Archive for August, 2022

Non, Je ne regrette rien: update

August 26, 2022

Friends, last week I wrote about my embarrassingly low energy bills, and compared them with the shockingly high energy bills I would be facing if I had spent my pension lump sum on a world cruise and a car: Non, je ne regrette rien.

But after writing that article, I quickly realised that it needed updating.

  • Firstly,  although I have agreed an electricity contract for the year to September 2023, I underestimated how much I would have had to pay for gas. These new ‘energy cap’ prices were estimated early this week and confirmed today.

Energy Cap Prices (Source: Cornwall Insight)

  • Secondly, several people were puzzled about how I did the calculations for both my actual gas and electricity use, and the counterfactual estimate.

In this article I hope to clarify both of these issues.

Modelling Consumption Patterns

Since November 2018 I have read my gas and electricity meters each Saturday morning and so I know my weekly gas and electricity consumption for the last 4 years or so.

This allowed me to get a characteristic consumption pattern from June 2019 to May 2020 before the External Wall Insulation, Solar Panels, Battery and Air Source Heat Pump were installed.

To model the alternative counterfactual reality I have imagined that the 2019/20 pattern of consumption simply repeated indefinitely. I could then compare that with what has actually happened.

Modelling Costs

I have then assumed different costs for different periods as summarised in the table below.

Click for larger version. These are the prices per unit and daily charges that I have assumed. See text for details.

Working out these costs has been tricky.

Historically, I don’t recall the price of either electricity or gas changing much for the many years we have been in the house. It was not until EDF increased the price of cheap electricity by 73% that I thought to look elsewhere, and I switched to Octopus energy a year ago in August 2021.

I signed a fixed-price 1 year deal for electricity that gave me 4 hours of electricity at 5p/kWh and a peak rate of 16p/kWh.

I recently renewed that deal at increased rates of 7.5p/kWh off-peak and 46p/kWh peak.

The gas charge changes with the market and has increased from around 3p/kWh to around 7.3p/kWh but I expect that to increase

Looking ahead I have assumed that in a year’s time I will renew the electricity contract with a similar deal that will be more expensive.

Regarding future gas prices, I have assumed ‘Energy Price Cap Prices‘ for October 2022 that have recently been published. I have made conservative guesses for how these prices will vary in future – but I expect them to increase throughout the whole of 2023.

I have not included any government interventions.

Actual Costs 

The graphs below show my actual electricity and gas costs over the last three and half years, and my projected costs for the next year and a half.

Click on image for a larger version. My weekly gas and electricity costs for the last three and a half years. Also shown in red is my projection for my bills based on currently signed contracts. The figures in boxes show yearly costs. Note the vertical scale is £120/week – much larger than the scale I used in my previous article.

 

Prior to 2021 electricity usage was pretty constant at around 10 kWh/day costing around £15/week.

But after the installation of solar panels and a battery, the pattern of consumption of grid electricity changed significantly, with the house being almost off-grid for three to four months a year, and with electricity consumption usage peaking in winter.

The winter costs of this are low – peaking at £15/week – because we buy most of our electricity ‘off-peak’ and store it in the battery and then run the household from the battery for most of the next day.

Looking ahead, (red) if I assume that the coming winter is similar to last winter, then these projected costs will increase in the year ahead.

Regarding gas usage, one can see the winter consumption declining year-on-year as a result of first triple-glazing and then External Wall Insulation.

And then in 2021 gas usage flatlines after the installation of the Air Source Heat Pump. The residual gas usage is just for cooking – roughly 1 kWh/day – which I hope to stop in the next few months by switching to an induction hob – that’s why the projected gas costs for 2023 are zero.

If I had done nothing 

The graphs below show my estimates for gas and electricity costs assuming I had not installed External Wall Insulation, Solar PV, a battery and an Air Source Heat Pump.

Click on image for a larger version. Estimated weekly gas and electricity costs for the last three and a half years assuming that I had not installed External Wall Insulation, Solar PV, a battery and an Air Source Heat Pump. Also shown in red is my projection for the coming year. The figures in boxes show yearly costs. Notice that the vertical scale of this graph is £120/week – much larger than the scale I used in my previous article.

The same patterns of electricity and gas usage are repeated year after year.

The effect of forthcoming price rises for 2023 are estimates based on Octopus Energy prices.

I have assumed that the electricity price is fixed and so not affected by energy price cap rises. I have not assumed any increase in September 2023 after the fixed deal comes to an end, but there will probably be a rise of some kind.

However gas costs are extremely high and subject to whatever the market demands.

