Archive for the ‘Climate Change’ Category

Heating Degree Days:2: Do they work?

March 15, 2022

Friends, in the last article I explained how the concept of Heating Degree Days (HDDs) allowed one to estimate the Heat Transfer Coefficient (HTC) for a house (a.k.a. its ‘thermal leakiness’) in a simple way.

  • Find out how many kWh per year it takes to keep a dwelling warm.
    • For gas users, use the number of kWh of gas consumed each year
    • For oil users, multiply the volume of oil used annually (in litres) by 10.
  • Find the number of HDDs for your locale,
    • or use 2,150±150 °C-days per year as a guess for most of the southern UK
    • or use 2,350 ± 150 °C-days per year as a guess for most of the northern UK.
  • And then divide, the number of kWh/year by the number of HDDs per year to yield the overall HTC for your dwelling.

In this article I want to explain how I checked this calculation using a much more complicated process. Read on if you want to know the gory details!

Basic Observations

The reason I love the idea of HDDs so much is because I spent such a long time – several years! – trying to work out the heat transfer coefficient (HTC) for my home the long way.

Click on Image for a larger version. The graph shows weekly measurements over the last three years. In light blue, the graph shows weekly gas consumption in kWh. In green, the graph shows the difference between the internal temperature and the external temperature. In dark blue, the graph shows weekly heat output from the heat pump in kWh. It’s clear that gas consumption and heat pump output follow the heating demand quite closely.

For me it all started back in late 2018 when I bought a weather station. Fired by ‘new toy’ enthusiasm, I recorded the average daily and weekly temperatures, and wondered whether the gas consumption increased as the outside temperature fell. I started to read the gas meter, at first daily, but then settled down to reading it weekly.

Although it is completely obvious, I felt surprised to ‘discover’ that gas consumption did indeed increase as the outside temperature fell.

On the graph above I have plotted temperature ‘demand‘ (the difference between the inside and outside temperatures) and gas consumption (kWh/day) on the same graph. The data on this has been smoothed, plotting the average of ±2 weeks around each data point.

You can see quite clearly that gas consumption follows temperature demand. The Heat Transfer Coefficient (HTC) is the constant of proportionality between these two quantities. But you can see that (as a result of the new glazing and insulation) the HTC changes through the years.

For example, the graph below shows the same data as in the graph above but highlights the effect of the new glazing and insulation. The heating demand in Jan/Feb 2021 was greater than in Jan/Feb 2019 but the gas consumption was only about half that in Jan/Feb 2019. In other words. In other words, I had reduced the HTC by about half.

Click on Image for a larger version. This is the same data as in the graph above but highlighting the effect of the new glazing and insulation. The heating demand in Jan/Feb 2021 was greater than in
Jan/Feb 2019 but the gas consumption was only about half that in Jan/Feb 2019.

The four phases

The graphs above cover 4 distinct phases of the work on the house.

Click on Image for a larger version. This same data as in the graph above but highlighting the four phases of the refurbishment.

  • Phase#1 is the period before works began.
  • Phase#2 is the period after the main Triple-Glazing work was done
  • Phase#3 is the period after the final Triple-Glazing was done and the External Wall Insulation was applied.

In each of these phases, we should expect a distinctly different proportionality between heating demand and gas consumption – i.e. they each have a distinct HTC.

In Phase 3 we have data for both gas consumption (Phase#3A) and for heat pump use (Phase#3B). These should both have the same HTC – the insulation was the same – but the data is acquired in quite different ways.

I took the data in each of the phases and plotted average daily gas consumption versus temperature demand. The graphs for phases 1, 2 and 3A are plotted below.

The graphs all have the same vertical and horizontal scales and you can see that as the works progressed, the slope of the data has decreased. In other words, as the re-furbishment progressed, it took fewer kWh of gas per day to keep the house warm.

Click on Image for a larger version. Graph of average daily gas consumption versus heating demand during Phase#1 i.e. before I made any changes.

Click on Image for a larger version. Graph of average daily gas consumption versus heating demand during Phase#2 of the refurbishment i.e. after the house was triple-glazed.

Click on Image for a larger version. Graph of average daily gas consumption versus heating demand during Phase#3A of the refurbishment i.e. after the external wall insulation.

These graphs are fascinating. Firstly we note that graphs consist of two regions:

  • At low heating demand, there is no temperature-dependence of the heating demand – the graph is flat at about 5 kWh/day. This is because during the summer, the heating is used for domestic hot water and cooking only.
  • At high heating demand the data fit plausibly to a straight line, but not one that goes through the origin. The slope intercepts the 5 kWh line at roughly 3.5±0.5 °C of demand. This slope is just the HTC that we are looking for. It tells us how many extra kWh/day it takes to warm the house for each extra °C of temperature demand

The fact that the gas consumption doesn’t start to increase immediately the outside temperature falls below the thermostat set-temperature is because there are other sources of heat in the house.

  • All the electrical items in our house typically consume around 200 W continuously – or 4.8 kWh/day.
  • And each person in the house contributes around 100 W continuously, so my wife and I contribute another 4.8 kWh/day.

I investigated this phenomenon in quite some detail in these articles (1, 2), but the upshot is that the heating in my home doesn’t switch itself on until the external temperature falls about 3.5±0.5 °C below the thermostat temperature.

Looking at the slopes of the graphs, I can plot them to show how the Heat Transfer Coefficient has been reduced as a result of my refurbishments.

The Red Circles on the graph below show estimates assuming that the gas boiler is 100% efficient i.e. all the energy of burning the gas is retained within my home. A more realistic estimate is that only 90% of the heat is retained within the house. The estimate of the HTC using this assumption is showing blue.

Click on Image for a larger version. Graph showing the Heat Transfer Coefficient for my home deduced from the  slopes of the previous three graphs. The Red Circles show estimates assuming that the gas boiler was 100% efficient. The Blue Circles show more realistic estimates assuming that the gas boiler was only 90% efficient. The left hand axis shows the HTC in kWh/day/°C and the right-hand axis shows the HTC in W/°C.

I have gone through this calculation of the HTC in some detail to show just how difficult it is. Now let’s look and see how much easier it is using degree days.

Calculation Using Degree Days

To calculate the same estimates for HTC I need to do the following:

  • Look up my records to find out how many kWh of gas I used in each of the three phases. All it requires is a single reading of the gas meter at the start and end of each phase. To gain extra accuracy one can assume that at best 90% of these kWh of gas consumed resulting in heating kWh.
  • Look up the Degree Days Website to find out the number of heating degree days in each of the three phases.
  • Divide the gas consumption by the number of HDDs.

During Phases #1, #2 and #3A, our thermostat was set to 19.0 °C, and so I used HDDs with a base temperature of 15.5 °C i.e. 3.5 °C lower than 19.0 °C.

The Calculational Steps outlined in the bullet points are summarised in the table below.

Phase Gas Consumption (kWh) Heating (kWh) at 90% Efficiency HDD15.5s


1 13,323 11,991 1,430 8.4 349
2 13,756 12,380 1,787 6.9 288
3A 6,902 6,212 1,773 3.5 146

The resulting HTC estimates are compared with those previously calculated using the long-winded method in the Graph below.

Click on Image for a larger version. Graph showing estimates for Heat Transfer Coefficient for my home during the three phases of refurbishment. The blue circles are the same data plotted in teh previous graph assuming that the gas boiler was 90% efficient. The Blue Circles. The Green Squares show the result of the same calculation using HDD15.5s. The agreement is striking. The left-hand axis shows the HTC in kWh/day/°C and the right-hand axis shows the HTC in W/°C.

The agreement between the two methods of calculating the HTC is striking.

