Archive for the ‘Personal’ Category

More Fusion Delusion

February 9, 2023

Friends, long term followers of this blog will know that I am sceptical of the relevance of nuclear fusion research to our climate emergency.

Despite my scepticism, there seems to be no end of investors willing to bet billions on projects which will inevitably fail.

This article is about a company called Helion which has a ‘new way’ of doing fusion.

There are videos describing the process which are extremely convincing and at first I just didn’t know what to make of technique: it all sounded so clever.

But eventually I came across a YouTuber (Improbable Matter) with experience in the field, and he made the major weaknesses clear.

This article is about that one major flaw in Helion’s technique which makes it inevitable that they will fail. There are many other flaws in the Helion approach, but I am concentrating on this one major and unavoidable flaw. Why? Because the processes are complicated and I don’t want to get sidetracked.

The conventional approach to fusion

To understand the novelty of the Helion technique, I will first briefly describe the conventional approach to fusion.

  • The conventional approach is to fuse deuterium (D) nuclei (1 proton and 1 neutron) with tritium (T) nuclei (1 proton and 2 neutron). This reaction is chosen because it is the easiest pair of nuclei to fuse. And it’s still very hard.
  • The idea is to get the mixture of these nuclei very hot – around 100 million °C – and maintain the pressure on the mixture with a strong specially-shaped magnetic field. When the pressure and temperature are sufficiently great, the fusion process starts and energy is released.
  • The reaction is written D + T → 4He + n . The energetic nucleus of 4He (pronounced as helium 4) stays in the plasma and heats the plasma.
  • Because the neutron (n) has no electrical charge, it is not confined by the magnetic fields, and it leaves the plasma and is captured outside the reactor and used to generate heat which is used to generate electricity in a conventional steam turbine.
  • The reaction would then run continuously with the fusion reaction maintaining the plasma temperature, and a continuous stream of neutrons providing heating.
  • The neutron flux from this reaction damages just about everything near the reactor and induces radioactivity in most substances.

The Helion approach

In contrast with the conventional technique,

  • Helion plan to fuse deuterium (D) nuclei (1 proton and 1 neutron) with 3-Helium (3He) nuclei (2 protons and 1 neutron) using the reaction D + 3He → 4He + H (corrected on 26.2.2023)
  • This reaction is called aneutronic because it doesn’t produce a neutron. This is important because it means that – in principle – the entire apparatus will not become intensely radioactive.
  • The Helion process is not steady state but instead involves episodic fusion reactions every second or so.
  • Their plan is to start with a mixture of D + 3He in a plasma which is then rapidly compressed using changing magnetic fields to cause the plasma to heat which triggers the fusion.
  • The heat of fusion then causes the plasma ball to expand against the compressing magnetic field, and as it expands in the magnetic field, it induces electrical currents directly in coils wrapped around the fusion chamber.
  • The electrical current would be ‘harvested’ directly without the need for steam generation and a turbine plant.

Helion say they have demonstrated the feasibility of this with small scale plant, and are building ever larger prototypes.

Why it won’t work

There are large number of reasons why the Helion scheme will fail. Perhaps the first and most obvious is that it uses 3He as a fuel.

The ‘conventional’ approach to fusion involves the raw materials deuterium – which is common and found in sea water – and tritium – which barely occurs naturally on Earth. Obtaining tritium is a major challenge for conventional fusionistas, but it nothing compared to the challenges of making 3He.

Helium-3 is even rarer than tritium and some You Tubers (link) are even suggesting that interplanetary mining will be the source for helium-3. Please pause at this point and reflect on just how bonkers this is.

Helion do not suggest interplanetary mining. They suggest building a completely separate and thoroughly energy consuming nuclear plant to generate helium-3.

But the reason for failure to which I would like to draw your attention today concerns the basic nuclear reactions they hope to exploit.

The graph below – taken from Wikipedia – shows how the reaction rate of several different nuclear reactions vary with temperature.

Click on image for a larger version. Graph showing the relative reactivity of different fusion reactions. Note that at 200 million °C, and assuming equal concentrations, the D-D reaction is just as likely as the Helion reaction D-3He. And the D-T reaction is around 100 times more likely.

Helion have only managed to heat their plasma to 100 million °C so far, but they state that they will shortly achieve a staggering 200 million °C. This will be tough but let’s believe them for now.

