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Aviation is considered one of the biggest contributors to climate change, which is why a decarbonizing solution for that sector is so attractive. It would prove that a big challenge could be overcome and pave the way for other “difficult” sectors to follow suit. Sustainable aviation has been a sector Siemens Energy has been focused on for some time now, and we’re excited about the possibilities it holds.

Defining Terms

Before we get started, let’s be clear on our terms.


Blue hydrogen — Blue hydrogen is called so as it has a lower carbon dioxide impact on the environment because the carbon dioxide created in its manufacture is captured and stored.  Because the storage is costly and has challenges, blue hydrogen is often seen as an interim solution.


Gray hydrogen — This is derived from natural gas and made from fossil fuels. About 10kg of carbon dioxide is released into the atmosphere for every 1kg produced. This high ratio gives the “gray” designation to this hydrogen. Gray hydrogen is relatively inexpensive and is commonly used to make fertilizer and for refining oil. It is the most widely produced type of hydrogen.


Green hydrogen — This form of hydrogen is made in a completely different production format than either gray or blue hydrogen. It is done by electrolysis that is powered by renewables. This means that no harmful gases are created at any point in the production change.


Photovoltaic (PV) power electrolyzer — One way to use solar energy to produce hydrogen is by water electrolysis. The hydrogen produced this way is carbon neutral, and can then be combined with carbon dioxide to create an entirely green SAF.


Sustainable airline fuel (SAF) — SAF is a broad term that refers to non-fossil-derived aviation fuel. SAF is almost identical chemically and physically to jet fuel and hence can be safely mixed with the latter to certain degrees. It can use the same supply infrastructure and does not require any adaptation of existing aircraft or engines. Typical feedstocks used to create SAF are cooking oil and other non-palm waste oils from animals or plants. Solid waste from homes and businesses (e.g. packaging, paper, textiles, food scraps) along with waste from forestry and crops are also used.


Apart from lowering GHG emissions, SAF also includes some other less obvious benefits:

  • Extra revenue for farmers — feedstocks can be provided by farmers during off-seasons, growing biomass crops for SAF production.
  • Improved aircraft performance — SAF often contain fewer aromatic components, enabling them to burn cleaner, leading to lower emissions during takeoff and landing.
  • Environmental services — when wet wastes like manure and sewage sludge are used for SAF production, there’s less pollution pressure on watersheds and more removal of methane from the atmosphere.


Sustainable aviation — Sustainable aviation can be broken down into a number of areas, all seeking to achieve low-to-no carbon emissions:

  • Improving operational efficiency: this includes operations in the air, like more precise navigation for planes, better fuel efficiency, and limited holding times, as well as operations on the ground, like using electric-powered ground equipment.
  • Creating next generation aircraft: some electric-powered aircraft are already flying on smaller regional routes and Airbus is working on concepts for liquid hydrogen planes. The latter is still many years away from a working prototype.
  • Managing residual emissions: this is classic carbon capture and storage.
  • Switching to SAF: while not all SAF are created equal, most in the industry want to see at least a 70% reduction in emissions from the use of these alternatives.
Green hydrogen is done by electrolysis that is powered by renewables. This means that no harmful gases are created at any point in the production change.

The Abu Dhabi Project

Once you understand these terms, the import of our project with Masdar in Abu Dhabi becomes clear. This partnership, in cooperation with Etihad, Lufthansa, Marubeni, Khalifa University, and the Abu Dhabi Department of Energy, aims to establish a PV-powered electrolyzer facility that will showcase green tech production technology as well as offer SAF use cases.


An early phase of the program will utilize green hydrogen for passenger cars and buses in the Masdar City area.  A later phase will explore SAF production for the maritime sector.


Another one of those use cases is to create a kerosene-synthesis plant to combine PV-produced hydrogen and carbon dioxide to produce a SAF that can be used in existing airline technology.  But making sure that it works is only one part of the puzzle. As with any important project in renewables, the real test of viability is scaling, because when a technology can scale, then it can change an entire industry.


All great journeys have to start with those first steps and some big ones are being taken in the Middle East now. It has been a haven for the “old oil” of so many decades, but perhaps green hydrogen will prove to be its “new oil” in a less fossil-dependent age to come.

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