What this means is that instead of having to record external temperatures and gas consumption week-by-week as I did for three years, one can get equivalent results by using HDDs and just one or two gas meter records.

A final test: Phase#3B

I can check the calculational method and some of my assumptions by comparing the HTC in Phases 3A and 3B. There were no changes to the insulation in these phases: what changed was that I switched from heating using a gas boiler to heating with a heat pump.

So HTC should be the same in Phases 3A and 3B.

However there was one change that arose from etc heat pump switch. As I learned to use the controls of the heat pump, I eventually stuck with settings that resulted in the house being warmer (~20.5 °C) than it had been previously (~19 °C).

For this reason I calculated the number of degree-days in Phase#3B using a base temperature of 17.0 °C rather than 15.5 °C. The result is plotted in purple on the graph below.

Click on Image for a larger version. The same graph as shown previously, but now with the calculation for Phase 3B shown as a filled purple circle. The left-hand axis shows the HTC in kWh/day/°C and the right-hand axis shows the HTC in W/°C.

All three calculations of the HTC in Phase#3 agree within a range of 10%, which is pretty much as good as any calculation or measurement of HTC can hope for.

This gives me confidence that the HDD method does indeed work, and that the likely boiler efficiency in Phases #1, #2 and #3A was probably not very different from 90%.


Apologies for this very long article. You may be asking, as I am, “Why did I write this?”

The answer is that being able to calculate the HTC for a dwelling is important. And if using HDDs makes the calculation simpler, then maybe more people will do the calculation.

And this should enable more people to rationally plan their home refurbishment and estimate the size of the heat pump they require.

And it’s all thanks to the kind people over at Heating Degree Days.

In the next article I’ll look at how HDD’s vary with:

  • choice of base temperature,
  • location in the UK, and
  • from year-to-year.


Will aviation eventually become electrified?

March 2, 2022

Friends. I ‘have a feeling’ that aviation will eventually become electrified. At first sight this seems extraordinarily unlikely, but I just have this feeling…

Obviously, I could just be wrong, but let me explain my thinking.


The current technology for aviation – jet engines on aluminium/composite frames with wings – relies on the properties of jet fuel – kerosene.

There are two basic parameters for aviation ‘fuel’.

  • Energy density – which characterises the volume required to carry fuel with a certain energy content. It can be expressed in units of megajoules per litre (MJ/l).
  • Specific energy – which characterises the mass required to carry fuel with a certain energy content. It can be expressed in units of megajoules per kilogram (MJ/kg).

Wikipedia have helpfully charted these quantities for a wide range of ‘fuels’ and this figure is shown above with five technologies highlighted:

  • Lithium batteries,
  • Liquid and Gaseous Hydrogen,
  • Kerosene and diesel.

Click on image for a larger version. Chart from Wikipedia showing the specific energy and energy density of various fuels enabled energy technologies.

A general observation is that hydrocarbon fuels  have a much higher density and specific energy than any current battery technology. Liquid Hydrogen on the other hand has an exceptionally high specific energy, but poor energy density: better than batteries but much worse than hydrocarbon fuels.

Lessons from the EVs transition:#1

I think the origin of my feeling about the aviation transition stems from the last 20 years of watching the development of battery electric vehicles (BEVs). What is notable is that the pioneers of BEVs – Tesla and Chinese companies such as Xpeng or BYD – are “all in” on BEV’s – they have no interest in Internal Combustion Engine (ICE) vehicles or hybrids. They have no legacy market in ICE vehicles to protect.

‘Legacy Auto’ (short hand for VW, GM, Ford, Toyota etc) had poked their toe in the waters of alternative drive-trains quite a few years ago. GM’s Volt and Bolt were notable and Toyota’s Mirai hydrogen fuel cell car was a wonder. But Legacy Auto were comfortable manufacturing ICE vehicles and making profits from it, and saw these alternative energy projects as ‘insurance’ in case things eventually changed.

As I write in early 2022, all the legacy auto makers are in serious trouble. They can generally manufacture BEVs, but not very well – and none of them are making money from BEVs. Aside from Tesla, they have very poor market penetration in China, the world’s largest EV car-market. In contrast Tesla are popular in China and America and Europe and make roughly 20% profit on every car they sell.

So one lesson from the BEV transition is that the legacy industry who have invested billions in an old technology, may not be the pioneers of a new way of doing things.

Lessons from the EVs transition:#2

How did BEV’s overcome the awesome advantages of hydrocarbon fuels over lithium batteries in terms of energy density and specific energy?

First of all, ICEs throw away about 75% of their advantage because of the way they operate as heat engines. This reduces their energy density advantage over batteries to just a factor 10 or so.

Secondly, there is the fact that ICE cars contain many heavy components – such as engines, gearboxes, and transmissions that aren’t needed in a BEV.

But despite this, BEV cars still generally have a weight and volume disadvantage compared to ICE cars. But this disadvantage has been overcome by careful BEV-specific design.

By placing the large, heavy, battery pack low down, designers can create pleasant vehicle interiors with good handling characteristics. And because the ability to draw power rapidly from batteries is so impressive, the extra mass doesn’t materially affect the acceleration of the vehicle.

EV range is still not as good as a diesel car with a full tank. But it is now generally ‘good enough’.

And once EVs became good enough to compete with ICE vehicles, the advantages of EVs could come to the fore – their ability to charge at home, low-running costs, quietness, potential low carbon emissions and of course, zero in situ emissions.

And significantly, BEV’s are now software platforms and full electronic control of the car allows for some capabilities that ICE vehicles will likely never have.

Lessons from the EV transition:#3

Despite Toyota’s massive and long-term investment in Hydrogen Fuel Cell (HFC) cars, it is now clear that hydrogen will be irrelevant in the transition away from ICE vehicles. Before moving on to look at aviation, it is interesting to look at why this is so.

The reason was not technological. HFC cars using compressed hydrogen fuel were excellent – I have driven one – with ranges in excess of 320 km (200 miles). And they were excellent long before BEVs were excellent. But the very concept of re-fuelling with hydrogen was the problem. Hydrogen is difficult to deal with, and fundamentally if one starts with a certain amount of electrical power – much less of it gets to the wheels with a HFC-EV than with a BEV.

The very idea of a HFC car is – I think – a product of imagining that there would be companies akin to petrochemical companies who could sell ‘a commodity’ in something like the way Oil Companies sold petrol in the 20th Century. BEV’s just don’t work that way.

Interestingly, the engineering problems of handling high-pressure hydrogen were all solved in principle. But this just became irrelevant.

Cars versus Aeroplanes

So let’s look at how energy density and specific energy affect the basic constraints on designs of cars and aeroplanes.

50 litres of diesel contains roughly 1,930 MJ of energy. The table below shows the mass and volume of other fuels or batteries which contains this same energy.

Mass (kg) Volume (l)
Kerosene 45 55
Diesel 42 50
Hydrogen HP 14 364
Hydrogen Liquid 14 193
Lithium Battery 4,825 1,930

We see that batteries look terrible – the equivalent energy storage would require 4.8 tonnes of batteries occupying almost 2 cubic metres! Surely BEVs are impossible?!

But as I mentioned earlier, internal combustion engines waste around 75% of their fuel’s embodied energy in the form of heat. So a battery with the required stored energy would only need 25% of the mass and volume in the table above.

Mass (kg) Volume (l)
Lithium Battery 1206 483

So, we see that the equivalent battery pack is about a tonne heavier than the fuel for a diesel car.

But this doesn’t include the engine required to make the diesel fuel work. So one can see how by clever design and exploiting the fact that electric motors are lighter than engines, one can create a BEV that, while heavier than an ICE car, is still competitive.

