Sustainable energy without the hot air (2008) (withouthotair.com)
127 points by 0sake_rs 9 hours ago
_aavaa_ 9 hours ago
The books is good(ish) for it's time, but some of its analysis and forecasts are fundamentally flawed since it falls for the primary energy fallacy by comparing the chemical potential energy (in J) directly to electrical energy (also in J). The two are fundamentally different things and called be compared 1:1. E.g. To heat up your home with natural gas you need ~1J of chemical energy to get 1J of heat into the home, but with a electric heat pump you only need 1/6 J to get 1J of heat.
It is also a product of its time in terms of wind/solar vs nuclear. His forecasts of the impact of solar and wind is based on prices and performance from 2008. Prices have come down an order of magnitude since then, and performance and lifespan have increased drastically.
azornathogron 8 hours ago
Heat pumps, and their efficiency (getting more than X Joules of heating for X Joules of electricity) are discussed in chapter 21 Smarter Heating, see for example the diagram and discussion on page 150: https://www.withouthotair.com/c21/page_150.shtml
I imagine the economics (and perhaps technical improvements) of some things may have changed more than the book could forecast. But heat pumps were definitely understood by the author.
_aavaa_ 8 hours ago
I’m not saying he was unaware of heat pumps, I’m saying he’s comparing apples to oranges simply because they use the same units.
Look at “3 - Cars” on page 29. He says the typical car uses 40 kWh/day. 40 kWh of what? Chemical energy in the gasoline.
The go to page 33 where he looks at how much energy onshore wind could produce per days in the UK. His number is 20 kWh/d. 20 kWh of what? electricity
He then compares those two numbers directly and uses that comparison as the basis of his arguments: “Britain’s onshore wind energy resource may be “huge,” but it’s evi- dently not as huge as our huge consumption.”
This is simply incorrect. A combustion engine converts less than half of the chemical energy in the gasoline into mechanical work that can move the car. The electric model converts >90% of it. So we don’t have to replace 40 kWh/day, we have to replace less than half of that since the electric process is more efficient.
This same issues, the primary energy fallacy, underpins large parts of the book.
sideshowb 8 hours ago
TeMPOraL 8 hours ago
thelastgallon 3 hours ago
js8 8 hours ago
pfdietz 7 hours ago
kragen 7 hours ago
ZeroGravitas 8 hours ago
Yes, I disagree with some of his takes but he was spot on regarding heat pumps:
> Let me spell this out. Heat pumps are superior in efficiency to condens- ing boilers, even if the heat pumps are powered by electricity from a power station burning natural gas. If you want to heat lots of buildings using natural gas, you could install condensing boilers, which are “90% ef- ficient,” or you could send the same gas to a new gas power station making electricity and install electricity-powered heat pumps in all the buildings; the second solution’s efficiency would be somewhere between 140% and 185%. It’s not necessary to dig big holes in the garden and install underfloor heating to get the benefits of heat pumps; the best air-source heat pumps (which require just a small external box, like an air-conditioner’s) can deliver hot water to normal radiators with a coefficient of performance above 3.
bryanlarsen 8 hours ago
Which means that not including the conversion in the primary comparison is particularly egregious.
azornathogron 8 hours ago
kragen 7 hours ago
> His forecasts of the impact of solar and wind is based on prices and performance from 2008. Prices have come down an order of magnitude since then
This is going to sound like one-upmanship or nitpicking, but I think it's important to know that this understates the change. https://web.archive.org/web/20100722072720/http://www.solars... says that in May 02009, crystalline solar cells in China cost €2.17 per peak watt, a decline of 26.4% from January 02009, whose price is not listed directly but which we can calculate as €2.95 per peak watt. If the price had declined by only an order of magnitude since January 02009, it would now be €0.295 per peak watt.
But, according to https://www.in2013dollars.com/europe/inflation/2009?amount=1..., "€100 in 2009 is worth €145.57 today." So, if we adjust for inflation — as we should — if the real price had declined by only an order of magnitude since January 02009, it would now be €0.429 per peak watt.
In fact, today, "mainstream" solar modules are currently €0.130 per peak watt, according to https://www.solarserver.de/photovoltaik-preis-pv-modul-preis..., and those are Chinese monocrystalline modules.
So the price of solar modules now is actually 3.3 times lower than what a careful reader would infer from your remark. Solar module prices have declined since January 02009 by not merely an order of magnitude but 33×. That's slightly closer to two orders of magnitude than to the single order of magnitude you said. Now they are at 3% of the price they were at when MacKay wrote his excellent book.
