Archive for March, 2021

The Wuling Hongguang: the most popular EV in China

March 28, 2021

I like to look at news websites from other countries to try to counter my Teddingtono-centric view of the world.

My favourite foreign news website is Deutche Welle – its measured tones are a pleasing counterpoint to the BBC news website. But I also find the China Daily propaganda site interesting.

I call it a propaganda site rather than a news site because that’s what it is. It never contains anything which could be construed as negative about China and only contains negative stories about the West. However much the Chinese Communist Party would like to pretend otherwise, China is not a normal country.

Nonetheless, one can learn a great deal by seeing how they portray things. And their articles can also help to place a Teddingtono-centric view into a wider perspective. They rarely have stories about Teddington.

Electric Vehicles

Electric Vehicles (EVs) are the future of transportation. And China is the world’s largest market for EVs.

But as I understand it, in Beijing at least, one cannot simply buy a car. Instead, one enters into a lottery where the prize is permission to buy a car. The chance of winning permission to buy a car with an Internal Combustion Engine (ICE) is incredibly low, but the chance of winning permission to buy an EV is much higher.

With that in mind, an article caught my eye in the China Daily lauding the achievements the Wuling Hongguang Mini EV.

A mini-sized model from Chinese brand Wuling, the Hong Guang Mini EV, toppled Tesla’s Model 3 as the world’s best-selling electric car in January, with deliveries exceeding 36,000 in the month, more than those of the Model 3 and Model Y combined.

The BBC reported on this too.

Image Courtesy of Wikipedia

The car is very basic – its battery (9.2 kWh or 13.8 kWh) is typically just 20% the size of the batteries in EV’s on sale in the UK. Its range (~120 km or 170 km) is small, but perfectly adequate for a day of city driving. But its most shocking statistic is its cost: $4,200.

In contrast, the Tesla models it displaced as best sellers cost more than $30,000.

Why is this important?

The very existence of any car at that price has to be a manifestation of engineering fundamentals. In this case EVs are technically simpler to make than conventional cars.

So why are EVs in the UK (and Europe and the US) currently so expensive?

Well I don’t know, but I would guess it is a classical supply and demand situation – with supply severely limited. One bottleneck is the rate at which batteries can be made. Logically existing manufacturers want to put the limited numbers of batteries available into expensive cars. But that shortage won’t last for ever and the price of batteries is falling year on year.

And – batteries excepted – the simplicity of manufacture and assembly of the cars is such that China Daily asserts:

… Wuling does not see itself as a car manufacturer anymore. It aspires to become a creative, popular and boundary-free lifestyle brand.

The reason I am writing this is because it struck me that the Wuling Hongguang looked like it might be the 21st Century equivalent of The Mini. A cheap unpretentious way to get about.

If a basic EV similar to the Hongguang were sold in the UK for (say) £5,000 to £10,000, I think it would be wildly popular. And I suspect that time is coming.

As other people have speculated, the death of the ICE car may come sooner than anyone expects.

Battery Day. One week on…

March 24, 2021

Click for larger view. The graph shows daily electricity drawn from the grid (kWh). Before the solar panels were installed average usage was 10.9 kWh/day. After the solar panels were installed this fell by a couple of kWh/day. After an increase over Christmas when our son returned, we were back to normal. In the last month the solar electricity generated on the lengthening days have reduced the electricity drawn from the grid. Since the battery was installed a week ago, we have not drawn any electricity from the grid.


My wife and I have both been slightly gob-smacked by the Tesla Powerwall.

Since installation last week, without changing our daily habits, we have been off-grid, using only electricity which has been generated on our own roof.

In all likelihood, we will probably be substantially off-grid for the next six months.

The combination of the solar panels and the battery is transformational.

Solar Panels

Click for larger view. The graph shows daily electricity generated by the solar panels (kWh/day) since installation in November 2020. The solid green line shows my guess for what to expect and the yellow dots show the expected monthly average based on an EU website with historical data. The green dots show actual monthly averages and the pink line shows a 5-day running average.

Broadly, as the graph above shows, things are proceeding as I had foreseen.