The small reduction in 2023 electricity costs (£1,447) versus 2022 (£1,475)  is because the calculation is based on weekly consumption and one year has a nominal 53 weeks versus a nominal 52 in the other year.

Comparison

Finally, the graph below compares the actual bills I have paid with my estimate for what I would have paid if I had not improved the house. The graph combines gas and electricity costs.

Click on image for a larger version. Comparison of the actual annual combined gas and electricity bills with the counterfactual scenario in which I had not installed External Wall Insulation, Solar PV, a battery and an Air Source Heat Pump. Figures for 2023 are – obviously – projections. Notice that the project costs that I would have incurred are much larger than I estimated in my previous article.

I have stared at this graph over and over and thought: Michael: you have made a mistake. And that may be true. But if I have, I can’t find it.

The models have many assumptions and some may be not quite right. But I don’t think the figures are wrong by more than about 10%.

Payback Calculation

The difference between the two realities in the graph above is – in round terms – currently around £2,000/year and will likely grow to around £4,000 year in 2023 – much larger than I calculated in my previous article.

The difference in expenditure between the two realities is External Wall Insulation (£27k), Solar PV(£4k), a battery (£10k) and an Air Source Heat Pump (£8k) which comes to around £50k.

So the return on my investment is currently 4% and might rise to 8% – which is much better (for me) than I had thought.

Something must be done

The impact of forthcoming price rises is hard to comprehend. The consequences for people with low incomes are dire – and the consequences for hospitals, schools, libraries and business are also frightening.

Clearly ‘something must be done, but I have no confidence that any measures will be well-targeted. Obviously giving people like me more money is bonkers!

But whatever financial steps are taken, I hope the that one lesson will be learned: we need a renewable energy initiative on a wartime scale to build more wind and solar farms as rapidly as possible. If done at scale this could transform our energy infrastructure within a decade.

Non, Je ne regrette rien

August 18, 2022

=============================
UPDATE:

I have recalculated some of these costs using the latest ‘price cap’ figures.
Please see the next article for details.

=============================

Friends, one of the questions I am most often asked about the works I have had done on my house concerns the “Return on Investment” or “Payback Time”.

I hate this question for three quite distinct reasons.

Reason 1

Firstly, I hate it because it indicates that the questioner has misunderstood the nature of work I have undertaken.

For example, if someone has a leaking sewer repaired one doesn’t ask them about the “payback time”. Why? Because it’s just wrong to leak raw sewage into a public area. The repair is necessary.

That’s how I feel about putting carbon dioxide into the atmosphere when one has an alternative. It is similarly disgusting, except that carbon dioxide is dramatically more damaging in its effects than sewage.

Reason 2

Secondly, I hate it because the answer is quite difficult to work out!

I have never paid much attention to the magnitude of electricity or gas bills – I could afford them and I had no alternative but to pay!

I am conscious that the bills now are much smaller than they used to be, but it’s quite a lot of work to figure out exactly how much smaller. But that is what I have have done in this article.

Method

Since November 2018 I have read my gas and electricity meters each Saturday morning and so I know my weekly gas and electricity consumption for the last 4 years or so.

I have then trawled back through my records to find historical standing charges and unit rates, and re-constructed the actual weekly costs.

I have then modelled what the weekly costs would have been if we had not installed External Wall Insulation, Solar Panels, a Battery and an Air Source Heat Pump.

To do this I took the consumption between mid-2019 to mid 2020 and assumed that these patterns of consumption were repeated in future years. I have then re-calculated the weekly and annual costs.

Actual Costs 

From this data I can calculate weekly costs for electricity and gas, and then by adding up the costs for 52 weeks I can get an estimate of the annual costs. The results for my actual electricity and gas costs are shown in the figures below.

Click on image for a larger version. My weekly gas and electricity costs for the last three and a half years. Also shown in red is my projection for my bills based on currently signed contracts. The figures in boxes show yearly costs.

=============================
UPDATE:

I have recalculated some of these costs using the latest ‘price cap’ figures.
Please see the next article for details.

=============================

These graphs tell quite a story.

Prior to 2021 electricity usage was pretty constant at around 10 kWh/day costing around £15/week.

But after the installation of solar panels and a battery, the pattern of consumption of grid electricity changed significantly, with the house being almost off-grid for three to four months a year, and with electricity consumption usage peaking in winter.

The winter costs of this are low – peaking at £15/week – because we buy most of our electricity ‘off-peak’ and store it in the battery and then run the household from the battery for most of the next day.

Looking ahead, (red) if I assume that the coming winter is similar to last winter, then these projected costs will increase in the year ahead.

