Archive for May, 2021

COVID 19: What have we learned?

May 26, 2021

Click for a larger image. Logarithmic graph showing positive caseshospital admissions and deaths since the start of the pandemic. The blue arrows show the dates of ‘opening’ events. See text for further details. The red dotted line shows cases increasing by a factor 10 every 150 days.

Friends, so here we are, May 26th 2021, and I have spent the day listening to Dominic Cummings testify to the “Lessons to Learn” inquiry in Parliament.

  • I found his testimony compellingly plausible.

As I explained previously (link), I can forgive the government for failing to act at the start of pandemic. They should have known better, but actually very few people in this country could quite believe what was happening.

But I refuse to forgive the government’s failure to act in September last year. What was required was obvious even to an amateur like me (link).

Dominic Cumming’s testimony explained how, despite advice to the contrary, Boris Johnson refused to act, asserting he was the “The Mayor in “Jaws” and he would keep “the beaches” open.

But unlike the “Mayor in Jaws” who was responsible for a few fictional deaths, Boris Johnson was personally responsible for tens of thousands of real deaths – the majority of the 86,164 who died in the second wave.

I won’t go on about this, because this is not that sort of blog, but this is, in my opinion, a criminal failure.

So what can we learn now?

The graph at the head of page shows cases, deaths and admissions throughout the pandemic.

It is striking that deaths and hospital admissions are very similar now to what they were in between the first and second waves.

Positive cases are higher than at the end of the first wave, but this could easily be due to the current extensive testing of asymptomatic people. The actual prevalence of the virus is probably similar or less.

As I mentioned in my previous blog, we should not care about:

  • the absolute number of cases,
  • the population prevalence of cases,
  • or even the rate of change of cases.

What matters is this:

  • Is there the potential for the pandemic to expand into the general population and kill hundreds of thousands of people?

Last summer the answer was definitely ‘Yes’.

This summer the answer is still in my estimation probably ‘No’.

Why? Because 57% of the entire population, including practically all of the most vulnerable groups have received a first dose of the vaccine. Vaccination is reaching an additional 8% of the population per month.

Together with the 10% – 20% (roughly) of the population who have had the disease, we are close to herd immunity.

So what is the worst case?

The current resurgence in cases appears be localised in communities with low vaccination rates, having been seeded by people returning from India.

The public health response – local mass vaccination and surge testing – seems appropriate.

The likely worst outcome with 3000 cases/day amongst the least vulnerable groups – aged under 30 – is that deaths might amount to 0.1% of cases, or 3/day. Tragic as each death is, in the context of this pandemic, this seems to me “acceptable”.

Cases nationally are rising slowly: by a factor 10 in about 150 days – or 5 months.

However vaccinations are proceeding at a rate of about 8% per month, so in 5 months the entire population will be vaccinated with at least a first dose.

My guess – and it is just a guess – is that with continued attention to local outbreaks, and continued progress with vaccination, we will avoid any significant third wave.

So returning to the key question:

  • Is there the potential for the pandemic to expand into the general population and kill hundreds of thousands of people?

As far as I can tell, the answer is still ‘No’. Probably.

The Last Artifact – At Last!

May 20, 2021

Friends, at last a film to which I made a minor contribution – The Last Artifact – is available in full online!

It’s the story of the redefinition of the kilogram which took place on this day back in May 2019.

The director Ed Watkins and his team carried out interviews at NPL back in August 2017 (link) and then headed off on a globe-trotting tour of National Metrology Laboratories.

Excerpts from the film were released last year (link), but somehow the entire film was unavailable – until now!

So set aside 90 minutes or so, put it onto as big a screen as you can manage, and relax as film-making professionals explain what it was all about!


The Last Artifact

Gas Boilers versus Heat pumps

May 18, 2021

Click for a larger version. A recent quote for gas and electricity from Octopus Energy. The electricity is six times more expensive than gas.

We are receiving strong messages from the Government and the International Energy Agency telling us that we must stop installing new gas boilers in just a year or two.

And I myself will be getting rid of mine within the month, replacing it with an Air Source Heat Pump (ASHP).

