The Fool on the Hill: Aviation-fuel, and generating capacity

I wrote in my last piece on aviation fuel that I thought that electrolysing the amount of hydrogen needed to fuel the world's jetliner fleet would use more electricity than the world's entire generating capacity, but that I would have to run the numbers.

Well, now I have. It wouldn't. I was wrong. It would use just 19.25% of our entire current electricity production. Electrolysing and subsequently burning hydrogen is pretty inefficient, however; the round trip efficiency is only about 60%. Lithium ion batteries have much better round trip efficiency at around 95% (declining slightly over the life of the battery, but not much). So powering all our commercial air fleet with electricity from batteries would, at a first estimate, use only 12.3% of our current electricity production.

Not that I'm claiming you could replace all our current commercial aviation either with hydrogen or with battery powered planes; each technology has very real challenges, which might be insuperable. All I'm saying is that to do so would mean producing a lot more electricity than we currently do.

Production vs capacity

Because modern electricity systems don't have much storage capacity, it is current practice to switch generators off then they're not needed — to generate exactly as much electricity as is, from second to second, being consumed. Consequently, a lot of our current wind turbines and other zero-carbon generators spend a lot of their time switched off (in the jargon, 'curtailed'), either because the electricity they could be generating isn't needed at that precise moment, or because the grid infrastructure lacks the capacity to carry it to where it is needed.

If we had load which we could switch on and off instead of generators we can switch on and off, we could run our generating plant more of the time, generating more electricity without increasing total generating capacity. So you would not necessarily have to build 20% more generating capacity in order to fly planes with hydrogen, or 13% more to fly them with batteries.

But that raises a lot of other questions.

The generation game

A lot of the things we do with energy are vital. If we can't grow food, we die. If we can't mine ores and smelt metals, we can't build a lot of the new infrastructure we need to transition the economy to zero carbon, so we either die or become permanently extremely impoverished (because unable to generate the energy to drive the lifestyle to which we've become accustomed). To transition each one of those things to clean energy we're going to need a substantial increase in electricity production.

The world economy currently burns 19,473 million tons of oil equivalent, of which 80% is in the form of fossil fuels, per year (the page cited states that 76% of production equals 14,800 Mtoe, multiply by 100/76 give 19,473). 1 ton of oil equivalent is 11,630 kWh, or 11.6MWh. So 19,473 million tons of oil equivalent is 225,886,800,000 MWh, or 225,887 TWh.

Total annual world electricity production is 29,479 TWh, of which 30% is renewable, and 9% is nuclear. So we need to build electricity production capacity for a further 184,616 TWh to replace our current reliance on fossil fuels. That is to say, we need to build six times as much clean capacity as the total capacity we currently have. We're currently planning to build just one point three terawatt hours of new clean capacity per year, meaning it will take roughly 140,000 years to achieve this goal.

Meantime, we need to stop emitting carbon — to reach 'net zero' — by 2050, or else we will heat the planet to a point where it is no longer habitable.

So we have to prioritise what we spend our energy on.

Is air travel good use of scarce energy?

As we move into a zero carbon world — and we have to do that within 25 years, or essentially there is no future — many of the things we now do with fossil fuels we will have either to do by other means, mainly by electricity, or not do at all.

Some of those things which we currently do with fossil fuels include

1. Growing food;
2. Mining ores;
3. Smelting and forging metals;
4. Making cement and concrete;
5. Heating our homes;
6. Moving from place to place by road, rail, or ship;
7. Moving from place to place by air;
8. Training AI models.

Because we need to keep eating, we cannot abandon growing food. Because we need to build (at least some) more infrastructure, we cannot abandon smelting and forging metals, and we almost certainly need to continue to do at least some mining and to make at least some concrete.

So if we are to survive the transition at all, those are the things which cannot be, in the jargon, curtailed; those are the things for which, if we have limitations on our electricity production, we must prioritise. So everything else may have to be shut down.

