Concentrating sunlight to over 1000°C

Concentrating solar to glass melting temperatures

The production of cement, metals, glass and many chemical commodities requires extremely high temperatures of over 1000°C. At present, this heat is usually obtained by combusting fossil fuels.They are considered difficult to decarbonise.

Researchers at ETH Zurich have demonstrated, in the lab, 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 the production processes. The team led by Emiliano Casati, a scientist in the Energy and Process Systems Engineering Group, and Aldo Steinfeld, Professor of Renewable Energy Carriers, has developed a thermal trap. It consists of a quartz rod coupled to a ceramic absorber which, thanks to its optical properties, can efficiently absorb sunlight and convert it into heat.

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

Large-scale solar concentrating technologies are already established at an industrial scale for solar power generation, e.g. Spain, USA and China. These plants typically operate at up to 600°C. 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 minimises radiative heat losses.

"Our approach significantly improves the efficiency of solar absorption,” says Casati. “We are, therefore, confident that this technology supports the deployment of high-temperature solar plants.” However, detailed technical and economic analyses are still pending, he says. 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 optimise the process. The technology could one day make it possible to use solar energy not only to generate electricity, but also to decarbonise energy-intensive industries on a large scale: “To combat climate change, we need to decarbonise energy in general. People often think of energy in terms of electricity, but we actually use about half of our energy in the form of heat.”