The Death Of Fossil Fuels

[lpm]

A typical consumption of an EV that replaces a typical car, (as opposed to "the average EV") is something like 3 miles per kWh. The equivalent modern fossil fuel car might do about 11 miles per litre, as they are a lot more efficient these days, unless you are buying some sporty version. So with petrol at about 135p/l, then electricity becomes more expensive than petrol at about about 37p/kWh for such a car. Maybe your chosen EV does 4 miles/kWh, but then the equivalent fossil fuel car might do 14 miles/litre, so similar figures there.

My initial research shows EVs being quoted in kWh/100 km, with most cars scoring about 15 to 16. Which is about 3.9 to 4.1 miles per kWh. Are tw.t EVs as inefficient as tw.t ICE cars? Or is there less variation for EVs?

[bjn]

A typical consumption of an EV that replaces a typical car, (as opposed to "the average EV") is something like 3 miles per kWh. The equivalent modern fossil fuel car might do about 11 miles per litre, as they are a lot more efficient these days, unless you are buying some sporty version. So with petrol at about 135p/l, then electricity becomes more expensive than petrol at about about 37p/kWh for such a car. Maybe your chosen EV does 4 miles/kWh, but then the equivalent fossil fuel car might do 14 miles/litre, so similar figures there.

My initial research shows EVs being quoted in kWh/100 km, with most cars scoring about 15 to 16. Which is about 3.9 to 4.1 miles per kWh. Are tw.t EVs as inefficient as tw.t ICE cars? Or is there less variation for EVs?

The Porsche Taycan does from 20-27 kWh per 100km depending on the model. The top of the line one is about 750HP, so while inefficient and probably twatish, isn't as comparatively inefficient as some some ICE twatish car. The Tesla Model S Long Range is about 500HP and is 17.5. It can out accelerate pretty much any production ICE out there, so is probably twatish as well.

[Grumble]

There’s a rule of thumb that if you convert the energy units, EVs are about three times as efficient as combustion engine cars. Sporty EVs will probably be about 3 times as efficient as sporty ICE cars. All figures pulled from my arse.

[IvanV]

The Porsche Taycan does from 20-27 kWh per 100km depending on the model. The top of the line one is about 750HP, so while inefficient and probably twatish, isn't as comparatively inefficient as some some ICE twatish car. The Tesla Model S Long Range is about 500HP and is 17.5. It can out accelerate pretty much any production ICE out there, so is probably twatish as well.

The Taycan is a small sports car, very low down, very little interior capacity. Unsurprisingly it can have a relatively low electricity consumption in comparison to a practical car you can go shopping in, take rubbish to the tip, carry 2 children and a dog on a trip. You can doubtless get the acceleration, but it will have low consumption at a constant velocity, because such is the nature of electric vehicles, even electric sports cars. In fact, electric sports cars are a relatively easy trick, because the payload mass is small, and the aerodynamics are excellent.

This was my source of fuel consumptions, given in Wh/mile. 1000/number gives miles/kWh, which is a sensible unit given that we buy electricity in kWh and measure roads in miles. Similarly, that is why I gave fossil fuel consumptions in miles/litre. Unfortunately it is rare to see consumption given in these sensible units. Mpg seems to forget that we haven't bought fuel in gallons for a very long time. And l/100km seems to be something the car industry dreamt up so that normal not-very-numerate people would have little intuitive idea what the number meant in practice.

So at the very top of the list you can get a Fiat 500 EV which does a little over 4 miles/kWh (235Wh/mile). That's why I think 4 miles/kWh is a consumption for small cars, not an average car. I chose an average car (as opposed to an average EV) as something like the Renault Kangoo. Whilst not everyone's taste, it is a lot smaller/lighter/more economical than SUVs and people carrier thingies, but is a practical spacious vehicle with no pretence of sportiness. It does a little over 3 miles/kWh (310 Wh/mile). So that was my benchmark for an averagish car.

An EV would be lovely for every day use. Indeed for every day a range of 50 miles would be great. If you could tip most of the batteries out, and so avoid having to waste energy driving around with so much normally unused battery mass, that would greatly improve fuel consumption. But probably 25%-30% of our miles are on longer journeys, typically to rather lightly populated areas, where an EV would be a serious pain in the rear end. Especially remembering the difference between claimed ranges and realistic ranges. Two-car families solve this relatively easily - as indeed most Norwegians do - by retaining a liquid fuelled vehicle for longer trips. But we don't need 2 cars as we both do a lot of short local trips by bicycle.

