question, aka CO2 at such high temperatures and pressures that it exists somewhere between a liquid or gas.

This technique of collecting heat from the sun means that concentrated power plants get hot. The material of the plates used to transfer heat is one bottleneck in the system — the current stainless steel or nickel-based alloys hit capacity around 550 degrees Celsius before softening, just under 100 degrees hotter than the hottest planet in our solar system, Venus.

After mechanical tests at Oak Ridge National Laboratory, the team discovered the new composite lets us go even hotter, to about 750 degrees Celsius, which is on the cool side of lava. Purdue’s cermet is also two to three times as conductive as the current industry standard.

Apart from achieving scorching heat levels, this temperature difference allows a plant to increase its heat to electricity conversion more than 20 percent. Scaled up, the newfound efficiency from the ceramic-metal composite would be cheaper than the current materials and could help drastically reduce carbon dioxide emissions.

Impressive as ceramic-metals may be, the team first faced issues with corrosion, as the supercritical CO2 would oxidize the plates, reducing their productivity. But drawing on fundamental chemistry concepts, the figured out that adding a copper layer to the surface of the cermet plates and adding 50 parts per million of carbon monoxide to the supercritical CO2 mitigates the issue. The team has submitted a patent for the new material.

As of 2018, concentrated solar power plants produce about 1,400 MW of energy for the US per year. While it’s currently cheaper to harvest sunlight using traditional photovoltaics, batteries to store it are expensive — it’s actually cheaper to store heat, as done via concentrated solar. With this new composite, the cost of collecting heat falls. Combined with the ability to help bridge the gap of energy presented by solar during nighttime, this makes concentrated solar much more competitive.

“I think it’s an exciting time to be in materials engineering,” Sandhage comments. “There are very serious problems that we face, but it’s a matter of doing the dogged hard work of engineering to bring in the right materials, bring in the right design, and keep knocking down problems. We’re excited about the role we can play.”