We are currently using the battery in its default mode. In this mode it does not try to predict tomorrow’s sunshine ‘harvest’ and does not top-itself-up with night-rate electricity.

This seems to be fine with our relatively low usage and the increasing solar generation as we head into summer.

We will need to change mode to include off-peak top-ups when we head into winter, and possibly even in the summer after we scrap our gas boiler and install a heat pump for our domestic hot water requirements. But for now, it seems to work very straightforwardly.

I have – obviously – been analysing  the data and I will write about that in due course. But here I will just note two curiosities that make the analysis slightly tricky.

The first is that the battery itself consumes electricity, but the amount of power it uses is not declared. Using some secondary indicators I estimate that – as installed at the moment – it appears to be drawing about 50 W i.e. 1.2 kWh a day.

Click for larger view. On the App screen, energy flows between the grid, our home, the solar panels and the battery all appear equivalent.

A second curiosity  is that – as reported by the App – it looks like the energy flows in all directions are all equivalent. But this is not the case

  • For example, when the app reports 1 kW flowing into the battery for one hour one might expect the battery’s state of charge to increase by 1 kWh. But because of the conversion losses, the battery probably only stores about 0.95 kWh.
  • Similarly, on discharge, if the app reports drawing 1 kW from the battery for one hour one might expect the battery’s state of charge to decrease by 1 kWh. But because of the conversion losses, the state of charge probably falls by about 1.05 kWh.

The actual state of charge of the battery is indicated as a percentage on the app, but this data is not exported.

Altogether this makes, the state of charge of the battery – how many kWh of electricity are stored in it – quite tricky to estimate. But I am working on it.


Overall, I have the sensation of floating.

The thought that the combination of a battery and some solar panels is enough to disconnect from the grid for the next six months is truly transformational. Both from a carbon emission perspective, and from a financial perspective.


Click for larger view. The graph shows daily electricity drawn from the grid (kWh). Before the solar panels were installed average usage was 10.9 kWh/day. After the solar panels were installed this fell by a couple of kWh/day. After an increase over Christmas when our son returned, we were back to normal. In the last month the solar electricity generated on the lengthening days have reduced the electricity drawn from the grid. Since the battery was installed a week ago, we have not drawn any electricity from the grid.

Battery Day: First Results

March 20, 2021

Me and my new Tesla. This unit contains 13.5 kWh of battery storage along with a climate control system to optimise battery life. We have placed it in the porch so that (when visits are allowed again) everyone who visits will know about it!

Last September, Tesla held their ‘Battery Day‘ during which they unveiled their road map towards cheaper, better, batteries.

Not to be outdone, last Monday VW held their own ‘Battery Day‘ during which they unveiled their road map towards cheaper, better, batteries.

And last Thursday was my own battery day, when Stuart and Jozsef from The Little Green Energy Company came and installed a Tesla Powerwall 2 at Podesta Towers in Teddington. I was (and still am) ridiculously excited.

I am still evaluating it – obviously – but here are a couple of notes.

How it works

The system has two components. An intelligent ‘gateway’ that monitors loads and supplies, and a climate-controlled battery storage unit.

Click for a larger version. The left-hand graphic shows how AC power enters our house, and how DC power generated by solar panels is linked to the grid. When the Solar PV is sufficient ,power is exported to the grid. The right-hand graphic shows how the TESLA ‘gateway’ device monitors the solar PV, domestic loads and battery status and intelligently decides what to do.

The gateway (and the battery) are electrically situated between the electricity meter and all the loads and power sources in the house. So all energy enters or leaves the battery module as AC (alternating current) power.

But its internal batteries must be supplied with DC (direct current).

This makes it ideal for storing power from the AC grid, but less than ideal for storing the DC current generated by solar PV panels.

One might have expected that a device designed to store solar power might intrinsically operate using DC and indeed, some battery systems – positioned between the solar PV and the inverter – do this.

So the choice to place the Powerwall™ where it is, is a compromise between the extra functionality this location offers – it can back up the entire house – and the inefficiency of storing solar PV which is first converted to AC by the inverter, and then re-converted back to DC by the Powerwall. The support document states that the conversion from AC to DC and back to AC has 90% round-trip efficiency.

