What’s at the end of the rainbow?
This week, PHC's Senior Technology Partner Dr. John Buxton continues his "Demystifying Hydrogen" series with a look at the different colours of this - potentially - net zero fuel for transport
As I wrote in the first of PHC’s “Demystifying Hydrogen” series, Hydrogen is – in theory at least – a fabulous low-carbon fuel for commercial and public transport. Why? Because it’s a featherweight gas which packs a heavyweight energy punch.
So it’s easy to understand why hydrogen is in the glare ofthe net zero spotlight - especially in industry’s more shadowy corners (such as road transport). It’s got something like three times the energy per kilo than diesel, and is a whole lot less mucky.
But there is one thing I didn’t mention, which we’re picking up this week: like most gases, hydrogen is colourless. (Not all gases are: the halogens, for example, are colourful if very nasty. Chlorine is yellowy-green; bromine is rusty-red and iodine is a rather fetching Fiorentina purple). Still, for reasons we’re about to explore, a range of colours is used to indicate hydrogen’s environmental impact.
Hydrogen comes in different colours – and they ain’t all good
Using colours to distinguish different “sorts” of hydrogen may seem confusing and unscientific, but there’s method in the madness. Green is the symbol of wholesomeness and environmental virtue, and brown tends to be the symbol for something else.
So let’s look at the those colours and explain what the different colours mean. Our summary is in the table below, in order of worsening environmental harm, that is quantity of CO2 generated:
As you see, the CO2 emitted during production defines the colour of the hydrogen. Hydrogen can (and today,for the most part, does) produce CO2 in its production but is CO2-free when it is consumed. That’s the difference between hydrogen and fossil fuels –CO2 is released when we produce and consume conventional fuels – natural gas, gasoline, jet fuel etc, whereas CO2 is released only during the production, not consumption, of hydrogen.
Believe it or not, there are other colours too (including gold and black), but these are minor, niche routes to hydrogen and we will consider them in later posts after we’ve looked at Green hydrogen, the Batman in transport’s Gotham City.
Green is best…
Let’s kick off, then, with Green hydrogen. As we’ve seen,this is defined strictly by its means of production: it is hydrogen generated by electrolysis of water, with the electricity supplied by renewable sources such as wind, solar (or nuclear, although some sources call this ‘pink’ hydrogen; for the purposes of this post, we consider nuclear to be CO2-free and renewable.) When electricity generated by burning coal, oil or gas is used the hydrogen is disqualified from the Green badge– it just can’t be Green hydrogen. So this is the badge of honour and pretty much causes the least environmental harm of all known fuels.
There are many possible uses of Green hydrogen from direct use as a transport fuel to feedstock in Industry or even the production ofother fuels: for example, producing PtX or e-fuels through the combination of Green hydrogen with CO2 captured from the air or industrial flue gas. This is really sexy technology but is held back by lack of scale.
What about Transport?
For transport, hydrogen may be used either in a fuel cell (PEM – Proton Electron Membrane Fuel Cell or PEM-FC), where hydrogen is pumped into a unit that essentially a reverse of the electrolyser which generated the hydrogen in the first place, and with supercharged air pumped into the other side, water generated in the middle, plus electricity and heat. This isseriously clever stuff, but requires witheringly high capital investment. That’s because of the vast quantities of precious metals needed in the fuel cell (see our partner Jonathan Elton’s post from last week). What’s more, for PEM-FC usage, hydrogen needs to be extremely pure -ppb levels of sulphur, for example, will harm the catalyst irreversibly.
Or, more simply, hydrogen can be the fuel in an internal combustion engine (ICE), not dissimilar from an ICE running on diesel or gasoline, but without the CO2.
There are other uses of Green hydrogen, such as steel-making, heating, and energy for industrial plants - but transport is right up there among the most important in the race to net zero.
So where can I get some?
Aha. Not easily. And not very soon.
I wanna tell you a story……..
Recently, it was announced that a scaled-up solar plant is going to be built in the UAE (where sunshine abounds) to generate Green hydrogen. The proposal is for an electrolyser up to 20MW that could generate around 100kg/h. This is excellent, of course. But make no mistake – it’s also tiny. A massive PR campaign and hard-hitting media announcement to tell us that in the Middle East, of all places, this new plant will result in the equivalent of less than 3 barrels of gasoline per hour? This is why it’s hard, right now, to make these economics work.
Put that alongside the fact that there isn’t yet any viable supply, distribution and storage infrastructure for Green hydrogen; that there isn’t a mildly comprehensible market price for Green hydrogen and that there aren’t funding pathways to support transport operators in switching to Green hydrogen, and you get some sense of the challenges ahead.
Green hydrogen really is the fuel of the future – it’s wonderful, wonderful stuff: but making it commercially available, and viable, is a long-term mission which needs energy suppliers, governments, industries and international agencies to get themselves pointing in the same direction. And to put their hands in their pockets.
So, Green hydrogen is a technology in its infancy, and we should all recognise that. As we said at the beginning, in theory Green hydrogen is perfect. But in practice it’s difficult to see a significant role for it any time in the next decade.
We’re still searching for the rainbow’s end.
Come back next time, when I'll be concentrating on blue hydrogen and how to get off the horns of that dilemma......