But when a friend told me his gas boiler was failing, and asked for my advice, I paused.

Then after considering things carefully, I recommended he get another gas boiler rather than install an ASHP.

Why? It’s the cost, stupid!

Air Source Heat Pumps:

  • cost more to buy than a gas boiler,
  • cost more to install than a gas boiler,
  • cost more to run than a gas boiler.

I am prepared to spend my own money on this type of project because I am – slightly neurotically – intensely focused on reducing my carbon dioxide emissions.

But I could not in all conscience recommend it to someone else.

More to Buy

Using the services of Messrs. Google, Google and Google I find that:

And this does not even touch upon the costs of installing a domestic hot water tank if one is not already installed.

More to Install

Having experienced this, please accept my word that the installation costs of an ASHP exceed those of replacing an existing boiler by a large factor – probably less than 10.

More to Run

I have a particularly bad tariff from EDF,  so I got a quote from Octopus Energy, a popular supplier at the moment,

They offered me the following rates: 19.1 p/kWh for electricity and 3.2 p/kWh for gas.

Using an ASHP my friend would be likely to generate around 3 units of heat for every 1 unit of electricity he used: a so-called Coefficient of Performance (COP) of 3.

But electricity costs 19.1/3.2 = 6.0 times as much as gas. So heating his house would cost twice as much!

More to buy, install and run and they don’t work as well!

Without reducing the heating demand within a house – by insulation – it is quite possible that my friend would not be able to heat his house at all with an ASHP!

Radiator output is specified assuming that water flowing through the radiators is 50 °C warmer than the room. For rooms at 20 °C, this implies water flowing at 70 °C.

A gas boiler has no problem with this, but an ASHP can normally only heat water to 55 °C i.e. the radiators would be just 35 °C above room temperature.

As this document explains, the heating output would be reduced (de-rated to use the correct terminology) to just 63% of its output with 70 °C flow.

What would you do?

Now consider that my friend is not – as you probably imagined – a member of the global elite, a metropolitan intellectual with a comfortable income and savings. I have friends outside that circle too.

Imagine perhaps that my friend, was elderly and on a limited pension.

Or imagine that they were frail or confused?

Or imagine perhaps that they had small children and were on a tight budget.

Or imagine that they were just hard up.

Could you in all honesty have recommended anything different? 

These problems are well known (BBC story) but until this cost landscape changes the UK doesn’t stand a chance of reaching net-zero.



May 18, 2021

When I used to work at NPL, I remember being really impressed by the work of my colleague Andrew Levick.

Magnetic Resonance Imaging (MRI) machines are able to image many physical details inside human bodies.

One their little-used features is that they can also be used to image the variation of temperatures throughout bodies.

Andrew was working on a temperature standard that could be used to calibrate temperature measurements in MRI imaging machines.

This would be a device placed inside the imager that could create a volume of imageable organic material at a known temperature. But one of the difficulties was that there must be no metal parts – so it could not contain any heaters or conventional temperature sensors.

So Andrew had the idea of using a vessel containing a supercooled organic liquid. If the transition to a solid was initiated, then the released latent heat – the recalescence –  would warm the liquid back to the melting/freezing temperature, creating a region of liquid-solid mixture at a stable, known and reproducible temperature, ideal for calibrating MRI machines.


Early on in the research he was doing experiments on the different ways in which the liquid crystallised.

He was supercooling organic liquids and then seeding the solidification, and making videos of the solidification process using a thermal imaging camera.

I thought the results were beautiful and put them to music, and that’s what the movie is.

The music is Bach’s Jesu Joy of Man’s Desiring arranged for 12-string guitar by the inimitable Leo Kottke.

If you are interested You Tube has many versions and lessons!

That’s all. I hope you enjoy it.

COVID-19:Still Looking good, but stiiiiillll not over

May 17, 2021

Click for a larger image. Logarithmic graph showing positive caseshospital admissions and deaths since the start of the pandemic. The blue arrows show the dates of ‘opening’ events. See text for further details

Friends, so here we are, May 17th 2021, and I can finally resume the natural pastime of old men: sitting in cafes.