Notice that the reactivity of a D-3He plasma is roughly equal to the reactivity of a D-D plasma, and both are around 100 times less reactive than a D-T plasma. So using D-3He to start a fusion reaction rather than D-T is like using damp kindling rather than dry kindling to try to start a fire – it just makes everything harder.

But Helion insist this sacrifice is worth it because their reaction is aneutronic, and the energy of the expanding fusing plasma can be captured electromagnetically.

But let’s imagine a 50/50 mix of D/3He which starts to fuse. As you can see, the D-D reaction rate is equal to the D-3He reaction rate. So if we start out with a 50-50 mix, after a short while there will be D-3He reactions and D-D reactions.

So after a short while – nanoseconds in practice – the original 50% mixture will contain the products of both D-D fusion and the D-3He fusion. And one of the products of D-D fusions is tritium, T.

The promotional video at the start of this article discusses this (starting at 13m 58s) and says that the tritium T will be captured in the exhaust at the end of the reaction and stored. However, that won’t happen!

Because the D-T reaction is 100 times more likely than the D-3He reaction, even a small amount of T in the reaction mixture begins to ‘steal’ D, lowering the D concentration, and emitting neutrons. And leaving the 3He with nothing to react with. After spending a fortune preparing the 3He – the majority of the fuel will be left unused after the reaction cycle!


Helion propose that the nuclear reaction ‘should’ proceed as shown in the graph below.

Click on image for a larger version. Graph showing the expected relative concentration of species as the Helion reaction proceeds. Starting with a 50-50 mixture of D and 3He, these nuclei react and the amount 4He and H increases.

In this graph I altered the initial mix from 50-50 to 49.7-50.3 to allow the lines for 3He and D to show up separately. One can see that the D-3He fuel is consumed through the reaction and there are no neutrons produced.

However, this is just not what will happen. In fact – as discussed in the video – there are several reactions that can take place. Wikipedia helpfully summarises the reactions:

Click on image for a larger version. The four most prevalent fusion reactions. The bottom reaction is the one Helion wishes to focus on. However the D-D reaction produces both T, 3He, protons (H) and neutrons. And once there is T present in the reaction mix, the top reaction (D-T) will produce 4He and neutrons.

But what is not discussed in the video is the effect of the D-T fusion reaction which is around 100 times more likely than the D-3He reaction at 200 million °C.

Given all these reactions, it can be hard to anticipate exactly how things will proceed. But I have modelled all four reactions based on their approximate likelihood i.e. on the availability of the respective reactants and their reactivity as shown in the first figure. My spreadsheet is available here: Helion Fusion Simulation.

Inevitably the model is an approximation, but it is more realistic than the single-reaction Helion vision. Some example graphs are shown below.

Click on image for a larger version. Graph showing the expected relative concentration of species as a 3He-D mixture begins to fuse. The dotted green line shows the accumulated neutron dose. Notice that compared with the previous graph, less of the 3He is consumed, the D concentration falls rapidly, and the tritium concentration remains low but non-zero. See next graph for details.

Click on image for a larger version. Detail of the graph showing the tiny but critical concentration of tritium (T).

What we see in the above graphs is that the D-D reactions produce T which does not sit inertly in the mixture. Instead it ‘steals’ the remaining D in the mixture leaving the 3He substantially un-burned. There is also a very strong neutron dose: roughly 10% of the nuclear reactions produce a high energy neutron.


So in reality, the Helion approach will not be aneutronic. Their apparatus will become just as radioactive and be subject to just as much radiation damage as in any other fusion approach.

Also their very expensive 3He will remain unburned and need to be scavenged and separated from the ‘ashes’ of the reaction.

  • If just the Helion reaction occurred, then in the time window shown in the graphs above, 75% of the 3He would be consumed.
  • But when one considers all the other reactions, only a maximum of 35% is consumed – even if the initial D concentration is optimised.

So does all this mean that the Helion scheme won’t produce fusion? That it won’t work?

The Helion scheme begins with a plant for manufacturing 3He. This would be a massive complex proposal which would consume vast amounts of energy. It could only be justified if the Helion fusion process were somehow a straightforward way to generate even more vast amounts of energy at very low cost (aside from the 3He).

But the Helion fusion process is definitely not straightforward. It is not ‘aneutronic’ and D-T reactions will be a real problem for them.

