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.)
So I think as a conservative estimate, it kinda works.
- https://en.wikipedia.org/wiki/MStar (patent infringement, the remains bought by MediaTek)
- https://en.wikipedia.org/wiki/Green_Flash_Brewing_Company (succumbed to competition from local craft breweries, lender foreclosed, the remains bought by private equity)
- https://en.wikipedia.org/wiki/Primaris_Airlines (bankrupt in 02008, unclear why)
And those are cherry-picked from companies that got big enough to be "notable" by Wikipedia's guidelines. Far more companies never reach that level.
The conservative estimate is that any time someone tries to deploy a new technology, it will fail. Most innovations (new technologies or companies) do.
Take a look at the HN front page from 10 years ago: https://news.ycombinator.com/front?day=2016-09-28 There we see Uber's self-driving truck initiative Otto (an acquisition), deep learning startup Skymind, a new static Linux distro called Stali, and a bunch of things that weren't innovations. All three of those things failed; Stali hasn't been updated since 02019. LuaTeX, Coinbase, Linux, Wikipedia, and dyeing with indigo are other innovations that feature on that page, but they were already very old.
Chapter 21 of draft 2.9.3 from 02008 https://web.archive.org/web/20080906132444/http://www.infere... begins:
> In the last chapter, we learned that electrification could shrink transport’s energy consumption to one fifth of its current levels; and that public transport and cycling can be about 40 times more energy-efficient than car-driving. How about heating? What sort of energy-savings can technology or lifestyle-change offer?
and it goes on to talk about heat pumps, as today. So I think that even versions from 02008 got this right, though evidently that was at least the 13th numbered draft.
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.
And graphs like the one comparing wind turbine output to petrol car consumption are inherently deceiving. Two values are put side by side with the same units and then talk about directly as if they are comparable. But they simply are not. A kWh of chemical energy and a kWh of electricity have as much in common as a US dollar and a Jamaican dollar.
1. Sad that he died from cancer
2. Noticed he compared primary energy and felt stupid for missing that
MacKay's "renewables can't work alone" claim always seemed carefully scoped to the economics of 02008 (when solar modules cost 33× as much as they do now) and also his own densely populated, rather polar country. Renewables were already working nearly alone, at scale, in equatorial countries and more sparsely populated countries; I live in Argentina, whose grid was mostly hydroelectric at the time, and next door to Brazil, where a large fraction of the automotive fleet ran on sugar-cane-derived ethanol, which is a viable renewable energy source (unlike, apparently, corn ethanol).
There's some incredible progress for electricity generation, but there's still huge amounts of energy being used in ways that are not currently electrified and not close to electrifiable in the short term.
We should celebrate the forward progress, but also not be blind to what is not yet feasible (while also hoping that it may soon be so).
Thankfully, energy storage is being deployed worldwide, so this is a moot point, and renewables can and will replace fossil fuel electricity generation.
Ships, we'll see. Most shipping ships are container ships (as opposed to, say, tankers, cruse ships, or ship shipping ships shipping shipping ships), and those are already slow enough that a substantial part of world trade is by airplane now, because inventory on a container ship is inventory you can't sell yet, or at least can't deliver yet. You could imagine a future where container ships are partly powered by onboard sails and partly powered by giant lightweight solar farms towed behind them on hydrofoils, but I don't think we're going to see container ships powered by lithium-ion batteries. Aluminum-air, maybe.
(Yes, I know that makes me sound like an LLM.)
There's something really important to understand when evaluating non-fiction books: nobody reads the later chapters, and the authors generally know this. They can present tremendously one-sided information in the first few chapters, giving the spin that they want, and then in later chapters give a more balanced approach to shield themselves from criticism. Almost everyone who reads the book will read only the spin, but any criticism levied against the author will be met with "but I specifically say, in the later chapters ...". It's a slimy technique that you start to see everywhere once you're aware of it.
Asserted without evidence, and I very much doubt that it's true. I suspect it varies dramatically by subject matter, intended audience, book length, data density, and more. I have no evidence for any of that. Do you?
Not necessarily saying this generalises to all non fiction books though
I saw him present 18 years ago, and asked him why: he said that he didn't want to rely on any predictions or models, but only discuss real data. Which is sort of defendable as a position, but ignored the fact that renewable energy was progressing so incredibly fast, and that these engineering predictions were not speculative but very much concrete.
Similarly the silicon solar panel industry in 2008 had a roadmap to get to £1/Wp over the next few years (which they did, and which led to the ~2012 explosion in solar installations), by mass producing the 'expensive' ~20% efficient (mono-crystalline silicon) technology. Mackay uses a 10% figure throughout.
So overall this was a bit like making predictions in the year 2000 assuming everyone will be stuck on 56k dial-up forever, because most people are on 56k dial-up.
These biases are present in all of the discussion of renewable technology, yet nuclear gets a free-ride / magical thinking in terms of uranium extraction, waste disposal and cleanup. And then there is the persistent obsession with land use in the book.