Obviously, matters pandemical are not ideal, but they are in my estimation looking good.

To explain my uncharacteristic positivity, allow me to remind you how this summer differs from last.

I know what happened last summer…

As we look at the figure above covering positive cases, hospital admissions and deaths across the pandemic, we see that the second wave began in July 2020 – when cases began to rise. This was before the end of the first wave as judged by the minimum in the rate of deaths.

And after cases started to rise hospital admissions and deaths both fell for a further two months!

So now we should focus our attention on cases for first signs of a problem.

However what matters is:

  • not the absolute number of cases,
  • not the population prevalence of cases
  • not even the rate of change of cases

What matters is this:

  • Is there the potential for the pandemic to expand into the general population and kill hundreds of thousands of people?

Last summer the answer was definitely ‘Yes’.

This summer the answer is probably ‘No’.

Why? Because 55% of the entire population, including practically all of the most vulnerable groups have received a first dose of the vaccine.

Together with the 10% (roughly) of the population who have had the disease, we are close to herd immunity.

Herd Immunity is not an on-off thing.

As the prevalence of immune people approaches a critical prevalence – probably around 66% for the coronavirus – the speed of viral transmission slows as the virus finds it increasingly difficult to move from an infected individual to a vulnerable individual.

Once the prevalence of immune people has passed the critical prevalence – chains of viral transmission decay with increasing rapidity as immunity prevalence approaches 100%. For any physicists reading – it’s a continuous phase transition.


Careful readers may have noticed that I slipped in an italicised  ‘probably’ a few paragraphs back. Things could still go wrong.

Most notably, one variant of the virus or another could acquire the ability to escape the immunising effects of the vaccine.

This is possible, but it is – as far as I can tell – not a very likely outcome.

What will happen next?

Click for a larger image. Logarithmic graph showing positive cases, since the start of 2021. The blue arrows show the dates of ‘opening’ events. See text for further details

The figure above shows that the ‘openings’ (shown as blue arrows) are having an effect, because after each ‘opening’ step, the rate at which cases are falling slows down, because viral transmission chains can spread further in the more liberal environments.

And since the start of May, the daily rate of positive cases has been rising slowly.

So after today, with one has to expect that the daily rate of positive cases will rise faster, and that numbers will probably not decline for several weeks or months.

Also, the potential for tourists and returning tourists to re-seed infections of different variants around the country is a concern.

And many people will be distressed by this rise in cases and the (probably) ineffective controls at the borders.

But, as I said above, in my opinion the key question is:

  • Is there the potential for the pandemic to expand into the general population and kill hundreds of thousands of people?

And as far as I can tell, the answer is ‘No’. Probably.

Air Conditioning versus Air Source Heat Pump

May 15, 2021

Click for a larger version. Similarities and differences in how an air source heat pump (ASHP) or an air conditioning (AC) system warms a home. All the components inside the dotted green line are contained in the external units shown. A key design difference is whether or not the working fluid is completely contained in the external unit. See text for more details.

Regular readers will probably be aware that – having reduced the heating demand in my house – my plan is to switch away from gas heating and install an electrically-powered air source heat pump to heat the house and provide domestic hot water.

But next week I am also installing air conditioning, something which is traditionally not thought of as very ‘green’. What’s going on?

Why Air Conditioning?

I have two reasons.

My first reason is that, as you may have heard, the whole world is warming up! Last year it reached 38 °C in Teddington and was unbearably hot for a week. I never want to experience that again.

During the summer the air conditioning will provide cooling. But assuming the heating comes with good weather, the air conditioning will be totally solar powered, and so it will not give rise to any CO2 emissions to make matters worse!

My second reason is that in the right circumstances, air conditioning is a very efficient way to heat a house. That’s what this article is about.

Heat Pumps

Air Conditioners (AC) and Air Source Heat Pumps (ASHP) are both types of heat pumps.

In scientific parlance, a heat pump is any machine that moves heat from colder temperatures to higher temperatures at the expense of mechanical work.

