Has hydrogen’s time arrived?

There is a more serious concern for viability. Early on in the second wave, electrochemists were pointing out that the proposed applications of hydrogen for transportation would incur large energy losses. Thus a typical commercial hydrogen electrolyser had an efficiency of around 50%, as measured by energy consumption in relation to the theoretical requirement. Similarly the efficiency of electricity generation using hydrogen fuel, whether by combustion engine or fuel cell, was also reckoned to be around 50%. So in that case overall efficiency would only be 25%. Additional efficiency losses occur when processes like compression and liquefaction of hydrogen are taken into account.

These numbers meant that in the sequence electricity→hydrogen→electricity 75% of the initial electrical energy was lost (as heat). The conclusion then was that, at least for transportation, it was far preferable to use "raw" electricity to charge a battery electric vehicle than to rely on hydrogen as an energy intermediary.

On the matter of efficiency it's worth noting that there's always debate about how to express efficiencies of energy conversion devices where electrical and chemical energies are being compared. However with the kind of sequence shown above there is no argument; efficiency is a ratio of two electrical energy quantities, out and in. The ratio is a dimensionless number, a true efficiency.

Over time there has naturally been progress in raising these efficiencies. For example PEM electrolysers are said to run at efficiencies up to around 70%. The point is that efficiency is an important consideration in analysing any proposal involving hydrogen, a crucial parameter for industrial success. At present it seems ignored.

Efficiencies have to be measured and optimised in real plants, purpose-engineered and tested at successively increasing scales. Energy intermittency with solar and wind sources might pose special problems for Green Hydrogen production. Proper piloting and demonstration must be carried out. Shortcuts in process development engineering will add risks.

It's clear that energy losses in Green Hydrogen business models must be expected. They may well exceed 60%, which means that of the electrical energy going into Green Hydrogen only some 40%, and perhaps less, would appear in the final product. Is the impact of such losses on business viability being examined in the current Green Hydrogen frenzy? If so it's hard to spot.

Green Hydrogen businesses are not risk-free. Should governments take on any of that risk or should it all be borne by private investors? That needs explicit consideration. Also governments ought to be aware of the political dangers they face with involvement in ventures that look like they could squander a substantial fraction of the clean energy they consume. Ordinary consumers will no doubt like the idea of getting hold of electrical energy so cheap that their government doesn't mind wasting it.

Has hydrogen's time arrived? Perhaps, but it will be interesting to keep watching.