Regarding gas usage, one can see the winter consumption declining year-on-year as a result of first triple-glazing and then External Wall Insulation.

And then in 2021 gas usage flatlines after the installation of the Air Source Heat Pump. The residual gas usage is just for cooking – roughly 1 kWh/day – which I hope to stop in the next few months by switching to an induction hob – that’s why the projected gas costs for 2023 are zero.

If I had done nothing

The graphs below show my estimates for gas and electricity costs assuming I had not installed External Wall Insulation, Solar PV, a battery and an Air Source Heat Pump.

Click on image for a larger version. Estimated weekly gas and electricity costs for the last three and a half years assuming that I had not installed External Wall Insulation, Solar PV, a battery and an Air Source Heat Pump. Also shown in red is my projection for the coming year. The figures in boxes show yearly costs. Notice that the vertical scale of this graph (£50/week) is different to the earlier graphs (£30/week).

=============================
UPDATE:

I have recalculated some of these costs using the latest ‘price cap’ figures.
Please see the next article for details.

=============================

The same patterns of electricity and gas usage are repeated year after year.

The effect of forthcoming price rises for 2023 are estimates based on Octopus Energy prices.

Comparison

Finally, the graph below compares the actual bills I have paid with my estimate for what I would have paid if I had not improved the house. The graph combines gas and electricity costs.

Click on image for a larger version. Comparison of the actual annual combined gas and electricity bills with the counterfactual scenario in which I had not installed External Wall Insulation, Solar PV, a battery and an Air Source Heat Pump. Figures for 2023 are – obviously – projections.

=============================
UPDATE:

I have recalculated some of these costs using the latest ‘price cap’ figures.
Please see the next article for details.

=============================

Payback Calculation

So now we come to the third reason that I dislike calculating ‘Payback’: it is not very large.

The difference between the two realities in the graph above is – in round terms – currently around £1,000/year and will likely grow to around £2,000 year in 2023.

But the difference in expenditure between the two realities is External Wall Insulation (£27k), Solar PV(£4k), a battery (£10k) and an Air Source Heat Pump (£8k) which comes to around £50k.

So the return on my investment is just 2% and might rise to 4% – with payback periods of many decades.

But on the other hand, most people in the UK are at least slightly anxious about energy bills in the coming years, but I am not in the least concerned. And surely that has to be worth something too.

I honestly don’t regret a penny of the expenditure.

=============================
UPDATE:

I have recalculated some of these costs using the latest ‘price cap’ figures.
Please see the next article for details.

=============================

How big is that fire?

August 12, 2022

Click on the image for a larger version. The picture is courtesy of Michael Newbry.

Friends, you may have noticed that we have recently entered a period of what is euphemistically called “enhanced risk of wildfires”.

And reports of wildfires from around the world include some truly apocalyptic images.

But many of these reports fail to communicate clearly one of the key metrics for fires: the size of the fire.

Some reports do mention the area affected in hectares (abbreviated as ha) or acres, but while I can just about grasp the meaning of one acre or one hectare – I struggle to appreciate the size of a fire covering, say, 6,000 hectares.

In order to convert these statistics to something meaningful, I work out the length of one side of a square with the same area.

Areas expressed in hectares.

A hectare is an area of 100 m x 100 m, or 0.1 km x 0.1 km so that there are 100 hectares in a square kilometre.

So to convert an area expressed in hectares to the side of the square of equal area one takes two steps.

  • First one takes the square root of the number of hectares.
  • One then divides by 10.

So for a fire with an area of 6,000 hectares the calculation looks like this:

  • √6,000 = 77.4
  • 77.4÷10 = 7.74 km

Since the original area was probably quite uncertain I would express this as being equivalent to a square with a side of 7 or 8 km.

Areas expressed in acres.

An acre is an area of 63.6 m x 6.36 m, or 0.64 km x 0.64 km so that there are roughly 2.5 acres in a hectare.

I can’t think of an easy way to get a good approximation for acres, but a bad approximation is better than no estimate at all. So I recommend, the following 3- or 4-step process:

  • First one divides the number of acres by 2
  • Then one takes the square root of half the number of acres.
  • One then divides by 10.
  • This answer will be about 10% too large.

So for a fire with an area of 15,000 acres the calculation looks like this:

  • 15,000÷2 = 7,500
  • √7,500 = 86.6
  • 86.6÷10 = 8.7 km

At this point one can either just bear in mind that this is a slight over-estimate, or correct by 10%. In this context, the overall uncertainty in the estimate means the last step is barely worthwhile.