The photograph below shows the gateway installed under the stairs in our house.

Click for a larger version. The Tesla ‘Gateway’ installed in our house. The unit is positioned in between the electricity meter and all the domestic loads. The black conduit leads under the floor to the battery which is installed in the porch.


The system is controlled by an app which is – frankly – mesmerising. It shows how electrical power flows between:

  • the grid,
  • the battery,
  • our home, and
  • our solar panels

Click for a larger version. Screenshots from the app at various times yesterday.

There is less room to adjust the parameters of the system than I had anticipated. This appears to be because, in exchange for a guarantee that the battery will retain at least 80% capacity (10.8 kWh) after 10 years, one is required to relinquish detailed control to the Tesla Brain.

Through a built in network connection, the device is in constant touch with Tesla who monitor its performance and can detect if it is abused in some way. I am not sure how I feel about that – but then guaranteed long-term performance is certainly worth something.

One feature of this relinquishing of detailed control concerns ‘time-of-use’ tariffs. I anticipate that – especially in winter – I will need to charge the battery overnight on cheap rate electricity.

The system supports this mode of operation but is not yet operational. Apparently it needs to study the patterns of household use for 48 hours before being enabled.

When operational, one gives the system general instructions and then allows it to choose when, and by how much, to charge. There is for example no way to force the battery to charge to 100% on command.

In practice I suspect it will be fine, but at the moment it still feels a little weird.

Performance on Day#1

The simplest way to show how the Powerwall™ works is by looking at the data which the ‘App’ makes available.

The first graph shows the household demand through the day. It’s fascinating to look at this data which has 5 minute and 0.1 kW resolution. The metrologist in me would like more – but in honesty, this is enough to understand what is happening.

Click for a larger graph. See text for details.

Now we can look to see how that demand was met. Overnight, we relied mainly on the grid.

Click for a larger graph. See text for details.

The battery could have supplied this overnight electricity, but it had been set to hold a reserve of 16% of its capacity (~2 kWh) in case we required backup after a power cut. We have lowered that setting now because, thankfully, power cuts are rare in Teddington. The battery drew power from the grid overnight in two short periods to maintain this reserve.

Additionally, at the end of a sunny day in which the solar PV filled the battery, there was brief period where we returned electricity to the grid.

During the day – which was very sunny 🙂 – the household electricity demand was met by the electricity from the solar panels.

Click for a larger graph. See text for details.

Without the battery, most of this 16.91 kWh of electricity would have been sent to the grid. But now only a tiny fraction was returned to the grid, most of it being captured by the battery – see below.

Click for a larger graph. See text for details.

The graph above shows the battery maintaining its reserve charge at night, and then charging from the solar PV during the day. At peaks of household demand, the charging is paused. At around 16:00, the battery was briefly full, and shortly thereafter it began discharging to meet household demand.

As I write this at 1:00 p.m. on the day after the day shown (a rather dull day 😦 ), the battery is 56% full and charging.

The graph below shows all the above curves together.

Click for a larger graph. See text for details.


The Powerwall system is an object of wonder. It is beautifully engineered and miraculous in its simplicity.

It transforms the utility of the solar PV allowing me (rather than electricity companies) to benefit from the investments I have made.

I will post more about the performance in terms of cost, electricity and carbon dioxide when I have more data.

But for the moment I will just thank Jozsef and Stuart from The Little Green Energy Company for their professionalism and attention to detail. And ‘No’. I am not being paid to say that – quite the opposite!

Stuart and Jozsef from The Little Green Energy Company. You can’t see it, but they assure me they were both smiling. Click for a larger version


Sometimes I find it hard to like EDF

March 16, 2021

Click for larger version. EDF wrote to me today to say they are increasing the price of ‘night rate’ electricity by 73.7%.

Energy is a wonderful thing. But sometimes it can be hard to like the companies which sell it to us…

…especially when they increase the price of their product by 73% overnight!

As regular readers will know, since 2018 I have been working hard to reduce my household energy consumption and the concomitant carbon dioxide emissions.