[shpalman]

The Taycan, small? It's two tonnes. Compare it to the Panamera.

[dyqik]

l/100km are used because a 1 l/100km saving gives the same reduction in gas usage for your fixed driving habits, no matter what the baseline usage is.

1 mpg saving is not the same if you have a 50mpg car or a 25 mpg car.

[shpalman]

l/100km are used because a 1 l/100km saving gives the same reduction in gas usage for your fixed driving habits, no matter what the baseline usage is.

1 mpg saving is not the same if you have a 50mpg car or a 25 mpg car.

Obligatory https://what-if.xkcd.com/11/

Not sure how to physically interpret the EV usage figures.

[monkey]

l/100km are used because a 1 l/100km saving gives the same reduction in gas usage for your fixed driving habits, no matter what the baseline usage is.

1 mpg saving is not the same if you have a 50mpg car or a 25 mpg car.

Obligatory https://what-if.xkcd.com/11/

Not sure how to physically interpret the EV usage figures.

If your doing miles/kWh, you could write that as mph/kw, which seems to tell you something about how fast you go for each unit of energy you use.

[shpalman]

Oh wait. The kWh is a unit of energy (3.6 million joules) and energy divided by distance is force, so in the right units it's telling you the non-conservative "friction".

[bjn]

Nerds! I love you all though.

[basementer]

Not sure how to physically interpret the EV usage figures.

Thinking along monkey's lines, 60 mph ~ 100 kmph is a speed that's familiar to anyone who drives. You could rearrange the units to show how much power it takes to maintain that speed, coming out at around 20 kW per (100 kms per hour)?

[monkey]

Oh wait. The kWh is a unit of energy (3.6 million joules) and energy divided by distance is force, so in the right units it's telling you the non-conservative "friction".

Isn't it how much force the the motor is applying/applied on average to the wheels? It would only equal the friction/drag when you are not accelerating or decelerating.

[dyqik]

Oh wait. The kWh is a unit of energy (3.6 million joules) and energy divided by distance is force, so in the right units it's telling you the non-conservative "friction".

Isn't it how much force the the motor is applying/applied on average to the wheels? It would only equal the friction/drag when you are not accelerating or decelerating.

With 100% efficient regenerative braking, that evens out as long as you come to a complete stop at the end of the your journey.

Shades of keeping the number of landings the same as your number of takeoffs there.

[monkey]

Oh wait. The kWh is a unit of energy (3.6 million joules) and energy divided by distance is force, so in the right units it's telling you the non-conservative "friction".

Isn't it how much force the the motor is applying/applied on average to the wheels? It would only equal the friction/drag when you are not accelerating or decelerating.

With 100% efficient regenerative braking, that evens out as long as you come to a complete stop at the end of the your journey.

Shades of keeping the number of landings the same as your number of takeoffs there.

You have to apply force to go at a constant speed, there is still friction and drag to be in equilibrium with. So at a constant speed your instantaneous force is > 0. Most journeys aren't simply accelerate-stop, so the average force applied would be >0 too, 'cos of the constant speed bit, even if you include regenerative braking as a negative (which is fair).

But I suppose your journey might be a drag race, you do you.

[IvanV]

The Taycan, small? It's two tonnes. Compare it to the Panamera.

Small isn't really the word for it, I agree. It's a 4/5 seater car, and since sports cars are flattened and spread out, they occupy a surprisingly large footprint on the road given how little payload space they have. (The Panamera is physically larger than a Taycan.)

A lot of the mass is battery. The physical structure of EVs is light because of all the battery they have to push around. EVs are heavier than liquid fuelled cars of the same physical dimensions. So comparing it to the mass of a liquid fuelled car of similar dimension is not the point.

What I should have said, more precisely, is that, for a 4/5 seater car, it has a relatively low payload space, and low air resistance, in comparison to a car designed for practical family transport use. So it uses less energy than the latter.

