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/
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.
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.
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.
I remeber the book differently - I remember it being primarily about getting exactly this right. Lot of space spent discussing efficiency and losses and comparing apples to apples.
(Admittedly, I read it many years ago, my memory may be off, though I strongly doubt it.)
He does correct for the efficiency of both electric cars, and heat pumps in later chapters. His line of argument is "here is the current energy supply and demand - now here are ways we can increase one and reduce the other".
The wind analysis was reasonable for the time, iirc the main error there was that he failed to foresee offshore wind dropping in price so much.
I think in 2008, it wasn't clear whether cars are going to be replaced by electric and what the final efficiency will be. It could also have been more because you would need to convert electricity to fuel first.
So I think as a conservative estimate, it kinda works.
Which are you referring to as the primary comparison?
If I'm understanding the book's structure correctly, the comparison at the end of Part 1 (chapter 18 "Can we live on renewables?") is based on estimating existing demand. Deployment of heat pumps in Britain even today is woefully low, and when the book was written it was no doubt even lower, so of course it wouldn't make sense to include heat pumps as a significant factor when comparing actual demand when the book was written with potential supply.
Chapter 27 "Five energy plans for Britain" discusses large scale ways to make the energy budget "work", and those hypothetical comparisons do include use of heat-pumps. Maybe those numbers are inaccurate and a better hypothetical could be produced today, but I would first put that down to the difficulty of forecasting the future.
It's been a long time since I read the book fully though. Did I miss something?
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.
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/
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.
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.
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.
(Admittedly, I read it many years ago, my memory may be off, though I strongly doubt it.)
The wind analysis was reasonable for the time, iirc the main error there was that he failed to foresee offshore wind dropping in price so much.
So I think as a conservative estimate, it kinda works.
If I'm understanding the book's structure correctly, the comparison at the end of Part 1 (chapter 18 "Can we live on renewables?") is based on estimating existing demand. Deployment of heat pumps in Britain even today is woefully low, and when the book was written it was no doubt even lower, so of course it wouldn't make sense to include heat pumps as a significant factor when comparing actual demand when the book was written with potential supply.
Chapter 27 "Five energy plans for Britain" discusses large scale ways to make the energy budget "work", and those hypothetical comparisons do include use of heat-pumps. Maybe those numbers are inaccurate and a better hypothetical could be produced today, but I would first put that down to the difficulty of forecasting the future.
It's been a long time since I read the book fully though. Did I miss something?
$10/W to 0.30/W is closer to 2 orders of magnitude than 1.
https://itila.blogspot.com/2015/09/what-do-you-tell-children...
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/>.
https://news.ycombinator.com/item?id=34618613 ("Information Theory, Inference, and Learning Algorithms (2003) (inference.org.uk)")
It's a bit out of date at this point. The author passed away in 2016.
https://en.wikipedia.org/wiki/David_J._C._MacKay