Hydrogen is the most abundant element in the universe. It can be made safely from
renewable energy sources and can be used as a fuel for vehicles, to heat buildings,
to produce electricity, and to fuel aircraft. It is hence often stated that hydrogen is the
fuel of the future. Thanks to it, we are going to power clean planes, clean cars, clean
boats... In short, we can get rid of our polluted world in no time, while preserving all
the advantages we have so far.
Wonderful solution. But is it?
The first problem is that hydrogen as a gas cannot be found naturally on Earth. It is
always associated with other elements and must be manufactured. Long story short,
to be able to exploit hydrogen, you have to separate it from the other atom it is linked
to. Take the example of water (hydrogen + oxygen). To obtain hydrogen, the liaison
between the atoms must be broken, which costs the same amount of energy that
what will be gained in the end. This could be interesting. However, including all the
intermediary losses, it costs more energy to dissociate H and O2 than what will be
gained by combusting hydrogen in the end.
Secondly, almost all of the hydrogen is produced from hydrocarbons such as natural
gas and coal. As a consequence, in 2018, the global production of 70 million tons of
hydrogen generated the emission of 800 million tons of CO2, a figure comparable to
the emissions of commercial air transport (918 million tons in 2018), or the combined
CO2 emissions of the United Kingdom and France.
For instance, Hydrogen is created daily in our world, as its indispensable in the
synthesis of ammonia (NH3: Nitrogen + Hydrogen), to produce nitrogenous
fertilizers. In this equation, nitrogen, also known as azote, is recuperated from the
air. Hydrogen is recuperated from natural gas by heating water to a certain point
hence creating hydrogen and CO2. We do get hydrogen gas in this case, but also...
CO2. It comes both from the chemical reaction itself, but also from the combustion of
the natural gas that provided the energy for this reaction. For every tone of H2
produced, 10 tones of CO2 go into the air. As a result, a car using hydrogen
produced this way would emit around 120g/km of CO2 over its lifetime. In
comparison, the average new petrol car would emit between 120 to 130 grams of
CO2 per kilometre. Instead of being created in the car engine, CO2 is created in the
upstream production of hydrogen.
The hydrogen defenders argue that this amount of emission can be brought
significantly down when hydrogen is produced from renewables, even mentioning
sometimes that if renewable energy is used, the gas has a zero- carbon footprint.
First, it is important to recall that renewable energies are not carbon neutral. A wind
turbine produces 10g of CO2/kwh before storage, and a solar panel produces 50g of
CO2/kwh before storage. Some would say that this is still less than gas, which
produces 400g of CO2/Kwh. But it is still not carbon neutral. And maybe in 2020, we
can stop doing less bad and start doing more good.
Additionally, for hydrogen to be "green", water must be electrolysed with low-carbon
electricity (nuclear, wind or hydraulic energy). But there is a small magnitude
problem: in France, to replace all our fuels by hydrogen obtained by electrolysis from
wind power, we would have to multiply by 15 the number of modern windmills
installed in France, and double the total electricity production... This may be hard to
sustain…
In Conclusion, hydrogen presents several challenges that need to be addressed
before being able to say that it is the perfect energy source for the future. Its
defenders welcome the decrease in the costs of renewable electricity, in particular
solar photovoltaic and wind energy, to promote the efficiency and the capability of
Hydrogen to become the energy platform of the future. Even if some new studies
show that new means, like the power-to-gas systems harnessing renewable energy,
could produce cleaner, cost-effective hydrogen for industry, there is still a long time
to go before being able to fly from Berlin to Tokyo without polluting.
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