Storing solar heat at 1200 degrees and making it usable

Solar fuel Storing solar heat at 1200 degrees and making it usable

2024-09-30 Source: Empa | Translated by AI 3 min Reading Time

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The ETH spin-off Synhelion has inaugurated the world's first industrial plant for the production of solar fuels in Germany. At the heart of the plant is also a piece of Empa: Empa researchers developed a material for the high-temperature heat storage system that allows the plant to operate around the clock - even without sunlight.

The concentrated energy of the sun heats water vapor to a temperature of up to 1200 degrees Celsius. This high-temperature process heat is used to operate the reactor, even at night.(Image: freely licensed / Pixabay) — The concentrated energy of the sun heats water vapor to a temperature of up to 1200 degrees Celsius. This high-temperature process heat is used to operate the reactor, even at night.
(Image: freely licensed / Pixabay)

Converting climate-damaging carbon dioxide back into kerosene, petrol and diesel and thus closing the CO₂ cycle: That is the idea behind Synhelion. The ETH spin-off uses the heat of the sun to produce synthetic fuels (synfuels) from CO₂ and water. In June 2024, Synhelion opened DAWN in Jülich: the world's first industrial plant for the production of solar fuels. Thanks to a collaboration with the Empa Laboratory for Advanced Ceramics, the plant can produce renewable fuels around the clock - even at night.

Solar energy makes high-temperature processes possible

To turn CO₂ and water back into fuel, the system needs one thing above all: energy. A large field of mirrors focuses the sunlight onto a single point on the solar radiation receiver. This contains water vapor, which reaches a temperature of up to 1200 degrees Celsius thanks to the concentrated energy of the sun. The reactor is operated with this high-temperature process heat. Excess heat is stored in a chamber several cubic meters in size, filled with special bricks. These bricks - a joint development by Empa and Synhelion - serve as temporary storage for the enormous heat. Overnight, it is this heat reservoir that keeps the reactor running.

Wanted: The perfect ceramic

At 1200 degrees, however, not all bricks are the same. Direct contact with the ultra-high temperature water vapor even corrodes ceramics. None of the high-temperature bricks available on the market were designed for these conditions. So Synhelion approached Empa. In a two-year project funded by Innosuisse, Empa researcher Gurdial Blugan and Empa scientist Sena Yüzbasi joined forces with Synhelion to search for the perfect ceramic:

However, corrosion resistance was only one aspect.
The material should also have a high thermal capacity, be mechanically robust and withstand thermal shocks that can occur when the system is shut down.
It also had to be cheap to produce - because the plant in Jülich is just the beginning for Synhelion.

Gallery

Renewable fuels from solar energy and CO₂: there is also a piece of Empa at the heart of the DAWN plant.(Image: Synhelion)

The ceramic samples were tested for their corrosion behavior in a specially developed high-temperature tube furnace.(Image: Empa)

Lukas Geissbühler, Head of Thermal Systems at Synhelion, in front of the DAWN high-temperature heat accumulator.(Image: Synhelion)

So, together with the Empa workshop and Synhelion, the researchers designed their own high-temperature tube furnace. In it, they exposed various ceramic samples to the corrosive steam atmosphere - for up to 500 hours. "It got pretty hot in our laboratory during these experiments," smiles Blugan. But the sweating was worth it: the researchers found a material that withstood the extreme conditions.

Continue together

Together with their project partners, they refined the composition of the material and optimized the manufacturing process in order to further improve the properties and reduce costs. The bricks were then manufactured by a partner company in Germany and installed in DAWN. "As a researcher, it's not often that your research is applied on such a scale - it's a unique experience," says Yüzbasi.

While DAWN is starting up operations, Synhelion and Empa are already planning their next joint project. For the other plants, they want to further develop the material and make it even more durable. The second Synhelion plant for the production of solar fuel is to be built in Spain from 2025. The goal: even larger storage tanks, even higher temperatures. Because the higher the temperature, the more efficient fuel production becomes.

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