Indeed, BEVs now outperform ICE cars on almost every metric that anyone cares about, and will continue to get better for many years yet.

Let’s do the same analysis for aeroplanes. A modern jet aeroplane typically carries 100 tonnes of kerosene with an energy content of around 43 x 105 MJ. This is sufficient to fly a modern jet (200 tonnes plus 30 tonnes of passengers) around 5,000 miles or so.

The table below shows the mass and volume other fuels or batteries which contains this same energy. Notice that the units are no longer kilograms and litres but tonnes and cubic metres.

Mass (tonnes) Volume (m^3)
Kerosene 100 123
Diesel 94 111
Hydrogen HP 31 811
Hydrogen Liquid 31 430
Lithium Battery 10,750 4,300

Now things look irrecoverably impossible for batteries! The batteries would weigh 10,000 tonnes! And occupy a ridiculous volume. Also, turbines are more thermodynamically efficient than ICEs, so assuming say 50% efficiency, batteries would still weigh ~5,000 tonnes and occupy 2,000 m3.

Even with a factor 10 increase in battery energy density – which is just about conceivable but not happening any time soon – the battery would still weigh 1,000 tonnes!.

Does it get any better for shorter ranges? Not much. Consider how much energy is stored in 10 tonnes of kerosene (~43 x 104 MJ). This is sufficient to fly a modern jet – weighing around 50 tonnes unladen and carrying 20 tonnes of passengers around 500 miles or so.

Mass (tonnes) Volume (m^3)
Kerosene 10 12
Diesel 9 11
Hydrogen HP 3 81
Hydrogen Liquid 3 43
Lithium Battery 1,075 430

Even assuming 50% jet efficiency, batteries with equivalent energy would still weigh ~500 tonnes and occupy 200 m3. Even after a factor 10 increase in battery energy density, things still look pretty hopeless.

So can we conclude that battery electric aviation is impossible? Surprisingly, No.

And yet, it flies.

Jet engines burning kerosene have now reached an astonishing state of technological refinement.

But jet engines are also very expensive, which makes the economics of airlines challenging. And despite improvements, jets are also noisy. And of course, they emit CO2 and create condensation trails that affect the climate.

In contrast, electric motors are relatively cheap, which means that electric aeroplanes (if they are possible) would be much cheaper, and require dramatically less engine maintenance. These features are very attractive for airlines – the people who buy planes. And the planes would be quiet and have zero emissions – attractive for people who fly or live near airports.

And several companies are seeking to exploit these potential advantages. Obviously, given the fundamental problem of energy density I outlined above, all the projects have limitations. Mostly the aeroplanes proposed have limited numbers of passengers and limited range. But the companies all impress me as being serious about the engineering and commercial realities that they face. And I have been surprised by what appears to be possible.

Here are a few of the companies that have caught my attention.


In the UK, Rolls Royce and partners have built an impressive single-engined aircraft which flies much faster than equivalent ICE powered aircraft.

Their Wikipedia page states the batteries have a specific energy of 0.58 MJ/kg, about 50% higher than I had assumed earlier in the article. The range of this plane is probably tiny – a few 10’s of kilometres – but this number will only increase in the coming years.

This aeroplane is really a technology demonstrator rather than a seedling commercial project. But I found it striking to see the plane actually flying.

In Sweden, Heart Aerospace have plans for a 19-seater short-hop passenger craft with 400 km of range. Funded by Bill Gates amongst others, they have a clear and realistic engineering target.

In an interview, the founder explained that he was focussing on the profitability of the plane. In this sense the enterprise differs from the Rolls Royce project. He stated that as planned, 2 minutes in the air will require 1 minute of re-charging. He had clear markets in mind in (Sweden, Norway, and New Zealand) where air travel involves many ‘short hops’ via transport hubs. And the expected first flights will be soon – 2025 if I have it correct.

In Germany, Lillium are building innovative ducted-fan planes. Whereas Heart’s planes and Rolls Royce’s demonstrator projects are conventional air-frames powered by electric motors, Lillium have settled on completely novel engineering possibilities enabled by electrical propulsion technology. Seeing their ‘Star Wars’ style aircraft take off and land is breathtaking.

Back in the UK, the Electric Aviation Group are advertising HERA as a 90-seater short route airliner with battery and hydrogen fuel-cell technology (not a turbine). This doesn’t seem to be as advanced as the other projects I have mentioned but illustrates the way that different technologies may be incorporated into electric aviation.

What about Hydrogen Turbines?

Legacy Aeromaker Airbus are advertising development of a hydrogen turbine demonstrator. It’s a gigantic A380 conventional jet airliner with a single hydrogen turbine attached. (Twitter video)

Stills from a video showing how the hydrogen turbine demonstrator will work. A single turbine will attached to kerosene driven aeroplane by 2035.

The demonstrator looks very clever, but I feel deeply suspicious of this for two sets of reasons: Technical reasons and ‘Feelings’.


  • Fuel Volume: To have the same range and capabilities as an existing jet – the promise that seems to be being advertised – the cryogenic (roughly -250 °C) liquid hydrogen would occupy 4 times the volume of the equivalent kerosene. It likely could not be stored in the wings because of heat leakage, and so a big fraction of the useful volume within an aeroplane would be sacrificed for fuel.
  • Fuel Mass: Although the liquid hydrogen fuel itself would not weigh much, the tanks to hold it would likely be much heavier than their kerosene equivalents. My guess is that that there would not be much net benefit in terms of mass.
  • Turbine#1: Once the stored liquid hydrogen is evaporated to create gas, its energy density plummets. To operate at a similar power level to a conventional turbine, the volume of hydrogen entering the combustion chamber per second will have to be (very roughly) 40 times greater.
  • Turbine#2: Hydrogen burns in a different way from kerosene. For example embrittlement issues around the high pressure, high temperature hydrogen present at the inlets to the combustion chamber are likely to be very serious.
  • I don’t doubt that a hydrogen turbine is possible, but the 2035 target advertised seems about right given the difficulties.
  • Performance: And finally, assuming it all works as planned, the aircraft will still emit NOx, and will still be noisy.


  • I feel this a legacy aero-maker trying to create a future world in which they are still relevant despite the changed reality of climate crisis.
  • I suspect these engines assuming the technical problems are all solved –  will be even more expensive than current engines.
  • I feel the timeline of 2035 might as well be ‘never’. It allows Airbus to operate as normal for the next 13 years – years in which it is critical that we cut CO2 emissions.
  • I suspect that in 13 years – if electric aviation ‘gets off the ground’ (sorry!) – then it will have developed to the point where the short-haul end of the aviation business will be in their grasp. And once people have flown on smaller quieter aircraft, they will not want to go back.
  • Here is Rolls Royces short ‘Vision’ video.

And so…

I wrote this article in response to a Twitter discussion with someone who was suggesting that cryogenic liquid-hydrogen-fuelled jets would be the zero-emission future of aviation.

I feel that that the idea of a cryogenic hydrogen aircraft is the last gasp of a legacy engine industry that is trying to stay relevant in the face of a fundamentally changed reality.

In contrast, electrical aviation is on the verge of becoming a reality: planes are already flying. And motors and batteries will only get better over coming decades.

At some point, I expect that electrical aviation will reach the point where its capabilities will make conventional kerosene-fuelled aeroplanes uneconomic, first on short-haul routes, and then eventually – though I have no idea how! – on longer routes.


…I could be completely wrong.

Heat Pump Explainer

February 24, 2022

Friends, Everyone is talking about heat pumps!

But many people are still unfamiliar with the principles behind their ‘engineering magic’.

This ‘explainer’ video was shot on location in my kitchen and back garden, and uses actual experiments together with state-of-the-art Powerpoint animations (available here) to sort-of explain how they work.

