Saturday 15 February 2020

Electric vehicles - not particularly energy efficient

The conclusion to my previous post, Fun with numbers - what if we all had electric cars was this:

If electricity generation goes up 40% [to charge all the cars] and half of that is gas, oil or even coal, we simply use half of that 37 bn [fuel saved] in power stations, a net saving of 19 billion litres.

We could achieve much the same reduction by simply moving to hybrid cars (as recommended by Bayard), which can achieve 80 or 90 mpg. They can do 10 - 50 miles on battery alone, so you could turn off the petrol or diesel engine while in town, thus reducing pollution where people live (Mombers' argument in favour of electric cars, about the only valid argument in favour of them IMHO). This requires absolutely no changes to our infrastructure and the shift could happen organically.


The calculations were long and complicated, even by my standards, and I had to make quite a few assumptions and go back and tweak it several times.

There's a much easier way to compare and contrast, and ultimately, I don't think I was far off:

1. It takes 0.3 litres of diesel to generate 1 kWh of electricity (from here), and approx. 10% is lost in transmission (from here).

2. So 1 litre of diesel used in a power station = 3 kWh of electricity at the socket.

3. Electric cars do 2.9 miles/kWh (from here), so 1 litre in the power station = 3 kWh in the battery, x 2.9 miles/kWh = 8.7 miles/litre = 40 miles/gallon.

4. That is not particularly impressive by modern standards, and a hybrid diesel/electric (not plug in) can easily do 80 miles/gallon (from here).

"Ah yes," cry the Greenies, "But the electricity to power the vehicles wouldn't be generated from fossil fuels, it would be generated from renewables!"

For sure, but that logic applies to all electricity, about 50% of which is generated using fossil fuels in the UK, so it's not really an argument. We could tackle that issue first (to the extent you believe it is an issue, which frankly, I don't).

So if we all shifted to diesel- or petrol/electric hybrids*, that would halve the amount of petrol and diesel used, halving the CO2 emissions from that source, which I think is the object of the exercise. And of course, private vehicle use only accounts for about one-quarter of UK CO2 emissions, which have been declining by compound 1.5% a year since the peak in 1975 anyway, and we are back to the levels of 130 years ago (from here).

* This is much more feasible than going all-electric. The cars are much cheaper than all-electric. The batteries in diesel- or petrol/electric hybrids are much smaller than in fully electric vehicles, which means that it will not be quite as difficult rustling up all the rare metals required to make them. It would require no massive infrastructure investment (more power stations or at least, existing power stations running 24/7, installing tens of million of charging points etc) and everything continues pretty much as normal.

16 comments:

Blissex2 said...

«Electric cars do 2.9 miles/kWh (from here), so 1 litre in the power station = 3 kWh in the battery, x 2.9 miles/kWh = 8.7 miles/litre = 40 miles/gallon.»

The big picture however is that electricity is not a fuel but a means of transferring energy around, and the vital details here are, on both sides:

* Not all electrical power generation comes from diesel.
* Storing electricity is a lot more difficult than storing petrol.
* Pollution at the power station is a lot easier to deal with than at the car.
* A lot of electrical energy is lost in transmission, very little in transport of petrol.

«That is not particularly impressive by modern standards, and a hybrid diesel/electric (not plug in) can easily do 80 miles/gallon (from here).»

What matters is not miles/gallon *per car* but *per person*, and as to that the *total* efficiency of internal combustion engines used appropriately is huge, e.g the efficiency of a Honda C90 moped is very difficult to beat, but most people want to travel by themselves in large comfortable cars or pickup trucks with surround stereo, not by moped or tuktuks.

«So if we all shifted to diesel- or petrol/electric hybrids*, that would halve the amount of petrol and diesel used, halving the CO2 emissions from that source»

Whether one believes in "climate change", on balance I think that the "powers that be" use "carbon footprint" as a way to persuade the masses to consume less, and in particular less oil, without ending up like poor President Carter. In particular oil, because in the short-medium term supply is not elastic and price can swing hugely on relatively small changes in demand.

«which I think is the object of the exercise. And of course, private vehicle use accounts for about one-quarter of UK CO2 emissions,»

Ah a typical brexiter/little Englander attitude :-), that somehow England's is a Great Power also as global "climate change", and what England does matters globally. What matters to "climate change" is in our current era what matters in almost every other respect, what the continental powers (USA, China, EU, Russia, Brazil, India) do. It is nice for England/UK to also make their little contribution though, but in the bigger picture it is irrelevant...

