Only a few people live in the individual research stations in Antarctica, but they, too, must be supplied with energy. As a rule, this means transporting crude oil and gasoline there by ship at great expense – and high energy consumption. On top of that, even tiny leaks can damage the sensitive ecosystem. When environmental physicist Dr. Kira Rehfeld from Heidelberg University in Germany took part in an Antarctic expedition as part of her research, she became aware of this problem. At the same time, she noticed how intensely the sun shines there.
Together with colleagues, Rehfeld therefore looked for ways to replace fossil raw materials with environmentally and climate-neutral substances. To this end, a team from the HZB Institute for Solar Fuels, the University of Ulm and the University of Heidelberg investigated how to produce hydrogen at the South Pole using sunlight and what method is best suited for this purpose, as not every method works at extreme subzero temperatures. While cold temperatures generally increase the efficiency of most solar modules, the situation is quite different for electrolysis. Here, cold can significantly reduce efficiency. One of the advantages of hydrogen is that it can be used in a variety of ways and can also be stored very well at low temperatures.
Coupled vs. decoupled design
“Our idea was therefore to use solar modules to produce climate-neutral hydrogen on site during the Antarctic summer by splitting water into hydrogen and oxygen by electrolysis,” explains Dr. Matthias May, head of the Emmy Noether research group SPECSY at the University of Ulm. He was previously a postdoc at the HZB Institute for Solar Fuels. After a little more than two years, the researchers’ conclusion is that it makes the most sense to attach the photovoltaic modules directly to the electrolyzer, i.e., to thermally couple them, so that the waste heat from the PV modules increases the efficiency of the electrolysis.
To test this, May and his HZB colleague at the time, Dr. Moritz Kölbach, now a postdoctoral researcher at Ulm University, compared two different approaches in experiments. In a conventional setup, the photovoltaic module is separated from the electrolysis vessel. In the newer, thermally coupled setup, the photovoltaic module is in close contact with the wall of the electrolysis tank. This enables a direct heat exchange. The experiments were conducted in a freezer in which Kölbach cut a window in the door, which he sealed with quartz glass. This allowed the researchers to irradiate the inside of the cabinet with a solar simulator and simulate conditions in Antarctica.
The electrolysis container was filled with 30 percent sulfuric acid for the experiments. This substance, also known as battery acid, has a freezing point of about -35 degrees Celsius and is a good electrical conductor. After setting up the two experimental cells, Kölbach performed the series of measurements. It turned out that the thermally coupled cell produced more hydrogen than the thermally decoupled one. In the cell with the thermally coupled PV modules, the irradiated modules were able to transfer their waste heat directly to the electrolyzer. “We were even able to increase efficiency by adding thermal insulation to the electrolyzer. This increased the electrolyte temperature under exposure from -20 to as high as + 13.5 degrees Celsius,” says the scientist.
Mathias May acknowledges that it remains to be seen whether the advantages of thermally coupled systems can also be exploited economically. “That’s why we want to test prototypes under realistic conditions in the next phase. That will certainly be exciting and we are currently looking for partners for this,” he says.
The results of the study, published in Energy & Environmental Science, could also be applied to other extremely cold regions of the world besides Antarctica. For example, hydrogen could replace fossil fuels and eliminate CO2 emissions in northern Canada, Alaska, the Himalayas, the high Alps or the Andes. “Perhaps solar-generated hydrogen will first prove to be economical in such remote regions of the world,” May says. After all, he says, the triumphant advance of photovoltaics also first began in space about 60 years ago in supplying satellites.
The project is funded by the Volkswagen Foundation as part of the “Experiment!” funding initiative.
Cover photo: In polar regions and at extreme altitudes, the conversion of solar radiation into hydrogen could certainly be worthwhile. © Energy & Environmental Science
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