I hope it helps!


Nuclear Fusion is Irrelevant

February 14, 2022

Click for a larger image. News stories last week heralded a major breakthrough in fusion research. Links to the stories can be found below.

Friends, last week we were subjected to a press campaign on behalf of the teams of scientists and engineers who are carrying out nuclear fusion research.

Here are links to some of the stories that reached the press.

  • BBC Story
    • If nuclear fusion can be successfully recreated on Earth it holds out the potential of virtually unlimited supplies of low-carbon, low-radiation energy.”
  • Guardian Story #1
    • Prof Ian Chapman, the chief executive of the UK Atomic Energy Authority said “It’s clear we must make significant changes to address the effects of climate change, and fusion offers so much potential.”
  • Guardian Story#2 (from last year)
    • The race to give nuclear fusion a role in the climate emergency

The journalists add little to these stories – they mainly consist of snippets from press releases spun together to seem ‘newsy’. All these stories are colossally misleading.

Floating in the background of these stories is the idea that this research is somehow relevant to our climate crisis. The aim of this article is to explain to you that this is absolutely not true.

Even with the most optimistic assumptions conceivable, research into nuclear fusion is irrelevant to the climate crisis.

Allow me to explain how I have come to this conclusion.

Research into a practical fusion reactor for electricity generation can be split into two strands: an ‘old’ government-backed one and a ‘new’ privately-financed one.

The state of fusion research: #1 government-backed projects

The ‘old’ strand consists of research funded by many governments at JET in the UK and the colossal new ITER facility being constructed in France.

In this strand, ITER will begin operation in 2025, and after 10 years of ‘background’ experiments they will begin energy-generating experiments with tritium in 2035, experiments which are limited by design to just 4000 hours. If I understand correctly, operation beyond this limit will make ITER too radioactive to dismantle.

The key operating parameter for fusion reactors is called Q: the ratio of the heat produced to the energy input. And the aim is that by 2045 ITER will have achieved a Q of 10 – producing 500 MW of power for 400 seconds with only 50 MW of input energy to the plasma.

However ITER will only generate heat, not electricity. Also, it will not create any tritium but will instead only consume it. Following on from ITER, a DEMO reactor is planned which will have a Q value in the range 30-50, and which will generate electrical power, and be able to breed tritium in the reactor.

So on this ITER-proposed time-line we might expect the first actual electricity generation – may be 100 MW of electrical power – in maybe 2050.

And then assuming that these reactors take 10 years to build and that the design will evolve a little, it will be perhaps 2070 before there are ten or so operating around the world.

You may consider that research into a technology which will not yield results for 50 years may or may not be a good idea. I am neutral.

But it is definitely irrelevant to our climate crisis: we simply do not have 50 years in which to eliminate carbon dioxide emissions from electricity generation in the UK.

And this is on the ITER-proposed timeline which I consider frankly optimistic. If one considers some of the technical problems, this optimism seems – to put it politely – unjustified.

Here are three of the issues I keep at the top of my file in case I meet some fusion scientists at the folk club.

  • Q is the ratio of heat energy injected into the plasma to the heat energy released. But in order to be effective we have to generate net ELECTRICAL energy. So we really need to take account of the fact that thermodynamics limits the electrical generation to ~30% of the thermal energy produced. Additionally we need to include the considerable amounts of energy used to operate the complex machinery of a reactor. So we really need to consider a wider definition of Q, one that includes the ratio of input to output energies involving the entire reactor. Sabine Hossenfelder has commented on this issue. But basically, Q needs to be a lot bigger than 10.
  • Materials. The inside of the reactor is an extraordinarily hostile place with colossal fluxes of neutrons passing through every part of the structure. After operation has begun, no human can ever enter the environment again – and it is not clear to me that a working lifetime of say 35 years at 90% availability is realistic. Time will tell.
  • Tritium. The reactor consumes tritium – possibly the most expensive substance on Earth – and for each nucleus of tritium destroyed a single neutron is produced. The neutrons so produced must be captured to produce the heat for electrical generation. But the neutrons are also needed to react with lithium to produce more tritium. Since some neutrons are inevitably lost – so the plan is for extra neutrons to be ‘bred’ by bombarding suitable materials with neutrons, which then produce a shower of further neutrons – 2 or 3 for every incident neutron. And these neutrons can then in principle be used to produce tritium. But aside from being technically difficult, this breeding process also produces long-lived radioactive waste – something fusion reactors claim not to do.

If short, when one considers some of these technical problems, optimism that this research path will produce significant power on the grid in 2070 seems to me to be unjustified.

But what about this new ‘breakthrough’?

The breakthrough was not a breakthrough. It was undertaken because the walls of the previous reactor were found to absorb some of the fuel! So this ‘breakthrough’ represented a repeat of a previous experiment, but with new materials in place.

You can relive the press conference here.

Starting with a much larger amount of energy, they managed to produce 59 megajoules (MJ) of energy from fusion in about 8 seconds.

59 MJ is about 16.4 kWh of energy, which is sufficient to heat water for around 500 cups of tea, more than a cup of tea each for all the scientists and engineers working on the project.

For comparison, the 12 solar panels on my house will produce this easily in a day during the summer. To generate the energy in 5 seconds rather than 12 hours would require more panels: a field of panels roughly 200 m x 250 m, which would cost a little under 1 million pounds.

So the breakthrough is modest in absolute terms. But as I mentioned above, after billions more in funding, and another 20 years of research, the scientists expect to extend this generating ‘burn’ from 5 seconds to 400 seconds at a much higher power level.

In my opinion, JET and ITER are a complete waste of money and should be shut down immediately. The resources should be transferred to building out solar and wind energy projects alongside battery storage.

The state of fusion research: #2 privately-backed projects

The ‘new’ strand of fusion research consists of activities carried out primarily by privately-funded companies.

What? If the massive resources of governments can only promise fusion by 2070, how can private companies hope to make progress?

The answer is that JET and ITER were planned before a technical key advance was made, and they are committed to proceeding without incorporating that advance! Its a multi-billion pound version of “I’ve started so I’ll finish“. It is utter madness, and doubly guarantees the irrelevance of ITER.

The technical advance is the achievement of superconducting wire which can create magnetic fields twice as large as was previously possible. It turns out that the volume of plasma required to achieve fusion scales like the fourth power of the magnetic field. So doubling the magnetic field makes the final reactor potentially 16 times smaller!

This also makes it dramatically cheaper requiring amounts on the order of $100 million rather than billions of dollars. Critically, reactors can exploit the concept of Small Modular Reactors (SMRs) which can be mass-produced in a factory and shipped to a site. Potentially the first reactors could be built in years rather than decades, and the technology iterated to produce advances.

I have written about this previously. With some qualifications, I think this activity is generally not crazy  (it is certainly much less crazy than JET and ITER) but success is far from guaranteed.

A key unresolved question with this technology concerns its potential timeline for delivery of a working power plant.

The reactors face exactly similar problems to those in the much larger ITER reactor, and these are not problems that can be solved in months. So let’s suppose that the first demonstration of Q>1 is achieved in just 5 years (2027), and that all the technical problems with respect to electricity generation required only a further 10 years (2037). Given the difficulties in planning, let’s optimistically assume that the first production plant could get built just 5 years after that in 2042.

The ‘S’ in SMR means reactors would be small, with a thermal output of perhaps 150 MW and an electrical output of perhaps 50 MW. This is small on the scale of typical thermal generation plant. For example Hinckley C is designed to output 3,200 MW of electrical power i.e. more than 60 times larger than a hypothetical SMR fusion reactor.