And then one comes back to the even more basic problem of episodic nuclear fusion which I discussed in my previous article on laser fusion. That for a modest sized plant – say with 150 MW of electrical output – one would need to build an apparatus to withstand. an explosion of 0.1 tonnes of TNT once a second. Continuously. For 30 years. Really?

What is really going on?

Discussion of fusion as a viable option for future energy generation is a distraction from the urgent task at hand – to stop burning fossil fuels as rapidly as possible.

If holding out the illusion of a future magical technology delays climate action by even a year or two then it allows big oil, big gas, and big money in general, to reap extra profits.

So I urge you to ignore the siren calls of fusionistas. Ignore the talk of cheap and clean energy. Instead, close your ears and tie yourself to the mast of your boat, and sail on to a renewable future using truly miraculous technology such as solar and wind generation, technology which actually works.

Christmas Break

December 22, 2022

Friends, it’s been a busy year, and I’m going to take break from blogging for a week or so.

I am really grateful to everyone who reads this blog. I would probably be writing it whether or not you were reading it because writing helps me to clarify my thoughts. But I find the idea that anyone reads what I have written very moving.

So, thank you, and best wishes to you and yours for 2023.


The other day I clicked back through the 920 articles I have written since 2008 and came across this slightly chaotic video of a talk I gave at NPL in 2017 on the physics of candles.

And re-watching it I was amused and distracted, and so I thought I would re-post it in case you too might be amused or distracted!

Candles really are astounding! For example:

  • Did you know that wax in bulk is not flammable?
  • Did you know the temperature of a candle flame?
  • Did you know that a candle stores 8 times more energy than a stick of dynamite?

If would like to access some of the fancy PowerPoint™ animations you can download the PowerPoint file here.

The highlight of the talk is using a candle to power a thermo-electric generator, which in turn powers a USB port, which in turn powers a torch, which is brighter than the candle.


And by the way, here is the slow-motion candle-relighting movie that is embedded in the PowerPoint but which doesn’t show up well in the lecture theatre view.

Thanks again to Brian Madzima for the videography and editing, and Nikita Mezhnyakov for the photograph.

Tony Seba has got me thinking

December 4, 2022

Friends, while browsing on YouTube, The Algorithm suggested I watch videos by Tony Seba. And just as The Algorithm foresaw, I have found them fascinating.

The reason for my fascination is that he makes very specific predictions for the rate at which legacy industries (coal, oil, gas, automotive, and animal farming) will collapse.

In general he anticipates rapid changes – much more dramatic than is envisioned conventionally. He anticipates that all these industries will dramatically disrupted, and some of them eliminated, by 2030.

His reasoning is based on the idea of rational deployment of capital in a free market. His predictions do not require people to make choices on moral or environmental grounds. Rather he believes that in a free market, the collapse of these legacy industries will happen because it is economically inevitable.

I would very much like to see the collapse of the oil and automotive industries, and so some part of me would really like to believe his predictions. But while his arguments are compelling, I remain sceptical: I find it hard to believe it will all just ‘happen’: there are strong forces seeking to maintain the status quo. [Edit: The first comment on the article was also sceptical, but so well-worded that I have promoted it to the main text at the end of the article.]

So this article is about Tony Seba’s predictions, and my thoughts about whether or not they will come to pass.

Who is Tony Seba? 

Tony Seba’s web site says:

Tony Seba is a world-renowned thought leader, author, speaker, educator, angel investor and Silicon Valley entrepreneur

His work focuses on technology disruption, the convergence of technologies, business model innovation, organizational capabilities and product innovation that leads to the creation of new industries and societies and the collapse of existing ones.

Tony Seba’s basic ideas add up to Market Disruption

Tony Seba ideas focus on two types of technological change, which he calls change from above and change from below, and on developments in business models.

Change from above is when a new technology is superior to an existing technology, but initially much more expensive than a standard product. This is the case for many new products. However through the action of the learning curve (see below) the price of the superior product falls exponentially as its production volume increase. i.e. the price falls by a characteristic factor (say 20%) for each doubling of production. The compounding of these factors year-upon-year leads to dramatic and initially inconceivable falls in prices. Think Flat Screen TV’s etc.

Change from below is when a new technology is inferior to an existing technology, but much cheaper than a standard product. Through the action of the learning curve (see below) the quality of the inferior product increase exponentially as it’s production volume increase. i.e. some quality metric increases by a characteristic factor (say 20%) for each doubling of production. The compounding of these factors year-upon-year leads to the new product becoming superior to the standard product at a much lower price. Think Digital Cameras,  etc.

