Renewable energies: Natural hydrogen could drive the energy transition

Hydrogen, the great hope for the climate-neutral energy transition, has one major disadvantage: it first has to be produced. Either directly from fossil natural gas or with the help of electricity from water. A hydrogen economy therefore requires enormous quantities of climate-neutral electricity, which we do not yet have. However, there is another way to obtain the gas as an energy source. Hydrogen is also found underground - and the gas is probably constantly being produced.

Subterranean hydrogen deposits have been known since the 19th century; drilling companies keep coming across the gas. However, as most of the drilling was for oil and natural gas, underground hydrogen has so far been little more than a curiosity. One of the reasons for this is that it is still a mystery where the hydrogen comes from and why it collects underground. The molecules of the gas are actually too small to remain trapped underground. The lightest of all elements travels through pores and crevices that are impassable for larger molecules. In addition, hydrogen is comparatively reactive and combines easily with other substances, especially oxygen. It was therefore long considered unlikely that large, economically important deposits could exist.

However, this assumption may be wrong. In July the French National Centre for Scientific Research (CNRS) reported large hydrogen deposits under the Lorraine Basin near the German border. And even before that, studies on natural gas seeps and wells in the USA, Russia and West Africa indicated that unimagined quantities of the gas are also being produced and stored at depth elsewhere. In Mali, the local oil and gas company Petroma even extracted hydrogen from an accidentally discovered well for five years from 2011. However, it was unclear what these deposits were all about.

Deep hydrogen as a renewable resource

In 2017 and 2018, experts investigated more closely how Mali's hydrogen deposits come about. According to their findings, the hydrogen is not trapped in the rock for the long term, but is possibly constantly being formed in the deep layers of the Earth's crust. If this proves to be the case, hydrogen would be fundamentally different from other fossil raw materials, which are formed over millions of years and accumulate in deposits. Hydrogen sources would then be those areas of the earth's crust in which the gas rises from the depths, accumulates in less permeable layers and collects in the sediment. If such a well is drilled, it would produce a permanent supply - renewable energy.

The crucial question, however, is: Is there enough supply to make it worthwhile? That depends on how and where the hydrogen is produced in the earth's crust. It has long been known that the minerals olivine and pyroxene react with water to produce hydrogen. This process also takes place in remnants of the old seabed, which can be found in many places on the continents. In coal deposits, the gas is produced virtually as a by-product, and some other rocks also appear to produce hydrogen. Radioactive rock, for example, can split water directly.

The respective articles of these processes and how much gas is produced in total is still unknown. However, in recent years experts have repeatedly revised their estimates of the total amount of hydrogen produced upwards. The well in Mali, which has been in use since 2011, also suggests that at least in some areas of the continents there is enough supply coming from the depths to make the resource economically viable. And even if the gas does not flow out of the earth quickly enough to serve as a truly renewable resource for the energy transition, the available gas could well be enough to kick-start the global hydrogen economy in a climate-neutral way until enough green electricity is finally available.

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