Note: to distinguish between the general scientific idea of a heat pump, and the practical implementation in an air source heat pump, I will use abbreviation ASHP when talking about the practical device.

The general idea of a heat pump is illustrated in the conceptual schematic below.

As shown, the pump uses 1 unit of mechanical energy to extract two units of heat energy from air at (say) 5 °C and expel all 3 units of energy (1 mechanical and 2 thermal) as heat into hot water at (say) 55 °C.

Click for a larger version. Traditional representation of the operation of heat pump.

Heat pumps can seem miraculous, but like all good miracles, they are really just applied science and engineering.

A heat pump is characterised using two parameters: COP and ΔT.

  • A heat pump which delivers 3 units of heat for 1 unit of work is said to have a coefficient of performance (COP) of 3.
  • The temperature difference between the hot and cold ends of the heat pump is usually called ‘Delta T’ or ΔT.

Obviously engineers would like to build heat pumps with high COPs, and big ΔTs and they have used all kinds of ingenious techniques to achieve this.

But it turns out that heat pumps only operate with high COPs when the ΔT is small and when the heating power is low. There are two reasons.

  • Firstly, the laws of thermodynamic set some absolute limits on the COP achievable for a given ΔT.
    • Most practical heat pumps don’t come close to this thermodynamic limit for a variety of mundane reasons.
    • The maximum COP for moving heat from 5 °C to 55 °C is 6.6.
    • The maximum COP for moving heat from 5 °C to 20 °C is 19.5.
  • Secondly, in order to heat a room to (say) 20 °C, the hot end of the heat pump needs to be hotter than 20 °C.
    • Typically the hot end of the heat pump must be 5 °C to 10 °C warmer than the room in order that heat will flow out of the heat pump.
    • Additionally the cold end of the heat pump must be 5 °C to 10 °C colder than the external air in order that heat will flow into the heat pump.
    • The interfaces between the ends of the pump and the environment are called heat exchangers and designing ‘good’ heat exchangers is tricky.
    • A ‘good’ heat exchanger is one that allows high heat flows for small temperature differences.

So now we have seen how heat pumps are characterised, let’s see how heat pumps are used domestically.

Air Source Heat Pump (ASHP) versus Air Conditioner (AC)

The schematic diagrams  below show how a house is heated by an ASHP and an AC system. Both systems operate using a working fluid such as butane, which is ingeniously compressed and expanded. The details of this process are not the topic of this article so here I am glossing over the fascinating details of the device’s operation. Sorry.

Click for a larger version. How an air source heat pump (ASHP) warms a home. All the components inside the dotted green line are contained in the external unit shown. A key design feature is that the working fluid is completely contained in the external unit and heat is transferred to the central heating water by a heat exchanger.

Click for a larger version. How an air conditioner (AC) warms a home. All the components inside the dotted green lines are contained in either the external unit or the fan coil unit shown. A key feature is that the working fluid itself flows into the fan coil unit and heats the air directly.

We can compare the operation of the two systems in the table below.

Air Conditioner Air Source Heat Pump
Air at (say) 5 °C is blown over a heat exchanger and evaporates the working fluid.


The same.
The working fluid is then compressed – that’s the bit where the work is done – and liquefies, releasing the captured heat.


The same.
The hot working fluid – now at ~30 °C then flows through a pipe to an indoor heat exchanger (fan coil unit) where air is blown over the pipe and heated to 20 °C. The hot working fluid – now at ~60 °C then flows through a heat exchanger and transfers the heat to water in my central heating system at ~55 °C
No corresponding step  

The 55 °C water then flows through a radiator in my room, heating the room by radiation and by convective heat transfer to air at ~20 °C.

Looking closely at the figures and table above, one can see that the operation of the ASHP and the AC system are broadly similar.

However the ASHP has to operate with a bigger ΔT (~55 °C versus ~25 °C) than the AC system, and also has to transfer heat through an extra heat exchanger.

Both these factors degrade the achievable COP and so for my application, the specified COP for an ASHP is just over 3, but for the AC system, it is just over 5.