(Which does, as others have pointed out, explain the efficiency advantage of heat pumps.)
paimapi 6 hours ago
one thing to note is that the solar industry has receded quite a bit in the last two years in China due to overproduction (or, as the Chinese state likes to call it, 'involution' or 'too much competition'). solar is cheap now because 1) Chinese subsidies are reduced, shrinking their installation market and 2) overproduction leading to essentially fire sales. once production stabilizes against the market, costs will go back up. it's really never been a better time to buy panels than now
https://dialogue.earth/en/energy/behind-the-layoffs-in-china...
>Some observers estimate 20-30% capacity reductions are required, but demand shrinkage could increase that figure. “I’m particularly worried about the downstream side,” says Reis. “Even as prices collapsed, demand remained robust for three years, but power market reforms are now upending the entire renewables market.”
combine this with the global backing-off of the Paris Agreement (and subsequent subsidy defunding) and power utilities in the US abandoning clean energy goals in order to immediately increase output for proposed hyperscale facilities and you've got something of an enduring demand shortage
that said, there is a lot of automation happening in that industry right now (which is likely going to cause a small recession in China due to half a million to a million workers being out of a job, depending on how much the parts manufacturers also automate) so it's possible production with continue improving as more R&D is dedicated there. only time will tell!
epistasis 2 hours ago
Another thing to point out is that the geography in the book, the UK, has spectacularly bad resources for solar, just astoundingly bad.
So even with updated technology pricing numbers, the conclusions from it should not be lifted to other geographies without adjusting for that. We're talking worse resources than Germany (worse than an US state), and into Finland territory:
bryanlarsen 8 hours ago
> Prices have come down an order of magnitude since then
$10/W to 0.30/W is closer to 2 orders of magnitude than 1.
LogicFailsMe 5 hours ago
Not bad at all for an early amazingly influential AI researcher and Hopfield graduate who died tragically of pancreatic cancer just as AI took off.
pfdietz 7 hours ago
Didn't he also assume a significant amount of bioenergy, which ended up greatly inflating the land area needed?
sideway 5 hours ago
Any book recommendations on the subject (or similar subjects)?
antisthenes 8 hours ago
That doesn't mean it's flawed. It means the arguments are even MORE in favor of what is stated in the book.
The underlying fundamentals did not change since 2008. If Solar was good/viable back then, it can only get better if it got cheaper over time.
Same goes for the nuclear debate. Nuclear was losing back then, and now it has finally lost absolutely.
sideshowb 8 hours ago
The updated version of this book is available in game format with the blessing of UK government https://my2050.energysecurity.gov.uk/?levers=111111111111111
Risking the HN hug of death here, but my own prototype of a car miles model inspired by the David's approach can be found at https://trafred.cardiff.ac.uk/
ajb 5 hours ago
Oh, very interesting. Not sure it's working correctly though: set everything to ambition level 4, which takes us to net zero minus 4. Then, the following knobs have no effect: efficiency, nuclear power, carbon intensity, solar (!) and wave & tidal. That can't be true, so I think it's buggy
zbs1970 7 hours ago
Not commenting on the physics of this; I want to point out that I thought the narrative structure of this book was amazing. I have not read a hard-core piece of analysis in any field before or since that I thought was a page-turner the way this was. When I read it in 2008 I remember completing each chapter and feeling like "we're screwed" and then the next chapter feeling like "ok, we're going to make it." Presenting such analysis in the form of a race between supply and demand was narrative genius and I think should serve as an example of how ideas can be presented in a way that is both exciting and not-dumbed-down.
sam1r 8 hours ago
The original author was blogging just a couple days prior to his death. Rest in peace
https://itila.blogspot.com/2015/09/what-do-you-tell-children...
seltzered_ 2 hours ago
This needs a 2008 tag.
There was some rough discussion in 2025 about where Mackay's models ended up being off: https://bsky.app/profile/ketanjoshi.co/post/3lmdeoxe2pk2i
And of course some credit that he was right on some technologies not making much sense like electric planes: https://bsky.app/profile/thierryaaron.bsky.social/post/3mwjx... referencing ch 5 pg 35 of 'sustainability without the hot air'
nirinor 8 hours ago
Actually, the better link might have been <https://withouthotair.org/changes>.