How bad is the situation in Europe?

Click on Image for larger version. Estimates of the cumulative area (in hectares) burned by wildfires in each of the EU countries. The red bars show data for this year, and the blue bars show the average area burned between 2006 and 2021.

There is a wonderful website (linkwhich publishes estimates of wildfire prevalence in all the countries of the EU. One output of the website is shown above:

  • The blue bars shows the average area burned from 2006 to 2021
  • The red bars shows the average area burned so far this year.

You can immediately see that Spain, Romania, and France are having bad years for wildfires.

But how big an area is 244,924 hectares – the area burned in Spain so far? Using the rule above, one can see that it is an area equivalent to a square with a side of 50 km – roughly equivalent to (say) the area of Cheshire.

The area burned in France so far this year is 60,901 hectares. Using the rule above, one can see that it is an area equivalent to a square with a side of 25 km.

Michael, what was the point of this article?

When trying to visualise large areas expressed in hectares (or acres) I find it useful to work out the length of side of a square which would have the same area.

Tips for talking about Climate Change

August 8, 2022

Friends, isn’t it funny how sometimes you come across something at just the right time.

And since I have now become one of the ‘mad people’ you have to avoid eye-contact with as you walk past me in the street, I was happy to come upon these notes on Talking about Climate Change.

The notes were prepared by Richard Erskine as part of his work to raise consciousness of Climate Change in his local area. And the aim is to simply share some experiences and ideas about dealing with some of the most common situations one encounters.

  • You can find Richard’s blog here
  • You can follow him on Twitter here.
  • And you can download the notes as a pdf file here.

There is no point in me re-writing what Richard has written, but I thought I would just highlight some of the things the document covered that I felt were especially delightful. And the main feature I liked was the subtitle: you don’t have to be an expert.

On my first day out, I went equipped with a laptop loaded up with key graphs and animations. On contact with the public it immediately became obvious that these would not be needed. Talking to people in the street is absolutely NOT about lecturing clearly. And although Richard’s notes include some well-referenced ‘facts’, it is not about knowing the very latest facts.

The point of speaking to people in the street lies in the power of conversation, and the sheer pleasure humans take in ‘having a chat’. And meeting someone who is honest and straightforward and concerned, and not trying to sell anything is a pretty powerful event in most people’s days.

Contents

The document starts with some tips on starting conversations and some key Climate Facts. And then there are 10 questions which I have listed below together with my précis of the Richard’s more expansive comments.

Q1. CO2 is only a trace gas (0.04%) of the atmosphere. How can that affect the climate?

  • This drink contains 0.04% cyanide, would you like some?

Q2. CO2 is used by plants so isn’t more of it a good thing

  • Yes, CO2 is used by plants, but it also affects the climate, and many plants can’t cope with heat-induced stress. Look at the grass…

Q3. We’ve had heat waves before (1976) so what’s the fuss?

  • Heat waves have become more likely year-on-year, and this one has extended across much of the northern hemisphere. Reaching 40 °C in the UK would have been impossible without the underlying warming.

Q4. Aren’t Electric Vehicles (EVs) environmentally bad?

  • EVs are much better for the environment than petrol and diesel cars, but they are not perfect.

Q5. Don’t we need better public transport rather than Electric Vehicles (EVs)?

  • This is not an “either-or” decision.

Q6 What about China; our emissions are tiny compared to theirs?

  • China’s per person and historic emissions are much lower than ours, and they have become the factory of the world. Many items you own were probably made in China. 

Q7. The problem is population growth, so what can we do, and is it even worth trying?

  • This places the blame on the poorest people in the world who have NOT caused global warming. The problem is caused by our society’s consumption.

Q8. “What’s the big deal about the world warming by 1°C or 2°C?”

  • Like your body, the climate and ecology of the Earth are adapted to living at a particular temperature. Just like you, a rise in temperature of 2  °C or 3 °C is very serious.

Q9. Arctic methane and other tipping points have already been crossed, so we need to now just prepare for the worst, don’t we?

  • We don’t have runaway Climate Change yet – and we want to avoid that. So every action matters, every bit of warming matters, every choice matters.

Q10. I am not a denier, but we can’t afford to rush it; Net Zero by 2050 is just an arbitrary target, we need more time

  • It is not a choice between the economy and climate change measures. With consistent policies and investment in a low carbon economy, we can actually have a flourishing future, good for jobs and the planet.

Conclusion

Friends, Climate Change is real and terrifying, and it is easy to feel petrified into inaction. But having honest conversations with friends and acquaintances is a great way to clarify one’s own thoughts and to help others clarify theirs.