This led me to the conclusion (which I still hold) that this was an example of the tail wagging the dog: David MacKay wanted the 'obvious' physicists answer of nuclear power to be the natural conclusion, and by construction made it so in his book. Just because you are a Bayesian does not mean that you are unbiased!
David MacKay was an amazing scientist, but I do not think this book is accurate (even for its time), or that useful in public understanding of what we now call 'Net Zero'. It certainly popularised the idea of actually thinking through individual energy budgets, which can only be a good thing, but it was a massive missed opportunity to treat heat (chemical) energy (maximum entropy) and electrical (which can directly do work) as equivalent, just because they have the same unit.
Later on, as the 'Climate Tsar' he made a web app where you could play with the future balance of generation with a simulated model of the UK, and set your own costs for the different technologies, which I thought was much more useful. You could choose your own energy mix, and understand some of the tradeoffs.
And yes, very sad that he died so young. In the context of this book it would have been interesting to see how he dealt with the increasing mismatch of reality and his predictions as time passed.
> There is this appalling delusion that people have that we can take this thing that is currently producing 1% of our electricity and we can just scale it up and if there is a slight issue of it not adding up, then we can just do energy efficiency,” he said. “Humanity really does needs to pay attention to arithmetic and the laws of physics – we need a plan that adds up.”
> Prof MacKay had previously avoided being drawn into the political debate about energy, but told Lynas: “I have always tried to avoid advocating particular solutions but maybe because time is getting thinner I should call a spade a spade.”
> The key for the UK, he said, was a zero-carbon solution that works in the winter, when energy demand is highest but sunshine is lowest and winds can drop for days at a time. “The sensible thing to do for a country like the UK, I think, is to focus on CCS, which the world needs anyway, and nuclear,” said Prof MacKay.
> The decision on a new nuclear power plant at Hinkley Point, which the government hopes will be the first of a new generation of plants, has been delayed until September.
> “Then if you ask what is the optimal amount of wind and solar to add in then the answer is going to be almost zero,” he said. “I love wind turbines – they are the cathedrals of the modern age – but they are a waste of money if you have a low carbon solution that gets you through the winter … because when the wind blows you are going to have to either turn them down or something else down that you have already paid for like nuclear or CCS.”
Maybe he would have changed his mind as prices and delivery timelines diverged but many of the people who were most enthusiastic about his work because it reflected their nuclear preference didn't, so who knows.
Though maybe his kind of person that liked nuclear and heat pumps and EVs all just changed their mind based on new evidence and we are left with the people who mysteriously like nuclear but don't want to use the output for heat and transport.
Much less. Your typical gasoline IC vehicle converts maybe 1/4 of the chemical energy into work.
So really the comparison is 7.5kWh of electricity compared to 21.6kWh of petrol. The Prius gets 34% of the miles compared to the Tesla for a given energy input. In the olden days when renewables didn't do much, the chemical energy input for 7.5kW of electricity was probably 15 kWh. So the electric car is a little bit more efficient (taking advantage of the efficiency of large power plants).
These days, thanks to renewables the fossil fuel input into the electricity is lower.
Also, natural gas to electricity in CC plants is ~60% efficient.
Interestingly thanks to renewables the "carbon intensity" of a kWh of electricity is already better than a kWh of fossil fuels in some countries. A kWh of petrol releases about 250g of CO2, and quite a few countries (predominantly developed ones) have lower carbon intensities per kWh of electricity. Considering round trip efficiencies the carbon released by an electric car in those countries is easily 1/3 to 1/4 of the carbon released by a petrol car.
In the USA it's not as good, but electric cars are still releasing about half the carbon.
Technically you can interconvert grams of lead and grams of gold one to one, too, but interconverting electrical and thermal energy is so easy that it happens all the time unintentionally.
MacKay does in fact cover the Carnot factor you're talking about; his Chapter 21 http://www.withouthotair.com/c21/page_140.shtml begins:
> In the last chapter, we learned that electrification could shrink transport’s energy consumption to one fifth of its current levels; and that public trans- port and cycling can be about 40 times more energy-efficient than car- driving. How about heating? What sort of energy-savings can technology or lifestyle-change offer?
And then he goes into not just household heat pumps, and their achievable coefficients of performance, but also municipal combined heat and power, which take that ≈50% of the chemical energy "lost" from thermal power plants as waste heat and pumps it into your house.
So, far from being ignorant of the issue as you seem to be implying, he presents a more complete picture of the issues than you are presenting.
Specifically for household climate control, I suspect that both heat pumps and CHP are much less relevant now that we have cheap solar. You can think of a heat pump as a way to reduce the amount of solar-panel area that you need to heat your house. The trouble is that solar panels cost €0.13 per peak watt, while heat pumps cost closer to €1 per peak watt, so it may be cheaper to "waste" energy on heating your house resistively with a nichrome wire than to use a carefully engineered heat pump.