And aside from technological innovations, he discusses the importance of business models. For example, he discuss the demise of Kodak, a global giant in photography who made money every time anyone took a photograph or had a print made. Kodak invented digital imaging, and foresaw a world in which they would take a cut of every digital photograph taken, just like they had in the previous era. Of course, digital photography doesn’t work like that: Digital photos are essentially free and the companies that make money from digital photography are Facebook and Instagram – who use completely different business models.

Tony Seba calls the collective impact of these changes market disruption. In such processes, existing markets collapse, stable businesses operating on small margins go bankrupt even in the early stages of a transition, and new businesses emerge that work in ways that seem initially quite foreign.

In retrospect, these changes can appear to be inevitable, but that is not how they feel at the time: during a technology transition, things probably appear chaotic and confusing, with lots of hype and mis-information. Often long-standing traditions – ways of working and living that have stood for generations and seemed unalterable – disappear over short periods of time. These disruptions to the status quo are typically accompanied by the personal distress of many individuals and families, and societal upheaval. They also typically involve the creation of new industries and the destruction of old ones.

Tony Seba’s Predictions

Tony Seba has a list of technological changes (13m47s into the video below), and he looks at how convergence of these technologies, coupled with exponential changes in price or performance, will lead to disruption. [Note: exponential means changing by a constant factor per unit time, rather than changing by a constant increment per unit time]

Amongst the key technologies he looks at are:

  • Solar PV
  • Batteries
  • Computing: Artificial Intelligence

He predicts that the lowering in cost of Solar PV and Batteries, coupled with AI, will lead to disruptions of the entire energy industry, (oil and gas and coal) and transportation (automobiles, distribution). And his predictions are often quite specific and this – in general – means they are not quite right. But also not far off.

Overall, I think Tony Seba’s analysis is interesting and broadly sound, and I am grateful for even the chance to believe that Fossil Fuel industries will collapse in my lifetime. But his analysis is not beyond criticism and I have a list of comments on his work below the embedded video.

There are loads of Tony Seba videos on YouTube, and many of them are very similar. I’ve selected one long video below from April 2020 that covers most of his thoughts about this field.

Comment#1: The Learning Curve

The learning curve was something I had not fully appreciated as a general phenomena.

Tony Seba does not concern himself with the specifics of what gives rise to a particular learning curve. He takes the learning curve as an input, and then extrapolates to see what would happen if the learning trend continues.

In a way, this is a weakness, because understanding the details of how the learning curve works can really help to understand how the curve is likely to continue in the future. But in a way it is a strength, because it is very easy to get lost in details

As an example, lithium-ion batteries have fallen in price by around 19% for each doubling of cumulative production. Compounding these year-on-year change results in a factor 40 lowering price, as production increased by 50,000 times .

Click on image for a larger version. Learning Curves. The graph (with a logarithmic vertical axis) is from Our World in Data showing the decline of battery prices as cumulative production increased.

Comment#2: The S curve

A large part of Tony Seba’s analyses involve so-called S-curves that describe the way in which innovations diffuse through society. In particular, he points out that despite initial low market penetration, innovations can transform societies remarkably quickly. In almost all his talks he contrasts photographs of the New York City Easter Parade in 1900 and 1913. The parade has switched from being 99% horse-drawn carriages to 99% motor cars.

Click on image for a larger version. The S-curve describing the fractional market penetration of an innovation from 0% to 100%. In the early stages of the curve, the growth is typically exponential, but it can still be a very small fraction of the market, but full penetration of the market can happen very quickly. This graph is stolen from this excellent essay.

The importance of the S-curve is that it qualitatively describes the way technological disruptions occur: to use a literary metaphor, they happen “Slowly, then suddenly“. And when one is the lower part of the S-curve, it can be very difficult to anticipate what may be about to happen.

Comment#3: Are the Markets Free?

Perhaps my biggest concern about Tony Seba’s analysis is that there are a very large number of institutions and governments who are entangled with the oil and gas industries. These institutions value the ‘stability’ which would see oil and gas industries continuing exactly as they do now. Every extra year of extra production is a year in which existing investments in oil and gas infrastructure yield extra profit.