But our conversations have been seeded – deliberately I believe – with false narratives that

  • either deny that Climate Change exists,
  • or if it exists that it is important,
  • or if it is important that it’s our responsibility,
  • or if its our responsibility that we can afford to do anything
  • or if we do anything that it is just as bad as everything else

These notes might just help you to avoid getting sucked into those awful conversational paths.

Good Luck!

Sodium Acetate: Fun in the Kitchen with Phase Change Experiments

August 7, 2022

Friends, you may recall that in a recent article I wrote about Phase Change Materials (PCMs) used for thermal storage. I illustrated that article with a measurement of the temperature versus time as some molten candle wax solidified. I then tried to work out how much so-called ‘latent’ heat was released as the wax solidified.

A Twitter source then told me that the actual material used in commercial thermal storage units was sodium acetate trihydrate, and within 18 hours, a kilogram of the substance was delivered to my door.

NOTE: In this article I have used the term sodium acetate to mean sodium acetate trihydrate and in some locations it is abbreviated to SAT.

NOTE: Sodium acetate is pretty safe from a toxicity perspective: it’s an allowed food ingredient E262, but one needs to be careful not to scald oneself – or others – when handling the hot liquid.

So I began a series of experiments in which I made a great variety of very different, but similarly basic, errors. There really is nothing like a practical experiment for making one feel incompetent and stupid! Part of the problem was that I was trying to do other things at the same time as reading the temperature of the two samples (wax and sodium acetate).

To overcome these difficulties,  I eventually bought a thermocouple data-logger which can read up to 4 thermocouples simultaneously and save the data on an SD card. This allowed me (a) get on with life and (b) to do something clever: to measure the cooling curve of a sample of water at the same time. I’ll explain why this was important later.

Eventually – after a series of new basic mistakes such as setting the logging interval to 30 minutes rather than30 seconds – I began to get some interesting data. And sodium acetate really is an extraordinary substance.

Of course my experiments are not complete and I would really like to repeat the whole series of experiments based on the golden rule, but I really need to the clean up the kitchen.

Experiment#1

As shown below, I heated three samples of equal volumes of wax, sodium acetate and water to roughly 90 °C for around 10 minutes – sufficient to melt all the SAT.

I then transferred the samples – while logging their temperature – into a cardboard stand where I guessed that the cooling environment of each sample would be similar.

The results of the first experiment are shown below.

Click on image for a larger version. The temperature of the three samples of water, wax and sodium acetate as a function of time.

The first thing to notice is how odd the curves are for the wax and the sodium acetate. They both have discontinuities in their rate of cooling.

And strikingly, although they start at similar temperatures, they both stay hotter than the water for longer – this is what makes them candidate thermal storage materials. But precisely how much more heat have they released?

To work this out we need to start with the cooling curve for the water which (happily) behaves normally i.e. smoothly. We would expect…

  • …the cooling rate (°C/s) to be proportional to…
  • …the difference between the temperature at any particular time, and the temperature of the environment (roughly 27 °C during Experiment #1).

Using the magic of spreadsheets we can check if this is the case, and as the graph below demonstrates, it is indeed approximately so.

Click on image for a larger version. The cooling rate of the water  as function of the difference between water temperature and the temperature of the environment.

Because the heat capacity of water is reasonably constant over this temperature range, we can now convert this cooling rate into an estimate of how much heat was leaving the water sample at each temperature. To do this we note that for each °C that each gram of water cools, 4.2 J of heat must leave the sample. So if 1 gram of water cools at a rate of 1 °C/s, then the rate of heat loss must be 4.2 J/s or 4.2 W.

Click on image for a larger version. Estimate for the rate of loss of heat (in watts) of the water as function of the difference between water temperature and the temperature of the environment.

This last graph tells us that when the temperature difference from the environments is (say) 10 °C, then the water is losing 0.104 x 10 = 1.04 watts of heat. Based on the closeness of the fit to the data, I would estimate there is about a 10% uncertainty in this figure.

Finally, if we add the amount of heat lost during the time interval between each data point, we can estimate the cumulative total amount of heat lost.

It is this cumulative total that indicates the capacity of a substance to store heat.

Importantly, because all the samples are held similarly, at any particular temperature, I think the heat loss from each of the other samples must be the similar to that for water when it was at the same temperature – even though the cooling rates are quite different.

Using this insight, I converted the cooling curve (temperature versus time) for these materials – into curves showing cumulative heat loss curves versus time.

