Researchers Demonstrate Solar Thermal Trap Opening Path for Industrial Heat Decarbonisation

Researchers at ETH Zurich have experimentally demonstrated a thermal‑trap device that concentrates sunlight and suppresses radiative losses to achieve temperatures of 1,050°C.

A milestone for using solar heat in industrial processes that traditionally burn fossil fuels, the team engineered the device from a synthetic quartz rod coupled to an opaque ceramic absorber. 

Under concentrated illumination equivalent to about 135 suns, the absorber reached 1,050°C while the quartz rod’s far end remained near 600°C, showing how a semi‑transparent medium can trap thermal radiation and protect the receiver from emissive loss.

“To tackle climate change, we need to decarbonize energy in general,” said ETH Zurich researcher, Dr. Emiliano Casati. “People tend to only think about electricity as energy, but in fact, about half of the energy is used in the form of heat”.

High‑temperature process heat, which is needed for glass, steel, cement and ceramics, accounts for roughly a quarter of global energy use, yet existing concentrated solar receivers struggle above 1,000°C because radiative heat loss rises sharply with temperature. 

The thermal‑trap approach minimises those losses and could let solar receivers hit industrially relevant temperatures with far lower optical concentration or higher thermal efficiency than unshielded designs.

Modelling performed by the authors showed a quartz‑shielded receiver can reach target temperatures with smaller mirror fields or attain substantially higher conversion efficiency at equal concentration. 

For example, an unshielded state‑of‑the‑art receiver with 500‑sun concentration yields around 40% efficiency at 1,200°C, whereas a receiver shielded by 300 mm of quartz could deliver about 70% under the same conditions, or else match performance at roughly half the concentration.

“Previous research has only managed to demonstrate the thermal-trap effect up to 170 degrees Celsius (338 degrees Fahrenheit),” Dr. Casati added. “Our research showed that solar thermal trapping works not just at low temperatures, but well above 1,000 degrees Celsius. This is crucial to show its potential for real-world industrial applications”.

The team is now optimising materials, geometries and working fluids and exploring how alternative semi‑transparent media might extend the concept further.

While the laboratory results are promising, full technical and economic validation at scale remains to be done. If scaled successfully, thermal‑trap solar receivers could offer industry a practical, low‑carbon route to the extreme temperatures required for many manufacturing processes, reducing reliance on fossil fuels where electrification is impractical.
 

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