My 3-step plan has been:

  1. Reduce household heating requirement with insulation and triple-glazing.
  2. Switch from gas heating to electrical heating with a heat pump.
  3. Use solar panels and a battery to generate low-emission electricity and reduce the cost of switching to electrical heating.

Part#1 is complete: winter is not yet at an end, but heating demand appears to about 50% lower.

Part#2 is underway and I hope to have a heat pump installed this summer. But electrical heating is more expensive than gas heating.

Part#3 is underway: the solar panels are performing well and a battery should be installed this Thursday. The battery should allow me to use mainly my own solar electricity, or EDF off-peak electricity for most of the year.

I carried out extensive modelling of the effect of varying patterns of electricity consumption and compared different ‘tariffs’.

I had based my costings on the fact that the night rate for electricity would be about 5p/kWh and day rate would be about 25p/kWh. Of course I knew these costs could vary over time.

Nonetheless, it would be an underestimate to say that I was ‘disappointed’ when EDF wrote to me this morning to say that price of night time electricity was to rise from 4.99 p/kWh to 8.67 p/kWh…

…a 73% rise!

Like I said, sometimes it can be hard to like the companies which sell us energy.


I am thinking about it.

But switching is, in my opinion, a distraction. It is a way of distracting us ‘fish’ from the fact that we are in a ‘barrel’ and at the mercy of the confusopolists.


Previous articles about the house.




The Cat Sat on the Mat

March 14, 2021

While walking though Teddington the other day I saw tender sight which brought a smile to my eyes.

A man was mending his very old car – an Austin Maxi – and had tools and components laid out around the car.

And just by the car was a small mat on which his cat was very contentedly sat.

I commented to him that it was very considerate of him to put down a mat for the cat.

He smiled.

Then he told me that the mat was there to cover a drain so that he didn’t accidentally lose any parts. And the cat was sitting there opportunistically rather than by invitation.


Correlation does not imply causation

It had seemed so obvious that the man had placed the mat down for the cat. I had immediately intuited his state of mind and fondness for his cat.

In order to have fully appreciated what was happening, I would have needed to:

  • Imagine into being a drain – for which I had no evidence – it was completely covered.
  • And then understand that it would be sensible to cover the drain if working near it – a mat would be ideal.
  • And finally understand that cats will sit on mats unbidden.

And so I was reminded that even the simplest and most apparently obvious things are sometimes not what they seem.


See also these links suggested by astute commenter Dave Burton

COVID-19: What next?

March 14, 2021

Friends, if you are anything like me, you are most probably sick to death of this virus. And yet it goes on.

I have been looking back at my posts over 2020 and I still feel OK about most of my comments. But as we re-open schools I thought it would be an idea to look back at where we were last September 2020 when schools re-opened.

By 26th September 2020 it was obvious that the exponential growth in prevalence which marked the start of the second wave was underway. At the time I did not imagine that twice as many people would die in that second wave as in the first. I wrote: Here we go again.

I mention this because looking up the prevalence data today (below) I notice that the viral prevalence is currently greater than it was when schools last re-opened.

Click for a larger version. This

We are probably all more versed in anti-viral protocols than we were in September 2020, but nonetheless we have to expect some increase in viral transmission and prevalence.

The difference between then and now, is that now 35% of the UK population have had a single-shot of vaccine and a substantial number of the most vulnerable are fully immunised.

We should thus expect that rising cases will not necessarily lead to the same rise in hospital admissions and deaths that we saw previously.

What’s happening now?

The ONS prevalence data (above) necessarily lags what’s happening on the ground by about two weeks.

If we look at current cases, we can see that there has been a rise in cases – or at least a slowdown in the rate of decline –  in recent days.

An unknown fraction of this rise is definitely an artefact of the large number (more than 1 million per day) of lateral flow tests being done around the return to schooling. (See the first 20 minutes of this Independent Sage Presentation for an explanation). But the exact fraction is unclear.

Click for a larger version.

So at this point it is hard to know what this rise means: whether it could just be another wiggle. Or whether it could be – and I am being serious – the start of Wave 3.