The switch to a renewable energy infrastructure will require colossal amounts of capital investment, but will also result in the destruction of the colossal value of existing investments which will become ‘stranded’. Consequently, existing investors, and the institutions they influence, are heavily incentivised to do everything they can to prolong the lifetime of oil and gas by slowing the development of wind, solar PV and batteries.

Tony Seba and his colleague warn about this in the video below, but don’t perhaps clearly communicate the underhand ways in which oil and gas seek to affect discussion of their industry.


This article is about the future, and the future is fundamentally unknowable. But I think Tony Seba’s appreciation of some of the non-linear dynamics of markets is insightful. And it chimes with my own personal experience that the technology changes I have experienced in my lifetime have happened much faster than I personally anticipated.

But changes on the scale he foresees will bring phenomenal disruption across society and will be resisted furiously by those with vested interests in the status quo.

In the 2030’s will we look at the ruined infrastructure of coal, oil and gas as we now look at canals or closed down shipyards? Will these mighty industries be reduced to ruins, like the broken statue of Ozymandias in the desert. I do hope so.

Promoted Comment

Your skepticism is well founded because there is a fundamental error that most “free market” advocates make.

The belief is that companies will be driven to change by the pursuit of profit – that the drive to maximize shareholder value will drive them to pursue maximum profits.

However, the real motivation seems to be something adjacent but distinctly different: Companies – at least established ones – will always pursue the path of profitable least risk.

This makes sense through the “maximize shareholder value” lens: if we are making money now, why make major changes and put that at risk?

The answer of course is when the risk of getting upstaged by a competitor or upstart is sufficiently great, then _and_only_then_ will the company embrace radical change in pursuit of new profit opportunities.

The profit-maximization curve and the risk curve are related, but distinct, because the risk curve is a subject to restrictions in market access, industry inertia, and other factors that tend to retard change. Those factors are amplified significantly when there are other entities (either businesses or governments – in this case, both) that are heavily invested in the status quo.

In other words, your skepticism is warranted. The market is a useful tool, but it is far from perfect and it doesn’t work the way it’s biggest fans think it does. The economic case of non-fossil energy sources is compelling and becoming moreso every day. But we will not be able to rely on market effects alone – we’re already far behind where we need to be, and the incumbent market will do everything in its power to make sure we stay that way.

Greta’s Climate Book: An antidote to hope

November 21, 2022

Friends, as I have written before, I love and admire Greta Thunberg.

So when I heard that Greta had edited a collection of short essays on Climate Change, I ordered a copy immediately. Quietly I thought to myself: “Well that is Christmas gifts for everyone sorted.”

And when I collected my copy from the local bookshop I was delighted to find that Greta herself had signed the book! When I got home I sat down eagerly to read.

The book is attractive, covered in Climate Stripes but at 446  pages and 1.383 ± 0.002 kg, it was larger and heavier than I had anticipated.

It is also well-written. Greta’s essays that introduce the various sections are excellent: she writes with outstanding clarity. And the general standard of the short essays is excellent. I learned a lot about many different aspects of Climate Change that I had not previously focussed on.

However, I will not be gifting this book to anyone I love. Why? Because I found it overwhelmingly depressing.

Antidote to hope

Friends, Climate Change scares me. I feel the fragility of our way of life and I feel terrified for my children. And I am acutely aware of just how profoundly bad our situation is. In many ways, I am a natural ‘Doomer‘. But I resist that temptation and prefer to focus on what I can do to try to improve things – however marginally.

My resistance is not really supported by the weight of evidence which is probably on the side of the doomers. It’s a choice I have made.

And that’s my problem with the book. It amplifies every negative aspect of our situation in a way which I found overwhelmingly depressing. I appreciate the book’s straightforward honesty, but it doesn’t help me get by from day to day.

The book implies that there is no solution to the problem of climate change without simultaneously solving multiple problems of inter-national, inter-ethnic, inter-gender and inter-generational justice – problems that seem to me to be much harder than the fundamentally technical problem of stopping emitting carbon dioxide.

There is more than one thing happening

At the moment on Earth there are two epochal changes taking place. Climate Change is one of them, and its multiple levels and scales and implications of that change are well-described by Greta’s book.

But we are also undergoing an Energy Transition which I estimate will have impacts on the same scale as the Industrial Revolution.

Solar Energy, Wind Energy and Battery storage have plummeted in price and their deployment is accelerating exponentially. I’ll be writing more about this in coming weeks, but by most measures, some combination of these technologies provides the cheapest electricity humanity has ever known.