When that absolute worst case is happening in the house's living space, we can and do "convert" heat to electrical energy savings 1:1, because every joule "wasted" by cooking food with gas, or heating the house with a corn stove, or warming up the floor with sunlight for passive solar gain, is another joule earlier that the space heater's thermostat will turn it off.
Also, I don't think it's accurate to describe electrical resistance heating as "the thermodynamically worst heating technology possible". Electrical resistance heating is generally close to 100% efficient. It's actually thermodynamically possible to make heaters that are less than 100% efficient; MacKay explains, for example, that he heats his house with a 90%-efficient condensing boiler, and it's common for fireplaces to be around 20% efficient, because most of the heat goes up the chimney instead of heating your house.
Fireplaces are actually thermodynamically possible machines. I understand that you've never seen one, but I assure you that they do exist.
I've actually lived in houses where the fireplace had negative efficiency at times, sucking more heat out of the house (in the form of warm air) than they added back in the form of radiation.
We're suspecting there to be some symmetry breakage to explain why we don't really see any globs of antimatter with our telescopes (at least none that show any evidence of being antimatter), but so far no (real) luck.
As for the "0.13€ vs. 1€": you're not gonna get much solar yield in peak winter at least in Central Europe, especially it's gonna be that your PV is going to charge <100hour electricity storage when the sun shows up on those winter days and the heat pump (at least the part that spends a little electricity to lift a lot of heat energy from outside temps to indoor temps) runs approximately continuously.
You might have some kind of e.g. water/water heat pump with salted (not table salt though) water deliberately thawing during daytime (by turning on the circulation between it and outside air) to freeze at much warmer than night air temperatures to buffer those "only mildly freezing" temperatures to improve the efficiency (and at that point, likely also the thermal output power) of the heat pump.
The radiators inside and potential fans for them would also go up in flow to make up for the increased losses through the walls/window-glass.
A big reason why at least in e.g. Germany heat pumps are not at all irrelevant vs. electric resistance "space heaters" is that they're also very efficient at handling spring/autumn (lower thermal delta to lift against; referencing to a resistance heater for scale/reference purposes but clearly not expecting that to be a benchmark) while easily offering summer cooling (with relatively minor incremental complexity).
I don't really know how inherently expensive it is to keep around at least for parts of each city, but existing natural gas central heating boilers are very useful to not just trash before they're broken just because one uogrades to a heat pump, specifically because they are already there (sunk cost/little scrap value) and have basically zero issue delivering extremely spiky power during unannounced winter days (well, takes maybe a day of notice to actually get crew in to the storage&distribution facilities, but weather forecasts easily cope).
Sure, it's not _efficient,_ but we could just divert some synthetic methane during summer to refill the caverns: we kinda want that (at least for hydrogen but methane works too at least for storage) anyways for chemical synthesis factories if we're not just gonna feed them crude oil/natural gas, so other than that chemical factories probably/largely prefer direct hydrogen, continuing to use our existing seasonal storage even if it's not getting refilled from NordStream2 but from local summer-only electrolysis plants and with more hydrogen than methane where the geology allows, seems to me just frugal dealings with nature (reduce, Reuse, recycle).
I admit I don't know much about nuclear reactions, so please let me know if I'm talking nonsense here.
I agree that Central European capacity factors for solar are pretty bad, and that heat pumps are still economical in more polar countries, and will remain so for a few more years.
I'll answer the rest of your extremely interesting comment later, as I'm being drawn away at the moment, but I want you to know that I appreciate it very much.
This is right. This shows 63% wasted (as of 2024).
https://flowcharts.llnl.gov/sites/flowcharts/files/2026-08/2...
I remember this was 67% just a few years back. May have gone down because of increase in solar.
sustainabilitybynumbers (Hannah Ritchie) had an article talking about this, that we need only 25%-ish in renewables. I am unable to find that article.
(edit) found the article
https://hannahritchie.substack.com/p/electrification-energy-...: Global final energy demand today2 compared to a ‘post-transition’ energy system where suitable sectors are electrified, and the rest is fuelled by hydrogen. Electricity demand does increase – from 110 to 189 EJ, but total energy demand drops from 416 to 247 exajoules (EJ).
> 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.
They're just usually deployed for frozen warehouses, factories that actively freeze large amounts of (usually food), and AFAIK the occasional ice(hockey) rink.
Shitty types that don't even bother with any decent controls/pumps (those 90% boilers use a water loop circulation pump and a combustion air blower together with a bunch of sensors and valves) run propane-fired in many camper vans to do the fridge. But at the scale of an apartment building fit for 50+ residents, a natural gas fired central heat pump can be _quite_ efficient and economical.
Thermodynamically they're a heat engine with high combustion/flame temperature that uses the warm side as the heat sink, mated to a heat pump that consumes the produced "mechanical/electrical grade" power to pump heat from the cold side to _also_ the warm side. You save the turbine! Also the electrics but they're probably not even that expensive relative to the rest of the 200MW-class combined cycle natural gas power plant.
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?