What do hydrogen electrolysers actually do and why are they so important for the energy transition? Many facilities are planned. Experts consider their operation to be “largely harmless”.
Hydrogen produced in a climate-neutral manner should play a central role in the future economic system. As an energy source, it is intended to generate electricity in new gas power plants when the sun is not shining and the wind is not blowing. In industry, for example, it is intended to replace carbon in steel production and thus avoid large amounts of climate-damaging carbon dioxide. Because the waste product is simply water.
The problem: Huge quantities are required. They should be produced in special machines, so-called electrolysers. They also play a role in the key points of the federal government’s new power plant strategy published at the beginning of the week. Among other things, the construction and operation of electrolysers should be made easier, it says.
What is an Electrolyzer?
An electrolyzer is a high-tech device in which a substance is broken down into its components using electricity. When it comes to producing hydrogen, the starting material is water. Chemically, water consists of hydrogen and oxygen. The chemical formula is H₂O, which means that one oxygen atom is connected to two hydrogen atoms. If the electricity used is generated in a climate-neutral manner, it is referred to as green hydrogen. To distinguish the method of production, other colors are also attributed to it.
What is the difference to a fuel cell?
An electrolyzer is essentially a fuel cell in reverse. A fuel cell uses hydrogen and oxygen to produce electricity and heat, explains the German Aerospace Center. “Technically speaking, electrolysers and fuel cells are closely related.”
Are there different types of hydrogen electrolysers?
Yes. According to the Federal Ministry of Economics, there are currently four technologies: alkaline electrolysis (AEL), proton exchange membrane electrolysis (PEM), anion exchange membrane electrolysis (AEM) and high-temperature electrolysis (HTEL). “Alkaline electrolysis has been known and commercially usable for over a century, PEM electrolysis is a much younger technology that is also commercially ready for use,” explains the ministry. Compared to AEL, this technology still offers a lot of potential for technical developments and cost savings. HTEL is still in the pilot phase.
What sizes are electrolyzers available in?
The size usually indicates the maximum amount of electricity a system can absorb. This power consumption is measured in the unit Watt. So that the numbers don’t get so big, you put the usual prefixes kilo, mega or giga in front of them. A megawatt (MW) is a million watts. For example, on the site of the Shell Energy and Chemical Park near Cologne there is a 10 megawatt PEM system that is powered by renewable energies. The project is called Refhyne.
How much hydrogen can electrolyzers produce?
The Refhyne plant (10 MW) can produce up to 1,300 tons of hydrogen annually. According to previous information, the plant manufacturer Thyssenkrupp Nucera assumes that its 20 megawatt module can produce up to 3,100 tons of hydrogen annually.
How much hydrogen is needed?
When talking about quantities of hydrogen, the energy content in watt hours is also often mentioned. 100,000 tons of hydrogen have an energy content of 3.33 terawatt hours (TWh), i.e. 3.33 billion kilowatt hours.
Around 55 terawatt hours of hydrogen are currently needed in Germany every year. It is obtained primarily from natural gas using a process called steam reforming. The resulting carbon dioxide escapes into the atmosphere. The hydrogen produced in this way is called “gray”.
The federal government assumes that a further 40 to 75 terawatt hours of hydrogen will be needed in 2030, for a total of 95 to 130 terawatt hours, or up to 3.9 million tons. The amount also includes so-called hydrogen derivatives, i.e. energy sources that are based on hydrogen such as ammonia, methanol or synthetic fuels. The steel industry will be a large consumer of hydrogen. For example, Thyssenkrupp’s planned direct reduction plant in Duisburg, which is intended to replace a blast furnace in steel production, will need 143,000 tons annually.
Where should the hydrogen come from?
Mainly from abroad, but also from within the country. According to the National Hydrogen Strategy, Germany should build 10 gigawatts of electrolysis capacity by 2030. “The hydrogen that can be produced is sufficient to cover around 30 to 50 percent of Germany’s hydrogen needs in 2030,” explains the federal government. Germany should import the rest from countries such as Africa or Australia. A hydrogen import strategy is currently being developed.
However, Germany is still a long way from reaching 10 gigawatts. According to the hydrogen balance of the energy company Eon, 33 electrolysers with an installed capacity of 62 megawatts were in operation in August last year. At the same time, 111 systems with a total output of 8.7 gigawatts (=8712 megawatts) were planned for 2030. Large electrolysers with 100 megawatts or significantly more are to be built in Wilhelmshaven or Rostock.
Who builds electrolyzers?
The consulting and information organization Carmen, supported by the Bavarian Ministry of Economic Affairs, has published a market overview on the Internet. As of July 2023, it included 96 systems from 19 providers. The largest systems had an output of 20 MW, the smallest of 6 kilowatts, i.e. 0.006 megawatts.
Are electrolyzers dangerous?
“They are technologically controllable and largely harmless,” says Thomas Kattenstein from TÜV Nord subsidiary EE Energy Engineers. He considers it “very unlikely” that an ignitable air-hydrogen mixture would be created on an electrolyzer that could cause an explosion. “Hydrogen is lighter than air and rises immediately. If there is a leak somewhere, the hydrogen will evaporate very quickly.”
There are safety devices in the company buildings for such cases. “For example, flaps in the roof that open when detectors measure the corresponding hydrogen concentrations, so that, as far as human judgment is concerned, nothing can happen.” As a further safety measure, according to the expert, each system is connected to nitrogen cylinders that can flush the hydrogen out of the system so that no dangerous concentrations can form.
Are dangerous substances produced when operating electrolysers?
No, just oxygen and hydrogen. However, large systems require coolant, says Kattenstein. Water-glycol mixtures would be used, for example. “Of course, appropriate precautions have to be taken to ensure that they don’t end up in the ground.” There are catch basins to catch leaks.
The alkaline electrolysis process uses caustic potassium hydroxide, explains Jan Simoneit from Energy Engineers. “In case something spills out, there are catch basins here too.”
Are there also smaller electrolyzers for home use?
Yes. The Berlin company HPS, for example, offers hydrogen-based energy storage systems in which the solar power produced on the roof of a house produces green hydrogen in an electrolyzer. This can then be used again to generate electricity in winter, for example, using a fuel cell.
Source: Stern
