Green H2: a strong contender to replace fossil fuel
"...the simplest and most powerful molecule"
Hydrogen, the most abundant element in the universe, forms the fuel gas (H2: molecular hydrogen) with the highest energy/weight ratio. In a world ruled by fossil fuels (oil & gas), it can be positioned as the "new natural gas" [EFI, 2022].
H2 is known for its versatility i) in coupling sectors (energy, mobility, industry, heating), ii) for serving economic niches difficult to electrify (as they require high energy densities), and iii) for scalable seasonal storage, an attribute not contemplated in other forms of energy storage, such as Li-ion batteries.
Much attention has been paid for its potential role in combating climate change. Green hydrogen can clean up i) agribusiness chain with the production of nitrogen fertilizers from green ammonia (synthesized via Haber-Bosch process), ii) mining sector, with the decarbonization of its operations (by replacing diesel oil) and the production of green explosives (from green ammonia), iii) steel sector, with the production of green pig iron, and iv) cement industry, acting as fuel in high-speed furnaces.
Hydrogen is a synthetic energy carrier. Not existing in nature in its pure state, hydrogen can be produced from sources like natural gas (most used today) and water (the cleanest), via chemistry or electrolysis, respectively.
Making hydrogen from water electrolysis is one of the worst energy-intensive ways to get the fuel: about 30 to 35% of the energy used to produce green hydrogen is lost during the process, meaning that to get 1 MWh of hydrogen, around 1.5 MWh of electricity are needed [IRENA, 2021].
Also, H2 is a gas that is difficult to handle. Due to its low volumetric energy density, it has to be compressed at high pressures (up to 700 bar) to be packed into a tank in sufficient quantities to power a vehicle.
From the other side of the system, fuel cells generate electricity through the oxidation of H2 (oxygen is obtained from the air), powering electric cars/machines and producing water vapor as a by product. In this conversion, about 50% of energy is lost.
Other downside of hydrogen fuel cells is the high cost of the (critical) materials (e.g., Iridium and Platinum) used to produce the catalysts, raising the upfront cost of energy cells (and also water electrolysis systems).
H2 can also be burned in furnaces to generate heat or in internal combustion engines (ICE) for mobility applications, producing energy, water vapor, and NOx (nitrogen oxides), therefore not being classified as a zero-emission process, but pollutant of atmospheric air.
For large scale storage of renewable energy, hydrogen is the most suitable alternative. Nevertheless, H2 storage emerges as obstacle to establishing the infrastructure for hydrogen technology, having become one of the key research areas in the hydrogen topic.
Many questions, few answers
Figure 1 summarizes the hydrogen supply chain, highlighting H2 producing rainbow and end use. Within this figure, WoodMac reveals two of the most important questions related to the hydrogen paradigma, namely:
1. How competitive will each type (color) of H2 be?
2. What will future supply chains look like and what are the economics (*)?
(*) a composition between asset level economics & country level economics
Unfortunately, the answers are not straightforward. But we already have some (solid) bets, such as the one from Bloomberg, which states that the long-term goal for H2 to become a viable fuel is for it to cost btw 1 and 2 USD per kg, far from the current (levelized) cost of green H2, btw 3 and 5 USD [Bloomberg, 2022].
The only certainty is that there's no turning back: the direction is right, although we still don't know exactly which roads to take or avoid.
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