What colour is hydrogen?

11. March 2021

Hydrogen is widely regarded as a miracle cure for the energy transition. However, not all forms of hydrogen are the same – at least as far as the global climate is concerned. Depending on how it is produced, it gives rise to different amounts of CO2 emissions. For the sake of better classification, it is divided into colour categories. TÜV-NORD expert Verena Schneider explains what distinguishes green hydrogen from blue and which safety questions need to be answered when this volatile gas is used.

Verena Schneider: Gray hydrogen currently dominates the market. It is produced from fossil fuels, primarily natural gas and coal. In a process known as steam reforming, natural gas is converted into hydrogen and carbon dioxide under high heat. The CO2 escapes unused into the atmosphere, thereby exacerbating the greenhouse effect. Depending on the source and electricity mix, the production of one ton of hydrogen generates around ten tons of CO2—a considerable amount.

Green hydrogen is produced from water using renewable energy through an electrolysis process. During this process, the water molecule is split into its two elements: oxygen and hydrogen. If only electricity from renewable sources is used, the hydrogen is considered CO2-free—even though the production of a wind turbine, for example, is of course not entirely climate-neutral.

Blue hydrogen is actually gray hydrogen, meaning it is produced using fossil fuels. The key difference is that the resulting CO2 is captured, collected, and injected deep underground into suitable geological formations. It therefore does not escape into the atmosphere.

This process is known as Carbon Capture and Storage, or CCS for short. On balance, blue hydrogen is considered carbon-neutral. Possible storage sites include, for example, former oil or gas reservoirs and rock formations containing saltwater. In Germany, the process has so far only been used in pilot and test projects. At the end of 2020, Norway announced that it would invest 1.5 billion euros in the construction of a large CCS storage facility.

For us at TÜV NORD, hydrogen is, by definition, a diverse field. Looking ahead, hydrogen should become green. We support our customers in adapting the potential of hydrogen technology to their specific needs. In doing so, we do not yet limit ourselves to green hydrogen. This is because today’s business models often do not yet fully reflect a successful hydrogen economy, meaning that the issue of imports must also be considered. In general, our focus is on a safe and secure energy supply. Safety knows no colors.

Turquoise hydrogen is hydrogen produced through the thermal cracking of methane—a process known as methane pyrolysis. Instead of CO2, this process produces solid carbon. This process is carbon-neutral if the high-temperature reactor is powered by renewable energy sources. And, of course, the resulting carbon must be permanently sequestered. One advantage of this process is that carbon is easier to store than CO2 and could be used, for example, in the chemical and electronics industries or in road construction. Compared to the production of green hydrogen via electrolysis, methane pyrolysis is also said to require only one-fifth of the energy. So far, however, the process has only been tested on a laboratory scale. With funding from the Federal Ministry of Research, BASF has now built a test facility in Ludwigshafen that is scheduled to go into operation in the coming months once testing is complete.

Environmental groups have raised the issue that the extraction, processing and transport of natural gas is associated with high greenhouse gas emissions. So blue hydrogen would never be carbon neutral. What’s your assessment?

CO2 emissions from the extraction and processing of natural gas can be further reduced – but there’s no way they can be completely eliminated. In this respect, blue hydrogen would also not be completely carbon neutral. But we will need it as a transitional technology. This is because we don’t yet have enough renewable energy in this country to produce green hydrogen for all our needs. This is also one of the reasons why the Federal Government intends to produce green hydrogen abroad in the future and import it into Germany.

One key aspect is the safe transport of hydrogen. The repurposing of natural gas pipelines is under discussion as a way of allowing us to continue using the existing infrastructure. To date, it’s been possible to add a share of around ten percent of hydrogen to natural gas. We need to check here whether we can operate the existing pipelines without any problems with significantly higher mixture ratios or even with pure hydrogen. Or to what extent technical adaptations or new pipelines will be required. Some questions also need to be clarified on the production side: green hydrogen is currently produced in small electrolysers in the low megawatt range. In the course of the market ramp-up, which the Federal Government intends to push forward through its hydrogen strategy, large plants with outputs of more than one hundred megawatts are planned. We’re going to have to make these new energy infrastructure systems safe! in the best case scenario, the development and manufacture of these electrolysers will be supported by independent third parties like TÜV NORD. But we’re also going to have to increase confidence in the new energy source at other levels. Chemically speaking, green hydrogen is no different from grey hydrogen produced from natural gas, but it’s environmentally friendly and, at the same time, considerably more expensive. It would therefore make sense to establish proofs of origin. Customers in industry and transport would then be able to rely on being supplied with guaranteed 100% green hydrogen.