Hydrogen is often presented as the clean energy of the future. Associated with a fuel cell, it does not emit CO2 and can therefore be considered non-polluting. Brilliant, we have found the Holy Grail… Green or gray hydrogen, however, is not necessarily a miracle solution from an ecological point of view.
Hydrogen is the element most abundant in the universe. On Earth, it obviously enters into the composition of water (H2O) and that of living matter. For example, a tenth of our weight consists of hydrogen.
Hydrogen is everywhere but difficult to extract
But like electricity, hydrogen is not “technically” a source of energy, it is a gas 11 times lighter than the air we breathe. Hydrogen will rather be used to convey to an end user, energy produced by a primary energy source (such as oil or uranium) .
Unlike carbon-based fuels, hydrogen does not produce no harmful residue when it burns. When hydrogen is used to generate electricity in a fuel cell, the only waste generated is water vapor. There is no emission of pollutants or greenhouse gases.
In this sense, hydrogen is clean : is this green hydrogen? But hydrogen is a very sparse gas which must be compressed or liquefied to be used. This requires using a large amount of energy which is not necessarily clean…
Hydrogen practically does not exist not up to datet pure in nature, it is always coupled with at least one other molecule. To separate it from the other elements (carbon, oxygen, etc.), it is necessary, here again, to mobilize energy.
Depending on the processes used, the production of hydrogen will generate more or less carbon in the atmosphere:
- L’green hydrogenproduced by electrolysis of water, is potentially the most environmentally friendly.
- L’gray hydrogenproduced thanks to the methane present in natural gas, generates carbon emissions.
- L’black hydrogenmade from coal, is a terrible emitter of CO2.
Thereby 95% of the world’s hydrogen is produced from fossil fuelsfrom natural gas or charcoal, which emit CO2, the first of the greenhouse gases, which we are trying to get rid of as part of the energy transition.
So this gray or black hydrogen is all except clean. Except of course if we “graft” into the transformation system a process for capturing and CO2 storage. Only problem, it explodes production costs.
The advantages of hydrogen
As we have seen, hydrogen can be produced by water electrolysis. An old technique that allows the decomposition, thanks to a supply of electricity, of H2O molecules into dihydrogen (H2) and oxygen (O).
There it is downright brilliant, we useelectricity to producehydrogen which will allow us, in the end, to generateenergy. Are we walking on our heads?
A six-year-old child would ask: But, dad, why don’t we use the electricity directly? »
And his father would no doubt answer: To create a new industrial sector and new jobs, my son. »
More seriously, the interest of green hydrogen is real for two main reasons :
- It can be used for store electricitywhich makes it possible to compensate for the overproduction of renewable electricity (solar, wind, etc.) at certain times and its insufficiency at others.
- He is transportable and can therefore be used as fuel for cars (instead of batteries). Today, most car manufacturers have chosen to store it in gaseous form at high pressure (compressed hydrogen) to ensure a range of 400 to 600 km for their vehicles. For industrial quantities, the hydrogen transport (in gaseous form) can also be done by pipeline.
Where is the green hydrogen then?
However, the starting electricity must itself be electricity from a renewable source (hydraulic, solar or wind), in which case we could effectively speak ofgreen hydrogen.
This is the bet that the Nantes start-up Lhyfe, which adapts electrolysis to the intermittency of renewable energies. In the fall of 2021, it inaugurated its first green hydrogen plant in Bouin, in Vendée, by producing gas from wind turbines installed on the site. It plans to develop around sixty units across Europe.
The only problem, from an economic point of view, it doesn’t really make sense since this “clean” hydrogen is, for the moment, four times more expensive than that which is produced from fossil resources.
So before asserting that hydrogen is a clean energy (the quest for the famous green hydrogen) on the pretext that the H2 molecule does not pollute, we must consider its complete life cyclefrom its production to its use, including its compression.
Green hydrogen, a luxury energy
The first disadvantage of hydrogen is its performance. It takes about 7 liters of compressed hydrogen to provide as much energy as one liter of gasoline. Moreover, the energy efficiency of a hydrogen engine is currently three times lower than that of an electric motor.
To travel 100 km by car, you must use and therefore store 1 kg of hydrogen. Like him takes up a lot of space, to store it in bottles, tanks or drums, the automobile industry densifies it in gaseous form (by increasing the pressure of the gas). Otherwise, it would require considerable storage volume. This is obviously a very expensive process.
Another major drawback is its cost price if you want it to stay clean. The production cost of green hydrogen is between 4 and 6 €/kg while that of gray hydrogen is 1.5 €/kg. To date, green hydrogen is therefore infinitely less profitable than gray hydrogen.
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It’s not for tomorrow…
Technological challenges, high costs, infrastructure and other issues have so far encouraged the development of other renewable energy sources such as solar and wind.
However, all hopes are allowed. In July 2021, the European Commission announced a particularly ambitious course: by 2050, hydrogen should represent 14% of consumption energy in Europe.
Even if hydrogen is on the rise with, for example, new buses inaugurated in Auxerrethe road to success is still long… Hydrogen vehicles are still far too expensive and the number of charging stations in France is less than 40.
The International Energy Agency noted that in 2018, sales of hydrogen cars in the world had just exceeded 11,000 copies, mostly purchases by government organizations. 80% of vehicles sold were Toyota Mirai whose price is around 68000 euros.
By comparison, in the same year 79 million new cars were sold worldwide, including 1.26 million electric vehicles.