Click on image for a larger version. Estimates for the cumulative heat lost from the water, wax and SAT (sodium acetate) samples as a function of time. Also shown as dotted lines are the limiting extrapolations from (a) the first part of the cooling curve of the SAT and (b) the final part of the cooling curve. The difference between these two extrapolations is an estimate for the latent heat of the SAT.

We can apply a couple of sanity checks here. The first is that the heat lost from the water comes to about 10.7 kilojoules. Since the 60 g of water cooled from 70 °C to 28 °C then based on a heat capacity of water of 4,200 J/°C/kg we would expect a heat loss of (0.06 x 4200 x 42 =)10.6 kJ. This rough numerical agreement just indicates that the spreadsheet analysis has not resulted in any gross errors.

Looking at the difference between the extrapolation of the first part of the SAT curve, and the extrapolation of the final curve, we see a difference of approximately 23.8 kJ. This heat evolved from 88 g of SAT in the tube and so corresponds to 23.8/0.088 = 270 kJ/kg. We can check that against an academic paper, which suggests values in the range 264 to 289 kJ/kg. So that too seems to check out.

With everything sort of working, I tried the experiment a couple more times

Further Experiments: coping with super-cooling

The most striking feature of these experiments is that when the sodium acetate freezes, it releases its ‘latent heat’ and warms up to its equilibrium freezing temperature of roughly 58 °C.

From the first experiment – and the experiments I had done previously – it became clear that the sodium acetate tended to supercool substantially. This is the process whereby a substance remains a liquid even when it is cooled below its equilibrium freezing temperature.

[The physics of supercooling is fascinating but I don’t really have time to discuss it here. In facile terms, it is like when a cartoon character runs over the edge of a cliff but doesn’t fall until it realises that there is nothing holding it up!]

In this context, the supercooling is just an irritation! So I tried different techniques in each of the three difference experiments

  • In Experiment #1, I stirred the sample to initiate the freezing.
  • In Experiment #2, I placed spoons in each sample in the hope that some additional cooling would initiate the freezing. It didn’t.
  • In Experiment #3, I left the sample for as long as was practical in the hope it would spontaneously freeze. It didn’t.
  • In Experiment #4, I left the sample for longer than was practical. But it still didn’t freeze spontaneously.

So I didn’t manage to control the supercooling – in each case I initiated the freeze by poking, shaking or stirring. I’ll comment on this failure at the end of the article.

The data and analysis from experiments 2, 3 and 4 is shown below.

Click on image for a larger version. The upper three graphs show 3 cooling curves for wax and SAT. The water sample is not shown to simplify the graphs. The Lower 3 graphs show estimates for the cumulative heat lost from the wax and SAT samples as a function of time. Also shown as dotted lines are the limiting extrapolations from (a) the first part of the cooling curve of the SAT and (b) the final part of the cooling curve. The difference between these two extrapolations is an estimate for the latent heat of the SAT.

Conclusions

The most important conclusion from the analysis above is that a given volume of SAT releases much more thermal energy on cooling than the equivalent volume of either water or wax. This what makes it useful for thermal storage.

If we consider heat released above 40 °C, then the SAT releases around 3 times as much heat as a similar volume of water. This means an equivalent thermal store built using SAT can be up to 3 times smaller than the equivalent thermal store using a hot water cylinder.

The experiments gave four estimates for the heat related as latent heat which are summarised in the table below. Pleasingly all are in reasonable agreement with the suggested likely range of results from 264 to 289 kJ/kg.

Click on image for a larger version. Three estimates of the latent heat of Sodium Acetate Trihydrate (SAT)

Practical Devices

Scaling to a larger sample, 100 kg of sodium acetate would occupy a volume of 68 litres and fit in a cube with a side of just 40 cm or so, and release around 27MJ (7.5 kWh) of latent heat. This is roughly the equivalent of the heat stored in a 200 litre domestic hot water cylinder.

Sodium acetate is the thermal storage medium in a range of devices that can serve the same purpose as a domestic hot water cylinder but which occupy (in practice) rather less than half the volume. Clever!

Heat is stored by melting the sodium acetate in an insulated box, and released by running cold water through pipes immersed in the sodium acetate: the water is heated and emerges piping hot through your taps! As the sodium acetate freezes, the temperature remains stable – and the water delivered similarly remains piping hot.

But what about the supercooling? How do the devices prevent from the sodium acetate from supercooling? I’m afraid I don’t know. This paper discusses some practical considerations for thermal storage devices made using SAT, and it lists a number of additives that apparently rectify shortcomings in SAT behaviour. One of the additives is – curiously – wallpaper paste. I did try experiments with this but I didn’t observe any regular change in behaviour.

