Sunlight-trapping device can generate temperatures over 1000°C

Engineers have developed a device that can generate temperatures of over 1000°C (1832°F) by efficiently capturing energy from the sun. It could one day be used as a green alternative to burning fossil fuels in the production of materials such as steel, glass and cement.

Manufacturing these materials involves heating raw materials to above 1000°C by burning fossil fuels, which is extremely energy intensive. “About half of the energy we use is not actually turned into electricity,” says Emiliano Casati at ETH Zurich in Switzerland. “It’s used to produce many of the materials that we need in our daily lives and our industries.”

Solar furnaces, which use an array of moveable mirrors to focus sunlight onto a receiver that reaches high temperatures, could be used at manufacturing sites as an alternative to burning fossil fuels. However, they are currently quite inefficient at converting solar energy to temperatures higher than 1000°C, says Casati.

To improve the efficiency of such devices, Casati and his colleagues have designed a heat-trapping solar receiver with a 300 millimetre layer of quartz around it.

Quartz is a semi-transparent material that allows light energy to pass through it but blocks thermal energy. This means that as the silicon heats up from the concentrated sunlight, the quartz prevents thermal energy leaking back out, trapping the heat and reducing energy loss in the system.

The team tested the modified solar receiver in a facility that simulates sunlight using LEDs. Their initial experiments found that the silicon absorber easily reached 1050°C.

According to heat transfer models, the silicon shield could enable receivers to get to temperatures of up to 1200°C while keeping 70 per cent of the energy input in the system. Without the silicon shield, the energy efficiency drops to just 40 per cent for the same temperature.

While this is just a proof-of-concept device, Casati hopes that it will one day be widely used as a green way of producing the high temperatures needed in manufacturing. “We really need to tackle the challenge of decarbonising these industries, and this could be one of the solutions,” he says.