In my well-insulated house, when the external temperature is 5 °C, I require typically 36 kWh per day of heating, equivalent to 1.7 kW continuous heating. I can achieve this in several ways:

  • Using gas I must burn ~40 kWh of gas at 90% efficiency costing 40 x 3p (£1.20) and emitting 40 x 200 g = 8 kgCO2
  • Using an ASHP with a COP of 3, I must use ~36 kWh/3 = 12 kWh of electricity costing 12 x 25p (£3.00) and emitting 12 x 200 g = 2.4 kgCO2
  • Using an AC system with a COP of 5, I must use ~36 kWh/5 = 7.2 kWh of electricity costing 7.2 x 25p (£1.80) and emitting 7.2 x 200 g = 1.4 kgCO2
  • Using a domestic battery and buying the electricity at night for 8p/kWh, I can reduce the cost of using an ASHP or AC system by a factor of 3 to £1.00/day or £0.60/day respectively.

[Note: In these calculations I have assumed that the carbon dioxide emissions per kWh are same for both gas and UK electricity (200 gCO2/kWh) which is roughly correct for 2021]

So using an AC system I should be able to achieve domestic heating with lower carbon dioxide emissions than an ASHP.

My plan

In my case I need to heat water for my home to 55 °C for use in showers and basins. So I need an ASHP for that. And since I already have radiators in every room, hooking up the ASHP to the radiator circuits is smart double use.

The AC system I am having installed will have 1 external unit and 2 internal ‘fan coil units’. One unit will be in my bedroom (a sheer indulgence) and the other will be high up on the stairs, allowing air to be either blown down to the ground floor where I hope it will circulate, or blown towards the bedrooms.

My hope is that, when used together, the AC system (COP~5) will reduce the heating output required from the radiators so that I can reduce the flow temperature of the water from 55 °C to perhaps 40 °C. This reduces their heat output, but increase the COP of the ASHP from 3 to perhaps 4.

The main difficulty that I foresee is the extent to which the AC heating will actually permeate through the house and so reduce the amount of heating required by the ASHP.

So I am not sure how much heating will be required by the ASHP acting through the radiators, and whether the radiators will work at low flow temperatures. It is possible I might need to replace a few radiators with ones which work better at low temperatures.

It is not at all obvious that this plan will actually work at all – but I think it is worth a try.


The air conditioning I am having installed is a Daikin 2MXM40 multi-split outdoor unit with two FTXM25 indoor air units. (Brochure)

The model of heat pump I will have installed is a Vaillant Arotherm plus 5 kW. It can supply up 5 kW of heating at 55 °C with a COP of 3  – i.e. it will use just 1.6 kW of electrical power to do that – and heat water to 55 °C. Water storage will be a 200 litre Unistor cylinder. A brochure with technical details can be found here, and a dramatic video showing the kit is linked at the end of this article.

When I have come to terms with how much money I am spending on this, I will share that information. But at the moment it hurts to think about it!

Anyway: the adventure begins next week!


Sometimes things take unfathomably longer than one imagines possible.

May 8, 2021

Friends, in roughly 1999 the drawer in which we keep our kitchen implements – ladles, wooden spoons and similar – developed a fault.

The ball race that enables the draw to slide in-and-out with ease developed a fault. The steel balls spilled out making it hard to push the drawer in and out. It grated every time we used the drawer.

I did look for replacement fittings in DIY shops but I could not find any to match the drawers we had.

And so the drawer irritated every member of our household several times each day for – roughly speaking – the last 22 years

Meanwhile, the children grew into young men, and I aged and retired.

Today, as my wife and I discussed kitchen refurbishments that might be required after we remove our gas boiler, my wife remembered that, 24 years previously in 1996, the previous owners had left us a duplicate drawer mechanism.

It then took 20 minutes to replace the mechanism, and now the drawer glides in and out exactly like it should.

Sometimes, things take unfathomably longer than one imagines possible.