In any case, have fun with your sodium acetate experiments. It is available from here.

More Climate Communications

August 2, 2022

Friends, I have been out again in search of inspiration for how to encourage changes that will reduce carbon dioxide emissions.

In this article I am just noting down things that happened and reflecting on the interactions. It seems that there is widespread ignorance and misunderstanding of Climate Change coupled with bewilderment about what will actually make a difference.

These notes are for two quite contrasting days. As usual, a solid 99% of people just passed by. Of those who stopped, there was quite a bit of positivity, but also some bizarrely misinformed opinions.

I am still learning…

Thursday, July 28.

10:58 Set up outside CarpetRIght in Teddington.

11:05 John stopped by with many positive ideas. He suggested I put posters in the library and in the local community noticeboard on Broad Street which I could access through the library. He suggested my board should show the savings to be gleaned from using low carbon energy, such as solar power. John lived locally and his street had a WhatsApp group that could share information. It made me think that maybe the ‘Neighbourhood’ app might be useful.

11:12 When John walked back the other way he held up his fist and said “Viva La Revolution

11:23 A mother and her two children (a boy aged 12 and a girl aged 9) stopped by. She was very supportive but the children were obviously disinterested. I asked her what things I could do to communicate better, and she suggested my box should have more colour on it. The children then suggested there should be graphics showing a healthy earth and a poorly earth. The boy suggested I should use Instagram. The mother said they were going with the children to Bordeaux in France next week, and that they would see some of the evidence of wildfires. 

11:34 Three teenagers walked by and waved. But didn’t stop to talk

11:35 A lady caught my eye and said she was in a rush for work, but wished me good luck.

11:38 Man on a bright yellow Suzuki motorbike stopped at the traffic lights, and caught my eye. He nodded.

11:45 A regular at the Sidra café where I have my morning coffee stopped by. I said I was just trying to find out what people thought, and get out of my Twitter bubble. He told me that “almost everyone will agree with me, but that almost no one knew what to do“. I said that seemed a succinct précis of what people had said

11:48 A gentleman, quite elderly, with a straw hat stopped by and asked me “What’s going on with all this weather then? Are we going to get more of it?”. I said we probably were going to get more of it, one or two days like that every year and then slowly becoming more common. I asked him if he thought there was anything we could do about it, and he told me it was “...all those gases going up in the atmosphere“, a phrase he repeated several times. As he left he said “We’ll just have to see what happens then…“.

11:54 A lady called who works in the theology department at the local University stopped by. “Air-conditioning on the buses and trains” she said “that’s the solution“. She said she was out on the 40 °C day, and that the solution was to wear damp T-shirts and trousers. I suggested that some people might think it immodest for ladies to wear a wet T-shirt but she was unabashed.

12:10 An elegantly-dressed lady pushing her mother in a wheelchair stopped by. She said it wasn’t a popular thing to say but she wasn’t sure that it wasn’t the best thing for people to just destroy themselves, leaving just a few small tribes on Earth, and then people would be forced to live sustainably.

She said that what people want is to know what is the right thing, but something which will influence others. We discussed the idea of a Personal Carbon budget. For example, people could have a lifetime budget of 100 tons of carbon emissions by flying, which they could then sell, or buy from other people. She seemed to like this idea.

Her mother intervened to say that when she was younger, flying was very expensive and so people went by boat, and she had come to England from Canada on a freighter which had just a few cabins for passengers. “Flying was very expensive. Slower is better.” she said.

The lady thought that “Human beings will pay if they have too. Raising the price of things will eliminate frivolous use of things e.g., weekend trips”.

She said that  People are creative” and told me that in Lebanon people had rigged up makeshift solar systems with batteries to get by when there was no mains electricity and that people there cooked collectively. She said this was also done in Morocco and Algeria. 

She told me to look out for the ”The Boy Who Harnessed The Wind” a Netflix film about renewable energy in Africa

12:22 A lady carrying her lunch back to her office spoke as she passed, saying “Thank you for doing this.”, although I am not sure she knew what I was doing!

12:24 A gentleman passing by didn’t stop but looked at me, and raised his eyebrows and said “Alright!”

12:29 Colleagues from NPL passed by, and one person told me that his wife’s sister’s husband (!) had asked them if they had heard about this “Protons for Breakfast” site. So it does seem that news is travelling.

12:42 An ex-colleague from NPL stopped by. He was working on life-cycle impact assessments, and said he had done did a life-cycle assessment of the Audi E Tron (an EV) and that it was worse than petrol cars because of the massive embodied energy in the battery.

