Scientists Set A Solar Thermal Trap To Snare Fossil Fuels

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Fossil energy seemed to have an iron grip on cement, steel, and other industries just a few years ago. Well, that was then. New systems for harvesting and transferring solar energy are emerging, with the aim of producing the high heat needed for industrial processes. In the latest development, a Swiss research team is fine-tuning a solar thermal “trap” to achieve temperatures of 1,000°C and more. That should be high enough to do the trick.

Laying A Solar Thermal Trap For Fossil Fuels

The new solar thermal research comes from ETH Zurich, short for the well-known Swiss Federal Institute of Technology, where researchers have been exploring ways to improve concentrating solar power systems.

Unlike solar cells, which generate electricity directly, concentrating solar systems convert sunlight into solar thermal energy. The heat transfer medium — typically, molten salt — can be deployed to provide thermal energy for industrial processes. It can also  provide steam for generating electricity in a power plant.

That’s good as far as it goes, but the challenge is to design a concentrating system that can efficiently transfer heat up into the higher range of 1,000°C or more demanded by some industrial processes. To leap that hurdle, the ETH team decided to take a close look at the thermal-trap effect, which describes the ability of quartz, water, and other semitransparent substances to trap sunlight.

The thermal-trap effect was thought to work only at lower temperatures, making it unsuitable for decarbonizing high-heat industrial processes. Nevertheless, the ETH team took a crack at it.

“Previous research has only managed to demonstrate the thermal-trap effect up to 170°C (338°F),” explains the corresponding author of the research team, Emiliano Casati.

“The team crafted a thermal-trapping device by attaching a synthetic quartz rod to an opaque silicon disk as an energy absorber,” ETH Zurich recounted in a press release earlier today. When exposed to the equivalent of 136 suns’ worth of energy flux, the absorber plate reached 1,050°C. The other end of the quartz rod remained relatively cool at 600°C.

“Our research showed that solar thermal trapping works not just at low temperatures, but well above 1,000°C. This is crucial to show its potential for real-world industrial applications,” Casati, noted.

“Solar process heat at above 1,000°C can decarbonize key industrial applications such as cement manufacturing and metallurgical extraction,” the researchers emphasize in their study, available in the scientific journal Device under the title, “Solar thermal trapping at 1,000°C and above.”

A New Life For Solar Thermal Energy

Don’t get too excited just yet. The ETH solar thermal system is still in the proof of concept phase. However, it does represent a breath of fresh air for the concentrating solar industry. The team simulated their new solar thermal trap under various conditions and reported results that could lead to the design of more compact, efficient concentrating solar systems.

“For example, a state-of-the-art (unshielded) receiver has an efficiency of 40% at 1,200°C, with a concentration of 500 suns,” ETH Zurich explains. “The receiver shielded with 300 mm of quartz achieves 70% efficiency at the same temperature and concentration.”

“The unshielded receiver requires at least 1,000 suns of concentration for comparable performance,” ETH Zurich adds.

The prospect of leaner, meaner concentrating solar systems could help kickstart the industry here in the US. Though the technology has taken off in other parts of the world, the US has been slow to catch solar thermal fever.

It’s not for lack of trying. The US Department of Energy made a concerted effort to support next-generation concentrating solar technologies during the Obama administration. The agency’s concentrating solar programs also kept pace during the Trump administration, despite the former President’s oft-repeated promises to save coal jobs.

The Solar Thermal Chickens Are Coming Home To Roost

With much of the groundwork laid, the Energy Department has been readying itself for another concentrating solar push. In April, the agency’s Solar Energy Technologies Office announced announced a new $30 million round of funding under the topic of “Concentrating Solar Flux to Heat and Power,” aimed at accelerating the timeline towards large scale commercial deployment.

“CSP technologies offer unique value as a renewable energy resource that can readily deliver high-temperature heat for uses in the industrial sector and incorporate energy storage for on-demand solar power,” SETO explained.

The three-part funding round includes an assist for new solar collectors that help cut costs while improving reliability.

Another portion of the funding will go to one of our new favorite subjects, supercritical carbon dioxide. The use of sCO2 as a working fluid in solar thermal systems crossed the CleanTechnica radar back in 2020, when it emerged as a compact, low cost, energy efficient replacement for conventional steam turbines. Last fall we also took note of the Energy Department’s sCO2 demonstration showcase in Texas.

The third portion relates to the ETH team’s work. The funding will go to support “proposals for novel solar receivers and solar reactors that convert concentrated sunlight into usable thermal energy at high temperatures,” SETO explains.

Particle receivers make the cut for consideration, partly due to their potential for hitting the 90% efficiency mark.

Of Course, Green Hydrogen

Of course, no mention of new solar thermal technology would be complete without bringing up green hydrogen. The Energy Department is among the many funding organizations that are eyeballing concentrating solar technology as a means of bringing down the cost of green hydrogen.

SETO notes that its new round of funding supports the aims of the Energy Department’s Hydrogen Shot program, which aims to push the cost of “clean” hydrogen down to a competitive level with conventional hydrogen produced from natural gas or coal. The goal is to hit the level $1.00 per kilogram within 10 years, which is quite an ambitious considering that the ballpark figure for green hydrogen is about $5.00 per kilogram.