[Millennie Al]

Taxing electricity used for charging a car as opposed to used to boil water in a kettle is going to be very hard to do. Most likely it will be via some form of road usage fee. Count the miles each year, levy some sort of charge. You can link it to vehicle weight as well if necessary.

It should be quite easy as people will be accustomed to consuming the electricity in a traceable way (typically by using a phone app with a public charger), so it will be easy to make manufacturers of vehicles ensure that all charging is recorded and reported (probably in real time, but it could be at the annual MOT).

And why would you link it to vehicle weight?

[Martin_B]

Taxing electricity used for charging a car as opposed to used to boil water in a kettle is going to be very hard to do. Most likely it will be via some form of road usage fee. Count the miles each year, levy some sort of charge. You can link it to vehicle weight as well if necessary.

It should be quite easy as people will be accustomed to consuming the electricity in a traceable way (typically by using a phone app with a public charger), so it will be easy to make manufacturers of vehicles ensure that all charging is recorded and reported (probably in real time, but it could be at the annual MOT).

And why would you link it to vehicle weight?

The link to vehicle weight is (I presume from bjn's post) to link usage to road damage and repair. Vehicles with heavier axle weights cause more damage to roads (an argument against taxing bicycles for using roads, because they do very little damage to the road surface).

But vehicle weight is already used (IIRC, indirectly) in the calculation of vehicle duty, and sort of indirectly in the fuel tax anyway, as heavier vehicles will use more fuel and hence pay more tax.

Removing the fuel tax from the equation could lead to a greater reliance on vehicle weight in the calculation of vehicle duty, but low mileage users would be harder hit. An easier tax would be to record charging as you suggest and include some form of tax on that electricity. This would possibly prevent the use of cars as smart battery storage, though, as keeping track of charge flowing into and out of the batteries might be too complex to legislate/tax.

[Martin_B]

You are worrying about a corner case. Given that the average annual mileage in the UK for a car is 7,400 miles, of which 2,700 is commuting (just over 10 miles per working day) and 4,400 is for pleasure (12 miles per day over the year) with 400 miles for business (2 miles per working day on average), the vast majority of trips won't need rapid charging. Yes there will be spikey days where you drive to Lands End to John O'Groats and need rapid charging, and there will be road warriors driving stupid distances. However for most people on most days you can top up at home or at a cheap kerbside charger, eg: the 5KW lamppost charger literally outside my front gate with another 4 within eyeshot of my house which went in over the last few months. The infrastructure is appearing as needed. All my BEV owning neighbours had to do was phone the council and request a new charge point, who then told the charging companies about it gave them planning permission, hey presto, new chargers. This is Hounslow as well, not exactly a mega wealthy London borough.

I'm not sure that you can average out the pleasure usage of 4,400 miles a year to 12 miles per day on average, as this will be split into very different usages. Some might be driving to the supermarket/cinema/kid's swimming lessons, etc, which would be regular things and can be averaged. But other pleasure trips will be driving to see the relatives at Christmas, which can be well over 300 miles each way for some people. Taking a 30 minute break at a service station is fine, but if all cars are EVs, every parking spot at that service station will need to be a rapid or ultra-rapid charger to keep those breaks down to 30 minutes. The car parks might also need to be larger, as many people will only park up for a comfort break/grab a drink and be parked for ~5 minutes rather than 30 minutes.

Also, different countries have different ideas about what constitutes a long drive. From where I lived in the UK (Guildford), a 250 mile range covered most journeys (relatives in Cornwall, friends in Manchester, etc) which I would reasonably expect to perform without the need for a break.

But tomorrow I plan to drive down to Margaret River for the day with a couple of mates and do a bit of shopping and sight-seeing; with driving around the area down there this is about a 700 km (440 miles) round trip. We probably won't be anywhere long enough when we're down there to have a chance to recharge, and because of the nature of the roads between the two places (100-110 km/h speed limits, little traffic, etc) the driving is easy and I wouldn't expect to take a driving break on the way down or back to recharge. My current car (a Camry hybrid) will easily do the trip on a tank (probably less than 75% of my small 45 litre tank). This is hardly an uncommon trip for an Australian, and a simple one for an ICE car (or my hybrid) but suddenly becomes much more difficult for an EV.