The fact is, it's extremely unlikely that we're going to build out enough clean generating capacity to completely decarbonise all of our economy by 2050; the fact is, some energy-profligate activities are going to have to be shut down, at least until we have enough clean generating capacity.

So, in the scale of things from having food to eat to having an AI model to spout plausible nonsense at you, how important is air travel?

Is your journey necessary at all?

There are two major reasons people fly to other places.

The first is to meet with, to discuss with, to negotiate with, people who live in those places, or to interact with things which are in those places and can't be moved.

For some particularly tense, and particularly high stakes negotiations, being present in the room with the other person, being able to break bread, to share food, to share experiences which are peripheral to the formal business of the negotiation, may materially affect the outcome. For some problems requiring expert intervention, the expert may need to physically touch the thing being worked on.

But both are rare, and as telepresence improves, will become rarer.

The second is, for 'leisure,' which generally means, for the pleasure of actually experiencing those exotic (to you) places for yourself.

I've flown to a holiday destination and back only once in my life, in 1975. I've flown on about ten work assignments over my lifetime. Each of these journeys exposed me to very interesting places which I'm extremely glad to have seen, and yes, they have enriched me, in ways which journeys within my own country would not have. So travel is, in my opinion, a good thing. But is it necessary?

And if it is necessary, does it have to be by air?

Would high speed rail substitute?

High speed rail travel burns approximately 0.033 kWh per passenger kilometre. By contrast, air travel burns about 40kWh per hundred passenger kilometres, which means about 0.4kWh per passenger kilometre, which means air travel is more than twelve times as wasteful — or, to put it differently, you can transport twelve people by high speed rail for the same energy cost as transporting one person for the same distance by air. Slower trains are, unsurprisingly, even more energy efficient than faster ones.

Air travel is much faster than even high speed rail once you are actually moving, but the time to travel to the airport and the time waiting to board/disembark is typically a lot longer than for rail journeys. So air travel gives substantially shorter journey times only for quite long journeys, where there actually is high speed rail infrastructure. On the downside, the infrastructure cost of high speed rail is higher, both in terms of financial and land-use terms.

Would slow travel substitute?

I have travelled from Galloway to Gloucestershire by bicycle; personal friends have travelled from Britain to Turkey, and from Britain to India, also by bicycle. Other friends have travelled from Britain to Norway, and from Spain to Mexico, by sailing boat. Slow travel, of course, takes more time, but you see more and have more experiences along the way. Sure, Java is probably a wonderful place to visit; but how much more wonderful is it, than, say, Białowieża (my own personal dream destination)? And how much more wonderful is Białowieża than Glentrool, to which I can cycle in a day? The answer is 'a lot', of course; but is the cost — to the planet, not just to me — worth it?

Conclusion

I haven't, as I've said, flown for leisure since 1975, fifty years ago; I haven't flown at all since 2009, fifteen years ago. And the reason is, it isn't news that air travel is unsustainable. We've known that all my adult life. But I hadn't sat down and thought about how unsustainable it was until this year; and researching and writing this particular essay has brought home to me not only how unsustainable air travel is, but also how unsustainable much of our modern lifestyle is.

It hardly matters to me, of course. The years of a man's life are three score and ten, and I reach the end of that sentence this year. I will not live to see the costs we are imposing on the world. I have no children, so my children and grand children won't live to see them either. But I have friends who have children, and I would like those children, too, to have the privilege of living to be old.

But unless my calculations are wrong — which I hope they are, by at least three orders of magnitude — if we gave up burning fossil fuels today, we would have to reduce our energy consumption overnight to 6% — six percent — of what we currently consume; and our politicians are being so diligent, so responsible and so forward looking in their plans, that if we give up burning fossil fuels in 2050, the last year we can to escape disaster, we will then have to reduce our energy consumption to less than 20% of what we currently consume.

Do you still think it's worth digging up fertile farmland in southern England to build a new runway to fly even more planes?

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