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. Great, we have found the Grail… Green or gray hydrogen, this 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.
Gray hydrogen, green hydrogen
But like electricity, hydrogen is not “technically” a source of energy, it is a gas 11 times lighter than the air we breathe. The hydrogen will rather be used to transport to an end user, energy produced by a primary energy source (like petroleum 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 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 thin gas which must be compressed or liquefied to be used. This requires calling on a significant amount of energy which is not necessarily clean …
Hydrogen hardly exists not theret 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 again necessary to mobilize energy.
Thereby 95% of the world’s hydrogen is produced from fossil fuel sources, especially from natural gas or charcoal. These are the least expensive processes. But the major drawback (which we know only too well), fossil fuels emit CO2, the first of the greenhouse gases, which we are trying to get rid of at the start.
So this hydrogen is anything but clean: we are talking aboutgray hydrogen. Unless, of course, we “graft” into the transformation system a process of capture and CO2 storage. Only problem, it explodes the cost of production.
Electricity to produce hydrogen!
Hydrogen can also be produced by water electrolysis. An ancient technique which allows to decompose, thanks to a supply of electricity, the molecules of H2O into dihydrogen (H2) and oxygen (O).
This is downright awesome, we useelectricity to producehydrogen which will allow us, at the end of the day, to generateelectricity. The human brain is at the height of its power …
And still it is necessary that the starting electricity is itself an electricity coming from a renewable source (hydraulic, solar or wind), in which case one could indeed speak ofgreen hydrogen.
The only problem, economically speaking, does not really make sense since this “clean” hydrogen is four times more expensive than that produced from fossil resources.
So before asserting that hydrogen is clean energy because the H2 molecule does not pollute, we must consider its complete life cycle, from production to use, including compression.
Advantages and disadvantages of hydrogen
Burning 1kg of hydrogen releases three times more energy than 1kg of gasoline
Hydrogen is produced from renewable resources
The discharges are composed only of water vapor
Hydrogen allows more autonomy and storage (impossible with electricity)
On the other hand, it occupies more volume than any other gas and, above all, it is rarely found in its natural state.
It takes about 7 liters of compressed hydrogen to provide as much energy as 1 liter of gasoline.
It has to be transported in bottles or pipelines in compressed or liquid form, which is very expensive.
But could we reduce our dependence on fossil fuels by using another renewable source, hydrogen, in the years to come?
We can store this gas in drums, practical you say! Yes, except that it’s not that simple because you have to densify this gas to have a barrel no bigger than the car you want to move forward with …
The fuel efficiency of a hydrogen engine, no matter how you compress it, is more than 3 times lower than that of the electric motor.
For example, to travel 100 km by car, 1 kg of hydrogen is needed and to store 1 kg, you should already use the entire trunk. So, so that its storage does not take up too much space, it must be densified in the form:
gas, the gas pressure is increased. This is the method mainly proposed by automobile manufacturers for hydrogen vehicles;
It’s not for tomorrow…
Technological challenges, high costs, infrastructure and other issues have so far favored 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 final energy consumption in Europe.
Even if hydrogen is on the rise with, for example, new buses inaugurated in Auxerre, the road to success is still long… Hydrogen vehicles are still way 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 made by government organizations. 80% of vehicles sold were Toyota mirai whose price is around 68,000 euros.
By comparison, in the same year 79 million new cars were sold in the world, including 1.26 million electric vehicles.