So if we assume a rapid roll out and no technical or societal problems, then perhaps these reactors might generate significant power onto the grid in perhaps 2050. Nominally this is 20 years ahead of ITER.


With optimistic assumptions concerning technical progress, we might hope for fusion reactors to begin to make a significant contribution to the grid somewhere between 2050 and 2070, depending on which route is taken.

That is already too late to make any contribution to our climate crisis.

We need to deploy low-carbon technologies now. And if we have a choice between reducing carbon dioxide emissions now, or in 30 – 50 years, there is no question about what we should do.


We also need to consider the likely cost of the electricity produced by a fusion reactor.

Like conventional fission-based nuclear power, the running costs should be low. Deuterium is cheap and the reactor should generate a surplus of tritium.

The majority of the cost of conventional nuclear power is the cost of the capital used to construct the reactor. If I recall correctly, it amounts to around 95% of the cost of the electricity.

It is hard to imagine that a fusion reactor would be cheaper than a fission reactor – it would be at the limit of manageable engineering complexity. So we might imagine that the costs of fusion-generated electricity would be similar to the cost of nuclear power – which is already most expensive power on the grid.

In contrast, the cost of renewable energy (solar and wind) has fallen dramatically in recent years. Solar and wind are now the cheapest ways to make electricity ever. And their cost – along with the cost of battery storage – is still falling.

So it seems that after waiting all these years, the fusion-based electricity would in all likelihood be extraordinarily expensive.


The idea of generating electricity from nuclear fusion has been seen as technological fix for climate change. It is not.

Even the most optimistic assumptions possible indicate that fusion will not make make any significant contribution to electricity supplies before 2050.

This is too late to help in out in our climate crisis which is happening now.

Additionally the cost of the electricity might be expected to exceed the cost of conventional nuclear power stations – the most expensive electricity currently on the UK grid.

If as an alternative, we invested in renewable generation from wind, solar and tidal resources, together with ever cheaper storage, we could begin to address our climate crisis now in the knowledge that the technology we were deploying would likely only ever get better. And cheaper.



Reducing Carbon Dioxide Emissions from my home: Video and Slides

February 4, 2022

Friends, Good Evening.

As I mentioned in my previous post I gave a talk to Richmond & Twickenham Friends of the Earth on Wednesday, 2nd February 2022.

The video above is the dullest of the dull repetition of that presentation.

It lasts 45 minutes, so make yourself a cup of tea before you start!

You can also download the PowerPoint slides from this presentation using this link.

Me and Tea.

January 20, 2022

Friends, I have given up putting milk in my tea.

Why? Because as I wrote a few days ago, putting milk in my tea gives rise to annual methane emissions equivalent to almost a third of tonne of carbon dioxide.

On balance, I would rather avoid those emissions than experience the pleasure of putting milk in my tea.

My life in tea

I can still hazily remember being served milky tea with sugar as a child – perhaps I was 6 or 7.

Later on, drinking tea became a habit, and when I was probably 11 or 12, I gave up putting sugar in my tea.

And I have been drinking large amounts of tea each day – maybe 6 cups – ever since.

Around 12 years ago, I was concerned about my son’s seemingly unbreakable attachment to his iPod. To my surprise, he agreed to surrender his iPod if I gave up tea. I agreed, pleased we had reached an amicable bargain.

However I gave him back his iPod after 3 days, because in truth I was – and am – addicted to tea!

So changing the way I drink my tea is changing a life-long habit.

Life-long habits

Carbon dioxide and methane emissions are not very obvious – we generally don’t see them: the gases are invisible and have no smell. And they frequently take place at distant locations such as power stations or farms.

But the emissions are nonetheless real and their long term damage is on a scale that it is scarcely possible to imagine.

Additionally these emissions are entwined with our familiar ways of living.

  • Gas boilers keep us warm.
  • Cars provide mobility.
  • Aeroplanes take us on holiday.
  • Milk and Cheese and Butter taste great.
  • Tea with milk is ‘how normal people have tea’.

So acknowledging the reality of the emissions we give rise to and the harm they cause is hard both intellectually and emotionally.

Writing the article last week it became clear to me that I had to overcome my emotional attachment to milk in my tea.

Breaking these life-long habits is something we will all have to do if we want to create a way of living which does not damage the climate of our children’s future more than we already have.

More than milk

After 10 days I am happy to report that I am enjoying my milk-free tea and have now almost stopped reflexive visits to the fridge each time I make a cup!

I think I taste the tea itself rather more, but it is a very different kind of drink.

I have also been reducing use of butter and cheese and I have found alternatives that are perfectly acceptable in most recipes.

I find it hard to believe my use of dairy products will ever reach zero. But I can easily imagine reducing consumption by 90% or so.

Life is a long journey, and I never thought my journey would take me here: milk-free tea and minimising use of cheese and butter which I love!

It feels strange and unfamiliar.

But here I am.

A Watched Pan…

January 18, 2022

Click on Image for larger version.  A vision of domestic bliss in the de Podesta household. Apparatus in use for measuring the rate of heating of 1 litre of water on an induction hob.

In the beginning…

Friends, my very first blog article (written back on 1st January 2008 and re-posted in 2012) was about whether it is better to boil water with an electric kettle or a gas kettle on a gas hob.

Back then, my focus was simply on energy efficiency rather than carbon dioxide emissions. I had wanted to know how much of the primary energy of methane ended up heating the water. I did this by simply timing how long it took to boil 1 litre of water by various methods.

Prior to doing the experiments I had imagined that heating water with gas was more efficient because the fuel was used directly to heat the water. In contrast, even the best gas-fired power stations are only ~50% efficient.

What I learned back then was that gas cookers are terrible at heating kettles & pans! They were so much worse than I had imagined that I later spent many hours with different size pans, burners, and amounts of water just so I could believe my results!

Typically gas burners only transferred between 36% and 56% of the energy of combustion to the water – the exact fraction depending on the size and power of the burner. Heating things faster with a bigger burner was less efficient. Using a small flame and a very large pan, I could achieve an efficiency of 83%, but of course the water heated only very slowly.

This inefficiency was roughly equivalent to or worse than the inefficiency of the power station generating electricity, and so I concluded that electric kettles and gas kettles were similarly inefficient in their use of the primary energy of the gas. But that using electric kettles allowed one to use the correct amount of water more easily, and so avoided heating water that wasn’t used.

14 years later…

After a recent conversation on Twitter (@Protons4B) I thought I would look at this issue again.

Why? Well two things have changed in the last 14 years.

  • Firstly, electricity generation now incorporates dramatically more renewable sources than in 2008 and so using electricity involves ever decreasing amounts of gas-fired generation.
  • Secondly, I am now concerned about emissions of carbon dioxide resulting from lifestyle choices.

Also being a retired person, I now have a bit more time on my hands and access to fancy instruments such as thermometers.

The way I did the experiments is described at the end of the article, but here are the results.

Results#1: Efficiency

The chart below shows estimates for the efficiency with which the electrical energy or the calorific content of the gas is turned into heat in one litre of water. My guess is these figures all have an uncertainty of around ±5%.

  • The kettle was close to 100% efficient:
  • The induction hob was approximately 86% efficient
  • The Microwave oven was approximately 65% efficient

In contrast, heating the water in a pan (with a lid) on a gas hob was only round 38% or 39% efficient.

Click on Image for larger version. Chart showing the efficiency of 5 methods of heating 1 litre of water. 100% efficiency means that all the energy input used resulted in a temperature rise. The two gas results were for heating pans with two different diameters (19 cm and 17 cm).

It was particularly striking that the water heated on the gas burner (~1833 W) took 80% longer to boil than on the Induction hob (~1440 W) despite the heating power being ~20% less on the induction hob.