ICE vs BEV vs FC

May 8, 2021

Friends, forgive my titular obscurantism. This is an article about how to compare the efficiencies and carbon emissions of cars of different types:

  • ICE = Internal Combustion Engine i.e. petrol and diesel cars
  • BEV = Battery Electric Vehicles
  • FC = Fuel Cell cars

A cloud over Teddington!

While relaxing at de Podesta Towers yesterday, a momentary cloud of worry passed through the otherwise blissfully blue sky of my retirement. I thought: how do you compare the efficiencies of these different classes of vehicles?

  • ICEs specify miles per gallon or litres of fuel per 100 km.
  • BEVs specify how many kilowatt hours (kWh) of energy are required to travel 100 km.
  • FCs specify how many kilograms of hydrogen (kgH2) are required to travel 100 km.

Comparing CO2 emissions

One way to compare these disparate types of vehicles is to compare their carbon dioxide emissions.

For all vehicles there are both proximate emissions which occur as the vehicle is driven, and source emissions associated with the charging – in the general sense – of the vehicle.

This categorisation is sometimes succinctly summarised as

  • well-to-tank emissions,
  • tank-to-wheels emissions,

which together add up to make well-to-wheels emissions.

  • For ICEs there are both well-to-tank emissions and tank-to-wheels emissions.
  • For BEVs ‘well-to-tank’ emissions occur at the power stations used to generate the electricity that charged the battery. There are no proximate or tank-to-wheels emissions.
  • For FCs, ‘well-to-tank’ emissions occur at the power stations used to generate the electricity used to separate and compress the hydrogen gas. There are no proximate or tank-to-wheels emissions.

For ICEs, the CO2 emissions per kilometre are a multiplier of the fuel efficiency, with different factors for petrol or diesel, plus a factor for the emissions associated with the preparation of the fuel.

  • Factor for creation of the fuel
  • Vehicle specification in Litres per 100 km
  • Factor for fuel type: petrol or diesel

For BEVs the the CO2 emissions per kilometre are the product of the three factors:

  • CO2 per kWh of the charging electricity – the so-called carbon intensity of the electricity.
  • The efficiency of the charging.
  • Vehicle efficiency specified as kWh per 100 km

For FCs the the CO2 emissions per kilometre are the product of the two factors:

  • CO2 per kWh of the electricity used in the electrolysis and compression of the H2 gas.
  • Vehicle efficiency specified as kgH2 used per 100 km

So lets look at some examples.

Toyota Mirai FC 

  • Specifications suggest an average of 0.75 kgH2/100 km
  • Wikipedia suggests Electrolysis at 80% efficiency and compression together take 65 kWh/kgH2
  • Current UK carbon intensity is 200g/kWh which is expected to fall to 100g/kWh in 2030.
  • Multiplying we find CO2/km = 0.75 [kgH2/100 km] x 65 [kWh/kgH2] = 49 kWh/100 km
  • Multiplying by the carbon intensity x 200 [g/kWh] = 97 gCO2/km in 2021 falling to 49 gCO2/km in 2030

Perhaps you can see why my brow furrowed over trying to figure this out!

Tesla Model 3 BEV

  • Specifications suggest 26 kWh/100 km
  • Charging efficiency is typically 90% i.e. if we use 28.6 kW of grid electricity to charge the car, 90% of that (26 kWh) will be stored in the battery.
  • Multiplying by the carbon intensity of 200 [g/kWh] = 57 gCO2/km in 2021 falling to 28 gCO2/km in 2030

It is hard to pick a single ICE car comparable with these rather premium BEVs and FCs. I have looked through the Mercedes A-class brochure which states that under the Worldwide Harmonized Light Vehicles Test Procedure (WLTP) the proximate CO2 emissions are in the range

  • 130 to 150 gCO2/km
  • This corresponds to about 6 litres/100 km or 47 miles per UK gallon
  • The above figures are only tank-to-wheels emissions. The well-to-tank emissions amount to roughly 36 gCO2/km (link)

Click for a larger version. Summary of the amount of carbon dioxide emitted per km of travel for a fuel call car (Toyota Mirai), a battery electric vehicle (Tesla Model 3), or a premium internal combustion engined car (Mercedes A Class). In the UK grid electricity is expected to have a lower carbon intensity by 2030 which should reduce the emissions associated with BEV and FC cars. This chart ignores any embodied carbon dioxide in the construction of the vehicles.