Note the .com->.org: its a version of the book whose numbers are maintained here <https://github.com/life-itself/without-hot-air/commits/main/>.
laurencerowe 3 hours ago
The 'Has It Held Up?' section seems a very good entry point. https://withouthotair.org/has-it-held-up
mbgerring 39 minutes ago
Site last modified in 2015
Lots of us working in clean energy read this book, and everything that’s happened since it was published makes the projections here useless
js8 8 hours ago
Love the book, but as others have noted, it is very much dated. Although I believe someone started a project some years ago to update it.
rjmunro 8 hours ago
https://withouthotair.org/ is the community updated version.
abetusk 3 hours ago
I find it interesting that the average energy consumption of a person (or household?) is roughly 30kWh/day and the energy usage of a car is roughly 40kWh/day. I wonder if it's some kind of truism that our transportation needs roughly equal our energy needs.
I'd be interested to know if that's just a coincidence or whether there's an underlying reason.
tomjakubowski 3 hours ago
A person riding a bicycle expends an order of magnitude less energy than does a car ferrying the same person the same distance. So I don't think this really holds.
For comparison: at 50 MPG, traveling one mile by car uses 0.02 gallons of gasoline. This is about 675 Wh of energy or 580 kcal. Travel by bicycle for a ~180lb person is about 60 kcal per mile.
abcd_f 3 hours ago
And a straight angle is just 10 degrees away from the water's boiling point. Might be something in it too :)
hungryhobbit 5 hours ago
Dear god, this page is like an argument against every person who has ever said "graphic design doesn't matter".
The colors are gross, it took me ten minutes just to figure out what I was looking at (a book), and heaven help me if I actually wanted to read that book in that format!
slibhb 2 hours ago
Hmm, I kind of like it. It comes across as hand-crafted and I spent longer there than I planned.
peri-cl 8 hours ago
The author is coincidentally the author of a (free-to-read) information theory book which is also popular on HN,
https://news.ycombinator.com/item?id=34618613 ("Information Theory, Inference, and Learning Algorithms (2003) (inference.org.uk)")
myrmidon 6 hours ago
I knew I had seen the name before.
That book significantly decreased my appreciation of our statistics professor @uni, because it presented the same topics in a much more interesting and digestible way. Can recommend.
That book and Gershgorin circles (to work around all the stupid, constructed 3x3 matrix eigenvalue problems that they love to sprinkle into literally every early stem exam) helped more in university than anything else.
esafak 8 hours ago
The late author.
ml_basics 5 hours ago
The untimely death of David MacKay was a tragic loss for the scientific community. It's astonishing that he wrote the textbook on information theory for the ML community as well as his contributions to rational discussion about energy policy.
He had a direct personal impact on my life since my introduction to ML came from video recordings of his lectures on ML and information theory. I am grateful to have learned from such an excellent teacher. Like a Feynman of our times.
PaulDavisThe1st 3 hours ago
The publisher of this book (and the series) was my second programming mentor, and the person who introduced me to the GNU Project and libre software in general, back in 1986/87. I call him Dr. X and he calls me "The Professor".
bencord0 4 hours ago
RIP Professor MacKay
I remember him giving this talk to my physics class when I was in University. It was so inspirational to me that the UK just might be able to go 100% renewable.
From what I remember, the calculation worked out how we could do it all with Solar. I don't think he quite saw how close we are to achieving the goal, not with Solar, but with Wind within the next decade.
danrecht 8 hours ago
David McKay was a great public speaker as well: https://youtu.be/GFosQtEqzSE?si=Gyrcep1VDae6xDo1&t=110
rekabis 14 minutes ago
Holy 1997 web design, Batman.
citizenfishy 6 hours ago
Lings Cars!
perennialreport 8 hours ago
Worth reading even with the dated numbers. MacKay's lasting contribution isn't any specific forecast - it's the discipline of expressing everything in the same units (kWh per day per person), which makes energy arguments commensurable instead of vibes-based. Once you've internalized that, most energy coverage in the media starts reading like category errors. The specific figures have moved - solar costs, EV adoption, heat pump uptake - but the arithmetic habit hasn't aged at all.
bryanlarsen 7 hours ago
kWh of work and kWh of primary energy are two different measurements with the same unit. Mixing the two is invalid.
zahlman 5 hours ago
I'm pretty sure you're replying to an LLM bot.
throwawayffffas 6 hours ago
I see a lot of hot air in this.
Two quick points:
1. Gasoline powered energy metrics do not translate to electric vehicles, due to the much higher efficiency of electric motors.
2. There are about twice as many people as cars in the UK so the comparison between 40 kwh/d per car and 20 kwh/d per person for the wind energy is at minimum misleading.