Click on Image for larger version. Chart showing the rate of heating for each of the 5 methods of heating 1 litre of water. Notice that the water heated on the gas burner (~1833 W) took 80% longer to boil than on the Induction hob (~1440 W) despite the heating power being ~20% less on the induction hob. Notice that up until 40 °C, the microwave oven heats water as fast as the gas hob, despite using half the power!

Results#2: Carbon Dioxide Emissions 

Based on the average carbon intensity of electricity in 2021 (235 g CO2/kWh), boiling a litre of water by any electrical means results in substantially less CO2 emissions than using a pan (with a lid) on a gas burner.

I performed these experiments on 17th January 2021 between 4 p.m. and 7 p.m. when the carbon intensity of electricity was well above averages: ~330 g CO2/kWh. In this case, boiling a litre of water in a kettle or induction hob still gave the lowest emissions, but heating water in a microwave oven resulted in similar emissions to those arising from using a pan (with a lid) on a gas burner.

Click on Image for larger version. Charts showing the amount of carbon dioxide released by heating 1 litre of water from 10 °C to 100 °C using either electrical methods or gas. The gas heating is assumed to have a carbon intensity of 200 gCO2/kWh. The left-hand chart is based on the carbon intensity of 330 gCO2/kWh of electricity which was appropriate at the time the experiments were performed. The right-hand chart is based on the carbon intensity of 235 gCO2/kWh of electricity which was the average value for 2021. Electrical methods of heating result in lower CO2 emissions in almost all circumstances.

Results#3: Cost 

Currently I am paying 3.83 p/kWh for gas and 16.26 p/kWh for electricity i.e. electricity is around four times more expensive than gas.

These prices are likely to rise substantially in the coming months, but it is not clear whether this ratio will change much.

So sadly, despite gas being the slowest way to heat water and the way which releases the most climate damaging gases, it is still the cheapest way to heat water. It’s about 40% cheaper than using an electric kettle.


For the sake of the climate, use an electric kettle if you can.


That was the end of the article and there is no need to read anymore unless you want to know how I made these measurements.


Estimating the power delivered to the water + vessel

  • For electrical measurements I paused the heating typically every 30 seconds, and read the plug-in electrical power meter. This registered electrical energy consumed in kWh to 3 decimal places.
    • I fitted a straight line to the energy versus time graph to estimate power.
  • For gas measurements I read the gas meter before and after each experiment. This reads in m^3 to 3 decimal places and I converted this volume reading to kWh by multiplying 11.19 kWh/m^3.
    • The gas used only amount to 0.025 m^3 so uncertainty is at least 4% from the digitisation.
    • I divided by the time – typically 550 seconds – to estimate the power.

Mass of water

  • I placed the heating vessel (kettle, pan, jug) on the balanced and tired (zeroed) the reading.
  • I then added water until the vessel read within 1 g of 1000 g. Uncertainty is probably around 1% or 10 g.

Heating rate with 100% energy conversion

  • Based on the power consumed, I estimated the ideal heating rate if 100% of the supplied power caused temperature rises in the water by using the equations.

  • I assumed the average specific heat capacity of water of the range from 10 °C to 100 °C was 4187 J/ (kg °C)

Measuring the temperature.

  • For electrical measurements I paused the heating typically every 30 seconds, stirred the liquid with a coffee-stirrer for 2 or three seconds, and then took the temperature using a thermocouple probe..
  • For gas measurements it wasn’t possible to the pause the heating because of the way I was measuring the power. So about 10 seconds before the reading was due I slipped the coffee stirrer under the lid to mix the water.

Estimating the rate of temperature rise.

  • For all measurements I fitted a straight line to the temperature versus time data, using only data points below approximately 80 °C to avoid the effects of increased temperature losses near to the boiling point.

Mass of the ‘addenda’.

  • The applied power heated not only the water but also its container.
  • The heat capacity of the 19 cm stainless steel pan (572 g) was roughly 6% of the heat capacity of the water.
  • I chose not to take account this heat capacity because there was no way to heat water with a container. So the container is a somewhat confounding factor, but allows more meaningful comparison of the results.

Efficiency of boiling

  • I estimated efficiency by comparing the actual warming rate with the ideal warming rate.
  • I then calculated the energy required to heat 1 kg of water from 10 °C to 100 °C, and multiplied this by the efficiency.
  • In this way the result is relevant even if all the measurements did not start and stop at the same temperatures.


  • I heated the water in the microwave in a plastic jug which did not have a tight fitting lid. I am not sure if this had an effect.
  • I did notice that the entire microwave oven was warm to hot at the end of the heating sequence.

Would you like milk with your tea?

January 9, 2022

Every blog article starts with a mug of tea.

Friends, I am addicted to tea.

I like all kinds of tea, but my favourite is a basic brew, with milk.

The ritual of settling down with a mug of hot tea is an essential pre-requisite for any kind of concentration – such as writing this article.

This the main use of milk in the household and each week my wife and I consume around 2 litres.

So per year we use roughly 100 litres of milk.

Looking online, I find this corresponds to emissions (mainly of methane) which are equivalent to 315 kg of carbon dioxide per year: almost a third of a tonne!

I think there is a lot of uncertainty in that estimate, and it probably varies from country to country. But taking it at face value, it is a truly colossal impact from a very mundane activity.

Click image for a larger version. The graph shows the global warming impact of emissions associated with production of milk and cheese in terms of the equivalent amount of CO2 emissions which would have the same impact. The data is from Our World in Data

After all the work I have had done on the house, annual heating and electrical emissions have fallen from 3.7 tonnes to about 0.7 tonnes.

So emissions from drinking tea alone have become a significant fraction (∼50%) of general household emissions!

What to do?

As far as I know, the only way to avoid these emissions, is to stop drinking milk –  or to reduce the amount I drink substantially.

The problem

The problem with this solution is that I – like millions of other people – really like having milk in my tea.

I have tried using milk alternatives derived from oats, almonds, and soya. These products look like milk and come in packaging which suggests they are in some way similar to milk.

But they do not taste even remotely like milk.

Additionally, I am emotionally attached to the idea that milk comes from cows that live on farms. For someone who is basically a city-dweller, this connection feels meaningful.

So at the start of this new year I am facing a dilemma.

What to do?

As far as I know, the only way to avoid these emissions, is to stop drinking milk –  or to reduce the amount I drink substantially.

Switching to the plant-based alternatives is just not acceptable, which leaves me with just two options:

  • Abandoning milk in my tea altogether. This is an extreme option, but one I am keeping under review.
  • Currently I am experimenting with a 50:50 mixture of milk with Oat ‘derivative’ product. It is predictably, not as nice as just milk, but it is borderline acceptable. But the emissions are still substantial.

I will let you know how it goes when I have a few more weeks under my belt.

The wider problem

The wider problem with this solution is that I haven’t even mentioned butter or cheese, other dairy-based staples of my diet.

Because of the large amount of raw milk used, each kilogram of cheese is apparently is associated with 24 kg of CO2 equivalent emissions (mostly as methane).

My wife and I eat – and enjoy prodigiously – about 0.5 kg of Davidstow Cheddar each week. This corresponds to around 25 kg per year, and emissions with the equivalent impact of 600 kg of carbon dioxide per year.

Basically the emissions associated with our cheese consumption have an impact roughly equivalent to all the electricity we use to heat and run the house for a year!

Fortunately Our World in Data does not have information about butter. I say ‘fortunately’ because I feel sure it will be bad.

The wider truth is that in regards to my house, all the changes I have made to reduce carbon dioxide emissions have been expensive, but they have not really affected my quality of life.

But it seems that emissions from some of the basics of my diet, foods I love and have eaten all my life, are apparently responsible for more annual carbon dioxide emissions than my entire house!

