Posts Tagged ‘ICE’

Our Old Car is Dead. Long Live The New Car!

July 28, 2021

Click for larger image. Our old and new Zafira cars

After 20 years and 96,000 miles, our 2001 Vauxhall Zafira is close to death.

We bought it for £7000 when it was three years old in 2004. Back then it was all shiny and new, but over the last 17 years it has developed a very long list of faults.

Alexei Sayle once said of his car: “When one door closes, another one opens.”. This was one of the faults our car did not have. But it did have a feature such that: “When one door closes, all the electric windows operate simultaneously.”

Over the last few weeks the engine has begun making horrific noises, the engine warning light is on permanently, and there is an acrid stench of burning oil in the cabin.

After much deliberation, we have replaced it with a closely similar car, a 2010 Zafira with only 52,000 miles on its ‘clock’. The new car lacks our old car’s charmingly idiosyncratic list of faults, but what can you expect for £3,200?

In this post I would like to explain the thinking behind our choice of car.

Do we need a car?

Strictly speaking, no. We could operate with a combination of bikes and taxis and hire cars. But my wife and I do find having a car extremely convenient.

Having a car available simplifies a large number of mundane tasks and gives us the sense of – no irony intended – freedom.

Further, although I am heavily invested in reducing my carbon dioxide emissions, I do not want to live the life of a ‘martyr’. I am keen to show that a life with low carbon dioxide emissions can be very ‘normal’.

So why not an electric car? #1: Cost

Given the effort and expense I have gone to in reducing carbon dioxide emissions from the house, I confess that I did want to get an electric car.

I have come to viscerally hate the idea of burning a few kilograms of hydrocarbon fuel in order to move myself around. It feels dirty.

But sadly buying a new electric car didn’t really make financial sense.

There are lots of excellent electric family cars available in the UK, but they all cost in the region of £30,000.

There are not many second-hand models available but amongst those that were available, there appeared to be very few for less than £15,000.

Click for larger version. Annual Mileage of our family cars since 1995 taken from their MOT certificates. The red dotted line is the Zafira’s average over its lifetime.

Typically my wife and I drive between 3,000 and 5,000 miles per year, and we found ourselves unable to enthuse about the high cost of these cars.

And personally, I feel like I have spent a fortune on the house. Indeed I have spent a fortune! And I now need to just stop spending money for a while. But Michael: What about the emissions?

So why not an electric car? #2: Carbon Dioxide

Sadly, buying an electric didn’t quite make sense in terms of carbon emissions either.

Electric cars have very low emissions of carbon dioxide per kilometre. But they have – like conventional cars – quite large amounts of so-called ’embedded’ carbon dioxide arising from their manufacture.

As a consequence, at low annual mileages, it takes several years for the carbon dioxide emissions of an electric car to beat the carbon dioxide emissions from an already existing internal combustion engine car.

The graph below compares the anticipated carbon dioxide emissions from our old car, our new car, and a hypothetical EV over the next 10 years. The assumptions I have made are listed at the end of the article.

Click for larger version. Projected carbon dioxide emissions from driving 5,000 miles per year in: Our current car (2001 Zafira); Our new car (2010 Zafira); and a typical EV. The dotted line shows the effect of grid carbon intensity falling from around 200 gCO2/kWhe now to 100 gCO2/kWhe in 2030.

For an annual mileage of 5000 miles, the breakeven point for carbon dioxide emissions is 6 or 7 years away. If we reduced our mileage to 3000 miles per year, then the breakeven point would be even further away.

Click for larger version. Projected carbon dioxide emissions from driving 3,000 miles per year in: Our new car (2010 Zafira); and a typical EV. The dotted line shows the effect of grid carbon intensity falling from around 200 gCO2/kWhe now to 100 gCO2/kWhe in 2030.

However, we are a low mileage household. If we drove a more typical 10,000 miles per year then the breakeven point would be just a couple of years away. Over 10 years, the Zafira would emit roughly 12 tonnes more carbon dioxide than the EV.

If we took account of embodied carbon dioxide in a combustion engine car, i.e. if we were considering buying a new car, the case for an EV would be very compelling.

Click for larger version. Projected carbon dioxide emissions from driving 10,000 miles per year in: Our new car (2010 Zafira); and a typical EV. The dotted line shows the effect of grid carbon intensity falling from around 200 gCO2/kWhe now to 100 gCO2/kWhe in 2030.


By replacing our old car with a closely similar model we have minimised the cognitive stress of buying a new car. Hopefully it will prove to be reliable.

And however many miles we drive in the coming years, our new car will reduce our carbon dioxide emissions compared to what they would have been in the old car by about 17%. And no new cars will have been built to achieve that saving.

Assuming that our new car will last us for (say) 5 years, I am hopeful that by then the cost of electric cars will have fallen to the point where an electric car – new or second-hand – might make sense to us.

Additionally, if the electricity used to both manufacture and charge electric cars increasingly comes from renewable sources, then the reduction in carbon dioxide emissions associated with driving electric cars will (year-on-year) become ever more compelling.

However, despite being able to justify this decision to myself, I must confess that I am sad not to be able to join the electric revolution just yet.


For the Zafiras:

  • I used the standard CO2 emissions per kilometre (190 and 157 gCO2/km respectively) in the standard government database.

For the hypothetical EV

  • I took a typical high efficiency figure of 16 kWh per 100 km taken from this article.
  • I assumed a charging inefficiency of 10%, and a grid carbon intensity of 200 gCO2/kWhe reducing to 100 gCO2/kWhe in 10 years time.
  • I assumed that the battery size was 50 kWh and that embodied carbon emissions were 65 kg per kWh (link) of battery storage yielding 3.3 tonnes of embodied carbon dioxide.
  • I assumed the embodied carbon dioxide in the chassis and other components was 4.6 tonnes.
  • For comparison, the roughly 8 tonnes of embodied carbon dioxide in an EV is only just less than the combined embodied carbon dioxide in all the other emission reduction technology I have bought recently:
    • Triple Glazing, External Wall Insulation, Solar Panels, Powerwall Battery, Heat Pump, Air Conditioning

I think all these numbers are quite uncertain, but they seem plausible and broadly in line with other estimates one can find on the web


ICE vs BEV vs FC

May 8, 2021

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

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

A cloud over Teddington!

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

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

Comparing CO2 emissions

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

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

This categorisation is sometimes succinctly summarised as

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

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

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

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

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

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

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

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

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

So lets look at some examples.

Toyota Mirai FC 

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

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

Tesla Model 3 BEV

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

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

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

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

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


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

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

BEV vs ICE: Efficiency

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

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

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

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

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

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

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

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

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

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

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

Blue sky 

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


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