As someone who is planning to operate their home entirely from solar power for 6 months of next year, this technological shift feels very real. And this change has taken place in my lifetime.

Cost is the key. Because these technologies are cheaper than building any other kind of power, they will – even in the face of strong opposition – inevitably win. In the end, the fossil fuel technologies will simply not be able to compete. In the end we will make the energy transition, not because it is the moral thing to do, but because it is economically essential.

And this transition seems to me to offer some hope to people living in both developed and developing countries.

The Energy Transition will not bring with it solutions to the multiple problems of inter-national, inter-ethnic, inter-gender and inter-generational justice. But it does offer at least a realistic opportunity to reduce carbon dioxide emissions relatively quickly.

And for me, that would be enough.


Is it possible to live a carbon-zero life?

November 21, 2022

Friends, on Monday 21st November 2022 – which as I write this is ‘later today’ – I will be talking to hundreds of 6th Formers in London on the topic of whether it’s possible to live a carbon-zero life.

This is part of the Physics in Action series of events. As a retired person, I had thought my days of addressing such groups were over, and I feel honoured to have been asked to speak.

In case people can’t attend, I have recorded a version of the 40 minute talk which you can see below. It’s a bit flat compared to the verve of a live event, but hopefully it’s better than nothing.

And in case people – particularly teachers – wanted them I thought I would put the Powerpoint slides here. They contain many slides which are hidden but may contain useful illustrations or animations. Somehow the file is 100 Mb in size (Link). Sorry.


The thesis of the talk is that at the moment there are two epochal changes taking place on Earth.

The first is Climate Change, and my aim in this talk is to explain exactly why our emissions of carbon dioxide matter so much.

The second change is the Energy Transition. Independent of our need to respond to Climate Change, renewable technologies (solar, wind and batteries) have become the cheapest way to make electricity in human history.

This provides an economic imperative for action where moral imperatives have failed. The switch to renewable technologies will become inevitable, not  because it’s ‘the right thing do’, but because it is the cheapest thing to do.

So the second part of the talk is about some of the technologies which will enable this transition: heat pumps, solar PV and batteries.

My aim is to provide the audience with a visceral understanding of the need to change. But I hope to also provide a clear understanding that massive reductions in carbon dioxide emissions are possible right now, without the need for any new inventions or discoveries, and without the need for degradation of our quality of life.

What I did on the hottest day of the year.

November 6, 2022

Friends, do you remember 19th July 2022: The day when temperatures in the UK reached 40 °C for the first time?

I wrote about that day on the 20th July – reflections here – but I didn’t mention that I had also had a conversation that day with Gregg from the Take it EV podcast.

It was a long conversation (80 minutes) because I tend to go on on and on and Gregg is a kind interviewer, but it is now available for your delectation either as a podcast (link) or as a YouTube video below.



New Solar Panels

October 27, 2022

Friends, back at the start of September, I noted that it had been a sunny summer and I resolved to add more solar panels to the house in order to increase the solar harvest next year.

I ordered the system just a few days after writing that article and it is now being installed.

In this article I thought I would describe the new installation and how it will (hopefully) integrate with the existing installation.

Click on image for a larger version. The arrangement of the solar cells on the roof of Podesta Towers. The grey panels have been installed for two years, and the red panels were installed this week. I had hoped to fit four panels on the flat roof, but in fact I can only fit three.

The Existing Installation

The existing system was installed back in November 2020 and consists of:

Why did I select these items? The installer recommended them and they seemed to have adequate performance. And happily, they do seem to have worked OK.

Some key features of these items are:

  • 340 watts is the nominal output of a panel illuminated perfectly by sunlight with an intensity 1000 W/m^2 – this is roughly full sunlight on a UK summer day.
  • Since the panels are 1.7 m x 1.03 m one can work out that around 20% of the solar energy is converted to electrical power.
  • The panel is constructed as two half-panels wired in parallel, each with 60 individual solar cells.
  • A silicon solar cell generates around 0.6 V so the 60 cells on a half-panel together generate around 36 V.
  • Splitting the panel like this improves the panel performance when one half of the panel is shaded.
  • The MPPT acronym stands for Maximum Power Point Transfer and is system for extracting maximum power from solar panels as the intensity of illumination changes.

