Using solar energy to generate heat at high temperatures
The production of cement, metals and many chemical raw materials requires extremely high temperatures of more than a thousand degrees Celsius. Currently, this heat is usually obtained from the combustion of fossil fuels such as coal or natural gas, which emit large amounts of greenhouse gases. Heating with sustainable electricity is not an efficient alternative at these high temperatures. Although much of our economy and society will need to become carbon neutral in the coming decades, these industrial processes will likely continue to be powered by fossil fuels for the foreseeable future. They are considered difficult to decarbonize.
Researchers from ETH Zurich have now demonstrated a way to make these industries independent of fossil fuels. Using solar radiation, they have developed a device that can provide heat at the high temperatures required for these production processes. The team, led by Emiliano Casati and Aldo Steinfeld, has developed a thermal trap. It consists of a quartz rod coupled with a ceramic absorber, which can efficiently absorb sunlight and convert it into heat.
In their laboratory experiments, the team used a quartz rod with a diameter of 7.5 centimeters and a length of 30 centimeters. They exposed it to artificial light with an intensity equal to 135 times that of sunlight, reaching temperatures of up to 1050 degrees Celsius. Previous studies by other researchers have reached a maximum of 170 degrees with such thermal traps.
Large-scale solar energy concentration technologies have already been developed on an industrial scale for solar energy generation in countries such as Spain, the US and China. These plants typically operate up to 600 degrees. At higher temperatures, heat loss by radiation increases, reducing the efficiency of the plants. A major advantage of the thermal trap, developed by researchers at ETH Zurich, is that it minimizes losses due to radiant heat.
“We are therefore convinced that this technology supports the deployment of high-temperature solar power plants.” says Casati. “To combat climate change, we need to decarbonize energy in general,” says Casati. “People often think of energy in terms of electricity, but we actually use about half of our energy in the form of heat.” However, detailed technical and economic analyzes are still pending. Such an analysis is beyond the scope of the current experimental study, which the researchers published in the scientific journal *Device*.
Casati continues his research to optimize the process. The technology could one day make it possible to use solar energy not only to generate electricity, but also to decarbonize energy-intensive industries on a large scale. “To combat climate change, we need to decarbonize energy in general,” says Casati. “People often think of energy in terms of electricity, but we actually use about half of our energy in the form of heat.”
Research report:Solar thermal insulation at 1,000 °C and higher
