Contribution to climate protection: Solar mini-refinery produces CO2-neutral fuel.
The chemical process is powered by solar energy. © ETH Zurich / Alessandro Della Bella

The demand for energy, it is predicted, will continue to rise both in industry and in private households. This also affects the mobility sector, among others. At the same time, fuels derived from fossil fuels such as petroleum should no longer be used, as petrol and paraffin contribute significantly to global greenhouse gas emissions. If, on the other hand, fuels can be produced from plant material, plastic waste or CO2, they have less of an impact on the climate and can even become climate-neutral. In a test facility for a solar mini-refinery on the roof of ETH Zurich’s machine laboratory, which will go into operation in 2019, it has been demonstrated that it is possible to produce liquid fuel from sunlight and ambient air. Now the scientists have presented a strategy for how their approach can be implemented on an industrial scale.

The solar mini-refinery requires nothing more than air, sunlight and a catalyst. CO2 and water are separated directly from the ambient air and split up with solar energy. The product is syngas, a mixture of hydrogen and carbon monoxide, which is then processed into paraffin, methanol or other hydrocarbons that can be used directly in the existing transport infrastructure. The fuels then only release as much CO2 during combustion as was previously taken from the air. “We were able,” explains team leader and professor of renewable energy sources Aldo Steinfeld, “to successfully demonstrate the technical feasibility of the entire thermochemical process chain for converting sunlight and ambient air into drop-in fuels.” Production has proven stable and reliable under real field conditions and even with Zurich’s less than optimal solar radiation, he said. The efficiency of the solar reactor is still low, but nevertheless, the researcher says, the sun-to-liquid technology is now ready for industrial use.

According to the researchers, a commercial-scale solar refinery could, for example, consist of ten heliostat fields, each capturing around 100 megawatts of thermal solar energy. “Such a plant could already produce 95,000 litres of paraffin a day at an efficiency of around ten per cent – enough to take an Airbus A350 from London to New York and back.” The costs for fuels obtained in this way would, of course, initially still be significantly higher than for conventional paraffin from petroleum because of the high investment costs for the plants.

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