[bjn]

Taxing electricity used for charging a car as opposed to used to boil water in a kettle is going to be very hard to do. Most likely it will be via some form of road usage fee. Count the miles each year, levy some sort of charge. You can link it to vehicle weight as well if necessary.

It should be quite easy as people will be accustomed to consuming the electricity in a traceable way (typically by using a phone app with a public charger), so it will be easy to make manufacturers of vehicles ensure that all charging is recorded and reported (probably in real time, but it could be at the annual MOT).

And why would you link it to vehicle weight?

I normally have you on ignore.

You can charge from any 240V outlet, you can charge at home from higher power outlets. That is going to be the bulk of the charging, not at specialist charging stations. Did that 240 volt outlet get used for a kettle or a Kia?

[lpm]

The Kia would know.

[lpm]

This was my source of fuel consumptions, given in Wh/mile. 1000/number gives miles/kWh,

Thanks, that's really useful.

Is it as simple as a car scoring 375 will take 50% longer to get 200 miles worth of electricity than a 250? I'd rather be 30 mins at a services than 45 mins. Or is this too simplistic?

[Gfamily]

This was my source of fuel consumptions, given in Wh/mile. 1000/number gives miles/kWh,

Thanks, that's really useful.

Is it as simple as a car scoring 375 will take 50% longer to get 200 miles worth of electricity than a 250? I'd rather be 30 mins at a services than 45 mins. Or is this too simplistic?

Yes, as total battery capacity is also important as your concern is having 200 miles worth when you leave the charging point. If your 250 scoring car only has a 150 mile range, then you'll have to stop a second time.

[lpm]

Well, yes, the 250 scorers seem to be city cars with limited range (except for Tesla). But some 260 scorers get 200 real world miles.

I suspect a lot of drivers are lugging around too much battery because they got obsessed about range when purchasing, instead of getting into efficiency numbers for their 10 mile drive to work. The basic economics are you pay more upfront vs an ICE car, you then get it back over the years in cheaper fuel, tax and maintenance - so it's a bit mad to pick inefficiency and delay that payback.

But then most people seem to choose cars based on mad reasons.

[shpalman]

Oh wait. The kWh is a unit of energy (3.6 million joules) and energy divided by distance is force, so in the right units it's telling you the non-conservative "friction".

It comes out at 687 N for the "Average" figure in that Wh/mi table. That would be the "force" which the electric is doing work against, incorporating inefficiencies in the motors, mechanical friction, air resistance and (depending on the kind of cycle it's measured on) the inefficiencies in the braking regeneration system.

But if you do a similar calculation for, say, 10l/100 km (0.1 square mm) of petrol, using figures I found of 46 MJ/kg and about 0.75 kg/l, you get a "force" of 6100 J. Most of that would be the inefficiency of internal combustion itself (limited by the compression ratio apparently) plus that braking involves throwing away energy.

Anyway I thought of something more interesting. Going back to that 687 N "force", it's actually 687 J/m. A voltage is a certain number of joules per coulomb of charge, so arbitrarily choosing 220 V we can convert that to 3.1 C/m. But when a charge moves, that's a current. If you're travelling at 70 mph, which is 31.1 m/s, then it converts to 97 amps.

Is there a physical interpretation of that? Not sure.

[tom p]

She is in a high-profile climate-related role, though.

It's perhaps not unreasonable to expect somebody being paid to represent the country's low-carbon ambitions to suck up some mild personal inconvenience, especially as the government's strategy is to try to push the blame for emissions onto individual consumers. Reap what you sow, etc.

She could've said "I'm going to drive it till the wheels fall of before I replace it, cos I heard someone say that was better for carbon", and then we'd all have an argument about whether that was true or not.

Going back to this, would it be true?

Her argument was she lives in North London & needs to visit family in 3 different places which are ~200 miles away.
Living in North London, she probably doesn't need to use her car often & almost certainly wouldn't use it for commuting. Having youngish kids and family who live a long way away, she's probably only making each of those trips once or twice a year.
So if she's using a 3rd hand (so probably suboptimal engine efficiency) diesel for 1,350 miles of motorway driving and probably another 500 miles of city driving a year, how much carbon is she likely to release and how does that compare with scrapping this old car & buying a new one?
What would actually be the environmentally optimal choice?