Part of the reason why China matters is that the "the powers that be" in the USA, UK etc. decided that trade unions and pollution should be "NIMBY"fied away to China, exporting most of the related plants and jobs to that country, in the hope/delusion that the headquarters would stay in this green and pleasant land. But the "slanted eyed yellow monkeys" (so called by a GM executive) at Toshiba, Honda, Kia, Samsung, Huawei, Foxconn, etc. dared to disagree.

Tim Almond said...

is that 80mph realistic on hybrids, or just how it comes out in official tests where they can presumably load up the battery for the first few miles? Honest John has real MPG figures and hybrids are better than petrol cars, but not by much (like 55 vs 40)

Mark Wadsworth said...

B2, I considered most of your points before writing the post, try reading between the lines.

"Ah a typical brexiter/little Englander attitude :-), that somehow England's is a Great Power also as global "climate change", and what England does matters globally."

That is a arse-about-face. Clearly, what the UK in isolation does is entirely irrelevant on a global scale, I would have thought that to be obvious.

It is the Greenies who insist that "the UK must be a global leader in abating climate change", and the cynics/realists among us (whom the Greenies decry as Little Englanders) are the first to point out that what the UK in isolation does is irrelevant, which they take to mean there is no point bothering (rightly or wrongly).

But what goes for the UK goes for other European countries and all other developed countries, I couldn't be bothered scaling all the numbers up to a global level.

Mark Wadsworth said...

TS, I can't cross reference everything and some things I just take at face value.

Bayard said...

TS, but Honest John is talking about parallel hybrids, which are just an ICE vehicle with a big starter motor and battery, and have to lug around two complete powertrains. If you want 80mpg you need to ditch the mechanical transmission and have full regenerative braking, the latter being something not possible in a parallel hybrid AFAIK.

benj said...

If you live in a city, pollution from outside the city or from within the home is more of a factor than vehicles. That's with the current fleet of vehicles. Emissions from Euro 6 engines pose a negligible health risk. So when new ICE engines are combined with hybridisation and stop/start, its not something we should worry about too much. Dust from brakes becomes more of a problem. Something EVs suffer from equally (if not more given their added weight)

Robin Smith said...

This is all ancient knowledge, discovered centuries ago by the late great Professor David MacKay of Cambridge UK.

The only solution able to deliver on all counts is a new fleet of Generation III+ nuclear power stations (70+ = ~100GW) plus CCS(in the UK only)

Wind is a high carbon basket case - it needs copious natural gas to normalise the grid

Then you have charging. Think terraced housing with no consistent parking

Lekky cars are excellent once the power supply is available

This, even if climate change politics is actually true, which is by no means certain.

I love the ignorance on this forum, its so entertaining.

Bayard said...

"This is all ancient knowledge, discovered centuries ago by the late great Professor David MacKay of Cambridge UK."

Er, centuries ago? Prof McKay was only born in 1967.

Lola said...

Well, quite. Clearly plug in or not plug in hybrids are a Good Idea, but they have to be made much lighter. I drive a 2106 Disco Sport. It's about 1850 kg. The 2020 model hybrid version is 2000 kg. (from memory). Weight = increased fuel consumption, which is a major critique of battery power - a lot of energy is used to move the battery pack alone. A light vehicle with an ICE gets impressive mpg/low CO2. And you can build light vehicles. Look at the iStream https://www.gordonmurraydesign.com/en/istream.html

Robin Smith said...

You got me there Bayard.

Mark Wadsworth said...

L, yes. There's a trade off between engine size and battery size; there's a trade off between weight and fuel economy; there's a trade off between ICE charging a battery, with no need for charging stations; there's a trade off between using the oil (petrol) to power an engine or to generate electricity; endless trade offs.

I'll stick with proper cars, if that's OK.

Robin Smith said...

Get Nuke. That's it.

All the 'waste' is buried away safely, waiting to be dug up for fuel. It's just a matter of time. Maybe not in your lifetime

Bayard said...

"I'll stick with proper cars, if that's OK."

Yup, that's exactly where the marketing of hybrids went wrong: they're not seen as "proper cars".

Mark Wadsworth said...

B, engineers have spent decades making ICEs sound good. The noise is half the fun.

Bayard said...

Ok, so you have series hybrids with variable speed engines for the petrol heads: you'd get more performance out of your ICE engine if it is variable speed, and ones with constnt speed engines for those more interested in fuel economy.

Diesel locomotives are just big series hybrids. I remember the drivers of the HSTs revving their engines until the turbochargers went supersonic pulling out of Durham station, which is on a fairly steep gradient (for a railway that is). It certainly sounded like fun.

Robin Smith said...

You get a small dose of radioactivity by sleeping next to your wife. She gets a dose off you. No one harmed. I found a site in Cornwall with relatively high background level (200 times normal) and right on top of it was a kids trampoline in their back garden:

https://youtu.be/QyR9KCLkSSM