Smelting Steel With Sunlight: New Solar Trap Tech Could Help Decarbonize Industrial Heat

Some of the hardest sectors to decarbonize are industries that require high temperatures like steel smelting and cement production. A new approach uses a synthetic quartz solar trap to generate temperatures of over 1,000 degrees Celsius (1,832 degrees Fahrenheit)—hot enough for a host of carbon-intensive industries.

While most of the focus on the climate fight has been on cleaning up the electric grid and transportation, a surprisingly large amount of fossil fuel usage goes into industrial heat. As much as 25 percent of global energy consumption goes towards manufacturing glass, steel, and cement.

Electrifying these processes is challenging because it’s difficult to reach the high temperatures required. Solar receivers, which use thousands of sun-tracking mirrors to concentrate energy from the sun, have shown promise as they can hit temperatures of 3,000 C. But they’re very inefficient when processes require temperatures over 1,000 C because much of the energy is radiated back out.

To get around this, researchers from ETH Zurich in Switzerland showed that adding semi-transparent quartz to a solar receiver could trap solar energy at temperatures as high as 1,050 C. That’s hot enough to replace fossil fuels in a range of highly polluting industries, the researchers say.

“Previous research has only managed to demonstrate the thermal-trap effect up to 170 C,” lead researcher Emiliano Casati said in a press release. “Our research showed that solar thermal trapping works not just at low temperatures, but well above 1,000 C. This is crucial to show its potential for real-world industrial applications.”

The researchers used a silicon carbide disk to absorb solar energy but attached a roughly one-foot-long quartz rod to it. Because quartz is semi-transparent, light is able pass through it, but it also readily absorbs heat and prevents it from being radiated back out.

That meant that when the researchers subjected the quartz rod to simulated sunlight equivalent to 136 suns, the solar energy readily passed through to the silicon plate and was then trapped there. This allowed the plate to heat up to 1,050 C, compared to just 600 C at the other end of the rod.

Simulations of the device found that the quartz’s thermal trapping capabilities could significantly boost the efficiency of solar receivers. Adding a quartz rod to a state-of-the-art receiver could boost efficiency from 40 percent to 70 percent when attempting to hit temperatures of 1,200 C. That kind of efficiency gain could drastically reduce the size, and therefore cost, of solar heat installations.

While still just a proof of concept, the simplicity of the approach means it would probably not be too difficult to apply to existing receiver technology. Companies like Heliogen, which is backed by Bill Gates, has already developed solar furnace technology designed to generate the high temperatures required in a wide range of industries.

Casati says the promise is clear, but work remains to be done to prove its commercial feasibility.

“Solar energy is readily available, and the technology is already here,” he says. “To really motivate industry adoption, we need to demonstrate the economic viability and advantages of this technology at scale.”

But the prospect of replacing such a big chunk of our fossil fuel usage with solar power should be motivation enough to bring this technology to fruition.

Image Credit: A new solar trap built by a team of ETH Zurich scientists reaches 1050 C (Device/Casati et al.)

Edd Gent
Edd Gent
I am a freelance science and technology writer based in Bangalore, India. My main areas of interest are engineering, computing and biology, with a particular focus on the intersections between the three.
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