The quotation suggested that I might reasonably expect 3,780 kWh of generation each year and this year we look on track to exceed that. Last year we generated only 3,517 kWh.

Click on image for a larger version. Cumulative generation from the existing solar panels in 2021 and 2022. The dotted blue lines are based on the expected output according the installer’s initial calculation.

This first installation was done quickly to take advantage of the fact we had scaffolding around the house for the external wall insulation. Because of this, we couldn’t wait six weeks for permission for a larger installation from the local Distribution Network Operator (DNO): these are the people who manage the local electricity networks.

So I opted for a standard installation (for which no permission is required) with a maximum output of 3.6 kW peak and we used the best sites available. I resolved to learn what I could about solar power, and after two years, I feel I served my apprenticeship.

The New Installation

To move beyond the standard system one needs to apply to the DNO, a process that takes about 6 weeks and which was thankfully handled on my behalf by the installer.

My aim was to get as much solar PV on the roof as I could – while not making the house look horrible! For that reason, we avoided using a patchwork of panels across the roof – sacrificing some performance for aesthetics.

Since the best sites had been taken by the first installation – I simply went with what was available.

I had noticed during the summer that in the mornings the Sun rises well north of east, and the east-facing roof of Podesta Towers was in full sun up until solar midday. Similarly, the flat roof was more or less un-shadowed over the same period.

My performance calculations using the excellent Easy PV site were very similar to the suggested performance from the installer.

  • The 5 panels on the east-facing roof will hopefully generate ~1,300 kWh/year
    • The panels are tilted at ~ 40° and face roughly ~ 20° north of east.
  • The 3 panels on the flat roof – might generate ~900 kWh/year
    • The panels are tilted at ~ 12° but face roughly 20° east of south –

This would correspond to 2,200 kWh/year, an additional 60% of generation bringing the total close to 6,000 kWh/year. If actual performance gets anywhere close to this I would be delighted.

To put these figures in perspective, we can compare them with household consumption.

  • Last year the house used ~5,400 kWh –
  • Roughly 3500 kWh of that (~65%) was for day-to-day household ‘stuff’
  • Roughly 1,900 kWh of that (~35%) was used for the heat pump.
  • The heat pump operated with an average COP of 3.6 to deliver 6,800 kWh of heat.

So the enlarged system will hopefully generate more electricity than we use in a year. Sadly the peak of generation (in May or June) is quite out of phase with the peak of demand (in January or February). But nonetheless, it’s a milestone of sorts.

The new system consists of:

Again, I just accepted the installer’s recommended suggestions.

The Panels.

The new panels are similar to the old ones: the 390 W nominal peak output of the new panels is larger than the 340 W peak of the previous panels simply because the new panels are larger. The efficiency remains around 20%.

Each panel consists of two half-panels, each with 9 rows of 6 rectangular half-cells.

Click on image for a larger version.

When illuminated, each individual cell generates a voltage between 0.5 V and 0.7 V between the top of the cell (the part you can see) and the bottom of the cell (that is at the back of the panel).

Fine aluminium wires cover the top of the cell to collect the generated electrons, and the wires then connect the top of one cell to the underside of the neighbouring cell so that their generated voltages add together. In each half-panel, 54 cells in series generate a voltage ~ 36 V at a current of roughly 5 amps.

Click on image for a larger version. Top: Illustration of the way in which sunlight generates a voltage between the bottom and the top (illuminated) surface of the cell. Right: The fine wires collect electrons generated from within the silicon. The filigree wiring pattern is optimised to collect as many photo-electrons as possible, while not blocking the sunlight. Left: Details of the wiring showing the top surface of the lower scale is connected to the underside of the neighbouring cell.

The two half panels are wired together in parallel so that the peak output of the whole panel is ~ 36 V at a current of roughly 10 amps.

Panels which are similarly illuminated are wired in series in a so-called ‘string’. In this installation, the 5 panels on the east-facing roof are wired in one string and the 3 panels on the flat roof are wired in another.

The inverter design has two independent inputs and the DC currents from the two ‘strings’ are combined to create an AC current at 220 V.

This arrangement works excellently when all cells in a panel and all panels in a string are illuminated similarly. But if one cell in a panel is shaded, then not only does that cell not generate a current, its electrical resistance increases dramatically, and this can restrict the current which is able to flow through the whole string of which it is a part. Fortunately, clever electrical tricks can minimise the shading problem as explained in this excellent video.

Peak Power.