So in terms of carbon dioxide emissions, a BEV is likely to be better than an FC car and both are much better than comparable ICE cars.


The reason that the FC car is so much poorer than the BEV is because of the complexities of first obtaining hydrogen, compressing it (link), and then converting the chemical energy back to electricity in the fuel cell.

The advantages of fuel cell cars over BEVs (faster re-filling and longer ranges) are slowly being eroded by advances in battery technology. And  given the paucity of hydrogen filling stations, I think FC cars will prove to be a historical dead end.

BEV vs ICE: Efficiency

The key to the success of ICEs has been the astonishing energy density of their fuels.

Click for a larger version. This graphic (modified Wikipedia graphic) shows the energy density (kWh/litre) versus specific energy (kWh/kg) for various fuels. Strikingly, batteries have very low energy density and specific energy than ICE fuels. Note also the very high specific energy density of hydrogen (per unit mass), but the the very low energy density (per unit volume).

As the chart above shows the energy density of either petrol or diesel – whether expressed per kilogram or per litre – is way more than that of lithium ion batteries used in BEVs.

If we average gasoline (12.9 kWh/kg, 9.5 kWh/l) and diesel (12.7 kWh/kg, 10,7 kWh/l) we get a rough figure for liquid fuels of 12.8 kWh/kg and 10.1 kWh/l.

In contrast the figures for a lithium ion battery are in the range 0.1 – 0.24 kWh/kg and 0.25–0.73 kWh/l, smaller than liquid fuel by factors of at least 53 for per unit mass and 14 per unit volume.

It might seem that there would be no way that batteries could ever compete. But in fact ICEs are profilgate with their energy use.

ICEs only extract about 35% of this chemical energy as mechanical energy and then frictional losses in the engine and drivetrain reduce this to about 20%. So that makes the advantage factors of roughly 10 per unit mass and 2.8 per unit volume.

In contrast, after taking account of regenerative braking, BEVs can convert about 90% of their stored energy to motive power.

This still leaves ICEs with an advantage and to compete BEVs end up with a heavy battery which takes a large volume. And it can’t quite be made big enough to challenge the range of ICEs.

But it seems that BEVs have become ‘good enough’.

ICEs are very highly evolved with more than 100 years of continuous development, but lithium ion batteries are still relatively new and are likely to continue to get incrementally better and cheaper. And as the carbon intensity of the grid reduces over the coming years the cars will become greener still.

Blue sky 

And thus the cloud passed, and the sky cleared, and life at de Podesta Towers returned to its previous untroubled pace.


A Bright Future?

May 3, 2021

Click for a larger Image of the book covers.

Friends, a few weeks ago I reviewed two books about our collective energy future: Decarbonising Electricity Made Simple and Taming the Sun.

Summarising heavily

  • Decarbonising Electricity Made Simple
    • A detailed look at how the UK can attain very low carbon intensity electricity – perhaps less than 50 gCO2/kWh in 2030 – by just doing more of what we are already doing
  • Taming the Sun
    • A look at the role of solar power globally, addressing the fact that every ‘market’ will reach the point where super-cheap solar electricity is so abundant that nothing else will compete – during the day. But because of the lack of storage, solar will never be a sufficient answer.

This weekend I read A Bright Future by Joshua Goldstein and Staffan Qvist. The strapline is “How some countries have solved climate change and the rest can follow”.

Their answer is simple:

Start building nuclear power stations now and don’t stop for the next 50 years.

The authors point out

  • The astonishing safety record of nuclear power which is in direct contrast to the coal industry in which thousands of people die annually – and which releases more radioactivity and toxic compounds than nuclear power stations ever have.
  • The enormity of the climate peril into which we are collectively entering.
  • The scale of output which is achievable with nuclear power stations – generating capacity can potentially be added much faster than renewable generation.
  • The reliability of nuclear power and they contrast this with the variability of wind and solar generation.

