Using solar energy to generate heat at high temperatures

Using solar energy to generate heat at high temperatures
by Robert Schreiber
Berlin, Germany (SPX) May 16, 2024

The production of cement, metals, and many chemical commodities requires extremely high temperatures of over a thousand degrees Celsius. Currently, this heat is usually obtained by burning fossil fuels like coal or natural gas, which emit large amounts of greenhouse gases. Heating with renewable 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 are likely to continue to be powered by fossil fuels for the near future. They are considered difficult to decarbonize.

Researchers at ETH Zurich have now demonstrated a way to make these industries independent of fossil fuels. Using solar radiation, they have engineered a device that can deliver heat at the high temperatures needed 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 to a ceramic absorber, which can efficiently absorb sunlight and convert it into heat.

In their lab experiments, the team used a quartz rod measuring 7.5 centimeters in diameter and 30 centimeters in length. They exposed it to artificial light with an intensity equivalent to 135 times that of sunlight, reaching temperatures of up to 1050 degrees Celsius. Previous studies by other researchers have achieved a maximum of 170 degrees with such thermal traps.

Large-scale solar concentrating technologies are already established at an industrial scale for solar power generation in countries like Spain, the US, and China. These plants typically operate at up to 600 degrees. At higher temperatures, heat loss by radiation increases and reduces the efficiency of the plants. A major advantage of the thermal trap developed by ETH Zurich researchers is that it minimizes radiative heat losses.

"We are, therefore, confident that this technology supports the deployment of high-temperature solar 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 analyses are still pending. Such analysis is beyond the scope of the current experimental study, which the researchers have published in the scientific journal *Device*.

Casati is continuing 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 trapping at 1,000C and above