12:52 A lady was walking slowly past with a stick. I caught her eye and commented that it was warm now. She nodded and said “As long as it doesn’t get too warm…

12:58 A man who worked at a local e-bike shop stopped and suggested I should get a giant banner and block the entire road. He said he had heard that the materials mined for batteries involved child labour. I told him I was pretty sure that involved the cobalt and not the lithium and that modern batteries use no cobalt or nickel. 

13:00 An expert in Climate Change science and an ex-colleague from NPL stopped by – remember this is Teddington!. She told me she’d read a book of random facts about climate change, but had had to stop because it was too depressing.

13:15 A lady passed by without stopping but said she had had lots of conversations about climate change with friends. I told her to keep talking.

13:17. E-bike man passed  by again having bought his lunch, and he said that he had seen an article on associated press that morning about fugitive methane

13:26. Stopped

Tuesday, August 2nd.

11:03 I ventured away from Teddington to nearby Hampton Hill and set up outside a parade of shops near a local Tesco.

11:25 Interesting interaction with two air-conditioning servicing engineers who had just emerged from Tesco with their lunch.

The younger one engaged me and said “We’re part of the problem mate”. he said, “We’re 7% of emissions.”.  I said he was also part of the solution. We’re all going to need air-conditioning in the future, and installing heat pumps is going to be a big business. He acknowledged that, but said that the refrigerant was harmful, and the less harmful it was, the worse it was as a refrigerant.

Then his older and fatter colleague came out. He said “I’m not going to get drawn into this because we’ll end up having an argument.” And then he got drawn into it. He said there may be some emissions he said, but there is also a natural cycle. I told him that actually it’s all human emissions.

He then went on about ice ages, and the massive emissions in the Victorian era when there was no global warming. I told him emissions in the Victorian era were low: around 1 billion tonnes of CO2 per year and that now emissions are 36 billion tonnes per year.

He then went on to say “Anyway it’s not us, 72% of emissions come from China”. I pointed out that it wasn’t that high and that the US and China pollute similarly. He wandered off saying “I knew we’d have an argument.”

After that interaction, two people at the bus stop spoke to me and said “Sorry you had to have that, he was like that in Tesco!”. Then they said “Good luck!”

11:35 A man about 60 years of age with long hair approached me and asked me what I was an expert in. I said I was an expert in measurements of temperature and explained how I had made the most accurate temperature measurements ever made. He said he had studied particle physics so I included some slightly more technical details. He told me he was in the film and graphics business but didn’t do much these days, just built websites.

I asked him his take on the climate crisis and he said he wasn’t concerned. He said global warming was 0.2°C, and that NASA had edited the data for specific years. I told him that wasn’t true but he insisted and named the individual years in question. Then he had to get on the bus   

11:41 A young man with a ponytail and some over-ear headphones nodded to me. Then an elderly man with smart grey hair and wearing cool summer shorts said good morning. 

11:51 A black man stopped by and said “He didn’t know what to say because things may get political”. He said first he was from Africa and then changed his mind – he sounded very English to me, like he came from Henley or similar – but he did trade with Africa. He said that the UK was exporting polluting old cars to Africa. I said that was shameful and then I asked what he thought we should do about the climate crisis. 

He said that heating has always been terrible in the UK, and that when he was a child (he said he was 61) he would go out to the library to get warm during the day, and when he was at home they would wear cardigans and pullovers. Now he said his children want to wash a T-shirt then put it in the dryer so they can wear that same day. He thought the price rises that are happening at the moment, although they were very hard on people, might help people value energy more.

He said he couldn’t understand how people in Africa, Nigeria in particular were still using diesel generators so much, when Solar is so cheap. Then he had to go and catch a bus. 

11:59  An elderly man called stopped by, he said it was really warming up. I said yes, but that you had to be something like our age to understand just how different the climate was now to how it was when we were young. He said the government needed to sort it out, and I said I didn’t think the government would be able to sort out their own bedroom, and he laughed and agreed.

I asked him what he thought could be done. He asked me “What could we do?” And I told him that our house in Teddington had been off-grid for a quarter of a year. I said there were things that people could do, but it would take the people who had the money to do them first. He said he was really impressed by news of my house and he would tell his friends. As he left he said good luck to me.

12:35 A lady was just waiting for a bus, but caught my eye and said she hoped I was getting lots of interest. I said I”n fact No, most people just didn’t want to think about it” She said that she had just joined Extinction Rebellion and was waiting to go on the first training course.

13:00  After 25 minutes with no interactions I thought it was time to call it a day.


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