"To tackle climate change, we need to decarbonize energy in general," said Emiliano Casati of ETH Zurich. "People tend to only think about electricity as energy, but in fact, about half of the energy is used in the form of heat."
The production of glass, steel, cement, and ceramics requires high temperatures, traditionally achieved by burning fossil fuels. These industries account for about 25% of global energy consumption. Researchers have explored using solar receivers to concentrate and build heat, but transferring solar energy efficiently above 1,000 degrees Celsius has been challenging.
Casati's team enhanced solar receivers using quartz, which traps sunlight through the thermal-trap effect. They created a device with a synthetic quartz rod and an opaque silicon disk to absorb energy. When exposed to intense sunlight, the device's absorber plate reached 1,050 degrees Celsius, while the quartz rod's other end remained at 600 degrees Celsius.
"Previous research has only managed to demonstrate the thermal-trap effect up to 170 degrees Celsius," Casati said. "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."
Using a heat transfer model, the team simulated the quartz's efficiency under various conditions. The model showed that thermal trapping achieves target temperatures at lower concentrations with similar performance or higher efficiency at equal concentrations. For example, a state-of-the-art receiver has an efficiency of 40% at 1,200 degrees Celsius with a concentration of 500 suns. A receiver shielded with 300 mm of quartz achieves 70% efficiency at the same temperature and concentration. The unshielded receiver requires at least 1,000 suns for comparable performance.
Casati's team is optimizing the thermal-trapping effect and exploring new applications. They have tested other materials, such as different fluids and gases, to reach even higher temperatures. The ability of these semitransparent materials to absorb light or radiation is not limited to solar radiation.
"Energy issue is a cornerstone to the survival of our society," Casati said. "Solar energy is readily available, and the technology is already here. To really motivate industry adoption, we need to demonstrate the economic viability and advantages of this technology at scale."
Research Report:Solar thermal trapping at 1000C and above
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