Reducing these emissions is going to be much tougher and feel much more like a personal sacrifice with a very direct and (at least initially) negative impact on my quality of life.

I guess nobody said it would be easy.

I am going to sit down now with a nice cup of tea to think about this…





Carbon accounts 2021: looking back and looking ahead

January 2, 2022

Click the image for a larger version. Representation of the reduction in domestic carbon dioxide emissions from gas and electricity over the last four years. Also shown are the steps I have taken to achieve these reductions.

[Article Summary: it is actually pretty difficult to estimate carbon dioxide emissions – but it is important to try.]

Friends, it’s New Year’s Day.

And at this still point in the ever-rolling cycle of the years, it seemed like a good time to summarise progress on my project to reduce carbon dioxide emissions from the house.

It may seem like a good time, but actually this is not a good time at all to summarise annual emissions. The best time to do this is 6 months away in the summer. This is because household emissions peak in the winter and fall to practically zero in the summer.

You can see this on the graphs below which show cumulative electricity and gas consumption through the last few years.


To estimate the emissions from gas I have estimated the meter reading which I would have had in the summer of 2018 and used this as a baseline.

I then subtract weekly meter readings from this baseline and convert them to kWh of thermal energy, and then multiply the number of kWh of gas by 200 gCO2 per kWh.

Burning methane gas in a boiler releases around 183 gCO2 per kWh of gas – as documented in this official spreadsheet. (Look up the ‘Fuels’ tab and use cell F42) But some additional CO2 emissions are associated with delivering the gas to my home: compressors drive the gas along pipelines and ships deliver gas across the oceans.

The actual value of these ‘upstream’ emissions is difficult to know precisely, but actual experts suggest it amounts to roughly 24 gCO2 per kWh of gas delivered. So in principle the best estimate of CO2 emissions from gas delivered would be 183 + 24 = 207 gCO2 per kWh. This figure is 4% larger than the figure I used.

However, it is likely that direct methane leaks at wells and in handling plants are underestimated (example). Evaluated over a decade after leakage, methane is 84 times more powerful as a greenhouse gas than CO2. So if even 0.1% of methane leaked on its way to my home, the CO2 equivalent emission would be increased by 17 gCO2/kWh. However some people estimate that actual leakage is more than 1%. If that were so that would practically double the climate impact of using gas to nearly 400 gCO2 per kWh. The unknown magnitude of leaks is just one more reason to stop using methane gas.

Given these uncertainties I have used a figure of 200 gCO2 per kWh as a likely underestimate of true emissions which is not obviously wrong, but which is a convenient round number.

Click the image for a larger version. The graph shows the cumulative emissions of carbon dioxide emissions from domestic gas use over the last three years.

The graph above is based on weekly gas meter readings.

The data form a series of ‘steps’ and it is clear that measuring from one step level to the next gives a better estimate of the yearly emissions than choosing an arbitrary point on the ‘riser’ of the staircase. This implies measuring from summer to summer

The reason is that if the winter is mild before the New Year but cold after New Year, the emissions fall in different years even though they arise from the same winter.

But however one analyses the data, it is clear that there has been no step this winter of 2021/22. We now use gas only for cooking and I hope shortly to stop even this use and make that curve go entirely flat. For ever!


To estimate the emissions from electricity I have multiplied meter readings in kWh by 230 gCO2 per kWh.

As with gas, it is not obvious how much carbon dioxide is emitted for each kWh of electricity consumed from the grid. Depending on the generation source, the so-called carbon intensity of the electricity can vary significantly. For example, as I write – with low demand and high winds – the carbon intensity of the electricity is just 111 gCO2 per kWh.

The MyGridGB web site maintains a live monitor of carbon intensity, and shows an annual summary of average carbon intensity through the year.

Over the last 3 years the average carbon intensity in the UK has been 245, 222, and 235 gCO2 per kWh. Since these figures are within a few percent of each other I have used a rounded value of 230 gCO2 per kWh for the entire range of the measurements.

Click the image for a larger version. The graph shows the average carbon intensity for each year. The values for eth last three years have been 245, 222, and 235 gCO2 per kWh. The red line at 100 gCO2 per kWh is the target carbon intensity for the year 2030.

Multiplying the number of kWh used by 230 gCO2 per kWh tells me the emissions associated with my use of grid electricity. This is shown below on the same vertical scale as on the gas graph above.

Click the image for a larger version. The graph shows the cumulative emissions of carbon dioxide emissions from domestic electricity use over the last three years. The scale is the same as in the previous graph showing carbon dioxide emissions from gas use.

The graph above is based on weekly electricity meter readings.

During 2019 and 2020 carbon emissions occurred at a regular rate with no seasonal steps. Even, looking closely, I cannot detect the point in November 2020 when solar panels were installed.

But in March 2021 when our Powerwall battery was installed, the curve goes flat as the combination of solar panels and battery was sufficient to take us practically off-grid for the summer.

In September 2021, as solar generation weakened, we began to draw electricity from the grid again, and also began heating with electricity using our air-source heat pump. Currently we are using 20 to 25 kWh/day – more than twice the previous rate. This will probably continue until March

It is hard to estimate precisely, but I think – with colder months ahead – the summer-to-summer emissions will be similar or slightly less than last year.

Gas and Electricity

To estimate the emissions from both gas and electricity use, I have added the data from the two previous graphs together.

Click the image for a larger version. The graph shows the cumulative emissions of carbon dioxide emissions from domestic gas and electricity use over the last three years. The scale is the same as in the previous graphs.

Anticipating data from the spring of 2022, it looks like emissions will have fallen from about 3.6 tonnes in 2018/2019 to (hopefully) only 0.7 tonnes in 2021/22. This is an 80% reduction.

But even though this has already been a tedious article, this is not quite the end of the story.

Embodied Carbon

To achieve that 80% cut in annual emissions, I had to buy things which involved the emission of carbon dioxide – so called embodied carbon.

It is difficult to estimate the amount of embodied carbon in a particular object, but after quite some effort I have come up with the following estimates.


Embodied tonnes of CO2

EWI PU Boards


EWI Mortar


Argon Triple Glazing


Solar Panels




Heat Pump


Air Conditioning




They amount to 10.5 tonnes of embodied carbon. To find out when this embodied carbon has been ‘paid for’ I need to compare the CO2 emissions described above with the so-called counter-factual: the emissions which would have occurred if I had done nothing.

If I had done nothing then my guess is that emissions over the last 4 years would be simply 4 x 3.6 tonnes of CO2 – or 14.4 tonnes.

Actually, CO2 emissions over the last 4 years have been 3.6 + 2.9 + 2.0 + 0.7 = 9.2 tonnes.

So my ‘investment’ of 10.5 tonnes of embodied carbon will have saved 5.2 tonnes of emissions by summer 2022, and should continue to save (3.6 – 0.7) = 2.9 tonnes per year for several years to come. So I should ‘break even’ during the year 2024. Everything beyond that will be pure emissions savings.

Looking ahead

Click the image for a larger version. The graph shows the estimated household emissions from 2018 to 2040. The red line shows the emissions which would have occurred if I had done nothing. The green line shows the emissions according to the current plan. The dotted line shows emissions if the money I pay to Climeworks is not a scam.

Looking further ahead, the tonnes of carbon ‘debt’ I have incurred seems less significant. And carbon dioxide emissions avoided by 2040 amount to 60 tonnes.

Additionally since March 2021, I have been paying Climeworks £40/month to permanently remove 50 kg/month (0.6 tonnes/year) of carbon dioxide. If they are actually doing this – and I have no real way of knowing! – then our household is very nearly carbon neutral.