One aspect of the installation which concerns me is whether all the electrical circuits can cope with the sheer amount of power this system might generate.

To estimate this, I downloaded generation data from 22 June this year, a day which was nearly perfect for solar generation: close to the solstice and almost completely cloudless. This data is shown in red on the graph below.

I then made guesstimates of the generation from the two new strings:

  • I guessed the 5-panels on the east-facing roof would begin generating earlier in the day and reach maximum power (5 x 390 W = 1,950 W) just before solar noon (1:00 p.m. BST). This is shown as a green dotted line.
  • I guessed the 3-panels on the flat roof would generate roughly symmetrically around solar noon (1:00 p.m. BST) with a maximum power of 3 x 390 W = 1,170 W. This is shown as a blue dotted line.

Click on image for a larger version. Graph comparing a perfect midsummer generating day with the existing system (red curve) with the likely generation from the expanded system (purple curve). See text for details.

Altogether (dotted purple line) the total power could potentially exceed 5 kW – a worryingly high power level.


Friends, as usual, I have gone on for too long. But this is a significant – and possibly final – step in the house refurbishment.

It offers the possibility of being off-grid for 6 months a year and of generating more electricity than the household consumes (averaged over a year). I think these are significant upgrades.

The cost is not completely clear yet, but looks like it will be just under £5,000. This is more than the initial system (£4,200 in November 2020) but this seems reasonable given the extra scaffolding required.

As I write, the panels are installed but the internal electrical wiring is not complete – but hopefully that will be done soon!

And if you have read this far, thank you! Please allow me to reward you with a video of the installation.



Grounds for Cautious Hope on Climate

October 19, 2022

Friends, ‘doomerism is – understandably – everywhere. But it is such a corrosive perspective.

So I was pleased to encounter a one hour talk by Zeke Hausfather on the The Case for Cautious Climate Hope.

This is Zeke’s précis to which I have added some punctuation.

The world is currently on the brink of both potential climate catastrophe and rapid decarbonization.

On one hand the climate crisis has become too severe to ignore; what was once a problem that people thought their children would face is now something that is impossible to ignore, with record-breaking heat, droughts, wildfires, flooding, and other climate impacts happening on a daily basis. While climate change is not necessarily happening faster than we thought, many of the impacts of climate change are proving more severe than we initially expected. Atmospheric CO2 has now risen to levels last seen more than four million years ago, and current global temperatures are likely higher than any multi-century period in at least the last 125,000 years.

At the same time, the energy transition is happening far faster than anyone predicted a decade ago. Solar and battery prices have fallen by a factor of ten in a decade, global coal use peaked back in 2013, around 14% of new vehicles sold globally are electric, and the darkest climate futures where emissions doubled or tripled by the end of the century are now receding from view.

Close to 90% of global emissions are covered by pledges to get to net-zero around the middle of the 21st century, and countries are starting to pass meaningful climate policy to put us on a path toward achieving those goals.

But it is increasingly clear that the world will overshoot our most ambitious climate change target of limiting warming to 1.5°C in the next decade or two, even though our ability to limit warming to below 2°C is growing much stronger.

It is a time for a cautious climate hope that both acknowledges the progress we have made and how far we still have to go. 

If you have an hour to spare, the talk is worth listening to. In particular because it realistically acknowledges the depth of the hole we are in – which is deep –  while pointing out that we have made real and measurable progress.

If you only have 30 minutes, then just listen to the start. Despite a few IT problems it does manage to convey that although things are still bad, they are not as bad as we thought they were going to be.

Heating My Home

October 18, 2022

Friends, I have made a 5-minute video about heating my home with a heat pump.

It’s nonsense, but once I had thought of the idea of using coloured water to represent heat, I felt compelled to make the video: I hope you enjoy it.

Talk about Heat Pumps

October 5, 2022

Friends, this evening I will be giving a talk about Heat Pumps to the Richmond and Twickenham Branch of Friends of the Earth.

Specifically the talk is about switching from using a gas boiler to a heat pump

But I have already given the talk!

I recorded a version of the talk this morning and you can see it below!

If you want you can download the Powerpoint Slides using this link  (15 Mb)

Sadly, the talk is an hour long, but given the list of 25 things I had to talk about, I guess that was inevitable.

Viewers who liked that talk may also be interested in…

How heat pumps work

A Rule of Thumb for sizing heat pumps

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