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an interminable conversation 11: Hydrogen?

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yeah, hang on a minute

Jacinta: So green hydrogen – what is it, is it real? Does it really have a future? Where, if anywhere, does it fit in that future? It keeps getting put down, it keeps getting talked about, and it seems most experts say, yeah, it’s in the mix, but at a fairly low concentration.

Canto: Good topic – this will allow us to look back at some videos we’ve viewed which have left me scratching my head. So first, on the inestimable Fully Charged podcast, Robert Llewellyn interviewed a clearly Australian Prof, David Cebon…

Jacinta: And this interview received really rave reviews in the comments, I noticed, which surely says something.

Canto: Yes, so let’s try and get our heads around it… and wow, having watched that interview, I feel a bit dumb for having vaguely hyped green hydrogen’s promise, and for being overly skeptical of Elon Musk’s dismissal of hydrogen a few years go – especially in light of the difficulty of compressing and moving the stuff.

Jacinta: So let’s start at the beginning. Prof Cebon is with the Hydrogen Science Coalition (https://h2sciencecoalition.com), and is a professor of mechanical engineering at Cambridge University. He’s the Director of the Centre for Sustainable Road Freight, and he’s co-authored over a hundred papers etc etc, so he’s super-knowledgeable about this stuff, especially when it comes to vehicular transport.

Canto: So Robert started by talking positively about hydrogen fuel cell cars as clean and green – no toxic fumes. But, nowhere to refuel them – and refuelling is one of many issues.

Jacinta: And then it was onto the colours of hydrogen, which I didn’t know about. So you ‘make’ hydrogen in two ways – electrolysing water, that is separating into hydrogen and oxygen by means of an electric current, which is energy-intensive. Pulling the H2O molecules apart isn’t easy. If the electricity you use for this is renewable, that makes ‘green hydrogen’. If that energy isn’t renewable it’s called ‘yellow hydrogen’. Of course, energy out of the grid may be a mix – here in South Australia it’s largely gas and renewables, whereas in the eastern states a lot of it is coal – nasty brown coal in Victoria. And so on.

Canto: And as Prof Cebon points out, using green energy to produce hydrogen, rather than to grid it directly into houses and businesses, might seem a bit odd. He calls it an opportunity cost.

Jacinta: The next main ‘colour’ of hydrogen comes from fossil fuel, particularly gas (mostly methane, CH4). By treating gas with super-hot steam, you can break it down into hydrogen and CO2. That carbon dioxide normally goes into the atmosphere. Some 2% of the world’s carbon emissions comes from producing this sort of ‘grey’ hydrogen, which is used to make ammonia (NH3) for fertiliser, and in the petrochemical industry. That percentage is about as much as aviation uses (though fertiliser is pretty essential). However, if you can ‘carbon capture and storage’ that CO2, then the hydrogen involved becomes lovely blue hydrogen.

Canto: Yes but as the Prof points out, once you’ve stripped the carbon from the methane, the remaining hydrogen isn’t very energy intensive, so you need a lot of methane to make a useful amount of hydrogen. Better to use the methane directly via the grid!

Jacinta: As Prof Cebon says, you need more methane to fuel your economy via hydrogen (around 40% more) than if you just used natural gas directly. All very attractive to the natural gas industry!

Canto: Right – what with the ‘electrify everything’ trend, the gas industry will be worried about its market, so here’s an opportunity – pump up hydrogen. Beware of the fossil fuel industry’s lobbying! And it’s blue hydrogen they’re really after, for financial reasons.

Jacinta: So back to electrolysis, green hydrogen, and efficiency. The electrolysis process is about 75% efficient, but importantly the energy has changed form. Think of energy as either work or heat, and forget kWhs for the moment. It’s work that’s important. You want the energy to produce more work and less heat (as with LED versus incandescent light globes). The combination of the two is the total energy output according to the first law of thermodynamics, or the law of energy conservation. Electricity from your battery produces work (eg in an EV) with very high efficiency. Diesel, petrol and other chemical fuels, including hydrogen, produce a lot of heat. According to the prof, the efficiency of an infernal combustion engine, which is essentially its work to heat ratio, is around 30%. Diesel may get up to maybe 45% but that’s the limit. Electricity can reach 90 to 95% efficiency. Chemical energy apparently runs up against the second law of thermodynamics, which limits the conversion of heat back to work. There’s always going to be a loss.

Canto: Right again. So 25% of the energy used in electrolysis is lost as heat. You have to convert the heat back to electricity via a fuel cell, which also has limited efficiency. And this efficiency reduction is before the energy required for compression, transportation, etc. So it’s all very problematic, though hydrogen has been touted as a miracle energy source since the early days of the nuclear industry.

Jacinta: Yes, and there are plenty of other problems with hydrogen – first, it’s colourless and odourless, and it’s very hard to contain without leaks, being of course the most molecularly tiny element in existence, so to use it as a home fuel would require a massive infrastructural upgrade, and of course it’s highly explosive and generates high NOx emissions when burned in the home – more so than methane. It’s also very inefficient compared to electrified heat pumps, which the prof calculates as about six times more efficient. So why would you use renewable energy in this inefficient way? The industry, according to the prof, is trying to hide this impracticability from the public.

Canto: Professor Cebon is involved with, or maybe heads up, the Hydrogen Science Coalition, which highlights five principles. First, the only acceptable form, in terms of fuel, is green hydrogen, using electrolysis via green energy. Blue hydrogen isn’t clean – being gotten from ‘dirty’ methane, and what Cebon calls fugitive methane, emissions from flaring and venting and leaking, amounts to the total annual carbon emissions of Europe – it’s a huge problem, due partially to the unregulated nature of the gas industry in Russia, the Middle East and elsewhere. Carbon capture and storage, which has been mooted for decades, has gotten nowhere, because – where are the profits in it? No private enterprise would touch it.

Jacinta: The second principle, or project, is to clean up the chemical use of hydrogen in ammonia fertilisers and in the steel and petrochemical industries by preventing the escape of so much of the C02 byproduct from escaping into the atmosphere. Not so much via CCS as by more efficient processing. The third project is to speed up electrification – let’s not pretend that hydrogen is an option for heating homes, for example, or that hydrogen fuel cell vehicles can be competitive with EVs. That battle has already been won.

Canto: Fourth is to rid ourselves of the idea that blending hydrogen into gas for any energy purposes is going to be useful. Hydrogen is a low energy replacement for methane, so you would need much more of the stuff, with all the attendant problems. And fifth and last is that hydrogen can only be used locally – that’s to say, at source. Transporting hydrogen safely is hugely expensive – being very light, many vehicles would be required to transport a sufficient energy load – 16 to 1 compared to diesel, according to our Prof. Not at all practicable.

Jacinta: And apparently hydrogen fuel cell vehicles are much more expensive to run than EVs, requiring replacement parts and so forth. So why are people still touting hydrogen. We’ll look more into that in a future piece.

Canto: Yes, Australia’s ‘Engineering with Rosie’ vodcaster has participated in a webinar for Mission Hydrogen, which sounds ominous, but I’ve heard her being skeptical about the green hydrogen movement, so we’ll see what she has to say.

 

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Written by stewart henderson

October 11, 2022 at 6:18 pm