However none of what I have discussed accounts for emissions arising from consumption, or travel, or from my pension investments – all of which are likely to be quite significant.

So there is still lots to do in the new year.

I love Greta Thunberg

December 30, 2021

Click image for a larger version. My son gave me a Christmas Tree decoration in the likeness of Greta Thunberg.

Friends, love is a strong word.

Back in 2012 I wrote that I loved James Hansen. If you haven’t heard it, I strongly recommend his TED talk.

I wrote:

When I hear him speak I feel I am listening to a human being who understands enough to feel compelled to shout ‘Fire’ in the ‘cinema’ of the modern world. He feels that no matter what the consequences, we must face up to the climate challenge ahead. Being prepared to be arrested for his insistence that the US government should listen to what the science (they have paid for!) has to say seems like an act of great bravery to me.

And today I would like to declare a similar – but different – admiration for Greta Thunberg. Greta is not after all, a world-leading scientist.

The fact that my son gave me a Christmas Tree decoration in the likeness of Greta Thunberg – but not James Hansen – is testament to their different roles. He also gave me a book of Greta’s speeches and not a copy of James Hansen’s papers (e.g. this one from 1981).

Greta Thunberg has unintentionally become a global cultural phenomenon. But having read her book, I can assure you it is not because of her oratory. It is because of her unflinching honesty.

Reading her words addressed to old people like me, I do not feel inspired: I feel shamed.

I will leave you with a quote from the book: Greta’s speech to the UK Parliament in 2019. I hope you too will be as affected by her honesty as I have been.

UK Parliament 2019

23 April 2019:

Is my microphone on? Can you hear me?

Around the year 2030, 10 years 252 days and 10 hours away from now, we will be in a position where we set off an irreversible chain reaction beyond human control, that will most likely lead to the end of our civilisation as we know it. That is unless in that time, permanent and unprecedented changes in all aspects of society have taken place, including a reduction of CO2 emissions by at least 50%.

And please note that these calculations are depending on inventions that have not yet been invented at scale, inventions that are supposed to clear the atmosphere of astronomical amounts of carbon dioxide.

Furthermore, these calculations do not include unforeseen tipping points and feedback loops like the extremely powerful methane gas escaping from rapidly thawing arctic permafrost.

Nor do these scientific calculations include already locked-in warming hidden by toxic air pollution. Nor the aspect of equity – or climate justice – clearly stated throughout the Paris agreement, which is absolutely necessary to make it work on a global scale.

We must also bear in mind that these are just calculations. Estimations. That means that these “points of no return” may occur a bit sooner or later than 2030. No one can know for sure. We can, however, be certain that they will occur approximately in these timeframes, because these calculations are not opinions or wild guesses.

These projections are backed up by scientific facts, concluded by all nations through the IPCC. Nearly every single major national scientific body around the world unreservedly supports the work and findings of the IPCC.

Did you hear what I just said? Is my English OK? Is the microphone on? Because I’m beginning to wonder.

During the last six months I have travelled around Europe for hundreds of hours in trains, electric cars and buses, repeating these life-changing words over and over again. But no one seems to be talking about it, and nothing has changed. In fact, the emissions are still rising.

When I have been travelling around to speak in different countries, I am always offered help to write about the specific climate policies in specific countries. But that is not really necessary. Because the basic problem is the same everywhere. And the basic problem is that basically nothing is being done to halt – or even slow – climate and ecological breakdown, despite all the beautiful words and promises.

The UK is, however, very special. Not only for its mind-blowing historical carbon debt, but also for its current, very creative, carbon accounting.

Since 1990 the UK has achieved a 37% reduction of its territorial CO2 emissions, according to the Global Carbon Project. And that does sound very impressive. But these numbers do not include emissions from aviation, shipping and those associated with imports and exports. If these numbers are included the reduction is around 10% since 1990 – or an an average of 0.4% a year, according to Tyndall Manchester.

And the main reason for this reduction is not a consequence of climate policies, but rather a 2001 EU directive on air quality that essentially forced the UK to close down its very old and extremely dirty coal power plants and replace them with less dirty gas power stations. And switching from one disastrous energy source to a slightly less disastrous one will of course result in a lowering of emissions.

But perhaps the most dangerous misconception about the climate crisis is that we have to “lower” our emissions. Because that is far from enough. Our emissions have to stop if we are to stay below 1.5-2 °C of warming. The “lowering of emissions” is of course necessary but it is only the beginning of a fast process that must lead to a stop within a couple of decades, or less. And by “stop” I mean net zero – and then quickly on to negative figures. That rules out most of today’s politics.

The fact that we are speaking of “lowering” instead of “stopping” emissions is perhaps the greatest force behind the continuing business as usual. The UK’s active current support of new exploitation of fossil fuels – for example, the UK shale gas fracking industry, the expansion of its North Sea oil and gas fields, the expansion of airports as well as the planning permission for a brand new coal mine – is beyond absurd

This ongoing irresponsible behaviour will no doubt be remembered in history as one of the greatest failures of humankind.

People always tell me and the other millions of school strikers that we should be proud of ourselves for what we have accomplished. But the only thing that we need to look at is the emission curve. And I’m sorry, but it’s still rising. That curve is the only thing we should look at.

Every time we make a decision we should ask ourselves; how will this decision affect that curve? We should no longer measure our wealth and success in the graph that shows economic growth, but in the curve that shows the emissions of greenhouse gases. We should no longer only ask: “Have we got enough money to go through with this?” but also: “Have we got enough of the carbon budget to spare to go through with this?” That should and must become the centre of our new currency.

Many people say that we don’t have any solutions to the climate crisis. And they are right. Because how could we? How do you “solve” the greatest crisis that humanity has ever faced? How do you “solve” a war? How do you “solve” going to the moon for the first time? How do you “solve” inventing new inventions?

The climate crisis is both the easiest and the hardest issue we have ever faced. The easiest because we know what we must do. We must stop the emissions of greenhouse gases. The hardest because our current economics are still totally dependent on burning fossil fuels, and thereby destroying ecosystems in order to create everlasting economic growth.

“So, exactly how do we solve that?” you ask us – the schoolchildren striking for the climate.

And we say: “No one knows for sure. But we have to stop burning fossil fuels and restore nature and many other things that we may not have quite figured out yet.”

Then you say: “That’s not an answer!”

So we say: “We have to start treating the crisis like a crisis – and act even if we don’t have all the solutions.”

“That’s still not an answer,” you say.

Then we start talking about circular economy and rewilding nature and the need for a just transition. Then you don’t understand what we are talking about.

We say that all those solutions needed are not known to anyone and therefore we must unite behind the science and find them together along the way. But you do not listen to that. Because those answers are for solving a crisis that most of you don’t even fully understand. Or don’t want to understand.

You don’t listen to the science because you are only interested in solutions that will enable you to carry on like before. Like now. And those answers don’t exist any more. Because you did not act in time.

Avoiding climate breakdown will require cathedral thinking. We must lay the foundation while we may not know exactly how to build the ceiling.

Sometimes we just simply have to find a way. The moment we decide to fulfil something, we can do anything. And I’m sure that the moment we start behaving as if we were in an emergency, we can avoid climate and ecological catastrophe. Humans are very adaptable: we can still fix this. But the opportunity to do so will not last for long. We must start today. We have no more excuses.

We children are not sacrificing our education and our childhood for you to tell us what you consider is politically possible in the society that you have created.

We have not taken to the streets for you to take selfies with us, and tell us that you really admire what we do.

We children are doing this to wake the adults up.

We children are doing this for you to put your differences aside and start acting as you would in a crisis.

We children are doing this because we want our hopes and dreams back.

I hope my microphone was on. I hope you could all hear me.

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