And while I could disagree with the authors on several details, the basic correctness of their assertion is undeniable.

  • In the UK if we had one or two more nuclear power stations our climate goals would be dramatically easier to meet.
  • Globally, there are currently 450 nuclear power stations undramatically providing emission-free electricity. If there were 10 times this number our collective climate emergency would be easier to address.

And while it would be an understatement to say that nuclear power is without controversy – it seems to me that a massive investment in nuclear power plants worldwide would be a good move.

But it is not going to happen.

I am sure the authors know that their arguments are futile.

Although I personally would welcome a nuclear power plant in Teddington, most people would not.

Similarly most people in Anytown, Anywhere would not welcome a nuclear power station.

But as the authors point out – correctly – there is no renewable energy technology that match the characteristics of nuclear power.

And we need every possible low-carbon generating source to address humanity’s needs

Despite the authors’ positivity, I have never felt more depressed after reading a book than this.


Retirement: One year on…

May 2, 2021

Click for a larger version. Clouds and blossoms. Sometimes I think to myself, it’s a wonderful world…

Friends, it is now one year (and a day or so) since I retired from NPL. And it’s been an… interesting year.

Please allow me a few moments of reflection.


It took months for the poison that flows through that institution to leave my system.

I wrote about it a bit, (here and here and here and here) but writing about the inanity of management systems and the poisonous individuals that colonise them is such a negative activity I felt obliged to just leave that all behind.

I did worry that I might miss the physics, but in fact I am doing much more physics now at home than I was at NPL.

In the same way that Neo could read the code in The Matrix, so I see the world. As I walk into Teddington for a cup of coffee each morning, I see in the blossoms and the clouds, multiple unfolding physical principles creating a world of beauty and wonder.

I literally catch my breath at the intricate complexity of it every day.


I have written a lot about the pandemic in the last year, but as I reflect on the year, I am genuinely lost for words.

Some of my articles on the subject now seem especially prescient. See for example this 1st January 2021 article which predicted the daily death toll in May 2021 would be roughly 75 people per day.

Click for larger view. Prediction of the daily death toll on 1st May 2021 – it’s a little pessimistic but not far off given that the UK’s vaccine rollout had barely begun.

And recent news stories that our Prime Minister said he would rather see “bodies piled high than have another lock down” finally explains why we did not lock down in October 2020. Read my article from 26th September 2020 here.

If these reports are correct, then the number of deaths personally ascribable to the Prime Minister’s actions is now way more than the 19,000 I estimated previously.

While I myself would not want to occupy such a job, I can’t imagine the depravity of someone who could make, and then fail to acknowledge such a catastrophic error.

Carbon dioxide

Retirement (and the tax-free lump sum from my pension) has allowed me to make headway on reducing my household’s carbon dioxide emissions.

The house now has triple-glazing and external wall insulation that have reduced the heating demand (and CO2 emissions) by more than 50%.

In the next few months I will install a heat pump and air conditioning which should reduce CO2 emissions by a further factor 4±1.

And our solar panel/battery combination will keep us more-or-less off-grid all summer.

But as I seek to become a genuine Carbonaut, I am faced with some terrible questions:

  • Can I live a life without milk in my tea?
  • Is a life without bacon every once in a while a life worth living?
  • And cheese? Could a life without 12-month old Davidstowe cheddar genuinely be called ‘living’?

I am writing in jest, but the questions are deadly serious.

In the coming year I will write about this more, but already there are tonnes of carbon dioxide which have not been emitted due to my actions.

By my anticipated date of death in 2040, I hope to have avoided at least 60 tonnes of carbon dioxide emissions.


I am feeling my age. I am in good health, but at 61 I am realistically in the last ‘third’ of my life.

And before the ravages of age slow me down, I realise I have a window of unknown length in which – perhaps for the first time in my life – I am genuinely free to do whatever I want to do.

What an exhilarating and terrifying challenge.

Thank you

And to all those people – genuine friends – who have communicated their support throughout this year – thank you.

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