Green hydrogen: what it is and why it can lead decarbonization

Green hydrogen: what it is and why it can lead decarbonization

The technological commitment to green hydrogen is becoming more and more intense and many companies see this sustainable energy method as the key to decarbonisation. We tell you their secrets.

Hydrogen is one of the most present elements in the universe (it is considered to be present in 75% of matter), so it can be considered unlimited. But obtaining it is not as simple as it may seem, since it has such a low density that cannot be found independently on earth.

This means that hydrogen is always associated with one or more elements. The most common way to find it is through its combination with oxygen to form water (H₂O). And it is this precious well formed by two molecules of hydrogen and one of oxygen that is the key to the industry and technology associated with this element.

Replacing all the gray hydrogen in the world with green would mean the equivalent of the current electricity demand in Europe

We have already talked to you before about the environmental implications of obtaining hydrogen from water, but this time we will focus on the green hydrogen or renewable hydrogen.

And there are different methods of obtaining hydrogen, but only green is the one that can lead the way towards the decarbonization of industry and transport.

what is green hydrogen

Green hydrogen is that produced through sustainable procurement methods and respectful with the environment, so that no emission of carbon dioxide (CO₂) is generated into the atmosphere.

There are three main methods of obtaining hydrogen:

  • molecular transformation: a series of chemical reactions are practiced to obtain hydrogen. The most widely used is made from the reforming of natural gas from oil fields and high-temperature steam is used to dissociate the carbon from the hydrogen that makes up the natural gas. In two successive reactions, dihydrogen is obtained on the one hand and CO₂ on the other. It is the most widely used method today.
  • Gasification: it is made with water vapor and pure oxygen and is made from coal or biomass. Through a reactor, coal or biomass is burned at very high temperatures. Combustion releases gases that give rise, on the one hand, to dihydrogen and, on the other, to CO₂.
  • Electrolysis: electric current is used to separate hydrogen from oxygen present in water. But, for the hydrogen obtained to be green, said electricity must come from renewable sources.
So is the process of electrolysis. Photo: Depositphotos.com

These methods give rise to three types of hydrogen based on their polluting emissions:

  • gray hydrogen: is obtained from the reforming of fossil fuels, especially natural gas. It is the cheapest and most used, although it emits large amounts of CO₂ into the atmosphere.
  • blue hydrogen: Fossil fuels are also used, although they are complemented by methods of capturing and storing CO₂ to reduce their pollution.
  • green hydrogen: when electrolysis is used with renewable or green energy, the process does not generate any type of polluting emission, therefore being a clean and sustainable hydrogen.

According to reports from the International Energy Agency (IEA), using a green method to obtain hydrogen has the potential to save 830 million tons of CO₂ per year compared to conventional production through fossil fuels.

In fact, replacing all of the world’s gray hydrogen with green would mean an additional 3,000 renewable TWh per year, the equivalent of current electricity demand in Europe.

How is green hydrogen obtained?

Obtaining green hydrogen from electrolysis using renewable energy sources such as solar or wind power is done as follows:

  1. The water used for electrolysis must include salts and minerals that allow the conduction of electricity.
  2. Two electrodes are immersed in the water. They connect to a power source that will apply direct current.
  3. occurs the dissociation of hydrogen and oxygensince the electrodes attract ions of opposite charge to their own.
  4. In this electrolysis process, a oxidation-reduction reaction thanks to the intervention of electricity.
  5. The cathodic reaction promotes the extraction of hydrogen, while the anode separates oxygen.
  6. The emissions resulting from the process are, in addition to hydrogen and oxygen, water steam. Therefore, the process is totally respectful with the environment.
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Advantages and disadvantages of green hydrogen

Like all current energy sources, green hydrogen offers advantages and disadvantages. They are the following:

  • Does not emit polluting gases neither during combustion nor during the production process.
  • It is easy to storewhich allows its subsequent use in other uses and at times other than its production.
  • can transform into electricity or synthetic fuels and used for domestic, commercial, industrial or mobility purposes.
  • can be mixed with natural gas by up to 20% and travel through the same gas channels and infrastructures (although it would require changing different elements of the existing gas networks to make them compatible).
  • Energy from renewable sourceskey to generating green hydrogen through electrolysis, is more expensive to generate, which in turn makes it more expensive to obtain hydrogen.
  • Hydrogen production in general and green in particular requires more energy than other fuels.
  • It is a very volatile and flammable element.so it requires high safety requirements to prevent leaks and explosions.

Main applications of green hydrogen

When we need to convert it into energy, the hydrogen stored in specific tanks is channeled into a fuel cell. There it unites again with oxygen from the air and electrical energy is obtained. In this way, the only residue left by the process is watera clean, sustainable system in which not an iota of CO₂ is emitted to produce energy.

clean fuel

The use of green hydrogen as fuel will be one of the keys to help the decarbonization of transportespecially long-distance and air travel.

In maritime transport, very cheap but highly polluting fuels are normally used, so green hydrogen is presented as a decisive alternative for deep-draft ships that travel long distances.

In aviation, for its part, green hydrogen can be the basis for synthetic fuels that radically reduce emissions in this sector. It will also be essential for other modes such as rail or heavy goods transport by road.

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Heavy industry

Hydrogen is used as raw material in the chemical industry to manufacture ammonia and fertilizers, in the petrochemical industry for oil refining and in metallurgy to obtain steel.

The use of hydrogen in these three industries produces a large amount of carbon dioxide emissions. For example, the steel making it constitutes between 6 and 7% of global CO₂ emissions, between two and three times the emissions of all world aviation. We could use green hydrogen as a raw material and produce steel without emissions, which would be a very important step for the urgent decarbonization of these industries.

Domestic use

Green hydrogen is capable of reaching temperatures difficult to achieve with other clean processes. That is why its use in electricity and heating for homes is one of the most promising applications of green hydrogen.

Energy storage

Green hydrogen can serve as an energy storage system thanks to its high volume and long lasting in a similar way to how we now use strategic reserves of natural gas or oil. In this way, we could supply renewable hydrogen reserves to support the electricity grid.