Using solar energy to generate heat at high temperatures

The production of cement, metals and many other chemical products requires temperatures in excess of one thousand degrees Celsius. Currently, this heat is usually obtained by burning fossil fuels: coal or natural gas, which emit large amounts of greenhouse gases. Heating with renewable electricity is not an alternative, as it would be inefficient at these high temperatures. Although much of our economy and society must become carbon neutral in the coming decades, these industrial processes will continue to be powered by fossil fuels for the foreseeable future. They are considered difficult to decarbonize.

The main component of the heat trap is a cylinder made of quartz. In tests, it reached a temperature of 1050 degrees Celsius and glowed at this temperature. Photo credit: ETH Zurich / Emiliano Casati

Researchers at ETH Zurich have now demonstrated in the laboratory a way to make these industries independent of fossil fuels. They have designed a device that can use solar radiation to provide heat at high temperatures required for manufacturing processes. A team led by scientist Emiliano Casatti of the Energy and Process Systems Engineering Group and Professor Aldo Steinfeld of Renewable Energy Carriers has developed a thermal trap. It consists of a quartz rod attached to a ceramic absorber that, thanks to its optical properties, efficiently absorbs sunlight and converts it into heat.

In lab-scale experiments, the team used a quartz rod 7.5 centimeters in diameter and 30 centimeters long. They were exposed to artificial light 135 times more intense than sunlight, reaching temperatures of up to 1050 degrees Celsius. Previous studies by other researchers have reached a maximum of 170 degrees with such heat traps.

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Large-scale solar concentrator technologies have already been installed on an industrial scale for solar power generation in Spain, the United States, and China. These plants typically operate up to 600 degrees. At higher temperatures, heat loss by radiation increases and decreases plant efficiency. A key advantage of the heat trap developed by ETH Zurich researchers is that it reduces radiative heat loss.

High temperature solar plants

Our approach significantly improves the efficiency of solar absorption. says Cassati. „Therefore, we are confident that this technology supports the use of high-temperature solar plants.” However, he says a detailed technical and economic analysis is still pending. Such an analysis was beyond the scope of the current experimental study, which the researchers published in the scientific journal Devicecall_made.

Cassati continues his research to improve this process. This technology makes it possible to one day use solar energy 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 Cassati. „People often think of energy in terms of electricity, but we actually use about half of our energy in the form of heat.”


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