If we look at the long term graph of positive cases, we see that back in July 2020 (~Day 191) when prevalence and cases were 10 times lower, cases suddenly began to rise and kept rising.

Click for a larger version.

Hospital Admissions and Deaths did not start to rise for another 8 weeks.

Click for a larger version.

This time – the vaccine makes things different – and in 8 weeks time a full 50% of the entire population should have had at least a first shot. So we should not expect a rises in cases to lead to rises in hospital admissions and deaths.

But if the viral prevalence becomes widespread again then we risk breeding variants that can spread under the new conditions in which they find themselves.

For completeness, here are the data on hospitalisations and deaths

Click for a larger version. The pink shading shows that hospitalisations have now fallen below their trend since late January 2021.

Click for a larger version. The pink shading shows that deaths have now fallen below their trend since late January 2021. The blue line shows 1st-shot vaccinations and the light blue line shows 2nd shot vaccinations . Dotted lines show projections and trends.

COVID-19 Milestones

March 4, 2021

Friends, allow me to highlight three upcoming COVID milestones.


  • First the positive: Tomorrow I will receive my first shot of vaccine. Hurray!
  • Second, and more tragically, tomorrow or Saturday will mark the date on which the death toll from the second wave will reach 82,732 which is double the death toll from the first wave. Words fail me.
  • Thirdly, Monday will mark the re-opening of schools. And two weeks later we will be able to see the effect on the rates of COVID cases.

Intriguingly, the populations who will be mixing (directly or indirectly) after schools re-open – parents, teachers, and children – will be mainly unvaccinated. But the most vulnerable people will be mainly vaccinated.

Measuring the resultant extra cases and the way they feed through to hospital admissions and deaths will likely be critical to the development of the Government’s ‘re-opening’ strategy.

Update on Cases

As I am sure you know the data are looking good – the daily rate of positive tests for COVID-19 is falling with a halving-time which may be even less than 16 days.

Click for a larger version.

The number of positive cases per day is shown above on a linear scale. The red dotted curve shows the rate at which cases fell after the first lockdown.

One can see that just over two weeks ago (~day 410) the rate at which the cases were falling reduced, but the rate of decrease now appears to be even faster than before – but we only have a few days data.

It is easier to see the trends if the data is plotted on a graph with a logarithmic vertical axis. On this graph (below) exponential trends show up as straight lines.

Extrapolating the trend of the last few days, we might hope for around 1000 cases per day by Easter (4th April). At that level, track, trace, support and isolate really should – after a year of utter failure – be able to cope.

However, we should more reasonably expect the rate at which cases are falling to slow (to some extent) after the schools re-open.

Click for a larger version.

Update on Hospital Admissions

The rate at which people are admitted to hospital is also falling, but unfortunately the data file of the ‘dashboard’ website is corrupted.

As you can see in the screenshot below for today 4th March 2021, the daily figure is 757. But in the data file, this figure is recorded as being appropriate to the 28th February. So using the data file would lead one to think that cases were falling more rapidly than they are.

Click for a larger version.

Using daily figures as they were reported, I find that hospital admissions are falling with a halving time of 21 days – surprisingly the same as after the first lockdown.

However the recent daily admissions data looks to have ‘steps’ in it – and given the errors above – it may not be reliable.

Click for a larger version.

Update on Deaths 

The rate at which people are dying from COVID is falling, faster and faster.

The figure below shows that after falling with an initial halving-time of about 16-days (orange dotted curve), daily deaths are now falling even faster.

The difference between the extrapolated 16-day halving time trend and the actual data is shaded in pink.

This is almost certainly the vaccine taking effect.

Click for a larger version.

Also shown in blue is percentage of the entire UK population (adults and children) who have received a first dose of vaccine.

The rate appears to have slowed a little in the last week or so – presumably as second-doses are prioritised.

Nonetheless, the rate is impressive: roughly 50% of the population will have received a first shot of vaccine by Easter.


So here we are… in the sad shadow of a gigantic second wave of deaths.

But with a little luck, the army of elderly vaccine gladiators which I will join tomorrow will vanquish the Covidian contagion before it can mutate.

Death to the Covidians!

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